Tests in the discipline mechanical engineering technology. Collection of practical problems in the discipline “Mechanical Engineering Technology” Discipline: Mechanical Engineering Technology
Problem 1.66 option 3.
Given: d (shaft base surface size) = 80-0.039 mm,
? (processing method accuracy) =60 microns,
Tizn (permissible wear of the bushing) = 10 microns,
A2 =50±0.080 mm.
Determine the executive dimension D of the centering sleeve, which ensures the specified accuracy of dimension A2 when milling the groove.
Solution.
Analysis of the installation diagram shows that the accuracy of the hole diameter of the centering sleeve D affects the accuracy of dimension A2 specified from the axis of the workpiece to the machined surface. From the installation diagram it can be seen that the fastening error (?з) for size A2 is zero. Based on this, we assume as a starting point that the accuracy of size A2 is: TA2=?bA2 + Tizn. + ?, where?bA2 = TD + Smin + Td – basing error of size A2. The components TD and Smin are unknown quantities.
Solving the equality with respect to these unknowns, we get:
(Smin + TD) = TA2 – (Td + Tizn. + ?) = 0.16 – (0.039 + 0.010 + 0.060) = 0.051 mm.
From the tables of GOST 25347-82 we select the hole tolerance field so that the condition is met: Smin + TD? ES.
Comparing the calculated value (Smin + TD) = 0.051 with the table value of the upper deviation of the hole (ES), I take the tolerance field G7 (), which can be taken as the executive dimensions of the bushing:
D = 80G7.
Problem 1.67 option 3.
Given: mandrel material – steel 20Х,
workpiece material – bronze,
E 1 (steel) = 210 GPa
E 2 (bronze) = 100 GPa,
?1(steel)= 0.3
?2(bronze)= 0.33
f bronze to steel = 0.05
u?1,2 (Rz1 + Rz2)
d = 30+0.013mm
L = 40 mm
d1 = 70 mm
K = 2.0
Rz (mandrels) – 1.6
Rz (blanks) – 3.2
Рz = 240 N
Tizn=10 µm.
Solution.
The starting point for performing calculations is the condition KMres = Mtr,
where: Мrez= Рz - cutting moment when turning the surface
Mtr = lfp – friction moment of the contact surface of the workpiece with the mandrel.
p = - contact pressure on the mating surface.
Required minimum interference: Ncalc. min=
When using a solid mandrel: c1=1-?1 > c1=1-0.3=0.7
с2= +?2 > +0.33=1.78
Ncalc. min= = =3.767
Taking into account the correction u for the height of the roughnesses crushed during pressing, we find the value of the measured interference:
Nmeas. min= Ncalc. min+u > 3.767 + 1.2 (1.6+3.2)=3.767+5.76=9.5 µm;
From the tables of GOST 25347-82 we select the shaft tolerance field so that
(Td+Nmeas. min +Tizn.)?ei, where Tizn. is the permissible wear of the mandrel.
In our case (13+9.5+ Tizn) ?ei.
For my version, the tolerance fields of the shaft (mandrel) can be accepted
p5() or p6() with permissible mandrel wear of 3.5 µm.
Then the executive dimensions of the mandrel are:
d=30p5()mm or d=30p6()mm.
Pressing force at maximum tension, taking into account the safety factor K=2: P=Kfp?dl,
р => р= = =15,
P=2·0.05·15·3.14·30·40=5652N.
Problem 1.57 option 1.
Given: ?b=0.05 mm, ?z=0.01 mm, ?us=0.01 mm, ?c=0.012 mm,
Ng=3000pcs.,
Workpiece: material – non-hardened steel, hardness – HB 160, base surface – cylindrical, Тl=0.2 mm.
Device: prism, Steel 20, hardness – HV 650, F=36.1 mm2, Q=10000H, L=20 mm.
Processing method – milling with cooling, ? (processing method accuracy) =0.1 mm, tm=1.95 min.
Determine the between-repair period of the device.
Solution.
We determine the permissible value of [?i] using the equations:
?у = + > ?у = + =
=0,051+
?у = Тl – ?, > 0.051+ = Тl – ?, >0.051+ = 0.2-0.1>
> = 0.049 > [?and] = = 0.04644 mm =46.44 microns.
The permissible number of installed workpieces [N] up to the maximum wear of the installation elements of the device is found from the equation:
[N] = , from the reference book – we find m=1818, m1=1014, m2=1309, wear resistance criterion P1=1.03, correction factor taking into account processing conditions Ku=0.9.
[N]= = = =21716 pcs.
The time between repairs, which determines the need to replace or restore the installation elements of the device, is found from the equation:
PC = = = 73.8 months.
Problem 1.43
Given: D1 = D2 =50+0.039 mm, dts = dc = 50f7 mm,
TL = 0.1 mm, ? (processing method accuracy) =0.050 mm.
Determine the accuracy of size 70 of the connecting rod head and the possibility of processing the surfaces of the connecting rod with a set of cutters, maintaining a dimensional accuracy of 45+0.4 mm.
Solution.
Based on the installation diagram of the workpiece in the fixture, the basing error when performing size 70 is determined by the equation:
?b70 = Smax=TD + Smin + Td = 0.039+0.025+0.025=0.089 mm,
Since the problem statement does not say anything about errors in fixing and positioning of the workpiece, then?з = ?п.з.= 0. Then
T70 = ?b70 + ? = 0.089+0.05=0.139 mm.
For size 45, a tolerance is added for the size between the axes of the holes (it could also affect size 70 if the fingers did not have the same tolerance range):
?b45 = Smax=TD + Smin + Td + TL = 0.039+0.025+0.025+0.1=0.189 mm,
T45 = ?b45 + ? = 0.189+0.05=0.239 mm.
As we can see, the calculated tolerance is 0.239< 0,4 мм допуска заданного, следовательно, мы можем применить набор фрез для обработки головки шатуна.
Literature:
1. Machine tools. Directory. /Ed. B.N. Vardashkina et al. M., Mechanical Engineering, 1984.
2. Metalhead's Handbook. /Ed. M.P. Novikova / M., Mechanical Engineering, 1977.
Solution given practical problems for all main sections academic discipline"Mechanical Engineering Technology". Variants of individual tasks for practical work are given with a description of the methodology for their implementation using the example of solving one of the variants of the task. The appendices contain normative and reference materials necessary to carry out practical work.
The textbook can be used when studying the general professional discipline “Mechanical Engineering Technology” in accordance with the Federal State Educational Standard for Secondary Professional Education for specialty 151901 “Mechanical Engineering Technology”.
An electronic educational resource “Mechanical Engineering Technology” has been released for this textbook.
For students of secondary educational institutions vocational education.
DETERMINING THE AMOUNT OF ALLOWANCES.
A workpiece is a production item, the shape of which is close to the shape of the part from which a part or one-piece assembly unit is made by changing the shape and roughness of surfaces, their dimensions, as well as the properties of the material. It is generally accepted that a workpiece enters any operation, and a part leaves the operation.
The configuration of the workpiece is determined by the design of the part, its dimensions, material and operating conditions of the part in finished product, i.e. all types of loads acting on the part during operation of the finished product.
The initial workpiece is the workpiece entering the first operation technological process.
Allowance is a layer of workpiece material that is removed during the process. machining to obtain the required accuracy and parameters of the surface layer of the finished part.
An intermediate allowance is a layer of material removed when performing one technological transition. It is defined as the difference between the size of the surface of the workpiece obtained in the previous operation and the size of the same surface of the part obtained when performing this transition to process the surface of the workpiece in one operation.
TABLE OF CONTENTS
Preface
Chapter 1. Fundamentals of mechanical engineering technology
1.1. Production and technological processes machine-building enterprise
Practical work No. 1.1. Studying the structure of the technological process
1.2. Determining the amount of allowances
1.3. Calculation of workpiece sizes
1.4. Preliminary assessment of options for obtaining blanks
and their manufacturability
Practical work No. 1.2. Purpose of operating rooms
allowances for processing the part with a graphical representation of the location of allowances and tolerances for operational dimensions
1.5. Selecting bases when processing workpieces
1.6. Sequence of operations
1.7. Choosing an installation base
1.8. Selecting a source base
Practical work No. 1.3. Positioning of workpieces in the machine processing area
1.9. Precision machining
1.10. Determining the expected accuracy when automatically obtaining a coordinating dimension
Chapter 2. Technical standardization technological operations
2.1. Piece time structure
2.2. Rationing of operations
Practical work No. 2.1. Standardization of the turning operation of the technological process
Practical work No. 2.2. Standardization of the milling operation of the technological process
Practical work No. 2.3. Standardization of the grinding operation of the technological process
2.3. Operations development
Practical work No. 2.4. Development of a cylindrical grinding operation technological process
Practical work No. 2.5. Development of a surface grinding operation technological process
Chapter 3. Surface treatment methods used in the manufacture of main parts
3.1. Shaft production
3.2. Disc manufacturing
3.3. Manufacturing of gears
3.4. Manufacturing of spur gears
3.5. Manufacturing of bevel gears
Chapter 4. Manufacturing of ring parts
Chapter 5. Manufacturing parts from sheet materials
Chapter 6. Selection of devices for basing (installation and securing) workpieces
Chapter 7. Assembling connections, mechanisms and assembly units
7.1. Development of route and assembly diagram
7.2. Assembly dimensional chains
7.3. Ensuring Assembly Accuracy
7.4. Control of assembly and technological parameters
7.5. Balancing parts and rotors
Chapter 8. Course design
8.1. Basic provisions of the course project
8.2. General requirements for the preparation of a course project
8.3. General methodology for working on a project
8.4. Technological part
Applications
Annex 1. Approximate form title page explanatory note
Appendix 2. Sample form of an assignment form for a course project
Appendix 3. Units of measurement of physical quantities
Appendix 4. Rules for the design of the graphic part of the course project
Appendix 5. Tolerances in the hole system for external dimensions according to ESDP (GOST 25347-82)
Appendix 6. Approximate routes for obtaining parameters of external cylindrical surfaces
Appendix 7. Approximate routes for obtaining parameters of internal cylindrical surfaces
Appendix 8. Operating allowances and tolerances
Appendix 9. Time indicators of technological operations
Appendix 10. Technical specifications technological equipment and materials
Appendix 11. Cutting parameters and processing modes
Appendix 12. Indicators of accuracy and surface quality
Appendix 13. Dependence of type of production on output volume
Appendix 14. Approximate indicators for economic calculations
Appendix 15. Surface treatment methods
Appendix 16. Values of coefficients and quantities
Appendix 17. Brief specifications metal cutting machines
Bibliography.
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1 FEDERAL AGENCY FOR EDUCATION State educational institution higher professional education "TOMSK POLYTECHNIC UNIVERSITY" YURGA TECHNOLOGICAL INSTITUTE A.A. Saprykin, V.L. Bibik COLLECTION OF PRACTICAL PROBLEMS IN THE DISCIPLINE “MECHANICAL ENGINEERING TECHNOLOGY” Textbook Publishing house of Tomsk Polytechnic University 2008
2 BBK 34.5 i 73 UDC (076) C 19 C 19 Saprykin A.A. Collection of practical problems in the discipline “Mechanical Engineering Technology”: tutorial/ A.A. Saprykin, V.L. Bibik. Tomsk: Publishing house of Tomsk Polytechnic University, p. The manual contains examples and problems with solutions. It will help you acquire skills in solving technological problems, identifying improvements to existing ones and developing new technological processes. Designed to perform practical work in the discipline “Mechanical Engineering Technology” by university students specializing in “Mechanical Engineering Technology”. UDC (076) Reviewers Doctor of Technical Sciences, Professor of TPU S.I. Petrushin Deputy Head of Workshop 23 of Yurginsky Machine Plant LLC P.N. Bespalov Yurga Technological Institute (branch) of Tomsk Polytechnic University, 2008 Design. Publishing house of Tomsk Polytechnic University,
3 CONTENTS CHAPTER 1. BASICS OF DESIGNING TECHNOLOGICAL PROJECTS PRODUCTION AND TECHNOLOGICAL PROCESSES.4 2. ACCURACY OF MECHANICAL PROCESSING BASES AND PRINCIPLES OF BASIS MANUFACTURABILITY OF DESIGN MECHANICAL ALLOWANCES BOOT. OPERATING DIMENSIONS AND THEIR TOLERANCES PROCEDURE FOR DESIGNING TECHNOLOGICAL PROCESSES PRODUCT QUALITY CONTROL METHODS FOR INSTALLING WORKPIECES. INSTALLATION ELEMENTS OF DEVICES 57 CHAPTER 2. METHODS OF PROCESSING MAIN SURFACES OF BLANKS PROCESSING EXTERNAL SURFACES OF BODIES OF ROTATION...62 CHAPTER 3. TECHNOLOGY OF MACHINE ASSEMBLY DESIGN OF THE TECHNOLOGICAL PROCESS OF ASSEMBLY...75 APPENDIX A ..83 REFERENCES 94 3
4 CHAPTER 1. BASICS OF TECHNOLOGICAL PROCESS DESIGN 1. PRODUCTION AND TECHNOLOGICAL PROCESSES When working on the design of a technological process and its implementation and when preparing technological documentation, it is important to be able to determine the structure of the technological process and correctly formulate the name and content of its elements. This work is guided by GOST and an important stage in the development of the technological process is also the determination of the type of production. Approximately the type of production is established at the initial design stage. The main criterion in this case is the transaction consolidation coefficient. This is the ratio of the number of all technological operations performed during a certain period, for example a month, in a mechanical section (O), and to the number of jobs (P) of this section: K z.o = O/P. (1.1) Types machine-building industries are characterized by the following values of the transaction consolidation coefficient: K z.o<1 массовое производство; 1<К з.о 10 крупносерийное производство; 10<К з.о 20 среднесерийное производство; 20<К з.о 40 мелкосерийное производство; К з.о не регламентируется единичное производство. Формулирование наименования и содержания операции Пример 1.1. Деталь (втулку) изготовляют в условиях серийного производства и из горячекатаного проката, разрезанного на штучные заготовки. Все поверхности обрабатываются однократно. Токарная операция выполняется согласно двум операционным эскизам по установкам (рис.1.1). 4
5 1 â î ê Fig Operating sketches Required: analyze operational sketches and other initial data; establish the content of the operation and formulate its name and content; establish the sequence of processing the workpiece in this operation; describe the content of the transition operation. Solution. 1. Analyzing the initial data, we establish that in the operation under consideration, consisting of two installations, nine surfaces of the workpiece are processed, which will require nine technological transitions in succession. 2. To perform the operation, a lathe or screw-cutting lathe will be used, and the name of the operation will be “Lathe” or “Screw-cutting” (GOST). According to the same GOST, we determine the operation group number (14) and the operation number (63). To record the contents of the operation, if operational sketches are available, an abbreviated form of recording can be used: “Cut three ends”, “Drill and bore a hole”, “Bore one and sharpen two chamfers”. 3. We establish a rational sequence of technological transitions for installations, guided by operational sketches. In the first installation it is necessary to trim 5
6 end 4, sharpen surface 2 to form end 1, sharpen chamfer 3, drill hole 6 and bore chamfer 5. In the second installation, you need to trim end 9, sharpen surface 7 and chamfer 8. Table 1.1 Initial data View Contents of transition transition transition 1 PV Install and secure the workpiece 2 PT Trim the end 4 Grind surface 2 to form an end 1 3 PT (when turning surface 2, 2 working strokes are made) 4 PT Grind chamfer 3 5 PT Drill a hole 6 6 PT Bore the chamfer 5 7 PT Reinstall the workpiece 8 PT Trim end 9 9 PT Sharpen the surface 7 10 PT Sharpen the chamfer 8 11 PT Control the dimensions of parts 12 PT Remove the part and place it in a container 4. The content of the operation in the technological documentation is recorded by transitions: technological (PT) and auxiliary (PT). When formulating the content of transitions, the abbreviated notation according to GOST is used. Table 1.1 shows the records of the example under consideration. Task 1.1. For the turning operation, an operational sketch has been developed and as-built dimensions with tolerances and requirements for the roughness of the machined surfaces have been specified (Figure 1.2). Each surface is treated once. 6
7 3 I, V I R a Å Ç 2 5 H 1 2 I I, V I I 2 45 Å 3 2 ô a ñ ê è Ç 9 4, 5 h 1 4 Ç 9 5 h 1 4 Ç 8 0 h j s h h h 1 4 I I I, V I I I R a V I, I X R a 2 0 Ç 6 0 h 1 1 Ç 5 0 h 1 1 Ç 4 5 H 1 2 Ç 6 5 H 1 2 Ç H * 2 5 * * ð à ç ì å ä ë ÿ ñ ï ð à â î 4 5 ± 0, ± 0. 3 3 V, X R a 1 0 Ç , 5 Ç 5 5 H 1 2 Ç h h ± 0.5 Fig Operational sketches 7
8 Required: specify the machine type; determine the configuration and dimensions of the workpiece; establish a basing scheme; number all treated surfaces on the sketch; formulate the name and content of the operation for recording in technological documents; write down the content of all technological transitions in the technological sequence in full and abbreviated forms. Establishing the name and structure of the operation and recording its content in the technological documentation Example 1.2. In Fig. 1.3, which is a fragment of a working drawing of a part, a structural element of a part that is subject to processing under serial production conditions is highlighted. R a 20 Ç 18 H 12 6 î ò â. Ç ± 0.2 8 Ç * * ð à ç ì å ä ë ÿ ñ ï ð à â î ê Fig Working drawing Required: analyze the initial data; choose a processing method for a structural type of production; select the type of metal-cutting machine; set the name of the operation; record the contents of the transaction in full form; formulate a record of the content of the technological transition operation. Solution. 1. We establish that six holes in the housing flange are subject to processing, evenly located on a circle Ø 280 mm. 2. Holes in solid material are made by drilling. 3. For processing, select a radial drilling machine. 4. Name of the operation (in accordance with the type of machine used) “Radial drilling”. 5. The complete recording of the contents of the operation looks like this: “Drill 6 through holes Ø18H12 sequentially, maintaining
9 d = (280 ± 0.2) mm and surface roughness Ra = 20 µm, according to the drawing. 6. Recording the contents of transitions in full form is as follows: 1st transition (auxiliary). Place the workpiece in the jig and secure it. 2,..., 7th transitions (technological). Drill 6 holes Ø18H12, maintaining dimensions d = 280±0.2; Ra20 in series across the conductor. 8th transition (auxiliary). Size control. 9th transition (auxiliary). Remove the workpiece and place it in a container. Problem 1.2. Establish the name and structure of the operation in the conditions of serial production for processing structural elements of a part (Fig. 1.4). Option numbers are indicated in the figure in Roman numerals. I, I I I I I, I V 3 R a 5 R a Ç 3 4 h 1 0 M g V, V I 4 0 ± 1 V I I, V I I I Ç 6 0 H 1 2 R a 1 2.5 R a 5 Ç 6 0 H ± 0 , 3 I Õ, X 1 5 H 1 0 Fig. Operational sketches 9
10 Establishing the type of production at the site Example 1.3. There are 18 workplaces on the machine shop site. During the month, 154 different technological operations are performed on them. Required: establish the load factor for operations on the site; determine the type of production: state its definition according to GOST Solution. 1. The coefficient of consolidation of operations is established according to formula (1.1): K z.o = 154/18 = 8.56. In our case, this means that on the site, each workplace is assigned an average of 8.56 operations. 2. The type of production is determined according to GOST and Since 1<К з.о <10, тип производства крупносерийное. 3. Серийное производство характеризуется ограниченной номенклатурой изделий, сравнительно большим объемом их выпуска; изготовление ведется периодически повторяющимися партиями. Крупносерийное производство является одной из разновидностей серийного производства и по своим техническим, организационным и экономическим показателям близко к массовому производству. Задача 1.3. Известно количество рабочих мест участка (Р) и количество технологических операций, выполняемых на них в течение месяца (О). Варианты приведены в табл Требуется: определить тип производства. Таблица 1.2 Данные для расчета коэффициента закрепления операций варианта I II III IV V VI VII VIII IX X Количество рабочих мест (Р) Количество технологических операций (О)
11 2. ACCURACY OF MECHANICAL PROCESSING One of the main tasks of technologists and other production participants in machine shops is to ensure the required accuracy of manufactured parts. Real machine parts manufactured using mechanical processing have parameters that differ from ideal values, that is, they have errors; the size of the errors should not exceed the permissible maximum deviations (tolerances). To ensure a given processing accuracy, the technological process must be properly designed taking into account the economic accuracy achieved by various processing methods. Standards of average economic accuracy are given in the sources. It is important to consider that each subsequent transition should improve the accuracy by a degree. In some cases, calculation methods are used to determine the possible magnitude of the processing error. This is how turning errors are determined from the action of cutting forces arising due to insufficient rigidity of the technological system. In a number of cases, the accuracy of processing a batch of parts is analyzed using mathematical statistics methods. Determination of the economic accuracy achieved with various methods of processing external rotating surfaces Example 2.1. The surface of the step of a steel shaft 480 mm long, made from a forging, is pre-processed on a lathe to a diameter of 91.2 mm (Fig. 2.1). R a 2 0 Ç 9 1, 2 Fig Stepped shaft Determine: economic accuracy of processing size 91.2; quality of precision of the processed surface and its roughness. eleven
12 Solution. To determine economic accuracy, use the “Economic accuracy of machining” tables, which are given in various reference books. In our case, after rough turning, the accuracy of the machined surface should be within the 1st grade (we accept the 13th grade). Taking into account that at l/d = 5.3, processing errors increase by 1.5...1.6 times, this corresponds to a decrease in accuracy by one grade. We finally accept accuracy according to the 14th qualification. Since during rough turning the size of the workpiece is intermediate, this size is set for the outer surface with a tolerance range of the main part Ø91.2h14, or Ø91.2-0.37. Surface roughness Ra = µm (in factory practice, with well-made workpieces and normal production conditions, higher processing accuracy is achieved). Task 2.1. One of the shaft stages is machined using one of the specified methods. Option numbers are given in table Required: to establish the economic accuracy of processing; make an operational sketch and indicate on it the size, accuracy grade, tolerance size and roughness. Assume that the surface of the shaft step under consideration has a tolerance field of the main part (h). option Initial data Table 2.1 Processing method and its nature Shaft length, mm I Lapping II Semi-finish grinding III Fine grinding IV Single grinding V Superfinishing Step diameter, mm VI Pre-grinding VII Fine grinding VIII Final grinding IX Diamond smoothing X Final grinding
13 Determination of the accuracy of the shape of the surfaces of a part during processing Example 2.2. On the outer surface of the shaft (Fig. 2.2) a shape tolerance is specified, indicated by a symbol according to STSEV. The final processing of this surface is supposed to be performed by grinding on a cylindrical grinding machine model ZM151. Required: establish the name and content of the symbol for the specified deviation; establish the ability to withstand the requirement of accuracy of the shape of this surface during the intended processing. 0.01 Ç 7 0 Fig Sketch of the shaft Solution. 1. According to the presented sketch, the accuracy of the shape of the cylindrical surface is expressed by the roundness tolerance and is 10 microns. According to GOST, this tolerance corresponds to the 6th degree of shape accuracy. The term “steepness tolerance” refers to the largest permissible deviation from roundness. Particular types of deviation from roundness are ovality, cutting, etc. 2. On a cylindrical grinding machine model ZM151, it is possible to process workpieces with a maximum diameter of up to 200 mm and a length of up to 700 mm. Therefore, it is suitable for processing this workpiece. The deviation from roundness when processed on this machine is 2.5 microns. Based on the above, we conclude that it is possible to perform processing with the specified accuracy. Task 2.2. In Fig. 2.3 and in table. 2.2 indicates surface options with permissible shape deviations. Required: establish the name and content of the designation of the indicated deviations; establish the ability to perform processing on a specified machine, maintaining the specified accuracy. Ask about the missing dimensions. 13
14 I 0, V, V I Ç , 0 5 Ç 5 0 I I, I I I 0.02 А 0.02 V I I 0, А I V 0.0 2 V I I I 0.1 5 I X, X 0, Fig. Operational sketches 14
15 Initial data Table 2.2 options Surface shape Machine type I Hole Internal grinding II Plane Surface grinding III Plane Surface grinding IV Edge Cylindrical grinding V, VI Hole Honing VII Cylinder Screw-cutting VIII Plane Longitudinal planing IX Cylinder Multi-cutting lathe X Cylindrical grinding Defined the accuracy of the relative position of the surfaces of the part when processing Example 2.3. The sketch (Fig. 2.4) indicates the technical requirement for the accuracy of the relative position of the surfaces of the part. It is proposed that the final processing of the upper plane be carried out by finishing milling on a vertical milling machine according to the operational sketch shown in Fig. 2 / õ À 0, 2 / õ À À Fig Design requirements À Fig Operational sketch Required: state the name and content of the technical requirement; establish, using technological reference books, the accuracy of the relative position of the surfaces of the part, depending on the type of equipment; draw a conclusion about the possibility of fulfilling the specified requirement. Solution. 1. The symbol on the working drawing shows the parallelism tolerance of the upper plane relative to the lower plane, designated by the letter A. The parallelism tolerance is understood as the largest permissible deviation value from 15
16 parallelism. In our case, the tolerance is 0.2 mm over an area of mm. 2. In the tables of technological reference books, for example, we find the maximum deviations in our case: they are equal to µm and µm at a length of 300 mm, which means that at a length of 150 mm they will be equal to 12, µm. Of all these data, we take for guarantee the largest value of 100 microns, i.e. 0.1 mm. 3. We conclude that the required accuracy of the relative position of the processed plane relative to the base plane A will be ensured. Problem 2.3. In Fig. 2.6 shows surface treatment options. Required: decipher the designation of the content of the permit; develop technological measures to ensure the fulfillment of this requirement. À I, I I 0, À À I I I, I V 0, À V, V I V I I, V I I I 0, 1 5 À Á 0, 0 4 À Á I X, X 0, 0 5 À À Fig Surface treatment options 16
17 3. BASES AND PRINCIPLES OF BASEMENT In order to process a workpiece on a machine, it must be fixed on it, having previously selected the bases. By basing we mean giving the workpiece the required position relative to the machine and tool. The accuracy of processing depends on the correct location. When developing a basing scheme, the issues of selecting and placing reference points are resolved. In production conditions, there are always processing errors ε lips, depending on the installation conditions, i.e. from the basing ε of the bases, the fastening ε of the closed workpiece, and from the inaccuracy of the device ε etc. The installation error is expressed by the formula: ε = ε + ε + ε. (3.1) mouth bases To reduce these errors, it is important to follow the basing rules: the “six points” rule, the “constancy of bases” rule, the “combination of bases” rule, etc. Error values can be determined by various methods. The tabular method allows you to determine installation errors depending on production conditions. The calculation method for determining errors in basing, fastening and those caused by inaccuracy of the device is performed using formulas given in the literature. If the rule of “combining bases” is not observed, there is a need to convert design dimensions into technological ones (Fig. 3.1). The purpose of recalculation is to determine the error in the size of the closing link and compare it with the design size tolerance. Á Ê closed pr H = 7 5 h 9 h = 3 0 H * À 1 Ò = À 2 À S Á Ò Fig. Technological dimensional chain 17
18 Calculation of dimensional chains is carried out in accordance with GOST and one of the methods specified therein (“maximum minimum”, probabilistic, etc.). In these calculations, formulas are used to determine the nominal size of the closing link: h = H T, (3.2) where H is the size connecting the design and technological bases; T dimension connecting the technological base with the surface being processed. The error in the size of the closing link ε h =ε Δ when solving using the “maximum minimum” method is determined by the formulas: ε = T + T ; ε = T =, (3.3) h H T n h Σ T i 1 where Ti is the tolerance for the size of each chain link; T N tolerance for dimension H established in the drawing; T T tolerance for technological size, the value of which depends on the processing method and is set in accordance with the standard of average economic processing accuracy; n is the number of constituent links. When calculating using the probabilistic method, use the formulas T n 2 = t λiti, (3.4) i= 1 where t is the risk coefficient (t = 3); λi is the relative scattering coefficient (for the normal distribution law λi = 1/9). When the distribution laws are unknown, t = 3 and λi = 1/6 are taken, therefore n T i i= 1 2 T 1.2t. (3.5) = As a result of the calculation, the condition T h T Σ must be met. (3.6) 18
19 à Selecting a technological base taking into account the technical requirements for the part Example 3.1. The technological process for manufacturing the housing provides for the operation of boring a hole with a diameter of D (Fig. 3.2). When making a hole, size a and technical requirements regarding the correct relative position of the hole relative to other surfaces of the part must be met. Â H 0.1 À 6 Ã Á 6 Â D 4 5 4.5 Á 0.1 Â 22 0.1 Á Fig. Working drawing À À , Fig.3.3. Basing scheme Required: select the technological base for the operation in question; develop a basing scheme. Solution. 1. One of the design bases is plane A of the base. It should be taken as a technological installation base, creating three support points 1, 2 and 3 for its basing (Fig. 3.3). The technological guide base should be plane B with two reference points 4 and 5. This base will allow you to process the hole perpendicular to this plane. To ensure the symmetry of the location of the hole relative to the outer contour, surface B can be used as a technological base, but it is structurally easier to use surface D of a half-cylinder for this purpose and use a device with a movable prism for this purpose. Based on the above, we will apply a technological base of three surfaces: A, B and D (Fig. 3.3). 2. The basing diagram, which represents the location of support points on the workpiece bases, is shown in Fig.
20 a Problem 3.1. For a machine operation to process the specified surface of a part, it is necessary to select a technological base and draw up a basing scheme. The options are shown in Fig. 3.4 and in table d I, I I I I I, I V, V à 0 0 d 1 d d 2 V I, V I I, V I I I I X, X a h b 0, 1 A À D 1 Á d 1 0, 1 Á À d 2 Á d 1 d 2 0 , 1  0, 1 À 0, 1 Á Fig Operational sketches  option I Name and content of operations Name of operation Contents of operation Vertical drilling Drill a hole in the ball Table 3.1 II Lathe Drill a hole in the ball III Lathe Sharpen the surfaces finally Grind the indicated IV, V Final cylindrical grinding surfaces VI, VII Horizontal milling Mill the groove VIII Vertical milling Mill the groove IX Vertical drilling Drill 2 holes X Fine boring Boring 2 holes 20
21 Determining the technological base and drawing up a workpiece basing scheme Example 3.2. Required: consider the installation elements of the existing fixture (Fig. 3.5) and establish the workpiece surfaces that form the technological basis for securing the workpiece in the fixture; develop a workpiece basing scheme and conclude that the six-point rule is observed. Solution. 1. In the device shown in the figure, we identify its installation elements: body plane 2, cylindrical installation pin and cut-off installation pin 3. The technological basis of the workpiece is the following surfaces: the bottom plane of the workpiece A and two holes located diagonally. 2. In accordance with the identified technological bases and the installation elements used, we develop a basing scheme (Fig. 3.6): for basing the plane (installation base), three reference points (1, 2, 3) are formed; for basing on the first hole (using a cylindrical pin), two more reference points (4, 5) are formed, and for basing on the second hole, a cut pin (6) is used, forming the 6th basing point. 3. As can be seen from Figure 3.6 and the above reasoning, the six-point basing rule is observed, the workpiece is deprived of six degrees of freedom À Fig. Workpiece basing 21
22 Fig. Base scheme 6 Task 3.2. In Fig. 3.7 shows a device for processing on a machine. It is necessary, using the drawing, to identify the technological basis adopted for basing the workpiece, and to present a scheme for basing the workpiece; draw a conclusion about the correctness of the choice of reference points based on their number and placement. The option number is indicated in the figure in Roman numerals. I, I I A - A I I I, I V, V À À V I, V I I V I I I, I X, X Fig. Accessories 22
23 Calculation of a linear technological dimensional chain Example 3.3. On a configured horizontal milling machine, working on adjustment, the specified plane is finally processed. In this case, the coordinating dimension h = (70 ± 0.05) mm must be maintained (Fig. 3.8). Size tolerance h = 0.1 mm. Required: to establish whether the specified size accuracy will be maintained during processing. Á - ê î í ñ ò ð ó ò î ñ ê à ÿ á à ç à À h 8 (- 0.) À Σ = h = 7 0 ± 0. 0 5 À 1 = 8 5 h 8 (- 0,) À - ò å í î ë î è å ñ ê à ÿ á à ç à Fig Technological dimensional chain Solution. 1. From the conditions of the example and from the operational sketch it is clear that the lower plane A of the workpiece is taken as the technological base. The design and measuring bases for controlling size h are the upper plane B. Due to the fact that the bases do not coincide, it became necessary to recalculate the design dimensions to technological ones. In this case, it is necessary to calculate the error with which the size h can be made and compare it with the tolerance T h of this size; the condition ε h T h must be met. 2. The dimensional chain under consideration is linear and consists of three links: the size we are interested in, h = 70 mm, will be considered a closing link. And the first component link, size A 1 = 85h8(85-0.04) between the previously processed planes, is an increasing link; the second component link, size A 2, is technological, reducing, and its accuracy is determined by the standards of economic accuracy of processing on machine tools (see GOST). For our case, the error in this size is 0.06 mm. The nominal dimensions of this circuit are related by equation 23
24 A = A 1 A 2 = = 70 mm. 3. When calculating a linear dimensional chain (Fig. 3.8) using the method of complete interchangeability, i.e. using the maximum minimum method, determine the maximum deviations (processing error) of the initial (closing) link using formula (3.3): T n = Ti = (TA 1 + TA2) = (0.06) = 0.114 mm Σ. i= 1 As follows from the solution, the tolerance according to the drawing T h = 0.1 mm is less than the possible error during processing T = ε h = 0.114 mm, which is completely unacceptable. Consequently, it is necessary to take measures to ensure that the condition ε h T h is met. To do this, firstly, the designer can be asked about reducing the accuracy of size h, i.e. about expanding the tolerance T h to a value of 0.12, then T = ε h = (0.06) T h. Secondly, use fine milling or fine grinding as the final (finishing) processing. The economic accuracy of these processes is higher and with them T A2 = 0.025 mm (GOST). Then T = (0.025) = 0.079 mm. Condition T T h is met. Thirdly, the component size A = 85h8 was obtained by processing planes A and B before the operation in question. If the previous processing is performed more precisely by one quality, then the size tolerance will be 85h7(-0.035). Then the processing error T = (0.035 +0.06) = 0.095 mm. The condition is met T T h. Fourthly, when calculating the dimensional chain, you can use the probabilistic method according to the formula n T i i= 1 2 T 1.2t. 2 2 Then T = 1.2 0.060 = 0.097 mm and the condition T Th is met. Fifthly, the tolerance of the closing link is calculated using probability theory for the case of dispersion of deviation errors according to the law of normal distribution according to formula (3.5). In our case, 2 2 TΣ = 0.060 = 0.08 mm. Condition T T h is satisfied. Sixth, with a small volume of production of parts, i.e. in single or small-scale production, you can work not on adjustment, but, for example, with the removal of test chips. When processing each part, the size h is controlled. = 24
25 Problem 3.3. In Fig. 3.9 and in table. 3.2 presents options for operations. Required: determine the possible size basing error as a result of the specified processing. I, I I I I I, I V 1 2 l V, V I l 2 l 1 l h 9 Ç Ç Ç l 1 l 2 V I I, V I I I h 9 1 l 2 l 1 2 Ç Ç Ç h h h 1 0 l 1 I X, X 1 2 l 2 Fig Options for calculating dimensional chains Initial data Table 3.2 options Operation content Dimension l, mm I Plane plane 1 first l 1 = 150+0.2 II Plane plane 2 finally l 2 =170±0.1 III Trim end 1 first l 1 =60+0.3 IV Trim end 2 finally l 2 =30+0.1 V Trim end 1 preliminary L 1 = 100+0.2 VI Trim end 2 finally l 2 =50+0.1 25
26 Continuation of table 3.2 VII Grind plane 1 first l 1 =75+0.1 VIII Grind plane 2 finally l 2 = 175+0.2 IX Mill plane 1 first l 1 =70+0.4 X Mill plane 2 finally l 2 =30+0.2 4. TECHNOLOGICAL DESIGN Successful solution of the problems that are and will continue to be faced by mechanical engineering is only possible by creating new and improving existing machines in order to achieve higher performance characteristics while simultaneously reducing their weight, dimensions and cost, increasing durability, ease of maintenance and operational reliability. At the same time, in mechanical engineering itself it is necessary to improve the technological processes of manufacturing products, improve the use of all means of technological equipment, and introduce progressive methods of organizing production into production. One of the effective ways to solve these problems is to introduce the principles of manufacturability of structures. This term refers to a design that, while maintaining all operational qualities, ensures minimal manufacturing labor intensity, material consumption and cost, as well as the ability to quickly master the production of products in a given volume using modern processing and assembly methods. Manufacturability is the most important technical basis, ensuring the use of design and technological reserves to perform tasks to improve the technical and economic indicators of manufacturing and product quality. Work to improve manufacturability should be carried out at all stages of design and development in the production of manufactured products. When performing work related to manufacturability, one should be guided by a group of standards included in the Unified System of Technological Preparation of Production (USTPP), namely GOST, as well as GOST “Technological control in design documentation”. The manufacturability of the design of parts is determined by: a) rational choice of initial blanks and materials; b) manufacturability of the part’s shape; c) rational statement 26
27 sizes; d) assignment of optimal accuracy of dimensions, shape and relative position of surfaces, roughness parameters and technical requirements. The manufacturability of a part depends on the type of production; selected technological process, equipment and accessories; organization of production, as well as the operating conditions of the part and assembly unit in the product and repair conditions. Signs of the manufacturability of the design of a part, for example, a subclass of shafts, are the presence of stepped shafts with small differences in the diameters of the steps, the arrangement of stepped surfaces with a decreasing diameter from the middle or from one of the ends, the availability of all machined surfaces for machining, the ability to use an initial progressive workpiece for the manufacture of a part , which in shape and dimensions is close to the shape and dimensions of the finished part, the ability to use high-performance methods for processing. Improving the manufacturability of the original workpiece Example 4.1. Two variants of the design of the initial blank, obtained by casting, were made for the manufacture of the support body (Fig. 4.1, a, b). It is necessary to establish which of the options has a more technologically advanced design of the original workpiece. Solution. The body (Fig. 4.1, a) has a tubular cavity in the lower part. To form it in a casting mold, you will have to use a cantilever rod, and this will complicate and increase the cost of manufacturing the casting. A smooth hole of considerable length at the top will complicate machining. The body (Fig. 4.1, b) in the lower part has a cross-shaped section, which has high strength and rigidity and does not require a rod to make the casting. This greatly facilitates the production of casting molds. The casting is symmetrical relative to the vertical plane and will be easily molded in two flasks. The hole in the middle part has a recess and therefore the length of the hole surface to be machined is reduced, and this, in turn, greatly facilitates and reduces the cost of machining. Based on the above considerations, we can conclude that the second option is more technologically advanced. 27
28 À À À - À à) b) Fig Variants of casting shape Problem 4.1. When designing the initial workpiece or its elements, two designs were proposed (options are shown in Table 4.1, Fig. 4.2). Table 4.1 Initial data of option Name of part Workpiece type I; VI II; VII III; VIII IV; IX V; X Gear wheel Lever Cover Body neck Round body Stamped forging Same Casting Welded Casting I, V I I I, V I I I I I, V I I I I V, I X V, X Fig Options for the design of blanks 28
29 It is required to outline considerations for assessing the manufacturability of the design of each of the options for the initial workpiece and establish a more manufacturable one. Improving the manufacturability of parts and their elements Example 4.2. In order to increase the technical and economic indicators of the technological process, two options have been proposed for the design of elements in the design of a body made from castings (Fig. 4.3, a, b). It is necessary to evaluate their manufacturability. Solution. The bosses and plates on the body of the part (Fig. 4.3, a) are located at different levels, and each boss has to be processed individually. Insufficient rigidity of the upper part of the part does not allow the use of high-performance processing methods. In the design in Fig. 4.3, b all processed surfaces are located in the same plane and therefore can be processed on one machine, for example, on a vertical milling or longitudinal milling machine. a) b) Fig Casting options Ribs added to the inside of the part increase the rigidity of the body. During processing, this will help reduce the deformation of the workpiece from cutting and clamping forces and will allow processing with high cutting conditions or several tools simultaneously. At the same time, the accuracy and quality of processed surfaces will increase. 29
30 The level of unprocessed surfaces available on the part is below the machined surfaces. This will allow more productive processing “on pass”. Problem 4.2. One and the same design element of a machine part can be structurally designed differently. These solutions are presented in two sketches (options in Fig. 4.4). It is required to analyze the compared design sketches for manufacturability and justify the choice of the design element of the part. I, I I V I I, V I I I I I I, I V V, V I I X, X R Fig Design options Determination of quantitative indicators of the manufacturability of a part design Example 4.3. The body weighing m D = 2 kg is made of cast iron grade SCh 20 GOST The method of obtaining the initial workpiece is casting in an earthen mold, according to accuracy class I (GOST); workpiece mass m 0 = 2.62 kg. thirty
31 The labor intensity of machining the part T and = 45 min with the basic labor intensity (analogue) = 58 min. Technological cost of the part C t = 2.1 rub. at the basic technological cost of the analogue C b.t = 2.45 rubles. Data from the design analysis of the part by surface are presented in Table Table 4.2 Initial data Name of surface Number of surfaces Number of standardized elements Main hole 1 1 Flange end 2 Chamfer 2 2 Threaded hole 8 8 Top of base 2 Base holes 4 4 Bottom of base 1 Total... Q e =20 Q a.e. = 15 It is required to determine the manufacturability indicators of the part design. Solution. 1. The main indicators of the manufacturability of the design include: the absolute technical and economic indicator of the labor intensity of manufacturing the part T and = 45 min; level of design manufacturability in terms of manufacturing labor intensity K U.T = T and /T b.i = 45/58 = 0.775. The part is technologically advanced according to this indicator, since its labor intensity is 22.5% lower compared to the basic analogue; technological cost of the part C t = 2.1 rub.; level of manufacturability of the design at technological cost K y. c = C t / C b.t = 2.1/2.45 = 0.857. The part is technologically advanced, since its cost compared to the basic analogue decreased by 14.3%. 2. Additional indicators: coefficient of unification of structural elements of the part K y. e = Q y.e /Q e = 15/20 = 0.75. 31
32 According to this indicator, the part is technologically advanced, since K y. e >0.6 part mass m D = 2 kg; material utilization coefficient K i.m = m d / m 0 = 2/2.62 = 0.76. For an initial workpiece of this type, this indicator indicates satisfactory use of the material. Problem 4.3. The part in question, its original blank and its basic analogue or prototype are known; basic data given in table. 4.3 for ten options. It is required to determine the manufacturability indicators of the part design. Table 4.3 Initial data of the variant Number of surfaces of the part Qе Number of standardized elements Qу.е Weight, kg Parts mд of the Initial workpiece m0 Labor intensity, min Parts Ti of the Basic analog Tb.i Cost, rub. Details St of the Basic analogue S6.g I; VI .8 1.7 2.1 II; VII .3 0.9 1.3 III; VIII .1 3.4 4.1 IV; IX,2 0.2 1.4 V; X .8 5.8 5.3 5. MECHANICAL ALLOWANCES. OPERATING DIMENSIONS AND THEIR TOLERANCES When considering the elementary surface of the original workpiece and the corresponding surface of the finished part, the total allowance for machining is determined by comparing their sizes: this is the difference in the sizes of the corresponding surface on the original workpiece and the finished part. When considering the outer surface of rotation (on the left in Fig. 5.1), the total allowance is: 2P totald = d 0 d D; (5.1) 32
33 at the inner surface of rotation (in the center in Fig. 5.1) the total allowance is: 2P totald = D D D 0; (5.2) for a flat surface (on the right in Fig. 5.1) the total allowance on the side is: P totalh = h 0 h D, (5.3) where d 0, D 0, h 0 are the dimensions of the original workpiece; d D, D D, h D the corresponding dimensions of the finished part; 2P general and 2P general allowances for diameter, outer surface and hole; P is the total allowance per side (end, plane). Allowance for machining is usually removed sequentially in several transitions and therefore for surfaces of revolution and for flat surfaces 2P totald = 2P i; 2P totald = 2P i; P totalh = 2P i, (5.4) where Pi are intermediate allowances performed during the i-th transition, and at each subsequent transition the size of the intermediate allowance is smaller than at the previous one, and also with each subsequent transition the accuracy increases and the roughness of the machined surface decreases. Ï Ï d ä d 0 D ä D 0 h ä h 0 Ï Ï Ï Fig Types of allowance for machining An important and responsible job when designing technological processes for machining parts is to establish the optimal intermediate allowance for a given transition, after which it is possible to determine very important part processing technology parameters intermediate dimensions of the workpiece, which appear in the technological documentation, depending 33
34 from which performers select cutting and measuring tools. Intermediate allowances for each transition can be established by two methods: the experimental-statistical method, using tables in GOSTs, technological reference books, departmental guidance technological materials and other sources. These sources often do not contain tables for determining operating allowances for the first rough transition. The operational allowance for the rough transition is determined by calculation using the formula P 1 = P total (P 2 + Pz P n), (5.5) where P is the general allowance for machining, established when designing the workpiece; P 1, P 2 ;..., P p are intermediate allowances for the 1st, 2nd,..., nth transitions, respectively; calculation and analytical method using special formulas, taking into account many processing factors. When calculating using this method, the operating allowances are smaller than those selected from the tables, which allows you to save metal and reduce the cost of processing. This method is used when designing technological processes for processing parts with a large annual output. In technological documentation and in processing practice, intermediate nominal dimensions with permissible deviations are used. As can be seen in the diagram (Fig. 5.2) of the location of allowances and tolerances during processing, the nominal intermediate dimensions depend on the nominal allowances, which are found using the formula P nomi = P min i + T i-1, (5.6) where T i-1 is the tolerance for intermediate size on the previous transition. For various surfaces, the following formulas are used: for surfaces of revolution, except for the case of processing in the centers: 2П nomi = 2(R zi-1 +h i Δ i 1 + ε) + T i-1; (5.7) 2 i for surfaces of revolution when processing in centers: 34
35 for flat surfaces 2P nomi = 2(R zi-1 +h i-1 +Δ Σi-1) + T i-1; (5.8) П nomi = 2(R zi-1 + h i-1 + Δ Σi-1 +ε i) + T i-1 ; (5.9) for two opposite flat surfaces while processing them simultaneously: П nomi = 2(R zi-1 + h i-1 + Δ Σi-1 +ε i) + T i-1, (5.10) where R Zi-1 the height of microroughnesses on the surface after the previous transition; h i-1 thickness (depth) of the defective layer obtained at the previous adjacent transition, for example, casting skin, decarburized or work-hardened layer (this term is not taken into account for cast iron parts, starting from the second transition, and for parts after heat treatment); Δ Σi-1 the total value of spatial deviations of interconnected surfaces from the correct shape (warping, eccentricity, etc.) remaining after the previous transition (the total value of spatial deviations decreases with each subsequent transition: Δ Σi = 0.06 Δ Σ0 ; Δ Σ2 = 0.05 Δ Σ1; Δ Σ3 = 0.04 Δ Σ2. When the workpiece or tool is not rigidly secured, for example, in swinging or floating holders Δ Σi-1 = 0); ε i is the error in installing the workpiece on the machine when performing the transition in question: 2 bases 2 closed 35 2 adjust ε = ε + ε + ε, (5.11) where ε base, ε closed, ε adjust are respectively the errors of basing, fastening and fixture (when installed in centers ε i = 0, when processing multi-position operations when changing positions, the indexing error ε ind = 50 μm is taken into account according to the formula ε i = 0.06 ε i-1 + ε ind); T i-1 tolerance for the intermediate size (when determining the allowance for the first rough transition for external surfaces, only its minus part T is taken into account, and for internal surfaces the plus part of the tolerance of the original workpiece is taken into account). Intermediate dimensions when processing external surfaces of rotation (shafts) are set in reverse order
36 technological process for processing this surface, i.e. from the size of the finished part to the size of the workpiece by sequentially adding allowances P nom4 to the largest limiting size of the finished surface of the part (the original design size); P nom3; P nom2; P no.1. The tolerances of these dimensions are established according to the shaft system with a tolerance range h of the appropriate quality. The largest limiting size of the finished surface is taken as the initial design size. Rounding of intermediate dimensions is carried out in the direction of increasing the intermediate allowance to the same sign as the tolerance of this size. Features of calculating intermediate allowances and dimensions for internal surfaces are as follows: a) tolerances of intermediate (interoperational) dimensions are established according to the hole system with a tolerance field H of the corresponding quality; b) nominal dimensions and nominal allowances, at all transitions except the first, are related by the dependence П nomi = П mini +T i-1, (5.12) and the nominal allowance for the first (rough) transition is determined by the formula where П nomi = П mini + T 0 +, (5.13) + T 0 plus part of the workpiece tolerance; c) intermediate dimensions are established in the reverse order of the technological process from the size of the finished hole to the size of the workpiece by subtracting allowances P nom3 from the smallest limit size of the finished hole (initial size); P nom2; P no.1. Their tolerances are set according to the hole system with a tolerance field H; d) the smallest maximum size of the finished hole is taken as the initial design size. The diagram of the tolerance fields of the outer surface of the part, workpieces at all stages of processing and the initial workpiece and the fields of general and intermediate allowances are presented in Fig.
37 + T 0 - d 0 í î m = d 1 í î ì + 2 Ï 1 í î ì 2 Ï 1 í î ì T 1 d 1 í î ì = d 2 í î ì + 2 Ï 2 í î ì 2 Ï 2 í î ì ï î å ä î ó ñ ê à - ï î ë å ï ð è ï ó ñ à - ì à ò å è à ë ä å ò à ë è T 2 d 2 í î ì = d 3 í î ì + 2 Ï 3 í î ì 2 Ï 3 í î ì T 3 d 3 í î ì = d 4 í î ì + 2 Ï 4 í î ì 2 Ï 4 í î ì T 4 I ï å ð å õ î ä I I ï å ð å î ä I I I ï å ð å õ î ä I V ï å ð å î ä È è ñ õ î ä í à ÿ ç à ã î ò î â ê à Fig Scheme of tolerance fields à î ò î â à ÿ ä å ò à ë ü Selection of intermediate allowances when processing a rolled shaft and calculation of intermediate dimensions Example 5.1. A stepped shaft with a length L D = 480 mm (Fig. 5.3) is manufactured in small-scale production from round hot-rolled steel of normal accuracy with a diameter d 0 = 100 mm. The largest diameter shaft step Ø90h10(90-0.35) with surface roughness Ra5 (Rz20) is processed twice: preliminary and final turning. Required: establish a general allowance for machining of the diametrical size; set intermediate allowances for both processing transitions using the statistical method; calculate the intermediate size. R a 5 Ç 9 0 h * Fig Stepped shaft 37
38 Solution. 1. The total allowance for machining for the diameter is determined by formula 5.1: 2П totald = = 10 mm. 2. Intermediate allowance for diameter during finishing turning of the shaft. 2P 2table = 1.2 mm. For small-scale production, the allowance is increased, for which the coefficient K = 1.3 is introduced, i.e. 2P 2calc = 1.2 1.3 = 1.56 mm 1.6 mm. Since there are no instructions regarding the size of the operational allowance for diameter during rough turning in technological reference books, we determine it by calculation using formula (5.4): 2P 1 = 2P totald 2P 2calc = 10 1.6 = 8.4 mm. So, the initial calculated diameter size (the largest limiting size) is d and cx = 90 mm, the operational allowance for finishing turning is 2P 2 = 1.6 mm. The diameter of the workpiece after rough turning is equal to d 1 = d out + 2P 2 = 91.6; it is also with tolerance: d 1 = 91.6h12, or d 1 = 91.6-0.35; surface roughness Ra20. In the technological documentation, operational sketches are made for both transitions (Fig. 5.4, a, b) R a 20 Ç 9 1, 6 h 1 2 a) R a 5 Ç 9 0 h 1 0 b) Fig. Operational sketches Task 5.1. For the manufacture of a stepped shaft (Fig. 5.5), round hot-rolled steel of normal precision with a diameter d 0 is used as a workpiece. The largest diameter step of this shaft with a diameter d D, manufactured with an accuracy of 11th grade and a surface roughness of Ra10, is processed 38
39 twice by preliminary and final turning. Variants of the problem are given in table d 0 d ä L ä Fig Blank circle Initial data Table 5.1 option I II III IV V VI VII VIII IX X d L mm 75h11 85a11 65b11 95a11 60d11 95d11 70a11 90h11 80d11 55h11 do mm L L mm Required: install using tables, general and intermediate allowances; calculate the intermediate size and make operational sketches. Establishment of intermediate allowances for each transition using a statistical method (using tables) and calculation of intermediate dimensions of the workpiece Example 5.2. The multi-stage shaft (Fig. 5.6) is made from a stamped forging of high precision (class I). The workpiece underwent milling and centering processing, as a result of which the ends were trimmed and center holes were created. 39
40 Ç 8 5 p 6 Ç 9 1, 2 + 0, 3-0, * Fig Forging blank The outer cylindrical surface of one shaft stage has a diameter d = 85p6(85) * roughness Ra1.25. Stage D of the initial workpiece (see example P1.2) has a diameter d 0 = 91, and a roughness of Rz250 (Ra60). The accepted sequence of processing the specified surface is given in table Required: analyze the initial data; establish by statistical method (using tables) operational allowances for each transition; calculate intermediate dimensions for each technological transition. Solution. 1. The total machining allowance for the diameter is 6.2 mm. The hardening coefficient of the size of the processed surface is K hard.r. = T 0 /T D = 2000/22 = 91. Table 5.2 Initial data Sequence of processing (transition content) Pre-sharpen the surface Sharpen the surface for grinding Pre-grind the surface Grind the surface finally Accuracy quality Roughness parameter Ra, µm 20.0 5.0 2 .5 1.25 Note that the permissible deviation of the diameter of the original workpiece corresponds to approximately the 16th accuracy grade (IT16), and the finished part corresponds to the 6th accuracy grade (IT6). Thus, processing accuracy increases by approximately ten grades. Such a difference in accuracy can be achieved in four processing stages, so 40
41 how each processing stage increases dimensional accuracy by an average of quality. 2. We select operational allowances for diameter according to the tables. Total allowance 2P total = 6.2 mm. The tabulated value of the operational allowance for diameter during grinding is 0.5 mm, we distribute it for preliminary and final grinding (approximately in the ratio of 3:1) and obtain 2P 3 = 0.375 mm and 2P 4 = 0.125 mm. In round numbers we take 2P 3 = 0.4; 2P 4 = 0.1. Allowance for turning for grinding 2P 2 = 1.2 mm. From here we find the allowance for rough turning: 2P 1 = 2P total 2P 2 2P 3 2P 4 = 4.5 mm. The surface parameters after machining for each transition are presented in table According to the data in table. 5.3, the following conclusions can be drawn: a) the total allowance is divided by transitions in the ratio of 72.5%, 19.5%, 6.5% and 1.5%, which corresponds to the rules of machining technology; b) after each transition, the accuracy increases in the following sequence (according to qualifications): and accordingly, the size tolerance decreases (the tolerance becomes tighter) by 4.3; 3.8; 2.6 and 2.1 times; Table 5.3 Initial transition data Designation and size of intermediate allowance for diameter 0 2P total = 6.2 mm Tolerance field IT 16 (I class according to GOST) 1 2P 1 =4.5 mm h13 2 2P 2 =1.2 mm h10 3 2P 3 = 0.4 mm h8 4 2П 4 = 0.1 mm р6 41 Permissible size deviation, mm +1.3 0.4 0 0.054 +0.059 +0.037 Surface roughness, μm Ra60 (Rz250) Ra20 Ra5.5 Ra2.5 Ra1.25
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Ministry of Education and Science of the Samara Region
GBOU SPO Tolyatti Mechanical Engineering College
Reviewed Approved
at the meeting of the MK Deputy. director for research and development
specialty 151901 __________ Lutsenko T.N.
Protocol No.______
"___"___________ 2013 "___"___________ 2013
Chairman of the MK
__________ /Bykovskaya A.V./
Test materials
in the discipline "Mechanical Engineering Technology"
specialties: 151901 Mechanical Engineering Technology
for 4th year students
Developed by teacher Ivanov A.S.
Specialty: 151901 Mechanical Engineering Technology
Discipline: Mechanical Engineering Technology
Section 1. Specification of educational elements
№ p/p
Name of educational elements
(Didactic units)
The purpose of training
must know
must know
must know
must know
must know
must know
must know
must know
must know
Technological setup diagrams
must know
must know
Time norm and its structure
must know
must know
must know
must know
must know
must know
must know
must know
Machine assembly technology.
must know
must know
must know
must know
Section 2 Test tasks
Option 1
Block A
Assignment (question)
Response standard
№ tasks
Possible answer
1
1-B,2-A,3-B
Establish a correspondence between the name of the surface and the graphic image
1 – B;
2 – B;
3 – A;
4 – G.
IMAGE
Surfaces:
A) main
B) auxiliary
B) executive
D) free
Establish a correspondence between the name and designation of calving
1 – G;
2 – D;
3 – A;
4 – B;
5 B.
Name
A) cylindricity
B) roundness
B) flatness
D) straightness
D) longitudinal section profile tolerance
Establish correspondence with what types of directions of irregularities are indicated in the diagrams.
1 – B;
2 – D;
3 – G;
4 – A;
5 B.
Name of irregularities
parallel
crisscrossing
perpendicular
arbitrary
radial
Designation on diagrams
A. G.
B. D.
The completed part of the technological process performed by a worker at one workplace is
operation
Serial production is characterized
the number of products does not affect the type of production
The criterion for determining the type of production is
range of manufactured products and the coefficient of consolidation of operations
product release cycle
3. qualifications of workers
Accuracy in metalworking can be achieved using methods
method of passes and measurements
on configured machines
points 1 and 2
measuring the machined surface
The minimum operating allowance for bodies of revolution is determined by the formula
surface roughness that is not subject to treatment is indicated by the SIGN
1. 3.
2. 4. all of the above
The datum used to determine the position of the workpiece during the manufacturing process is called
design base
technological base
main base
support base
Operating time is determined by the formula
T OP =T O +T V
T DOP =T SB +T OP
T SHT =T O +T V +T OB +T OT
T Sh-K =T ShT +T P-Z /N
A base that deprives the workpiece of three degrees of freedom is called
double support
installation
guide
The base of the workpiece, which appears as a real surface, is called
open
measuring
Determine the type of production if the coefficient of consolidation of operationsTO Z =1
small-scale production
medium-scale production
large-scale production
mass production
The set of all irregularities on the surface under consideration is called
the surface of the part is not straight
surface waviness
Part surfaces are not parallel
surface roughness
The set of dimensions forming a closed contour and assigned to one part is called
dimension line
dimensional chain
size group
dimensional link
Define the term - general allowance
Basing errors arise if they do not match
design and technological bases
technological and measuring bases
design and measurement bases
When choosing finishing bases for processing in all operations, you must use
principle of combining bases
principle of constancy of bases
installation bases only
installation and design bases
The ability of a structure and its elements to resist external loads without collapsing is called
rigidity
sustainability
strength
elasticity
Block B
Assignment (question)
Response standard
Limited application of the principle of interchangeability and the use of fitting work is typical for ____________
single assembly production.
The main basing schemes in metalworking are _________________________________________________
basing of prismatic blanks, basing of long and short cylindrical blanks.
The degree to which a part corresponds to the specified dimensions and shape is called ________________________________
processing accuracy.
The amount of movement of the tool per revolution of the workpiece is called ___________________
Based on their purpose, the surfaces of parts are classified into ___________________________________________________
into main, auxiliary, executive, free
A working drawing of a part, a drawing of a workpiece, technical specifications, and an assembly drawing of a part are the initial data for the design _____________________________
technological process.
To compensate for errors that arise when selecting workpieces, __________________________________ is prescribed.
allowance for processing.
A set of periodically alternating elevations and depressions with a ratio is called _____________________
surface waviness.
One of the sizes forming a dimensional chain is called ________________________________
dimensional unit.
The assembly of blanks, components or the product as a whole, which are subject to subsequent disassembly, is called _________________________
pre-assembly
Option-2
Block A
Assignment (question)
Response standard
Instructions for completing tasks No. 1-3: correlate the content of column 1 with the content of column 2. Write down the letter from column 2 in the appropriate lines of the answer form, indicating the correct answer to the questions in column 1. As a result of completion, you will receive a sequence of letters. For example,
№ tasks
Possible answer
1
1-B, 2-A, 3-B
Establish correspondence: to determine which parameters for analyzing the manufacturability of a part, these formulas are used
1 – G;
2 – B;
3 – A;
4 – B
Coefficient
A. Processing accuracy coefficient
B. Surface roughness coefficient
B. Material utilization rate
D. Coefficient of unification of structural elements
Match the graphic designation with the name of the support, clamp and installation device.
1 – B
2 – B
3 – A
4 – G
graphic designation
1. 3.
Name
A – collet mandrel
B – floating center
B – fixed support
G – adjustable support
Establish a correspondence between the processing sketch and its name
1 – B
2 – G
3 – A
4 – B
Name
A. Parallel multi-tool single.
B. Sequential multi-tool single.
B. Parallel-sequential multi-tool single.
G. Parallel single-tool single
Instructions for completing tasks No. 4-20: Select the letter corresponding to the correct answer and write it down on the answer form.
- this is the formula to determine
piece time
main time
auxiliary time
technological norm of the time
route map
process map
transaction card
technological instructions
Machine tools, intended for the manufacture of products of the same name and different sizes
universal
specialized
special
mechanized
Determine the type of production if the coefficient of consolidation of operations KZ = 8.5
small-scale production
medium-scale production
large-scale production
mass production
surface roughness formed by removing a layer of material is indicated by the sign
2. 4.
Mass production is characterized
narrow range of manufactured products
limited range of products
wide range of manufactured products
different range of manufactured products
– this is the formula for determining
cutting speed
minute feed
spindle speed
cutting depths
An item or set of items of production to be manufactured at an enterprise is called
assembly unit
product
4. as a set
Connections that can be disassembled without damaging the mating or fastening parts are called
mobile
detachable
permanent
motionless
When planning the area in front of the machines, a worker's space with a width of
– this is the formula to determine
design interference
interference in mating
temperatures of mating parts
effort when pressing parts
Define the term – defective layer
a layer of metal designed to be removed in one operation
the minimum required thickness of the metal layer to perform the operation
a surface layer of metal whose structure, chemical composition, and mechanical properties differ from the base metal
a layer of metal intended for removal during all operations
When basing a workpiece in a fixture using technological bases not related to measuring ones, problems arise.
fastening errors
installation errors
processing errors
basing errors
Single, non-regularly repeated deviations from the theoretical shape of the deviation surface are called
surface waviness
macrogeometric deviations
surface roughness
microgeometric deviations
The error that occurs before applying clamping force and during clamping is called
reference error
installation error
fixing error
fixture error
To ensure high hardness of the working surfaces of wheel teeth, a type of heat treatment is used
carburization followed by hardening
nitriding followed by hardening
cyanidation followed by hardening
oxidation followed by hardening
the property of a product that allows it to be manufactured and assembled at the lowest cost is called
repair manufacturability
production manufacturability
operational manufacturability
product manufacturability
Block B
Assignment (question)
Response standard
Instructions for completing tasks No. 21-30: In the appropriate line of the answer form, write down a short answer to the question, the end of a sentence or missing words.
To clearly illustrate the technological process, use ____________________
sketch map
Automated process control systems, in which the development of corrective actions on the controlled technological process occurs automatically, are called ________________________
managers
Surface irregularities formed as a result of the impact of the cutting edge of the tool on the machined surface are called _________________________
microgeometric deviations.
Deformation and wear of machine tools, wear of cutting tools, clamping force, thermal deformation affect __________
processing accuracy
A product whose components are interconnected is called ____________________________
assembly unit.
The technological process of manufacturing a group of products with common design and technological features is called ________________________
When processing the base surfaces of body parts, _________________________ is taken as the primary base.
rough main holes
A part formed from a set of bushings interconnected by rods is called ______________________
Compliance with the exact compliance of the technological process of manufacturing or repairing a product with the requirements of technological and design documentation is called _________
technological discipline
Products that are not connected at the manufacturer, representing a set of auxiliary products, are called _________________________________
set
Section 3 Codification system
Name of didactic unit
Option number
Question numbers
Technological processes of mechanical processing
4; 5; 6; 10, 14, 25
Precision machining.
Surface quality of machine parts
Selecting bases when processing workpieces
3, 12, 13, 18, 19, 22
Machining allowances
Design principles, rules for the development of technological processes
Concept of technological discipline
Auxiliary and control operations in the technological process
Calculations for the design of machine operations
Technological setup diagrams
Requirements for the development of calculation and technological maps for CNC machines
Time norm and its structure
Methods for standardizing labor processes, standards for technical standardization
Organization of technical and regulatory work at a machine-building enterprise
Methods for processing the main surfaces of typical machine parts
Programming the processing of parts on machines of different groups
Technological processes, production of standard parts for general engineering applications
Technological processes for manufacturing parts in a flexible production system (FPS), on automatic rotary lines (ARL).
Automated process design
Machine assembly technology.
11; 12; 14; 25; 30
Methods of implementation, production debugging of technological processes, monitoring compliance with technological discipline
Product defects: analysis of causes, their elimination
Fundamentals of designing machine shop sections
Section 4 References
Averchenkov V.I. and etc. Mechanical engineering technology. Collection of tasks and exercises. – M.: INFRA-M, 2006.
Bazrov B.M. Fundamentals of mechanical engineering technology. – M.: Mechanical Engineering, 2005.
Balakshin B.S. Fundamentals of mechanical engineering technology - M.: Mashinostroenie, 1985.
Vinogradov V.M. Mechanical engineering technology. Introduction to the specialty. – M.: Mechanical Engineering, 2006.
Gorbatsevich A.F., Shkred V.A. Course design in mechanical engineering technology - Mn.: Higher School, 1983.
Danilevsky V.V.. Mechanical engineering technology. – M.: Higher School, 1984.
Dobrydnev I.S. Course design in the subject "Mechanical Engineering Technology". – M.: Mechanical Engineering, 1985.
Klepikov V.V., Bodrov A.N. Mechanical engineering technology. – M.: FORUM – INFRA-M, 2004.
Matalin A.A. Mechanical engineering technology - L.: Mechanical Engineering, 1985.
Mikhailov A.V., Rastorguev D.A., Skhirtladze A.G. – Fundamentals of designing technological processes of mechanical assembly production. – T.: Tolyatti State University, 2004.
