Firstly, the processed parts are analyzed and studied, and part drawings are drawn.
After getting the design topic, we must first analyze the structure and technology of the processed parts. Its main contents are:
(1) Find out the structural shape of the parts, understand which surfaces need to be machined and which surfaces are the main machined surfaces, and analyze the shape, size, accuracy, surface roughness and design basis of each machined surface;
(2) Make clear the functions and working conditions of all components on the whole machine;
(3) Define the material, heat treatment and technical requirements on the part drawing;
(4) Analyze the manufacturability of the parts structure and understand the manufacturing difficulty of each machining surface.
The purpose of drawing the machined parts is to deepen the understanding of the above problems, not to copy the drawings mechanically, but to analyze and understand the parts during the drawing process. If there are omissions, errors, poor workmanship or places that do not meet the national standards on the part drawing, suggestions for revision should be put forward and corrected during drawing. Students should draw carefully according to the national standard of Mechanical Drawing, and unless the tutor agrees in special circumstances, draw according to the ratio of 1: 1.
Second, make clear the production type and determine the basic characteristics of the process.
(1) According to the size of the product and the production procedure of the parts, it is clear whether the production type is single piece and small batch production, batch production or batch production.
(2) According to the production type and production conditions, determine the basic characteristics of the process, such as: whether the process is centralized or decentralized, whether to use special machine tools or CNC machine tools, whether to use conventional process methods or new or special processes.
Thirdly, choose the type and manufacturing method of the blank, determine the size of the blank and draw the blank map.
Blanks are divided into castings, forgings, weldments, profiles, etc. The selection of blank should be considered comprehensively from the size of production batch, the complexity of parts, the technical requirements of machined and non-machined surfaces and so on. Correct selection of blank manufacturing method can make the whole process more economical and reasonable, and should be treated with caution. The working steps are as follows:
(1) Determine the type and manufacturing method of the blank according to the production type, materials and requirements for material performance, the complexity of the shape and size of parts, technical requirements and the possibility in production;
(2) Determine the total machining allowance (blank allowance) of each machining surface;
(3) Calculate the blank size, determine the blank size tolerance and technical requirements, and draw the blank map.
In the blank drawing, the outline of the blank is required to be drawn with thick solid lines, and the physical dimensions of the parts are drawn with two-dot chain lines, with the ratio of 1: 1. At the same time, the size, tolerance, technical requirements, parting surface, fillet radius and draft angle of the blank should be marked on the drawing.
Fourth, choose the processing method and draw up the process route.
(1) Select the positioning datum.
According to the structural characteristics, technical requirements and the specific situation of the blank, the positioning datum of each process is reasonably selected according to the principle of datum selection. Generally, the fine benchmark is considered first, and then the coarse benchmark is selected. When the positioning datum of a process is inconsistent with the design datum, its process size needs to be transformed. The selection of positioning datum has an important influence on ensuring machining accuracy, determining machining sequence, number of processes and fixture structure. The positioning datum, machining surface and clamping position on the parts should be coordinated and unified and comprehensively considered.
(2) Select the processing method and processing scheme of each surface.
There are many cutting methods, such as turning, drilling, boring, milling, planing, grinding and drawing. According to the processing requirements of each surface, the final processing method is selected first, and then the processing methods of each subsequent process are determined forward. When determining the surface processing methods, we should also consider the economic processing accuracy and surface roughness that each processing method can achieve. Generally, the main surface processing, main technical requirements and key technical problems are concerned first.
(3) Arrange the processing sequence, divide the processing stages and work out the process route.
Determine the processing sequence of each surface, including cutting processing sequence, heat treatment process and auxiliary process. The general processing sequence should be: roughing first, finishing second, surface first, hole later, base surface first, others, interspersed with heat treatment in sections, and inspection arranged as required. Problems such as centralization and decentralization of working procedures should also be considered. On the basis of the above parts analysis, the process route is formulated. For more complex parts, several schemes can be considered first, and then a more reasonable machining scheme can be selected after analysis and comparison.
5. Process design and process calculation.
(1) Determine the machine tools, fixtures, tools, measuring tools and auxiliary tools used in each process.
The types, specifications and accuracy of selected machine tools, fixtures, cutters and measuring tools should be suitable for the scale, accuracy, production type and specific conditions of the factory. The choice of machine tool equipment should not only ensure the processing quality, but also be economical and reasonable. Under the condition of mass production, general machine tools and special fixtures should be used.
At this time, you should carefully consult the relevant manuals or field surveys and record the relevant parameters of the selected machine tool or fixture, such as machine tool model, specification, workbench width, T-groove size, etc. Tool form, specification and connection with machine tools; Design requirements of fixtures and special tools, and connection mode with machine tools, etc. Make necessary preparations for filling in the process card and fixture design in the later stage to avoid repeated references.
(2) Determine the machining allowance and the size and tolerance between processes.
According to the arrangement of process route, it is required to determine the machining allowance step by step and face by face. The dimensional tolerance between processes should be determined according to economic accuracy. The total machining allowance of surface is the sum of machining allowance of each process of surface.
In this design, students can directly check the allowance and tolerance of each machining surface from the Concise Handbook of Mechanical Manufacturing Process Design or other related materials.
(3) Determine the cutting parameters of each process.
In single piece and small batch production, the cutting quantity is often not specified in detail, but determined by the operator according to the specific situation to simplify the process documents. In mass production, cutting parameters should be selected scientifically and strictly to give full play to the potential and role of efficient equipment.
In this design, students are required to calculate the cutting parameters of 1 process by formula on the basis that the machine tool, cutter and machining allowance have been determined. The cutting parameters of other processes can be found in the cutting parameter manual or other relevant materials.
(4) Calculate the time quota
As an understanding of the method of determining the working hours quota, the curriculum design can only determine the single working hours quota of 1 process, which can be determined by table lookup method or calculation method.
Six, fill in the process documents
The process planning and design results of the above parts need to be expressed in the form of charts, cards and written materials for implementation. These charts, cards and written materials are collectively referred to as process documents. There are many process documents used in production, such as machining process cards and machining process cards. For details, please refer to the mechanical industry standard "Process Specification Format JB/T9 165". 2-1998 ".If the above contents and processing sketches of each process are filled into the machining card and machining card, it meets the actual requirements of the factory, but the space is large.
In order to reduce the space, the special machining card and machining card for curriculum design are used, which can be filled in separately or together.
The process drawing in the machining process card can be scaled down and drawn with as few projections as possible. The sketch can also only draw partial views related to the machined parts, and other lines can be omitted except the machined surface, the locating surface, the clamping surface and the main contour surface, subject to the necessity and clarity.
The machined surfaces in the sketch are represented by thick solid lines, and the rest are represented by thin solid lines. The size, tolerance and surface roughness of each machined surface after this process should be marked. Positioning and clamping surfaces shall be marked with specified symbols. See the machining positioning and clamping symbol JB/T5061-1991for details.
Seven, design special fixture
On the basis of completing the design of parts processing procedure, a special fixture for a certain process is designed. Obviously, the production procedure, part drawing and process drawing of parts are the basis of fixture design. The production procedure determines the complexity and automation of the fixture; The part drawing gives the specific requirements of the size, shape, position accuracy and surface roughness of the workpiece. The process diagram gives the process benchmark, process size, machined surface and surface to be machined, as well as the positioning and clamping principle scheme of the process, which is the direct basis for fixture design.
(1) Make overall planning and sketch the structure.
The determination of the overall scheme of special fixture is a very important design procedure, and the scheme often determines the success or failure of fixture design. Therefore, it is necessary to conduct sufficient research and discussion to determine the best scheme, rather than rushing to draw and engage in hasty work.
Sketch can be done by hand, or directly modified by drawing on the drawing paper according to the size ratio. Draw only the main part, not the same detailed structure. The drawing process of the sketch is as follows.
(1) Take the position of the workpiece faced by the workers in this process as the main view, draw the three-view outline of the workpiece with two-dot chain line on the sketch, pay attention to the need to draw the positioning surface, clamping surface and machined surface, and sometimes make necessary changes to the part drawing.
(2) According to the machining requirements of this process and the selection of benchmarks, determine the positioning mode of the workpiece and the structure of the positioning element. This is a process to realize the positioning method on the process diagram. It is necessary to select positioning elements and their installation methods on the fixture, and draw these positioning elements on the corresponding positions of the machined parts on the sketch.
(3) Determine the tool guide and tool alignment mode, and select the guide and tool alignment parts. Generally speaking, different types of fixtures (drilling fixture, boring fixture, milling fixture, etc. ) has different tool guidance and tool alignment methods. When designing, we must first determine what kind of fixture it is, and then choose its guiding and tool alignment methods. Similarly, the selected guiding and tool setting elements and their installation methods are also drawn on the sketch at the corresponding positions of the machined parts.
(4) According to the basic principle of clamping, determine the clamping mode of the workpiece, the direction of clamping force and the position of the action point, select the appropriate clamping mechanism and draw it on the corresponding position of the machined part in the sketch.
⑤ Determine the structural forms of other components or devices, such as connectors and indexing devices. These structures have some commonly used standard structures and standard parts, which are selected and confirmed after being found in the data. It is also drawn on the corresponding position of the machined part in the sketch.
⑥ Specially designed fixture. All devices, such as positioning elements, tool setting elements, clamping elements and other elements, are connected into a whole by clamping bodies. The fixture body is also used to ensure the correct position of the fixture relative to the machine tool. The milling fixture should have positioning keys, and the drilling fixture should pay attention to the structural design of drilling template and lathe fixture connected with spindle.
⑦ Calculate the positioning error and clamping force. After the sketch of fixture structure is completed, the positioning error of fixture should be analyzed and calculated to check whether the tolerance and technical requirements of fixture meet the dimensional tolerance and technical requirements of workpiece technology. If the calculation results are out of tolerance, it is necessary to change the positioning method or improve the manufacturing accuracy of the positioning parts and surfaces, so as to reduce the positioning error and improve the machining accuracy. Sometimes it is even necessary to fundamentally change the arrangement of process routes to ensure the smooth processing of parts.
When using electric clamping, the clamping force should be calculated. It should be pointed out that due to the great differences in machining methods, cutting tools and clamping methods, there is no ready-made formula for the calculation of clamping force in some cases, and students need to analyze and study according to the theories they have learned in the past to determine a reasonable calculation method.
(2) Draw the fixture assembly drawing.
Drawing fixture assembly drawing is an important part of fixture design, and the matters needing attention are as follows.
① Draw with the ratio of 1: 1 as far as possible to make the graph intuitive. Depending on the view size, the ratio of 1: 2 or 2: 1 can also be adopted.
(2) Draw the outline, positioning datum, clamping surface and machining surface of the machined part with two-dot chain line. The workpiece is transparent in the drawing, which will not affect the projection of fixture components.
③ Try to give priority to the view of the operator's relative position in front, which is based on the complete and clear expression of the working principle, structure and assembly relationship of each part of the fixture. In general, it is best to draw three views, and if necessary, draw a partial view or a section.
(4) Refer to the sketch, select and arrange the views reasonably, and pay attention to leave enough distance between the views, so as to draw out the part number, mark the dimensions and technical requirements. Draw a scaled-down process drawing at an appropriate position for inspection, manufacture, assembly and inspection when reading the drawing.
⑤ Draw the assembly drawing according to the clamping state of the clamping mechanism. For some jigs whose positions may change in use and have a wide range, such as clamping handles or other moving or rotating elements, if necessary, the limit positions are indicated by two-dot chain lines to check whether they interfere with other elements, parts, machine tools or cutters.
⑥ In order to reduce the machined surface area and the number of machining strokes, the joint surface of the fixture and other fixture components should be designed as a boss with the same height, and the height of the boss is generally 3-5mm higher than that of the non-machined casting surface. If the joint surface is processed by other methods, its structural size can also be designed as counterbore or groove.
⑦ All parts on the clamp body should be reliably connected with the clamp body. In order to ensure the safety of workers' operation, socket head cap screws (GB/T 70. 1-2000) are generally used for firm connection. If relative position accuracy is required, two cylindrical pins (GB/T 1 19-2000) are needed for positioning.
⑧ For standard parts or standard institutions, such as standard hydraulic cylinders, cylinders, etc. , it is not necessary to show the section structure.
Pet-name ruby after the completion of the assembly drawing, according to a certain order leads to the part number of each component and parts. Usually, starting from the segment with the part number 1, each part number is led out clockwise. If it is necessary to replace fixture parts during work (such as quick-change drill sleeves for drilling, reaming and reaming), three part numbers should be led out at one lead-out end.
Attending if some parts need to be replaced in use, it will be drawn by a part in the view. In order to express the replaced parts, the assembly relationship of the replaced parts can be expressed by local section, and explained under technical requirements or local section.
In addition, the dimensions, tolerances and technical requirements should be reasonably marked on the fixture assembly drawing. Finally, draw the title bar and parts list, indicating the name, quantity, material grade and heat treatment hardness of the parts.
(3) Drawing part drawings
Draw 1 key and nonstandard fixture parts, such as fixture body. Draw a special part drawing according to the drawn assembly drawing. The specific requirements are as follows:
(1) The projection of the part drawing should be as consistent as possible with the projection position on the general drawing for easy reading and inspection;
(2) The dimensions should be complete and clear, so as to avoid omission and facilitate drawing reading and processing;
③ The shape, size, mutual position accuracy, surface roughness, material, heat treatment and surface treatment requirements of the part should be fully expressed;
(4) The machining surface size of the same type of work should be concentrated as far as possible;
⑤ For the dimensions that can be guaranteed by combined processing after assembly, the words "according to the general drawing" should be marked after the dimension value, such as the dimension between the drill sleeve and the locating pin;
⑥ Pay attention to the selection of design benchmark and process benchmark;
⑦ Some form and position tolerances with low requirements are guaranteed by processing methods and can be omitted;
⑧ In order to facilitate processing, the dimensions should be marked in the processing order as far as possible to avoid size conversion.
Eight, the preparation of curriculum design instructions
Writing design instructions is an important part of the whole curriculum design. By writing instructions, students' ability of analysis, summary and expression is further cultivated, and the knowledge gained in the design process is consolidated and deepened.
Instruction is the summary document of curriculum design. After completing all the work of curriculum design, students should write all the design work into design instructions in order. It requires concise language, fluent words and clear illustrations. The specification shall give an overall introduction to the whole design. The contents of each part in the design should be emphasized, analyzed and demonstrated, and necessary calculations should be made. It is required to be systematic, vivid and illustrated, and to fully express their opinions, and strive to avoid scripted. The source of formulas, charts, data, etc. The reference number should be marked with [] in the text.
Students should always record the design contents, calculation results, analysis opinions and data sources, as well as teachers' reasonable opinions, their own opinions and conclusions from the beginning of design. After each design stage, the descriptions of related components can be sorted out and compiled immediately. After all the designs are completed, they can be bound into a book with a little finishing.
A complete manual generally includes the following items:
(1) cover.
(2) Directory.
(3) Design task book.
(4) Introduction or preface.
(5) Process analysis of parts, including function, structural characteristics, structural manufacturability and technical requirements analysis of key surfaces.
(6) Process design and calculation.
① blank selection and blank drawing description;
(2) Determination of process route, including selection of coarse and fine benchmarks, determination of surface processing method, consideration of concentration and dispersion of processes, principle of sequence arrangement of processes, selection of processing equipment and process equipment, analysis and comparison of different schemes, etc.
③ Determination of machining allowance, cutting dosage and working hour quota (explain the data source and calculate the working hour quota of the process specified by the teacher);
④ Determination of process size and tolerance (only the process size specified by the teacher is calculated, and the rest are simply explained).
(7) Fixture design.
① Comparison of design ideas of different schemes;
② Positioning analysis and positioning error calculation;
(3) the design of tool setting guide device;
④ Design of clamping mechanism and calculation of clamping force;
⑤ Operation instruction of fixture (also combined with item (1)).
(8) Design summary or experience.
(9) Bibliography of references (books have been numbered so as to be quoted in the text).