Welding Fixture and Checking Gauge Design for Clutch Pedal 檢查離合器踏板焊接夾具和量具的設(shè)計(jì)

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1、 Welding Fixture and Checking Gauge Design for Clutch Pedal Assembly CHAPTER 1: INTRODUCTION 1.1 Introduction The first manufactured products were made one at a time. Early artisans started with little more than raw materials and a rough idea of the finished pro

2、duct. They produced each product piece by piece, making each part individually and fitting the parts into the finished product. This process took time. Moreover, the quality and consistency of products varied from one artisan to the next. As they worked, early manufacturing pioneers realized the nee

3、d for better methods and developed new ideas. Eventually, they found the secret of mass production: standardized parts. Standard parts not only speeded production, they also ensured the interchangeability of parts. The idea may be obvious today, but in its time, it was revolutionary. These standard

4、parts were the key to enabling less-skilled workers to replicate the skill of the craftsman on a repetitive basis. The original method of achieving consistent part configuration was the template. Templates for layout, sawing, and filing permitted each worker to make parts to a standard design. While

5、 early templates were crude, they at least gave skilled workers a standard form to follow for the part. Building on the template idea, workers constructed other guides and work holders to make their jobs easier and the results more predictable. These guides and work holders were the ancestors of tod

6、ays jigs and fixtures. Yesterdays work holders had the same two basic functions as todays securely holding and accurately locating a work piece. Early jigs and fixtures may have lacked modern refinements, but they followed many of the same principles as today’s work holder designs. The project is

7、to design a fixture for Clutch pedal. The part is machined in two more industries increasing the cost and machining time of the part. To eliminate outsourcing of the part the company has designed a fixture. The project is to design a fixture which will perform the remaining operation. Fixture is d

8、esigned to hold the object during its operation to avoid any errors in the dimension and for mass production. In any industry the accuracy is much important. Any error in the product may be harmful or dissatisfactory to the customer. In order to avoid this checking fixture is essential. Checking fix

9、ture checks whether the product is dimensionally correct or not. If there is any error in the structure or dimension the product gets rejected. Welding fixtures are normally designed to hold and support the various components (workpieces) to be welded. It is necessary to support them in a proper

10、location which is capable of preventing distortions in workpieces during welding. For this the locating elements need to be placed carefully, clamping has to be light but firm, placement of clamping elements has to be clear of the welding area and the fixture has to be quite stable and rigid to with

11、stand the welding stresses. There is no limit of designing a welding fixture. Its design depends on and driven by the hard facts that are what you want, and how to overcome the problems appearing with the current fixture. Keeping the defect free fast production rate as major target. The famous sayin

12、g “Necessity is the mother of invention” hold perfectly true in case of welding fixture design. 1.2 Project Directives Objectives: The main purpose of our project is to design a welding fixture and checking gauge to manufacture Clutch Pedal for Mahindra & Ma

13、hindra M-star tractor as per requirements of inspection and testing department. This is done to provide fast mechanism to manufacture Clutch pedal as per requirement of client and also at minimum cost. Scope of work: Design is the major and important factor in determining efficiency an

14、d work ability of the machine. Working capacity, precision, rate of production etc. are the factors affecting the basic designing of Clutch pedal. This project is an endeavor towards sophisticating ways of designing the given component to increase the accuracy and production rate of the

15、 work. This project will give us the exposure to different technical ideas regarding operation, design software and difficulties while operating them. Constraints: The main constraints are Critical Characteristics and Significant Characteristics which are mentioned in 2D Product Dra

16、wings, Any failure in archiving Significant Characteristics may led to fouling or the part may not fit properly in vehicle and any failure in archiving in Critical Characteristics may led even led to accidents. So Design Constraints must be archived within tolerance limit. This is mainly manufacturi

17、ng based project hence the main constraints is to achieve this at minimum cost and with required flexibility by using existing equipment available in the workshop. CHAPTER 2: LITRATURE SURVEY 2.1 Welding The term welding refers to the process of metallurgical joining of two similar or diss

18、imilar metals by heating them to their melting temperature and causing the molten metal to flow together with or without application of pressure, with or without use of filler material. Welding is widely used by metalworkers in the fabrication, maintenance, and repair of parts and structures. While

19、 there are many methods for joining metals, welding is one of the most convenient and rapid methods available. Welding is not new. The earliest known form of welding, called forge welding, dates back to the year 2000 B.C. Forge welding is a primitive process of joining metals by heating and hammerin

20、g until the metals are fused (mixed) together. Although forge welding still exists, it is mainly limited to the blacksmith trade. Today, there are many welding processes available. The primary differences between the various welding processes are the methods by which heat is generated to melt the m

21、etal. The most common types of welding are oxy-fuel gas welding (OFW), arc welding (AW), and resistance welding (RW). Fig. 2.1.1: MIG Welding 2.2 Welding Process Involved Fig. 2.2.1: Typical Arrangement of MIG Welding Process Company uses MIG (Metal Inert gas welding) welding process

22、 This process is also popularly known as CO2 Welding process because shielding inert gas used contains 80% Argon & 20% CO2, Also called as GMAW (Gas Metal Arc welding). Metal electrode used is consumable and made of Copper Material It is a Fusion Welding process 2-4 mm of gap is maintained b

23、etween workpiece and electrode No special flux material is required Direct Current Reverse Polarity (DCRP) connection is used (negative terminal connected to work and positive terminal connected to electrode) Fig. 2.2.2: MIG Welding Machine 2.3 Welding Parameter Table 2.3.1: Welding Para

24、meters Sr. No. Parameter Value 1 Voltage 25 – 35 V 2 Current 140 – 150 Amp 3 Gas Flow 10 – 12 dm3/min 4 Wire Speed 12 – 17 m/min 5 Wire Diameter 0.8 mm 2.4 Fixture A fixture is a work holding or support device used in the manufacturing industry. What makes a fixture unique

25、is that each one is built to fit a particular part or shape. The main purpose of a fixture is to locate and in some cases hold a work piece during either a machining operation or some other industrial process. A jig differs from a fixture in that it guides the tool to its correct position in additio

26、n to locating and supporting the work piece. Fixtures are devices which are used to increase the production rate of similar parts and reduce human efforts. Fixture varies in design from relatively simple tools to expensive, complicate devices. The primary purposes of fixtures are: Reduce the cos

27、t of production Maintain consistent quality Maximize efficiency Fixture is device which i. Locates job. ii. Clamps job. iii. But does not guide/locate tool used for operation Fixture serves to reduce production time and production cost. It assures high accuracy for job, safety in work i

28、s archived. With the help of fixture operations such as marking, measuring, laying out are totally eliminated. Some basic elements of fixture are a. Body b. Locating Elements c. Clamping Elements d. Setting Elements e. Positioning Elements f. Indexing Elements Fixtures are basically of two

29、 types viz. 1) Permanent Fixture 2) Modular Fixture. Modular fixture is a work holding device that uses standard reusable to construct and customize work holding device. Modular fixtures are just like permanent fixture with some key differences they are as follows: Modular Fixtures can be asse

30、mbled entirely from off the shelf components without machining. Many modular components are adjustable and universal. Specially designed tooling plates and blocks with standard grid pattern are foundation of good modular fixture Tooling plates and blocks are main structural elements of any mod

31、ular fixture system. Any fixture should be designed such that it maintains a proper workpiece control. Several theories and techniques to maintain work piece control are as follows: 1. Equilibrium theories 2. Concept of location 3. Geometric control 4. Dimensional control 5. Mechanical co

32、ntrol 6. Alternate location theories 2.4.1 Classification of fixture: There are many ways to classify fixture: 1) Classification according to the operation These are drilling, milling, boring, assembly, inspection, transfer, welding, spraying fixture etc. 2) Classification based o

33、n the mode of working Hand or manually operated fixture, pneumatic fixture, hydraulic fixture, automatic fixture etc. 3) Universal fixtures Devices in this class can hold any job within their design capacity eg. Mechanical vise is a universal fixture, which can hold any jobs in the jaws. A

34、three jaw self centering chuck can hold any cylindrical job in it jaws and a four jaw chuck can hold the job having an irregular cross section. A part having a machine tool bedplate is also a universal fixture on which any job can be clamped using T-slots on it. An indexing head is universal holding

35、 and positioning fixture. It can hold on a chuck or plate. Following are the purpose and advantages of fixtures: It reduces or sometimes eliminates the efforts of marking, measuring and setting of workpiece on a machine and maintains the accuracy of performance. The workpiece and tool are r

36、elatively located at their exact positions before the operation automatically within negligible time. So it reduces product cycle time. Variability of dimension in mass production is very low so manufacturing processes supported by use of jigs and fixtures maintain a consistent quality. Due to

37、 low variability in dimension assembly operation becomes easy, low rejection due to les defective production is observed. It reduces the production cycle time so increases production capacity. Simultaneously working by more than one tool on the same workpiece is possible. The operating conditi

38、ons like speed, feed rate and depth of cut can be set to higher values due to rigidity of clamping of workpiece by jigs and fixtures. Operators working become comfortable as his efforts in setting the workpiece can be eliminated. Semi-skilled operators can be assigned the work so it saves the

39、cost of manpower also. There is no need to examine the quality of produce provided that quality of employed fixtures is ensured. 2.4.2 General requirement of fixture In order to maintain the workpiece stability during a machining process, an operational fixture has to satisfy several requirem

40、ents to fully perform its functions as a workholding device. The following constraints must be observed while designing a viable fixture: Deterministic location: A workpiece is said to be kinematically restrained when it cannot move without losing contact with at least one locator. The workpiece

41、 is constrained by a set of appropriately placed locators so that it is presentable for the machining operation. Locating errors due to locators and locating surfaces of the workpiece should be minimized so as to accurately and uniquely position the workpiece within the machine coordinate frame. T

42、otal constraint: A workpiece should be fully constrained at all times to prevent any movement. Clamps should provide locking forces to hold the workpiece in place -once it is located. A totally restrained part should be able to remain in static equilibrium to withstand all possible processing forc

43、es or disturbance. A necessary and sufficient condition to warrant workpiece stability is to satisfy the condition of force closure. Contained deflection: Workpiece deformation is unavoidable due to its elastic/plastic nature, and the external forces impacted by the clamping actuation and machin

44、ing operations. Deformation has to be limited to an acceptable magnitude in order to achieve the tolerance specifications. Geometric constraint: Geometric constraint guarantees that all fixturing elements have an access to the datum surface. They also assure that the fixture components do not inte

45、rfere with cutting tools during a machining operation. In addition to these requirements, a fixture design should have desirable characteristics such as quick loading and unloading, minimum number of components, accessibility, design for multiple cutting operations, portability, low cost, etc.

46、 2.5 Checking Gauge Fixture is designed to hold the object during its operation to avoid any errors in the dimension and for mass production. In any industry the accuracy is much important. Any error in the product may be harmful or dissatisfactory to the customer. In order to avoid this che

47、cking gauge is essential. Checking gauge checks whether the product is dimensionally correct or not. If there is any error in the structure or dimension the product gets rejected. 2.5.1 Points to be considered while designing checking gauge: 1) Measuring places of part: Checking gauge should be a

48、pplicable for inspecting the places indicated by Plan sheet and Quality list the following places should be inspected generally. a) Assembled surface with other parts. b) Gap surface or gap line (parting line) between other parts. c) Touching surface (mainly with weather strip) d) Flushing lin

49、e (joint area, touching place) e) Surface on stepped touching area, joggling line f) Fastening hole for screw g) Inserting hole for part h) All other holes (Holes with unnecessary for inspection can be excluded, such as drain holes obvious for its position) i) Trim line j) Locator position

50、 2) Panel setting a) Panel with datum hole should be located by the datum hole. b) Place a panel on a datum face and setting surface, and the surface should be clamped basically. Datum face means the surface with coordinate holes and the surface indicated on quality list setting surface means as

51、followed. The place on which panel is located by assembly jigs in following operation Fixed place with screws on loose parts (panel fixed with screws). Surface which have large effect on that part or on the other part the minimum places should be selected as setting surface most appropriate for sett

52、ing the panel shape. c) Full examination is required for setting the loose parts. Fixed place with screws on loose parts as setting surface. Loose parts (Hood, Door, Fender, etc.) should be provided on C/F by coordinate holes. 2.6 Degree of Freedom A body in a space c

53、an have following motions or movements a) Translation motion i. Along ‘X-X’ Axis ii. Along ‘Y-Y’ Axis iii. Along ‘Z-Z’ Axis b) Rotary motion iv. Along ‘X-X’ Axis v. Along ‘Y-Y’ Axis vi. Along ‘Z-Z’ Axis Thus a free body in space has three translation motion and three rotary motions. Thes

54、e are six degree of freedom of free body in space. The main purpose of this concept is that the workpiece in fixture is fully constrained with the help of locator and clamping device. Fig. 2.6.1: Degree of Freedom of Body in Free Space Degrees of freedom are to be constrained in the fixture and

55、checking gauge to serve the purpose of location. 2.7 M – Star Tractor Clutch Pedal Fig. 2.7.1: Clutch Pedal Figure above shows clutch pedal which is to be welded on welding Fixture. It has five basic parts viz. 1. Clutch Pivot Assembly 2. Clutch Pedal 3. Foot Pedal 4. Pedal Bush M-S

56、tar 5. Support Gusset Clutch Pedal The Weld length is 306 mm. CHAPTER 3: DESIGN & MANUFACTURING Successful fixture designs begin with a logical and systematic plan. With a complete analysis of the fixtures functional requirements, very few design problems occur. When they do, chances a

57、re some design requirements were forgotten or underestimated. The workpiece, processing, tooling, and available machine tools may affect the extent of planning needed. Preliminary analysis may take from a few hours up to several days for more complicated fixture designs. 3.1 Five-step problem sol

58、ving process Fixture design is a five-step problem-solving process. The following is a detailed analysis of each step. Step 1: Define Requirements To initiate the fixture-design process, clearly state the problem to be solved or needs to be met. State these requirements as broadly as possible, b

59、ut specifically enough to define the scope of the design project. The designer should ask some basic questions: Is the new tooling required for first-time production or to improve existing production? If improving an existing job, is the goal greater accuracy, faster cycle times, or both? Is the t

60、ooling intended for one part or an entire family of parts? The tooling designer must determine how much freedom and input there is on each project. If many choices regarding machine tools, operations, and cutting tools have already been made, the designers role will have a relatively narrow focus.

61、 Step 2: Gather/Analyze Information Collect all relevant data and assemble it for evaluation. The main sources of information are the part print, process sheets, and machine specifications. Make sure that part documents and records are current. For example, verify that the shop print is the curre

62、nt revision, and the processing information is up-to-date. Check with the design department for pending part revisions. An important part of the evaluation process is note taking. Complete, accurate notes allow designers to record important information. With these notes, they should be able to fil

63、l in all items on the "Checklist for Design Considerations." All ideas, thoughts, observations, and any other data about the part or fixture are then available for later reference. It is always better to have too many ideas about a particular design than too few. Four categories of design consider

64、ations need to be taken into account at this time: workpiece specifications, operation variables, availability of equipment, and personnel. These categories, while separately covered here, are actually interdependent. Each is an integral part of the evaluation phase and must be thoroughly thought ou

65、t before beginning the fixture design. Workpiece specifications usually are the most important factors and have the largest influence on the fixtures final design. Typically, these considerations include the size and shape of the part, the accuracy required the properties of the part material, the

66、locating and clamping surfaces, and the size of the run. Operation variables include the type of operations required to make the part, number of operations performed, and sequence of operations, inspection requirements, and time restrictions. Availability of equipment required to machine, assemble, and inspect a part often determines whether the fixture is designed for a single part or multiple parts. A process engineer sometimes selects the equipment to machin