385004424-Unit-6-Jigs-and-Fixture1s.pptx

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1. JIGS AND FIXTURES Presented by : NILAY SARKAR of CAMELLIA INSTITUTE OF TECHNOLOGY (3 rd year 6 th Semester) Roll No. - 23000723043

2. Introduction Jig: A device that holds the work and locates the path of the tool. Fixture: A device fixed to the worktable of a machine and locates the work in an exact position relative to the cutting tool

3. Jigs Device that holds, supports, or is placed on a part to be machined. locates and holds the work piece Guides the cutting tool For repeatability and exact duplication of a part for reproduction

4. jigs

5. Fixture Strong and rigid mechanical devices which attaches to a machine For quick and consistently accurate locating, supporting and clamping, blanks against cutting tools Much-wider scope of application than jigs Common fixtures include milling fixtures, lathe fixtures, sawing fixtures, and grinding fixtures

6. Material for jigs and fixtures Materials used in Jigs and fixtures are made from a variety of materials, some of which can be hardened to resist wear. Given below are the materials often used in jigs, fixtures, press tools etc. Some common materials are as following:  Hardened Steel.  Carbide.  Bronze.  Stainless Steel.

7. Basic element A sufficiently rigid body (plate, box or frame structure) into which workpiece is loaded. Locating elements Clamping elements Tool guiding elements (for Jigs), Tool setting elements (for Fixtures) Elements for positioning or fastening the jig or fixture on the machine on which it is used

8. Three two one locating principle All possible movement of an object in space can be describe with reference to linear motions along three perpendicular axes defining space and three rotational about these axes. These six basic movements can take place in a total of 12 different direction. The location system must stop movement in six directions of movement and the clamping forces must stop the others in the opposite directions. A definite pattern of placement of locators should be developed to constrain the movement of a body in space.

9. To illustrate the system of location the movement of the cube in space are considered. The pattern of arrangement is called the 3-2-1 location system. A triangle symbol is used to schematically represent a locator.

10. Considering the six degree of freedom of a rectangular block It is made to rest on several points on the jig body. Provide a rest to workpiece on three points on the bottom x-y surface. This will stop the movement along z-axis, rotation with respect to x-axis and y-axis. Supporting it on the three points is considered as better support then one point or two points. Rest the workpiece on two points of side surface (x-z), this will fix the movement of workpiece along y-axis and rotation with respect to z-axis.

11. Provide a support at one point of the adjacent surface (y-z) that will fix other remaining free movements. This principle of location of fixing points on the workpiece is also named as 3-2-1 principle of fixture design as number of points selected at different faces of the workpiece are 3, 2 and 1 respectively.

12. For a fixture designer, the major portion of design time is spent deciding how to locate the work piece in the fixture. You know that any free body has a total of twelve degrees of freedom as below: 6 translational degrees of freedom : +X, -X, +Y, -Y, +Z, -Z And 6 rotational degrees of freedom:  Clockwise around X axis ( CROT-X ) Anticlockwise around X axis ( ACROT-X ) Clockwise around Y axis ( CROT-Y ) Anticlockwise around Y axis ( ACROT-Y ) Clockwise around Z axis ( CROT-Z )  Anticlockwise around Z axis ( ACROT-Z )

13. You must fix all the 12 degrees of freedom except the three transitional degrees of freedom (-X, -Y and -Z) in order to locate the work piece in the fixture. So, 9 degrees of freedom of the work piece need to be fixed. But, how? By using the  3-2-1 method  as below: Rest the work piece on  three  non-collinear points of the bottom surface (XY), and you will be able to fix the  +Z ,  CROT-X ,  ACROT-X ,  CROT-Y  and  ACROT-Y  degrees of freedom . Now, rest the work piece at  two  points of side surface (XZ), and you will be able to fix the  +Y  and  ACROT-Z  degrees of freedom.

14. Now, rest the work piece at  one  point of the adjacent surface (YZ), and you will be able to fix the  +X  and  CROT- Z degrees of freedom. So, you can successfully fixate  9  required degrees of freedom by using the 3-2-1 principle of fixture design.

15. IMPORTANT CONSIDERATIONS WHILE DESIGNING JIGS AND FIXTURES Study of workpiece and finished component size and geometry. Type and capacity of the machine, its extent of automation. Provision of locating devices in the machine. Available clamping arrangements in the machine. Available indexing devices, their accuracy. Evaluation of variability in the performance results of the machine. Rigidity and of the machine tool under consideration. Study of ejecting devices, safety devices, etc. Required level of the accuracy in the work and quality to be produced

16. MEANING OF LOCATION The location refers to the establishment of a desired relationship between the workpiece and the jigs or fixture correctness of location directly influences the accuracy of the finished product. The jigs and fixtures are desired so that all undesirable movements of the workpiece can be restricted. Determination of the locating points and clamping of the workpiece serve to restrict movements of the component in any direction, while setting it in a particular pre-decided position relative to the jig. Before deciding the locating points it is advisable to find out the all possible degrees of freedom of the workpiece. Then some of the degrees of freedom or all of them are restrained by making suitable arrangements. These arrangements are called locators.

17. PRINCIPLES OF LOCATIONS Any rectangular body many have three axis along x-axis, y-axis and z-axis. It can more along any of these axes or any of its movement can be released to these three axes. At the same time the body can also rotate about these axes too. So total degree of freedom of the body along which it can move is six. For processing the body it is required to restrain all the degree of freedom (DOF) by arranging suitable locating points and then clamping it in a fixed and required position.

18. Principle of location The principle of minimum locating points The principle of mutually perpendicular planes The principle of extreme position of pins Relief should be provided where burr or swarf will get collected Locating surface should be raised above the surrounding surfaces of J/F so that chips can be swept off readily. Sharp corners in the locating surfaces must be avoided Adjustable type locators to be used for rough surfaces

19. Locating principle To position the work piece w.r.t. to tool, to ensure precision in machining Locating: dimensional and positional relation- ship b/w work piece and tool Locator: device to establish and maintain position of a part in a jig or fixture

20. Principle of Clamping 1)The clamping pressure applied against the workpiece must counteract the tool forces 2) The clamping pressure should not be directed towards the cutting operation. Wherever possible it should be directed parallel to it. 3) The clamping pressure must not damage/deform the work surface. 4) Clamps should be arranged directly above the points supporting the work, otherwise distortion of work may occur.

21. Principle of clamping 5) Clamping pressure should be directed towards the points of support, else the work will tend to rise from support 6) Clamping should be simple, effective and foolproof. 7) Fibre pads should be riveted to clamp faces to avoid damage to fragile workpieces

22. Types of jigs Jigs may be divided into two general classes: Boring jigs and Drill jigs Boring jigs are used to bore holes that either is too large to drill or must be made an odd size. Drill jigs are used to drill , ream, tap, chamfer, and counter bore, countersink . Basic jig is almost the same for either machining operation. The only difference is in the size of the bushings used

23. Channel Jig The work-piece is mounted against the top and one side of the jig. It is clamped from the third side It’s a type of box jig Provides better stability and support for workpiece This type is limited to work-pieces of simple symmetrical shapes It mainly consist of the jig body, jig bush and screws and w.p is clamped inside the channel with the help of screw.

24. Channel Jig

25. Template jigs Template jigs are normally used for accuracy rather than speed. This type of jig fits over, on, or into the work and is not usually clamped. Least expensive and simplest type of jig to use.

26. Plate jigs It is the modified form of the template jig with jig bushes incorporated on the temple Consist of a single bush plate with a provision for locating and clamping of w.p. They have built-in clamps to hold the work They use a flat plate containing bushing as their main structural member All the details are attached and referenced to this plate May or may not have legs Easy part loading and unloading, chip removal by providing clearance b/w plate and the w.p.

27. Plate jigs Similar to templates, The only difference is that plate jigs have built-in clamps to hold the work. Made with or without bushings, depending on the number of parts to be made.

28. Box jigs Surround the part totally Shape resembles a box In the figure, for loading, the cam rod is taken out of the jig and the w.p placed in position inside the jig. The cam rod is then replaced and rotated to its locking position This holds the work-piece firmly so that the drilling operation can be performed

29. Such jigs are generally used for components having irregular shapes or that cannot be held by common methods. Number of holes can be drilled economically with box jig. One side is open for loading and unloading the w.p and provided bushing arrangements. The box jig can permits drilling of holes in three sides of the work-piece and saves times and increase production.

30. Box jigs

31. TEMPLATE JIGS It is the form of jig consisting of a suitable material having holes for correct location. The plate serve as a template which is fixed on the component to be drilled. Temple jigs are normally used for accuracy rather than speed. Used for locating hole pattern on large workpieces. Usually not clamped (self-clamping). It is the least expensive . Simplest type of jigs. They may or may not have bushings. When the bushings are not used, the whole jig plate is normally hardened.

32. ANGLE-PLATE JIGS Used to machine parts at right angles to their locators. Pulleys and Gears use this type of jig. The locators are generally fixed to the vertical wall of the angular body. The central locator has groove for the passage of the drill after passing through the workpiece. The cylindrical locator and diamond pin locator are fixed to the vertical wall. C Washer and hexagonal screw is provided for clamping.

33. Latch type jigs Leaf jig has hinged jig plate. Drill bushes are fitted on the jig plate which is hinged at one end. The jig plate can be swung aside to provide clear path for workpiece loading and unloading. Clamping screw and drill bushes are accommodated in jig pate. The jig plate must have positive resting surface. The jig plate is clamped against the resting face by an eyebolt. Quick clamping and unclamping of the jig plate is possible. Handknob is provided to facilitate clamping

34. Types of fixture TYPES OF MILLING FIXTURES Milling Fixtures can be classified in a variety of ways: (1) According to the way the workpiece is clamped, such as hand-clamping fixtures, power-clamping fixtures, toggle fixtures etc. (2) According to the way the workpiece is located, such as center fixtures, V-block fixtures etc.

35. 3)According to the method of presenting the workpiece to the cutter, as rotary fixtures where the workpiece is rotated under the cutter. Indexing fixtures where the workpiece is indexed into the next position during the machining cycle. (4) According to the milling operation performed on work, such as face-milling fixtures, slabmilling fixtures, slotting fixtures, string-milling fixtures etc.

36. STRING or LINE MILLING FIXTURES: A number of components strung behind each other in a line The fixture moves relative to the cutters

37. HYDRAULIC CLAMPING FIXTURE:

38. SPRING TYPE FIXTURE:

39. CLAMP TYPE FIXTURE:

40. Welding Fixture The welding fixture is used where two or more parts needed to be welded with high accuracy. The fixture should be strong enough to withstand the welding.

41. Assembly Fixture The assembly fixture is used to assemble many parts of a component with ease. The processes can be carried on the part and desired component can be achieved.

42. Poka yoke In jigs and fixture Poka yoke is quality management concept developed by shigeo shingo to prevent occurrence of human error in the production line. It means avoiding inadvertent errors. It is one of the many component of shingo’s zero quality control which aims at elimination of defective products. Poka yoke is implemented by using simple devices that should prevent the people from committing mistakes.

43. Poka yoke In jigs and fixture Shigeo Shingo defined poka-yoke as POKA- ‘Inadvertent mistake that anyone can make’ and YOKE- ‘To prevent or proof’ Poka-yoke is a tool to have “zero defects” and even reduce or eliminate quality control. Poka-yoke is a Japanese name for “fool-proofing”. Poke-yoke represents the intelligence of the operator by excluding repetitive actions that require a thinking process.

44. Characteristic of devices that are used for poka yoke Poka yoke are expected to have the following characteristics Useable by everybody Simple in design Low cost Should not require continuous attention from the operations should provide instantaneous , response, prevention or corrections. Poka yoke is best when it prevents mistakes not when it identifies the occurrence of a mistakes

45. Application of Poka Yoke Jigs and fixtures in which components cannot be loaded wrongly. Pins, screws dowels placed non symmetrically so that a component cannot be assembled incorrectly. Plugs that can be inserted only in right type of holders and in correct direction. Interlocked controls so that a machine will not start unless both hands of the operator are not out. button covers so that the button can not be pressed accidently. Simplicity of design so that minimum effort is necessary for loading and unloading Design for safety.