Uint 1 locating and clamping devices

Design of jigs and fixtures -consist of locating and clamping principles

1. S.DHARANI KUMAR Asst.professor Department of Mechanical Engineering Sri Eshwar college of Engineering ,Coimbatore. UNIT-1 LOCATING AND CLAMPING

2. Definitions 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. Superior Jig Flexible Fixturing Systems

3. FUNDAMENTAL PRINCIPLES OF JIGS AND FIXTURES DESIGN LOCATING POINTS: The article to be machined must be easily inserted and quickly taken out from the jig so that no time is wasted in placing the workpiece in position to perform operations . The position of workpiece should be accurate with respect to tool guiding in the jig or setting elements in fixture. FOOL PROOF: The design of jigs and fixtures should be such that it would not permit the workpiece or the tool to inserted in any position other than the correct one.

4. REDUCTION OF IDLE TIME WEIGHT OF JIGS AND FIXTURES- It should be easy to handle, smaller in size and low cost in regard to amount of material used without sacrificing rigidity and stiffness . JIGS PROVIDED WITH FEET: Jigs sometimes are provided with feet so that it can be placed on the table of the machine . MATERIALS FOR JIGS AND FIXTURES : CLAMPING DEVICE: It should be as simple as possible without sacrificing effectiveness . The strength of clamp should be such that not only to hold the workpiece firmly in place but also to take the strain of the cutting tool without springing when designing the jigs and fixtures.

5. ESSENTIAL FEATURES OF JIGS AND FIXTURES Reduction of idle time – Should enable easy clamping and unloading such that idle time is minimum. Cleanliness of machining process – Design must be such that not much time is wasted in cleaning of scarfs, burrs, chips etc. Replaceable part or standardization – The locating and supporting surfaces as far as possible should be replaceable, should be standardized so that their interchangeable manufacture is possible. Provision for coolant – Provision should be there so that the tool is cooled and the swarfs and chips are washed away.

6. Hardened surfaces – All locating and supporting surfaces should be hardened materials as far as conditions permit so that they are not quickly worn out and accuracy is retained. Inserts and pads – Should always be riveted to those faces of the clamps which will come in contact with finished surfaces of the work piece so that they are not spoilt. Fool-proofing – Pins and other devices of simple nature incorporated in such a position that they will always spoil the placement of the component or hinder the fitting of the cutting tool until the latter are in correct position.

7. Economic soundness – Equipment should be economically sound , cost of design and manufacture should be in proportion to the quantity and price of producer. Easy manipulation – It should be as light in weight as possible and easy to handle so that workman is not subjected to fatigue , should be provided with adequate lift aids. Initial location – Should be ensured that work piece is not located on more than 3 points in anyone plane test to avoid rocking, spring loading should be done. Position of clamps – Clamping should occur directly above the points supporting the work piece to avoid distortion and springing.

8. Clearance – Sufficient amount of clearance should be provided around the work so that operator’s hands can easily enter the body for placing the work piece and any variations of work can be accommodated. Ejecting devices – Proper ejecting devices should be incorporated in the body to push the work piece out after operation. Rigidity and stability – It should remain perfectly rigid and stable during operation. Provision should be made for proper positioning and rigidly holding the jigs and fixtures. Safety – The design should assure perfect safety of the operator.

9. LOCATING PRINCIPLES Location of the component is very important aspect to influence the accuracy of the finished product. The each successive work piece when loaded and clamped will occupy the same position in the jig or fixture. Work holding device mainly depends on the nature of work piece and requirement of the machining operation.

10. Principles of location Principles of Six point Location Principle of least point Principle of Extreme positions Principle of mutually perpendicular planes Principle of fool proofing Redundant Locators

11. Six point Location Principles Pin 1,2 and 3 for z-z axis translation y-y axis rotation x-x axis rotation Pin 4 and 5 for y-y axis translation z-z axis rotation Pin 6 for x-x translation

12. 3-2-1 Principle FIGURE 27-4 Workpiece location is based on the 3-2-1 principle. Three points will define a base surface, two points in a vertical plane will establish an end reference, and one point in a third plane will positively locate most parts.

13. Principle of fool proofing

14. Principle of mutually perpendicular planes The "3-2-1" principle can also be put as a work piece may be fully located by supporting it against three points in one plane, two points in second plane and one point in a third plane. These three planes are not parallel and are preferably perpendicular to one another. If the locating surfaces are not perpendicular to one another, the difficulties will arise

15. LOCATING METHODS AND DEVICES Locators are those parts of a jigs or fixture which helps a work piece to seat in proper position in it . Depend upon type of work, locators are designed . The various locating devices and methods are shown in next.

16. PIN AND BUTTON LOCATORS Button is used to support the job firmly and holds it in position. Only difference between pins and buttons is length . The length of the buttons smaller than pins. Buttons generally used for vertical locations. Pins generally used for horizontal locations.

17. DIFFERENT TYPE OF PINS USED FOR LOCATING Cylindrical locating pins Conical locating pins Supporting pins or flat locators Adjustable pin locator Jack pin locator Diamond pin locators

18. Cylindrical pin used to locate a work piece from a hole produced by previous operation. The locating diameter of the pin is made a push fit with the hole in the work piece. The top portion of theses pins is given a sufficient lead by chamfering. 1. Cylindrical locating pins

19. 2.Conical locating pins Locators are proffered over the cylindrical locators where it is necessary to accommodate variation in the diameter of the work piece with out affecting the accuracy location .

20. Exercise 4-4 Determine the basic size and type of fit given the limits for the shaft and hole. Shaft Limits Hole Limits Basic Size Type of fit 1.498 - 1.500 1.503 - 1.505 .751 - .755 .747 - .750 .373 - .378 .371 - .375 .247 - .250 .250 - .255 1.5 Clearance .75 Interference .375 Transition .25 Line

21. 3.Supporting pins or flat locators Supporting work piece by supporting pins from a flat surface . Pins are fitted into the jigs or fixture body with interference fit.

22. 3.Adjustable pin locator Adjustable pin locators are used when the surface is rough or uneven, such as in castings ,forgings or non machined surfaces . Lock nut Jig body Adjustable knob

23. Prepared Compression Die Bottom Die plate Top Punch Plate Height Adjustment Pin 1/8/2015 28

24. 4.Diamond pin locators

25. 6.V -Locator V-locators are widely used for locating cylindrical surfaces from outside . V-locators are classified in two types 1.Fixed V-locator 2.Adjustable type V-locators (a)Cam –operated adjustable type V-locator

26. 1.Fixed V-locator

27. 1.Fixed V-locator

28. 2.Adjustable Type V-locator The sliding Vee block may be actuated by means of a hand operated screw.

29. 7.Bush Locators Shaft type work pieces can be easily locate in a hardened steel bushes. The bushes can be plain or flanged type.

30. Nest or cavity Locators

31. Principles of Clamping 1 . It is used to hold the work piece in the correct relative position . 2. The clamping pressure must only hold the work piece and should never be great enough so as to damage, deform or change any dimensions of the work piece . 3.The clamping and cutting forces should be directed towards the locating pins, otherwise the work piece may get bent or forced away from the locating pins during machining.

32. 4 . Clamping should be simple, quick and foolproof. Complicated clamps lose their effectiveness as they wear. 5 .The movement of a clamp should be strictly limited and if possible it should be positively guided. 6 .Whenever possible, the lifting of the clamp by hand should be avoided if it can be done by means of a spring fitted to it.

33. 7 .The clamps should always be arranged directly above the points supporting the work, otherwise the distortion of the work can occur . 8 .Fiber pads should be riveted to the clamp faces, otherwise soft and fragile work piece can get damaged. 9 .Clamping pressure should be directed towards the points of support, otherwise work will tend to rise from its support . 10. The clamps should always be arranged directly above the points supporting the work, otherwise the distortion of the work can occur.

34. Clamping pressure

35. Clamping pressure

36. Position of Clamping

37. Distortion During Clamping

38. Clamping Examples

39. Clamping Devices 1.Mechanical actuating clamps Screw clamps Lever clamp or Strap clamp Bridge clamp Heel clamp Edge clamp 3.Latch clamps 4.Hinged clamps 5. C-clamps 6.Cam operated clamps 7.Wedge clamp 8.Quick acting nut 9.Toggle clamps 10.Bayonet clamp 11.Hook bolt clamp 12.Equalizing clamp

40. 1.Screw clamp

41. 2.Lever clamp or Strap clamp

42. a. Bridge clamp

43. b. Heel clamp

44. c.Sliding heel clamp Clamping movement Keyway

45. solid heel clamp

46. e . Edge clamp

47. 3.Swinging latch clamp

48. 4. Hinged clamps

49. a. Cam-operated clamp

50. c. Two way hinged clamp

51. 5.Free ‘C’ clamp

52. a. Captive C-clamp

53. 6.Cam actuated plate clamp

54. 7 . Wedge clamp

55. 8 .Quick acting nut

56. 9.C-frame type toggle clamp

57. A.Pusher type toggle clamp

58. 11. Bayonet clamp

59. 12. Hook clamp

60. 13.Equalising clamp

61. 14.Hydraulic clamping

62. 15.Air to hydraulic booster

63. Parts of Jigs and Fixture Base Buttons Pins Handles and knobs Lifting ring Stock section Press fit Bushes Renewable Bushes Slip Bushes Linear Bushes Threaded Fasteners

64. Parts of Jigs and Fixture Base Buttons Pins Handles and knobs Lifting ring Stock section Press fit Bushes Renewable Bushes Slip Bushes Linear Bushes Threaded Fasteners

65. Base

66. Buttons

67. Pins

68. Handles and knobs

69. Lifting ring

70. Stock section

71. Press fit Bushes

72. Renewable Bushes

73. Slip Bushes

74. Linear Bushes

75. Threaded Fasteners