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Jigs & Fixtures
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- 2. BY ARNAB PAUL2 Definition of Jig: A jig is a work-holding device that holds, supports, and locates the workpiece and guides the one or more tools to perform a specific operation. In other words, this can also be defined as, used for holding the tools and also guiding the cutting tools.
- 3. BY ARNAB PAUL3 The main purpose of a jig is to provide repeatability, accuracy, and interchangeability in the manufacturing of products. Some important points to remember about Jigs: It is used in uni- dimensional machining processes like drilling, tapping, and reaming, etc. This system is found to be light and has a complex shape. Gauge blocks are not necessary and the cost of jigs is higher. Jigs are not fixed to the machine table until a large operation has to be performed.
- 4. BY ARNAB PAUL4 Definition of Fixture: Fixtures are the work holding device, which holds, supports and locates the workpiece but not guides the cutting tool to perform a specific operation. In other words, the fixtures are only the work holding device that holds, supports and locates the workpiece in the desired position to perform any operation. The main purpose of the fixtures is to hold and locate the workpiece during any machining operation and to provide repeatability, accuracy, and interchangeability in the manufacturing of products.
- 5. BY ARNAB PAUL5 Some important points about fixtures: Fixtures are used in multi- dimensional machining like milling, grindi ng, turning, etc. This system found to be heavy in weight, have simple designing. Gauge blocks provided for effective handlin g and the cost is average. Fixtures are having specific tools that use particularly in the milling machine, s hapers and slotting machines. Fixtures are fixed to the machine table.
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- 7. BY ARNAB PAUL7 Elements of Jigs and Fixtures 1: Body 2: Locating devices 3: Clamping devices 4: Tool guide(jigs bushing)
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- 9. BY ARNAB PAUL9 Body: The jig body is generally made of cost iron by casting process or fabricated by welding together various slabs and bars of mild steel. It may be heat treated to relief the stresses. Body is the most prominent feature of the jig. Its main purpose is to support and house the job.
- 10. BY ARNAB PAUL10 3-2-1 Principle of Location:
- 11. BY ARNAB PAUL11 Degrees of Freedom in space A work-piece free in space can move in an infinite number of direction. For analysis, this motion can be broken down into 12 directional movements or "degrees of freedom". All 12 degrees of freedom must be restricted to ensure proper referencing of a work-piece. As shown in Fig 1, the 12 degrees of freedom all relate to the central axis of the work-piece. Notice the 6 axial degrees and 6 radial degrees of freedom. The axial degrees of freedom permit straight-line movement in both directions along the 3 principle axis shown as X, Y & Z. The radial degrees of freedom permit rotational movement, in both clockwise & counterclockwise radial directions around the same three axis.
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- 13. BY ARNAB PAUL13 Primary Locators First the three locators or supports are placed under the work-piece. It will be positioned on the primary locating surface also known as datum. It will restrict 5 degrees of freedom. •Axial Movement downward along Z- axis ( No.6 in Fig 2 ) •Rotation about the X & Y axis ( No. 7, 8, 9 & 10 in Fig 2 )
- 14. BY ARNAB PAUL14 Secondary Locators The next two locators are normally placed on the secondary surface, restricting an additional 3 degrees of freedom. Axial movement along the Y+ axis ( No.3 in Fig 2 ) Rotation about the Z axis ( No. 11 & 12 in Fig 2 )
- 15. BY ARNAB PAUL15 Tertiary Locator This locator is positioned at the end of the part. It restricts 1 degrees of freedom Axial movement along the X axis ( No.2 in Fig 2 )
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- 31. BY ARNAB PAUL31 Using gooseneck clamps is one way to reduce the height of the clamps.
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- 33. BY ARNAB PAUL33 Fool-Proofing:
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- 35. BY ARNAB PAUL35 6: Inserts: To avoid any damage to fragile and soft work piece and also to the finished surfaces of the work piece while clamping. Inserts of some soft material such as copper, lead , fiber , leather , hard rubber and plastic should be fitted to the faces of the clamps. 7: Design for Safety: Jigs and fixtures must be safe and convenient in use, following are the some Factors for the safety of worker working on jigs and fixtures. (A): Sharp corner on the body of jig and fixture should be avoided. (B): Sighting surfaces should be cleared. (C): Bolt and nut should be inside the body of jig or fixture and not protrude on the surface.
- 36. BY ARNAB PAUL36 8: Sighting Surface: Machining on the work piece must be clearly visible to the worker. He should not be required to bend is neck for seeing the work piece or work surfaces. 9: Simplicity in design: Design of the jig and fixture should be a simple one. A completed design require a large maintenance. They should be easily to set , cheap in manufacture. 10: Economical: Jig and fixtures should be simple in construction, give high accuracy , be sufficiently rigid and lightly weight. To satisfy these conditions an economical balance has to be made.
- 37. BY ARNAB PAUL37 Types of Jigs & Fixtures
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- 47. BY ARNAB PAUL47 Turning Fixtures: These fixtures are generally mounted on the nose of the machine spindle or a faceplate, and the work-pieces held them. Whenever necessary, the fixture may have to be provided with a counterweight or balance the unbalance fixture.
- 48. BY ARNAB PAUL48 Milling Fixtures: Milling fixtures are typically mounted on the nose of the machine spindle or a faceplate, and the work-pieces held them. The table is shifted and set in proper position, in relation to the cutter. The work-pieces are located in the base of the fixture and clamped before starting the operation.
- 49. BY ARNAB PAUL49 Broaching Fixtures: Broaching fixtures are used on different types of broaching machines to locate, hold and support the work-pieces during the operations, such as keyway broaching operations, such as keyway broaching, hole broaching, etc.
- 50. BY ARNAB PAUL50 Indexing Fixtures: Several components need machining on the different surface such that their machined surface surfaces or forms are evenly spaced. Such elements are required to be indexed equally as many as the number of surfaces to be machined. The holding devices (jigs or fixtures) used are made to carry a suitable indexing mechanism. A fixture carrying such a device is known as an indexing fixture.
- 51. BY ARNAB PAUL51 Grinding Fixtures: These fixtures may be the standard work-holding devices, such as chucks, mandrels, chuck with shaped jaws, magnetic chucks, etc. Boring Fixtures: This fixture incorporates almost all the prevailing principles of jig and fixture design, their construction need not be as sturdy as that of the milling fixtures, because they never have to bear as heavy cutting loads as involved in milling fixtures, because they never have to endure as heavy cutting loads as involved in milling operations. Tapping Fixtures: Tapping fixture is specially designed to position and firmly secure identical work-pieces for cutting internal threads in drilled holes in them. Odd shaped and unbalanced components will always need the use of such fixtures, especially when the tapping operation is to be carried out repeatedly on a mass scale on such parts.
- 52. BY ARNAB PAUL52 Welding Fixtures: Welding fixtures are carefully designed to hold and support the various components to be welded in proper locations and prevent distortions in welded structures. For this, the locating element need to be carefully; clamping has to be light but firm, placement of clamping elements has to be clear of the welding area. The fixture has to be quite stable and rigid to withstand the welding stresses. Assembly Fixtures: The function of these fixtures is to hold different components together in their proper relative position at the time of assembling them.