Introduction to jigs and fixtures.ppt
- 1. Introduction to Jigs and Fixtures
- 2. Introduction Jig: A jig is a special device that holds, supports, or is placed on a part to be machined. It is a production tool made so that it not only locates and holds the workpiece but also guides the cutting tool as the operation is performed. Jigs are usually fitted with hardened steel bushings for guiding drills or other cutting tools . Fixture: A fixture is a production tool that locates, holds, and supports the work securely so the required machining operations can be performed. Set blocks and feeler or thickness gauges are used with fixtures to reference the cutter to the workpiece. A fixture should be securely fastened to the table of the machine upon which the work is done.
- 3. Design objectives of Jigs and Fixtures • The tool must be foolproof to prevent any mishandling or accidental usage by the operator. • Easy to operate for increasing efficiency. • Easy to manufacture using the lowest costs. • Its ability to weather the tool life instead of appropriate materials. • Must be consistent at producing high-quality parts. • Must be safe and secure to use.
- 4. Design objectives of Jigs and Fixtures • Cycle time. • Type of Jig/Fixture. • Part Assembly sequence or Machining locations. • Joining or machining process. • Clamping method and clamping sequence. • Required output accuracy. • Type of equipment to be used with the jig. • Method of ejecting finished output and transferring it to the next. Platform, whether the manual or automatic mode. • The type of material, recommended weight, number of spots involving welding.
- 5. Basic principles of Jigs and Fixtures design • LOCATING POINTS: Locating the work is a prime necessity and requires suitable facilities. The correct setup ensures smooth insertion of a workpiece in the proper position and removing a workpiece from a jig without operational hassles or time consumption. The workpiece position needs to be precise with the guiding tool in the jig or setup pieces in the fixture. • FOOLPROOF: A foolproof design of jigs and fixtures does not permit a tool or workpiece to be placed in any other way other than the intended one. • REDUCTION OF IDLE TIME: Jigs and Fixtures must be designed in such a way that ensures smooth loading, clamping, machining,
- 6. Basic principles of Jigs and Fixtures design • WEIGHT OF JIGS AND FIXTURES: A jig and fixture must be compact, easy to handle, and low cost regarding the number of materials used without giving up stiffness and rigidity. • JIGS PROVIDED WITH FEET: Some jigs require feet so that they can be placed on the table firmly. • MATERIALS FOR JIGS AND FIXTURES: Jigs and Fixtures are usually created with hardened materials to resist wear & tear and avoid frequent damage—for example, Mild steel, Cast iron, Die steel, High-speed steel, Caesium. • CLAMPING DEVICE: A suitable clamp is rated for its strength. It should be able to hold a workpiece firmly in its position while bearing the strain of the cutting tool simultaneously, without springing.
- 7. 3-2-1 Principle of Location used in Jig & Fixtures • It is also known as a six-pin or six-point location principle. In this, the three adjacent locating surfaces of the blank (workpiece) are resting against 3, 2, and 1 pin respectively, which prevent 9 degrees of freedom. • The rest three degrees of freedom are arrested by three external forces usually provided directly by clamping.
- 8. 3-2-1 Principle of Location used in Jig & Fixtures
- 10. Methodology of 3-2-1 Principle • The workpiece is resting on three pins A, B, and C which are inserted in the base of the fixed body. • The workpiece cannot rotate about the axes XX and YY and also cannot move downward. • In this way, the five degrees of freedom 1,2,3,4 and 5 have been arrested. • Two pins D and E are inserted in the fixed body, in a plane perpendicular to the plane containing pins A, B & C. • Now the workpiece cannot rotate about the Z-axis and also it cannot move towards the left. • Hence the addition of pins D and E restrict three more degrees of freedom, namely 6, 7, and 8. • Another pin F in the second vertical face of the fixed body, arrests degree of freedom 9
- 11. Summary of 3-2-1 Principle: • A workpiece will be completely confined when blanked against: • 3 points in one plane: The “3” in 3-2-1 refers to 3 locators (passive fixture elements) on the primary locating/datum surface. • 2 points in another plane: The “2” in 3-2-1 refers to 2 locators on the secondary locating/datum surface. • 1 point in a third plane: The “1” in 3-2-1 refers to 1 locator on the tertiary locating/datum surface
- 12. Types Of Locators used In Jig And Fixture For supporting • Flat locators: These are used for the location of the flat machined surfaces of a component. • Cylindrical locators: These are used for the location of components with drilled holes. • Conical locators: These locators are used to support the workpieces with cylindrical holes. • Jack pin locators: These locators support rough workpieces. • Drill bush locators: These locators hold and locate the cylindrical workpieces. • Vee locators: These locators hold circular and semicircular workpieces.
- 14. CLASSES OF JIGS • Jigs may be divided into two general classes: boring jigs and drill jigs. • Boring jigs are used to bore holes that either are too large to drill or must be made an odd size
- 15. CLASSES OF JIGS • Drill jigs are used to drill, ream, tap, chamfer, counter bore, countersink, reverse spot face, or reverse countersink. The basic jig is almost the same for either machining operation. The only difference is in the size of the bushings used. • Drill jigs may be divided into two general types, open and closed. Open jigs are for simple operations where work is done on only one side of the part. Closed, or box, jigs are used for parts that must be machined on more than one side
- 18. FIXTURES • It is a work holding device that holds, supports and locates the work piece for a specific operation but does not guide the cutting tool. • It provides only a reference surface or a device. What makes a fixture unique 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 a it guides the tool to its correct position in addition to locating and supporting the work piece. • Examples: Vises, chucks
- 20. How do jigs and fixtures differ • JIGS FIXTURES • 1. It is a work holding device that holds, • supports and locates the workpiece and • guides the cutting tool for a specific • operation • 1. It is a work holding device that holds, • supports and locates the workpiece for a • specific operation but does not guide the • cutting tool • 2. Jigs are not clamped to the drill press • table unless large diameters to be drilled • and there is a necessity to move the jig to • bring one each bush directly under the drill. • 2. Fixtures should be securely clamped to • the table of the machine upon which the • work is done.
- 21. • JIGS FIXTURES • 3. The jigs are special tools particularly in • drilling, reaming, tapping and boring • operation. • 3. Fixtures are specific tools used • particularly in milling machine, shapers and • slotting machine. • 4. Gauge blocks are not necessary. 4. Gauge blocks may be provided for • effective handling. • 5. Lighter in construction. 5. Heavier in construction
- 22. Advantages of Jigs and Fixtures • PRODUCTIVITY: • Jigs and fixtures increases the productivity by eliminating the individual marking, positioning and frequent checking. • The operation time is also reduced due to increase in speed, feed and depth of cut because of high clamping rigidity. • INTERCHANGEABILITY AND QUALITY: • Jigs and fixtures facilitate the production of articles in large quantities with high degree of accuracy, uniform quality and interchangeability at a competitive cost .
- 23. • SKILL REDUCTION • There is no need for skillful setting of work on tool. • Jigs and fixtures makes possible to employ unskilled or semi skilled. • machine operator to make savings in labour cost. • COST REDUCTION: • Higher production, reduction in scrap, easy assembly and savings in labour cost results in ultimate reduction in unit cost.
- 24. Fundamental principles of Jigs and Fixtures design • LOCATING POINTS: • Good facilities should be provided for locating the work. 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 work piece in position to perform operations. • The position of work piece 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 work piece or the tool to inserted in any position other than the correct one.
- 25. • REDUCTION OF IDLE TIME: • Design of Jigs and Fixtures should be such that the process, loading, clamping and unloading time of the Work piece takes minimum as far as possible. 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.
- 26. 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 iscooled and the swarfs and chips are washed away
- 27. • 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 for a long time. • 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 pos
- 28. • 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
- 29. • 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
- 30. General rules for designing • Compare the cost of production of work with present tools with the expected cost of production, using the tool to be made and see that the cost of buildings is not in excess of expected gain. • Decide upon locating points and outline clamping arrangement. • Make all clamping and binding devices as quick acting as possible. • Make the jig fool proof . • Make some locating points adjustable. • Avoid complicated clamping arrangements.
- 31. • Round all corners. • Provide handles wherever these will make handling easy. • Provide abundant clearance. • Provide holes on escapes for chips. • Locate clamps so that they will be in best position to resist the pressure of the cutting tool when at work. • Place all clamps as nearly as possible opposite some bearing point of the work to avoid springing action. • Before using in the shop, test all jigs as soon as made.
- 32. MATERIALS USED • Jigs and Fixtures are made of variety of materials, some of which can be hardened to resist wear. Materials generally used: High speed Steel:- Cutting tools like drills, reamers and milling cutters. Die steels:- Used for press tools, contain 1% carbon, 0.5 to 1% tungsten and less quantities of silicon and manganese. Carbon steels:- Used for standard cutting tools. Collet steels:- Spring steels containing 1% carbon, 0.5% manganese and less of silicon.
- 33. • Non shrinking tool steels:- • High carbon or high chromium • Very little distortion during heat treatment. • Used widely for fine, intricate press tools. • 6. Nickel chrome steels: • Used for gears. • 7. High tensile steels: • Used for fasteners like high tensile screws • 8. Mild steel: • Used in most part of Jigs and Fixtures • Cheapest material • Contains less than 0.3% carbon
- 34. • (9.) Cast Iron: • Used for odd shapes to some machining and laborious fabrication. • CI usage requires a pattern for casting. • Contains more than 2% carbon. • Has self lubricating properties. • Can withstand vibrations and suitable for base. • (10.) Nylon and Fiber: • Used for soft lining for clamps to damage to work piece due to clamping pressure • (11.) Phospher bronze: • used for nuts as have high tensile strength • Used for nuts of the lead screw
- 35. Factors to be considered for design of Jigs and Fixtures • 1. Component • Design to be studied carefully. • Ensure work is performed in a proper sequence. • Maximum operations should be performed on a machine in single setting. • 2. Capacity of the machine- • Careful consideration to be performed on type and capacity of machine. • 3. Production requirements- • Design to be made on basis of actual production requirements. Then comes decision on manual and automatic tooling arrangements.
- 36. • 4. Location • Location should ensure equal distribution of forces throughout all sequence of operation. • Location should be hard resistant, wear resistant and high degree of accuracy. Movement of work piece should be restricted. Should be fool proofed to avoid improper locations of the work piece. Should facilitate easy and quick loading of work piece. Redundant locators should be avoided. Sharp corners must be avoided. At least one datum surface should be estabilsed.
- 37. • 5. Loading and Unloading arrangements- • There should be adequate clearance for loading and unloading. Hence process becomes quick and easy. • Size variation must be accepted. • It should be hardened material and non sticky. • 6. Clamping arrangements- • Quick acting clamps must be used as far as possible. • The clamping should not cause any deformation to the Work piece. • It should always be arranged directly above points supporting the work. • Power driven clamps are favoured as they are quick acting, controllable, reliable and operated without causing any fatigue to the operators.
- 38. • Features of clamps:- • Clamping pressure should be low • Should not cause distortion • Simple and fool proof • Movement of clamp should be minimum • Case hardened to prevent wear • Sufficiently robust to avoid bending • 7. Clearance between Jig and Component- • To accommodate various sizes if work • Chips to pass out of the opening between them • 8. Ejectors- • To remove work from close fitting locators. • Speeds up unloading of the part from the tool and hence production rate.
- 39. • 9. Base and Body construction- • Methods used: Machining, Forging and machining, Casting, Fabricating, Welding. • 10. Tool guiding and cutter setting- • By adjusting the machine or using cutter setting block, the cutter is set relative to the work in a fixture. The drill bushes fitted on jig plates guides the tools. • 11. Rigidity and vibration- • Must possess enough rigidity and robustness. • Should not vibrate as it may lead to unwanted movement of Work piece and tools. • 12. Safety- Operation should be assured full safety
- 40. • 13. Cost- • Should be simple as possible. • Cost incurred should be optimum. • - S.NO. PART NAME MATERIAL 01 Jig body CI 02 Stud MS 03 Drill/bush GUN METAL 04 Pin MS 05 Nut MS
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