Ch1- Jigs & Fixtures.ppt

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Chapter 1 Jigs and Fixtures Tool and Die Design – MEng 5263

Transcript of Ch1- Jigs & Fixtures.ppt

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Chapter 1Chapter 1

Jigs and Fixtures

Tool and DieDesign – MEng 5263

Tool and DieDesign – MEng 5263

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Chapter 1Jigs and Fixtures

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Jigs and Fixtures

Instructional objectives This lesson will enable the students

(i) Define Fixture and Jig that aid machining (ii) Conceive the purposes of use of jigs and fixtures (iii) State the design considerations for jigs and fixtures (iv) Illustrate the methods of

(a) locating (b) supporting and (c) clamping of blanks (d) guidance of cutting tools in fixtures and jigs to facilitate machining

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TOOL DESIGN

Tool design is the process of designing and developing the tools, methods, and techniques necessary to improve manufacturing efficiency and productivity.

It gives industry the machines and special tooling needed for today’s high-speed, high-volume production.

It does this at a level of quality and economy that will ensure that the cost of the product is competitive.

Since no single tool or process can serve all forms of manufacturing, tool design is an ever-changing, growing process of creative problem solving.

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1-1 Jig and Fixture Design

Jigs

Drill jigs

Drill bushings

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What are Jigs and Fixtures Jigs and fixtures are

production-work holding devices used to manufacture duplicate parts accurately.

Anything used to hold a workpiece in a desired location

Locate parts for precision Repeating process on a series

of parts Holding parts for machining,

painting, assembly

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Why are they important in Machine design

Parts should be designed to accommodate standard fixturing components

Designs should accommodate fast and repeatable fixturing

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Basic Categories of Jigs

ClampsChucksVisesBushingsModular Fixtures

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Clamps

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Chucks

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Vises

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Bushings

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Modular Fixturing

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Definitions

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

Superior Jig

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DefinitionsFixture: 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.

Flexible Fixturing Systems

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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.

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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.

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Types of jigs:

For machining purposes Locates the component, holds

it firmly in place, and guides the cutting tool.

For assembly purposes Locates separate component

parts and holds them rigidly in their correct positions while they are being connected.

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TYPES OF JIGS

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.

The names used to identify these jigs refer to how the tool is built.

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Types of jigs Open jig (also called plate jig or drill template)

The simplest type of drill jig Consists of a plate with holes to guide the drills,

and may have locating pins that locate the work piece on the jig

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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 . Templates are the least expensive and simplest type of jig to use. They may or may not have bushings. When bushings are not used, the whole jig plate is normally hardened.

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Plate jigs

Plate jigs are similar to templates. The only difference is that plate jigs have built-in clamps to hold the work. These jigs can also be made with or without bushings, depending on the number of parts to be made.

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Table jig

Plate jigs are sometimes made with legs to raise the jig off the table for large work. This style is called a table jig

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Sandwich jigs

Sandwich jigs are a form of plate jig with a back plate. This type of jig is ideal for thin or soft parts that could bend or warp in another style of jig. Here again, the use of bushings is determined by the number of parts to be made.

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Angle-plate jig

Angle-plate jigs are used to hold parts that are machined at right angles to their mounting locators (a). Pulleys, collars, and gears are some of the parts that use this type of jig. A variation is the modified angle-plate jig, which is used for machining angles other than 90 degrees (b).

(a) Angle-plate jig. (b) Modified angle-plate jig.

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Box jigs

Box jigs, or tumble jigs, usually totally surround the part. This style of jig allows the part to be completely machined on every surface without the need to reposition the work in the jig.

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Channel jigs

Channel jigs are the simplest form of box jig. The work is held between two sides and machined from the third side. In some cases, where jig feet are used, the work can be machined on three sides.

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Leaf jigsLeaf jigs are small box jigs with a hinged leaf to allow for easier loading and unloading. The main differences between leaf jigs and box jigs are size and part location. Leaf jigs are normally smaller than box jigs and are sometimes made so that they do not completely surround the part. They are usually equipped with a handle for easier movement.

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Indexing jigs

Indexing jigs are used to accurately space holes or other machined areas around a part. To do this, the jig uses either the part itself or a reference plate and a plunger. Larger indexing jigs are called rotary jigs.

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Trunnion jigs

Trunnion jigs are a form of rotary jig for very large or odd-shaped parts. The part is first put into a box-type carrier and then loaded on the trunnion. This jig is well suited for large, heavy parts that must be machined with several separate plate type jigs.

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Pump jigs

Pump jigs are commercially made jigs that must be adapted by the user. The lever-activated plate makes this tool very fast to load and unload. Since the tool is already made and only needs to be modified, a great deal of time is saved by using this jig.

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Multi-station jigs

Multi-station jigs are made in any of the forms already discussed. The main feature of this jig is how it locates the work. While one part is drilled, another can be reamed and a third counter bored. The final station is used for unloading the finished parts and loading fresh parts. This jig is commonly used on multiple-spindle machines. It could also work on single-spindle models.

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Drill jig terms

Drill bushings Precision tools that

guide cutting tools such as drill and reamers into precise locations in a workpiece.

Accurate Bushing Co.

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1-2 Drill Jig Components

Jig body

Cap screws and dowel pins

Locating devices and clamping devices

Locking pins

Drill jig design

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Drill jig components Jig body

Holds the various parts of a jig assembly. Cap screws and dowel pins

Hold fabricated parts together

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Drill jig components Locating devices

Pins, pads, and recesses used to locate the work piece on the jig.

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Drill jig components Clamping devices

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Drill jig components Locking pins

Inserted after the first hole is drilled to lock or hold the workpiece securely to the jig plate while subsequent holes are being drilled.

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1-3 Dimensioning Jig Drawings

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1-4 Fixtures

•Types of fixtures

•Classification of fixtures

•Fixture components

•Fixture design considerations

•Sequence in laying out a fixture

Standard Parts Co.

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Plate fixtures

Plate fixtures are the simplest form of fixture. The basic fixture is made from a flat plate that has a variety of clamps and locators to hold and locate the part. The simplicity of this fixture makes it useful for most machining operations. Its adaptability makes it popular.

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angle-plate fixture

The angle-plate fixture is a variation of the plate fixture (a). With this tool, the part is normally machined at a right angle to its locator. While most angle-plate fixtures are made at 90 degrees, there are times when other angles are needed. In these cases, a modified angle-plate fixture can be used (b).

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Vise-jaw fixtures

Vise-jaw fixtures are used for machining small parts. With this type of tool, the standard vise jaws are replaced with jaws that are formed to fit the part. Vise-jaw fixtures are the least expensive type of fixture to make. Their use is limited only by the sizes of the vises available.

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Indexing fixtures

Indexing fixtures are very similar to indexing jigs. These fixtures are used for machining parts that must have machined details evenly spaced.

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Uses of indexing fixture

Parts machined with an indexing fixture.

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Multi-station fixtures

Multi-station fixtures are used primarily for high speed, high-volume production runs, where the machining cycle must be continuous. Duplex fixtures are the simplest form of multi station fixture, using only two stations. This form allows the loading and unloading operations to be performed while the machining operation is in progress. For example, once the machining operation is complete at station 1, the tool is revolved and the cycle is repeated at station 2. At the same time, the part is unloaded at station 1 and a fresh part is loaded.

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Profiling fixturesProfiling fixtures are used to guide tools for machining contours that the machine cannot normally follow. These contours can be either internal or external. Since the fixture continuously contacts the tool, an incorrectly cut shape is almost impossible. The operation in the figure shows how the cam is accurately cut by maintaining contact between the fixture and the bearing on the milling cutter. This bearing is an important part of the tool and must always be used.

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CLASSIFICATION OF FIXTURES

Fixtures are normally classified by the type of machine on which they are used. Fixtures can also be identified by a sub classification. For example, if a fixture is designed to be used on a milling machine, it is called a milling fixture. If the task it is intended to perform is straddle milling, it is called a straddle milling fixture. The same principle applies to a lathe fixture that is designed to machine radii. It is called a lathe-radius fixture. The following is a partial list of production operations that use fixtures:

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Fixture components

Fixture base Fixture components and the work piece are

usually located on a base, which is securely fastened to the milling machine table.

Standard Parts Co.

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Fixture components

Clamps Clamps counteract forces from the feed of the

table and rotation of the cutter.

American Drill Bushing Co.

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Fixture components

Set blocks Cutter set blocks are mounted on the fixture to

properly position the milling cutter in relation to the work piece.

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SUMMARY

The following important concepts were presented in this unit:• Jigs and fixtures are production work holding devices designed to hold, support, and locate a workpiece.

– A jig guides the cutting tool with a drill bushing.– A fixture references the cutting tool with a set block and feeler, or thickness gauges.

• Jigs are divided into two general classes: drill jigs and boring jigs.• The type of jig is determined by how it is built. The two types of jigs are open and closed.

– Template, plate, table, sandwich, and angle plate jigs are all open jigs.– Box, channel, and leaf jigs are all closed jigs.

• Other variations, such as indexing, rotary, trunnion, pump, and multi station jigs, are made as either open or closed jigs.• Fixture types are determined by the way they are built. The most common types are plate, angle plate, vise-jaw, indexing, and multi station fixtures.• Fixture classes are determined by the machine tools on which they are used and sometimes by the operations performed. A fixture used for a straddle milling operation is classed as a mill fixture, but it may also be classed as a straddle-milling fixture.

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Quick Quiz

What is another name for a plate jig?

An open jig or a drill template.