introduction to jig & fixture design1 for student

Introduction to Jig & Fixture

Design

FGB40103 - Jigs & Fixtures

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Outcomes

After completing this topic student should be able to:-

�Identify the jigs & fixtures.

�Objective of tool design

�Define the elements consist in the jigs & fixtures.

�Identify limits and fits

�Define the material used in jigs & fixtures.

Jigs & Fixtures

� General definitions

� Jigs and fixtures are production-work holding devices used to manufacture duplicate parts accurately.

� The correct relationship and alignment


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� The correct relationship and alignment between the cutter, or other tool, and the work-piece must be maintained.

� To do this, a jig or fixture is designed and builtto hold, support, and locate every part toensure that each process of drilled ormachined within the specified limits.

� Jigs?

Cutting tool guided(x fix kt machine table)

� It provided with tool guiding elements such as

drill bushes. These direct the tool to the


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drill bushes. These direct the tool to the

correct position on the work-piece.

� Fixtures?

Work-piece guided(selalu fix kt machine table)

� To hold the work-piece securely in the correct

position with respect to the machine/cutter

during operation.

Objective

� The main objective of tool design is to lower manufacturing costs while maintaining quality and increased production.

� To accomplish this, the tool designer must satisfy the following objectives:� Provide simple, easy to operate tools for maximum efficiency


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� Provide simple, easy to operate tools for maximum efficiency

� Reduce manufacturing expenses by producing parts at the lowest possible cost.

� Design tools that consistently produce parts of high quality

� Increase the rate of production with existing machine tools

� Design the tool to make it foolproof and to prevent improper use.

� Select materials that will give adequate tool life,

� Provide protection in the design of the tools for maximum safety of the operator.

Elements of Jigs & Fixtures

� Generally all the jigs and fixtures consist of:

� Locating Elements: these position the workpiece

accurately with respect to the tool guiding or setting

elements in the fixture.

� Clamping Elements: these hold the workpiece


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� Clamping Elements: these hold the workpiece

securely in the located position during operation.

� Tool Guiding and Setting Elements: these aid

guiding or setting of the tools in correct position

with respect to the workpiece.

Advantages of Jigs and Fixtures

� Productivity: jigs and fixtures eliminate individual marking process, positioning and frequent checking. This reduces operation time and increases productivity

� Interchangeability: jigs and fixtures facilitate uniform quality in manufacture. There is no


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Interchangeability: jigs and fixtures facilitate uniform quality in manufacture. There is no need for selective assembly. Any parts of the machine fit properly in assembly, and all similar components are interchangeable.

� Skill Reduction: jigs and fixtures simplify locating and clamping of the workpieces. Tool guiding elements ensure correct positioning of the tools with respect to the workpieces. There is no need for skillful setting of the workpiece


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is no need for skillful setting of the workpiece of tool.

� Cost Reduction: higher production, reduction in scrap, easy assembly and savings in labor costs result in substantial reduction in the cost of workpieces produced with jigs and fixtures.

Limits and Fits

� The largest and the smallest of the shaft (or hole) are called the high and low limit, respectively. The difference between these limits, i.e. the permission variation, is called tolerance. If tolerance is allowed only on one


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tolerance. If tolerance is allowed only on one side of the nominal dimension it is called unilateral. For example, has got unilateral tolerance. If tolerance is allowed on both sides of the nominal dimension (e.g

it is called bilateral.

02.0

00.000.20

+

−

01.0

01.000.20

+

−

Classification of Fits

� Running fits: this provides for easy rotation as well as axial movement of shaft (male part) in hole (female part). It is used for bearing diameters of rotating shafts. Locators in production devices are made running fit with


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production devices are made running fit with workpiece for quick loading and unloading.

� Push fit: this fit requires light hand pressure or tapping for assembly of the mating parts. It is used mainly for precise assembly of replaceable locators in jigs and fixtures.

� Press Fit: the mating parts are assembled y

hammering or with a press. There is a positive

interference between the hole and the shaft.

This prevents rotary as well as axial

movement between the assembled parts.


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movement between the assembled parts.

� Force Fit: this is used for permanent

assemblies such as wheels and hubs on shaft

force fit parts require heavy pressure for

assembly.

� The clearance or interference provided

for obtaining the various fits is called

allowance.


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� In shaft basis of fits the diameter of the shaft is kept constant while that of the hole is varied.

� In hole basis, the hole size is kept constant and the shaft size is varied to obtain the various fits.


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various fits.

� The tolerance depends upon the mating diameter sizes. The distribution of the tolerance is specified by alphabets.

� Holes are specified by capital letters A,B,C,D, etc. whereas shafts are specified by small letters a,b,c,d, etc.

� The alphabets are suffixed by digits 1,2,3,4,5;.16

showing the grade of accuracy. Digit 1 signifies the

highest accuracy and digit 16 the least.


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� In tool making accuracy grades 7 to 11

have been found most convenient.

Generally unilateral H type tolerance

distribution is preferred.


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distribution is preferred.

� Most of the accurate holes are made to

H7 limits which can be obtained by

careful reaming. For mass production,

the less accurate H8 holes are used.

� The following combinations are widely used in tool

making.


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� For example for a 20ø H7 hole, the shaft should be:

Materials used in Jigs and Fixtures

� 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, collects, etc.

� High Speed Steels (HSS)

� Die Steels

� Carbon Steels


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� Collet Steels (Spring Steels)

� Oil hardening Non-Shrinking Tool Steels (OHNS)

� Case Hardening Steels

� High Tensile Steels

� Mild Steel

� Cast Iron

� Steel Castings

� Nylon and Fibre

� Phospher Bronze


� Common materials used in jigs and fixtures construction;

� Cast iron

It used for tool bodies and some commercial of jig and fixture

components. The advantages of this material, it can absorb

vibration during machining operations.

� Carbon Steel


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� Carbon Steel

Carbon steel is the primary material of jig or fixture tooling. Its

ease of fabrication, low cost, availability and versatility have made

it popular for tool construction.

� There 3 types of this steel as follows:

Low Carbon Steels

Medium Carbon Steels

High Carbon Steels


� Low Carbon Steels

� Low Carbon Steels are used mainly for structural part of a jig or

fixture. They should only be used in areas where mass is required

and no wear or stress will occur such as base plate or support

plate. The carbon contents of this steel is between 0.05 to 0.30

percent, which is allow cast hardening to resist wear for low


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percent, which is allow cast hardening to resist wear for low

production tools.

� Medium Carbon Steels

� It used in much the same way as low carbon steels, but in areas

of tooling require more strength. It works well as clamps, studs,

and nut and in almost any area where toughness is required. The

carbon contents are between 0.3 to 0.50 percent. It can be

hardened by case hardening or other conventional hardening

processes.


� High Carbon Steels

� High Carbon Steels are generally limited to tool constructions in

areas that are subject to most wear. Parts such as drill bushings,

locators for clamp, wear pads, and supports can be made of this

material. The carbon contents are between 0.50 to 2.0 percent

and easily hardened by conventional hardening process.


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and easily hardened by conventional hardening process.

Basic Type and Function of

Jig & Fixture

Outcomes


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Outcomes

After completing this topic student should be able to:-

�Identify the classes of jigs & fixtures.

�Identify the types of jigs and fixtures.

�Choose a class and type of jig and fixture for selected operations on sample parts.

Classes of Jigs

� Divided into 2 classes: - boring & drill

� 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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size

� Drill jigs are used to drill, ream, tap, chamfer, counterbore, countersink, reverse spotface 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.

Classification of Fixtures

Fixtures are normally classified by the type of

machine on which they are used.

Fixtures can also be identified by

subclassification. For example, if a fixture is


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subclassification. For example, if a fixture is

designed to be used in a milling machine, it

is called a milling fixture.

Template Jig

� Normally used for accuracy rather than speed.Workpiece


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speed.

� This type of jig fits over, on, or into the work and is not usually clamped.

� Least expensive and simplest type of jig.

Template JigWorkpiece

Plate Jig

� Similar to templates

� The difference is that plate jigs have built-in clamps to hold the work.


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hold the work.

� This jig can be made with or without bushing, depending on the number of parts to be made.

� Sometimes made with legs to raise the jig off the table for large work.

Sandwich Jig


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� A form of plate jig with a back plate.

� Ideal for thin or soft parts that could bend or warp in another style of jig.

Angle - plate Jig


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� Used to hold parts that are machined at right

angles to their mounting locators.

� Pulley, collars, and gears are some of the parts

that use this type of jig.

Box Jig

� Usually totally surround

the part.

This style of jig allows the


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� This style of jig allows the

part to be completely

machined on every

surface without the need

to reposition the work in

the jig.

Channel Jig

� The simplest form of

box jig.

� The work is held

between two sides and


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between two sides and

machined from the

third side.

Leaf Jig

� A small jigs with a hinged leaf to allow for easier loading and unloading.

� The differences between leaf jigs and box jigs are


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leaf jigs and box jigs are size and part location.

� Leaf jig normally smaller than box jigs

� Usually equipped with a handle for easier movement

Indexing Jig

� A jig that is specifically

designed to locate a

part in multiple

positions, one after


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positions, one after

another.

� Indexing jigs are often

used to drill holes

around the surface of a

cylindrical workpiece.

Plate Fixture with hydraulic Swing

clamps

� Simplest form of

fixture. The basic

fixture is made

from a flat plate


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from a flat plate

that has a variety

of clamps and

locators to hold

and locate the part.

Angle-plate fixture

� Is a variation of the

plate fixture.

� With this tool, the part

is normally machined


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is normally machined

at a right angle to its

locators.

Vise-Jaw Fixture

� Used for machining

smalls parts.

� With this type of tool,

the standard vise jaws


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the standard vise jaws

are replaced with jaws

that are formed to fit

the part.

Indexing Fixture

� Similarly to indexing

jigs.

� These fixtures are

used for machining


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used for machining

parts that must have

machined details

evenly spaced.

Multi-station Fixture

� Used primarily for

high speed, high-

volume production

runs, where the


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runs, where the

machining cycle

must be continuous.

Profiling Fixture

� Used to guide tools for machining contours that the machine cannot normally follow.


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� Since the fixture continuously contact the tool, an incorrectly cut shape is almost impossible.

introduction to jig & fixture design1 for student

Documents

carbon contents

mating parts

tool guiding

indexing jigs

topic student

axial movement

nominal dimension

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