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DESIGN OF JIG AND FIXTURE FOR MILLING MACHINE

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1NIRODUCTION


One of the most time-consuming and labor extensive processes in the manufacturing of a
mechanical part is the process of work holding or fixiuring. It is often remarked that
only approximately 10-15% of the overall time required to produce a part is spent
actuaii); on cutting or drilling a work piece; the other time is spent primariiy pianning for
executing part setup or work holding which is still performed by highly skilled
machinists based on their experience. Kecently, industries have begun to experience
difficulty finding highly skilled machinists because the number of apprentices is
decreasing and it is iikeiy that the situation wit1 worsen in the future.


Problem Statements

Manufacturing in its broadest sense is the process of converting raw material into
products. it encompasses the design of the product, the selection of raw nlaterials and
the sequence of processes through which the product will be manufactured.
klanufacturing is the backbone of any industriaiized nation. Its impor'ance is
emphasized by the fact that, as an economic activity, it comprises approximately 20% to
JO'% of the vaiue of atl goods and services produced. Manufacturing also involves
activities in which the manufactured product is itself used to make other products.
Examples of these products are large presses to shape sheet metal tbr car bodies,
machinery to make bolts and nuts and sewing machines for making clothing.


Scope of Project

Jigs and fixtures are production-work holding devices used to manufacture duplicate
parts accurately. Ajig is a special device which 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 work
piece, but also guides the cutting tool as the operation is performed. A fix-ture is a
production tool that locates, holds and supports the work securely so the required
machining operations a n be performed. A fixture should be securely fastened to the
table of the machine upon which the work is done.



Introduction to the Jigs and Fixtures

Mast production aims at high productivity to reduce unit cost and interchange ability to
facilitate cost assembly. 'l'his necessitates production devices to increase tlie rate of
manufacture devised, to speed up the inspection devised and to speed up the inspection
procedure.

Definition of Jigs and Fixtures
Jigs:

Budget may be defined as the device which holds and positions the work piece, iocates
or guides the cutting tool related to the work piece and usually is not fixed on the
machine table.

DESIGN OF JIG AND FIXTURE FOR MILLING MACHINE


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INTRODUCTION

Over the past century, manufacturing has made considerable progress. New
machine tools, high-performance cutting tools, and modern manufacturing processes
enable today's industries to make parts faster and better than ever before. Although work
holding methods have also advanced considerably, the basic principles of clamping and
locating are still the same.
Mass production methods demand a fast and easy method of positioning work for
accurate operations on it. Jigs and fixtures are production tools used to accurately
manufacture duplicate and interchangeable parts. Jigs and fixtures are specially designed
so that large numbers of components can be machined or assembled identically, and to
ensure interchangeability of components. The economical production of engineering
components is greatly facilitated by the provision of jigs and fixtures. The use of a jig or
fixture makes a fairly simple operation out of one which would otherwise require a lot of
skill and time. Both jigs and fixtures position components accurately; and hold
components rigid and prevent movement during working in order to impart greater
productivity and part accuracy. Jigs and fixtures hold or grip a work piece in the
predetermined manner of firmness and location, to perform on the work piece a
manufacturing operation.

JIGS

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.
A jig is any of a large class of tools in woodworking, metalworking, and some
other crafts that help to control the location or motion (or both) of a tool. Some types of
jigs are also called templates or guides. The primary purpose for a jig is for repeatability
and exact duplication of a part for reproduction. An example of a jig is when a key is
duplicated, the original is used as a jig so the new key can have the same path as the old
one. Since the advent of automation and CNC machines, jigs are often not required
because the tool path is digitally programmed and stored in memory.
The most-common jigs are drill and boring jigs. These tools are fundamentally the
same. The difference lies in the size, type, and placement of the drill bushings. Boring
jigs usually have larger bushings. These bushings may also have internal oil grooves to
keep the boring bar lubricated. Often, boring jigs use more than one bushing to support
the boring bar throughout the machining cycle.
Jig that expedites repetitive hole center location on multiple interchangeable parts
by acting as a template to guide the twist drill or other boring device into the precise
location of each intended hole center. In metalworking practice, typically a hardened
bushing lines each hole on the jig to keep the twist drill from cutting the jig.

FIXTURES

A fixture is a device for locating, holding and supporting a workpiece during a
manufacturing operation. It is a production tool that locates, holds, and supports the work
securely so the required machining operations can be performed.
Fixtures have a much-wider scope of application than jigs. These workholders are
designed for applications where the cutting tools cannot be guided as easily as a drill.
With fixtures, an edge finder, center finder, or gage blocks position the cutter. Examples
of the more-common fixtures include milling fixtures, lathe fixtures, sawing fixtures, and
grinding fixtures. Moreover, a fixture can be used in almost any operation that requires a
precise relationship in the position of a tool to a workpiece.
Fixtures are essential elements of production processes as they are required in
most of the automated manufacturing, inspection, and assembly operations. Fixtures must
correctly locate a workpiece in a given orientation with respect to a cutting tool or
measuring device, or with respect to another component, as for instance in assembly or
welding. Such location must be invariant in the sense that the devices must clamp and
secure the workpiece in that location for the particular processing operation. There are
many standard work holding devices such as jaw chucks, machine vises, drill chucks,
collets, etc. which are widely used in workshops and are usually kept in stock for general
applications.

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 or sometimes two
sides of a workpiece. Closed jigs, on the other hand, operate on two or more sides. The
most-common open jigs are template jigs, plate jigs, table jigs, sandwich jigs, and angle
plate jigs.
Typical examples of closed jigs include box jigs, channel jigs, and leaf jigs. Other
forms of jigs rely more on the application of the tool than on their construction for their
identity. These include indexing jigs, trunnion jigs, and multi-station jigs. The names
used to identify these jigs refer to how the tool is built. 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.

Modified angle-plate jig

A variation in the angle-plate jig is called as modified angle-plate jig, which is
used for machining angles other than 90 degrees . Both of these examples have clearance
problems with the cutting tool. As the drill exits the product being drilled, it has little or
no room for the drill point to clear the product completely, produce a round hole all the
way through the part wall, and avoid drilling the part locator. This is most noticeable in
Figure , where an angled hole requires additional clearance to the relieved portion of the
part locator. Additional clearance here would allow the drill to complete the hole and
avoid drilling the relieved portion of the locator. The part locator will most likely be
hardened and the drill will be lost as a result of any attempted drilling. Additional
clearance on the relieved diameter of the part locator may be possible. A larger clearance
hole in the locator could also be added if the relieved diameter cannot be reduced. The
additional design consideration added to the locator would include the feature to provide
the correct orientation of this clearance hole or machined relief to line up with the
bushing location.

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Jigs and Fixtures:
Some machining operation are so simple’ which are done quite easily, such as turning, the job is held in position in the chuck and turning operation is done easily. No other device is required to hold the job or to guide the tool on the machine in such an operation. But some operations are such type in which the tool is required to be guided by means of another device and also some jobs are of such forms which are required to be held in position on the machine by means of another device.
The device which guides the tool is called jig and the device which holds the job in position is called fixture.
Jigs and fixtures are special purpose tool which are used to facilitate production (machining, asslembling and inspection operations), when work piece is based on the concept of interchangeability according to which every part will be produced within an established tolerance. Jigs and fixtures provide on means of manufacturing interchangeable parts since they establish a relation with predetermined to tolerance between the work and cutting tool. They eliminate the necessity of a special set up for each individual park. So’ A jig is may be de-fined as a device which hold and position the work; locate or guides the outing tool relative to the work piece and usually not fixed to the m/c table. It is usually lightly in construction.
A fixture is a work holding device and position the work; but doesn’t guide ‘locate or position the cutting tool’ the setting of the tool is done by machine adjustment and a setting blocker using slip gauges. A fixture is hold or clamp-ed to the machine table. It is usually heavy in construction. Jigs are used on drilling , reaming , tapping and couter boring operations , while fixtures are used in connection with turning , milling , grinding , shaping , planning and boring operations.
The use of jig and fixture makes possible more rapid and more accurate manufacturing at a reduction of cost.
Uses of Jigs and Fixtures:
Jigs and fixtures are used to reduce the cost of production as there use elimination being out work and setting up of tools.
To increase the production.
To assure the high accuracy of the parts.
To provide for interchangeability.
To enables heavy and complex shaped parts to be machined by holding rigidly to a machine.
To control quality control expenses.
Less skilled labor.
Saving labor.
There use partially automates the machine tool.
Improve the safety at work, thereby lowering the rate of accidents.
Jigs

The most-common jigs are drill and boring jigs. These tools are fundamentally the same. The difference lies in the size, type, and placement of the drill bushings. Boring jigs usually have larger bushings. These bushings may also have internal oil grooves to keep the boring bar lubricated. Often, boring jigs use more than one bushing to support the boring bar throughout the machining cycle.


reference;
http://www.mechengg2016/07/design-of-jig...lling.html