JIG: Increasing the Productivity

INTRODUCTION OF JIG

It is a work holding device that holds, supports and locates the work piece and guides the tool for a very specific operation.

Increasing the productivity and accuracy are the two basic aims of mass production. As we know the solution to this is by reducing the set up cost of the machine and also reducing the manual fatigue. In this case the device that caters our needs is the use of jigs. Let us take one example.

Let us consider that one gets an order of say 1000 products. There need to be three holes drilled on this product. Accuracy is the main problem in such cases. In doing so it increases the work load on the operator. Hence using of jig to position and guide the tool to its right path is preferred rather than using scribers, square, straighteners or centre punch etc.

Thus the productivity is increased which is done by eliminating individual positioning, marking and frequent checking.

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Interchangeability is the chief advantage here. All the parts fit in properly except only the similar components are interchangeable. One does not need to repeatedly clamp and unclamp the object for various purposes like positioning as the locating, clamping and guiding of the tool is done by the jig itself. Bushing which is a tool guiding tool is used. So it red uses the presence of skilled labourer. Drill jig helps to drill, ream and tap at a much faster speed and with great accuracy as compared to holes done conventionally by hand.

In case of a drill jig bushings are used. These drill bushings guide the drill bit during the drilling operation. Generally work piece is held by a fixture and the fixture is arranged in such a way that the loading and unloading of the job is quick.

LITERATURE REVIEW

Plans of Movement

An unrestricted object is free to move in any of twelve possible directions. An object with three axis or planes along which movement any occur. An object is free to revolve around or move to parallel to any axis in either direction. To illustrate this plane have been marked X-X, Y-Y and Z-Z the directions of movement are numbered from one to twelve.

Restricting Movement

To accurately locate a part in jig or fixture movement must be restricted. This is done with locators and clamps. The fixture for the part in fig. 3-8 illustrates the principle of restricting movement. By placing the part on a three-pin base, five directions of movement are restricted using pin or button type locators minimizes the change of error by limiting the area of contact and raising the part above the chips.

Flat bases many also be used. But these should be installed locators are less expensive to use because they take less time to install and are replaceable. If button or flat locators are used the most important consideration is keeping the part above the chips and in constant contact with all three locators. To restrict the movement of the part around the Z-Z axis and in direction eight two more pin type locators are positioned. To restrict direction seven a single pin locators is used. The remaining direction nine, ten, eleven are restricted by a clamping device. This three-two-one or six point locating method is the most common external locators for square or rectangular parts. When a workpiece having holes is located the holes provide an excellent method of locating the complete part.

OBJECTIVE

Jig and fixture are so closely related that the terms are sometimes confused or used interchangeably. The difference is in the way the tool is guided to the work piece.

As a rule small jigs are not fastened to the drills press table. If however holes above 25 inch in diameter are to be drilled, it is usually necessary to fasten the jig to the table securely.

Jig & fixture are Work holding Devices Used to Manufacturer duplicate parts accurately. The correct relationship and alignment between the cutter or other tool and the work piece must be maintained. To do a this jig or fixture is designed built to hold, support, and locate every part to ensure that each is drilled or machined within the specified limits.

Jigs are work holding devices which are used in Drill Press and Boring Machine for performing operations like drilling, reaming, tapping, countersinking etc. The main objective of this project is that this model can be used for students of mechanical engineering to understand the concept of Jigs and hence can be used for teaching purposes.

Other objective of this project was to understand the practical manufacturing techniques which have to be used for manufacturing Jigs. Knowledge about designing jig to fundamental level has been cleared to us and hope the same model of jig can be used for students in future to understand what basically Jig is.

In our project we had selected Acrylic as Jig body material so that one can see through it all the other parts and how those parts are assembled on Jig body. Since the project is a working model we had chosen a wooden work piece to work upon.

ELEMENT OF JIG

The Body

As the most outstanding element of jigs and fixtures, the body is constructed by welding of different slabs and metals usually mild steel or by casting of cast iron. After the

Fabrication, it is often heat-treated for stress reduction as its main objective is to accommodate and support the job.

Clamping Devices

Without sacrificing efficiency and effectiveness, the clamping devices must be very simple and easy to operate. Apart from holding the work-piece securely in place, the strong point of clamping devices is its ability to withhold the strain of the cutting tool during operations. The bench vice is a popular example of a clamping device. The need for clamping the work-piece on the jig or fixture is to apply pressure and press it against the locating components, thereby fastening it in the right position for the cutting tools. The familiar clamping devices include.

Locating Devices

Made with hardened steel and with different designs, the pin is the most popular device applied for the location of work-piece in jigs and fixtures. The pin's shank is press-fitted or driven into a jig or fixture. The locating width of the pin is made bigger than the shank to stop it from being pressed into the jig or fixture body because of the weight of the cutting Tools or work-piece.

Jig Bushing or Tool Guide

Guiding parts like jig bushings and templates which must be wear resistant, interchangeable, and precise, are used to locate the cutting tool relative to the component being machined. Jig bushes are applied in drilling and boring, here for the drill to pass through, a bush fits into the hole of the jig.

The jig bushings are categorized into three: the linear wearing bushes, press-fit wearing bushes, and renewable wearing bushes.

SELECTION OF MATERIAL

There are a wide range of materials from where jigs and fixtures could be made, to resist tear and wear, the materials are often tempered and hardened. Also, phosphor bronze and other non-ferrous metals, as well as composites, and nylons for wear reduction of the mating parts, and damage prevention to the manufacturing part is also used. Some of The materials are discussed below:

High Speed Steels: high speed steels which contain more quantity of tungsten and less quantity of chromium and vanadium has high toughness, hardenability, hardness retention at high temperature, and good wear, tear and impact resistance. When

Tempered, they are applied in the production of jigs and fixtures for reaming, drilling, boring, and cutting operations.

Mild steels: mild steel which contain about 0.29% of carbon are very cheap and because of their easy availability are often the choicest material for the making of jigs of fixtures.

Other materials for the making of jigs and fixtures include Nylon and fibre, steel castings, stainless steel, cast iron, high tensile steels, case hardening steels, and spring steels.

Die Steels: the three variants of die steel - high chromium (12 %), high carbon (1.5 to 2.3%), and cold working steels are applied in the production of jigs and fixtures for the making of thread forming rolls, as well as cutting of press tools. When alloyed with vanadium and molybdenum for it to retain toughness at very high temperature, die steels are applied in the fabrication of jigs and fixtures that are used in high temperature work

Processes which include extrusion, forging, and casting processes.