Some operations are carried out with the help of commonly used tools and do not require special tooling in order to hold the job or for machining or other processes. But some operations are of such type that tools are required to be guided by means of some other external devices and also some jobs are required to be held in a position on the machinery by means of another device.
The device which guides the tool is known as Jig and the device which holds the job in a position is known as Fixture. In this post, we are going to discuss the design considerations for jig and fixture.
|Example of Jig and Fixture|
Jig and Fixtures are commonly used in production methods to reduce production time, cycle, and hence reduction of the cost. In this topic, we will discuss the factors considered while designing Jig and Fixtures.
Design Considerations for Jig and Fixture
Fundamental principles for the design of Jig and Fixture are
- Positioning points
- Idle time reduction
- Foolproof design
- Provision of feet
- Clamping devices
Proper and accurate facilities should be provided for positioning the work. The job that is to be machined must be easily inserted and removed from the jig so that time is not wasted while positioning the workpiece in the operation. This reduces cycle time and hence increased production.
Idle Time Reduction
The design of the Jig and Fixture should be such that operations on a workpiece such as loading, clamping, and unloading time is minimum.
The design of the Jig and Fixture should be such that it does not permit the tool or the workpiece to be inserted in an incorrect position.
The design should be such that it should be easy to handle, smaller in size, and use the minimum amount of material without lowering rigidity and stiffness.
Provision of feet
Jigs sometimes are provided with the feet so that they can be placed on the table of machines.
Design for clamping should be as much as possible simple without sacrificing effectiveness. While designing Jig and fixtures, it should be noted that the strength of the clamp should be such that it not only holds the workpiece but also take the strain of the cutting tool without spinning.
General rules for the design of jig and fixture
- Make Jig foolproof
- Decide on locating point and clamping arrangement.
- Make some locating points adjustable.
- Always avoid complicated clamping arrangements.
- The cost of tooling should not exceed the expected cost.
- Make provision of handles wherever necessary.
- Remove sharp corners.
- Make holes to escape the chips.
Essential Features for the design of jig and fixture.
Idle time reduction
The design should be such that it should enable easy clamping and unloading so that idle time is minimum.
Standardization of parts
Use of standard parts as much as possible.
Cleanliness of the machining process
The design should be such that not much time is wasted in cleaning the machine.
Pins and other devices of simple nature are incorporated in such a position that they will always spoil the placement of components or hinder the fittings of the cutting tools until the latter is in correct position.
All locating and supporting surfaces should be hardened materials as much as possible so that they are not worn out quickly because of wear and tear.
It must be ensured that the workpiece is not located on more than three points in any one plane test to avoid rocking, spring loading should be done.
Position of clamps
Clamping should be directly above the point where it is supporting the workpiece to avoid springing and distortion.
It should be light in weight and must be easy to handle so that the worker is not subjected to fatigue.
The proper ejecting device should be given in order to remove the workpiece after the operation.
The design should be economic and manufacture should be in proportion to the quantity and price of the producer.