Jigs and fixtures ease for the production of components in mass within a very economical manner. These serve as most important role in mass production system. These are a special kind of work holding and tool guiding devices. The quality of performance in production depends on usage of jigs and fixtures for that production system. Generally mass production of work methods will demand a fast and easy method to position the work in order to perform accurate operations. These are used as the production tools for accurate manufacturing duplication and also for easy interchangeable parts. These are specially designed for large number of components and can be machined or assembled easily, that ensures interchangeability of the components.
Jigs are special purpose work holding devices that holds supports and locates the work piece in addition used as guides the cutting tool to perform a specific operation. Jigs are generally fitted with hardened steel bushings that guide the cutting tools. Jigs are the tools that are used to control the motion as well as the location of other tool.
In the manufacturing purposes jigs provides accuracy, interchangeability and repeatability of the process. In simple words jigs are the devices that support tool guidance and work holding purposes in the production process. A key duplication is an example of jig that uses original one as a jig in order to have the same path as that of the old one.
Fixtures are a work holding device that holds supports and also locates the work piece in order to perform a specific operation. It does not guide the cutting tool. It just acts as a reference to the surface as well as device. It is specially designed to fit a part and shape in particular. The main purpose of this tool is to locate or hold the work piece during machining operations or for some industrial processes. Chucks and vices are examples of fixtures.
Types of jigs and fixtures:
Drilling jigs are most commonly used for large number of operations.
- Template jig
- Plate type jig
- Open type jig
- Swinging leaf type jig
- Box type jig
- Solid type jig
- Pot type jig
- Index jig
- Multi station jig
- Universal jig
In order to carry out the operations properly and hold the work pieces, the types of fixtures used are:
- Turning fixtures
- Milling fixtures
- Grinding fixtures
- Broaching fixtures
- Drilling or boring fixtures
- Tapping fixtures
- Welding fixtures
- Fixtures for assembly
Location and principle of locations:
- Location refers to the relationship establishment in between the work piece plus the jigs and fixtures for the correctness of location that has its direct influence on the finished product’s accuracy. These locations are desired by jigs and fixture to arrest the undesirable movements of the work piece and to set the pre decided position to the jig. Locators are used to restrain the degrees of freedom with the help of suitable arrangements. Location plays a key role in the purpose of usage of jigs and fixtures in production processes.
- A rectangular body has three axes where its movement can be released. The body can also rotate along these axes. Therefore for a body it is required to restrain these six degrees of freedom. Six point location methods for a rectangular block are used for this purpose. This method is also known as 3-2-1 principle. In this method the block is made to rest on many points of the jig body. First when a rest is provided to work piece on three points in the x-y plane, this will arrest movement along z-axis and rotation along x and y-axis. Next rest the work piece on two points of the x-z plane that fixes the movement along y-axis and rotate with respect to z-axis. A support is to be provided at one point on the y-z surface that fixes the other free movements. In this way a rectangular block can be located with desired restrictions in its degrees of freedom.
- Location methods:
The location arrangement depends on the type of operation, degrees of required accuracy.
- Flat locators: These are used for the location of the flat machined surfaces of a component.
- Cylindrical locators: These are used for the location of components with drilled holes.
- Conical locators: These locators are used to support the work pieces with cylindrical holes.
- Jack pin locators: These locators support rough work pieces.
- Drill bush locators: These locators hold and locate the cylindrical work pieces.
- Vee locators: These locators hold circular and semicircular work pieces.
The work piece is restrained completely with the clamping device in addition to the location devices as jigs and fixtures. It secures the work piece in a jig or a fixture against the forces that are applied over the work piece during an operation. Requirements of clamping device:
- Should possess rigidity in holding the work piece.
- The work piece should not be damage due to clamp tool.
- Clamping pressure is to be applied to over the operating pressure on the work piece.
- The clamping process should not consume more time.
- The clamping faces are to be sufficiently hardened by proper treatments before its usage.
- The fragile materials are to be handled with fiber padded clamp faces.
Types of clamps:
Strap clamps or edge clamps are used to strap on the work piece with the help of the lever pressure.
- Heel clamps
- Bridge clamps
- Side clamp or edge clamp
- Screw clamp
- Latch clamp
- Equalizing clamps
- Power driven clamps
Advantages of jigs and fixtures:
- The productivity is increased by the usage of jigs and fixtures in the production process.
- High degree of accuracy is offered along with uniform quality in the interchangeability at a modest cost.
- There is no need for any skill in the work tool setting in an operation.
- As the production rate is increased with a reduction in scrap that finally reduces the unit cost.
- The dimensional variability can be achieved easily with low manufacturing processes that support consistent quality in the usage of jigs and fixtures.
- The production life cycle is reduced.
- Quality examination is not required as the usage of jigs and fixtures are employed with ensured quality of employment.
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