Jigs and fixtures are manufacturing tools that are employed to produce interchangeable and identical components. They are unique tool-guiding and work-holding devices designed specifically for machining and assembling large number of parts. The purposes of jigs and fixtures reduction of production cost, increase of production rate, high accuracy of products without any manufacturing defects, provision of interchangeability, easy machining of complex shaped parts, reduction of quality control costs, etc.
JIGS: A jig is a work-holding device that holds, supports, and locates the work piece and guides the one or more tools to perform a specific operation. The main purpose of a jig is to provide repeatability, accuracy, and interchangeability in the manufacturing of products. It is used in uni-dimensional machining processes like drilling, tapping, and reaming, etc. This system is found to be light and has a complex shape. Gauge blocks are not necessary and the cost of jigs is higher. Jigs are not fixed to the machine table until a large operation has to be performed.
FIXTURE: Fixtures are the work holding device, which holds, supports and locates the work piece but not guides the cutting tool to perform a specific operation. The main purpose of the fixtures is to hold and locate the work piece during any machining operation and to provide repeatability, accuracy, and interchangeability in the manufacturing of products. Fixtures are used in multi-dimensional machining like milling, grinding, turning, etc. This system found to be heavy in weight, have simple designing. Gauge blocks provided for effective handling and the cost is average. Fixtures are having specific tools that use particularly in the milling machine, shapers and slotting machines. Fixtures are fixed to the machine table.
In a jig design for manufacturing usage, the jig designer must consider the following points before starting to design the jigs:
Designs jig that are fool proof to prevent any misuses by production operator
Design jig that is easy to operate to increase efficiency
Design jig that can be manufactured at the workshop using lowest costs
Design jig that can withstand the tool life by select the appropriate materials
Design jig that consistently produce parts with consistent high quality
Design jig that will provide the safety to production operator that fulfils the customers OSHA requirement
Therefore for jig designers, it is important for them to be involved in concurrent engineering. Concurrent engineering allows the jig designer to be involved for the products design and productions where their expertise of jigs and manufacturing processes will result in fewer errors to be discovered in productions.
Advantages of Jigs and fixtures:
It eliminates the setting time required before machining.
It increases the machining accuracy and also increases production capacity.
Requires less skilled operation.
They reduce the production cost.
Increases machine and labour utilization.
They simplify the work handling.
Increases the quality of production in the industry.
They enable the quick setting of a tool and the proper positioning of the work.
DESIGN: Fixtures should be designed with economics in mind; the purpose of these devices is often to reduce costs, and so they should be designed in such a way that the cost reduction outweighs the cost of implementing the fixture. It is usually better, from an economic standpoint, for a fixture to result in a small cost reduction for a process in constant use, than for a large cost reduction for a process used only occasionally.
Most fixtures have a solid component, affixed to the floor or to the body of the machine and considered immovable relative to the motion of the machining bit, and one or more movable components known as clamps. These clamps (which may be operated by many different mechanical means) allow work pieces to be easily placed in the machine or removed, and yet stay secure during operation. Many are also adjustable, allowing for work pieces of different sizes to be used for different operations. Fixtures must be designed such that the pressure or motion of the machining operation (usually known as the feed) is directed primarily against the solid component of the fixture. This reduces the likelihood that the fixture will fail, interrupting the operation and potentially causing damage to infrastructure, components, or operators.
Fixtures may also be designed for very general or simple uses. These multi-use fixtures tend to be very simple themselves, often relying on the precision and ingenuity of the operator, as well as surfaces and components already present in the workshop, to provide the same benefits of a specially-designed fixture. Examples include workshop vises, adjustable clamps, and improvised devices such as weights and furniture.
Each component of a fixture is designed for one of two purposes: location or support.