Jigs & Fixtures with differences, Types of Jigs & Fixtures and Constructional details of Jigs & Fixtures

Jigs & Fixtures with differences, Types of Jigs & Fixtures and Constructional details of Jigs & Fixtures

Jigs:

           Jig is a special device that holds, supports the work piece and guides the cutting tool during the operation performed.
Jigs

Fixtures:

           Fixtures holds, locates and supports the work piece securely in the correct position with respect to the machine/cutter during operation and does not guide the cutting tool.
Fixtures

Advantages of jigs and fixtures:

•Jigs and fixtures eliminate individual marking, positioning, and frequent checking. This reduces operation time and increases productivity.
•They enable quick setting and proper locking of work.
•Jigs and fixtures facilitate easy and quick assembly.
•There is no need for skillful setting of the work piece and tool.
•High production, reduction in scrap, and savings in labor costs results in substantial reduction in work piece cost.
•The parts produced with their use are very accurate.
•Inspection and quality control of finished product is less.
•Higher speeds, feeds can be used for machining.
•Different machining operation can be done in single stroke.

Jigs:

           In metalworking, a jig is a type of tool used to control the location and motion of another tool. A jig's primary purpose is to provide repeatability, accuracy, and interchangeability in manufacturing products. A jig is often confused with a fixture. A fixture holds the work in a fixed location. A device that does both functions [holding the work and guiding a tool] is called a jig. Jigs or templates have been known long before the industrial age. There are many types of jigs, and each one is custom-tailored to do a specific job. Many jigs are created because there is a necessity to do so by the tradesmen, to increase productivity, to do repetitious activities and to do a job more precisely & for faster rate of production. Easy to perform the operations even by unskilled workers. Layout and marking on individual parts eliminated.

Types of jigs:

Jigs are divided into two types:
•Open jigs - Work is done on only one side of work piece.
•Closed jigs - Work is done on more than one side of work piece.

Main types of jigs:
•Template jig
•Plate jig
•Leaf jig
•Box jig
•Channel jig


1. Template jig:
           It is a simple plate of metal which carries correct locations. These types of jigs fits over, on, or into the work and is not usually clamped. They may or may not have bushings. This will reduce the marking time. Orientation of the whole pattern to work piece datum's may not be as accurate as other types. They are usually not practical when locating datum's are dimensioned.
Template jig
2. Plate jig:
           Plate jigs are similar to template jig. This jig consists of a drill plate which rest on the component to be drilled For correct positioning locating pins and clips are provided. A simple clamp will be there to hold the jig over the work piece. Generally a base plate will not be available for this type of jigs.
Plate jig
3. Leaf jig:
           Leaf jig is a open type jig in which a leaf or a plate is arranged to swing about a hinged point so that it completely clears the jig for easy loading and unloading of the workpiece. In this, the drill bushes are fitted into the leaf.

Leaf jig

4. Box jig:
           Box jigs, or tumble jigs, usually totally surround the part. This style of jig allows the part to be completely machined on every surface without the need to reposition the work in the jig. This jig is designed for the components which need a very rigid support and difficult to be hold.
Box jig
5. Channel jig:
           Channel jigs are the simplest form of box jig. The work is held between two sides and machined from the third side. In some cases, where jig feet are used, the work can be machined on three sides.
Channel jig

Constructional details of jigs:

1.Base plate or jig body, 
2.Drill plate or jig plate, 
3.Drill bushes, 
4.Locating pins, 
5.Clamps.
1. Jig body:
            This provides a rigid support for locating pins and clamps. Sometime components directly rest on the jig body.
2. Jig plate:
            It holds the drill bushes. Unbushed holes made on the jig plate.
3. Jig bushes:
           They are used to locate and guide drills. They are hardened and ground to exact sizes. Different types of bushes used in jigs based on the requirements.
elements of jigs & fixtures
4. Locating pins:
           They restrict the movement of the component. Locators position the work piece with respect to the tool. They facilitate easy loading and unloading of components. It must be assist the operator for correct loading. Different types of locating pins are used according to the shape of the components.
5. Clamps:
           Standard bolts and hinged bolts used for clamping. Various types of set screws also used for clamping. C and U shaped slotted washers are commonly used. Standard clamping components also used for clamping.

Types of fixture:

1. Vise fixture:
           Vise is a mechanical screw apparatus used for holding or clamping a work piece to allow work to perform work. Vise usually have one fixed jaw and another parallel jaw which is moved towards or away from the fixed jaw by the screw. The fixed jaw is moulded with the vise body and movable jaw is mounted on a screw. Rotation of screw causes the movable jaw to open and close. This jaw may include a dog hole to hold a bench dog. This vise are made up of cast steel or malleable cast iron for high strength.
Vise fixture

2. Turning fixture:
           Regular shaped work pieces is easy to hold in lathe using chucks. Holding irregular shaped components in lathe is very difficult. For simple irregular component can be hold by for jaw chucks. But adjustment ofjaws in a four-jaw chuck is not easy for production jobs. So, complicated shapes have to be necessarily held in position with the help of turning fixtures. The fixtures are normally mounted on the nose of the machine spindle or on a face plate.
Turning fixture

3. Milling fixture:
           Pressure of cut should always be against the solid part of the fixture. Clamps should always operates from the front of the fixture. The work piece should be supported as near the tool thrust as possible. A milling fixture is a work holding device which is firmly clamped to the table of the milling machine. Keys are provided on the bottom of the base plate which are used for easy and accurate aligning of the fixture on the milling machine table T-Slots. The fixture is fastened to the machine table with the help of two T-bolts engaging in T-slots of the work table. The setting block is fixed to the fixture which have reference planes.
Milling fixture
4. Grinding fixture: 
           Every grinding operation needs some sort of fixture. The work piece should be supported as near the tool thrust as possible. Normally grinding divided into two groups,
(i) Cylindrical grinding:
a) Internal grinding,
b) External grinding.
(ii) Surface grinding.
Grinding fixture
Cylindrical grinding utilizes mandrels for external surface grinding. The mandrel may be plain or tapered. Mandrel is hardened and is held between centers of a machine. The work piece is located and held on the mandrel with the help of the bore so that the external surface may be machined truly concentric to the bore. For internal grinding the chuck is the most standard fixture. For holding irregular shaped component, the fixture designed same as turning or boring fixture. The work piece can be held for machining on a surface grinder in the following ways:
  It may be clamped directly to the machine table or to an angle plate and so on.
It may be held in a vice.
The work piece may be held by means of a magnetic chuck or a vacuum chuck. Here the work piece is held without any mechanical clamping.
The work piece may be held in a special fixture same as milling fixture.
grinding fixture
5. Indexing fixture:
           Indexing fixtures are very similar to indexing jigs. These fixtures are used for machining parts that must have machined details evenly spaced. Such components are required to be indexed equally as many times as the number of surfaces to be machined. The work holding devices carry the indexing mechanism.
Indexing fixture
6. Welding fixture:
           A welding fixture clamps the parts together and simultaneously supporting them, the objective being to effect a weld in the flat position. Joints must be readily accessible for welding. The fixture should permit quick and easy positioning [by one hand, if possible]. Whenever possible, a fixture should be enable all welds to brought to a convenient welding position. Clamps must operate quickly. Screws and moving parts should be protected against weld spatter. Methods of grounding the work are important considerations in fixture design, since they affect arc action, quality of weld.
Welding fixture

Constructional features of a fixture:

           These fixtures consist of a base plate, standard clamps and locators, setting blocks and balancing weights.
1. Base plate:
           The base plate for a milling fixture is provided with tensions at its bottom for proper location of the fixture with the machine table through Tee slots.
Constructional features of a fixture
2. Standard clamps and locators:
           These are provided for clamping and locating the work pieces with the fixture as in the case of drill jigs. The clamps used in the fixtures are very rigid and sturdy.
3. The setting blocks:
           These are used to position the fixture and work relative to the cutter before machining. A feeler is introduced between the cutter and the setting faces of the block for correct positioning of the cutter with the fixture.
Constructional features of a fixture
4. Balancing weight:
           This is used dynamically balancing the irregular work piece fixed to the turning or cylindrical grinding fixture. In the case of a turning fixture, normally the base plate of the fixture is clamped to the face plate.
Constructional features of a fixture


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