Assignment # 03-tool Design

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DESIGN OF FIXTURE NAME: USMAN AHMED

TOOL DESIGN Roll No. 08MR08MR-20

ASSIGNMENT # 03 -----------------------------------------------------------------------------------------------------1) How was the term fixture derived? A fixture is a device for holding a work piece during machining operations. The name is derived from the fact that a fixture is always fastened to a machine or bench in a fixed position. It does not contain special arrangements for guiding the cutting tool. In a setup using a fixture the responsibility for accuracy depends upon the operator and the construction of the machine tool. Other type of tooling for positing parts relative to each for fabricating purpose are also referred as fixture. 2) What is the major difference between a drill jig and a fixture? Drill jig not fastened to the machine on which it is used and may be moved around on the table of the drilling machine to bring each bushing directly under the drill. Jigs physically limit and control the path of the cutting tool. A fixture holds the work piece during machining operation but does not contain special arrangements for guiding the cutting tool, as drill jigs do. A fixture is also fixed to the machine. 3) What are economic aspects of the use of fixture? The economic aspects of the use of a fixture can be considered on the following basis: 1. The production per year necessary to pay out of savings for a fixture of given estimated cost. 2. The maximum allowable cost of a fixture to break even for a given saving in operating cost per piece and specific number of parts produced during a year. 3. The number of year it will take to pay out of savings for the proposed fixture with a given saving in operating cost per piece and given yearly production. 4. The net savings from the use of a fixture of a given cost, for an estimated saving in operating cost per piece at a given output. 4) Why are keys mounted to the base of mill fixtures? The base of mill fixture has a keyway running lengthwise. The base is provided with slots for the purpose of clamping the fixture to the mill table. In the base two keys are used to align the fixture on the milling-machine table. The keys are passed into the keyway at both ends of the fixture and held there.

2 5) What are the various methods of production milling? The various methods of production milling are as follow:

Single-piece milling: One work piece is held in a vise or fixture and fed through the milling cutter. The mill table is returned to its starting point before inserting another work piece.

String milling: A series of identical work piece is mounted in line parallel to the table feed movement and fed in successive order into the mill cutter.

Reciprocal milling: Fixtures are mounted on each end of the mill table with the mill cutter in the middle. The operator unloads and loads one work piece while the other is being machined.

Progressive milling: In progressive milling method two or more milling operations are performed at the same time on separate but one and the same work piece, which may be completed with each pass of the mill table, but it is necessary to move a partially finished part to the next station in the fixture and insert a new part in its place.

Index milling: Duplicate fixtures are mounted on a table which is pivoted in such a manner that it can be rotated and indexed into position.

Rotary milling: A series of fixture is mounted on a large rotary table which in turn rotates the work piece consecutively under the cutter. The table must be large enough to give the operator ample time to remove and insert a new work piece with stopping the table. 6) What are the major advantages of magnetic and vacuum milling fixtures? Magnetic milling fixtures have low-voltage great deals with more holding power because of the increased efficiency of the magnetic path. The low-voltage feature ensures safety to the operator and provides heat free holding. Vacuum milling fixtures are being used for holding nonferrous and nonmagnetic parts for milling operations where holding without distortion is vital. Magnetic and Vacuum chucks can be more economical. These are used in production milling. 7) What is the basic difference between a lathe fixture and other types of fixtures? Lathe fixture is commonly used for round work pieces and it revolves with work piece. On the other hand, other fixtures are fixed on machine tables and these fixtures are not only use for round work pieces but also used like for square, irregular and regular shapes.

3 8) How is face plate fixture located on the lathe face plate? It is usually located on the faceplate by means of two dowel pins and secured by cap screws inserted through the faceplate into tapped holes in the fixture or T bolts into T slots in the faceplate. 9) What is the standard taper on a plain mandrel? The mandrels provide more holding power because the tapered head acts on the extreme ends of the split and does not allow deflection. Plain mandrels have about a 0.006-in taper per foot. 10) What conditions unique to a grinding process must be taken into consideration when designing grinding fixtures?

There are, however, conditions unique to the grinding process that must be taken into consideration. The grinding operation is usually a finishing operation where the work piece dimensions are held to close tolerance; therefore great accuracy is required in the design and construction of grinding fixture. Work pieces cannot deflect under clamping pressure and locating methods must be precise and exacting. Location of work pieces is made easier, however, since by the time they are ready for grinding. 11) What is the standard method of holding parts for surface grinding operations?

The standard method of holding parts for surface grinding operations is magnetic chucking. Work piece can be quickly mounted and removed and distortion caused by mechanical clamping is eliminated. A number of parts can be mounted at one time, the only restriction being the size of chuck.