Design Of Fixtures
Design Consideration in Fixtures
(a) The major frame of fixture must be strong enough so that deflection of the fixture is as minimum as possible. This deflection of fixture is caused since of forces of cutting and clamping of the workpiece or clamping to the machine table. The major frame of the fixture should have the mass to avoid vibration and chatter.
(b) Frames may be built from easy sections so that frames may be fastened along with screws or welded whenever essential. Those elements of the frame which remain permanently with the fixture may be welded. Those elements that required frequent changing may be held along with the screws. In the condition, where the body of fixture has complex shape, that may be cast from good grade of cast iron.
(c) Clamping should be fast enough and need least amount of effort.
(d) Clamps should be arranged so in which they are readily available and may be simply removed.
(e) Clamps should be supported along with springs so which clamps are held against the bolt head wherever possible.
(f) If the clamp is to swing off the work, it should be allow swinging as far as it is essential for removal of the workpiece.
(g) All locator's clamps should be simply visible to the operator and simply accessible for positioning, tightening or cleaning.
(h) Provision should be made for simple disposal of chip so which storage of chips does not interfere with the operation and that their removal during the operation does not interfere with the cutting procedure.
(i) All clamps and support points which require to be adjusted along with a wrench should be of similar size. All clamps and adjustable support points should be capable of being operated from the fronts of the fixture.
(j) Workpiece should be stable while it is placed in fixture. If the workpiece is rough, three fixed support points should be used. If workpiece is smooth, more than three fixed support points might be used. Support point should be placed as farthest as possible from each another.
(k) The three support points should circumscribe the middle of gravity of the workpiece.
(l) The surface area of contact of support should be as little as possible without causing damage to the workpiece. This damage is because of the clamping or work forces.
(m) Support points and other elements are designed in such a way in which they may be simply replaced if they break.