Machining

Machining

1. Chip formation

   • Continuous Chip: Formed from cutting soft,ductile metals e.g aluminium and copper. Can be a disadvantage if gets long and tangles into cutting operation, can be prevented with use of chip-breaker which winds and snaps chip.
   • Discontinuous Chip: Formed from cutting hard, brittle materials e.g brass, as these materials cannot withstand high shear forces and therefore the chips formed are sheared cleanly away. With discontinuous chip, there is a higher chance of tool chatter unless tool, tool holder and piece are held rigidly.
   • Built- up Edge: A built up ede is formed when particles from the piece are welded onto the cutting tool. Built up edge causes a bad surface finish, and can be prevented with cutting fluid

2. Tool Wear

   • Crater wear: Occurs on the rake face just behind the cutting edge and is caused by the rubbing of chip across this surface. Cratering thins out the cutting edge which can lead to tool failure.
   • Flank wear: Occurs on the clearance angle of the tool causing rubbing and degradation of the surface finish.

3. Turning Operations

   • Turning produces solids of revolution. Turning is performed on a lathein which the tool is stationary and the part is rotated.Lathes are designed for turning operations, the work piece is mounted on the chuck which rotates relative to the stationary tool.
     • Parallel Turning, Tapered Turning, Facing Off, Parting Off, Grooving, Drilling/Boring, Knurling, Threading.

4. Grinding Tool

   • Process to improve finish and slightly alter surfaces tolerances by removing a small amount of the material. An abrasive material is rubbed against a metal piece and and a small amount of material is removed.
   • Reasons for grinding: 1; Material is too hard to be machined. 2; Tolerances need to be adjusted for machining. 3; Removing of excess material.
   • Loading: When a grinding wheel is loaded with small debris between the abrasive grains. Glazing: The abrasive material on the grinding wheel has been worn away. Dressing: This is the cleaning of the grinding wheel to prevent and fix glazing and loading.

5. Milling

   • Up cut Milling: Direction of the cutter rotation is opposite to the feed motion – cutter may want a lift workpiece, make sure it is secured down. Down cut Milling: Direction of the cutter is the same as the feed motion - cutter may want to pull workpiece under, make sure it is secured into place.
   • Peripheral / slab Milling: Milled surface generated by teeth on cutter in a plane parallel to the workpiece surface. Face Milling: Cutter on a spindle on a axis of rotation perpendicular to the workpiece surface. End Milling: Cutter in end milling rotates on a axis vertical to the workpiece. Can be tilted to machine tapered surfaces. Gang Milling: Use of two or more milling cutters mounted on the same arbor for cutting horizontal surfaces. The cutters may or may not perform different types of operation.
   • Cutting away material by feeding workpiece past a rotating multi-tooth cutter. Machine that holds workpiece, cutter and feeder is known as a milling machine. Horizontal Milling: Spindle held horizontally, Vertical Milling: Spindle held vertically.