1. Fabrication us the process of forming, casting, machining and welding of the machine.
2. Metal working processes inclued casting, forming, heat treatment, welding and surface treatment.
3. Casting may be defined as a molten material that has been poured into a prepared cavity and allowed to solidify. Types are casting are green sand casting, dry sand casting, Centrifugal casting, Die casting, Investment casting, Permanent mould casting, Plaster mould casting.
4. Forming processes are those which accomplish the rough sizing or shaping of manufactured articles. Any cutting tl which produces a desired contour on the work piece comes under forming process. :
5. Heat treatments:
Annealing - Thorough heating short of critical point followed by gradual cooling. It softens the metal..
Case Hardening - it involves two processes. The first is a carburizing process where carbon is added to the outer surface by heating low carbon steel. The second operation is heat treatment of the carburized parts so that the outer surface becomes hard.
Hardening - it is the process of heating a metal to the decalescence point, soaking it for a considerable time to allow thoroughly penetration of the heat in the metal structure and then suddenly quenching it in cold liquid.
Normalising - cooling at room temperature.
Quenching - rapidly cooling the metal from a high temperature.Rapid cooling is required for obtaining high strength and hardness and the purpose is to harden steel so that it can withstand wear and tear.
Tempering - reheating for reducing brittleness and softening. This process is required after quenching.
6. Welding - it is a process of joining similar metals by the application of heat, with or without application of pressure and addition of filler material. Gas or Electric arcs are used for the purpose of heat. Electrodes are used for filling in and reinforcement. There are 8 welding processes one of them is called brazing.
7. Brazing is a metal-joining process whereby a filler metal is heated above melting point and distributed between two or more close-fitting parts by capillary action.
8. Surface Treatment processes are chemical or mechanical in nature and alter the surface characteristics of the metal. Eleven types of surface treatments are mentioned below:
Anodizing - an electro-chemical process which gives a slight anticorrosion protection.
Enameling - anti-rust zinc coating involving a hot-dip process.
Galvanising - makes the surface anti-corrosive and gives a better finish.
Honing - an abrading (wear away the surface) operation for hole finishing done by a tool fitted with a bonded abrasive stone.
Lapping - surface smoothing operation by hand or machine.
Painting - protective coating and better appearance.
Plastic coating - more durable than paining.
Plating - an electrolytic process which provides anticorrosive finish.
Shot Blasting - small shots usually in the form of iron balls are made to blast on the metal required for making it resistance to wear and tear, remove the stresses and hardness.
Shot penning - an air basting the small shots against the metal surface in order to increase the hardness of surface.
Tumbling - castings are tumbled in a tumbling barrel together with an abrasive substance. The friction created in this way will clean the surface.
Other processes of Surface Treatment may be Buffing, Polishing, Power brushing, Sandblasting, Washing, Waxing etc.
9. Machining Process : Machinability is the is the case with which metal can be removed.Various machining processes are :
Blanking - it produces necessary depressions and cut-outs with "punch and die"
Boring - it may be straight or tapered.
Broaching - produces slots and gear teeth with the help of a cutter called broached.
Die Cutting - are of two types - punch I g and blanking types.
Drilling
Facing
Flame cutting and gas cutting
Grinding
Milling
Parting
Plaining and Shaping
Punching
Reaming - smoothing of the whole through reamer
Sawing
Screw Cutting
Slotting
Taper turning - produces conical shape instead of cylindrical shape
Tapping - multiple cutting tool called tap is used for making threads on the inside surface of a hole.
Turning - it is the operation of cutting and removing material from the surface of the job producing cylindrical external surface.
10. Classes of Machine tools :
General purpose or Standard Machine tools - Drilling machine, Grinding machine, Lathe (centre or engine lathe), Milling machine, Plaining machine, Shaping machine etc.
Special purpose Machine tools - Boring machine, Broaching machine, Gear-cutting machine, Honing machine, Lapping machine, Turret and Capstan lathe.
Broaching Machines are used for altering the size of finish of holes in metallic parts.
Lapping Machines are used for finishing cuts.
Turret and Capstan lathe with appropriate tools are used for turning, forming, parting off, boring and screw-cutting.
