Forging--Introduction

1. Forging--Introduction • It is the process by which metal is heated in closed furnace and is shaped by plastic deformation by suitably applying compressive force. • Compressive force are either from impact of hammer or pressure exerted by large mechanical presses. • Applied pressure is continuous / intermittent. • Forging refines the grain structure and improves physical properties of the metal.

5. Forging was first used to make jewelry, coins, by hammering metal with tools made of stone. • Capable of making parts ranging in size of a bolt to a turbine rotor typical parts forged are bolts, rivets, connecting rods, shaft for turbines, gears, hand tools, transport equipments, trucks, aero plane . • Most forged metals & alloys are carbon steels, stainless steel, copper base alloys.

7. Because of higher strength of material, cold forging requires greater force, parts have good surface finish & dimensional accuracy, strength. • Hot forging requires smaller forcesbut produces dimensional accuracy, finish which are not good. • Forging produces products without any porosity, voids, inclusions & other defects as in casting.

8. Process advantages: • Improves structure of metal. • Closing of voids in the metal, grains refined. • Reduced machining time. • Porosity in cast steel ingots is eliminated. • Close tolerances, weight saving • Surface finish smooth, speed of production. Process disadvantages: • Tooling cost can be high & maintenance. • Due to hot forging, scaling of surface results in poor surface finish.

9. Applications : • Crankshafts & connecting rods for engines. • Turbine discs, gears, wheels, bolts, headed pins, nuts, nails, keys, hooks. • Structural parts for machinery, transformation equipment. • Riveting of shells for boilers, tanks, furnaces. • Fixtures & fastening devices like clamps, hinges, racks

10. Forging is done by • Impact pressure / striking with hand or power hammer. • Squeeze pressure / shaping by power presses. Smithying or hand forging: • Itis done where small parts are shaped. • Either cold/ by heating them in open fire • shaping is carried out with help of anvil & hand hammers. • Place where hand forging is carried out is called smithy shop.

11. Smithying or hand forging

13. Power forging • refers to production of heavy parts. • uses forging dies, mechanized power hammers or presses for forging operations. • Machine forging is term used for operations carried out under forge hammers (light work), large presses (heavy work).

14. Power forging

15. Basic Die Forging Processes • It is an example of power forging where in forgings are made in steel dies made of tough, hard, wear resistant. • Die is made into 2 halves, each carrying impression / cavity resembling half portion of part to be forged. • As mating halves of die close, metal is shaped into the form of die under blows of hammer/ press. • Dies used for forging may be : • Open type die forging. • Closed / impression type die forging

17. Open Die Forging

19. It is carried out between 2 flat dies or dies of very simple shape. • The process is used for mostly large objects or when the number of parts produced is small. • In this process forging is carried out in large hydraulic presses/ power hammers. • In this type w/p is larger than tool, at any point of time, deformation is confined to small portion. • Numerous blows are applied to different portions of w/p .

20. OPEN DIE FORGING: COGGING

21. Advantages: • Simple to operate. • Useful for small quantities. • Inexpensive dies & equipment. Disadvantages: • For simple shapes & short productions only. • Difficult to maintain close tolerances, high skill labour. Applications: • Ship propeller shaft, rings, pressure vessels.

22. [Heated] metal is beaten with a heavy hammer to give it the required shape Hot billet, open-die

23. Open die forging can be explained in simple way by following 2 open die operations: • Cogging / Drawing out: • It is a open die forging process in which thickness of bar is reduced by successive steps at specific intervals.

24. 2. Upsetting / Flat die forging: • Solid w/p is placed in between 2 flat dies and reduced in height by compressing. • Die surfaces may be flat. • Deformed part develops barrel shape due to expansion of metal in lateral directions. • Barreling is caused due to frictional forcesat die w/p interface.

25. CLOSED / IMPRESSION DIE FORGING

26. W/p is deformed between 2 die halves which have the impressions of the desired final shape. • Since w/p is deformed under high pressure in the closed die cavity precision forgings with close dimensional tolerances are obtained. • Formation of flash which is excess metal is trimmed off.

30. COINING: • It is closed die forging process used in mining, medals, jewellery. • Slug is coined in a completely closed die cavity. • Bcz of high pressures involved, process is limited to soft metals.

31. Advantages: • Complex shapes, better properties than open die forging. • Good dimensional accuracy. • High production rates. Disadvantages: • High equipment , tooling cost for small scale. • Die design more complex.

33. Related Forging Operations • Heading: It is an upsetting operation, usually performed at end of round bar/ wire in order to produce larger cross section. • Ex: Heads of bolts, screws, rivets, nails. • Heading process can be carried out cold, hot. • Performed on machines called headers. • It can produce hundreds of pieces/ minute for small parts.

35. Starting material for bolt is a round rod . • First step consists of preforming: gathering material at one end of rod to prepare it for heading. • Second operation produces round head, while reducing the diameter of long section to small. • Last operation produces hexagonal head on bolt.

36. 2. Swaging/ Rotary forging/Rotary swaging: • It is process used to reduce the diameter of solid tube, rod. • It is often performed on end of w/p to create a taperedsection. • A solid rod/ tube is subjected to radial impact by set of rotating dies.

39. Radial movements to dies are obtained by rotating them between pairs of opposite rollers in a cage. • W/P is stationary & die rotates striking the w/p in the centre of die housing. • Mandrel is some times used to control the shape, size of internal diameter of tube parts that are swaged.

40. Swaging process to reduce stock , the dies rotate as they hammer the work

42. 3. Roll Forging/ Roll die forging/: • Used to reduce the c.s of bars by passing it through set of opposing rolls that have grooves matching the desired shape of final object. • It is used to produce tapered shafts, leaf springs, table knives, hand tools with stronger & posses favorable grain structure.

44. 4. Hubbing: • It is a deformation process into which hardened steel form(hub) is pressed into soft steel block (soft metal). • The cavity produced is then used as die for forming operations. • Substantial pressures are required to force the hub into soft block, this is usually accomplished by press.

46. Selection of Forging Machines • Force/ energy requirements. • Size, shape & complexity of forging. • Strength of w/p material. • Production rate • Dimensional accuracy. • Maintenance. • Operating skills required. • Noise level • Cost

47. METHODS OF FORGING • Smith Die forging • Hand forging • Power forging • Hammer Forging • Press forging • Impression die forging • Drop forging • Machine forging