Smithing force is applied to manipulate the metal Forging force is applied to manipulate the metal

Transcription

1 FORGING

2 Smithing It is a process of performing various operations on relatively small work pieces, heated in an open fire (hearth) and force is applied to manipulate the metal by means of hand hammers or small power hammers in a smithy shop. Forging It is a process of producing those parts, which must be heated in a closed furnace, and force is applied to manipulate the metal by means of heavy hammers or forging machines or presses.

3 Forging Temperature For forging, a metal must be heated to a temperature at which it will possess high plastic properties both at the beginning and at the end of the forging process. For instance, the temperature to begin the forging for low carbon steels is 1,250 to 1,300 C, the temperature to finish forging is 800 to 850 C.

4 FORGING TOOLS Anvil: Provides a support for workpiece when hammering. -Beak is used for bending the workpieces

5 FULLER: Used for Necking down a piece of workpiece i.e reduce thickness 2) Fuller Swages: Workpiece to be reduced and finished to round, square or hexagonal form 5) Swage - Made with half grooves of dimensions to suit the workpiece being reduced

6 Flatter: To give smoothness and accuracy to parts requiring flat surfaces which have been already shaped by fullers.(after drawing out operation) 4) Flatter Punch: Used for making holes in heated metal part. 3) Punch

7 Tongs: To hold the workpiece during forging operation. 1) Flat Tong : For holding work of rectangular section 2) Ring Tong : For holding work of circular section 3) Gad Tong : For general pick-up, either straight or tapered 6) Flat tongs 7) Ring Tongs 8) Gad Tongs

8 Swage block: Used for squaring, sizing, bending operations Chisels: For cutting metals They may be hot or cold depending on the metal to be cut is hot or cold. 9) Swage block Chisels Hot Chisel

9 Hand hammers: They may be classified as a) Ball peen hammer b) Cross peen hammer c) Straight peen hammer d) Sledge hammer a) Ball peen b) Cross peen Sledge Hammer c) Straight peen Set hammer: Used for finishing corners in shouldered workpiece, where flatter is inconvenient. Set hammer

10 Classification of Forging

11 Smith forging or open die forging Flat dies are used and simple shaped forgings manufactured. The final shape of the forging depends largely on the skill of the smith for size and shape. These processes produce work-pieces of lesser accuracy than impression die forging. Production of a large variety of shapes.

12 Smith forging or open die forging Hand forging is employed only to shape a small number of light forgings chiefly in repair shops. Large machine parts cannot be forged by hand, since the comparatively light blow of a hand-or sledgehammer is unable to produce a great degree of deformation(change in size and shape) in the metal being forged. Moreover, hand forging is a lengthy process and requires repeated heating of the metal.

13 Smith forging or open die forging This has led to the use of power hammers and presses in forging. Machines which work on forgings by blow are called hammers, while those working by gradual pressure are called presses.

14 Power Hammer -Also called as an air or steam hammer Ram -Operated by either steam or Upper Die Work Lower Die compressed air -Require additional facilities for supplying high pressure steam or compressed air. Anvil block Fig. Steam Hammer

15 Power forging The part of the hammer which serves as a rigid support during forging is called the anvil block. The heavy falling part of the hammer is called the ram. The anvil block and the ram each has one die called lower-die and upper-die respectively for squeezing the metal to be forged. In smith forging, the working surfaces of both the upper and lower dies are flat and horizontal. Larger forgings are manufactured in large quantities.

16 Impression die forging More complex shape of greater accuracy cannot be formed by open-die forging techniques. Commonly known as die forging or drop forging, impression-die forging makes use of cavities in specially prepared dies to produce forged shapes in large quantities. When large quantities of smaller identical forgings are required as is necessary in mass production, drop forging iscommonly employed to do the job.

17 Impression dies

18 Drop Forging (Stamping/ Die forging) Roll Board Upper Die work Lower Die Fig. Board Hammer -Also called as Board or Gravity Hammer Working: -Ram is fixed to the lower end of the vertical hardwood board -Board is placed between 2 rolls -Ram will be lifted, when both rolls are pressed against the board -Working stroke is produced when the rolls are released. -Process continues till operator holds down the treadle

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20 Drop forging Drop forging are made by squeezing of hot metal into shaped impressions cut in steel blocks called dies. The bottom die is fixed to the anvil, and the upper die is attached to the ram of the drop hammer. Generally, half the impression is cut on one die and the remainder in the other, so that when the faces of the dies meet the metal is squeezed into the cavities and a complete stamping is formed.

21 Drop forging The ram is fastened to the lower end of a vertical board; the upper part of this board is placed between two counter-revolving rolls. The metal is heated and placed on lower die. When both rolls are pressed against the board between them, they drive them upward, lifting the ram. When the rolls are released, the ram falls down producing a working stroke. As long as the operator continues to hold down the treadle, the hammer will continue to strike.

22 Drop forging But when the treadle is depressed, the ram will return to and will remain in its top position. The board drop hammer is generally driven by electric motor. Due to lower maintenance costs, and easier operation, air hammers are replacing board hammers.

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25 Smith forging operations Most commonly used forging operations are: 1. Upsetting 2. Bending 3. Punching 4. Drawing down 5. Setting down 6. Welding 7. Cutting 8. Fullering

26 UPSETTING (HEADING) 9 Upset forging operations Process of increasing the thickness of a bar by reducing its length by end pressure.

27 Upsetting Fig. (a)shows the effect of heavy hammer blows on a uniformly heated bar ; (b) shows the effect of comparatively light hammer blows. Local upsets may be obtained as shown Fig.(c) and at (d), by heating only the end or the middle of the bar respectively.

28 BENDING Process of producing curvilinear or angular bends on a bar. Done on the edge of the anvil face or beak or swage block Curvilinear Angular Bending operations

29 Punching operation Process of producing holes by using Figure 1 a hot punch over the pritchel hole of the anvil. Figure 2 Figure 3

30 FULLERING Reduce thickness of workpiece. Form grooves. CUTTING Cutting-off is a form of chiseling whereby a long piece of stock is cut into several specified lengths, or a forging is separated (cut-off) from its stock.

31 Drawing down or Swaging Process of increasing the length of a bar at the expense of its width or thickness or both. Fig(A) represents the original stock, B shows the stock after hammering with a straight peen hammer or with a top fuller and hammer, and C shows the finished forging after the flatter has been used. Setting Down: It is a localized drawing down or swaging operation.

32 WELDING(Forge Welding) Joining process performed in the smithy shop. The first essential to the production of a sound weld is that the surfaces in contact must be perfectly clean so that cohesion will take place when the metal is in a plastic state. A protection to the metal is a coating of flux which covers the surfaces of the metal and prevents atmospheric contamination.

33 Four forms of welded joint commonly employed are: (a) the lap or scarf weld, in which the ends are prepared so that they may be welded one upon the other, with the joint in an inclined direction; (2) the butt weld, in which the ends of the pieces to be joined are butted(end to end) together, the weld being between the ends at right angles to the length of the piece ; (3) the 'T' or jump weld, in which one piece is placed at the centre of another at right angle to each other in the form of an inverted 'T' ; and (4) the split, fork, or 'V' weld in which the ends are first brought to the shape of fork and tongue respectively.

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35 Forged parts vs. cast parts FORGED PARTS ARE STRONGER THAN CASTING Forging refines the structure of metal by smashing up large grain formations and closing up any cavities that may be present i.e. cracks and blow holes are welded up. The original crystals typical of the cast structure are destroyed, hard films of brittle constituents or impurities are broken up or rolled in to fibers and a uniformity is established. Certain mechanical properties, particularly elongation percentage, resistance to shock and vibration are improved. Pieces formed by forging exhibit directional properties indicated by the flow lines.

36 Fig(a) shows component manufactured by forging process in which grains elongated or flow in particular direction. Forging has true grain flow.

37 Fig(b) shows bar stock or workpiece in which grain flow is broken. Fig(c) shows component manufactured by casting process in which there is no grain flow and grains are randomly oriented.