Forging process

Forging: Manufacturing process

Forging is a process of shaping or forming metals by using compressive force/pressure. Majority of forging is done by heating the metal which is called Hot Forging , but some times fishing is done on cold metals at room temperature called Cold Forging. Forging used to make from nuts and bolts to Ship propellers.

      Forged parts are more stronger than cast one because in cast metals grains are random oriented but in forging , they are oriented in a same pattern.

● Normally metals are cold forged and alloys are hot forged.

      Forging is used in manufacturing industries for making hardware product, automotive parts, aerospace parts, machine parts and equipment etc.

   Operations in forging : 1. Fullering 2. Edging 3. Flatting 4. Swaging 5. Bending (V-bending,L-bending)

   Classification of forging on the basis of temperature :

1. Cold forging : Cold forging is done when metal is already soft like aluminum. After cold forging metal needed to be annealed to regain the grains. It is done at room temperature.

2. Warm forging : Warm forging is done at between room temperature and metals recrystallization temperature.

3. Hot forging : It is done at temperature above the recrystallization temperature. It gets high grain rate . Due to sudden contact of hot metal with air, oxidation occurs which causes scaling.

Types of forging : 

1. Open die forging (smith forging)

2. Impression die drop hammer forging(close die / drop forging)

3. Press forging.

4. Upset forging.

5. Roll forging.

1. Open die hammer forging : It is a traditional method of forging which is done openly, in this upper die acts like a hammer. It I used in Small forging  or custom forging works.

2. Impression die drop hammer forging : In this method, hot metal is kept in mould die that is lower die having shape like final product. In this two dies are used i.e upper die and lower die. Upper die is attached with ram/hammer and lower die with anvil . As hammer falls , metal fills in cavity and gets shape of mould. In drop forging , hammer stays in contact with workpiece for sOme mili seconds. If metal is complex then time will be same but it gets multiple impacts. Ex. Crank shaft , connecting rod, wrenches etc.

3. Press forging : It is similar to Impression drop forging. In press forging , slow and continuous compressive force is applied. In press forging forging, time of contact between die and workpiece is of seconds. Press forging can deform whole workpiece while in Impression forging, only deform contact part. But disadvantage of press forging is that when die is in contact with metal for such a long time then heat loss increases in atmosphere, so ductility decreases and cracks may form, to prevent it heated die is used in press forging.

4. Upset forging: In this type of forging, length of workpiece is decreased by increasing dia. For this forging, initial workpiece could be a rod/bar or wire. In upset forging, multiple dies are used with multiple cavities, that is why it is used in mass production. Gripper dies hold the bar or rod and punch presses the head of workpiece.

Above image : upsetter of upset forging

Above Images : Upset forging

5. Roll forging : In this process , we reduce the thickness of metal piece and length is increased by rollers.

 Defects in forging : 

1. Unfilled/underfilled section : It's cause is poor design of die, less raw material and poor heating.

2. Cold shunt : In this defect, small cracks occur at corners of objects. It is caused by improper design of forging die, sharp corners of object, excessive chilling of forged surface.

 3. Scale pits : Scaling occurs in open environment forging. It is caused by improper cleaning of forged surface.

4. Die shift : It causes when upper and lower dies are not properly aligned with each other. It leads to improper dimensions of product.

5. Flakes : It is internal crack. It's cause is when metal cool rapidly and reduces strength of forge product. It occurs due to improper cooling of forged product.

6. Surface cracking : It occurs due to forging at low temperature which leads to occurrence of cracks on workpiece.

7. Residual stress in forging : It occurs when forged parts are not properly cooled.

8. Incomplete forging penetration : It is caused by rapid hammer blows.

Above image: Extrusion forging