Forging

Question 1

Open-die forging

Answer 1

Solid work piece is compressed between two flat dies, thus allowing the metal to flow without constraint in a lateral direction relative to the die surfaces. Produces rough forms and requires subsequent operations. Friction between work and die surfaces constrains lateral flow of work, resulting in barreling effect. In hot open-die forging, effect is even more pronounced due to heat transfer at and near die surfaces, which cools the metal and increases its resistance to deformation.

Question 2

Impression-die forging

Answer 2

Compression of the work piece by dies with the inverse of the desired part shape. Often only achieved by several forming step and with separate die cavities for each step.

Question 3

Parting line

Answer 3

is located at the largest cross-section of the part

Question 4

Webs and ribs

Answer 4

thin sections parallel/perpendicular to the parting line

Question 5

Land and gutter

Answer 5

control the pressure increases in the die

Question 6

Edging

Answer 6

material is gathered into a localized area

Question 7

Fullering

Answer 7

material is distributed away from an area

Question 8

Blocking

Answer 8

part is shaped into a rough shape using blocker dies

Question 9

Impression

Answer 9

part is shaped into a final shape using impression dies

Question 10

Trimming

Answer 10

extra flash in the land and gutter is removed

Question 11

Closed-Die Forging

Answer 11

A bit like impression die forging, but rough shape. Material is restricted in the lateral direction.

Question 12

Flashless Forging (precision forging)

Answer 12

Starting work piece volume must equal die cavity volume within very close
tolerance (blank volume and shape – die design)

Process control more demanding; higher forces to achieve fine detail

Best suited to part geometries that are simple and symmetrical

Question 13

Coining – closed-die forging

Answer 13

 Little flow of material
 5x higher forces compared to the material strength to produce fine details
(minting of coins, jewellery and parts for high accuracy)

Question 14

Heading – upset forging

Answer 14

 Nails, screws, bolt etc. forged from
round bars or wire
 Problem of buckling if unsupported
(length-to-diameter ratio 3:1)

Question 15

Roll Forging

Answer 15

 Round or flat bar stock is reduced the cross-section and increased in length
 Heated bar is inserted between 2 cylindrical or semi-cylindrical rolls, each containing shaped grooves that create a repeating pattern along the bar.

Question 16

Swaging

Answer 16

 Reciprocating dies hammer a tube radially inward to reduce its diameter and produce a taper or point.
 Internal diameters and shapes of tubes can be produced by using a mandrel with longitudinal or spiral grooves

Question 17

Surface cracking

Answer 17

 Incorrect temperature, strain rate and design of dies

 Excessive tensile forces on the surface due to sticking and barreling

Question 18

Internal defects

Answer 18

 Non-uniform deformation of the material in the die cavity
 Incorrect billet volume
 Temperature gradients in the workpiece during the deformation
 Microstructural changed caused by phase transformation

Question 19

Fatigue failures

Answer 19

 May lead to corrosion and wear during the service life

Question 20

Incorrect billet volume causes

Answer 20

Volume too small:

• buckled webs
• laps in finished forging
• incorrect sized part (too small)

Volume too great:

• excess flash
• internal cracks (propagate through ribs)
• incorrect size part (too big)

Question 21

Types of hammer

Answer 21

Gravity drop
Power drop
Counter blow (two rams)
High pressure gas