5.2.4.3 Product Advantages of Cold Forging

The major advantages of cold forging are close dimensional tolerances, good surface finish quality, and the use of lower cost materials to obtain the required strength by work hardening without requiring heat treatment.

The normal value of surface roughness, R_a, is in the range 1.6 to 25 microns (64 to 1000 micro inches). The lower values require additional attention in processing, particularly the maintenance of tool surface finish.

Table 5-2 compares two processes for manufacturing a wheel hub, based on hot and cold forging. The cold forging develops approximately 8% lower yield strength from less expensive material and is not heat treated. It requires one-third as much machining time, and weighs 24% less. A comparative cost analysis would also include processing cost as well as the costs of manufacturing and maintaining the tools, which are not included in this comparison.

Table 5-2 Comparison of Hot Forging and Cold Extrusion for
Manufacturing a Wheel Hub*

 

Steel Alloy	8620	1010
Weight kg (lb) Finish machining time, min. Finish treatment Yield strength MPa (ksi)	2.85 (6.3) 4.5 Hardening and tempering 600 (87)	2.3 (4.8) 1.5 None 550 (80)

*Ref Forging Handbook, Table 4-3 p 182