Review: IPMD 14th Edition 2010-201, 8 pages, 4866 words

Author: Dr David Whittaker, DW Associates, UK

DW Associates, 231 Coalway Road, Wolverhampton WV3 7NG, UK

In his second review of developments in structural Powder Metallurgy parts, Dr David Whittaker looks at the different manufacturing options available to produce high density high performance PM parts, many of which are particularly suited to automotive applications.

Introduction

The origins of the Powder Metallurgy (PM) industry were in the manufacture of products such as self-lubricating bearings, which were simple in shape but where the technology offered a unique capability (in this case, the generation of a porous structure to hold a reservoir of lubricant).

The expansion of the PM business into structural parts, beginning around 70 years ago, brought a different scenario. PM was now in competition with other means of manufacturing the same component, routes which would usually involve significant finish machining operations. The key to winning this type of competition lay in the technology’s cost effectiveness, in turn based on reduced material and energy consumption compared with the more traditional routes (Fig. 1).

These competitive advantages were enhanced by PM’s ability to hold close dimensional tolerance control and by the continuing developments in the technology’s capability for forming ever more intricate shapes (at least in the radial directions, perpendicular to the pressing direction); both of these factors contributing to the elimination of expensive machining operations.

So, for a sustained period in its development, the major driving force for PM was the development of ever-greater complexity of shape, in applications that generally required little in the way of structural strength. However, as long ago as the 1970s, there was a growing recognition that there was a large potential market to be tapped, particularly in automotive engine and transmission applications, if higher performance levels could be attained in PM products. Interestingly, this view continues to be reinforced virtually up to the present day. A series of studies, during the late1990s, concluded that there is a potential market in PM automotive parts, with at least three times the size of the current one, if this objective of serving higher performance applications can be achieved...........

Further sections of this article include:

• Powder forging
• More recent material/process developments
• Improved densification in compaction
  - Higher pressure cold compaction
  - Warm compaction
  - High velocity compaction
  - Die wall lubrication
• Densification in Sintering
  - Fine powder additions
  - Liquid phase sintering
  - Ferrite phase sintering
• Post sintering densification
  - Surface cold rolling
• Conclusions
• References

Figures and Tables:

Fig. 1 Material wastage and energy consumption of metal manufacturing processes. (Source: EPMA, Shrewsbury, UK)

Fig. 2 Powder forged automotive connecting rod produced by Metaldyne

Fig. 3 Blended steel powders are compacted to produce near net shape con rod preforms for subsequent sintering and powder forging (Courtesy GKN Sinter Metals; photo Bernard Williams)

Fig. 4 Warm compacted spiral bevel gear for power saw (Courtesy Porite Taiwan Ltd)

Fig. 5 Warm compacted and sintered output shaft hub produced by Chicago Powdered Metal Products Co for Ford Motor Company to a density of 7.2 g/cm3 (Courtesy MPIF)

Fig. 6 Existing compacting presses can be retrofitted for warm compaction such as this ‘El-Temp’ system from Cincinnatic Inc.

Fig. 7 High velocity compaction (HVC) has the potential to achieve high green density

Fig. 8 Relative cost comparisons for various die compaction processes (Courtesy Hydropulsor AB, Sweden)

Fig. 9 This PM M2 high speed steel tool bit is pressed and liquid-phase sintered to full density (8.1 g/cm3) and is heat treated to 61-63 HRC. The PM material’s wear resistance outperformed machined M2 barstock (Courtesy MPIF)

Fig. 10 Surface densified engine balancer gear with 360 helix angle. (Courtesy Stackpole Ltd, Canada)

Fig. 11 (left) Density profile of selectively densified helical gear tooth flank; (middle) as-sintered density; (right} surface densified material (Courtesy Stackpole Ltd, Canada).

Fig. 12 The differing effects of post-sintering treatment on fatigue life of PM steel (Fe2Cu-2.5Ni). (from: J.Y. Thieleux, Paper published in Proc. of EuroPM2003 Congress, Valencia. EPMA, Shrewsbury, UK)

Fig. 13 Camshaft gear produced by Miba AG, Austria for BMW, is made in a pre-alloyed Fe-Mo base steel at a “core” density level of 7.0 g/cm3. Post-sintering surface densification of the tooth roots and flanks provides performance similar to the case hardening steel, 16MnCr5 (Courtesy EPMA)

Table 1 Reduced finish machining process steps and material waste for competing con rod manufacturing processes. (From SAE Technical Paper 2001-01-0351; ‘Machinability and Performance of Precision PF Connecting Rods’ by T. Geiman, et al (GKN Sinter Metals), presented at SAE World Congress, 2001.)