Page 469 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Section 17.3 Compaction of Metal Powders

EXAMPLE l'I.| Hot Isostatic Pressing of a Valve Lifter
An HIP-clad valve lifter used in a full range of isostatically pressed to provide a very strong bond. The
medium- to heavy-duty truck diesel engines is shown HIPing takes place at 1010°C at a pressure of
in Fig. 17.16. The 0.2-kg valve lifter rides on the 100 MPa. The tungsten-carbide surface has a density
camshaft and opens and closes the engine valves. of 14.52 to 14.72 g/cm3, a hardness of
Consequently, it is desired to have a tungsten-carbide 90.8 :t 5 HRA, and a minimum transverse rupture

face for wear resistance and a steel shaft for fatigue strength of 2450 MPa.
resistance. Before the HIP valve lifter was developed, Secondary operations are limited to grinding the
parts were produced through furnace brazing, but re- face to remove any protruding sheet-metal cap and to
sulted in occasional field failures and relatively high expose the wear-resistant tungsten-carbide face. The
scrap rates. The required annual production of these high reliability of the HIP bond drastically reduced
parts is over 400,000, so high scrap rates are particu- scrap rates to under 0.2%. No field failures have been
larly objectionable. experienced in over four years of full production.
The HIP~clad product consists of a 9% Co Production costs also were substantially reduced
bonded tungsten-carbide (WC) face made from because of the hot isostatic pressing step.
powder (pressed and sintered), a steel sheet-metal cap
fitted over the WC disk, a copper-alloy foil interlayer,
and a steel shaft. The steel cap is electron-beam welded Source: Courtesy of the Metal Powder Industries
Tungsten-carbide
to the steel shaft, and then the assembly is hot Federation.

Steel shaft

wif.,

rr.rr r.tt
'ff"
,./<‘*
° i_e1 Copper interlayer
,.., .'ss
at Steel can

FIGURE l1.l6 A valve lifter for heavy~duty diesel engines
produced from a hot-isostatic-pressed carbide cap on a steel
shaft. Source: Courtesy of the Metal Powder Industries
Federation.

I7.3.3 Miscellaneous Compacting and Shaping Processes
Powder-injection Molding. In this process, also called metal-injection molding
(MIM), very fine metal powders (<10 /sim) are blended with a 25 to 45% polymer or
a wax-based binder. The mixture then undergoes a process similar to die casting
(Section 11.3.5; see also injection molding of plastics in Section 19.3); it is injected into
the mold at a temperature of 135° to 200°C. The molded green parts are placed in a
low-temperature oven to burn off the plastic (debinding), or the binder is removed by
solvent extraction. The parts then are sintered in a furnace at temperatures as high as
1375°C. Subsequent operations (such as hole tapping, metal infiltration, and heat
treating) also may be performed.
Generally, metals that are suitable for powder-injection molding (PIM) are those
which melt at temperatures above 1000°C; examples are carbon and stainless steels,
tool steels, copper, bronze, and titanium. Typical parts made are components