Potential Applications of Warm Compaction

Because warm compaction is a single-press and single-sinter process, the process is ideal for complex multilevel P/M parts that require high mechanical properties that cannot be obtained at conventional compaction densities. Higher density (or equivalent density at lower compaction pressures) can be achieved with warm compaction as compared with cold compaction (Table 6).

Table 6 Density and process comparison between warm and cold compaction

Base powder

Graphite

Lubricant

Compaction

Sintering

Sintered density, g/cm3

Distaloy

AE(a)

0.5 %

0.7% Kenolube

600 MPa cold compaction

1120 °C, 30 mm, Endogas

7.07

0.6% Densmix

600 MPa warm compaction

1120 °C, 30 mm, Endogas

7.31

0.6%

650 MPa cold compaction

1120 °C, 30 mm, 90% N2/10% H2

7.1

Kenolube

0.6%

500 MPa warm compaction

1120 °C, 30 mm, N2/10% H2

7.1

Densmix

DC(b)

0.5 %

0.6% Kenolube

650 MPa cold compaction

1120 °C, 30 mm, 90% N2/10% H2

7.1

0.6%

500 MPa warm compaction

1120 °C, 30 mm, 90% N2/10% H2

7.1

Densmix

Distaloy AE

0.8 %

0.6% Kenolube

600 + 500 MPa cold compaction

(DPDS)(c)

750 + 1120 °C, 20 + 30 mm, 90% N2/10% h2

7.3

0.6%

700 MPa warm compaction

1120 °C, 30 mm, 90% N2/10% H2

7.3

Densmix

(a) Distaloy AE is a diffusion bonded powder utilizing pure iron with 4.0% Ni, 1.5% Cu, and 0.5% Mo.

(b) Distaloy DC is a diffusion bonded powder utilizing a prealloy 1.50% Mo powder with 2.0% Ni.

(c) DPDS, double-press double sinter.

Recent articles have demonstrated the usefulness of the warm-compaction process in the fabrication of an automotive turbine hub for high-performance engines (part weight 1100 g), the manufacture of helical gears with gear densities in excess of 7.3 g/cm3, lock components (part weight 27 g), and gearing with complex gear forms or spiral gears requiring high gear densities (Ref 22, 23, 24). The current production parts made by warm compaction are parts with a complex shape that are not adaptable for double pressing and double sintering. Warm compaction offers a simplified manufacturing process with resulting mechanical properties that met or surpassed the part specification.

Mechanical properties of warm-compacted steel powders were compared to selected wrought and forged alloys (see Table 7). Note that the yield and tensile strengths of the warm-compacted alloys were equivalent to those of wrought alloys. Thus it would seem that components made from these alloys are suitable candidates for the warm-compaction process. It must be noted that the elongation of the P/M materials is significantly lower than the wrought alloys chosen (except for the heat-treated ductile iron). Thus, proper application of the warm-compaction process must consider the reduced elongation and impact energy of the P/M part.

Table 7 Comparison of warm-compacted materials to selected wrought and cast alloys

Material

Yield

Tensile

Elongation,

Hardness

strength

strength

%

MPa

ksi

MPa

ksi

AISI 1020

345

50

440

64

35

77 HRB

AISI 1050

427

62

745

108

20

96 HRB

AISI 8620

358

52

635

92

26

90 HRB

AISI 8620 Heat treat

1390

202

1482

215

10

45 HRC

Ductile iron 120-90-02

860

125

965

140

2

36 HRC

Powder forged F-0005

765

111

827

120

10

27 HRC

Powder forged FL-4605

1172

170

1455

211

9.5

47 HRC

FLN-4205 at 7.39 g/cm3

1220

177

1503

218

1.9

42 HRC

FD-0405 at 7.33 g/cm3

938

136

1248

181

1.7

41 HRC

One significant advantage of the warm-compaction process is the increased density uniformity achieved in the compacted part (Ref 22, 23). Quantitative metallographic techniques demonstrated this feature in both a helical gear and an automotive turbine hub. Figure 9 demonstrates the greater uniformity of sintered density achieved with a turbine hub compared to a conventionally compacted part. This enhanced density uniformity results in increased load-carrying capacity with reduced dimensional variations because of the uniform density.

Fig. 9 Variation in sintered density and dimensional change of turbine hub processed by conventional P/M and warm compaction

Future applications of the warm-compaction process will exploit the ability to achieve higher green densities at lower compaction pressures, thus minimizing the tooling stresses. Additionally, with the increased interest in the sinter-hardening process, warm compaction offers the potential to green machine these components prior to sintering and subsequent hardening.

0 0

Post a comment