PFD = l/[e (% element in premb/specific gravity of additive)] (Eq 1)

Transcription

1 ASM Handbook, Volume 7: Powder Metal Technologies and Applications P.W. Lee, Y. Trudel, R. Iacocca, R.M. German, B.L. Ferguson, W.B. Eisen, K. Moyer, D. Madan, and H. Sanderow, editors, p Copyright 1998 ASM International All rights reserved. Warm Compaction Francis G. Hanejko, Hoeganaes Corporation THE FERROUS P/M INDUSTRY continues to grow because of developments in raw materials and part production processes enabling the manufacture of components with greater complexity and higher levels of performance. Advances in raw materials include higher compressibility iron powders, molybdenum prealloyed steels, diffusion-alloyed powders, and the use of binder-treated iron powders. These new powders and premix technologies offer P/M users greater flexibility in mechanical properties at traditional part densities, typically less than 7.1 g/cm 3. However, end users of P/M parts are demanding still higher levels of mechanical properties available solely through higher part densities. Traditional methods used to achieve higher densities include the use of copper infiltration, doublepressing/double-sintering (DP/DS), and powder forging. Because these techniques involve the use of secondary processing, significant cost penalties are encountered, often negating the potential cost savings realized by powder metallurgy. Warm-compaction process is a technique to achieve DP/DS densities and mechanical properties utilizing a single compaction process. The process incorporates the use of heated powder and heated tooling in standard compacting presses to achieve higher green and sintered densities. Temperatures above room temperature and below the hot-forging range are used extensively in wrought steels to lower forging loads and minimize distortion. Work at MeriSinter AG in the mid-1980s found certain advantages to be present when ferrous, bulk lubricated powders were heated in the vicinity of 100 C. It was of particular interest that compressibility improved with heating as compared to the some powders in an unheated condition (Ref 1). The practical application of warm compaction of powders was realized in 1994 with the introduction of Hoeganaes Inc. Ancordense and Densemix powders (Ref 2). Figure 1 schematically illustrates the warm-compaction process. The powder and die temperatures used vary from 75 to 150 C, with every 100 C rise in compaction temperature resulting in a 0.08 g/crn 3 increase in green density (Ref 3). Experimental work at H6gantis AB showed a 30% decrease in the compressive yield strength of iron powder when the powder was heated to 150 C (Fig. 2) (Ref 4). The maximum green density achieved via P/M techniques depends on the amount and type of premix additives used with iron powder. To calculate the maximum green and sintered densities attainable, it is useful to review the concept of pore-free density (PFD). Pore-free density is defined as the density of a green compact in which all the interparticle porosity is eliminated (Ref 2). This PFD can he calculated from the specific density and percentage of each additive in the premix. The calculation for PFD is given as: PFD = l/[e (% element in premb/specific gravity of additive)] (Eq 1) in which the percentage of each element is the weight percentage used and is expressed as a decimal. Once the PFD is calculated, a practical upper limit of green density is 98% of the calculated value. The specific density of several common ferrous powders and typical premix additives are listed in Table 1. Additions of materials with specific densities higher than the base iron increase the PFD, while additions of materials Powder l I Powder I I Heated I = Single'pressed ~ high-density prem,x 1 - I he=or I- I tooling I1 P/M part Press ready binder-treated premix Fig. 1 Warm-compaction process EITemp Abbott heater Slotheater Powder and die 0.10 to 0.25 g/cm 3 heated to improvement in C, +2.5 C green density ( F, _+5 F) high green strength improved ejection with lower specific densities (lubricants and graphite) will lower the PFD. Because of the reduced compressive yield strength at 150 C, attaining 98% of the PFD is achieved with lower compaction pressures. In addition, compaction at 150 C reduces the amount of lubricant between the particles while simultaneously increasing the amount of added lubricant reaching the die-part interface (Ref 5). This redistribution of the lubricant not only increases the green density, but reduces the ejection forces by 25 to 33% (Ref 2, 5). This enhanced lubricity implies that lower amounts of lubricant are necessary (typically 0.60% lubricant for warm compaction compared to 0.75% in conventional compaction), which again contributes to the attainment of higher green and sintered densities. Advantages of the warm-compaction process include higher green densities, enhanced green strength, improved mechanical and soft magnetic properties, and greater uniformity of den- Table I Specific density as measured by pycnometry Specific density, Material g]cm 3 Ancorstee11000B Ancorstee14600V Distaloy 4800A Atomized copper Inco nickel powder Graphite Lubricants to 260 g ~ 140 loo o 50 1 oo Temperature, C Fig. 2 Effect of temperature on the yield strength of pure iron powder. Source: Ref4

2 Warm Compaction / 377 sity throughout the as-sintered part. The balance of this article details the process and the im- proved properties resulting from warm compaction. Effects on Green and Sintered Properties Warm compaction results in a 0.10 to 0.25 g/cm 3 increase in the green and sintered densities of P/M parts (Ref 2). Figure 3 shows the improved green and sintered densities achieved with a diffusion-alloyed powder premixed with 0.6% graphite. At lower compacting pressures, the beneficial effect of warm compaction is greater than the improvement observed at higher compaction pressures. Figure 4 summarizes the transverse rupture strength results of the diffusionbonded material compacted by both conventional and warm-compaction techniques under compaction conditions of 410 to 690 MPa. Table 2 summarizes the as-sintered mechanical properties of various warm-compacted premix compositions (Ref 6). This processing is applicable to all iron and low-alloy powder compositions. The magnitude of the increase in sintered density depends on the material system and subsequent part processing. Premixes containing copper additions exhibit growth during the sintering process; this growth negates the beneficial effects of the warm-compaction processing. Con- Compaction pressure, MPa I I I I Siniered Warm compacted at 150 C 7.3 I I I 1 ~ "~;"" ~Green.~i I ~ Sintered.~7.1 (9 c P'~ p, ~,_ r Green [ 6.9,~,,~ - Conventional Compaction pressure, tsi Fig. 3 Compressibility of diffusion-bonded 4% Ni, 1 % Cu, and 0.5% Mo with 0.6% graphite and 0.6% lubricant ~ 260. = ( (9 o 180 ~ sequently, copper-containing premixes are not considered ideal candidates for warm compaction (Ref7). Rotating bending fatigue testing was performed on a variety of warm-compacted materials in both the as-sintered and heat-treated conditions; Table 3 summarizes the available data (Ref 8, 9). As expected, increasing the density increased the fatigue endurance limit; however, higher-temperature sintering did not consistently improve the fatigue endurance limit. Reviewing Table 3, it is observed that no generalized correlation exists between the fatigue endurance limit and the tensile strength of P/M materials. It is recommended that designers use available data when specifying the fatigue endurance limit of P/M components. Double pressing of conventionally compacted parts results in improved part densities and mechanical properties. In experimental work per- formed by Donaldson and others, warm-compacted P/M parts were presintered at 870 C (1600 F) and subsequently re-pressed at up to 690 MPa (50 tsi) at room temperature (Ref 10-12). Following re-pressing, the part was then sintered at either 1120 C or 1260 C, resulting in sintered densities ranging from 7.5 to 7.6 g/cm 3. Figures 5 and 6 present data on transverse rupture strength and impact energy from this study. These higher densities of the doublepressed/double-sintered (DP/DS) warm compacted materials produced an approximately 15% improvement in the transverse rupture strengths (Fig. 5), but more importantly resulted in a 50 to 80% improvement in the impact energy (Fig. 6) when compared to the 7.4 g/cm 3 density level (Ref 10). This study demonstrated the potential for significantly improved mechanical properties of P/M materials via DP/DS of a warm-compacted component. The resultant Table 2 As-sintered tensile properties of warm-compacted P/M materials, sintered at 1120 C (2050 F) Sinlered 0.2 % offset density, yield strength Ten.~le strength Elongation, Composition(a) g/cm 3 MPa ksi MPa ksi % ~rn~t laardaes~ BRB FL-4405 with0.6% graphite FLN with 2% Ni and 0.6% graphite FL-4205 with 0.6% graphite Ancorstee1150Mo (b) with 2% Ni and 0.6% graphite FDr0405 with 0.6% graphite Iron plus 0.45% phosphorus FN 0250 with 0.6% graphite (a) MPIF designations, based on MPIF Standard 35, 1997 edition. (b) Hoeganaes Corporation prealloyed powder with nominal 1.5% Mo Table 3 Fatigue data of warm-compacted ferrous materials Simering 50% fatigue 99% fatigue tempermure Heat Dendty, endurance Ihnit endurance limit Material *C OF treat g/tin a MPa ksi MPa kd Fe-0.45 wt% P Fe-0.45 wt% P FC-0208 FD-4805 FD-4805 r r t I 1800 ~. FD-4805 Warm compacted at 150 C ~'o 1700 ~ t,~ ~ 16oo 1500 rn 1400 ~nventional 1300 ( Sintered density, g/cm 3 12oo >= oo Fig. 4 Sintered transverse rupture strength of diffusionbonded 4% Ni, 1.5% Cu, and 0.5% Mo with 0.6% pmrnixed graphite 1100 ~ A41AB A150HP, 2% Ni and0.6 Gr A 150HP, 2% Ni and 0.6 (Jr FLN FLN FLN A41AB FN0250 FL-4405 FD No No No No No Yes No No No No No No Yes Yes Yes Yes Temne MI~ k t ,

3 378 / Shaping and Consolidation Technologies mechanical properties of such parts are equivalent to the properties of ductile cast irons and machined carbon steel forgings. Green Strength Enhancement. Warmcompaction processing provides improved green strength of the as-compacted component. This increase in the green strength results from the synergy of greater powder particle deformation with enhanced particle welding during compaction, plus the presence of the unique binder and lubricant utilized in the ANCORDENSE material (Ref 2, 5). The improved green strengths are realized at densities significantly below the porefree density (Fig. 7). These data imply the potential of warm compaction being used in lowerdensity applications where the enhanced green strength reduces part breakage or part chipping of fragile features. A consequence of the enhanced green strength via warm compaction is the ability to green machine the as-compacted part. This concept has been used in a commercial application of a P/M safety locker part (Ref 13). After compaction, the component was milled in the green condition, thus reducing the overall part cost. A machinability study utilizing a drilling test was conducted on a molybdenum prealloyed material premixed with 2% Ni, 0.5% graphite, and 0.6% lubricant (Ref 14). This study concluded that satisfactory surface finishes are achieved with machining conditions using high speeds and high feed rates. Additionally, modifications of the standard drill bit geometry from a standard 38o 34O e 320 3oo ~. 280 m 260 >m 240 I- &--'f 2300 i= (1260 C'), DPDS OF (1260 C), SP I~ I ~ L~5011*F (1120 C), 2050 Fl(1120 C), I SP-~ Density, g/cm 3 I / 2452 ~ 2316 ~ ~. DPDS 1772 ~ Fig. 5 Transverse rupture strength of diffusion-bonded 4% Ni, 1.5% Cu, and 0.5% Mo prernixed with 0.3% graphite subsequently carburized and tempered Table 4 Magnetic and mechanical properties of a warm-compacted iron-phosphorus steel versus AISI 1008 Property Fe-0.45 wt % P AIS11008 Density, g/cm N/A Sintering temperature, oc ( F) 1120 (2050) N/A 0.2% yield strength, 285 (42) 285 (42) MPa (ksi) Tensile strength, 405 (59) 383 (56) MPa(ksi) Elongation, % Maximum permeability Coercive force, Oe Saturation at 15 Oe, G 15,000 14,400 N/A, not applicable 90 chisel bit to a 135 split-point drill bit enhanced the as-machined surface finish. Prior to establishing green-machining parameters, it is recommended that testing be conducted to examine the effects of tool-bit geometry, machining feed rate, and machining speed. Green machining of P/M parts in combination with sinter hardening offer the part designer greater flexibility in part design and material selection. Magnetic Applications The use of warm compaction of P/M magnetic alloys effects higher sintered densities with corresponding higher saturation induction levels and higher permeabilities with no change in the coercive force (Ref 15). Sintered densities in excess of 7.4 g/cm 3 are possible using warm compaedon of iron-phosphorus alloys. At this density level, the magnetic and mechanical performances of this family of materials are equal to the properties of a low-carbon steel forging. Table 4 summarizes the mechanical and magnetic property data for a 0.45% P/M phosphorus steel processed to 7.4 g/cm 3 and an AISI 1008 steel forging. From these data, the P/M material is a suitable replacement for the wrought steel. Warm-compaction processing enables the introduction of a new class of P/M materials for use in alternating current (ac) magnetic applications (Ref 15-17). These materials utilize a high-strength polymer and warm-compaction processing to produce components that do not require sintering. The polymer acts to both electrically insulate the powder particles and provide strength without the need for sintering. As-compacted green densities in excess of 7.2 g/cm 3 are possible. Manufacturing flexibility can produce a variety of material options with unique magnetic performance. Applications for these materials include automotive ignition coils and stators for high-speed eleclric motors. 5O = 40 cm 30 ~. 2o g F (1260 C) sinter 7 / DPDS s. ~'_.2 " s o!,,1 oo0, isn Sintered density, g/cm ~" 43.6 =~ 33.6 ~ 23.6 g Fig. 6 Impact energy for diffusion-bonded 4% Ni, 1.5% Cu, and 0.5% Mo premixed with 0.3% graphite subsequently carburized and tempered Table 5 summarizes these ac magnetic materials and their magnetic performance. These materials are ideally suited for applications with operating frequencies above 400 Hz. Optimizing the amount and type of insulation produces components that can operate at frequencies up to 50,000 Hz. The unique three-dimensional structure of these materials can be used to carry magnetic flux in any direction. The strength of these materials in the as-compacted condition is approximately 103 MPa (15 ksi) transverse rupture strength. Employing a 315 C (600 F) thermal treatment to the as-compacted part raises the transverse rupture strength to approximately 240 MPa (35 ksi). Commercial Powder Heating and Delivery Systems Successful utilization of the warm-compaction process necessitates that the powder, powder shuttle, and compaction tooling be heated to the proper temperature. Recommended temperature control of the heated powder and tooling is _+2.5 C. It is imperative that the ~mperature of the powder not exceed 170 C (320 F); above this temperature the lubricant and binder degrade, resulting in diminished powder flow. Heating of the tooling is accomplished using cartridge heaters embedded in the stress ring of the die. Typically, eight to twelve 500 W cartridge heaters are required to heat the tooling to 150 C (300 F) in approximately 30 min. Heating of the powder shuttle is necessary to maintain the powder temperature during the transfer of the powder into the die cavity. Top-punch heating is recommended to eliminate the possibility of a tool binding between the top punch and core rod(s). Heating the core rod and lower punches is not necessary; where practical, incorporating a car- Compacting pressure, MPa ~" 7.0 J (27.5) ~, ~6.8 v - Green density - f I \ / 3000 "~ 8884 (20.5) 2oo0 g 6.2 (13.75) m O 6.0.~ 10oo o 5" ~ (7"0) Compacting pressure, tsi Fig. 7 Table 5 Magnetic performance of insulated iron powders Green density and green strength of warm-compacted FN0205 at low compacting pressures Initial Ma.~mum Coercive Induction Material permeability permeability farce, Oe 40 Oe, G Iron powder with 0.6% plastic ,200 Iron powder with 0.75% plastic ,900 Iron powder with oxide coating and 0.75% plastic ,700

4 tridge heater in the core rod will provide greater temperature uniformity. Currently, three commercial powder heating and delivery systems are available. Each system is capable of delivering heated powder at the proper temperature. Additionally, each has the capability of heating and controlling temperatures in the die, the punches, and the powder shuttle system. The three systems are: Cincinnati Inc. El Temp System Abbott Furnace Company Thermal Powder Processor Slotheater The Cincinnati Incorporated E1 Temp system utilizes an auger to both heat and transport the powder from the powder feed hopper to the heated shuttle (Ref 18). The auger operates within a resistively heated shell; additionally, the auger is hollowed, allowing preheated air to provide for additional heating capability. The amount of powder heated is determined by the part weight and press speed. Production systems are available that heat up to a maximum of 9 kg/min (20 lb/min). A unique feature of the E1 Temp system is its direct interface with the Cincinnati computer operating system of the press, allowing for control of all press and heating functions from a single touch screen. The Abbott Furnace Company Thermal Powder Processor, TPP 300 (patent pending) uses a low-pressure fluidizing air 35 kpa (5 psi) to heat the powder within a sealed reactor. Heating of the powder is accomplished in a stream of air that passes across resistively heated elements. As powder is withdrawn from the bed into the delivery system, additional powder is drawn into the reactor. This system uses a stand-alone programmable logic controller (PLC) controller to heat the powder, die, and powder shuttle. Units are available that can deliver powder up to 3.5 kg/min (8 lb/min) and 3.5 to 9 kg/min (8 to 20 lb/min). The TPP 300 is portable and can be adapted to any press. These units have no moving parts, thus minimizing maintenance. The Slotheater uses the principle of direct contact of the powder with the heated surfaces of an oil-filled slotted heat exchanger (Ref 4). The powder flows via gravity from the press feeder hopper into the slot heater where it is heated and then flows into the powder delivery system. The temperature of the heated oil is controlled to a temperature approximately 4 C (7 F) hotter than the desired temperature of the powder. To achieve uniform temperature of the powder, the residence time of the powder in the heater must be at least 5 min. Commercial units are available that can deliver 3.5 kg/min (8 lb/min) of hot powder. However, the design is scalable to achieve up to 9 kg/min (20 lb/min). Considerable attention has been given to the actual mechanism of heating the powder; however, attention must also be given to the powder shuttle system. Although no commercial systems exist, it is a relatively easy task to design and build a hot powder feed shoe. Heating of the feed shoe is accomplished by embedding car- tridge heaters and a thermocouple in the aluminum feed shoe. Temperature control of the feed shoe is necessary to prevent any heat loss during the residence time of the powder in the shoe. Both a closed shoe and an open shoe have been successfully used. Unlike conventional powder shoes, the amount of powder in the feed shoe is critical. Excessive amounts of powder in the feed result in a long residence time within the feed shoe, possibly resulting in a temperature drop causing excessive part-to-part weight variations. Tooling Design for Warm Compaction The tooling design for warm compaction is essentially the same as for regular compaction with typical radial tooling clearance of 0.01 to 0.02 mm ( to in.). The choice of carbide inserts or tool steel inserts is not critical. Carbide inserts have proven to be successful; however, the designer is cautioned that additional interference fits are required to compensate for the differential thermal expansion of the carbide insert compared to the steel stress ring. One word of caution in the design of tooling is the stress involved during the compaction to near-pore-free densities. As the density increases, the tooling loads increase rapidly. This increase in tooling pressure necessitates that thicker stress rings be used and the allowances made for the greater tool deflections. Shown in Fig. 8 is the green expansion as a function of the green density Of powder compacts compacted using both conventional room-temperature compaction in addition to warm-compaction conditions. Note that the green expansion at equivalent density is lower for the warm-compacted material. The rationale for the lower green expansion for the warm compacted material is explained by the fact that lower compacting pressure was required to achieve this same density; thus the tooling load was decreased. However, as the green density increases to near-pore-free density, the green expansion increases dramatically. With this increased density, the tooling loads increase, resulting in greater expansion of the part. This increased green expansion can cause microlaminations in the compacted part. These microlaminations are serious problems because they reduce the structural integrity of the sintered component. In multilevel parts, these microlaminations usually occur at the transition from one level to another. Incorporating toppunch hold-down during the ejection cycle often prevents these cracks from occurring. However, even top-ptmch hold-down is not sufficient to prevent microcracking if the density of the part exceeds 98% of the theoretical density. Part Processing Considerations Studies conducted by Hoeganaes, Presmet, QMP, and others demonstrated that the part-to- Warm Compaction / i i ~ 02 ~/ t~ -- 0 Conventional -0.2 ~ Sintered dimensional change _ -03 I I I Density, g/cm 3 [:: o.r Green expansion and sintered dimensional ~n~ V change of warm-compacted material relative to conventional compaction techniques part variability of the warm-compaction process is equivalent to conventional compaction (Ref 10, 19, 20). Equal press speeds were achieved with the warm-compaction process compared to conventional compaction. The limiting feature in part production is the rated capacity of the powder heating system and the part weight. Although conventional compacting presses are used, attention must be given to prevent the heat generated in the tooling from reaching critical bearing components. Cincinnati Inc. recommends that stainless steel adapter plates be used to minimize the flow of heat to the critical components (Ref 18). Additionally, incorporating an air gap between the die body and die pot within the press minimizes the transfer of heat. Effects of Prolonged Time at Temperature and Regrinding of Green Parts. Laboratory testing performed by Hoeganaes demonstrated that binder-treated powder can be reheated to warm-compaction temperatures a maximum of 4 cycles with minimal loss of powder flow and compressibility (Ref 4). Additionally, the powder can be held at temperature up to 4 h with no degradation of the apparent density, flow, green density, and green strength. Although powder metallurgy is considered a low-scrap manufacturing process, nonusable parts are generated during the setup stage. To address this issue of potential green scrap, laboratory work was initiated at Hoeganaes Corporation to study the effects of adding reground warm-compacted powder into new premixes. This work demonstrated that additions up to 5% regrind can be successfully compacted without any degradation in the strength or flow characteristics of the premix. Although it is not recommended that regrind additions be made to critical components, this work demonstrated that additions can be made without any loss in powder or sintered properties. 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

5 380 / Shaping and Consolidation Technologies Table 6 Density and process comparison between warm and cold compaction Base Sintered powder Graphite Lubricant Compaction Simermg density, g/cm3 Distaloy AE(a) 0.5% 0.7% Kenolube 600 MPa cold compaction 1120 C, 30 rain, Endogas % Densmix 600MPa warm compaction 1120 C, 30 min, Endogas % Kenolube 650 MPa cold compaction 1120 C, 30 rain, 90% N2/10% H % Densmix 500 MPa warm compaction 1120 C, 30 min, N2/10% H2 7.1 Distaloy DC(b) 0.5% 0.6% Kenolube 650 MPa cold compaction 1120 C, 30 rain, 90% N2/10% H % Densmix 500 MPa warm compaction 1120 C, 30 min, 90% N2/10% H2 7.1 DistaloyAE 0.8% 0.6%Kenolube MPacoldcompacdon C,20+30min, 7.3 (DPDS)(c) 90% N2/10% % Densmix 700 MPa warm compaction 1120 C, 30 rain, 90% N2/10% H2 7.3 (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. Source: Ref 21 Table 7 Comparison of warm-compacted materials to selected wrought and cast alloys Material Ylekl Tensile areagth strength Eiongatiaa,... MPa ~ MPa I~ % hardness AIS HRB AIS HRB AIS HRB AIS18620 Heat treat HRC Ductile iron HRC Powder forged F HRC Powder forged FL HRC FLN-4205 at 7.39 g/cm HRC FIMM05 at 733 g/cm HRC Warm comp~ed turbine hub ~b Conventionally compacted turbine hub ::t ' Y 6.00 ' ' ', ' ' Distance along spllne from bottom, mm Fig. 9 Variation in sintered density and dimensional change of turbine hub processed by conventional P/M and warm compaction 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). Recent articles have demonstrated the usefulness of the warm-compaction process in the fabrication of an automotive turbine hub for highperformance engines (part weight 1100 g), the manufacture of helical gears with gear densities in excess of 7.3 g/cm, 3 lock components (part weight 27 g), and gearing with complex gear forms or spiral gears requiring high gear densities (Ref 22-24). 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. One significant advantage of the warm-compaction process is the increased density uniformity achieved in the compacted part (Ref 22, 23). Quantitative metallographic techniques demonslrated 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. 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 sinterhardening process, warm compaction offers the potential to green machine these components prior to sintering and subsequent hardening. REFERENCES 1. G.E Bocchini, The Warm Compaction Process: Basics, Advantages, and Limitations, Society of Automotive Engineers, H.G. Rutz and EG. Hanejko, High Density Processing of High Performance Ferrous Materials, Advances in Powder Metallurgy and Particulate Materials--1994, Vol 5, Metal Powder Industries Federation, 1994, p E Chagnon and Y. Tmdel, Effect of Compaction Temperature on the Sintered Properties of High Density P/M Materials, Advances in Powder Metallurgy and Particulate Materials-1995, Vol 2, Part 5, Metal Powders Industries Federation, 1995, p U. Engstrom, B. Johansson, H. Rutz, F. Hanejko, and S. Luk, High Density Materials for Future Applications, Advances in Powder Metallurgy and Particulate Materials--1995, Vol 3, Part 11, Metal Powders Industries Federation, 1995, p M. Gagne, "Behavior of Powder Mix Constituents During Cold and Warm Compaction" presented at the 1997 International Conference on Powder Metallurgy & Particulate Materials, 29 June to 2 July 1997, Chicago, IL 6. H.G. Rutz and T.M. Cimino, Advanced Properties of High Density Ferrous Powder Metallurgy Materials, Advances in Powder Metallurgy and Particulate Materials--1995, Vol 3, Part 10, Metal Powders Induslries Federation, 1995, p S. Luk, H. Rutz, and M. Lutz, Properties of High Density Ferrous P/M Materials--A Study of Various Processes, Advances in Powder Metallurgy and Particulate Materials , Vol 5, Metal Powder Industries Federation, 1994, p H.G. Rutz, T. Murphy, and T. Cimino, The Effect of Microstructure on Fatigue Properties of High Density Ferrous P/M Materials, Advances in Powder Metallurgy and Particulate Materials--1996, Vol 13, Metal Powder Industries Federation, 1996, p R. O'Bfien, "Fatigue Prolxxfies of P/M Materials" Technical Data, Hoeganaes Corporation, I. Donaldson and E Hanejko, An Investigation into the Effects of Processing Methods on the Mechanical Characteristics of High Performance Ferrous P/M Materials, Advances in Powder Metallurgy and Particulate Materials-1995, Vol 5, Metal Powder Industries Federation, 1995, p S.R. Sun and K. Couchman, Repressing of Warm Compacted Materials, Advances in Powder Metallurgy and Particulate Materials-1996, Vol 5, Metal Powder Induslries Federation, 1996, p I. Donaldson, An Evaluation of High Performance Materials Processed Using Warm Compaction Technology, Advances in Powder Metallurgy and Particulate Materials--1996, Vol 5, Metal Powder Industries Federation, 1996, p

6 Warm Compaction / U. Engstrom, B. Johansson, and O. Jacobson, "Properties and Tolerances of Warm Compacted PM Materials" presented at Euro '95 (Birmingham), Oct T. Cimino and S.H. Luk, Machinability Evaluation of Selected High Green Strength P/M Materials, Advances in Powder Metallurgy and Particulate Materials 1995, Vol 2, Part 8, Metal Powders Industries Federation, 1995, p C.G. Oliver and H.G. Rutz, Powder Metallurgy in Electromagnetic Applications, Advances in Powder Metallurgy and Particulate Materials-1995, Vol 3, Part 11, Metal Powders Industries Federation, 1995, p S. Pelletier, L.P. Lefebvre, and C. Gelinas, Resin Impregnation of Soft Magnetic Materials for Low Frequency Applications, presented at the 1997 International Conference on Powder Metallurgy and Particulate Materials (Chicago, IL), 29 June to 2 July D.E. Gay, Higher Performance Microencapsulated Powders for Various P/M Applications, Advances in Powder Metallurgy and Particulate Materials--1995, Vol 3, Part 11, Metal Powders Industries Federation, 1995, p R. Unkel, Additional Applications of Cincinnati EL-Temp TM, Advances in Powder Metallurgy and Particulate Materials--1995, Vol 2, Metal Powders Industries Federation, 1995, p S. St.-Laurent and F. Chagnon, "Designing Robust Powders Mixes for Warm Compaction," presented at the 1997 International Conference on Powder Metallurgy and Particulate Materials (Chicago, IL), 29 June to 2 July E Hanejko, H.G. Rutz, U. Engstrom, and B. Johansson, Properties of Diffusion Bonded Alloys Processed to High Densities, Advances in Powder Metallurgy and Particulate Materi- als--1995, Vol 3, Part 10, Metal Powders Industries Federation, 1995, p O. Mars and U. Engstrfrn, Warm Compaction and Its Influence on the Dynamic Properties of Sintered Steels, Powder Metallurgy in Automotive Applications, P. Ramarlaishnan, Ed., Science Publishers Inc., 1998, p J. Chemlar, B. Nelson, H. Rutz, M. Lutz, and J. Porter, An Evaluation of the ANCOR- DENSE Single Compaction Process and HPP Processing Technique on Fine Pitched Spur and Helical Gears, Advances in Powder Metallurgy and Particulate Materials , Vol 5, Metal Powder Industries Federation, 1994, p T. Miller and E Hanejko, "Development of a Warm Compacted Automatic Transmission Torque Converter Hub" Paper , Society of Automotive Engineers 24. Advertising Literature on W~a'rn Compaction, Porite Taiwan Company, LTD