Fig. 31 Density distribution along axis of cylindrical bushing: FEA predictions versus experimental results This article has examined the general structure of constitutive laws for the compaction of powder compacts and demonstrated how these material models can be used to model the response of real world components to a series of complex die operations. It identified the general structure of the constitutive law and described a number of models that have been proposed in the literature. This field is still evolving, and it is evident that there will be significant developments in this area over the next few years as a wider range of experimental studies are conducted, providing greater insights into the compaction process. At the current time, there is no universally accepted model. Therefore, a pragmatic approach and a relatively simple form of empirical model were adopted requiring, for the determination of the unknown functions, a limited range of experiments. This selection allowed an examination of the compaction of axisymmetric components in detail and a comparison of general features of the component response with practical measurements. Similar procedures could have been adopted for any of the methods described, although in general, more sophisticated experiments are required in order to determine any unknown function or coefficients, particularly if the shape of the yield function is not known, or assumed, a priori. References cited in this section 2. ABAQUS/Standard User's Manual, Version 5.7, Vol 1- 3, Hibbitt, Karlsson, & Sorensen, Inc., Providence, RI, 1997 3. N. Aravas, On the Numerical Integration of a Class of Pressure-Dependent Plasticity Models, Int. J. Numer. Meth. Eng., Vol 24, 1987, p 1395-1416 4. Y. Kergadallan, G. Puente, P. Doremus, and E. Pavier, Compression of an Axisymmetric Part, Proc. of the Int. Workshop on Modelling of Metal Powder Forming Processes (Grenoble, France), 1997, p 277-285 14. E. Pavier and P. Doremus, Mechanical Behavior of a Lubricated Powder, Advances in Powder Metallurgy & Particulate Materials-1996, Vol 2 (Part 6), Metal Powder Industries Federation, 1996, p 27-40 40. J.R.L. Trasorras, S. Krishnaswami, L .V. Godby, and S. Armstrong, Finite Element Modeling for the Design of Steel Powder Compaction, Advances in Powder Metallurgy & Particulate Materials-1995, Vol 1 (Part 3), Metal Powder Industries Federation, 1995, p 31-44 42. Powder Compaction Simulation Software (PCS Elite) User's Manual, Concurrent Technologies Corp., Johnstown, PA 44. B. Wikman, H.A. Häggblad, and M. Oldenburg, Modelling of Powder- Wall Friction for Simulation of Iron Powder Pressing, Proc. of the Int. Workshop on Modelling of Metal Powder Forming Processes (Grenoble, France), July 1997, p 149-158 45. E. Pavier and P. Dorémus, Friction Behavior of an Iron Powder Investigated with Two Different Apparatus, Proc. of the Int. Workshop on Modelling of Metal Powder Forming Processes (Grenoble , France), July 1997, p 335-344 46. J. Hallquist, "NIKE2D-A Vectorized, Implicit, Finite Deformation, Finite- Element Code for Analyzing the Static and Dynamic Response of 2-D Solids," Technical report UCRL- 19677, Lawrence Livermore National Laboratory, Livermore, California, 1993 Mechanical Behavior of Metal Powders and Powder Compaction Modeling J.R.L. Trasorras and R. Parameswaran, Federal-Mogul, Dayton, Ohio; A.C.F. Cocks, Leicester University, Leicester, England References 1. R. German, Particle Packing Characteristics, Metal Powder Industries Federation, 1989 2. ABAQUS/Standard User's Manual, Version 5.7, Vol 1- 3, Hibbitt, Karlsson, & Sorensen, Inc., Providence, RI, 1997 3. N. Aravas, On the Numerical Integration of a Class of Pressure-Dependent Plasticity Models, Int. J. Numer. Meth. Eng., Vol 24, 1987, p 1395-1416 4. Y. Kergadallan, G. Puente, P. Doremus, and E. Pavier, Compression of an Axisymmetric Part, Proc. of the Int. Workshop on Modelling of Metal Powder Forming Processes (Grenoble, France), 1997, p 277-285 5. K.T. Kim, J. Suh, and Y.S. Kwon, Plastic Yield of Cold Isostatically Pressed and Sintered Porous Iron under Tension and Torsion, Powder Metall., Vol 33, 1990, p 321-326 6. H.A. Kuhn and C.L. Downey, Material Behavior in Powder Preform Forging, J. Eng. Mater. Technol., 1990, p 41-46 7. S. Shima and M. Oyane, Plasticity Theory for Porous Metals, Int. J. Mech. Sci., Vol 18, 1976, p 285-291 8. S.B. Brown and G.A. Weber, A Constitutive Model for the Compaction of Metal Powders, Modern Developments in Powder Metallurgy, Vol 18-21, 1988, MPIF, p 465-476 9. T.J. Watson and J.A. Wert, On the Development of Constitutive Relations for Metallic Powders, Metall. Trans. A, Vol 24, 1993, p 2071-2081 10. A.R. Akisanya, A.C.F. Cocks, and N.A. Fleck, The Yield Behaviour of Metal Powders (1996), Int. J. Mech. Sci., Vol 39 (No. 12), 1997, p 1315-1324 11. S. Brown and G. Abou-Chedid, Yield Behaviour of Metal Powder Assemblages, J. Mech. Phys. Solids, Vol 42 (No. 3), 1994, p 383-399 12. W. Prager, Proc. Inst. Mech. Eng., Vol 169, 1955, p 41 13. R. Hill, The Mathematical Theory of Plasticity, Oxford University Press, 1950 14. E. Pavier and P. Doremus, Mechanical Behavior of a Lubricated Powder, Advances in Powder Metallurgy & Particulate Materials-1996, Vol 2 (Part 6), Metal Powder Industries Federation, 1996, p 27-40 15. C.J. Yu, R.J. Henry, T. Prucher, S. Parthasarathi, and J. Jo, Advances in Powder Metallurgy & Particulate Materials, Vol 6, Metal Powder Industries Federation, 1992, p 319-332 16. N.A. Fleck, L.T. Kuhn, and R.M. McMeeking, Yielding of Metal Powder Bonded by Isolated Contacts, J. Mech. Phys. Solids, Vol 40, 1992, p 1139-1162 17. N.A. Fleck, On the Cold Compaction of Powders, J. Mech Phys. Solids, Vol 43 (No. 9), 1995, p 1409-1431 18. J. Gollion, D. Bouvard, P. Stutz, H. Grazzini, C. Levaillant, P. Baudin, and J.P. Cescutti, On the Rheology of Metal Powder during Cold Compaction, Proc. Int. Conf. on Powders and Grains, Biarez and Gourves, Ed., Clermont-Ferrand, France, 4-8 September 1989, p 433-438 19. R.M. Govindarajan and N. Aravas, Deformation Processing of Metal Powders, Part 1: Cold Isostatic Pressing, Int. J. Mech. Sci., Vol 36, 1994, p 343-357 20. A.L. Gurson, Continuum Theory of Ductile Rupture by Void Nucleation and Growth, Part 1: Yield Criteria and Flow Rules for Porous Ductile Media, J. Eng. Mater. Technol., Vol 99, 1977, p 2-15 21. A.C.F. Cocks, The Inelastic Deformation of Porous Materials, J. Mech. Phys. Solids, Vol 37 (No. 6), 1989, p 693-715 22. Y-M. Liu, H.N.G. Wadley, and J. Duva, Densification of Porous Materials by Power-Law Creep, Acta Metall. Mater., Vol 42, 1994, p 2247-2260 23. A.R. Akisanya, A.C.F. Cocks, and N.A. Fleck, Hydrostatic Compaction of Cylindrical Particles, J. Mech. Phys. Solids, Vol 42 (No. 7), 1994, p 1067-1085 24. Z. Qian, J.M. Duva, and H.N.G. Wadley, Pore Shape Effects during Consolidation Processing, Acta Metall. Mater., Vol 44, 1996, p 4815 25. P. Ponté Castañeda and M. Zaidman, Constitutive Models for Porous Materials with Evolving Microstructure, J. Mech. Phys. Solids, Vol 42, 1994, p 1459-1497 26. K.T. Kim and J. Suh, Elastic-Plastic Strain Hardening Response of Porous Metals, Int. J. Eng. Sci., Vol 27, 1989, p 767-778 27. S. Brown and G. Abou-Chedid, Appropriate Yield Functions for Powder Compacts (1992), Scr. Metall. Mater., Vol 28, 1993, p 11-16 28. D.C. Drucker and W. Prager, Q. Appl. Math., Vol 10, 1952, p 157-165 29. A.L. Gurson and T.J. McCabe, Experimental Determination of Yield Functions for Compaction of Blended Powders, Proc. MPIF/APMI World Cong., on Powder Metallurgy and Particulate Materials (San Francisco), Metal Powder Industries Federation, 1992 30. A. Schofield and C.P. Wroth, Critical State Soil Mechanics, McGraw-Hill, 1968 31. D.M. Wood, Soil Behavior and Critical State Soil Mechanics, Cambridge University Press, 1990 32. S. Shima, "A Study of Forming of Metal Powders and Porous Metals," Ph.D. thesis, Kyoto University, 1975 33. Y. Morimoto, T. Hayashi, and T. Takei, Mechanical Behavior of Powders in a Mold with Variable Cross Sections, Int. J. Powder Metall. Powder Technol., Vol 18 (No. 1), 1982, p 129-145 34. J.R.L. Trasorras, S. Armstrong, and T.J. McCabe, Modeling the Compaction of Steel Powder Parts, Advances in Powder Metallurgy & Particulate Materials-1994, Vol 7, American Powder Metallurgy Institute, 1994, p 33-50 35. J. Crawford and P. Lindskog, Constitutive Equations and Their Role in the Modeling of the Cold Pressing Process, Scand. J. Metall., Vol 12, 1983, p 271-281 36. J.R.L. Trasorras, T.M. Kraus s, and B.L. Ferguson, Modeling of Powder Compaction Using the Finite Element Method, Advances in Powder Metallurgy, Vol 1, T. Gasbarre and W.F. Jandeska, Ed., American Powder Metallurgy Institute, 1989, p 85-104 37. B.L. Ferguson, et al., Deflections in Compaction Tooling, Advanced in PM & Particulate Materials, Vol 2, Metal Powder Industries Federation, 1992, p 251-265 38. H. Chtourou, A. Gakwaya, and M. Guillot, Assessment of the Predictive Capabilities of the Cap Material Model for Simulating Powder Compaction Problems, Advances in Powder Metallurgy & Particulate Materials-1996, Vol 2 (Part 7), Metal Powder Industries Federation, 1996, p 245-255 39. D.T. Gethin, R.W. Lewis, and A.K. Ariffin, Modeling Compaction and Ejection Processes in the Generation of Green Powder Compacts, Net Shape Processing of Powder Materials, 1995 ASME Int. Mechanical Engineering Congress and Exposition, AMD- Vol 216, S. Krishnaswami, R.M. McMeeking, and J.R.L. Trasorras, Ed., The American Society of Mechanical Engineers, 1995, p 27-45 40. J.R.L. Trasorras, S. Krishnaswami, L.V. Godby, and S. Armstrong, Finite Element Modeling for the Design of Steel Powder Compaction, Advances in Powder Metallurgy & Particulate Materials-1995, Vol 1 (Part 3), Metal Powder Industries Federation, 1995, p 31-44 41. S. Krishnaswami and J.R.L. Trasorras, Modeling the Compaction of Metallic Powders with Ductile Particles,Simulation of Materials Processing: Theory, Methods and Application, Shen and Dawson, Ed., Balkema, Rotterdam, 1995, p 863-858 42. Powder Compaction Simulation Software (PCS Elite) User's Manual, Concurrent Technologies Corp., Johnstown, PA 43. H- A. Haggblad, P. Doremus, and D. Bouvard, An International Research Program on the Mechanics of Metal Powder Forming, Advances in Powder Metallurgy & Particulate Materials-1996, Vol 2 (Part 7), Metal Powder Industries Federation, 1996, p 179-192 44. B. Wikman, H.A. Häggblad, and M. Oldenburg, Modelling of Powder- Wall Friction for Simulation of Iron Powder Pressing, Proc. of the Int. Workshop on Modelling of Metal Powder Forming Processes (Grenoble, France), July 1997, p 149-158 45. E. Pavier and P. Dorémus, Friction Behavior of an Iron Powder Investigated with Two Different Apparatus, Proc. of the Int. Workshop on Modelling of Metal Powder Forming Processes (Grenoble, France), July 1997, p 335-344 46. J. Hallquist, "NIKE2D-A Vectorized, Implicit, Finite Deformation, Finite- Element Code for Analyzing the Static and Dynamic Response of 2-D Solids," Technical report UCRL-19677, Lawrence Livermo re National Laboratory, Livermore, California, 1993 Powder Metallurgy Presses and Tooling Revised by John Porter, Cincinnati Incorporated Introduction POWDER METAL COMPACTING PRESSES, equipped with appropriate tooling, frequently are used for producing P/M components. Although commonly called P/M presses, use is not limited to the pressing of metal powders. Almost any alloy or mixture of materials produced in powder form can be compacted into suitable end products. The majority of components fabricated by P/M presses, in number of pieces and pounds of product produced, consists of compacted metals. Ferrous-base metals constitute the largest usage. Powder metallurgy compacting presses usually are mechanically or hydraulically driven, but they can incorporate a combination of mechanically, hydraulically, and pneumatically driven systems. Table 1 summarizes some of the developments for P/M presses in the last 40 years. Other recent improvements in compaction technology include: • Split- die techniques to make multilevel parts having different peripheral contours at different levels • Punch rotation capability to facilitate production of helical gears and other helical shapes • Higher compaction pressures by using stronger tool materials, advanced pressure control methods, and die wall lubricants • Better process control with computerized tool motion monitoring • Warm compaction and improved "segregation-free" powders with enhanced flow characteristics Table 1 History of development in P/M presses Years Compacting press 1955-1959 Cam press, HP 1960-1964 Toggle press, MP 1965-1969 Large size HP (500 +), large size MP (500 +) 1970-1974 Multistepped MP, double die compacting press 1975-1979 Large size MP (750 +), tool holder quick change 1980-1989 NC press, multistepped HP (800 +), large size rotary press 1990-1994 Large size MP, automatic P/M manufacturing line 1995-present Hybrid (mechanical/hydraulic) presses (800 tons) HP, hydraulic press; MP, mechanical press; NC, numeric controlled Powder Metallurgy Presses and Tooling Revised by John Porter, Cincinnati Incorporated Compacting Press Requirements Although P/M presses resemble stamping and forming presses, several significant differences exist. Press frames generally have straight sides. Gap-type or "C" frame presses are not suitable because the frame deflects in an arc under load, resulting in a slight out-of-alignment condition between the bed and side of the press. This arrangement produces a compacted part that is slightly out of parallel, top to bottom. Because P/M tooling clearances are generally 0.025 mm/25 mm (0.001 in./1 in.) total, bending deflection can cause broken tooling or excessive tool wear. Powder metallurgy presses apply sufficient pressure from one or both pressing directions (top and bottom) to achieve uniform density throughout the compact. Design should include provision for ejecting the part from the tooling. Pressing and ejection occur during each cycle of the press and must be accurately synchronized. Presses need sufficient connected horsepower to compact and eject the part. In most press-working applications, the working stroke is a small portion of the total stroke of the press. In P/M presses, the working stroke during the compaction portion of the cycle is usually greater than the length of the part being produced, and the ejection portion of the cycle has a working stroke equal to or greater than the length of the part by a factor of approximately two or three. In some cases, the power required during the ejection cycle is greater than that required during compaction. Presses should provide for adjustable die filling (the amount of loose powder in the tooling cavity). Automatic powder feeding systems that are synchronized with the compaction and ejection portion of the press cycle are desirable. Finally, P/M presses must meet federal, state, and local design and construction safety laws. Metal Powder Industries Federation (MPIF) standard 47 details safety standards for P/M presses. Mechanical presses are available in top-drive and bottom-drive arrangements. In top-drive presses, the motor, flywheel, and gearing system are located in the crown or upper structure of the press. Presses with pressing capacities of 1780 kN (200 tons) are floor mounted, requiring little or no pit. Top-drive presses with pressing capacities >1780 kN (200 tons) usually require a pit to maintain a convenient working height for the operator. In bottom-drive presses, the drive mechanism, motor, and flywheel are located in the bed of the press. These presses usually are "pulled down"; that is, the top ram of the press is pulled downward by draw bars or tie rods. Bottom-drive presses with pressing capacities of >445 kN (50 tons) usually require pits. Top-drive and bottom-drive presses are comparable in terms of partmaking capability, reliability, and equipment cost. Press Tonnage and Stroke Capacity. Required press capacity to produce compacts in rigid dies at a given pressure depends on the size of the part to be pressed and the desired green density of the part, which in turn is determined by requirements for mechanical and physical properties of the sintered part. Compacting pressures can be as low as 70 to 140 MPa (5 to 10 tsi) for tungsten powder compacts or as high as 550 to 830 MPa (40 to 60 tsi) for high-density steel parts. When a part is pressed from the top and bottom simultaneously, the press should apply the required load to the upper and lower ram of the press. To eject the pressed compact, an ejection capacity must be available that is sometimes divided into the load for the breakaway stroke (which is the first 1 to 12 mm ( to in.) of the ejection stroke and the load for a sustained stroke). The load for a sustained stroke is generally one-fourth to one-half of the breakaway load. The stroke capacity of a press, or the maximum ram travel, determines the length of a part that can be pressed and ejected. In presses used for automatic compacting, the stroke capacity is related to the length available for die fill and ejection stroke. Load Requirements. The total load required for a part is determined by the product of the pressure needed to compact the part to the required density and the projected area of the part. Compaction curves relate pressure, P, to the required density, q, and are usually obtained from compacting tests on cylindrical shapes with the height, L, equal to the diameter, D. For thicker parts the load must be increased, by as much as 25% for a length to diameter ratio of 4 to 1, to give the required density. Required compacting pressures can be estimated with a correction factor, k, such that (Ref 1): P = P 1 (1 + k) where P is the compaction pressure for a larger part and P 1 is the compaction pressure for a "standard" part (i.e., L = D). The correction factor is: k = (0.25/3)(L/D - 1) for L/D >1 k = 0 for L/D < 1 For parts that are not cylindrical, an equivalent L/D ratio can be used: L e /D e = (V · p)/(2 · A 2 ) where V is the part volume and A is the projected area. The press load required is then obtained by multiplying the required compaction pressure by the projected area of the part. Reference cited in this section 1. W.A. Knight, Design for Manufacture Analysis: Early Estimates of Tool Costs for Sintered Parts, Annals of the CIRP, Vol 40 (No. 1), 1991, p 131-134 Powder Metallurgy Presses and Tooling Revised by John Porter, Cincinnati Incorporated Mechanical Presses In most mechanical P/M compacting presses, electric motor-driven flywheels supply the main source of energy used for compacting and ejecting the part. The flywheel normally is mounted on a high-speed shaft and rotates continuously. A clutch and a brake mounted on the flywheel shaft initiate and stop the press stroke. To initiate a press stroke, the brake is disengaged and the clutch is engaged, causing the energy stored in the rotating flywheel to transmit torque through the press gearing to the final drive or press ram. Clutch and brake systems should be of the partial revolution type that can be engaged and disengaged at any point in the pressing cycle. The clutch usually is pneumatically engaged with a spring release, and the brake is pneumatically released with a spring set, thereby providing full stopping ability in the event of loss of air pressure. An adjustable speed device normally is supplied with electric drive motor, providing production rate adjustment as indicated by pressing and ejection conditions. On presses that have main motor capacities up to 19 kW (25 hp), the adjustable speed drive is usually of the variable- pitch pulley or traction-drive type. Above 19 kW (25 hp), direct-current or eddy-current control devices are preferred. The motor and drive must be totally enclosed to prevent contamination by metal powder dust. Gearing systems usually are either single-reduction (Fig. 1) or double-reduction (Fig. 2) arrangements. Single-reduction gearing frequently is used in lower tonnage presses ( 445 kN, or 50 tons) that have stroking rates of 50 strokes/min. Higher tonnage presses use double-reduction gearing and commonly have maximum stroking rates of 30 strokes/min. Fig. 1 Single-reduction gearing systems for P/M compacting press Fig. 2 Double-reduction gearing systems for P/M compacting press The low-speed shaft of the press, normally called the main shaft, is linked to the press ram, causing motion of the tooling for the compacting and ejection cycles. Ram driving mechanisms can be either cam- or eccentric-driven arrangements. Cam-driven presses generally are limited to pressing capacities 890 kN (100 tons). The main shaft of the press has two cams one cam operates the upper ram, and the other cam operates the lower ram for compacting the part. The cam that operates the lower ram also controls the powder feed into the die and ejects the part from the die after compacting. Cams normally operate linkages that convert the main shaft rotary motion into the linear motion of the tooling. Figure 3 shows a schematic of a cam-driven press. The cams in this type of press can be adjusted or arranged with removable sections, thus allowing cam motion to be varied to produce special motions to compact the part. Pressure can be applied either simultaneously or sequentially to the top and bottom of the compact. Anvil and rotary presses are types of cam-driven machines. These presses are described in more detail later in this article. Fig. 3 Schematic of cam-driven compacting press Eccentric-Driven Presses. Presses that have a final drive mechanism consisting of an eccentric or crank on the main shaft are the most widely used type of mechanical press. A connecting rod is used to convert the rotary motion of the main shaft into the reciprocating motion of the press ram. Generally, an adjustment mechanism is built into the connecting rod or press ram assembly, thus permitting the height position of the press ram to be changed with respect to the main shaft or press frame, thereby controlling the final pressing position of the ram. This adjustment mechanism can be used to control the length of the compacted part. Standard eccentric-driven presses have pressing capacities ranging from 6.7 to 7830 kN (0.75 to 880 tons). Powder Metallurgy Presses and Tooling Revised by John Porter, Cincinnati Incorporated Hydraulic Presses Hydraulically driven compacting presses are available with pressing capacities ranging from 445 to 11,100 kN (50 to 1250 tons) as standard production machines, although special machines with capacities 44,500 kN (5000 tons) have been used in production. Hydraulic presses normally can produce longer parts in the direction of pressing than mechanical presses, and longer stroke hydraulic machines are less expensive compared to an equivalent stroke produced in a mechanical press. The maximum depth of powder fill in mechanical presses is 180 mm (7 in.), while 380 mm (15 in.) of powder fill is common in hydraulic presses. The maximum production rate for hydraulic presses producing a single part per stroke is 650 pieces per hour. The slower speed of a hydraulic press when pressing long parts is preferable, because the longer time during pressing permits trapped air within the powder to escape through the tooling clearances. Most hydraulic presses are considered top-drive machines because the main operating cylinder is centrally located in the top of the press. This main cylinder provides the force for compacting the part. Hydraulic presses have three distinct downward speeds: • Rapid advance: Produces minimal pressing force, used for rapid closing of the die cavity • Medium speed: Pressing capacities 50% of full- rated capacity, used during initial compaction when lower pressing force is required • Slow speed: Maximum capacity available for final compaction Two types of hydraulic pumping systems are commonly found in P/M presses: the high-low system and the filling circuit system. The high-low system has a double-acting main cylinder. A regenerative circuit is used for rapid approach. Initially, the piston of the cylinder is activated by a high-volume, low-pressure pump; the fluid from the bottom of the cylinder is directed into the top of the cylinder in addition to the low-pressure pump volume. At medium speed, the regenerative circuit is deactivated, while the piston remains activated by the low-pressure pump. In full-tonnage press, the low-pressure pump is deactivated, and a high-pressure pump activates the piston. The filling circuit hydraulic pumping system has a single-acting main cylinder, and ram motion is controlled by small double-acting cylinders. The ram control cylinders are smaller than the main cylinder, so only a low flow rate of fluid is needed to cause rapid movement of the ram. During approach and return cycles, however, the fluid flow rate into and out of the main cylinder is high. The main cylinder is fitted with a large two-way valve that allows fluid to flow at low pressures (usually gravity feed). During pressing, the two-way valve is closed, and high pressure from the pump is applied to the main cylinder piston. Ejection of the part usually is accomplished by a cylinder that is centrally located in the bed of the press. The cylinder either upwardly ejects the part or pulls the die downward from the part, depending on the type of tooling used. When pressing parts to a given thickness, positive mechanical stops are used on hydraulic presses to control downward ram movement. When pressing parts to a desired density, downward ram movement is controlled by adjustment of the pressure to the cylinder. When the part is pressed to the desired unit pressure, the press ram stops and returns to the retracted position. Some types of P/M materials, such as P/M friction materials, are always pressed to density rather than size, because uniform density provides uniform friction and wear properties. The drive-motor horsepower on a hydraulic press is considerably larger than on an equivalent mechanical press. A mechanical press has a flywheel from which energy is taken during the pressing and ejection of the part. Energy is restored to the flywheel during the die feeding portion of the cycle. The motor on a hydraulic press must supply energy directly during the pressing and ejection portion of the cycle. Powder Metallurgy Presses and Tooling Revised by John Porter, Cincinnati Incorporated Comparison of Mechanical and Hydraulic Presses In terms of partmaking capability, no distinct advantage is gained by using either a mechanical press or a hydraulic press. Any part can be produced to the same quality on either type of machine. However, the following parameters influence press drive selection. Production Rate. A mechanical press produces parts at a rate one and one-half to five times that of a hydraulic press as a result of inherent design of the energy transfer systems and stroke length. Operating cost of a hydraulic press is higher, because the total connected horsepower of a hydraulic press is one and one-half to two times that of an equivalent mechanical machine. Theoretically, the required energy to compact and eject a part is the same for a hydraulic or a mechanical press, except that the overall efficiency of a mechanical press is slightly higher than that of a hydraulic press. Also, the kilowatt usage of the larger motor on a hydraulic press is greater than that of a mechanical press during the idle portion of the machine cycle. Machine overload protection is an inherent feature of a hydraulic press. If the hydraulic system is operating properly, the machine cannot create a force greater than the rated capacity. Consequently, overload of the machine frame is not possible, even if a double hit or operator error occurs in adjusting the machine. Misadjustment or double hits can cause a mechanical press to overload, can damage the machine, or may cause tooling overload and failure if the tooling cannot withstand full machine capacity. Some new mechanical presses are equipped with hydraulic overload protection systems. Equipment cost of a hydraulic press generally is one-half to three-quarters that of an equivalent mechanical press. Facility, foundation, installation, and floor space costs generally are comparable. Die Sets. The mounting into which the tooling is installed is known as the die set. Generally, the die set must be well guided because of the close tooling clearances used. Guide bearings must be protected with boots or wipers to prevent powder particles from entering guiding surfaces. Tooling support team members should have high stiffness to minimize deflection. The die set must be free of residual magnetism. The maximum acceptable level is 2 G. To ensure press operator safety, die sets should be adequately guarded. In a complex tooling arrangement, as many as seven independent tooling members and supports are moving relative to one another during the pressing and ejection cycles. Die sets can be classified as removable or nonremovable. Both types are used in mechanical and hydraulic presses. Nonremovable die sets are used throughout the entire tonnage requirements of available presses. Manually removable die sets are used primarily in presses with pressing capacities up to 2670 kN (300 tons). Above this press size, the die set assembly is moved by a powered system, and removable die set presses with capacities of 17,800 kN (2000 tons) are available. The major advantage offered by nonremovable die sets is flexibility in setup and operation. Presses equipped with nonremovable die sets usually have all adjustments required for setup and operation built into the press and die set, including: • Part length adjustment: Any dimensions of the part in the direction of pressing c an be quickly changed during production. • Part weight: Material weight in any level of the part can be changed easily during production. • Tooling length adjustment: Adjustments are provided to accommodate shortening of punch length due to sharpening or refacing. Another advantage of nonremovable die sets is the greater space available for tooling, compared to the removable type. This space provides more freedom in tooling design. However, presses incorporating nonremovable die sets must be shut down during tooling changes or maintenance. Tooling change and setup time generally is from 1 to 4 hours but sometimes substantially longer, depending on the complexity of tooling. Nonremovable die sets are well suited for developing new P/M parts, because press and tooling adjustments can be made quickly to achieve the desired weight, density, and part dimension. Adjustment features of nonremovable die sets make them desirable on long production runs, where changes in powder quality among lots require frequent tooling adjustment to maintain part quality. Users of removable die sets normally have two or more die sets per press. Tooling can be set up in a spare die outside the press. Removable die sets normally can be changed in less than 30 min, so loss of production time is minimal. On small presses where the die set is also small, the die set is restricted to a given set of tools and is considered semidurable tooling. One disadvantage of many removable die sets is that pressing is controlled by pairs of pressing blocks made of hardened tool steel, such as D-2. The height of the pressing block controls the height of the part. If the part length dimension is changed due to design, or if the tooling length is changed due to repair, the pressing blocks must be changed accordingly. Removable die sets are ideally suited for shorter production runs. On newer presses with removable die sets, complete powder adjustment is available, even when the die set is outside the machine. [...]... Composition Fe-14Cr-1Si-1Mn-0.3C Fe-18Cr-1Si-1Mn-1C Fe-5Cr-1.5Mo-1Si-1V-0.4Mn-0.4C Fe-6W-5Mo-4Cr-2V-0.3Mn-0.8C Fe-1.7Cr-0.8Mn-0.5Mo-0.4V-0.35C WC-10Co Hardness, HRC 50 57 50 61 30 80 Suggested applications Corrosion-resistant cavities, cores, inserts Wear-resistant, small inserts, cavities, cores Larger or intricate cavities, high toughness, low wear Core and ejector pins General purpose, hot runner,... Fe 4 m Fe-2Ni 2.5 m Mo 10 m stainless 15 m stainless 12 m tool steel 8 mW 1 m W-10Cu 60 PW-40PE 55PW-45PP-5SA 90PA-10PE 60 PW-35PP-5SA 55PW-45PP-5SA 90PA-10PE 90PA-10PE 65 PW-30PP-5SA 60 PW-35PP-5SA Solids loading, vol % 58 61 58 58 67 62 62 56 64 Density, g/cm3 4.90 5.12 4.52 5.97 5 .60 5.33 5.33 11.22 11.41 Molding temperature, °C 120 150 180 113 130 190 190 142 135 Viscosity, Pa · s 35 19 190 200 100 80... production experience In simple parts, such as single-level class I and II parts, these determinations proved successful As state-of-the-art materials and presses advanced to the production of complex, multilevel parts, the "cut -and- try" method of tool design became obsolete The high cost of complex tooling and adapters, plus downtime to redesign and rebuild tooling, requires the partmaking system, including.. .Powder Metallurgy Presses and Tooling Revised by John Porter, Cincinnati Incorporated Part Classification The Metal Powder Industries Federation has classified P/M parts according to complexity Class I parts are the least complex, and class IV parts are the most complex To better understand the types of commercially available P/M compacting presses, and their advantages and limitations, an understanding... Estimates of Tool Costs for Sintered Parts, Annals of the CIRP, Vol 40 (No 1), 1991, p 13 1-1 34 2 S.D.K Saheb and K Gopinath, Tooling for Powder Metallurgy Gears, Powder Metall Sci Technol., Vol 2 (No 3), 1991, p 2 5-4 2 3 Powder Metallurgy Design Manual, 2nd ed., Metal Powder Industries Federation, 1995 Powder Injection Molding Randall M German, The Pennsylvania State University Introduction INJECTION MOLDING... licensing and technological barriers, allowing rapid growth in the field Table 1 details the composition of a few common injection molding feedstocks, showing the binder, powder, and formulation details Table 1 Examples of powder injection molding feedstock Powder Binder, wt% 4 m Fe 4 m Fe 4 m Fe-2Ni 2.5 m Mo 10 m stainless 15 m stainless 12 m tool steel 8 mW 1 m W-10Cu 60 PW-40PE 55PW-45PP-5SA 90PA-10PE 60 PW-35PP-5SA... understanding of P/M part classification and tooling systems used to produce parts is necessary Part thickness and number of distinct levels perpendicular to the direction of powder pressing determine classification not the contour of the part Class I parts are single-level parts that are pressed from one direction, top or bottom, and that have a slight density variation within the part in the direction... both top and bottom The lowest density region of these parts is near the center, with higher density at the top and bottom surfaces Class III parts have two levels, are of any thickness, and are pressed from both top and bottom Individual punches are required for each of the levels to control powder fill and density Class IV parts are multilevel parts of any thickness, pressed from both top and bottom... S.D.K Saheb and K Gopinath, Tooling for Powder Metallurgy Gears, Powder Metall Sci Technol., Vol 2 (No 3), 1991, p 2 5-4 2 Powder Metallurgy Presses and Tooling Revised by John Porter, Cincinnati Incorporated Tool Materials Dies In the most common type of die construction, wear-resistant inserts or liners are held in place by clamping or shrink fitting The amount of interference between the insert and the... particles are small to aid sintering, usually between 0.1 and 20 m with near-spherical shapes For example, a 5 m carbonyl iron powder is widely used in the PIM process, as is a -1 6 m gas-atomized stainless steel powder Most common engineering alloys are used, including various steels, tool steels, and stainless steels Likewise, ceramics, refractory metals, and cemented carbides are processed in a similar manner . Lubricated Powder, Advances in Powder Metallurgy & Particulate Materials-19 96, Vol 2 (Part 6) , Metal Powder Industries Federation, 19 96, p 2 7-4 0 15. C.J. Yu, R.J. Henry, T. Prucher, S. Parthasarathi,. 18, 19 76, p 28 5-2 91 8. S.B. Brown and G.A. Weber, A Constitutive Model for the Compaction of Metal Powders, Modern Developments in Powder Metallurgy, Vol 1 8-2 1, 1988, MPIF, p 46 5-4 76 9. T.J Model for Simulating Powder Compaction Problems, Advances in Powder Metallurgy & Particulate Materials-19 96, Vol 2 (Part 7), Metal Powder Industries Federation, 19 96, p 24 5-2 55 39. D.T.