DFM_Handbooklj

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11 Design for Powder Metal Processing 11.1 INTRODUCTION A variety of structural parts, bearings, gears, and so on, are produced from raw materials in the form of powders. This area of processing is generally called powder metallurgy, although parts can also be made from nonmetallic powders, such as ceramics, by these methods. In the main processing sequence used, raw material powders are mixed and then compressed into the required shape. The compact is then heated in a controlled atmosphere (sintered) to bond the particles together and produce the required properties of the part. The powder metallurgy process has a number of features that are not found in other metalworking processes, including [1—4]: 1. Precise control of material and product properties. Through careful control of the constituent powder materials, compaction levels, and so on, precise control of the final product properties can achieved. 2. Unique material compositions. Although most powder metallurgy parts are produced with standard material compositions [5,6], a wide range of compositions can be produced by the powder metallurgy process, including combinations impossible by other means. For example, metals and ceramics can be combined by compaction and sintering. 3. Unusual physical properties. Physical properties can be readily varied by powder metallurgy from low-density, highly porous filters to high-density parts with low porosity. Tensile strengths can also be varied from low to very high. It is possible to compact dissimilar materials in layers to obtain different properties at various places in the part. The porosity can be 461
462 Chapter 11 - 120 8 ioo 95. I 80 ^ ro 60 I 40 | 20 I 0 Cold Hot Casting Powder Metal Forging Forging Metallurgy Removal Process Type FIG. 11.1 Material utilization for basic shape-producing processes. (Adapted from Ref. 7.) controlled so that impregnation with oil or other lubricants can lead to self- lubricating properties for bearings. Net-shape manufacturing. Complex-shaped parts that require no further processing can be produced by the powder metallurgy process. Many gears, cams, and so forth, which can require expensive machining to produce from wrought material stock, can be readily produced from metal powders. 100 80 60 40 20 Cold Hot Casting Powder Metal Forging Forging Metallurgy Removal Process Type FIG. 11.2 Energy utilization per unit part weight for basic shape-producing processes. (Adapted from Ref. 7.)
Design for Powder Metal Processing 463 Counter bores, holes, flanges, and similar features can be formed when the parts are compacted. Little material wastage and loss. Material wastage from the powder metal process is very low, as illustrated in Fig. 11.1, which compares the overall material wastage for a range of processes [7]. 6. High accuracy and repeatability. Close tolerances and a high degree of repeatability, particularly in the transverse direction, can be readily obtained. 7. Low overall energy utilization. The total energy usage by the process is low compared to other forming and shaping processes (Fig. 11.2) [7]. 11.2 MAIN STAGES IN THE POWDER METALLURGY PROCESS Unlike some other material shaping processes, such as injection molding or casting, the powder metallurgy process consists of several independent stages involving different equipment. The basic processing stages are shown in Fig. 11.3. 11.2.1 Mixing The initial stage in the powder metallurgy process is blending and mixing of the powder materials, together with additives such as lubricants, which are included to aid the compaction process. Metallic stearates, such as zinc stearate, are commonly used as lubricants for compaction and usually form 0.5 to 1.5% of the Base powders Alloying elements ,————, Lubricants, etc. Filling Pressing Ejection SINTERING FIG. 11.3 Main processing stages for sintered powder parts. (Adapted from Ref. 2.)
464 Chapter 11 mixture. Premixed powders are available direct from suppliers, for some standard materials, but, in general, mixing from constituent elemental or pre-alloyed powders within the plant will be necessary. A variety of mixers are available with different configurations and capacities. The overall purpose of mixing is to obtain as homogeneous a mixture of powders and lubricants as possible. 11.2.2 Compaction For the majority of engineering powder metallurgy parts, the next stage is cold compaction of the mixed powders. This is most often achieved by die pressing, but other methods are available. Hot compaction, which eliminates the subse- quent sintering stage, is used for some specialized applications. In this chapter only cold die pressing is considered in detail as this is the most commonly used method of compaction. A wide variety of different densities, porosities, and tensile strengths can be obtained by using different degrees of compaction or compaction pressures. During the compaction process, the mixed powders are pressed, usually from both sides, by a number of separately moving punch elements, depending on the complexity of the part. The output of the process is a "green" compact, which has sufficient "green strength" properties to allow handling without damage prior to sintering. The final material properties are directly related to the compaction density achieved, as discussed in more detail in Section 11.4. 11.2.3 Sintering During sintering the compacted parts are passed through a controlled atmosphere furnace and heated to a temperature below the melting point of the constituent powders. The individual particles become bonded together by diffusion bonding. A variety of different furnace types are available. Most commonly, continuous flow furnaces are used for high productivity, but batch furnaces are also used, particularly if special atmosphere conditions or high temperatures are required. 11.3 SECONDARY MANUFACTURING STAGES A number of secondary manufacturing processes can be used in conjunction with the main processing steps, usually to refine material properties and to produce features not obtainable from the basic processes. The commonly utilized secondary processes are shown schematically in Fig. 11.4. 11.3.1 Repressing and Resintering In order to achieve high component densities, partial sintering, followed by repressing and a further sintering stage, is usually necessary. The part is
Design for Powder Metal Processing 465 1 Tumbling SINTERING n—— L$ —————————— *_ "^ ^ o \ "te^j SIZING i Ul ^ £ •
466 Chapter 11 11.3.2 Sizing and Coining Secondary pressing operations (sizing) are used to refine dimensional accuracy or compensate for warpage, and so forth, in the sintered part, with little increase in density occurring. Coining may also be used to engrave or emboss small features in the faces of the part. In each case a suitable die set must be designed and manufactured, in addition to the compaction tools. 11.3.3 Infiltration For some structural applications it is necessary to eliminate any residual porosity from the powder metallurgy part and to increase strength properties. This can be achieved by infiltrating the sintered part with a lower melting point metal, such as copper, with metal being taken up into the part by capillary action. Infiltration is often carried out by placing a suitable slug of the lower melting point material on the base material compact and then heating to a temperature above the melting point of the infiltrant material. Infiltration can be carried out during the initial sintering process, but is most often done in a second pass through the furnace. In both cases a compact of the infiltrant material must be prepared, in addition to the main part compact, which requires an additional compaction process and corresponding die set. A range of standard copper-infiltrated steels can be produced by this process [5]. These materials can only be produced by the powder metal process in combination with infiltration. 11.3.4 Impregnation Self-lubricating properties can be achieved by impregnating the porous sintered parts with oil. The sintered parts are usually submerged in a bath of oil for several hours, but for the best results vacuum impregnation should be used. A range of standard self-lubricating bearing materials are used [6], but most moderate density parts can be given self-lubricating properties by impregnation if required. 11.3.5 Resin Impregnation Parts can also be impregnated with plastics, such as polyester resins, either to improve machinability or to remove porosity, which could adversely affect such finishing operations as plating or interfere with a requirement for gas tightness. The process is similar to oil impregnation, with the interconnected porosity filled with resin by capillary action.
Design for Powder Metal Processing 467 11.3.6 Heat Treatment Sintered parts may require heat treatment, particularly ferrous-based powder metal parts and some aluminum alloy parts. The heat treatment processes are generally the same as those used for wrought parts. 11.3.7 Machining Machining may be required, in particular to produce features that cannot be produced, or may be uneconomical to produce, by sintering. However, because powder metallurgy is a net shape process, the amount of machining required is generally small. Such machining is usually restricted to undercuts or threaded holes, for example. The machining properties of sintered materials are similar to the equivalent wrought materials and can be enhanced sometimes by resin impregnation. 11.3.8 Tumbling and Deburring Burrs produced during the compaction process can be removed by tumbling in a barrel or by vibratory deburring. In this process the parts, after sintering, are loaded into a container, together with some abrasive particles, and then tumbled or vibrated together sufficiently to remove burrs and sharp edges. 11.3.9 Plating and Other Surface Treatments All of the common plating processes and other surface protection treatments, such as painting, can be used for powder metal parts. Residual porosity can cause plating solution entrapment; consequently, plating is often preceded by resin impregnation. 11.3.10 Steam Treating Steam oxidizing can be used to increase surface wear and corrosion resistance of iron-based parts. Strength properties and density are also improved. Surfaces are coated with a hard black magnetic iron oxide (Fe3O4). The process closes some of the interconnected porosity and all surface porosity. Parts are heated to 480 to 600°C and exposed to superheated steam under pressure. Heat-treated parts cannot be steam-treated since the properties obtained by heat treatment will be altered. 11.3.11 Assembly Processes Joining powder metal parts is not commonly required because complex shapes can be achieved relative to other forming processes. Should joining of powder
468 Chapter 11 Upper Punch xk_. Die-*- 7] •-'•'? ?• / 1/ 7 N, 71 m ^ / / / 1' \ •Y ; : / / / .•:••' / \\ / ^ / / / i ,/ /: 1 ;/ jL Z Lower 1 ^ Punch —fc 1 Fill Die Press Ejection Closure Position FIG. 11.5 Basic compaction sequence for powder metal parts. (From Ref. I . ) metal parts be required, many of the commonly used welding processes for wrought parts can be used. As a result of the residual porosity in powder metal parts a unique joining process is possible. Parts are assembled and then infiltrated with a lower melting point metal to effect a bond similar to brazing and soldering. 11.4 COMPACTION CHARACTERISTICS OF POWDERS During compaction loose powders are poured into a die cavity with the compaction punches retracted (Fig. 11.5). Then the punches are moved relative to the die to compact the powder and increase the density. Subsequently, the "green" compact is ejected from the tooling, prior to transfer to the sintering process. TABLE 11.1 Extract from Data on Standard Iron Based Materials Material Material designation condition Yield stress Ultimate tensile Part density or name (AS or HT) (N/mm2) (N/mm2) (g/cc) F-0000-10 AS 89.6 124.1 6.10 F-0000-15 AS 124.1 172.4 6.70 F-0000-20 AS 172.4 262.0 7.30 F-0005-15 AS 124.1 165.5 6.10 F-0005-20 AS 158.6 220.6 6.60 F-0005-25 AS 193.1 262.0 6.90
Design for Powder Metal Processing 469 The final material properties of the part are largely determined by the compaction density achieved. For example, Table 11.1 shows an extract from the data in the Metal Powder Industries Federation (MPIF) standard on materials [5] and shows the designation and material properties of some standard powder metal (PM) carbon steels. As can be seen, the composition of some of these standard materials is the same, but increased strength and modification of other properties are achieved by compaction to increased densities. For example, see the group of materials designated F-0005-15, F-0005-20, and F-0005-25, which are all low-carbon steel with a 0.05% carbon content; the different properties are achieved by the final density to which the material is compacted. The conse- quence of this is that for reasonably uniform properties in powder metal parts, it is necessary to achieve relatively uniform density in the "green" compacts. The basic mechanics of the powder compaction process influence the ways in which this can be done. 11.4.1 Powder Compaction Mechanics The mechanics of powder compaction is governed by friction between the die and the powder and between the individual powder particles. Friction losses cause localized reductions in compaction pressure, and as a result stresses are not distributed uniformly throughout the compact. First, for all but very thin parts (< 6 mm), it is necessary to compact the powder from both sides. Figure 11.6 [8] shows the density distribution in a nickel powder compact pressed only from one side. The highest densities are found in the upper outer circumference, where the wall friction causes the maximum relative motion of the particles. The lowest densities occur in the bottom of the compact remote from the moving punch. Thus, in order to achieve more uniform density, it is necessary to press from both sides with independently moving punches. However, in this case the lowest densities are in the middle of the part due to the effects of container wall friction (Fig. 11.7). Even with double compaction the density gradients impose a limit on the total length of the compact. Successful compaction becomes difficult to achieve when the length-to-diameter ratio of the compact exceeds 5 to 1 [1]. Many powder metal parts consist of a number of levels of different thicknesses in the compaction direction. In order to achieve uniform density in the compact, and hence uniform properties, these different levels must be compacted by separately moving punches. For example, Fig. 11.8 shows a cross section through a part with two levels [8]. If this is compacted with only one lower punch, with a step machined in the upper face, different compression ratios will be achieved in the columns of powder associated with each level, resulting in higher densities in the thinner portion of the compact. In order to achieve more uniform density, it is necessary to separate independently moving lower punches, with the relative movements controlled, to obtain the same compression ratio within each level.
470 Chapter 11 17.5 7.3 / 7.2 7.3 15.0 12.5 E 10.0 Q. O o "B 7.5 1 2 "o 5.0 2.5 10 7.5 5.0 2.5 0 2.5 5.0 7.5 10 Radial distance, mm FIG. 11.6 Density distribution in a nickel powder specimen compacted from one side only (densities in gm/cc). (From Ref. 8.) Pressed from Pressed Jrom top top only and bottom FIG. 11.7 Density variations during two-sided compaction.
Design for Powder Metal Processing 471 One lower punch Two lower punches FIG. 11.8 Density variations in a two-level part. (From Ref. 8.) From this it can be seen that to achieve uniform properties in a part, the overall complexity of the tooling must increase with the number of different thicknesses or levels in the parts produced. 11.4.2 Compression Characteristics of Metal Powders The loads required during compaction are determined from the pressures required to achieve a certain density in the parts. Figure 11.9 shows some typical compaction curves for different materials [8]. Such curves are usually obtained Compacting pressure, tsl 10 20 30 40 50 ••- Atomized Aluminum -m~ Atomized Iron •+• Electrolytic Copper 30 -*- Sponge Iron 100 200 300 400 500 600 700 Compacting pressure, MPa FIG. 11.9 Typical compression curves for metal powders. (From Ref. 8.)
472 Chapter 11 TABLE 11.2 Typical Compaction Pressures for Powder Materials Material Tons/in2 MPa Aluminum 5-20 69-276 Brass 30-50 414-687 Bronze 15-20 207-276 Carbon 10-12 138-165 Carbides 10-30 138-414 Alumina 8-10 110-138 Steatites 3-5 41-69 Ferrites 8-12 110-165 Iron (low density) 25-30 345-414 Iron (medium density) 30-40 414-552 Iron (high density) 35-60 483-827 Tungsten 5-10 69-138 Tantalum 5-10 69-138 From Ref. ! from standard tests using short, cylindrical specimens. As can be seen, as the compaction pressure is increased, the density increases rapidly at first and then slows down, so that the curve eventually becomes asymptotic to a density somewhat below the wrought density of the material. It is difficult to obtain high-density parts because at higher densities the applied loads must be increased by large amounts to obtain even small increases in the part density. For this reason the maximum density obtained using a single compaction operation and sintering is usually around 90% of the equivalent wrought density of the material. Typical compaction pressures for a range of materials are given in Table 11.2. In order to achieve near full density parts it is necessary to use additional processing steps. In particular, repressing and resintering can be used. This can be illustrated by Fig. 11.10, which shows compaction curves for iron powders for single pressing and for repressing. It can seen that to achieve a part density of, say, 7.3 g/cc by single pressing, it will be necessary to use compaction pressures of 65 tons/in. (896 MPa), which will produce high loads and require tooling of increased strength. By repressing and resintering, the initial compaction can be reduced to 6.85 g/cc, with moderate pressures of around 35 ton/in.2 (483 MPa). Repressing is then carried out at the same compaction pressure to achieve the required density. The total costs of the part will, however, be increased considerably because of the extra processing stages required and a second set of compaction tooling for repressing. Compaction curves for most materials follow the basic configuration shown in Fig. 11.8, with the precise shape of the curve dependent on the material and shape
Design for Powder Metal Processing 473 300 400 500 600 700 800 900 MPa 7.6 I Re-pressed and 7.4 resin te red 3 7.2 u » 7.0 $ 2 fi 6.8 6.6 ' Zinc stearate 0.5 6.4 . . I . . . . . * 20 30 40 50 60 70 Compacting pressure, tons per sq tn. FIG. 11.10 Compression curves for single compaction and repressing of iron powder. of the raw powder particles among other things. Compaction curves can be approximated by a power law relationship such that: P = Apb where P is the compaction pressure and p is the part density. The constants A and b can be determined from two values of P and p obtained from suitable tests (Fig. 11.11). Compaction curves are usually obtained from tests on cylindrical shapes with the height equal to the diameter. Consequently, for thicker parts the load must be increased for the required density to compensate for the increased container wall friction. This correction should be around 25% for a part length-to- diameter ratio of 4 to 1. Thus the required compacting pressure can be obtained by increasing the value Pl (Fig. 11.11 a), obtained from the basic compaction curve, by a factor K, obtained as illustrated in Fig. 11.lib; i.e., for L/D > 1 K=0 for L/D < 1 Therefore, the total pressure required is given by
474 Chapter 11 v> z lil Q (a) COMPACTION PRESSURE, P 1 4 (b) EQUIVALENT L/D FIG. 11.11 Correction of compaction pressures for increased part thickness. For parts that are not cylindrical, an equivalent L/D ratio can be used given by where V is the part volume and A is the projected area in the compaction direction. 11.4.3 Powder Compression Ratio The depth of loose powder (fill height) required to give the final thickness of the compacted part is determined from the powder compression ratio at the required density (Fig. 11.12). The compression ratio of the powder is given by kt = p / p a
Design for Powder Metal Processing 475 COMPRESSION FILL FIG. 11.12 Fill height and ejection stroke during powder compaction. (From Ref. 9.) where pa is the apparent density of the loose powder, which is dependent on the size and shape of the powder particles in the mixture. The compression ratio determines the fill height of powder required for any thickness variations in the final part. 11.5 TOOLING FOR POWDER COMPACTION The requirement of maintaining relatively uniform densities means that each separate thickness in powder metal parts must usually be compacted by separately moving punch elements. Small thickness changes (< 15% of the part thickness) can be accommodated by steps in the punch faces with little loss of density uniformity. Various mechanisms are used for achieving the necessary relative motions in the tooling for successful compaction. The main elements for a typical tool set for a multilevel part are shown in Fig. 11.13. The tool set consists of a die, inside which the relative movement of the punch elements to compact the powders takes place. Any through holes in the part are formed by core rods which remain at the same relative position to the upper die surface during the compaction cycle. Other ancillary elements such as punch holder rings, core rod holders, stops, and so on, are required to complete the tool set.
476 Chapter 11 FILL POSITION COMPACTED POSITION FIG. 11.13 Typical compaction tool elements for a multilevel part. (From Ref. 9.) During the compaction cycle, the punches are initially retracted to positions to accommodate the fill of loose powder. The retracted positions of the lower punches during filling are determined by the product of the corresponding part thicknesses and the powder compression ratio, kt. Following filling, the compac- tion is achieved with the various punches moving relative to each other to give similar compaction densities in the various thicknesses in the part. Finally, after compaction, the "green" compact is ejected and the compression cycle is repeated for the next part. The complexity and cost of compaction tooling increase as the number of levels or thickness changes in the part increases, since each separate level must be compacted by separately moving punch elements. Many presses utilize standard die sets, with an inserted die held by a suitable tool steel clamping ring. These die sets may be removable or nonremovable. In either case the die sets must be well guided because of the small clearances between tooling elements required. Removable die sets are normally used for press capacities up to around 300 tons, after which the die sets become too large to be readily handled into and out of the press, but occasionally larger removable die sets are used.
Design for Powder Metal Processing 477 11.5.1 Compaction Dies The die controls the outer peripheral shape of the part, which can contain intricate detail of almost any shape. Compaction dies are usually cylindrical, with the overall thickness dependent on the part thickness and the fill height of powder required. Die surfaces must be highly wear resistant, and the preferred material is tungsten carbide. However, because the cost of carbide is over 10 times that of tool steel, dies are usually constructed with inner carbide inserts, which are shrink-fitted into a tool steel ring. This tool steel ring has a standard outside diameter to suit the recess in the die set or press bed being used. The die insert size that can be accommodated on a particular press is limited. The required die insert size for a specific part is dependent on the shape being compacted. Preferably any core rods should be as near to the center of the press as possible, and for parts with multiple through holes, positioning the centroid of the projected area of the part at the die center is usually appropriate. A basic rule for determining the carbide insert size required is the diameter of the circle enclosing the part, centered on the centroid, plus an extra amount of material (Fig. 11.14), which is usually not less than 10 mm. The outer die ring, as a practical rule, has a diameter at least three times that of the carbide insert. 11.5.2 Punches for Compaction Separate punches are required for each level or thickness of the part. These punches move relative to each other during compaction, with the longer punches passing through the shorter punches. Punches must be carefully lapped to ensure close fitting with each other and with the die inner profile. Punches are usually manufactured from cylindrical tool steel stock, by combinations of turning, milling, profile grinding, and lapping. 11.5.3 Core Rods for Through Holes Through holes of almost any profile can be achieved in powder metal parts, which allows features very difficult or costly to produce by other processes to be readily obtained. Through holes are produced in the part by core rods of the appropriate cross section. Core rods are the longest elements in the tool set. They may have very small cross sections, but such small cross-section rods are relatively difficult and expensive to manufacture. In addition, since core rods are subjected to a cycle of compressive stresses during compaction and tensile stresses during part ejection, the fatigue life of small cross-section rods may be severely reduced. Core rods are produced from tool steel and carbide by similar methods to those used for punches. In all cases, holes of the appropriate shape must be machined in the punches through which the core rods pass.
478 Chapter 11 CARBIDE INSERT DIAMETER FIG. 11.14 Compaction die insert dimensions. 11.5.4 Die Accessories All die sets require a number of additional accessories to be produced, including core rod holders, punch adapters, stops, fasteners and so on. In general, these are produced from tool and other alloy steels. 11.6 PRESSES FOR POWDER COMPACTION Powder compaction presses may be mechanically or hydraulically driven and differ mainly in the number of actions present in the press mechanisms. Presses are available in a wide range of capacities up to around 25,000 kN (2800 tons). Single-action presses and tooling, in which parts are compacted from one side only, are restricted to relatively thin one-level parts. Double-action presses and tooling systems allow compaction of the part from both sides. Various tool set mechanisms allow the compaction of multilevel parts to be accommodated, although two-level parts are most commonly processed. Multiple-action (adjus-
Design for Powder Metal Processing 479 table stop) presses, which are capable of producing the most complex parts, are also available. 11.6.1 Factors in Choosing the Appropriate Press Table 11.3 lists some relevant data for a representative range of compaction presses. The main items that determine the appropriate press for a particular part are as follows: The number of vertical punch motions possible Load capacity of the machine Maximum fill height possible Maximum ejection stroke possible Maximum die diameter that can be accommodated TABLE 11.3 Data on a Range of Typical Compaction Presses Maximum Minimum Maximum Maximum Type of Capacity stroke rate stroke rate fill height die insert press (kN) (per min) (per min) (cm) diameter (cm) SA 36 150 25 1.524 5.72 DA 45 90 15 3.810 7.30 SA 53 150 20 1.905 9.52 DA 89 60 10 5.080 11.18 DA 134 60 10 6.985 15.24 SA 142 100 15 1.905 13.34 DA 178 50 8 8.255 20.99 DA 267 50 8 8.255 20.32 SA 312 60 10 1.905 15.24 DA 400 40 7 11.430 15.24 DA 534 40 7 15.875 20.32 MA 534 40 7 15.875 20.32 DA 587 34 12 11.430 19.20 DA 890 30 7 15.875 20.32 DA 979 30 12 15.240 21.74 MA 1113 40 7 15.875 21.59 DA 1335 30 7 15.875 21.59 MA 1780 30 7 15.875 22.86 DA 1958 30 10 15.240 26.67 DA 2670 25 7 11.430 25.40 DA 3115 25 7 15.875 25.40 MA 4450 20 7 15.875 25.40 DA 4895 18 6 11.430 50.80 SA, single action; DA, double action; MA, multiple action.
480 Chapter 11 Punch Motions Some machines are only capable of pressing from one direction and consequently can only be used for relatively thin single-sided parts. Other machines can press from above and below using separate punch actions at the same time, and with suitable tooling they can be used to produce multilevel parts. Load Required 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 in the compaction direction. Determination of the compaction pressure has been described in Sec. 11.4.2. Fill Height The fill height or depth of the fill (Fig. 11.14) is the height of the loose powder required to give the part thickness after compaction. The value is determined by the compressibility of the loose powder at the required density. The fill height is obtained by multiplying the finished part height by the compession ratio of the material: Fill height, hf = tkt where t is the part thickness and kt is the compression ratio. If the fill height is greater than the maximum that can be accommodated in the press selected on the basis of the compacting load required, a larger-capacity machine must be used. This may be necessary for thick parts with a relatively small cross-sectional area. Ejection Stroke The ejection stroke is equivalent to the part thickness plus the penetration of the upper punch into the die (Fig. 11.12). If a greater ejection stroke is required than is available on the press selected on the basis of compacting load, then a large- capacity machine must be used, but often this problem can be overcome by suitable design of the tooling. Consequently, ejection stroke is not a major determining factor in press selection. Maximum Die Diameter Presses and tool sets have a maximum die size that can be accommodated. The required die size for a particular part is determined by the procedure described in Sec. 11.5.1. If the required die size is greater than can be used in the press selected from the compaction load, it will be necessary to use a press of larger capacity that can accommodate the required die size. This may be necessary for a part that has a large circumscribing circle diameter, but a relatively small projected area in the compaction direction.