Material Selection

Once the die-compaction processing method has been selected the designer must consider the product configuration and material requirements. Previous sections have discussed the design constraints regarding shape and configuration. The next step in the procedure (see Fig. 5) is comparing the critical part performance requirements with the available P/M materials. Reference 5 serves as a very useful source of material property data. In many cases, more than one material can satisfy the design performance requirements. Therefore, the various production methods must be considered because these affect the ultimate cost of the product.

Fig. 5 Material selection method

Figure 6 provides the second evaluation scheme. Starting from the material selected, this leads directly to the density needed in the critical section of the part. Knowing the desired density leads to a preliminary selection of the powder and press size necessary to reach the required density. From this point the remainder of the processing steps are considered. For example, is a conventional sintering process or a "high-temperature" process needed? Will a repressing-resintering process be necessary to achieve the density selected? What secondary processing treatments are needed, and how will the density affect these processes? Using a standard press-and-sinter process as a baseline, the cost of high-temperature sintering may add a 10 to 20% premium, while a double-press/double-sinter process could result in as much as a 40% premium (Fig. 7). Therefore, the designer must recognize that selecting a material and density level leads directly to a processing cycle and the cost associated with the process. A judicious review and selection of materials can ensure the most cost-effective product design.

Material

Material

Heat Repress treat res inter

Fig. 6 How material selection affects process

Fig. 6 How material selection affects process

Fig. 7 Relative cost versus ferrous density of several P/M processes. Source: Hoeganaes Corporation

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