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Design Recommendations

As mentioned before, the green part (before sintering) is produced by either compaction of powder or injection molding. Those stages restrict the shapes and kinds of parts the user can design. When injection molding is used, the designer should follow the good practices mentioned in the metal/ceramic injection molding design guide.

When compaction is used, the designer should take into account the following. During compaction of the part, pressure is applied equally from above and below to the powder being compacted. The powder is comtained in a die. Due to the irregular shape of the powder particles employed, the powders interlock mechanically and become a coherent mass. This interlocking characteristic will forbid the powder from flowing under pressure as plastic material would flow during molding. Hence the importance of designing the component such that the powder can be conformed to the required shape during filling and before pressing commences.

The removal of volatile materials, if present in appreciable quantities in the compacts, will produce a porous and permeable product. The designer should take advantage of this feature in designing products such as metal filters.

We mention some general design guides that fall in the category of designing of the manufacturing line:

• In the first stage in the furnace, the temperature of the compacts should be raised in a controlled manner. Air and volatilizing liquids entrapped in closed pores during rapid heating produce high internal pressure. This would result in swelling or fracture of the compacts.