Powder molding is a process where metal is ground into powder and injected into a mold. This process, also called metal injection molding or sintering, has several advantages over traditional processes. A powder-molded part is generally just as dense and strong as a typically-cast metal piece, with much higher-potential complexity. Metal pieces made using this process may have much more precise tolerances and finer pieces than those made using other techniques. While the price-per-part of a piece made with powder molding may be higher, less secondary processes generally mean the parts are made much faster.
This first step in powder molding is reducing the metal to a powder, a process generally done using an industrial grinder. Since it doesn’t use high heat, this actually takes less power than processes that melt the metal first. The powdered metal is mixed with a plastic bonding agent and injected into the mold. Inside the mold, the mixture is exposed to high heat and pressure, which allows the part to harden. The hardened mixture is removed from the mold and allowed to cool and cure.
After cooling for a time, the plastic binders are removed through the use of solvents and rapid heating of the part. The plastic comes loose from the metal and leaves behind a solid piece. Since the part has small pockets in it where the plastic used to be, its next stop is a sintering furnace. While sintering, the part is heated to near its melting temperature. This forces the metal to bond across the pockets, but the part doesn’t lose its shape.
A traditional molding process uses pure liquid metal to create the shape. This metal will often have difficulties flowing into extremely tight spaces, making fine work difficult. In addition, the overall reduction in size after curing is difficult to predict, making parts with very tight specifications hard to produce. Powder molding avoids both these pitfalls. The plastic and metal mixture flows into tight areas easily and has much less size variation than liquid-cast metals.
In order to work around their problems, traditional casting processes use several additional steps after the part is finished. Powder molding generally has very little secondary processing once the part is finished. This means that the parts are often produced much faster than parts made using comparable methods.
Parts made using powder molding are often used for situations that require a lot of precise small pieces. Common applications include the aerospace and miniaturized technology fields, as well as the computer and medical industry. Parts made using powder molding are becoming more common as the technology advances and devices become smaller.
