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As explained in the previous article about moulding, after the part comes out of the metal injection moulding machine, it is considered "green" and is approximately 20% larger than the final part. To enter the sintering phase without defects, the part needs to be debound. Once the debinding process is complete, the part is considered "brown".
The debinding process removes the primary binder from the moulded component. Typically, the debinding process involves several steps, and the part undergoes more than one cycle to ensure as much binder as possible is removed before sintering. After the debinding step, the part is semi-porous, allowing the secondary binder to escape easily during the sintering cycle. Many question why debinding is needed, but without this critical step the part would not be as robust. Debinding also prevents furnaces from becoming clogged, which can lead to additional manufacturing costs. It is also faster to debind and then sinter than to sinter alone. Debinding can be performed using several methods. The three most common methods are explained in detail below.
Debinding methods
Three types of debinding methods are typically used – thermal, supercritical fluids (SFC), and solvent. Thermal debinding is carried out in a temperature-controlled environment. It requires inexpensive equipment but has a long processing cycle and results in poor "brown" strength. Supercritical fluid debinding takes place in a gaseous acid environment. This method provides good "brown part" strength and is environmentally friendly, but uses a patented process with few suppliers and limited materials. The final method is the one most commonly used by MIM manufacturers – solvent debinding. Solvent debinding is a process that uses acetone, heptane, trichloroethylene, and water. It provides good "brown part" strength and is a consistent process that uses a closed-loop system. Solvent debinding is not as environmentally friendly as the other methods, which is one of the few disadvantages of using this type of debinding.
In the final part of this series, you will learn about the sintering phase. This is the final phase in the MIM process and produces the finished part.
Other articles in the series:
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