MIM series part 5: debinding

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 about 20% larger than the final part. To proceed to the sintering phase without defects, the part needs to be debinded. After the debinding process is complete, the part is considered "brown".

The debinding process removes the primary binding material from the moulded component. Typically, the debinding process involves several steps, and the part undergoes more than one cycle to ensure that as much binding material 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 clogging, which can lead to additional manufacturing costs. It is also faster to debind and then sinter, compared with sintering alone. Debinding can be performed using multiple methods. The three most common methods are explained in detail below.

Debinding methods

There are three types of debinding methods typically used – thermal, supercritical fluids (SFC), and solvent. Thermal debinding is a method performed in a temperature-controlled environment. It uses inexpensive equipment but has a long processing cycle and results in poor "brown" strength. Supercritical fluid debinding is a method performed in a gaseous acid environment. This method provides good "brown part" strength and is environmentally friendly, but it 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 results in 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 only disadvantages of using this type of debinding.

In the final part of this series, you'll learn about the sintering phase. This is the final phase in the MIM process and creates the finished part.

Other articles in the series:

• MIM series part 1
• MIM series part 2 – feedstock
• MIM series part 3 – compounding
• MIM series part 4 – moulding
• MIM series part 6 - sintering