Technical ceramics for metal injection molding processes

1. Introduction

Metal Injection Molding (MIM) is an advanced metal forming technique that combines the advantages of plastic injection molding and powder metallurgy. This process allows the production of complex metal parts with high precision and excellent mechanical properties.

It is also an extremely sensitive process, carrying several risks and challenges that can affect the final product quality and production efficiency. Issues such as excessive adhesion, uneven thermal distribution, and binder removal or non-uniform shrinkage of the component can arise. Many of these problems can be eliminated by using technical ceramics.

2. Introduction to Metal Injection Molding (MIM)

Metal Injection Molding (MIM) is a manufacturing technique that involves injecting "feedstock" into molds to create complex-shaped components with high repeatability. The feedstock is a mixture of powdered metal and a polymer binder that holds the material together. Before the components can be used, the binder must be removed and the internal structure of the parts strengthened; this is achieved by subjecting the components to debinding and sintering heat treatment processes in a furnace.

3. MIM Stages

Debinding

This is the process of removing the binder from the green part. It can be achieved either catalytically, where the binder is removed using a combination of catalytic additives, solvents, and water, or thermally, which requires heat treatment in a modified atmosphere in a furnace. The required method depends on the type of feedstock used. Components that have undergone this process are then referred to as "brown" parts. Depending on the type of feedstock used, both chemical and thermal debinding may be necessary. The chemical process removes most of the binder, while the thermal process removes the remaining binder, also known as "skeleton binder." This process is often referred to as "rest debinding."

Sintering

This is the heat treatment process of metal injection molded (MIM) components that have first undergone the debinding process (brown parts). The goal of sintering is to alter the internal microstructure of the components to improve their overall density and ultimately their strength. This is achieved by heating the metal parts in a furnace under an inert atmosphere to a temperature about 20% below the metal's melting point, allowing the atoms to diffuse through the microstructure and join into denser formations. During sintering, the metal parts will experience some shrinkage, with a 15-22% size reduction depending on the metal used and the final density of the parts. Temperature profiles, atmosphere, and temperature uniformity in the furnace during both debinding and sintering must be very precisely controlled to avoid distortion and the formation of cracks and blisters. An inert or reducing atmosphere is also important to prevent oxidation of the parts.

4. Use of Ceramic Plates in the Metal Injection Molding (MIM) Process

Ceramic plates are used to transport components produced in the metal injection molding process through all stages. Their application helps eliminate many problems occurring in the process.

• Porous yet smooth surface - no adhesion or melting of binders, uniform shrinkage of the part
• Plates made of porous, high-purity 99.5% alumina oxide ceramic - uniform shrinkage, no discoloration, less or no need for further processing
• Porosity makes the material lighter - less heat is required

Due to their high resistance to temperature cycles and high temperature (1500°C), one plate can be used for transport, debinding, and sintering. This results in cost savings – no additional tools are needed for each process.

The plates can be cut to any size, allowing for the creation of holes tailored to the product being processed. They are laser-cut, meaning no additional tooling is required – another cost-saving.

Fig. 2 Ceramic plates

Fig. 3 Plates with elements placed in the furnace

The use of ceramic plates in the metal injection molding process brings tangible benefits. It significantly increases production efficiency by reducing the number of defective products.

If you are interested in custom-sized ceramic plates – feel free to contact us.