Metal Injection Molding (MIM)
Epson Atmix's MIM Technology for Complex 3D Parts
Metal injection molding (MIM), which combines plastic injection molding and powder metallurgy
techniques, is gaining popularity as a relatively new metal processing alternative to conventional sheet metal
processing, milling, and casting. MIM can be used to make complex three-dimensional shapes, can be used with a
wide range of materials, and is suited to volume production. It is thus used to manufacture parts for
wearables, such as luxury watch casebacks, and complex external parts. It is also used to produce parts for
products ranging from printers to medical equipment.
Read on to learn more about the MIM technology of Epson Atmix, which has world-class metal powder manufacturing and MIM processing technology.
MIM manufacturing process and features
The MIM manufacturing process consists of the steps below.
Mixing and granulation
Metal powder and powdered binder are mixed under pressure and heat. The binder is composed of a binding material, plasticizer and lubricant, the latter two of which are wax components. Next, the mixture of metal powder and binder are extruded under pressure and cut, forming pellets like those of resin materials. High-quality metal powder developed and manufactured by Epson Atmix is used.
Parts are molded using an injection molder like that used for plastics. The molded workpieces are called green parts. Since the green parts contain a binder, they are made larger than the parts actually needed.
Degreasing is a process for removing the wax components (plasticizer, lubricants, etc.) that are contained in the binder. There are three means of degreasing:
- (1) Solvent degreasing, in which a solvent is used to dissolve the wax
- (2) Heat degreasing, in which heat is used to vaporize the wax
- (3) Catalytic degreasing, in which catalytic gas and heat are used to achieve degreasing
Workpieces that have been degreased are called brown parts. Care must be used in degreasing because the wax components escape from between the particles, which can lead to deformation and cracking. The degreasing process must be carefully controlled because if degreasing is not performed correctly, grease left behind will be present as carbon during sintering, affecting the composition of the metal after sintering.
The degreased brown parts are heated and sintered in a sintering furnace. The cubic volume of sintered parts will be reduced by an amount corresponding to the amount of binder lost. Sintered workpieces are called silver parts. Epson Atmix uses its own metal powder and MIM sintering technology to achieve a sintered density that was not possible with conventional MIM.
Sizing, machining (secondary processing), and surface finishing
If high dimensional accuracy is required or if additional processing such as screw tapping is required, sizing (coining) or machining are performed. Like any molten metal material, MIM materials can be heat-treated, plated, painted, or given other surface finishes. Therefore, surface treatment is performed as needed.
In addition to the same dimensional inspections as those used with other processing methods, MIM parts are also analyzed for sintered density and chemicals. In chemical analyses, it is particularly important to monitor the carbon content. Some parts may also be X-rayed or subjected to other non-destructive tests to check for cracks or other internal damage.
MIM for complex 3D parts
Among the advantages of MIM are:
- high productivity;
- a high degree of flexibility in terms of shape;
- flexibility in materials used; and
- excellent mechanical characteristics, including high density and high strength.
MIM allows you to create three-dimensional shapes that cannot be achieved by machining or sheet
metal working. As long as the shape can be achieved by injection molding, there are not many limitations.
Therefore, there are cases where multiple parts that were conventionally manufactured by milling or other
machining operations can be metal injection molded as a single part to reduce costs.
3D printing is one method that can be used to create three-dimensional shapes using metal powder. However, MIM has an advantage over 3D printing in that it lends itself better to volume production, is more flexible in terms of the materials that can be used, and requires less post-processing.
MIM is a relatively new processing method that takes time to learn, but Epson Atmix has been engaged in the MIM business since the 1980s when the technology was introduced to Japan. We are able to manufacture high-quality MIM parts because we have expertise in the entire production process, from the manufacture of our own powders to the molding process. Epson Atmix is differentiated by its ability to sinter workpieces to a density of 99.5%, stably produce very small parts with complex shapes in high volumes, and process parts made from titanium and titanium alloys using MIM.
Metal powder manufacturing technology
Epson Atmix manufactures its own metal powders. There are physical, chemical, and electrical methods for producing the metal powders used in MIM, but we use water atomization, a process in which molten metal is reduced to fine particles by blasting it with water. The features of water atomization are as follows:
Ultra-high pressure water atomization process
In this water atomization process, highly pressurized jets of water impinge on a stream of molten metal, causing it to atomize. Whereas conventional water atomization produces particles with an average diameter of 15 microns, Epson Atmix's process produces metal powder with an average particle size of 5 microns. MIM, which uses fine powder as a raw material, can obtain high mechanical strength even when sintered at relatively low temperatures such as 1,000℃, so energy can be saved in the manufacturing process. In addition, material made from such fine powder flows easily and fills molds well and can be used for very small and complex shapes. It also has good surface roughness, eliminating the need for surface treatment after sintering.
MIM parts can be used for everything from wearable products to printers to medical equipment.
MIM parts manufactured by Epson Atmix are used in a variety of fields. Some of the most common are listed below.
Examples of uses in the Epson Group
MIM parts are used as Epson luxury watch casebacks, cases, and external parts with complex shapes.
MIM parts are used in Epson's impact dot matrix printers. These parts are made from a material called permendur, an iron-cobalt alloy that has a high saturation magnetic flux density, so it is an indispensable part for high-performance impact dot matrix printers.
Digital textile printer parts
MIM parts are found in the printheads used in Epson's digital textile printers.
Parts used in force sensors for 6-axis robots
The upper and lower blocks used in force sensors for Epson's 6-axis industrial robots are also manufactured using MIM parts.
Examples of uses by Epson customers
Small stainless-steel brackets with a complex shape that are used in braces to hold a wire are made using an MIM process.
Dental handpieces and surgical instruments
Dental handpieces and surgical instruments are made of pure titanium and titanium alloys that are hygienic and have a low risk of triggering allergies. MIM is also used to volume-produce parts from difficult-to-process materials, where the parts are a single piece for reasons of hygiene and have a three-dimensional shape that fits the user's hand.