REINER MIM Metal Injection MoldingProduction of cost-efficient precision parts with complex geometries in the MIM procedure

Complex steel parts made by metal injection moulding
REINER offers a new option for producing precision steel parts with complex forms more economically than before with the MIM technology (metal injection moulding).

Hans-Peter Schmid - Regional Sales Manager
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Hans-Peter Schmid - Regional Sales Manager
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The concept of the MIM procedure has its origin in plastic injection moulding, offering the same near-unlimited design freedom for geometry and material. However, the result is a strong metallic high-precision part. Undercuts, bores, cross-bores, threads, lamellas and even relief-like structures and engravings (e.g. logo, item number) in the injection moulding production process can be produced in a single production process with the greatest detail. This is an essential advantage over classical machining: Many otherwise necessary individual post-processing steps are combined in a single process in metal injection moulding.

Like the alternative term "powder injection moulding" suggests, a very fine metal powder mixed with a binder and any desired alloy elements forms the material basis for injection moulding. Modern thermoplastic injection moulding machines melt the initial material ("feedstock") and feed it into the tool. After cooling, the plastic, which has a share of about 10% in the metal powder, is removed from the hardened piece ("green product") in the subsequent debinding phase. The resulting still-porous workpiece ("brown product") is sintered just below its melting point right after this.

REINER high-precision technology – ideas shaped precisely

Interesting information on the MIM procedure

Capability Overview

Dimensions
400x700mm tool opening area

Parts weight
max. 75g

Materials Different
low-alloyed steels, e.g. 100Cr6, non-corrosive and heat-resistant steels, e.g. 316LA other materials on request

Machine type
Arburg 270-MIM 50T closing force

Lot sizes
Depending on part geometry, e.g. 5,000 - 20,000 pcs.
Used at REINER since 2000

Advantages
MIM Metal injection moulding has a broad application area,
e.g. medicine, automotive, handheld/electrical tools, aviation and aerospace, defence industry, sensors, closing technology
Complex geometries with cross-bores, thread, lamellas
Cost-efficient production of high-volume parts
Many feedstock options
Production takes place with little material waste,
little post-/end processing
High sintering density, outstanding mechanic, magnetic, corrosive properties can be achieved by coatings, heat treatment

REINER´s Advantages
Own tool design/mould and tool construction with many years of experience
State-of-the-art CNC processing centres for complete/end processing
Surface treatment such as galv./chemical surface, etc., through reliable partners
Special Knowhow The focus is on small/technical parts

Origin and experience of the REINER metal injection moulding competence

What characterises the MIM parts made by metal injection moulding?

MIM technology frees designers and constructors from many earlier production and cost limitations where creative solutions for new products are concerned. Innumerable materials are available for their use, including low-alloyed steels such as the 100Cr6, as well as stainless steels such as 316LA. Ask your experts about further materials for your individual problem solution!
The smaller a part is to become, the better can metal injection moulding use its advantages. In everyday use, we find these parts, e.g., in the tiny, highly resilient hinges used in glasses.
In contrast to conventional machining on the lathe, injection moulding achieves high surface qualities without post-processing. The basic material properties of the sintered parts permit galvanic and electrolytic surface processing without pre-treatment. They can be nickel-plated or electro polished right out of production.

From the feedstock to the green product to the brown product to the injection moulded part – how is a metal injection moulded part made?

Sintered parts made by metal injection moulding can match machined parts in all chemical and mechanical material properties. They have a very high density in excess of 96%. The chosen material is used virtually without any waste, since even the material from the sprue can be reused. How is an MIM part made anyway?

Feedstock production

In the beginning, there is the desired material with its properties: For this, metal powders are mixed with the desired alloy and thermoplastic materials as a binder to form the "feedstock". This powder mix is kneaded into a viscous mass under application of heat. The binder is to ensure an evenly good metal powder transport during injection moulding and to warrant a high resilience of the raw part.

Metal injection moulding: The

The "green product", as the blank is also called, is produced in an injection moulding machine by injecting the "feedstock" into the tool under high pressure. This blank is 10 to 20% larger than the final product due to the binder share, but all geometrical properties of the desired parts are already defined precisely at the accordingly increased ratio. The sprue that remains at the material input of the injection moulding machine will be removed and completely returned to the production process again as material.

Debinding to become the

In the next step, the binder must be removed from the blank. Depending on the "feedstock" used, this can be done in debinding by using solvents, catalytically or thermally. In catalysis, for example, the catalyst is thermally evaporated, will react with the binder and escape from the part as a gas. After debinding, the end material will remain as an open-porous form.

Sintering

Depending on the alloy used for the material, the parts are sintered just below their melting point – between 1200 °C and 1400 °C. Sintering will cause the parts to "shrink" to the target size specified by the designer or the precise specification sizes. Metal injection moulding is therefore called a near-net-shape or net-shape production method.

Post-processing

MIM parts can generally be subjected to any imaginable heat and surface treatment that is available for conventionally produced metal or ceramics parts. They include:
  • Surface finishing: sand blasting, barrel finishing, polishing, lapping
  • Coating technology: thin-film technology, galvanisation, painting
  • Connection technology: laser cutting, soldering, installing
  • Heat treatment: curing, HIP (hot-isostatic pressing)
  • Machining: turning, cutting, drilling, grinding, grating, honing, thread-cutting
  • Forming technology: calibration

What advantages does production in the MIM procedure offer?

Metal injection moulding shows its advantages where complex geometries, special material requirements, high precision and low error ratios are required. The costly post-processing steps that are often needed in other methods can be avoided by smart design and foresighted construction, since the injection-moulded part will already contain all the bores, threads, logos and other labels after the work step of metal injection moulding. This way, an experienced designer can easily plan production of entire assemblies in a single piece. Overview of the advantages:
  • Economically efficient production of highly complex parts in large series production
  • Cost-efficient production of high-volume parts
  • Use of highly resilient metal materials and stainless steels with a high sintering density
  • Little material waste and high reusability
  • Saving cost-intensive assembly processes
  • Thread already included in the original shape
  • Detailed presentation of smallest geometries, scripts, reliefs and structures

Does the MIM process have any disadvantages?

As compared to simple, rotation-symmetrical parts using conventional metals and stainless steels, the MIM procedure is elaborate and expensive. The production process from the feedstock to the green product to the brown product to sintering of the parts requires high system accuracy in handling metal powders, binders, temperatures and tools. The larger the lot, the more economically efficient the use of the MIM metal injection moulding procedure will be.

What makes REINER particularly qualified as a manufacturer of injection moulding parts using MIM technology?

REINER has its own tool construction with many years of experience. Our employees in mould and tool construction have developed particular solution know-how in planning and design of small and technical parts. The MI parts are finished by complete and final processing in state-of-the-art CNC processing centres.

REINER high-precision technology – ideas shaped precisely