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Steps of the MIM process



Feedstock preparation

Parmaco generates a crucial advantage by mixing its feedstocks in house according to proprietary Parmaco specific feedstock formulations. Parmaco specializes in all kind of ferrous alloys (steels).

Independence of feedstock vendors.
Development of customer specific alloys if required.
Determination of feedstock properties by selecting
  the most appropriate binder system.

Goal of the mixing process:

Homogeneous mix of binder components and metal powders.
Mouldable viscous feedstock for stress free green parts.
Granulometry which allows for easy feeding of the moulding machine.

Shape giving process – Molding

The shaping process is performed with plastic moulding machines. The molten viscous feedstock is injected like plastic into molds which are clamped into the molding machines. Special attention is given to the moulding parameters. The injection is performed with pressures up to 2000 bars. Equally important is the fact that the parts must be handled with care. Each green part must be taken from the mold with robotic grippers due to the fact parts are sensitive to damage.

Goal of the molding process:

Completely packed green parts without cracks, flow lines
  or other imperfections.
As little burrs on the parting lines and ejector marks.
Injection gates which do not disturb the functionality
  of the finished parts.
As little molding induced distortion as possible.

Debinding process

The binder material of the feedstock must now be removed from the green parts. Parmaco performs this task with a two step debinding process. The first step is performed in a solvent which removes the soluble binder components (physical process). After this first step the parts have a porous structure. Only after this step the parts are thermally debound in hot air. This second process removes the remainder of the binder troughout the components and leaves the parts in a brittle state. The resulting parts are brown or blue depending on the chosen process parameters.

Goal of the debinding process:

Efficient removal of the binder components without deforming
  or damaging the parts.
Preparation of the parts for the sintering process.

Sintering process

During the sintering process the compacted and debound parts are transformed to solid metal parts by exposure to process gases at temperatures below the melting temperature of the of the metal powder alloy. The sintering process induces diffusion processes which result in gas tight metal parts with densities between 96 and 99% of the theoretical density of the alloy. During sintering the parts shrink to their final dimensions by between 12 and 20% depending on the metal powder content of the initial feedstock.

Goal of the sintering process:

Transformation of the debound parts which consist of metal powder
  into dense metal components.
Achieving the required final dimensions with as little variation
  as possible in order to meet the predefined tolerances.
Attaining the desired material properties.
  The sintering process is the last process of the MIM process.
Now a number of subsequent process steps can be performed
in accordance with the specific requirements of the parts.
Such additional process steps may be all kinds of machining operations
(milling, taping, grinding etc), any heat treatment (case hardening,
quench and temper, hipping, surface treatment (tumbling,
polishing etc.), plating operations (Ni, Zn, Sn, Cr, Au, Ag, anti friction
coating etc.). assembling operations (laser welding etc.).

Heat and surface treatment

MIM-Teile können ebenso wie mechanisch hergestellte Bauteile sowohl diversen Wärme- als auch Oberflächenbehandlungen unterzogen werden.

  Possible heat

(Depending on alloy)
salt bath nitriding (QPQ)
quench and temper
vacuum hardening
precipitation hardening
induction hardening
Possible surface

(je nach Anforderung
und Materialwahl)
Chemical deburring
Nickel, Chrome, Zink plating
Copper, Gold, Silver plating
Anti friction coating
  Oil or grease coating