News Center & Categories

DESIGN GUIDE

Designing components for MIM is more akin to designing for plastic injection molding than to designing for other metal-forming processes.

Location：HOME > NEWS CENTER > NEWS CENTER

MIM metal injection molding basic process

Writer： Sints; Source：未知; Date：2018-08-04

MIM(metal injection molding) basic process:
First,choosing proper powder metal and binders,then mixing them in presetting temperature by proper method to form feed stock,after granulation then injection,to obtain brown parts,then de-binder,sinteirng and post process to achieve final products.

1. MIM powder and pulverization technology
MIM shows high quality requirements on materials.powders must be suitable to mix,injection,de-binder and sinter,and these are always contradictory.Research for MIM material includes:powder shape,size,size composition and apparent etc.Table 1 listed the most suitable materials for MIM.

As it requires very thin on MIM materials,the price are always very high.Some of them can be 10 times than PM powder.This is one critical factor to limit the wide-use of MIM technology.

2. Binders
Binders are the heart of MIM technology.In MIM,binder can improve flow property to adapt injection and maintain the shape of brown parts.Also it should have the property of de-binder easily,no pollution,no poison and reasonable price.Therefore,there are various types of binders.
Recent years engineers are choosing de-binding ways and binder property not only by experience but designing binder system.
Binder are generally composed by low and high molecule group element with some necessary supplements.Low molecule group elements are with lower viscosity,good flow rate and easily removing;high molecule group elements are with higher viscosity,high strength and maintaining brown parts strength.Both of them can be assorted by proper percent to achieve high powder load volume,to get high precision and high uniformity products.

3. Mixing
Mixing is the process of mixing metal powder and binders to get even feed stock.As the property of feed stock will determine the property of final products,so this process is critical.It involves the binders and the method&order,mixing temperature,mixing equipment and etc of adding powder.At present,this process is still staying on the level of replying on experience.The final evaluation on the quality of feed stock is the uniformity and consistency.
MIM feed stock is finished by both thermal effect and shear force.The mixing temperature cannot be to high,or the binders might be decomposed or powder and binders dissociated because of too low viscosity.Among the size of shear force will be changed according to different mixing ways.The regular MIM mixing equipments are twin-screw extruder,Z shaped impeller mixer,single-screw extruder,plunger extruder,double planetary mixer,double cam mixer and so on.These mixing equipment are all suitable for making material that viscosity is around 1-1000Pa·s
The method of mixing is to add high melting point unit to metal,then cooling,adding low melting point unit,then adding metal powder by stages.This can avoid low melting point unit to vaporization or decomposition,adding metal powders by stages can avoid cooling too fast which causing torque increase and minimize equipment lost.

4. Injection
Injection can obtain no damage and brown parts.First heating feed stock to certain temperature to make it with flow property;then inject the feed stock into cavity to form brown part,then taking it out from cavity.This process is the same as plastic injection molding.But as the feed stock of MIM with more metal powder,it makes MIM very different in technical data and other aspects,improper contol will cause various damages.

5. De-binder
Since MIM technology is being developed,there are various of binder system,it provides more ways for MIM to de-binder. The de-binding process took several days in the beginning has been cut down to several hours now.From de-binding method can separate debinding into to types:One is two step de-binding way.Two step de-binding way includes solvent de-binding+thermal de-binding,siphonage de-binding and thermal debinding.One step de-binding way is one step thermal de-binding.Now the most advanced method is amaetamold.

6. Sintering
Sinteirng is the last process of MIM.Sintering eliminates the pore between metal powder,making MIM products to achieve full density or close full density.MIM process is using great amount of de-binder,so the shrinkage rate during sinteirng is very large.Generally the shrinkage rate can achieve 13%-25%,this will leave of problem of deformation and dimension precision.Especially due to MIM parts are all complex components,this causes the problem more obvious.Even feed stock is the critical factory of controlling the deformation and precision of sintered part.For iron and stainless steel parts,there is still a problem of carbon controlling problem.

Last：MIM materials
Next：Sints organization structure

News Center & Categories

DESIGN GUIDE

MIM metal injection molding basic process

Contact Us