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Precision Control Method for Powder Injection Molding Products

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-05-21 08:51:00
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The dimensional accuracy of powder injection molding products is 0.3%, while that of traditional powder metallurgy products is 0.1%, machining can reach higher levels. Therefore, the low precision control becomes the key factor restricting powder injection molding industrialization. Product precision can be improved by optimizing the process, which includes feed preparation, injection molding, debinding and sintering.

1.Feeding preparation control

The loading and uniformity of feed are the most important factors affecting the control of size precision. The interaction between powder and binder determines the loading and uniformity of feed. 

Methods:

? choose powder with smaller particle size and wider distribution;

? multi-component low-molecular weight polymers and waxes are used as binders, which can meet the requirements of higher loading viscosity and good powder wetting;

? add appropriate amount of surfactant to improve the interaction between powder and binder;

? adopt high-quality equipment for uniform mixing, such as double-screw mixer, etc.

2.Powder Injection Molding -Injection Control .

Injection molding determines green part’s dimension directly. In injection process, the evaluation of feed rheology and shape retention of green part is the key to control precision, but good feed rheology does not mean good shape retention of green parts. Methods:

? optimize injection parameters. Excessive injection pressure and temperature will increase the residual stress inside green part, which is prone to crack. It is found that prolonged cooling time can reduce the residual stress, and high-pressure and low-temperature injection can improve the dimensional accuracy of product.;

? reasonable mold design, especially gate design;

? advanced injection molding equipment.

3.Powder Injection Molding -Debinding Control

In the process of binder removal, product may appear cracking, warping and other deformation. Debinding methods include solvent debinding, thermal debinding, catalytic debinding and so on.

Methods:

? select appropriate debinding method according to the feed;

? observe green part’s weight change in the heating process, find out the intense thermal decomposition temperature of binder, and develop the best debinding cycle;

? choose right debinding atmosphere to control the carbon content of product.

4.Powder Injection Molding -Sintering Control 

Deformation in sintering process is mainly caused by uneven density distribution of green part, temperature gradient inside sintering equipment, different sintering atmosphere choice, creep deformation caused by gravity and the friction between product and sintering furnace. During sintering, the following two points should be achieved:

? reduce the temperature gradient inside sintering equipment;

? select appropriate sintering atmosphere according to the dewpoint and reducibility of atmosphere.


Keywords in the article: Powder Injection Molding
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