Metal Powder Injection Molding Technical Requirements for Testing and Evaluating Sintering Deformation in Forming Processes

 

Date：[2024/1/3]
 

In the powder injection molding process, a large amount of powder is used, which means that the final formed component will contain small pores. The size of the powder particles will significantly affect the internal structural performance of the component, such as porosity and grain size. Reducing the size of powder particles can improve sintering performance, but it will also increase the specific surface area and ultimately lead to an increase in the trend of oxygen concentration.
After powder injection molding, adhesive and sintering processes need to be carried out, and the adhesive scattered between the gaps of powder particles in these processes can cause changes in the shape of the formed part. In addition, due to the requirement of density, sintering must be carried out at high temperatures, and the sintering temperature is close to the melting point. At this time, it is necessary to consider the creep caused by gravity. The larger the size of the formed part, the greater the deformation it will produce. As a result, the required dimensional accuracy of the final part is difficult to guarantee. In actual production, the result of creep deformation at high temperatures is that the powder injection molding process can only be used for the production of lightweight small-sized components weighing less than 100g. Therefore, for the production of heavier large-sized components, it is necessary to find ways to suppress this deformation using powder injection molding technology, which is currently a huge challenge faced by powder injection molding technology.
For the production of lightweight small-sized components, in order to obtain high-precision and high-quality products, it is also necessary to accurately grasp the laws of this deformation behavior, and determine the sintering process parameters and the geometric dimensions of the billet before sintering based on the final characteristics of the product. The acquisition of the shrinkage law of product components during the rubber discharge and sintering process mainly involves the following two aspects:
(1) The shrinkage of product components during the sintering process cannot be accurately obtained solely by testing the thermal expansion coefficient through sampling. This is mainly due to the fact that the internal heat transfer of the sample during the sampling and testing thermal expansion process is completely different from that of the product components, and there may be significant errors in predicting the deformation of the components based on the measured thermal expansion coefficient. The best way is to test the overall deformation of product components in real-time during the simulation sintering process, using accurate, reliable, and efficient testing and numerical simulation methods to replace the current calculation of thermal expansion coefficient deformation and experience based repeated testing methods, thereby shortening the product development cycle and cost.
(2) During the sintering process, some unsupported parts of the product components may undergo downward bending deformation due to the influence of gravity due to material softening after reaching a certain temperature, as shown in Figure 5. For framed product components, after sintering, the side edges of the components often have a certain degree of concavity or convexity. From this, it can be seen that the influence of gravity can cause anisotropy in the shrinkage of product components and affect the final shape of product components. References 1-10 provide a detailed description of the influence of gravity in various sintering processes. In summary, whether all these deformations occur during the sintering heating process or the cooling process, as well as the specific temperature and magnitude of the deformation, are important parameters that need to be understood in the sintering process. However, these deformation parameters cannot be obtained through thermal expansion coefficient testing, and can only be accurately understood through overall measurement of the components.
In summary, the following issues need to be addressed regarding the shrinkage deformation of product components during injection molding sintering process:
1. Directly observe the overall dimensional changes of product components during the sintering process and the local bending deformation of components affected by gravity;
2. Adopting non-contact measurement methods to avoid the influence of contact measurement of top rod loading force on adhesive discharge and sintering deformation;
3. Adopt a large-area measurement method to directly test the deformation of the formed part, avoiding insufficient representativeness of the sample preparation;
4. Realize simultaneous measurement of two-dimensional deformation of formed parts or specimens, and have the function of simultaneous measurement of multi-point position changes;
5. Observe the changes in component dimensions under different heating systems (such as different heating and cooling speeds and constant temperatures);
6. Observe the effects of different atmospheres (vacuum, argon, nitrogen, hydrogen, etc.) and pressure conditions on the variation of component dimensions, as well as the effects of switching atmosphere conditions and constant pressure in different temperature ranges on the variation of component dimensions;
7. Simultaneously equipped with high-precision high-temperature thermal expansion coefficient testing function.