In the process of understanding powder metallurgy technology, we came across metal powder injection molding technology. Unexpectedly, it is completely different from the ordinary molding process, and it will be relatively much easier to manufacture parts with complex geometry, high performance and high precision in large quantities, thus pushing powder metallurgy manufacturers to obtain breakthroughs.
There are many processes involved in metal powder injection molding (MIM). While you may have been in the industry for a few years, you may not know all the processes. Share some questions about selecting process parameters for metal powder injection molding, including:
Metal powder injection molding
1、How to choose metal powder?
The relationship between powder particle size and sintering density
Sintering density of metal powder at four different sintering temperatures, PF-3F, PF-5F, PF-10F and PF-15F. It can be seen that in a certain temperature interval, the higher the sintering temperature, the higher the sintering density, beyond which the sintering density does not change much. In a certain range, the larger the particle size of the powder, the greater the sintering density.
Metal powder microstructure
Spherical powder is conducive to increasing the vibration density, increasing the powder load, increasing the sintering density.
2、What is the ratio of metal powder to binder?
MIM feed solid content-relative viscosity curve
It shows that the viscosity increases with the increase of solid content, when the solid content of the feed injected material reaches 62%, its viscosity rises sharply, i.e., the solid content (maximum) limit is 62%.
When the binding agent is insufficient, voids will appear between the powders, affecting the mechanical strength of the products; when the binding agent is too much, the solid content is too low, which will affect the degreasing, sintering and product shrinkage. Large.
3、How to choose the design of gate and overflow hole?
Comparison of advantages and disadvantages of gate design
The gate should be selected in a larger space, which can reduce the friction of the melt feeding mold reduces the injection pressure and reduces the possibility of product deformation. In addition, the design of overflow holes is also important. Overflow holes are used to load cold material during the injection process to ensure product uniformity.
4. What is the effect of C, N and O on sintered 316L?
C, N, O in the sintering process can adversely affect the sintering of 316L. Carbon has a strong affinity for chromium, the formation of Cr23C6, so that the chromium content in the solid solution at the grain boundary is reduced, the formation of chromium-poor areas. Nitrogen in stainless steel supersaturated dissolved and precipitated in the form of Cr2N at grain boundaries during the cooling process, which reduces the corrosion resistance of MIM products; oxygen and chromium can form an oxide film, Cr2O3 and the liquid phase wettability is poor, affecting the flow of the liquid phase, hindering the densification process.
5、How to choose the sintering atmosphere?
The effect of sintering atmosphere on density
Ar+H2 and vacuum atmosphere sintering density is high, N2 atmosphere sintering density is low. In addition, in the sintering process, the slower heating rate is conducive to the formation of regular grain boundaries and reduce the isolated closed pores, increase the sintering holding time, the sintered density increases slightly, but the mechanical properties decrease (grain growth). Therefore, increasing the sintering plateau at 800°C and decreasing the heating rate to 1100°C is a good choice!
Powder Metallurgy Manufacturers
In the whole process of metal powder injection molding, powder metallurgy manufacturers not only need to prepare a certain amount of powder for processing, but also need to add more binder to the powder. Therefore, both powder and binder should meet the requirements, otherwise it will affect the molding of powder metallurgy products.
Which should be used 10um ultrafine near-spherical powder as raw material, the process from mixing to degreasing and sintering is complicated, the process requirements are strict, especially the degreasing and sintering time is long, which is the main reason for the high manufacturing cost of powder metallurgy manufacturers. The amount of binder must be sufficient, otherwise it is difficult to achieve the corresponding performance.
For this reason, powder metallurgy manufacturers have developed a simplified method, i.e., flow temperature pressing technology, which combines the advantages of metal powder injection molding technology on the basis of temperature pressing of metal powders; then, by adding appropriate amounts of coarse and fine powders, and increasing the content of thermoplastic lubricants, the fluidity, filler, and molding properties of the mixed powders have been greatly improved.
As the mixed powder becomes a viscous fluid with good fluidity in the pressing process, it not only has the advantages of liquid, but also has high viscosity, which reduces friction and makes the pressing pressure evenly distributed and well transmitted in the powder. Because of this, the powder can flow to every corner without cracks in the pressing process, thus the density is greatly improved.
Currently, powder metallurgy manufacturers have extended the technology to precisely form workpieces with very complex shapes on conventional presses, which not only overcomes the shortcomings of conventional cold pressing in forming complex geometries, but also reduces the production costs of injection molding technology. Harbermetal.com is a professional manufacturer and solution provider of metal powder injection molding process (MIM) and PM process