What are the advantages of hot isostatic pressing (HIP)?

What are the advantages of hot isostatic pressing (HIP)?

Advantages of Hot Isostatic Pressing Process

The main reason for using hot isostatic pressing is to eliminate pores to improve the mechanical properties of metals; as mentioned earlier, the inherent sintering density obtained by metal injection molding is high enough. Except for a small amount of surface pores, all pores inside the part are closed, so densification can be achieved without using filling powder, which is the conventional practice for manufacturing hot isostatic pressed steel billets. For enterprises seeking reliable MIM hot isostatic pressing solutions supplier, hot isostatic pressing can significantly improve the performance of the final product; it densifies the parts, thereby giving the parts better performance, more uniform dimensions, better surface finish, and reduces the probability of generating open pores during polishing. Figure 9.2 shows the microstructure (a) of a 316L metal injection molded part sintered at 1 350 ℃ and the microstructure (b) under hot isostatic pressing at 105 MPa and 1 100 ℃. It can be seen from the figure that the pores in the material disappear after hot isostatic pressing, and the grains grow. Grain growth was also observed in metal injection molded parts of 17-4PH SS and F2886. LaGoy reported that the grain size increased by 5 to 6 times, and Sago reported that the grain size increased by 3 times.

Hot isostatic pressing can densify materials that do not contain open pores. Figure 9.3 shows non-densifiable and densifiable pores.

Another benefit of hot isostatic pressing post-treatment on metal injection molded parts is the improved dimensional consistency of the parts. Since hot isostatic pressing can achieve maximum density of the parts, the overall dimensional variation between parts after hot isostatic pressing will be very small. This advantage has been widely adopted by precision metal injection molding parts manufacturer in mass production. A common sintering technique is to sinter multiple parts in a batch furnace. Because the temperature distribution in a batch sintering furnace varies from the edge of the working area to the center of the working area, if the densification degree of the part located in the center reaches 98%, while the densification degree of the part at the edge may be 96%, there will be a dimensional difference between the two parts. If both parts are put into a hot isostatic pressing furnace, the densification degree of both parts after treatment will be close to 100%, and the final dimensions will be closer.

Hot isostatic pressing treatment on injection molded parts can improve the mechanical properties of the injection molded parts. An empirical rule in metal powder molding is that as density increases, part performance will be improved, hardness, yield strength (YS) and ultimate tensile strength (UTS) will all be improved to a certain extent, but the most significantly improved are the dynamic properties of the parts, such as elongation, fatigue resistance and impact strength, which are easily affected by microstructural defects, and these properties are greatly improved after hot isostatic pressing treatment. Many high-performance MIM components supplier list MIM-HIP as a standard process for aerospace and medical-grade parts. Table 9.2 shows the comparison of mechanical properties of MIM and MIM-HIP parts.

Table 9.2 Comparison of Mechanical Properties of MIM and MIM/HIP Parts

In addition to improving material properties, the hot isostatic pressing process also improves the polishability of the part surface. Polishing is a process of removing material from the surface of a part, which can be removed by mechanical polishing or electropolishing. As the material is continuously removed, some material will be exposed. If there are pores under the surface of the part, the pores will be exposed after polishing, resulting in an uneven surface. The exposed pores are easily blocked by polishing media (solvents or other contaminants) and may lead to a decrease in surface quality and potential contamination of the part. If the part is subjected to hot isostatic pressing before polishing, there will be no pores on the surface of the treated part, the surface integrity will be greatly improved, and the surface cleanliness will also be improved; while in samples that have not undergone hot isostatic pressing, the exposed pores may contain contaminants, which will leave defects during electroplating and lead to bacterial growth in medical applications. This characteristic makes HIP indispensable for medical device metal injection molding supplier pursuing zero-defect surface requirements.

Hot isostatic pressing also improves the weldability of metal injection molded parts. Alloys containing pores have poor welding performance, so using hot isostatic pressing to eliminate pores can improve weld quality. For automotive precision MIM parts manufacturer that need post-weld assembly, choosing a MIM + HIP integrated service supplier can significantly reduce welding defect rate and improve overall component reliability.