54 Years ago, we explored the possibility of producing our venting steel (Vortex) using the AM process. However, after extensive discussions with leading metallurgical experts worldwide, we found that the method of utilizing powdered metal (PM), pressed in a tool under significant pressure, followed by sintering and heat treatment to achieve a hardness of 420 Hv (43 HRc), was far superior to the AM process. This alternative approach proved to be more effective in creating higher quality and stronger mold and die parts. This has major advantages in plastic, wax molding (investment castings) and venting die cast tools. Here's what we discovered about high tonnage pressed steel, including H13, 420 stainless, P20, and Vortex, in comparison to additive manufacturing (AM) within the mold and die arena. 2. Surface finish Resembling a sand-casting, AM parts are too rough to use in a mold or die and therefore require post machining. Surface roughness is created in the layer by layer build up process of AM. 3. Dimensional accuracy, part distortion and cracking Residual stress buildup in the part is due to the nature of the AM laser sintering process. Sintering the powder in layers can also cause severe warpage and cracking of the mold or die part. Sometimes cracking happens much later during the heating and cooling cycles or ejection of the part during the plastic injection molding or die casting process. Even if the roughness problem (mentioned above) can be fixed in the future when better finishes become available, the dimensional accuracy and part distortion demand that the parts be made larger than needed, which means they still will need to be CNC machined. Even the newest thin layer build-up technology of DMLS or direct metal laser sintering still has these problems. 4. Mechanical properties Anisotropy is the structural property of being directionally dependent, a characteristic inherent in additive manufacturing. In contrast, isotropy, found in materials like forged steel and traditional mold and die steels, implies homogeneity in all directions. Unlike traditional mold steel, which undergoes a rolled or highRUSS BOWEN President Molder's World, Inc. ARTICLE TAKEAWAYS: • Considerations for producing stronger mold and die cast dies • Approaches specific to investment castings, plastics and venting die cast tools A COMPARISON OF TRADITIONAL STEELS VS ADDITIVE MANUFACTURING FOR MOLDS & DIES 1. Size, number, and placement of the pores in venting inserts The size of the slots or pores in AM parts tend to be much larger and not as many due to the strength needed to keep the part from failing. Larger pores or slots can also lead to poor part finish, premature clogging and part ejection problems (sticking). By comparison, Vortex can be made in large blocks with 25% porosity and pores that are 7-micron average diameter throughout the steel. That means a 4” x 4” molding surface (which is 16 square inches) has 4 square inches of venting pores on the surface. These pores are interconnected and evenly distributed throughout the material. Having small 7-micron pores is critical for part quality and release. Larger pore sizes for blow and vac-forming can also be made. We are asked all the time how our porous venting mold steel, Vortex® compares to additive manufacturing (AM) for venting molds and dies. AM is also known as direct metal laser sintering (DMLS) and 3D printed metal parts.
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