Gas-assisted powder injection molding: A study about residual wall thickness

• Published in: Powder technology Vol. 239; pp. 389 - 402
• Main Authors: Kim, Donghan, Ahn, Seokyoung, Lee, Kye Hwan, Nambiar, Rajiv, Chung, Sang Won, Park, Seong Jin, German, Randall M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.05.2013; Elsevier
• Subjects: Applied sciences; Chemical engineering; Exact sciences and technology; Gas penetration depth; Gas-assisted injection molding; Miscellaneous; Powder injection molding; Residual wall thickness; Solid-solid systems; Stereolithography cavity; Powder injection molding; Stereolithography cavity; Gas-assisted injection molding; Gas penetration depth; Residual wall thickness; Computer simulation; Stereolithography; Powder; Penetration depth; Stainless steel; Injection molding; Thermal conductivity; Numerical simulation; Delay time
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2013.02.032

The effects of processing variables on gas penetration depth and residual wall thickness (RWT) of gas-assisted injection molding (GAIM) parts were investigated for polypropylene (PP) and 316L stainless steel powder feedstock (SUS316). The processing variables were melt temperature, shot size, gas pressure, and gas delay time. By using a Taguchi L9 array, the results were compared with the previous work. Mold material was also investigated by molding with both aluminum and Stereolithography (SLA) mold inserts at varying temperatures. The most significant parameter affecting RWT was melt temperature for PP and gas delay time for SUS316. Additionally for SUS316, it was found that gas penetration depth and RWT were decreased with increasing mold temperature. While both computer simulation and experimental validation were carried out, the results from simulations failed to consider the effect of thermal conductivity differences between SLA and Al cavities due to lack of a coupled analysis capability in its module. The significance of gas delay time makes cooling from the surface of the cavity more sensitive to gas penetration depth and RWT in GAPIM. As the gas delay time increases, more time for heat transfer is provided to solidify the injected feedstock on the cavity wall. This directly affects the RWT and associated thickness of the frozen layer. [Display omitted] ► The most significant processing parameter for controlling RWT is gas delay time. ► RWT was thicker and more uniform with an Al cavity than the SLA cavity study. ► Gas penetration depth and RWT decreased with increasing mold wall temperature. ► Due to thermal conductivity, coupled analysis for filling process is essential.