Combination Parameter Strategy to Mitigate Geometric Deviation on SPIF UHMW-PE for Cranial Implants

Abstract

Single Point Incremental Sheet Forming is a promising technology to manufacture cranial prosthesis. It allows the possibility to produce complex geometries at lower cost and time than traditional forming or rapid prototyping techniques. However, this process is not commonly considered on the medical industry due to its lack of fulfillment of geometric accuracy and surface quality that are not able to reach the ASME or ISO tolerance standards stablished for medical devices. This study aims to evaluate the combinate effect of certain parameters process and conditions such as: depth step, dimensional geometric compensation, lubrication and external heat application to improve the geometric accuracy and surface quality on the final parts. External heat represented a key factor on geometric deviation and surface quality improvement, along with depth step 1mm and mineral oil lubricant, these parameters and conditions built the samples with best results. The lowest deviation achieved with the parameters and conditions, it was 0.1958 mm, in contrast with 0.8945 mm from the same sample manufactured in with the same values and conditions without external heat application. This reduction demonstrates the crucial role of heat application in geometric accuracy during ISF processes. So, it was possible to manufacture parts that met the tolerance of ± 0.2 mm for prostheses. Likewise, the surface quality was improved by the used of heat application combined with lubrication presence and depth step of 1mm generated the best results. The roughness reduction goes from 21.089 µm without heat, against 9.938 µm with external heat application, confirming the significance of heat presence in surface roughness mitigation. The results indicate that geometric inaccuracy and surface roughness quality can be controlled and mitigated to the point of accomplishing the tolerance and surface finishes stablished, by selecting the proper values of process parameters combined with external heat application and lubrication.