Experimental investigations for dimensional accuracy and surface finish of polyurethane prototypes fabricated by indirect rapid tooling: a case study

Abstract

In this research work, an effort has been made to study the influence of selected input parameters on the dimensional accuracy (linear as well as radial) and surface finish of polyurethane prototypes fabricated by vacuum casting (VC) process as a case study. The master pattern required for making a silicone mould has been fabricated by fused deposition modelling and its surface finish has been enhanced by chemical vapour smoothing process. Maximum shrinkage of 2.29 and 4.77% has been observed in the selected linear and radial dimension, respectively, after the VC process. Optimal parameter settings that were different for both the dimensions as well as surface finish have been obtained using Taguchi's L18 orthogonal array. Finally, parameter setting that simultaneously minimizes the dimensional deviation and surface roughness has been found out using response optimization module of Minitab 17 software and the results obtained have been verified by performing the confirmation experiments. The tolerance grades for the selected dimension of the prototypes were found to be acceptable as per the ISO standard UNI EN 20286-I (1995) and DIN16901 for plastic materials. In addition, the C pk value greater than 1.3 indicated that the proposed process is highly capable. The surface finish and dimensional accuracy of prototypes are at par with the traditional moulding patterns, and hence, they can be used as end-products or plastic-based master patterns for investment casting applications.

Comparison of different additive manufacturing patterns on the performance of rapid vacuum casting for mating parts via the Taguchi method

“…The surface roughness of casting parts decreased from master pattern about 0.23% to 2.85%. In contrast with the previous study, the Ra values for casting parts in this study were slightly reduced from the master pattern [8]. From the findings, the surface roughness of casting parts may increase or decrease slightly from the master pattern, depending on the type and properties of the material.…”

“…These parameters were selected after several trials and errors during preliminary testing were performed. The range of these selected parameters are also in line with other studies [7,8,16]. Selection of suitable orthogonal array (OA) depends on the total number of degrees of freedom (DOF) of the processing parameters and levels.…”

“…From the findings, the surface roughness of casting parts may increase or decrease slightly from the master pattern, depending on the type and properties of the material. The values of the surface roughness of casting parts produced using the master pattern that had undergone chemical vapour smoothing (CVS) processing were 0.319μm -0.667μm [8] and 0.455μm to 0.593μm [7] with ABS as casting material. It can be concluded that the casting parts produced from the master pattern with CVS processing showed a lower value of surface roughness compared to this study.…”

“…For instance, Fused Deposition Modeling (FDM) patterns have been used to produce final parts, such as gear [6], Bluetooth cover [7], hip joints [8] and thin wall-cover [9]. FDM is the most popular AM technique for constructing prototypes and parts that can be used directly as final products [7,8,10]. On the other hand, application of SLA patterns has been widely adopted in the investment casting process.…”

“…The Taguchi method was adopted in order to obtain optimal process parameters for the vacuum casting process. Based on previous studies, the Taguchi method was successfully utilized in the optimization of the vacuum casting process [7,8,16,17].…”