Optimization of fatigue strength of selective inhibition sintered polyamide 12 parts using RSM

Mesfin Sisay,Esakki Balasubramanian

doi:10.1051/mfreview/2020020

Abstract

Selective inhibition sintering (SIS) is a powder based that fabricate functional parts through fusion of powder bed on a layer by layer basis. Being a new fabrication method, the correlation between process variables and part properties are not fully comprehended. Polyamide 12 (nylon 12) is one of the widely used materials in powder based AM processes including SIS. Therefore, in this work, the effect of critical SIS process parameters on the fatigue behavior of polyamide 12 parts was experimentally investigated, and the parameter settings were optimized to maximize fatigue strength. The number of experimental runs was determined based on Box-Behnken design, and specimens were fabricated as per ASTM D7791. Specimens were tested by subjected them to fluctuating loading at a frequency of 3 Hz. The test results were analyzed using Minitab statistical analysis software. From the ANOVA result, it was identified that the fatigue life of SIS parts is significantly influenced by layer thickness, heater temperature, and heater feed rate. Optimization of process variables settings was performed using the Minitab response optimizer and maximum fatigue strength of 17.43 MPa was obtained. The verification experiment resulted in 17.93 MPa fatigue strength which is comparable to the predicted value and with the result from the literatures.

Highlights

Additive manufacturing (AM) processes are superior over the conventional fabrication methods in that they are not limited by geometric complexity of the part, their fabrication time and cost is relatively shorter and cheaper for low production volume [1]
Having determined the starting stress amplitude; the remaining stress amplitudes were calculated from the ultimate tensile strength
Based on the study the subsequent deductions have been made. – Based on Box-Behnken design, the fatigue strength for 29 datasets was tested experimentally and the prediction model was obtained through fitting second-order response surface model to the measured data

Summary

Introduction

Additive manufacturing (AM) processes are superior over the conventional fabrication methods in that they are not limited by geometric complexity of the part, their fabrication time and cost is relatively shorter and cheaper for low production volume [1]. Because AM does not require any tooling while fabricating parts with intricate details and comparing with conventional fabrication techniques it reduces the product lead time by about 60% [2]. Selective laser sintering (SLS) is the most widely used powder-based AM process for its applicability to processing a wide range of engineering materials including polymers without requiring support structure [3]. SLS uses a CO2 laser as a heat source for sintering the powder layer and build a three-dimensional solid [4,5]. The high power laser heating element incurs cost for SLS to build part which can be significantly reduced through replacing it with a low cost heating element [6]

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