# Milling Parameters and Quality of Machined Surface of Wire Arc Additive Manufactured AISI 321 Steel

## TL;DR

This study examines how milling parameters affect the quality of surfaces machined from wire arc additive manufactured AISI 321 steel.

## Contribution

The paper reveals how ploughing and machining parameters influence surface roughness and process responses in WAAM-fabricated stainless steel.

## Key findings

- Surface roughness is reduced by decreasing the primary feed per tooth, but small feed per tooth causes ploughing and increases temperature and vibration.
- Tool run-out and uncut chip thickness correlate the radial depth of cut with process responses, and ploughing occurs at small radial depths.
- A small-diameter mill causes severe ploughing, and climb milling at high table feed leads to cutter offset.

## Abstract

Due to the unique microstructure and mechanical heterogeneity of austenitic stainless steel made via wire arc additive manufacturing (WAAM), its machinability differs significantly from that of rolled material. Accordingly, this study systematically investigates the influence of milling strategies on key process responses (cutting forces, surface roughness, vibration displacement, and temperature) to reveal the mechanisms of machining parameters during the milling of WAAM-fabricated austenitic stainless steel. The material used in this study is ER321 austenitic stainless steel. During deposition, the fusion zone cools more slowly than the transition zone; consequently, the fusion zone exhibits a hardness approximately 20 HV0.1 lower than that of the transition zone. Surface roughness is primarily reduced by decreasing the primary feed per tooth. However, when the primary feed per tooth is small, ploughing is induced, which not only increases surface roughness by 25% but also causes abnormal increases in temperature and vibration displacement. Nevertheless, ploughing has little effect on the total milling force, and the feed per tooth shows a positive correlation with the total milling force. Tool run-out and an increase in the uncut chip thickness lead to a positive correlation between the radial depth of cut and the key process responses. Moreover, ploughing also occurs when the radial depth of cut is small. The axial depth of cut has almost no effect on the machining process. Moreover, a small-diameter mill leads to severe ploughing, and at a high table feed, climb milling leads to cutter offset.