Distortion in Hybrid Additive-Subtractive Manufacturing

Additive manufacturing (AM) is becoming more commonplace as the process has many benefits such as being able to create complex geometries with lower material usage than other processes and do so much faster. Two issues are that the process has a low accuracy and surface compared to other processes. This can be compensated by machining the AM parts with platforms that can perform both the AM and machining processes coming to market. This raises whether the two processes interact with each other when performed on the same platform, compared to performing them separately. Experimental trials were performed to analyse the distortion, machining error and surface integrity of parts produced by machining parts directly after the AM process whilst still hot, after they have cooled down and which have been machined in the middle of the AM process as well as directly after it has finished as an interruptive process. It was shown that that hot machining resulted in a better surface integrity, whilst the cold distorted the least and the interruptive the most. The machining error was not conclusive. This was coupled with a proposed analytical and numerical model. The numerical model showed that the hot machining allows the deposited geometry to distort more when machined. The analytical model could accurately model the thermal process of the laser deposition process accounting for a range of energy losses (including determining the best method to calculate the absorptivity of a material) and using a new powder distribution model accurately determine the geometry of deposited material. This body of work should help give a fundamental understanding of how the strategy used when creating a part using a hybrid platform could affect the resultant part, and give a starting point to understand how these issues could be mitigated.