Because the AM part is so near to net shape, it might seem as though machining it to its final form is a minor or fleeting concern. Far from it, says Gunnink. The team had machining challenges.
For example, positioning three parts on the build plate created a staggered configuration that caused the EDM wire to begin cutting one part while it was finishing the cut for another. Then, because the EDM cycle for that actual part did not line up with the first cut, the result was a slot in the OD of the part that caused problems when this face was turned to finished tolerance. The interrupted cut damaged a tool. (Other than this, however, turning went very well.)
In addition, the “tree” supports proved difficult to mill away. They bent instead of breaking. Meanwhile, tools broke because of built-up edge. Part of the problem, Gunnink admits, is that heat treating was overlooked. Delcam received the parts from the additive supplier without realizing that they had not gone through this step. With heat treating, the trees would have been less ductile and likely would have been easier to mill away. What this points to, he says, is the need for planning at the beginning of the additive process and clear communication throughout its steps.