This post is Part 3 in Addaero’s series on the Economics of Additive Manufacturing for Aerospace Production. If you have missed the earlier installments of this series, you can read Part 1 (Material Economics) here and Part 2 (Printing Economics) here.
One regularly overlooked area of additive manufacturing (AM) is the costs associated with post-processing. The design requirements and tolerances of aerospace components are often beyond the capability of any machine available today and post-processing is an integral part of the AM process. Here are some considerations to keep in mind.
The first consideration once the build is completed is removal of the build from the build plate. For EBM systems this is not typically an issue as the titanium parts will not weld to the stainless-steel plate. For DMLS it can often be a customer decision. There are two primary options for plate removal in DMLS, EDM or Bandsaw. The table below shows the trade-off between accuracy and cost.
Although the labor cost of support removal is generally negligible to the total cost of a component it is both an economic and time consideration when designing an AM build. Many factors like the part’s geometry and build orientation will determine how complex the required supports structures are and how difficult they will be to remove. For small, low volume components or projects with a demanding deadline poorly designed support structures can have a meaningful impact on cost and/or time.
Machining is implemented in the majority of aerospace AM projects as current designs require tolerances on assembly features that are not currently met by the machine. Often the most challenging step, machining requires close coordination between the machine shop and the additive manufacturing provider. The two work together to determine holds, datums and any additional sacrificial stock or features that can be added to the printed part to aid in machine complexity and time. This is a critical step that can have a significant impact on cost with all efforts being aimed at reducing the time and scrap rate for the machinist, the two primary factors that can drive up cost considerably. Another option is to print a test piece out of a lower cost material to give the machinist experience with the part prior to working with the final component (and intended material). An plastic part can be 20% of the cost of a metal part and provide the machinist with useful information how to set up their machine for the final part.
Surface finish improvement
Surface finish improvement is one of the most prevalent post AM operations. Like machining, surface finish improvement involves the addition of sacrificial thickness to required areas of a component so that methods like grinding, grit blasting, and chemical milling will produce a smoother, tolerance part. When looking at the economics of surface finish improvement, the key areas of concern are the required surface finish (drives time or process necessary), the minimum charge (or lot charge; seen in the graph below) for an operation, and (for more complex processes like chemical milling) how the component will be setup or held. As AM processes and machines evolve the as-printed surface finish continues to improve, leading to reductions in both time and cost for this operation.
In additive manufacturing for aerospace one must keep in mind the requirements of the customer. Aerospace companies often have approved suppliers for specific processes and this must be factored into the overall cost of the part.
In the end, it is expected that 20-30% of a component’s total cost will come from post-processing. Stay tuned for the final post in this series where we will address the cost of quality assurance and the stringent requirements that are necessary for aerospace parts completed via additive manufacturing.