Simple Solutions That Work! Issue 16

56 Contact: CHRIS BECK Chris.Beck@Innovative3DM.com PART GEOMETRY & PART DESIGN The AM process does not like “overhangs” on parts. This refers to a specific feature on a part hanging out in space with nothing underneath it to support it. Examples are boss or v-flanges that would be traditionally welded onto a part or built into a casting. These features need to have gussets or angles designed below them. They can be designed to be permanent or designed to be removed after the part is made. SURFACE FINISH Because the laser melts a straight line and the powder size varies; this can cause a rough surface finish. We like to tell our customers on average to expect a 250 Ra finish. With minimal work a Scotch Brite pad can bring this finish to 120 Ra. Most machined surfaces are 63 Ra or less. In the aerospace world this can be a problem because of air flow across turbine blades, veins, airfoils and swirlers. There are many post processing tricks to polish and get those surfaces to the desired finish. TOLERANCING Geometrical Dimensioning and Tolerancing (GD&T) seems to be a constant issue as this technology is only so accurate. Under normal conditions on a straight up and down feature the AM machine will hold .005” of diameter, length and true position. When the part is built at an angle the machine tolerance will open up to 2 or 3 times that it would be on a horizontal build and holes start to become oval shaped. In many instances we make parts without holes or make them undersized so that we can machine them later to hold tighter hole tolerancing and true positions. The design team can make or break an AM project with GD&T. DESIGN FOR ADDITIVE MANUFACTURING We build many parts that are a traditional casting design. The problem with this is that the part has not been modified for the AM process. In other words, the part will have features like bosses and flanges hanging out in space with no support structure underneath them. To accommodate this design, we add a support structure or some type of gusset design to support the geometry to make it a self- supported geometry. COST AND DELIVERY On average parts built by the DMLS process cost 2 to 4 times the price of a traditional investment casting. They will be as low as 25% the cost of traditional machining from solid billet stock. Deliveries average from 2 to 6 weeks including all post processing and machining. Parts that require X-ray, pressure test, and FPI may add additional time to delivery. SUMMARY Additive Manufacturing is here to stay. All of the large aerospace companies are adopting the technology. They are slow and cautious for flight approved hardware, but they are using it for R&D projects and other places that it makes sense for cost savings and deliveries. Machine work envelopes are getting larger and the development of multi-head lasering equipment is decreasing build time which makes it cost competitive. It’s not a technology that will take over mass production anytime soon but it can definitely make sense for low volume super alloy parts, prototypes, support tooling and fixturing. Reprinted with permission from the Part Buyers Authority.