Design for Additive: 7 Rules for Making Your Part Printable in Metal

Open a CAD file and almost anything looks printable. It uses gravity and thermal control during the layer-by-layer deposition of metal, with resistance in the form of a powder bed. Most metal print problems are detectable by an experienced eye on the screen. For success in metal additive manufacturing, follow these 7 rules.

Rule One: Keep Overhangs Steep Enough to Print Without Supports

Metal parts need a support structure. Surfaces built beyond a 45-degree angle require support and waste print time. Support structures often leave unwanted print artifacts. Designs can be self-supporting to reduce print time and improve part quality. Circular holes tend to print poorly, whereas teardrop or diamond-shaped holes usually result in better prints.

Rule Two: Choose the Build Orientation Before Finishing the Design

Where the part sits on the plate matters a lot. It changes how many supports are needed, how rough each face ends up, and how much the part might warp. Tall parts print slower than ones lying down. So pick a likely orientation early, then draw the part with it in mind.

Rule Three: Respect Minimum Wall Thickness and Feature Size

Thin walls and tiny features don't always make it. Some warp, some snap, and some just don't build. The safe minimums depend on the alloy and the machine, so ask the printer for its numbers rather than guessing. Keep it thicker where it counts and thinner where it doesn't.

Rule Four: Keep Thickness Changes Gradual and Round the Corners

Printing heats and cools metal fast, and that leaves stress behind. Abrupt jumps from thin to thick, sharp inside corners, and big flat areas are where parts tend to warp or crack. Smooth the transitions, add generous fillets, and the stress spreads out. The part comes off the plate in better shape.

Rule Five: Give Trapped Powder a Way to Escape

Powder fills every hollow in a build. If a cavity is sealed shut, the loose powder stays trapped inside. Channels and pockets need openings big enough to empty them, plus a way to flush them. Forget this one and a good design can turn into a very expensive paperweight.

Rule Six: Leave Extra Material on Surfaces That Will Be Machined

Printed surfaces are typically rougher than those that have been machined. Therefore, extra metal should be provided in areas that will require machining. This includes features like bores, sealing faces, threads, and tight tolerance features. As part of your plan, consider the fact that processes like heat treatment and hot isostatic pressing should come before machining.

Rule Seven: Make Sure Supports Can Be Reached and Removed

Supports have to come off. One buried inside a narrow channel is going to stay there. Check that tools can reach every support, and that pulling them won't damage thin features. A small redesign here can save hours of hand finishing.

How Additive Manufacturing & Engineering Helps Make Parts Printable

Additive Manufacturing & Engineering, known as AME, is a metal additive manufacturing shop in Huntsville, Alabama. It prints with laser powder bed fusion on an EOS M400, with a build volume up to 400 mm per side, in Inconel 718 and GRCop-42. AME doesn't design parts. Its FAQ says it makes sure a part is ready for printing and works through an iterative design process with the customer. To get started, customers can send:

• A 3D file in STL, STP, or OBJ format

• The alloy and any property needs

• What the part does, and which surfaces matter most

• Quantity and timing

FAQs

What is design for additive manufacturing?

Most machines don't support additive manufacturing, but the newer systems do. Metal printing parts require designers to consider build time rather than cutting time. Issues related to orientation, wall thickness, overhangs, powder removal, and post-processing need to be resolved. A metal printed part is most efficient when designed to be printable with minimal supports. Designers of additive manufactured parts will also likely end up with a simplified part that will ultimately weigh less than the originally designed part.

What is the minimum wall thickness for metal 3D printing?

There is no constant figure. There is a range, and that depends on the alloy used, the machine that prints the part, and the part itself. A majority of 3D print shops are able to print thin wall sections. These thin walls tend to fail and deform more often than not. 

Do all printed metal parts need support structures?

Not all, but most do. Faces leaning out past about 45 degrees from vertical usually need them, along with sideways holes and big flat undersides. Good design cuts them down, which saves print time, material, and cleanup. Supports get cut or machined off afterward. Fewer is better.

Can a part designed for CNC machining be printed without changes?

Not usually. Parts drawn for machining tend to have flat overhangs, sharp inside corners, and sealed pockets, and those cause trouble in a printer. Angled faces, radii, and drain holes often fix it. A printability check before the build catches most of the problems. Small edits go a long way.

Does AME design parts for customers?

No. AME says it doesn't currently design parts. What it does is make sure a customer's part is ready to print and work through the design with them, step by step. Customers should bring a 3D model in STL, STP, or OBJ format and a clear idea of the part's job.