How to Design for 3D Printing in Steel
Written by: Andrew Thomas
The possibilities of 3D printing in Stainless Steel are extremely exciting. 3D printing your model in a metal such as Stainless Steel does require a few special design considerations due to its unique printing process.
Designed by GothamSmith
This tutorial provides five tips to help you design specifically for 3D printed Stainless Steel. Whether you're a jeweler creating a new line of designs or an engineer prototyping your revolutionary invention, following these tips will help you make the most of your 3D model.
HOW STAINLESS STEEL IS 3D PRINTED
Stainless steel is 3D printed using binder jet printing, and then infused with bronze to create the final product.
- Printing: The printer deposits thin layers of stainless steel powder onto a print bed and applies a liquid glue, or binder, to each layer to create your 3D model.
- Green state: Once the printing phase is complete, your model is in a fragile "green state" with the consistency of wet sand (since models are made of steel dust that has been glued together). It's important to consider the design of your model to ensure it can be handled during this temporary but pivotal phase.
- Sintering: Your model cures in an oven to melt away the binding glue.
- Blasting: The loose steel powder around your model is removed by blasting it with air.
- Infiltration: Sprues, which are passages that allow the bronze to infiltrate, are added to your model. Since your model is still in its green state, it is placed with sand, which acts as a support material. Your model is then infused with bronze at an extremely high temperature, producing your stainless steel 3D print.
Check out this rad video (no, we didn't make it in the '90s, but it was a while ago) to see the process in action:
TIPS FOR DESIGNING FOR 3D PRINTED STEEL
1. Support geometries during the green state
Because of the temporary fragility of your model during the green state, certain geometries can't be supported. Your model may print without a problem, but we may not be able to handle it before it's hardened (when infused with bronze).
For example, imagine a fishing rod trying to support a bowling ball; the long, curving and thin structure (what we call a wire) holding the large ball will easily break at its weakest point. In Stainless Steel, anything longer than 25 mm may have issues being too fragile and need to be supported.
To print geometries like this, you may have to print a support structure as well to hold it together and then remove the structure after you receive your model.
2. Support walls during the green state
The same is true for unsupported walls in Stainless Steel. Any large surface that is unsupported may need a geometrically stronger structure, like a lattice, to help it hold its own weight.
3. Round any external edges
Sharp external corners and "knife edges" can chip and crack during depowdering, handling, or heating while your model is in the green state. Rounding off the edges with at least a 1mm fillet will prevent your model from breaking. If you need to sharpen the edges, you'll be able to do so during your own post-production processes.
Sometimes designers are reluctant to make these kinds of adjustments to models because they're so used to seeing the preferred, hard-edged geometry of the 3D model. Hey, we understand. But, what a render (particularly one without smoothing) depicts is sometimes virtually impossible to create in reality. For example, if you look at the edge of your desk, you'll see that the edge is slightly rounded off; this not only protects you from uncomfortable scratches but also the edge of the desk from chipping.
4. Round any internal edges
The need to round edges is true not only for “knife edges“ that are convex and point outward from the model, but for concavities and sharp connections that are on the interior of the model as well. Sharp intersections and angles can crack and break, so rounding them prevents these issues and improves the overall structural strength of the model.
5. Provide adequate surface area at connection points
During the infiltration phase, your model is surrounded by sand. The sand acts as a support material to keep your heated Steel model from moving or sagging while it's infiltrated with bronze powder through capillary action. This turns the Stainless Steel into an alloy of about 60% steel and 40% bronze, although this may differ per model.
The infiltration process requires multiple Stainless Steel models to be sprued together so that enough material exists for the bronze to flow through. The bronze infusion starts at one end of the furnace and moves through your model, its parts, and all connected models. One way to think of it is as a tree, with water and nutrients traveling from the roots up the trunk into the branches and to the leaves.
If the connection points between parts of your model are too thin, they can't properly be infiltrated. Models with abrupt changes in the amount of material (such as designs which go from very thick to very thin material volume) may break during this process. Connection points points in your model should be smooth transitions and provide sufficient surface material.
The opportunity to make your own 3D printed Steel product is a true depiction of the endless possibilities and innovation 3D printing allows. Its strength and permanence as a material are wonderful rewards for the thoughtfulness you put in to the design of your 3D model. As you design for Stainless Steel, be sure to check our Design Guidelines and Pre-Print Checklist to make sure that your design is ready to print so you can upload it to order. Once you hold your product in your hands, you'll be amazed that it was once made of powder and glue!
Render images provided by The ExOne Company.
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