Design Considerations for Metal Spun Parts
What is Metal Spinning: Metal spinning is a method of forming sheet metal, or cylinders, into hollow cylinders, cones, venturis, reducers or other circular shapes using a combination of rotation and force. A metal spinning lathe is used whereby a tool is mounted to a spindle and a blank is held against the tool. As the tool and blank spin, rollers form the material down around the tool to create the part.
While any metal ductile enough to be cold formed by other methods can be spun, Church Metal Spinning is primarily focused on austenitic (e.g., 304, 316 and 321) ferritic (e.g., 409,439) stainless steels and low carbon steel (ASTM A1008, 1011). In this article, we’re mainly discussing stainless steel parts, but the considerations are valid for other materials.
Stainless Steel is Challenging: Forming parts from the austenitic stainless steels is more challenging because of it’s greater initial strength, abrasiveness and great susceptibility to work hardening. Church Metal’s mix of machinery and expertise help provide our Customers’ with better results in terms of consistency of parts across production runs, surface finish and overall part cost. While we do not provide Design Engineering, we do provide Customer’s with insight into how small changes may improve the manufacturability of a part.
Tooling Must be Up to the Challenge: The first step in providing a high quality austenitic stainless part is by starting with a high quality spinning tool (block, chuck) used to form the part.
- Designed to account for material spring back
- Hardened to withstand the power required to form the part and withstand the abrasiveness of the material. Church Metal generally uses A2 material and after machining hardens the material to 60 Rockwell C.
Design Considerations: Church Metal may offer suggestions to improve the manufacturability of the part. Manufacturability can be improved by increasing/decreasing transition radii, modifying straight (parallel to center line) features to have a defined draft angle or converting to a seamed design (butt welded cylinder – using either TIG or laser seam welding). Other design considerations include:
- Material thickness variation: A seamless spun part will result in a decrease from the initial material thickness from 10% to 50% depending on the design of the part and methodology used to form. This can be positively impacted by increasing the number of tools/setups to make the part or including an anneal to reduce work hardening.
Seamed cylinder blanks can also be used. The advantages include potentially lower cost and that a longer part can be produced from spinning from a disc. Spinning a cylinder down to a smaller diameter results an increase in thickness thru the reduced end of the cylinder.
- Impact of Work Hardening: As austenitic stainless steel is cold worked, the material work hardens relatively quickly. Church seeks to reduce the number of spin strokes, to reduce the impact of work hardening. Designers should be aware that:
- If a part is spun thinner, the part will be less round after removal from the tool;
- Cutting features thru the edge or flange may cause the part to release malforming the finished diameter of the part;
- Properly planned annealing can reduce the impact of work hardening
- Conical Shapes: Conical shapes can be spun deeper than other cylindrical shapes if a 30 degree included angle or greater can be used. This type of spinning results in a defined material thickness, with greater reduction occurring the tighter the angle. For a part spun from 11ga, a 30 degree angle would result in a wall thickness of 0.028” while a 60 degree angle would result in a thickness of .058”.
- Good Material: Church Metal seeks out materials with the best forming characteristics and highest quality. While providing our Customer’s part with the material to specification is crucial, high quality material has a positive impact on overall cost by limiting scrap and rework caused by poorly performing material. Materials used for each part are tracked back to the original mill certification.
Examples of Spun Parts: Church Metal makes parts for industrial equipment, industrial process equipment, large engine air flow and guarding and architectural parts. Some examples of specific parts that we make now include:
- Heavy Duty Reducer: Spun from 10ga 304L stainless steel. Consultation with Customer allowed a 2-degree draft in the part, which allowed the part to be spun 11-1/2” deep with no anneal. The parts minimum thickness is 0.090”
- Air Flow Part: 20ga 321 stainless – thickness reduction of 35%; multiple forming operations with an anneal.
If you’re interested in learning how our stainless steel metal spun parts could be used for your business or products, please reach out to a team member who can provide you with more information or a quote.
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