KRYTON Metals Blog

Understanding Metal Spinning: Conventional vs. Shear Forming

Metal spinning is a common metallurgy process that turns a blank workpiece into an axially symmetrical part or component with a hollow inside. Machinists use lateral force to press rollers into their workpieces on a high-speed spinning mandrel. The result is a tailored shape that can be used in countless applications.

That’s because spun metal doesn’t lose its material volume or density during production. Instead, the workpiece is subjected to both compressive and tensile forces to achieve the desired effect. And while certain types of metals may react differently to spinning or sustain a minimal decrease in thickness, the overall characteristics of the finished product are indicative of this less invasive machining method.

 

What is metal spinning used for?

Also known as spin forming, metal spinning is usually performed by hand or with an advanced CNC lathe, and it’s one of the most beneficial methods when rounding metal components for practical and/or decoration purposes. In many large scale metal fabrication projects, however, the lathe can become automated. In turn, that helps to accommodate precision, consistency, product complexity, and lead time specifications.

In fact, metal spinning is often the preferred machining technique for a wide range of manufactured products, from common household goods and durable cookware to specialty instruments and aerospace parts. Meanwhile, nearly any ductile metal can be spun by skilled hands, including high-strength alloys. That’s why you’ll find spun metals in modern architecture, innovative art, contemporary lighting, and countless public amenities.

DID YOU KNOW: Despite the frequently interchanged name, conventional metal spinning and shear forming are two entirely different CNC machining processes.

 

Metal spinning vs. shear forming

Whether the blank is flat or a preformed metal sheet, it’s important to understand the differences between conventional metal spinning and shear forming. So, let’s go over the basics:

#1. Conventional Metal Spinning

Rollers push the material over the mandrel’s contour, leaving the material thickness at a constant throughout the process. The workpiece depth thereby increases as the diameter is reduced, making conventional metal spinning one of the simplest and most affordable tooling techniques available.

#2. Shear Spinning/Forming

This technique relies on rollers exerting enough downward force to stretch the workpiece over the mandrel contour. Thus, the material thickness is much less than the original blank, while the overall diameter remains intact. The workpiece strength and hardness generally receive a boost as well.

Accurate shear forming needs robust tooling structures and precision machining techniques. As such, the manufacturing method you choose can impact more than just the dimensional accuracy and/or finish of your machined part.

Shear forming instead of conventional metal spinning means more friction on the workpiece and mandrel. So, adequate cooling is always necessary to mitigate the heat that it generates. Be sure to ask your machining team which coolants are best for the metals and processes you’re using.

 

Common types of spun metal

Metal spinning usually requires a specific variety of materials, including soft, malleable, and ductile options such as:

  • Aluminum
  • Titanium
  • Bronze
  • Copper
  • Steel
  • Brass
  • Hastelloy

Because this machining technique is primarily used to fabricate hemispheres, parabolas, venturis, cylinders, and cones, it’s generally reserved for expert CNC machinists who know how to manipulate metals according to their innate properties. In turn, a unique design emerges despite the obvious benefits and drawbacks of the process.

 

The Pros and Cons of Metal Spinning

Not only is metal spinning an ideal machining method for prototype design and innovative product development, but it also involves the following advantages and disadvantages:

Pros

  • Metal spinning uses the entire sheer metal disc to create the finished product.
  • Most unused scrap metal gets recycled by conservative CNC machine shops.
  • Spun metal projects typically produce less waste than conventional metal forming.
  • In general, the overall tooling costs are low compared to other machining methods.
  • Manufacturing simplicity means lower costs for production and mass distribution.
  • The technique is more cost-effective than many other metal fabrication methods.
  • It can help shorten lead times on small-to-medium batch quantities.

Cons

  • The process may leave minuscule indents or small imperfections on the surface.
  • Due to the prevalence of imperfections, some parts may not pass inspection.
  • Product outcomes are generally dependent on staff training and expertise.
  • Maintaining a product quality consistency can be very difficult with this method.

NOTE: If you’re controlling spun materials in a CNC machine shop, be sure to check the offsets to determine the best machining conditions for each part.

 

Start your project today

Metal spinning is a quick and convenient way to transform raw materials into usable products for a variety of industries, and it’s one of the most affordable fabrication methods available as well. However, the process can be extremely complicated and dangerous, which means expert CNC machinists are always essential. Wondering if metal spinning might be right for your project? Contact KRYTON today.

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