Metal spinning, also known as spin forming, is a metalworking technique that uses a tool or die to shape a metal disc or tube into an axially symmetrical component by rapidly rotating it.
This method is similar to wheel-throwing pottery or woodturning, but instead of clay or wood, metal is used.
The spinning method is effective on various metals, and this versatility is a significant advantage of the process. Additionally, this approach can cure several metals, making it a popular choice in numerous industries.
Let’s get straight to the point
Metal spinning, or spin forming, is a versatile metalworking technique used to shape axially symmetrical components like spheres or cones from various metals.
The process, which can be done manually or with CNC machines, is popular due to its cost-effectiveness, speed, and design flexibility. Common metals used include stainless steel, aluminium, copper, and titanium, each offering unique benefits and challenges.
While metal spinning excels in producing seamless, high-quality parts, it can face issues like defects, consistency, and safety risks. Despite these challenges, it’s widely applied across industries like aerospace, construction, and medical devices.
What is Metal Spinning?
Metal spinning is an efficient and versatile process used to create spherical, conical, or hemispherical components.
This process is particularly advantageous for producing parts with intricate geometries and thin walls, such as pressure vessels, fuel tanks, and aircraft components. The process begins by clamping a flat metal ring or sheet onto a mandrel or chuck.
The metal is then shaped by applying pressure using a spinning tool, which can be either a hand tool or a lathe. The tool is typically made from a hard material like diamond or carbide and is shaped to fit the exact specifications of the desired final product.
Manual Metal Spinning
Manual metal spinning is a traditional approach where the metal is shaped by hand using a spinning tool.
This method has been used for centuries to create various metal items, including pots, pans, and decorative pieces. In modern times, manual spinning is still used to produce unique metal components for various industries.
CNC Metal Spinning
CNC metal spinning utilises computer numerically controlled (CNC) machinery to automate the metal shaping process.
This method offers significant benefits in terms of precision and repeatability, ensuring that each part is manufactured to exacting standards. CNC metal spinning is widely used in industries that require high-quality, consistent components.
Hydroforming
Hydroforming is a subset of metal spinning that uses high-pressure fluid to shape the metal.
This technique allows for the creation of intricate patterns and designs that are not achievable through traditional metalworking methods.
Hydroforming is highly efficient and produces parts with a high degree of accuracy and repeatability.
Types of Metals for Metal Spinning
Various metals are suitable for metal spinning, each offering distinct advantages and challenges. Below is a rundown of some of the most common metals used in metal spinning, along with their usual applications and unique difficulties.
Stainless Steel
Stainless steel is often chosen for applications requiring resistance to corrosion and high temperatures. It is particularly effective for creating large, deep vessels without seams, making it ideal for use in the kitchen and medical fields.
However, forming stainless steel can be challenging due to its work-hardening properties. Austenitic stainless steel is more prone to work hardening than ferritic types, which can be mitigated by periodically annealing the material during spinning.
Carbon Steel
Carbon steel is an inexpensive and malleable material commonly used in metal spinning. Its workability can vary depending on the carbon content, heat treatment, and any additional alloying elements.
While both cold-rolled and hot-rolled carbon steel can be spun, cold-rolled steel is generally preferred for its ease of use. To enhance its corrosion resistance, carbon steel can be painted after spinning.
Galvanized Steel
Galvanised steel is carbon steel that has been coated with a layer of molten zinc to improve its corrosion resistance. The spinning process typically does not damage the zinc coating, so additional corrosion protection is not necessary unless the item is cut after spinning.
Aluminum
Aluminium is highly favoured for metal spinning due to its malleability, corrosion resistance, and high strength-to-weight ratio. While unalloyed aluminium is the most malleable, it is not very strong mechanically, so alloy grades are usually preferred.
Aluminium is less prone to work hardening, making it easier and more cost-effective to spin compared to stainless steel.
Copper
Copper is an excellent choice for metal spinning because of its high formability and resistance to breaking or tearing during the process.
Its antibacterial properties, along with its thermal and electrical conductivity, make it suitable for various medical and industrial applications. However, copper lacks the mechanical strength required for some applications, where bronze or brass might be better alternatives.
Inconel
Inconel is a superalloy known for maintaining its mechanical strength and oxidation resistance even at extremely high temperatures.
Due to its tendency to work hard, Inconel often requires continuous heating during spinning to remain formable. Modern techniques focus heat with a laser to avoid heating the entire component.
Hastelloy
Hastelloy is another superalloy with exceptional resistance to corrosion under extreme stress. Like other superalloys and stainless steels, Hastelloy may require multiple annealing steps during spinning due to its strong work-hardening tendencies.
Titanium
Titanium is renowned for its low density, high strength-to-weight ratio, and excellent corrosion resistance.
These properties make it a preferred material for aerospace applications. However, titanium is notoriously difficult to shape, often requiring heating during spinning, typically with a blow torch, to facilitate the process.
Bronze
Bronze, an alloy of copper and tin, offers greater toughness than copper, making it more challenging to shape.
However, it retains some of copper’s advantages, such as strong thermal conductivity and better mechanical properties, including tensile strength. Bronze also has superior corrosion resistance compared to copper.
Brass
Brass is an alloy of copper and zinc, known for its corrosion resistance and biofouling prevention due to its high copper content. Brass is easy to spin because of its excellent formability, and its bright, lustrous finish makes it popular for decorative items like lampshades.
Benefits of Metal Spinning
When compared to other metal forming methods, metal spinning offers several significant benefits:
Cost-Effectiveness and Speed
Metal spinning is a cost-effective process due to its high speed and minimal material waste. It can be further optimised with robotic arms for loading and unloading the machine and post-processing the component, such as trimming. Additionally, CNC spinning machines can automate the process, reducing costs and improving efficiency.
Shorter Cycle Times
For prototypes or custom components that need to be produced quickly, metal spinning offers shorter cycle times compared to other methods. Automated systems eliminate downtime between processes, maximising production efficiency.
Design Flexibility for Axisymmetric Parts
Metal spinning is highly versatile, allowing for the creation of complex axially symmetrical components that would be challenging to produce using other methods like stamping or drawing. Multi-part specialised mandrels can also be used to create components with captive geometry.
Seamless, High-Quality Construction
Metal spinning produces seamless components with uniform thickness and a smooth surface, making it ideal for applications like pressure vessels, where integrity and reliability are critical.
Challenges of Metal Spinning
While metal spinning offers numerous advantages, it also presents some challenges:
Snarl
Snarl refers to defects in the spun component, such as creases and folds caused by the material refolding. These defects can result from improper tooling, over- or under-lubrication, or poor technique, but they are often due to design flaws and manufacturing difficulties.
Consistency
Achieving consistency in manually spun parts can be challenging, as it is difficult for the operator to apply the same pressure and follow the same forming procedures every time. However, CNC metal spinning machines can overcome this issue by ensuring precise and consistent production.
Ovality
Maintaining a high degree of circularity in spun components can be difficult due to material spring back and uneven pressure application. CNC spinning machines with multi-point pressure capabilities can mitigate these issues, though some degree of ovality is often unavoidable.
Long Processing Times
Some components may require multiple passes to achieve the desired shape, which can lengthen processing times. This is in contrast to faster methods like metal stamping or drawing, which can produce parts more quickly.
Safety Risks
Manual metal spinning, in particular, can be risky due to the need for the operator to be in close proximity to high-speed spinning metal components. While CNC spinning machines can reduce these risks, they are often more expensive and may not always be justified for smaller operations.
Applications of Metal Spinning
Metal spinning is widely used across various industries due to its versatility and ability to produce high-quality components. Some of the most common applications include:
- Aerospace and Aeronautics
- Agricultural Tools
- Home Appliances and Equipment
- Architecture, Construction, and Building
- Vehicle Components
- Chemical Processing Equipment
- Commercial Lighting
- Medical Devices
- Railway Components
- Amusement Devices
Conclusion
Metal spinning is a versatile and efficient metalworking technique that offers numerous advantages over other methods. It is particularly effective for producing axially symmetrical components with complex geometries and smooth finishes.
While it presents some challenges, such as maintaining consistency and circularity, the benefits of cost-effectiveness, speed, and design flexibility make it a valuable process in various industries.
Whether working with stainless steel, aluminium, titanium, or other metals, metal spinning provides a reliable and efficient method for creating high-quality, durable components.
