Chapter 1: What is Metal Spinning?
Metal spinning—also known as spin forming—is a precision metalworking process that transforms a flat, circular metal blank into a perfectly symmetrical round part. This is achieved by rotating the blank at high speed while applying lateral pressure with a roller against a shaped tool called a mandrel. The mandrel determines the final shape, while the roller gradually forms the metal over it to create the desired geometry.
Unlike other forming methods that cut away material, metal spinning reshapes the metal using controlled force, maintaining its integrity while achieving new dimensions. During the process, the blank experiences both tensile and compressive forces as it conforms to the mandrel. In some types of spinning, the metal thickness may reduce slightly—but this reduction is precisely managed to meet exact product specifications.
Precision Products Made by Metal Spinning
At USMS, metal spinning is more than just a manufacturing method—it’s a refined blend of engineering and craftsmanship. With origins dating back to ancient Egypt, the process has evolved from simple hand tools to highly advanced CNC (Computer Numerical Control) equipment, allowing for tight tolerances and repeatable accuracy.
During the Middle Ages, artisans used spinning techniques to create household and decorative items such as teapots, vases, and ceremonial trophies. These were crafted on wooden lathes powered manually by assistants turning a flywheel—a labor-intensive process that relied heavily on the skill of the craftsman.
Why Choose USMS for Metal Spinning?
Advanced CNC technology ensures accuracy and consistency
Traditional manual spinning expertise available for specialty parts
Ability to form complex round geometries without material waste
Controlled wall thickness and dimensional precision
Ideal for low-to-medium volume production with reduced tooling costs
Whether you need simple cones and hemispheres or more complex geometries, USMS Metal Spinning offers expert solutions tailored to your part’s shape, material, and performance requirements.
Chapter 2: Metal Spinning Machinery
Metal spinning machinery, also known as spinning lathes or flow forming machines, plays a central role in shaping flat metal blanks into cylindrical parts, cones, and complex round profiles. At USMS, we utilize both manual and CNC-operated spinning lathes that rotate the workpiece at high speeds while a roller gradually presses the metal over a mandrel to form it into its final shape.
These machines are compatible with a wide range of materials including aluminum, stainless steel, copper, brass, and titanium. The metal is shaped through applied pressure, not cutting, which retains material integrity and enables precise control of thickness, contours, and surface finish.
Key Components of a Metal Spinning Machine
A spinning system at USMS consists of several integrated parts, each critical to the performance, accuracy, and repeatability of the forming process:
Mandrel
The mandrel acts as the shaping tool and provides the internal profile of the finished part. It supports the metal blank during rotation and ensures uniform forming. Mandrels are made from various materials such as steel, aluminum, plastic, or wood depending on production needs. Lubricants like grease or wax are used to minimize friction and enhance surface finish.
Roller
The roller is a hardened tool that applies focused pressure to form the metal over the mandrel. It is guided either manually or by CNC to follow precise paths. The roller’s bearings ensure smooth operation, low heat, and minimal tool wear, especially when forming harder metals.
Tailstock and Follower
The tailstock holds the workpiece in position against the mandrel, while the follower—mounted on the tailstock spindle—applies even pressure to prevent shifting or slippage. This ensures consistent part dimensions and clean finishes during high-speed spinning.
Spindle and Headstock
The headstock contains the spindle, which is the rotating axis that drives the mandrel and workpiece. It houses the drive motor and gearing system, delivering the torque and RPM needed for spinning. A synchronized tailstock spindle ensures axial alignment and supports the rotating blank.
Lathe Bed
The lathe bed provides the structural foundation for the machine. It maintains alignment between the headstock and tailstock, absorbs vibration, and ensures stability throughout the forming process—especially important for heavy-gauge metals or high-speed operations.
CNC Metal Spinning at USMS
CNC metal spinning automates the shaping process using CAD-generated programs translated into G-code and M-code. These programs guide the roller’s path, pressure, and speed with extreme precision. CNC spinning allows USMS to produce high-accuracy parts with consistent wall thickness and smooth surface finishes, all while minimizing human error and production waste.
This method is ideal for both low- and high-volume production and is widely used across industries such as aerospace, automotive, industrial manufacturing, and lighting. CNC spinning delivers excellent material strength, dimensional control, and the ability to replicate complex profiles.
Playback Numerical Control (PNC) Metal Spinning
PNC spinning combines manual shaping with digital repeatability. An operator first forms the part manually using a joystick. The machine records this motion, allowing the same sequence to be replayed for future runs. PNC is suitable for mid- to high-volume production and enables quick refinement of part geometry between cycles.
Why Choose USMS Spinning Machinery?
Advanced CNC and PNC capabilities for repeatable quality
Manual spinning expertise for specialized, custom parts
Ability to form large diameters and complex curves with lower energy usage
Tight control over part thickness, strength, and finish
Efficient production for both prototypes and volume runs
Whether your part requires automated precision or artisan craftsmanship, USMS’s metal spinning machinery delivers high-strength, seamless components that meet your exact performance and design goals.
Chapter 3: Types of Metal Spinning
Metal spinning is a compressive draw forming process that uses a combination of radial, tensile, and compressive forces to shape metal over a rotating mandrel. As the roller applies localized pressure to the spinning blank, the material flows along a controlled path. Tensile stress develops as the roller makes contact and increases with axial feed, while compressive stress builds toward the center, affecting material thickness and potentially causing wrinkling. Proper feed direction and process adjustments are used to compensate for these effects.
Conventional Metal Spinning
Conventional spinning is the most basic form of the process. In this method, the roller gradually pushes the blank over the surface of the mandrel. Throughout the forming process, the material thickness stays the same. While the diameter of the part reduces, its depth increases. Conventional spinning requires relatively simple tools and machinery, making it a cost-effective option for many applications.
Shear Spinning
In shear spinning, downward force is applied by the roller as the material moves across the mandrel. This results in a part that has a smaller wall thickness than the original blank but retains the same diameter. The workpiece also becomes deeper during the process. Because of the higher compressive stresses involved, the finished part exhibits enhanced mechanical properties such as greater strength and hardness.
Shear spinning demands precise tooling and control, as it impacts both dimensional accuracy and surface finish. The process generates significant heat and friction, requiring the use of coolant to prevent damage to the mandrel and ensure a quality finish.
Law of Sines
The thickness of a part produced by shear spinning is theoretically determined by the Law of Sines. This mathematical rule states that the final thickness equals the original sheet thickness multiplied by the sine of the cone’s semi-apex angle. This applies specifically to conical shapes formed in a single spinning pass. Flat sections perpendicular to the spinning axis maintain their original thickness.
Hot Spinning
Hot spinning is used for metals that are too hard or thick to form at room temperature. The metal is heated with a torch during the forming process to bring it to forging temperature. This increases ductility and allows for greater deformation without cracking.
Hot spinning refines the grain structure of the metal, improving its strength and performance. However, the process is harder to control, more expensive, and the heated metal is prone to oxidation. Cold spinning, by contrast, is suitable for most metals and is easier to manage in terms of quality and cost.
Tube Spinning
Tube spinning is a variation of shear spinning used to reduce wall thickness and elongate hollow cylindrical parts. A preformed tube is clamped onto the mandrel, and multiple rollers apply pressure to draw it along the mandrel’s length.
There are two methods of tube spinning: external and internal. In external spinning, the rollers form the outer surface of the tube over a solid mandrel. In internal spinning, the tube is formed inside a hollow mandrel. This process is ideal for producing tubes with varying diameters, especially when wall thickness is not critical.
Adjustments and Specialized Forming
To achieve the desired thickness and finish, operators can adjust the roller pressure, attack angle, rotation speed, feed rate, and tool geometry. A second pass may be performed to reduce diameter or refine specific contours near the edges. However, repeated passes can harden the metal and make it more brittle, increasing the chance of tool bounce-back.
Metal spinning also allows for operations such as necking and expanding. Necking reduces the diameter at a specific section of the part, while expanding increases it. These modifications add further design flexibility to the spinning process.
Finishing Operations
After spinning, additional processes may be applied to finalize the part. Planishing is used to smooth out surface imperfections and eliminate wrinkles left by the roller. This is done at a lower speed with a smoothing tool. Trimming is then performed to remove any excess material or to clean up the edges of the part for a uniform finish.
Chapter 4: Metals Used in Metal Spinning
Metal spinning is a highly versatile process compatible with most metals. If a metal can be formed by stamping, it can generally be spun. In fact, metal spinning can shape certain materials that are difficult or impossible to stamp. With spinning lathes capable of exerting forces up to 15,000 psi, most metals can be formed—except for particularly hard materials like tool steel and certain grades of carbon steel.
Aluminum
Aluminum is the most commonly used metal in spinning due to its excellent strength-to-weight ratio, ductility, and malleability. It is corrosion-resistant, chemically stable, and thermally efficient. Aluminum offers a lightweight and cost-effective alternative to steel for many applications. Common alloys suitable for spinning include 1100, 2024, 3003, 5052, 6061, and 7075. Typical spun aluminum products include cookware, funnels, electronic housings, drums, decorative items, and components for appliances and furniture.
Steel
Steel is an alloy composed primarily of iron and carbon, with properties that vary based on its composition and processing method.
Stainless Steel
Stainless steel contains at least 10.5% chromium and may also include nickel, molybdenum, and manganese. It is known for excellent corrosion and chemical resistance, as well as high strength and durability—even under extreme pressure and temperature.
Carbon Steel
Carbon steel, mainly composed of iron and carbon, is stronger and more rigid than stainless steel but less ductile. It is categorized by carbon content: low (mild steel), medium, and high. While more brittle and prone to corrosion, carbon steel is an affordable option for many structural applications. Hot-rolled carbon steel is more flexible and easier to spin, whereas cold-rolled steel is stronger but less malleable. Both types are commonly used in heavy-duty parts for automotive, construction, manufacturing, and aerospace industries.
Brass
Brass is an alloy of copper and zinc with excellent conductivity and corrosion resistance. Its golden hue and antimicrobial properties make it ideal for both functional and decorative parts. It is highly workable and ductile, making it well-suited for spinning. Common spun brass products include musical instruments, fittings, furniture parts, and electronics housings.
Bronze
Bronze is an alloy primarily made of copper and tin, along with other elements such as manganese and phosphorus. It is stronger and heavier than brass, and it offers excellent conductivity and corrosion resistance. Though harder and less malleable than brass, bronze is durable and ideal for structural parts. Common uses for spun bronze components include sculptures, trophies, musical instruments, engine parts, and industrial assemblies.
Hastelloy
Hastelloy is a high-performance alloy made from nickel, molybdenum, and chromium. It is valued for its superior corrosion and chemical resistance, especially in aggressive environments. Metal-spun Hastelloy parts are widely used in pressure vessel components, chemical processing systems, power generation, and aerospace applications. It maintains strength and structural integrity under extreme pressure and heat.
Titanium
Titanium combines a high strength-to-weight ratio with excellent corrosion resistance, making it ideal for advanced engineering applications. It is lightweight, soft, and ductile enough for metal spinning, though it is rarely used due to its high material and processing cost. When used, it is typically found in aerospace, medical, and high-performance industrial components.
Chapter 5: Metal Spinning Applications
Metal spinning is widely used for producing low to medium volume runs of symmetrical, round parts where stamping dies would be too expensive. While stamping becomes more cost-effective at high volumes due to faster production rates, spinning remains the best option for custom, complex, or uniquely shaped metal parts that are difficult or impossible to form through stamping.
Hemispheres and Semi-Spheres
Semi-spheres are formed from flat metal sheets and represent half of a full sphere, where the height equals the radius or half of the diameter. They are a common product in metal spinning and are often used as tank ends, protective caps, and other dome-shaped components. These parts can feature either straight or curved walls and are formed by pressing the metal around a hemispherical mandrel. Typical materials include cold-rolled steel, stainless steel (304 and 316), aluminum, brass, and copper.
Spherical Spinning
The process for creating full spheres is an extension of hemisphere spinning. It involves forming two identical hemispheres that are then joined together through precision welding. High accuracy is required to ensure both halves align correctly. This process relies on skilled technicians to maintain consistent dimensions and surface quality during spinning.
Venturi Tubes
Venturi tubes, used in fluid dynamics applications, require precise shaping due to their narrow throat and flared ends. Metal spinning allows for seamless, accurate shaping of these complex profiles. CNC machines are often used to achieve the required tolerances and smooth internal surfaces. A Venturi-shaped mandrel supports consistent metal flow during forming.
Parabolic Shapes
Parabolic spinning is essential in industries like telecommunications and satellite technology, where accurate parabolic curves are required for signal reflection. Metal spinning is well-suited for this due to its ability to form smooth, continuous curves along parabolic geometries. These parts include dish antennas and reflective satellite components.
Cylindrical Components
Cylinders are commonly spun in metalworking but require high precision to maintain uniform wall thickness and surface finish. Cylindrical spinning involves forming a blank into an axially symmetric tube or housing. Force and speed must be carefully controlled to prevent defects such as uneven thickness or buckling. Applications include gas cylinders and storage tanks.
Conical Parts
Conical spinning uses a cone-shaped mandrel and applies shear spinning techniques to form tapered shapes. As the roller moves along the blank, compressive forces shape the material into a cone with a smooth and consistent taper. Conical components are used in funnels, nozzles, and other transition pieces.
Hopper Lids and Bases
Hopper components are typically hand spun from aluminum and tailored to customer specifications. These parts are used for dispensing solids or powders and may require secondary processing such as drilling holes or cutting slots. They are produced with tight tolerances and smooth edges to support reliable flow and operation.
Tank Heads
Tank heads are critical components used in pressure vessels and industrial storage tanks. These parts must meet strict standards for strength, shape, and material composition, especially in high-pressure environments. Metal spinning allows manufacturers to produce seamless, durable tank heads in a variety of profiles, including flanged only, dished only, flanged and dished, hemispherical, high crown, torispherical, and 2:1 semi-elliptical.
Toroidal Shapes
Toroidal spinning creates doughnut-shaped components with a circular cross-section. The process uses specialized mandrels and precise forming techniques to achieve the required shape. Toroids are commonly used as magnetic cores in electrical devices, where dimensional accuracy is critical to performance.
Chapter 6: Metal Spinning Advantages and Disadvantages
Metal spinning offers several important advantages, making it a preferred process for producing symmetrical, round metal parts.
One of the key benefits is the superior strength and reliability of spun parts. Because the process creates seamless components, there are no welds or joints that could weaken the structure. This makes spun parts more resistant to internal pressure and external forces. Additionally, metal spinning enhances the grain structure of the material, improving mechanical properties such as tensile strength, toughness, and hardness. As a result, lighter materials can be used while still meeting strength requirements—especially useful in applications where both low weight and high durability are essential.
Tooling for metal spinning is also simpler, cheaper, and easier to maintain compared to methods like stamping, forging, casting, or hydroforming. For low production volumes or prototypes, soft and inexpensive tools can be used. Higher production runs may require more robust tooling, but setup and changeover time are generally lower than in other manufacturing processes.
Another key advantage is flexibility. Making adjustments to part dimensions—particularly reductions in size—is straightforward and cost-effective in metal spinning. These changes usually only require a tooling modification. In contrast, altering part geometry in casting or stamping can be expensive and time-consuming.
Metal spinning also generates relatively little material waste. Because the process involves shaping rather than cutting, more of the original material is retained in the final product.
Despite these advantages, there are some limitations and drawbacks.
Metal spinning typically takes longer than other forming or casting processes, making it better suited for small to medium production volumes. For high-volume manufacturing, methods like stamping may be more time-efficient.
Manual metal spinning can lead to inconsistency in part quality. The outcome depends heavily on the skill and experience of the operator. While CNC spinning improves precision, not all shops have access to this technology.
The process is limited to creating axially symmetric shapes, such as cones, cylinders, parabolas, and hemispheres. Complex or asymmetrical geometries cannot be formed using this method.
There is also limited tolerance for production errors. If a defect such as a dent or crack forms during spinning, it is often not repairable, and the part must be scrapped. This increases material cost and waste if problems occur.
Finally, manual spinning poses safety risks. The high-speed rotation of parts can be dangerous if the workpiece is not properly secured between the mandrel and tailstock. Operators must maintain full attention throughout the process, as any lapse in focus could result in injury or damaged equipment.
