METAL SPINNING

Metal spinning is a forming process which produces hollow parts that are typically circular in cross-section. The basic spinning process starts with a flat metal disc (blank) which rotates on a lathe. This rotating blank is pressed against a tool (mandrel, chuck) which duplicates the interior of the part. This pushing action over the tool results in a formed part.

The basic metal spun shapes are the hemisphere, cone, cylindrical shell, and venturi as well as others, depicted in Figure 1 below.

THE METAL SPINNING PROCESS

The diagram below shows a basic setup for a horizontal spinning lathe. The tool (mandrel, chuck) is mounted to the headstock of the lathe. A follower block (tail block) is mounted to the tailstock. A circular blank is then clamped to the tool by advancing the follower. The tool rest and pin provide a support system for the lever arms, applies pressure to the blank via a roller or other forming tool. The movement of the roller across the blank is called a pass. A series of passes, which ultimately forms the completed part, is achieved by repositioning the lever arms incrementally.

Metal Spinning Equipment Metal spinning lathes can be grouped into three broad categories: manual, power assisted, and automatic. Each paragraph below provides a brief outline of the equipment and typical applications.

• Manual Spinning lathes typically accommodate blanks ranging from 0.25 in. (6.35 mm) to 72 in. (1.8 m) in diameter. Larger manual lathes are available to accommodate blanks of up to 160 in. (4.1 m) in diameter.
• Power Assisted Spinning is manual spinning augmented by hydraulic cylinders which provide additional force on the workpiece rather than only human force. This additional power is useful when forming strong metals such as stainless steel and exotic alloys.

Automatic Spinning is based on Computer Numerical Control (CNC) and Programmable Numerical Control (PNC). For PNC, the lathe is programmed through a "teach" mode where the first workpiece is manually spun while the computer records the movements. Once this initial workpiece has been spun, the lathe is put into "playback" mode for production. Blanks are positioned in the lathe by the operator and the playback cycle is initiated. The workpiece is then formed automatically, exactly duplicating the movements of the manual spinning.

ADVANTAGES OF METAL SPINNING

• Spinning tooling is relatively inexpensive due to its simplicity and composition.
• This simplicity translates into short lead times for new parts
• Design changes can usually be made at a minimum of expense again due to the inexpensive nature of the tooling.
• The factors above combine to make spinning ideal for prototypes.
• Spinning is typically a cold working process; therefore, spinning increases the tensile strength of the material.