Chapter 9 - 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
The basic metal spun shapes are the hemisphere, cone,
cylindrical shell, and venturi as well as others, depicted in Figure 1 below.
Figure 1. Typical shapes produced by the metal spinning
process. Products produced by spinning are utilized in many
industries: aerospace, agricultural, computer, ventilation, lighting, marine, food
service, automotive, etc.
Metal spinning used to be associated with prototypes and
low volume production only. However, with the introduction of automatic lathes, spinning
is now a cost effective option for both medium and high volume production. The relatively
inexpensive tooling price for spinning still makes this forming method a cost effective
one for fabricating prototypes.
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
Figure 2. Manual spinning. The sequential development
of the finished part in several passes is shown.
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.
Basic Operations of Metal Spinning
In forming a part by spinning, a combination of processes
may be utilized to complete a part. These processes include: preforms, conventional
spinning shear spinning, edge treatment (trimming, beading, curling, hemming) as well as
- Preforms. A preform is a partially formed part which
is used to increase the efficiency of the next forming process. Preforms may be in the
shape of cylindrical shells, cones, and more. These preforms can be achieved through
spinning or other forming operations such as drawing.
- Conventional Spinning. The spinning process usually
involves a series of passes to complete the formed part. During each pass the metal is
stretched thus thinning out the material. This thin-out characteristic is typical of the
conventional spinning process. If necessary thin-out can be minimized.
- Shear Spinning. is a variation of conventional
spinning. Shear spinning refers to the formation of a part in just one pass. This process
allows for an accurate prediction of finished material thickness. Shear spinning is
typically associated with conical and cylindrical shapes.
- Edge Treatment. The edges of a spun part can be
finished in many ways. Parts can be trimmed for a straight edge, hemmed for a folded edge,
or beaded for a rolled or curled edge. These edge treatments can be performed in a
spinning lathe or on a separate machine.
- Secondary Operations. Often spun parts require
secondary operations. This may range from piercing holes, to heat treating, to powder
coating, to laser cutting. Many metal spinning companies perform these operations in-house
or will subcontract them for you.
Tooling for spinning can be fabricated from various
materials. Many factors determine which material is most appropriate: production volume,
finish, tolerancing, metal, etc. The three basic alternatives are wood, plastic and steel.
- Wood tools are made from a variety of materials:
maple, fine grain particle board, etc. Wood tools are typically used for parts where
tolerancing and/or finish is not critical.
- Plastic. A paper-based plastic is also used for
tooling. As compared to wood, plastic tooling is generally more durable, provides a
superior surface finish and will maintain closer tolerances.
- Steel tools are mainly used to form shapes fabricated
from stainless steel or other strong metals. Due to the relatively hard, smooth surface of
steel tools, parts spun on steel tooling can achieve a superior surface finish and
maintain close tolerancing. Steel tools can be fabricated from both mild steel and tool
steel. The life of the tool can be increased through heat treating.
Spinning tooling can be grouped into three broad
categories: male, female, and collapsible
- Collapsible Tool (Segmented). A collapsible tool is
required when the diameter of the part becomes smaller as the part is formed. If a male
tool is used this smaller diameter or neck prevents the part from being removed from the
tool; therefore, a collapsible tool is required. A collapsible tool has a removable center
core which keeps the perimeter pieces in place during spinning. After the part is spun,
the core is removed which permits access to the perimeter pieces. Note that the use of a
collapsible tool involves assembling and disassembling the tool for each piece spun.
Advantages and Limitations of Metal Spinning
The metal spinning process has both advantages and
- Spinning tooling is relatively inexpensive due to its
simplicity and composition.
- This simplicity translates into short lead times for new
- 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
- Spinning is typically a cold working process; therefore,
spinning increases the tensile strength of the material.
- The spinning process can accommodate very large parts in
excess of 120 in. (3.0 m) in diameter as well as parts requiring thick material such as
0.500 in. (12.7 mm) mild steel.
- Extreme tolerancing requirements may dictate the use of
- Manual spinning is more labor intensive than automatic
spinning or other forming processes such as drawing.
- The uniformity of a manually spun part is closely associated
with the skill of the operator.
The following design guidelines for metal spinning can
affect quality and cost.
- It is preferable to specify the inside diameter (I.D.) and
associated tolerance since the outside diameter will vary due to material thin-out. If
necessary, a specific outside diameter (O.D.) can be maintained.
- If uniform wall thickness is required, identify the portion
of the part which is affected. Additional operations may be required to achieve this
uniform wall thickness.
- Corner radii should be specified at 2 to 3 times material
thickness. Tighter radii can be achieved on thicker material and through secondary
- If concentricity is critical, specify the total indicated
runout (TIR) and indicate if this applies in the restrained or unrestrained condition of
- Working closely with your spinning supplier during the
design phase may significantly improve formability and reduce cost.
- If tight tolerancing is required in a small area only,
specify that area. The erroneous assumption that the tight tolerancing applies to the
entire part will dramatically increase the price of the part.
- Surface finish is affected by the material, thickness, tool
condition, forming speed, and other factors. If the specified surface finish cannot be
achieved through spinning, secondary operations can be performed.
- Any formable metal can be spun. The stronger the material
the more difficult the spinning.
The tolerancing guidelines for spinning are shown in
Table I. Tolerances for metal spun
parts which are typically found practical for most applications
|Diameter of Finished Part
Up to 24" Diameter
+/- 0.015" to 0.031"
(0.38 mm to 0.79 mm)
+/- 0.001" to 0.005"
(0.02 mm to 0.13 mm)
|25" to 36" Diameter
(600 mm to 900 mm)
|+/- 0.031" to 0.047"
(0.79 mm to 1.19 mm)
|+/- 0.005" to 0.015"
(0.13 mm to 0.38 mm)
|37" to 48" Diameter
(900 mm to 1200 mm)
|+/- 0.047" to 0.062"
(1.19 mm to 1.57 mm)
|+/- 0.010" to 0.030"
(0.25 mm to 0.76 mm)
|49" to 72" Diameter
(1200 mm to 1800 mm)
|+/- 0.062" to 0.094"
(1.57 mm to 2.39 mm)
|+/- 0.015" to 0.045"
(0.38 mm to 1.14 mm)
|73" to 96" Diameter
(1800 mm to 2400 mm)
|+/- 0.094" to 0.125"
(2.39 mm to 3.17 mm)
|+/- 0.020" to 0.060"
(0.15 mm to 1.52 mm)
|97" to 120" Diameter
(2400 mm to 3000 mm)
|+/- 0.125" to 0.156"
(3.17 mm to 3.96 mm)
|+/- 0.025" to 0.090"
(0.64 mm to 2.29 mm)
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Excerpt taken from Design Guidelines for Metal Stampings and Fabrications -- 2nd Edition copyright © 1995 Precision Metalforming Association
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