BIZOMAT MAKEOS · Fabrication
Deep Drawing Reduction Sequence
How many draws does this shell need, and what diameter should each draw produce?
Sequence of shell diameters in successive deep drawing operations from the blank diameter, a first-draw ratio and a redraw ratio (each the drawn diameter divided by the previous diameter), the number of draws needed to reach the final diameter, and the reduction percentage at each step.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Blank diameter | mm | Diameter of the flat blank (from a shell-blank calculation). |
| Final shell diameter | mm | Mean diameter of the finished shell. |
| First draw ratio (d₁ ÷ D) | Limiting first-draw ratio for the material, thickness ratio and die (from drawing data or trials). | |
| Redraw ratio (dₙ ÷ dₙ₋₁) | Limiting ratio for each redraw (usually larger than the first). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Blank diameter
- What it is
- The diameter of the flat circular blank the shell is drawn from, usually worked out from the shell’s surface area.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Calculate it first with a shell-blank method; trim allowance should already be included.
What this means: Final shell diameter
- What it is
- The mean diameter of the finished drawn shell, measured to the middle of the wall thickness.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the mean diameter, not the inside or outside diameter; it must be smaller than the blank.
What this means: First draw ratio (d₁ ÷ D)
- What it is
- The limiting ratio of the first drawn diameter to the blank diameter: the smallest first cup that can be drawn without tearing.
- Units and format
- Enter a plain number with no unit. The form accepts 0.3 to 0.95. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.55 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller ratio allows a deeper first draw and may save draws.
- Get it right
- Take it from drawing data or trials for the material, thickness ratio, die radius and lubrication.
What this means: Redraw ratio (dₙ ÷ dₙ₋₁)
- What it is
- The limiting ratio of each redraw diameter to the diameter before it, applied to every draw after the first.
- Units and format
- Enter a plain number with no unit. The form accepts 0.4 to 0.98. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.75 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller ratio reduces the number of draws needed.
- Get it right
- Redraw ratios are usually larger than the first draw ratio; anneal between draws if the material work-hardens.
Method and formulas
- d₁ = m₁ D; dₙ = m_r dₙ₋₁ until the final diameter is reached.
- Number of draws n = 1 + ⌈log(d ÷ m₁ D) ÷ log m_r⌉ when d < m₁ D.
- The last draw is set to the final diameter; reduction = 1 − ratio.
- Example: a 100 mm blank to a 30 mm shell needs 4 draws.
Limitations
- Ratios depend on material, thickness-to-diameter ratio, die radii and lubrication; use your tested limits.
- Annealing between draws may be needed for work-hardening materials.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Plan the number of operations for a deep-drawn shell
- Lay out punch diameters for a draw sequence
- Check whether a shell can be drawn in fewer operations
Who it is for
- Toolmakers
- Press shop engineers
- Manufacturing engineers
What you get
- Number of draws
- Diameter after each draw
- Reduction at each draw
Interpreting the result
- Spreading reductions evenly over the draws, rather than leaving a tiny last draw, reduces risk of tearing.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1353–1359. Topic reference; no source tables or recommended settings are reproduced.
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