Study the deep-drawing process that forms a flat sheet-metal blank into a cylindrical cup. Adjust the blank diameter, cup diameter, sheet thickness and tensile strength to see the drawing force, blank-holder force, drawing ratio and cup height update in real time, and find forming conditions free of wrinkling and tearing.
Parameters
Blank diameter D
mm
Diameter of the flat circular disc before pressing
Punch diameter (cup diameter) d
mm
Inner diameter of the formed cup
Sheet thickness t
mm
Tensile strength σ_u
MPa
About 340 for mild steel sheet, about 600 for stainless
Results
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Drawing ratio DR
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Drawing force (kN)
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Blank-holder force (kN)
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Cup height (mm)
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Margin to limiting ratio
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Drawing verdict
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Deep-drawing operation — punch-stroke animation
The punch pushes the centre of the blank down, drawing the flange inward as the cup forms. The blank holder presses on the flange to suppress wrinkling.
Drawing ratio DR and drawing force F. D: blank diameter, d: punch diameter (cup diameter), t: sheet thickness, σ_u: material tensile strength. The larger the bracket, the larger the force.
Blank-holder force F_BH (about 35% of the drawing force) and the cup height h from area conservation (the blank area is distributed into the cup bottom and wall).
A drawing ratio beyond about 2.0 cannot be formed in a single draw — the wall would tear — and the part must be formed in several successive redrawing stages.
What is Deep Drawing?
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Deep drawing is that press process that turns a flat metal sheet into a cup shape in one go, right?
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Exactly. Beverage cans, kitchen sinks, cooking pots, car body panels, fuel tanks, cartridge cases — a huge range of the seamless hollow products around you are deep-drawn. The idea is to place a flat circular disc, called the BLANK, over a die opening, clamp it down, and push its centre into the die with a PUNCH, drawing the metal into the opening to form a cup.
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Just pushing it in sounds easy — is it really that hard?
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It is hard. The subtlety is in the deformation of the flange. As the outer flange of the blank is pulled inward, every element of it must shrink in circumference. It is stretched radially while being compressed circumferentially — and that circumferential compression is exactly what makes the flange buckle into WRINKLES, like a piece of paper pushed into a funnel.
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I see, so that is where wrinkles come from. How do you prevent them?
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That is why a deep-drawing tool always has a BLANK HOLDER, a hold-down ring. It presses on the flange with just the right pressure, keeping it flat and suppressing wrinkling. But press too hard and the metal can no longer flow into the die — a different problem appears. The slider on the left gives the drawing force; the blank-holder force is roughly 35% of it.
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What happens if you clamp too hard?
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Tearing — that is the other failure mode. The already-formed, work-hardened cup WALL carries the entire drawing force. If the force needed to pull the flange in exceeds what the wall can bear, the wall tears off at the punch radius. That is why the DRAWING RATIO — blank diameter divided by cup diameter — is the most important number. It measures how much metal must be drawn in, and a single draw can manage only about 1.8-2.0. Beyond that the wall tears, so the part must be formed in several successive REDRAWING stages, each one deepening and narrowing the cup.
Frequently Asked Questions
A standard estimate for the drawing force of a cylindrical cup is F = π·d·t·σ_u·(D/d − 0.7), where d is the punch diameter (cup diameter), t is the sheet thickness, σ_u is the material tensile strength and D is the blank diameter. The term (D/d − 0.7) subtracts an empirical constant 0.7 from the drawing ratio D/d, so the force grows with a larger drawing ratio and with thicker, stronger sheet. This tool evaluates that formula and shows the drawing force in kN.
As a rule of thumb the blank-holder force is about 30-40% of the drawing force; this tool uses 35%. As the flange is drawn inward it is compressed circumferentially, so it tends to buckle into wrinkles, and the blank holder presses on the flange to suppress that. Too little pressure lets the flange wrinkle; too much pressure stops material flowing in and the wall tears. In practice the pressure is tuned to a middle value where neither wrinkling nor tearing occurs.
The drawing ratio is the blank diameter divided by the cup diameter (DR = D/d) and measures how much metal must be drawn inward. Depending on the material and lubrication, the practical limit for a single draw is roughly 1.8-2.0. Beyond that the wall cannot withstand the tension and tears, so the part must be formed in several successive redrawing stages, each one deepening and narrowing the cup a little further. The drawing ratio is the single most important number governing deep drawing.
Tearing occurs at the punch-radius region — near the boundary between the cup bottom and the cup wall. All the force needed to draw the flange in is transmitted through the cup wall, so the wall carries the largest tensile load. When the already-formed, work-hardened wall can no longer bear the force required to pull the flange in, it tears off at the punch radius. Tearing is more likely with too large a drawing ratio, excessive blank-holder force, insufficient lubrication, or too small a punch-shoulder radius.
Real-World Applications
Beverage cans and food containers: Aluminium and steel beverage cans are the classic example of deep drawing — the can body is formed seamlessly in one stroke from a single thin disc. Real can production combines deep drawing with ironing, which thins and lengthens the wall further. At a production scale of hundreds of billions of units a year, optimising the drawing ratio, lubrication and tool life directly drives cost.
Automotive body panels and fuel tanks: Large parts such as door panels, fenders, roofs and fuel tanks are deep-drawn on huge presses. Their complex three-dimensional shapes make it hard to avoid wrinkling, tearing and springback at once, so forming simulation (FEM analysis) is now essential to die design. A cylindrical-cup estimate like this tool is useful for the first-pass feasibility check before that.
Kitchen and cookware: Stainless-steel sinks, pots, bowls and kettles are deep-drawn. Stainless has a higher tensile strength and more work hardening than mild steel, so the drawing force is larger and the choice of lubricant and tooling matters more. Deep products are finished to the target depth and diameter through several successive redrawing stages.
Cartridge cases, battery cans and motor housings: Bullet cartridge cases, cylindrical lithium battery cans and small-motor housings are also typical deep-drawn parts. These demand tight dimensional accuracy and uniform wall thickness, so the blank diameter, drawing ratio and number of stages are carefully planned. Deep drawing exploits its advantages of being seamless, strong and well suited to mass production.
Common Misconceptions and Pitfalls
The first big misconception is that matching the drawing force alone is enough to select a press. The press capacity needed for deep drawing is not just the drawing force (punch load). The blank-holder force (cushion force) clamping the flange is also required at the same time and reaches 30-40% of the drawing force. A knock-out force to strip the part off the punch is needed as well. This tool gives the drawing force and a blank-holder force of 35% of it as an estimate; for an actual press selection, also consider the forming speed, stroke and die-cushion specification.
Next, assuming the drawing-force formula gives an exact value. F = π·d·t·σ_u·(D/d − 0.7) is an empirical formula, and the constant 0.7 and the way tensile strength is used vary between references. The real drawing force depends strongly on the lubrication state, the punch- and die-shoulder radii, the blank-holder force, the forming speed, and the material's r-value (Lankford coefficient) and strain-hardening exponent n-value. Treat this formula as an estimate for the approximate load level and for whether the drawing ratio is feasible, and confirm the final figures with forming FEM or trials.
Finally, the misconception that a drawing ratio within the limit guarantees a successful draw. Even with a drawing ratio inside 1.8-2.0, an inappropriate blank-holder force will either wrinkle the flange or tear the wall. Deep drawing depends not only on the drawing ratio but on lubrication, the tool radius profile, the surface condition of the sheet, and earing caused by crystallographic anisotropy. When redrawing, an intermediate anneal between stages may be needed to remove work hardening. The drawing ratio is the most important indicator, but it alone does not guarantee formability.