Drawing Speed and Drawing Force in Drawing Dies

Drawing speed affects the drawn part’s uniformity and physical properties. Drawing speed is generally selected from practical values based on factors such as the part material’s type, thickness, the die and punch nose radii, die lubrication, and similar factors.

Drawing speeds for cylindrical parts, based on the part material’s type and values found through experiments, are given in the chart above.

Drawing Force

Various formulas are used to determine drawing force. However, they generally don’t produce very different results.

Drawing force in blank-holder-less drawing dies:
P = σ_b . π . d . T . (D/d – C)
P: Drawing force, kg
D = Blank diameter of the part to be drawn, mm
d = Drawn diameter, mm
T ~ Sheet metal thickness, mm
σ_b = Bending stress of the sheet metal, kg/mm²
C = constant coefficient (0.6 — 0.7)

In blank-holder-less drawing dies, if D/d – C = 1 is taken, the drawing force formula is written as follows.
Drawing force P = σ_b . π . d . T (kg)

In drawing dies with a blank holder, the drawing force is increased by the blank holder force. This is found with the formula below.
P_T = P . X₁ (kg)
P_T = Total drawing force
X₁ = Drawing force factor (found from the diagram below)

The bending stresses of some materials are given below.

Material Type	Bending Stress σb (kg/mm²)
Aluminum and its alloys	10 – 60
Brass	20 – 60
Zinc	15 – 20
Copper	25 – 38
Bronze	48 – 72
Steel	34 – 62
Stainless steel	30 – 62
Tin	1.5 – 2.5

The blank holder force is calculated separately and added to the drawing force. To do this, the unit surface pressure stress is found from the chart below and multiplied by the holding surface area. It’s then added to the drawing force to find the total press force.

Material type	Surface pressure stress q (kg/mm2)
Medium-hardness steel (T<0.5)	0.25 – 0.30
Medium-hardness steel (T>0.5)	0.20 – 0.25
Brass	0.15 – 0.20
Aluminum and its alloys	0.08 – 0.12

Chart of surface pressure stresses of some materials (above)

Blank holder force P_b = π/4 (D² – d²) . q
P_b = Blank holder force in the drawing die
D = Blank diameter of the part to be drawn
d = Drawn diameter
q = Unit surface pressure stress, kg/mm²

When the blank holder force (Pb) is added to the drawing force, the total drawing force, or press force, is found and expressed with the formula below.

Total drawing force P_T = P + P_b, kg