Roll Bending (2-, 3-, and 4-roll)

aPriori uses the formulas below to determine costs associated with this bending process (used for plate rolling).

Expendable Tooling Cost -- unused

Setup Cost = (Setup Time per Part * Labor Rate) + (Setup Time per Part * Overhead Rate)

Labor Cost = Labor Rate * Labor Time / 3600 (seconds per hour)

Overhead Cost = (Labor Cost * Overhead Multiplier) + (Overhead Rate * Cycle Time / 3600

Cycle Time Calculation (2-Roll Bending)

Cycle Time = Part Handling Time + Rolling Time

Cycle time for 2-Roll Bending is the product of the following:

• Rolling Time = (Arc Length) / (Machine Rolling Speed)

• Arc Length = Minimum Bend Radius * (Bend Arc Angle / DEGREES_PER_RADIAN)

Note: If yield strength reaches 90 % of ultimate tensile strength, then:
Rolling Speed = (Machine Rolling Speed) * (Plant Rolling Speed Adjustment Factor)

• Part Handling Time = load time + unload time

Note: Times are same as in Bend Brake.

Cycle Time Calculation (3- and 4-Roll Bending)

Cycle Time = Part Handling Time + (Rolling Time * Number of Passes) + Prebend Time

• Cycle time for 3- and 4-Roll Bending is the product of the following:

• Rolling Time = (Part Cross-Section Sheet Width)/(Setup Rolling Speed)

• Rolling Speed = Machine Rolling Speed

Note: If yield strength reaches 90 % of ultimate tensile strength, then:
Rolling Speed = (Machine Rolling Speed) * (Plant Rolling Speed Adjustment Factor)

• Part Handling Time = load time + unload time ( times same as in Bend Brake)

• Prebend Time = (2 * machine pre-bend)
Note: For 360 degree Roll Bending, each end is pre-bent to minimize flats.

• Number of passes: In 3- and 4-roll bending, some parts have to be rolled in multiple passes.

The component will be completed in one pass if:

Part Cross-Section Inside Diameter >= Machine property “Minimum Single Pass Diameter”

AND

Part Cross-Section Inside Diameter <= Machine property “Minimum Multi Pass Diameter”

AND

Part Cross-Section Thickness <= Machine property “Minimum Single Pass Thickness”

AND

Part Minimum Stock Length <= Single Pass Roll Length

Single Pass Roll Length depends upon the Material Strength Ratio.

If Material Strength Ratio <= 1, then
Single Pass Roll Length = (Machine Roll Working Length) * (materialStrengthRatio) *
((Minimum Single Pass Diameter) / (Part Cross-section Inside Diameter))

If Material Strength Ratio > 1, then

Single Pass Roll Length = (Machine Roll Working Length) *
((Minimum Single Pass Diameter) / (Part Cross-section Inside Diameter))

Material Strength Ratio = sqrt((Machine Reference Yield Strength) / (Material Tensile Yield Strength))

Note: Machine Maximum Working Length decreases when diameter increases and strength of material increases.

• Determining number of passes if greater > 1

The number of passes depends on the material springback, which increases with

o Higher yield strength

o High bend diameter to thickness ratio

o Bigger bend angle

• Number of Passes = Material Strength Pass + Diameter Thickness Pass + Bend Angle Pass +
Additional Pass

• where:

Material Strength Pass = +1 if (Material Yield Strength) > Plant Reference Tensile Strength

Diameter Thickness Pass = + 2 (diameter to thickness was checked in the single pass rule above)

Bend Angle Pass = +1 (all tubes are 360 degrees, which is > 180)

Additional Pass = +1 if Part Thickness reaches 90% Machine Maximum Machine Thickness ( to protect machine)

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