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

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

Routing

Roll Bending in the Bar & Tube Fab process group applies only to 360 degree tubes, and only applies to round tube cross sections. At large diameters and very thick tubes, round tubes are recognized as round bars, which causes sheet stock to fail. See Process Group Site Variables on page 218 for information about controlling this calculation.

Accounting Calculations

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 = (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)

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

Cycle Time = Part Handling Time + Rolling Time (Number of Passes + Number of Re-roll Passes) +
Prebend Time + Reroll Part Handling 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)

• Pre-bend Time = (2 * machine pre-bend)
Note: For 360 degree Roll Bending, each end is pre-bended 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 >= Minimum Single Pass Diameter

AND

Part Cross-Section Inside Diameter <= Minimum Multi Pass Diameter

AND

Part Cross-Section Thickness <= 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)

•

• Number of re-roll passes: Re-rolling occurs after rolling the part and welding the ends together. If you need to re-roll, you must specify the number of re-roll passes. If re-roll passes > 0, then Re-Roll Part Handling Time is Load Time + Unload Time.