Machine Selection
For all processes except the two-axis cutting processes, aPriori selects the feasible machine with the lowest overhead rate.
Overhead rate, here, is the sum of the machine properties Direct Overhead Rate and Indirect Overhead Rate:
Overhead Rate = Machine Direct Overhead Rate + Machine Indirect Overhead Rate
For the two-axis cutting processes (Laser Cut, OxyFuel Cut, Plasma Cut, and Waterjet Cut), aPriori selects the feasible machine with the lowest cut cost per part. The major component of cycle time that varies by machine is cut time (which is burn time, for laser, oxyfuel, and plasma), so machine selection picks the machine with the lowest cut cost per part:
Cut Cost per Part = (Labor Rate + Overhead Rate) * Cut Time
Here, cut cost per part is based on the following:
• Labor rate: specified by the machine property Labor Rate.
• Overhead rate: specified as described in
Direct and Indirect Overhead, except that the calculation here is implemented so as to take into account only those components of overhead that vary by machine.
• Cut time: cut length divided by cut rate, where
o Cut length is the sum of blank perimeter and hole perimeters.
o Cut rate (except for Waterjet cut rate) is looked up by machine power, part thickness, and material cut code in the lookup table sheetMetalNestingCutRate. The lookup finds the table row that exactly matches machine power and material cut code, and that has the smallest thickness value that is greater than or equal to the part thickness. The table value for Feed Rate Small Features is then selected for the calculation of cut cost.
Cut rate for Waterjet is calculated based on part thickness, the machine property Pressure, and the machine properties or setup options for Orifice Diameter, Abrasive Flow Rate, and Mixing Tube Diameter. The calculation uses an empirically validated formula.
aPriori selects only from preferred machines, if there is a feasible preferred machine and the cost model variable usePreferredMachines is set to true (the default in starting point VPEs). If there is no feasible preferred machine, or if the cost model variable usePreferredMachines is set to false, aPriori selects from all machines. A machine is preferred if the machine property isPreferred (typically displayed as Is Preferred) is true.
Machine Feasibility
Following are the machine feasibility rules:
• 3D Laser
o Part length, width, and height do not exceed machine dimensions.
o Blank thickness lies between the minimum and maximum thickness capabilities of the machine.
• Bend Brake
o Bend length does not exceed machine dimensions.
o Bend radius-to-thickness ratio does not exceed machine capability.
• Laser Cut, OxyFuel Cut, Plasma Cut
o Blank fits on machine table length and width.
o There is an entry in the lookup table sheetMetalNestingCutRate that exactly matches machine power and material cut code.
o Material thickness falls within the range of thicknesses covered by the lookup table sheetMetalNestingCutRate for the machine’s power and the current material’s cut code.
• Laser Punch, Plasma Punch
o Blank fits on machine table length and width.
o Material thickness does not exceed the machine property Max Sheet Thickness.
o Material thickness is not less than the minimum thickness that appears in the lookup table sheetMetalNestingCutRate for the machine’s power and current material’s cut code.
o There is an entry in the lookup table sheetMetalNestingCutRate that exactly matches machine power and material cut code.
o Required punch force (based on material shear strength, blank thickness, and largest hole perimeter) does not exceed machine’s press force.
o Part has no form whose length exceeds machine’s maximum punch size.
o Part has no form whose depth exceeds the machine’s maximum form depth.
• Waterjet Cut
o Blank fits on machine table length and width.
o Machine properties or setup options provide all values necessary for the determination of cut rate (see above).
• Cut –to-Length, Shear
o Material thickness does not exceed the machine’s Max Thickness for the current material type.
• Deslag
o None.
• Turret Press
o Blank fits on machine table length and width.
• 2 Roll Bending
o Part thickness does not exceed machine capability.
o Machine is capable of performing at least one bend.
• 3 & 4 Roll Bending
o Part thickness does not exceed machine capability.
o Machine is capable of performing at least one bend.
o Part weight does not exceed machine capability.
o Length of the bend does not exceed machine max working length.
o Bend diameter must be greater than machine single pass diameter (~1.3 x Top Roll Diameter)