Manual MIG Welding and Robotic MIG Welding

The Linear Rate Method is used by default in starting point VPEs. Administrators can customize the default (for both MIG and TIG welding) by setting the cost model variable weldLinearFeedRate to false. Users can override the default on a per-weld basis with the setup option Weld Cycle Time Method.

See the formulas for Volume Method Arc Time and Length Method Arc Time, below.

Volume Method Arc Time = Theoretical Arc Time * Arc Time Standard

Arc time is calculated using the volume method if the setup option Weld Cycle Time Method is set to Volumetric Rate Method. In this case, arc time is the product of the following:

• Theoretical arc time (see formula)

• Arc time standard: multiplier to account for any operator pauses or breaks between cycles. Specified by the machine property Arc Time Std.

Length Method Arc Time =

((Weld Length * Number of Weld Passes) / Travel Speed ) * Arc Time Factor

Arc time is calculated using the length method if the setup option Weld Cycle Time Method is set to Linear Rate Method (the default in starting point VPEs). In this case, arc time depends on the following:

• Weld length: imported from CAD or specified by the user.

• Number of weld passes: this is the number of times the weld head travels the length of the weld. By default, it is looked up by process type (MIG or TIG) and Weld Throat in the lookup table tblNumWeldPasses. Users can override the default, with the setup option Number of Welding Passes.

• Travel speed: this is the speed (distance per unit time) at which the weld head travels along the length of the weld. By default, it is looked up by Weld Throat and Filler Material Type in the lookup table tblWeldTravelSpeed. Users can override the default with the setup option Travel Speed.

• Arc time factor: this adjusts arc time according to weld type. It is looked up by weld type in the lookup table tblWeldArcTimeFactor.

Theoretical Arc time = GCD Volume / (Arc Efficiency * Deposition Rate)

Theoretical arc time depends on the following:

• GCD volume (based on geometry extraction or user-specified weld dimensions and weld type)

• Arc efficiency: fraction of welding wire that ends up in the weld and is not lost to spatter and evaporation. This value is specified by the cost model variable arcEfficency (0.5 in starting point VPEs).

• Deposition rate (see formula)

Deposition rate = Pi * (Wire Diameter/2)2 * Wire Feed Rate

Deposition rate is the weld volume per unit time that is deposited during the arcing phase. It depends on the following:

• Wire diameter (specified by the machine property Wire Diameter)

• Wire feed rate is the wire length per unit time that is deposited during the arcing phase (specified by the machine property Wire Feed Rate)

Gun Manipulation Time =

Number of Weld Segments * Gun Placement Time per Segment

Gun manipulation time includes all tasks between welds such as lifting the hood or visor, moving to the next location, repositioning the torch, readying to strike, and so forth. It is the product of the following:

• Number of weld segments (specified by the user or geometry extraction)

• Gun placement time per segment (specified by the machine property Gun Placement Time)

Gun Clean Time = Arc Time * Gun Clean Time per Unit Arc Time

Gun clean time is the time for robotic cleaning of weld spatter from around the contact tip and nozzle. It is the product of the following:

• Arc time (see formula)

• Gun clean time per unit arc time (specified by the machine property Gun Clean Time per Arc)

Operation Tack Time Calculations

Tack Time = Tack Arc Time + Tack Gun Manipulation Time + Tack Gun Clean Time

If tacking is enabled (see below) tack time is the sum of the following:

• Tack arc time (see formula)

• Tack gun manipulation time (see formula)

• Tack gun clean time (see formula)

If tacking is not enabled tack time is 0.

For robotic welding, by default in starting point VPEs, operators are assumed to perform tack welding in order to prepare the workpieces. VPE administrators can customize the default with the cost model variable enableTackingWithRoboticWelding. Users can override the default with the setup option Enable Tacking.

For manual welding, the cost model always assumes that tacking is performed.

Tack Arc Time = Theoretical Tack Arc Time * Arc Time Standard

Tack arc time is the product of the following:

• Theoretical tack arc time (see formula)

• Arc time standard: multiplier to account for any operator pauses or breaks between cycles. Specified by the machine property Arc Time Std.

Theoretical Tack Arc Time = Tack Volume / Arc Efficiency * Deposition Rate

Theoretical tack arc time depends on the following:

• Tack volume (see formula for appropriate weld type)

• Deposition rate (see formula)

Tack Volume for Slot and Plug Welds = gcd.volume * tackLength / tackPitch

The cost model assumes that the cross-section area of a tack weld is the same as the cross-section area of the robot-created weld—they differ only in length. For slot and plug welds, it assumes that the ratio of tack volume to the volume of the robot-created weld is the same as the ratio of tack length to tack pitch. (Tack pitch is the distance from the start of one tack weld to the start of the next tack weld.)

Tack volume for slot and plug welds depends on the following:

• GCD volume (based on geometry extraction or user-specified weld dimensions and weld type)

• Tack length (specified by the machine property Tack Length)

• Tack pitch (specified by the machine property Tack Pitch)

Tack Volume for Non-slot, Non-plug Welds =

Tack Cross-section Area * tackLength * numTacks

Tack volume for welds other than slot and plug welds is the product of the following:

• Tack cross-section area (see formula)

• Tack length. This is the length of a single tack weld, specified by the machine property Tack Length.

• Number of tacks (see formula)

Tack Cross-section Area = Weld Volume / Weld Length * Number of Weld Segments

Tack cross-section area is the area of a tack weld cross-section normal to the weld’s length direction (the direction of motion of the gun during arcing). It depends on the following:

• Weld volume

• Weld length

• Number of weld segments

Number of Tacks for Slot and Plug Welds= Number of Weld Segments

For slot and plug welds, the number of tacks is the same as the number of weld segments specified by the user or determined by geometry extraction.

Number of Tacks for Non-slot, Non-plug Welds= Roundup(Arcing Length / Tack Pitch )

For non-slot, non-plug welds, the number of tacks is the minimum number of tack welds required to have a tack weld at the beginning and end of the weld GCD, with tack welds in between spaced by no more than tack pitch. Number of tacks is the quotient of the following, rounded up the nearest whole number:

• Arcing length (see formula)

• Tack pitch (specified by the machine property Tack Pitch)

Arcing Length = Segment Length * Number of Segments

Arcing length is the total distance the point of deposition travels during arcing phase for all weld segments. It is the product of the following:

• Segment length (specified by the user or determined by geometry extraction)

• Number of segments (specified by the user or determined by geometry extraction)

Tack Gun Manipulation Time = Number of Tacks * Gun Placement Time per Segment

For tacking, gun manipulation time is the product of the following:

• Number of tacks (see formula)

• Gun placement time per segment (specified by the machine property Gun Placement Time)

Tack Gun Clean Time = Tack Arc Time * Gun Clean Time per Unit Arc Time

Gun clean time is the time for robotic cleaning of weld spatter from around the contact tip and nozzle. The gun cleaning time associated with tacking is the product of the following:

• Tack arc time (see formula)

• Gun clean time per unit arc time (specified by the machine property Gun Clean Time per Arc)

Weld Throat

Weld throat is the shortest distance from weld root to weld face, that is, the distance from root to face along the direction perpendicular to the face.

For the purpose of determining the number of welding passes required for a given weld, the weld throat calculation assumes a fillet weld:

Here, Ɵ is atn(Depth/Width), so weld throat is given by this formula:

Weld Throat = Weld Width * sin(arctan(Weld Depth / Weld Width))

For the purpose of determining travel speed, throat for an individual welding pass is determined in one of two ways:

• If the weld type is Plug or Slot, the throat is estimated as follows:

sqrt(Weld Width * Weld Depth / Number of Weld Passes)

• If weld type is not Plug or Slot, the throat is estimated as follows:

sqrt((Weld Cross-sectional Area / Number of Weld Passes) * 2)

Note that the formula for Arc Time includes an adjustment, Arc Time Factor, that reflects the weld type, which is specified by the lookup table tblWeldArcTimeFactor.

See also the formula for Length Method Arc Time in MIG Welding Operation Weld Time and TIG Welding Operation Weld Time.

MIG Welding Weld Weight

The formula in this section is used by both Manual and Robotic MIG Welding.

Weld Weight = GCD Volume * Weld Density

The weight of each weld GCD is used to calculate the total weld weight, which affects expendable tooling costs, as well as total assembly weight, which affects Pick and Place costs. The weight in kilograms of each weld GCD is the product of the following:

• GCD Volume (based on geometry extraction or user-specified weld dimensions and weld type)

• Weld density: specified in kg/m3 by the machine property Weld Density. aPriori converts this value to kg/mm3.

Manual MIG Welding Accounting Calculations

Amortized Batch Setup =

(Setup Time * (Labor Rate + Direct Overhead Rate)) / Batch Size

Amortized batch setup depends on the following:

• Setup time (specified as the machine property Setup Time)

• Labor rate (specified by the machine property Labor Rate)

• Direct overhead rate (see Direct and Indirect Overhead)

• Batch size (specified in the Production Scenario screen of the Cost Guide)

Labor Cost = Labor Time * Labor Rate / Final Yield

Labor cost depends on the following:

• Labor time (see formula)

• Labor rate (specified by the machine property Labor Rate)

• Final yield (see Yields)

Labor Time = Operation Weld Times * Labor Time Standard

Labor time is the product of the following:

• Operation weld times: sum of the weld times and tack times of all child operations—see MIG Welding Operation Weld Time.

• Labor time standard: specified as the machine property Labor Time Standard. This multiplier is used to account for otherwise unaccounted for factors that affect labor time, such as operator fatigue or time spent by the operator for cleaning or maintenance.

Note that labor time is independent of the number of operators, and cycle time is inversely proportional to the number of operators—see Manual MIG Welding Process Cycle Time.

Manual MIG Welding Process Cycle Time

Cycle Time = (Labor Time / Number of Operators) * Cycle Time Adjustment Factor

Cycle time depends on the following:

• Labor Time (see Manual MIG Welding Accounting Calculations)

• Number of operators: specified by the machine property Number of Operators. Note that cycle time is inversely proportional to the number of operators.

• Cycle time adjustment factor: specified by the cost model variable cycleTimeAdjustmentFactor; 1 in aPriori starting point VPEs. If you want to model an unbalanced, push assembly line, set cycleTimeAdjustmentFactor to a value greater than 1 in order to account for the cost of extra buffer capacity.

Note that indirect overhead depends on cycle time, while direct overhead depends on labor time. Cycle time contributes to part cost only via indirect overhead.

Robotic MIG Welding Labor Time

During the time the robot is welding one assembly, the operator (or operators or fraction of an operator) who tends the robotic welding machine is assumed to perform both the following tasks on the subsequent assembly:

• Pick and place (P&P in the diagram below)

• Manual tack welding (Tack in the diagram below)

Elapsed Time = max (

Pick And Place Labor Time + Operation Tack Times / Number of Operators,

Operation Weld Times / Number of Weld Heads)

Elapsed time for robotic welding is calculated based on two cases:

• Case 1: if tacking is completed before the robot finishes welding, elapsed time for this process is the elapsed time for the robot-performed welding (sum of the weld times on the child GCDs divided by the number of weld heads).

• Case 2: if tacking is completed after the robot finishes welding, elapsed time for this process is pick and place process time plus the elapsed time for tacking (sum of the tack times on the child GCDs divided by the number of operators).

Therefore, elapsed time depends on the following:

• Pick and place labor time (see Pick and Place Accounting Calculations)

• Operation tack times (sum of the tack times for all child operations--see Tack Time formula in MIG Welding Operation Weld Time)

• Number of operators: specified by the machine property Number of Operators or by the PSO Number of operators tending to this machine. This is the number of operators tending to the robotic welding machine, some or all of whom also do pick and place tasks.

• Operation weld times (sum of the weld times for all child operations--see Weld Time formula in MIG Welding Operation Weld Time)

• Number of weld heads (specified by the machine property Number of Weld Heads)

Note that the cost model assumes that elapsed tack time is inversely proportional to the number of operators, and elapsed robot-performed weld time is inversely proportional to the number of weld heads.

Labor Time = (Elpased Time * Number of Operators * Labor Time standard) –

Pick And Place Labor Time

Labor time for robotic MIG welding is the labor time for a robotic MIG welding cycle that is over and above the time spent on pick and place. In other words, the labor time for robotic MIG welding is the difference between the following:

• Elapsed time (see below) for robotic MIG welding multiplied by the number of operators (and adjusted by labor time standard)

• Labor time for one pick and place cycle

Therefore, labor time depends on the following:

• Elapsed time (see formula)

The corresponding Pick and Place machine property or PSO (see Process Cycle Time Calculation and Pick and Place Options) specifies the total number of operators performing pick and place tasks, including any Robotic MIG Welding operators who perform pick and place tasks—see Robotic MIG Welding Process-level Options for more information.

• Pick and place labor time (see Pick and Place Accounting Calculations)

Robotic MIG Welding Accounting Calculations

Amortized Batch Setup =

(Setup Time * (Labor Rate + Direct Overhead Rate)) / Batch Size

Amortized batch setup depends on the following:

• Setup time (specified as the machine property Setup Time)

• Labor rate (specified by the machine property Labor Rate)

• Direct overhead rate (see Direct and Indirect Overhead)

• Batch size (specified in the Production Scenario screen of the Cost Guide)

Labor Cost = Labor Time * Labor Rate / Final Yield

Labor cost depends on the following:

• Labor time (see Robotic MIG Welding Labor Time)

• Labor rate (specified by the machine property Labor Rate)

• Final yield (see Yields)

MIG Welding Expendable Tooling Calculation

The formula in this section is used by both Manual and Robotic MIG Welding.

Expendable Tooling Cost = ((Weld Weight * Wire Cost) +

Antispatter Spray Cost + Nozzle Cost + Tip Cost) / Final Yield

Expendable tooling cost accounts for the cost of the welding wire for the assembly. It depends on the following:

• Weld weight (see MIG Welding Weld Weight)

• Wire cost (specified by the machine property Wire Cost)

• Antispatter spray cost: cost per unit mass for antispatter spray. This is the sum of the spray costs for all the assembly's welds. By default in starting point VPEs, the cost for a given weld is specified by the formula Antispatter Spray Cost (see below). Administrators can customize the default, and specify no cost for antisplatter spray, by setting the cost model variable weldAntiSpatterSprayEnabled to false. Users can override the default on a per weld basis with the setup option Enable Anti-Spatter Spray.

• Nozzle cost (see formula)

• Tip cost (see formula)

• Final yield (see Yields)

Antispatter Spray Cost = Antispatter Spray Mass Applied *

Antispatter Spray Cost Per Unit Mass

This is the cost of antispatter spray for a given weld, provided that the setup option Enable Anti-Spatter Spray is set to true (the cost is 0 otherwise). It depends on the following:

• Antispatter spray mass applied (see formula)

• Antispatter Spray Cost Per Unit Mass

Antispatter Spray Cost Per Unit Mass =

(Spray Cost / (Spray Volume * Spray Density))

This is the cost per unit mass of antispatter spray for a given weld. It depends on the following:

• Spray cost: this is the Spray Cost of the lowest-Spray-Cost spray listed in the lookup table tblWeldAntiSpatterSpray. (Note that Spray Cost is not cost per unit mass or unit volume, but rather is cost per container.)

• Spray volume: this is the Volume of one container of spray for the lowest-Spray-Cost spray listed in the lookup table tblWeldAntiSpatterSpray.

• Spray density: this is the Density of the lowest-Spray-Cost spray listed in the lookup table tblWeldAntiSpatterSpray.

Antispatter Spray Mass Applied =

((Weld Length * Spray Time Per Weld Length) * Spray Discharge Rate)

The mass of the antispatter spray applied to a given weld depends on the following:

• Weld length: specified by the user or imported from CAD.

• Spray time per weld length: this is the time per unit length to apply the spray. It is the Spray Time Per Weld Length for the lowest-Spray-Cost spray listed in the lookup table tblWeldAntiSpatterSpray.

• Spray discharge rate: this is the mass per unit time that is expended during spraying.

Nozzle Cost = (Weld Weight / Weld Nozzle Replacement Rate) * Weld Nozzle Cost

Nozzle cost depends on the following:

• Weld weight: total weld weight for all the assembly's welds--see MIG Welding Weld Weight.

• Weld nozzle replacement rate: the mass of welding wire used per nozzle, specified by the cost model variable weldNozzleReplacementRate—18kg in starting point VPEs.

• Weld nozzle cost: cost per nozzle, specified by the cost model variable weldNozzleCost—13.57 U.S. dollars per nozzle in starting point VPEs.

Tip Cost = (Weld Weight / Weld Tip Replacement Rate) * Weld Tip Cost

Nozzle cost depends on the following:

• Weld weight: total weld weight for all the assembly's welds--see MIG Welding Weld Weight.

• Weld tip replacement rate: the mass of welding wire used per nozzle, specified by the cost model variable weldTipReplacementRate—9kg in starting point VPEs.

• Weld nozzle cost: cost per nozzle, specified by the cost model variable weldTipCost—0.32 U.S. dollars per nozzle in starting point VPEs.

Additional Direct Costs for MIG Welding

Additional direct costs consist of the sum of the gas costs for all the assembly's welds:

Gas Cost = Weld Time * Gas Cost Per Hour

Gas cost is the product of the following:

• Weld time: this is the sum of all the operation-level weld times--see MIG Welding Operation Weld Time).

• Gas cost per hour: this is looked up by Filler Material Type, Travel Speed, and Gas Type used for Welding in the lookup table tblWeldTravelSpeed.

Note that weld time is converted to hours in this formula, since gas cost is per hour.