High Pressure Die Casting and Gravity Die Casting Process Formulas
The cost model for these processes rely on the formulas below.
Cycle Time
Cycle Time = Process Time * Cycle Time Adjustment Factor
Cycle time is the product of the following:
• Process time (see formula below)
• Cycle time adjustment factor: specified by the cost model variable cycleTimeAdjustmentFactor; 1 in aPriori starting point VPEs.
Process Time = (Load Insert Time + Ladle Time + Injection Time + Cool Time +
Ejection Time + Lube Time) / Number of Cavities
Process time is a function of the following:
• Load insert time (increases with the number of insert cores)
• Ladle time (increases with part volume, if the material’s associated chamber type is cold; 0 otherwise)
• Injection time (increases with number of mold cavities and average part thickness; also depends on material injection and melting temperatures)
• Cool time (increases with maximum part thickness and material cooling factor; decreases with ratio of part surface area to projected parting area)
• Ejection time (see formula)
• Lube time (increases with part length and width)
• Number of cavities (see Number of Mold Cavities for Die Casting)
Note that for high pressure die casting, cleaning is assumed to be performed by the operator on one part while the machine is cycling on the next.
Ejection Time = Mold Open Time + Hydraulic Slide Time +
Ejector Plate Time + Part Removal Time + Mold Close Time
Ejection time is the sum of the following:
• Mold open time (see formula)
• Hydraulic slide time: (see formula)
• Ejector plate time (see formula)
• Part removal time: If the setup option Part Eject Method is set to Gravity (the default in starting point VPEs), the part removal time is the value of the cost model variable gravityDropTime (1.25 seconds in starting point VPEs). Otherwise, part removal time is the value of the cost model variable robotGrabTime (2.5 seconds in starting point VPEs).
Mold Open Time = Travel Distance / Max Machine Velocity
Mold open time depends on the following:
• Travel distance: see Travel Distance, below.
• Max machine velocity: see formula.
Travel Distance
Travel distance for mold open or close is generally 3 or 4 times the part height:
• If the setup option Part Eject Method is set to Gravity (the default in starting point VPEs), the travel distance is generally the product of part height and the cost model variable nominalHeightFactor (3 in starting point VPEs):
Travel Distance = Part Height * Nominal Height Factor
• If the setup option Part Eject Method is set to Robotic, the travel distance is generally the product of the following:
o Part height
o Sum of the cost model variables nominalHeightFactor (3 in starting point VPEs) and roboticClearanceFactor(1 in starting point VPEs)
Travel Distance = Part Height * (Nominal Height Factor + Robotic Clearance Factor)
See also Part Eject Method in High Pressure and Gravity Die Casting Process Inputs.
Max Machine Velocity =
(Dry Cycle Stroke Factor * Max Tie Bar Distance * 2) / Dry Cycle Time
The speed of travel during mold open and close is derived from the following:
• Dry cycle stroke factor: this is the fraction of the maximum tie bar distance that equals the stroke length. The fraction is specified by the cost model variable dryCycleStrokeFactor (0.7 in starting point VPEs).
• Max tie bar distance: this the larger of the machine properties Tie Bar Distance, H and Tie Bar Distance, V.
• Dry cycle time: specified by the machine property Dry Cycle Time.
Hydraulic Slide Time = (Hydraulic Slide Length / Slide Cycle Rate) * 2
A slide for a given undercut feature is required to be hydraulic (as opposed to mechanical) if the platen movement required to clear the mechanical slide from the undercut exceeds the mold open stroke. The presence of hydraulic slides contributes to the total ejection time because, unlike mechanical slides, hydraulic slides are retracted only after the mold is opened.
Hydraulic slide time depends on the following:
• Hydraulic slide length: this is 0 if hydraulic slides are unnecessary. If hydraulic slides are necessary, the hydraulic slide length is the maximum undercut depth plus some clearance (0.5 inch if there are multiple cavities, 5mm otherwise).
• Cycle rate per slide: this is the rate at which the hydraulic slides can move, specified by the cost model variable slideCycleRate (100mm per second in starting point VPEs).
Hydraulic slides are necessary if and only if the following condition holds:
Max Pin Travel Distance > Machine Opening Stroke
Here, Machine Opening Stroke is the value of the machine property Opening Stroke.
Max Pin Travel Distance is the distance along the draw direction that the platen would have to travel in order to retract a mechanical slide from the part’s deepest undercut. The cost model assumes that a retracting mechanical slide is guided by a pin that makes an angle of 15 degrees with the draw direction. If U is the maximum undercut depth (perpendicular to the draw direction) plus clearance (0.5 inch if there are multiple cavities, 5mm otherwise), then the required platen motion has a length along the draw direction of U/tan(15):
Max Pin Travel Distance = (Max Undercut Depth + Extra Clearance) / tan(15)
If the motion required for a mechanical slide (Max Pin Travel Distance) exceeds the value of the machine property Opening Stroke, then hydraulic slides are necessary for the part.
Ejector Plate Time = (Part Height * Ejector Distance Factor) / Max Machine Velocity
Ejector plate time depends on the following:
• Part height: determined by geometry extraction. Part height is measure along the draw direction.
• Ejector distance factor: this is the multiple of part height that equals the distance an ejector pin should move in order to eject the part. It is specified by the cost model variable ejectorDistanceFactor (3 in starting point VPEs).
• Max machine velocity: see formula.
Mold Close Time = Travel Distance / Max Machine Velocity
Mold close time depends on the following:
• Travel distance: see Travel Distance, above.
• Max machine velocity: see formula.