Machine Feasibility and Selection for Die Casting
This section contains the following subsections:
Melting Machine Selection
If aPriori is configured to automatically select a Melting machine (that is, a furnace), it selects the machine with the lowest machine overhead rate that satisfies all the feasibility rules. If two feasible machines have the same machine overhead rate, aPriori selects the one with the smallest capacity.
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.
The feasibility rules require that the furnace have a sufficient capacity and maximum temperature. More specifically, a machine is feasible only if both the following are true:
• The furnace’s maximum temperature is not less than the material’s injection temperature:
o Furnace maximum temperature: specified by the machine property Max Temperature.
o Material injection temperature: specified by the material property Injection Temp.
• The furnace’s capacity is sufficiently greater than the per-part pouring volume. In starting point VPEs, furnace capacity must exceed pouring volume by a factor of 1.5:
o Furnace capacity: specified by the machine property Furnace Capacity.
o Per-part pouring volume: depends on material density and pouring mass. Pouring mass is Mass Before Machining + Mass Waste + Mass Bad Parts + Mass Loss. See the formulas in
Material Cost and Utilization for Die Casting.
o Safety factor: specified by the cost model variable furnaceCapacitySafetyFactor (1.5 in starting point VPEs). Furnace capacity must be greater than or equal to the product of the pouring volume and the safety factor.
To manually select a machine for a given process, select Edit > Routing Selection in the Manufacturing Process pane, right-click on the process in the Routing Selection window, and select Machine Selection from the context menu (see also Selecting a machine for an operation in Manufacturing Process Information).
Molding Machine Selection
If aPriori is configured to automatically select a molding machine, it selects the machine with the lowest machine overhead rate (Gravity Die Casting) or clamp force (High Pressure Die Casting) that satisfies all the feasibility rules.
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.
The feasibility rules require that the mold required for the part can fit on the machine, and (for High Pressure Die Casting) that the machine has sufficient press force. More specifically, a machine is feasible only if all the following are true:
• High Ptressure Die Casting:
o Machine clamp force is greater than or equal to the required force.
o Horizontal machine tie bar distance is greater than or equal the horizontal dimension of the mold base.
o Vertical machine tie bar distance is greater than or equal to the vertical dimension of the mold base.
• Gravity Die Casting:
o Horizontal machine tie bar distance is greater than or equal the horizontal dimension of the mold base.
o Vertical machine tie bar distance is greater than or equal to the vertical dimension of the mold base.
o Machine maximum mold height is greater than or equal to the mold base height.
aPriori calculates the mold dimensions and clamp force required for a given part based on a number of factors, including the minimum required number of cavities in the mold. If you don’t use the PSO
Number of Cavities (see
User Inputs for Die Casting), the minimum required number of cavities is specified by the cost model variable
defulatNumCavities or
defulatNumCavitiesGravityDieCasting (1 in the starting point VPEs), so aPriori finds a machine that can accommodate at least a single-cavity mold.
By using the PSO, you can specify the number of cavities explicitly or specify that aPriori use the number of cavities required to meet the annual production volume. You can also use the PSO to specify that aPriori should use the combination of machine and number of cavities that results in the lowest per part cost. Calculation of clamp force is described in
Required Clamp Force. Calculation of the number of cavities assumed for cost estimates is described in
Number of Mold Cavities for Die Casting.
To manually select a machine for a given process, select Edit > Routing Selection in the Manufacturing Process pane, right-click on the process in the Routing Selection window, and select Machine Selection from the context menu (see also Selecting a machine for an operation in Manufacturing Process Information).
Cleaning Machine Selection
There are three types of cleaning machines, all of which use shot blast:
• Tumble Blast: Uses wheel blasting. Parts are moved by a conveyor belt, causing them to tumble, exposing all surfaces to the shot stream.
• Table Blast: Uses wheel blasting. One or more parts are placed on a table which rotates, exposing them to the shot stream. The cost model assumes that parts are turned over or re-positioned by hand during a pause in blasting. The machine property timePerLoad is the the total blast time, and does not include reorient time.
• Room Blast: For very large parts. Uses air blasting. In a cleaning room, an operator manually directs shot at the part, or a robot programmatically directs shot at the part. The cost model assumes that the parts are reoriented during a pause in blasting.
The machine type is specified by the machine property Type.
aPriroi selects the smallest machine (by weight capacity) that is feasible for the current part (see below). 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.
A machine is feasible if it can accommodate all the following:
• Weight of a load with at least the minimum number of parts required for an economic load.
• Height of the part.
• Length or width of the part, whichever is smaller
• Volume (for Tumble Blast) or area (for Table Blast) of a load with at least the minimum number of parts required for an economic load.
The minimum number of parts in an economic load is specified by the machine property Min Number Parts. This is an estimate of the minimum number of parts that would make the machine worth using instead of a smaller machine.
Trim Machine Selection
If aPriori is configured to automatically select a trim machine, it selects the machine with the lowest machine overhead rate that satisfies all the feasibility rules.
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.
The feasibility rules require that the trim mold required for the part can fit on the machine, and that the machine has sufficient clamp force. More specifically, a machine is feasible only if all the following are true:
• Machine clamp force is greater than or equal to the required force, where
o Machine clamp force is specified by the machine property Press Force.
o Required clamp force is the product of material shear strength and total trim area. Trim area is the area covered by removed material. Removed material is assumed to run along the parting line, as well as the surfaces of holes and voids for which trimming is feasible (see below).
• Mold height plus bottom parallel height is no greater than the machine shut height, where
o Mold height is calculated based on a number of factors, some which are affected by Trim setup options. See
Part Height Allowance,
Minimum Part Height Plus Allowance, and
Post Height Multiplier for more information.
o Bottom parallel height is specified by the cost model variable bottomParallelHeight (101.6mm in starting point VPEs).
o Machine shut height is specified by the machine property Installation Height.
Trimming is feasible for those holes and voids that meet the following requirements:
• Hole is known not be obscured, undercut, or blind.
• Hole diameter is no less than the cost model variable minTrimHoleDiameter (25.4mm in starting point VPEs). Note that for threaded holes, hole diameter is the diameter prior to threading, that is, final hole diameter minus twice the value of the cost model variable finishAllowance (0.25mm in starting point VPEs).
• Hole’s diameter to length ratio is no less than the cost model variable trimDiaToDepthRatio (0.5 in starting point VPEs).
• Hole does not require secondary operations to achieve required tolerance.
• Hole is not a complex hole. (Trimming of complex holes is not supported in this release.)
To manually select a machine for a given process, select Edit > Routing Selection in the Manufacturing Process pane, right-click on the process in the Routing Selection window, and select Machine Selection from the context menu (see also Selecting a machine for an operation in Manufacturing Process Information).
Coremaking Machine Selection
For Coremaking, aPriori selects the machine with the smallest corebox capacity that meets the following requirements:
• Machine can accommodate a corebox with at least one cavity for the part’s largest hole or void. Note that the machine must be able to accommodate the largest hole or void, regardless of whether aPriori determines that the hole or void requires a core, since any hole or void could potentially be manually assigned a coring operation.
• Currect scenario’s annual productionvolume falls within the machine’s minAnnualVol and maxAnnualVol limits (if limits are set).
A machine’s corebox capacity is given by the machine properties Max Corebox Length, Max Corebox Width, and Max Corebox Height. A machine can accommodate a GCD if these dimensions equal or exceed the dimensions of the corebox required for the GCD. The dimensions of the requied corebox are the dimensions of the GCD’s smallest enclosing box, extended to account for coreprints (extensions of sand for hanging the core in the mold), and supplemented by the corebox wall thickness (specified by the cost model variable coreboxLengthAllowance--19mm in starting point VPEs).
The GCD properties Dir CorePrints Box Length, Dir Core Prints Box Width, and Dir Core Prints Box Height indicate which dimensions should be extended, and whether the dimension should be extended in one or both directions. For example, if Dir Core Prints Box Length is 0, this indicates that an extension along the length dimension is not required (because both directions are blocked by the part); if Dir Core Prints Box Length is 1, this indicates that the length should be extended in one direction to account for coreprints (because the other direction is blocked by the part); if Dir Core Prints Box Length is 2, this indicates that the length should be extended in both directions to account for coreprints (because neither direction is blocked).
The cost model variable lengthCorePrint (10mm in starting point VPEs) indicates the extension length in each direction. So, for example, if Dir Core Prints Box Length is 2, the GCD’s box length dimension is extended by 10mm in each direction (20mm total), in starting point VPEs.
Refractory Coat Oven Dry Machine Selection
Machine selection for Refractory Coat Oven Dry picks the lowest-volume feasible machine. A machine is feasible if it can accommodate, individually, each of the part’s oven-dryable cores.
A core is oven-dryable if it can fit in the largest available oven. Cores that are too large for any available oven are air dried.
Note that the cost model assumes the use of a single oven for a given part, that is, the cost model assumes that the same oven is used for all the part’s oven-dried cores.
Machine volume is the product of the machine properties Bed Length, Bed Width, and Bed Height.
In starting point VPEs, which assume a spacing factor of 0.8, an oven can accommodate a core (or, equivalently, a core can fit in an oven) if all the following hold:
• Longest dimension of the bounding box of the core is no greater than 80% if the machine Bed Length.
• Shortest dimension of the bounding box of the core is no greater than 80% if the machine Bed Height.
• Intermediate dimension of the bounding box of the core is no greater than 80% if the machine Bed Width.
Administrators can configure the spacing factor with the cost model variable defaultRefractoryCoatOvenSpaceAvailableFactor (0.8 in starting point VPEs).