Setup Axes and Operation Feasibility
As part of the process of costing a part for a particular process routing, aPriori traverses the part's GCD hierarchy and performs operation assignment (that is, it assigns an operation sequence to each GCD). In the course of performing operation assignment, aPriori is often faced with a choice between alternative operations. In such situations, aPriori uses heuristics to make some inferences about the following costs of each operation for the current GCD:
• Required cutting time
• Setup requirements (how the part must be oriented on the machine in order to make the current GCD accessible to this operation; whether the operation requires an orientation not required by any other operation)
For example, in choosing between Facing and Side Milling for a particular feature of a particular part, aPriori might take into account both the following:
• Facing typically requires less cutting time, but in this case (let us suppose) has the disadvantage of requiring an extra setup.
• Side Milling typically requires more cutting time, but in this case (let us suppose) has the advantage of being able to use a setup already required by another operation on the current part (thus saving the time required to re-orient the part).
When aPriori makes such choices, it does not fully cost each possible operation sequence and compare the results (as it does for each process routing, once it has performed operation assignment). Instead, it attempts to choose the best operation sequence by doing both the following:
• aPriori considers candidate operations in order, from typically faster operations (in terms of cutting time) to typically slower ones. So, for example, when Facing and Side Milling are considered as alternatives, Facing is considered before Side Milling (since, when feasible, Facing generally requires less cutting time for a given GCD than Side Milling). Similarly Side Milling is considered before Contouring.
• When aPriori considers an operation for a given GCD, the operation’s feasibility module uses various heuristics to judge whether the costs associated with the operation’s setup requirements are likely to outweigh the benefits of shorter cutting time. If the setup costs are likely to outweigh the cutting time benefits, aPriori considers the operation infeasible.
For example, facing a planar face on a 3-Axis Mill is infeasible if the operation requires a special setup to accommodate it, unless the planar face has a sufficiently large surface area (as a fraction of the part’s total surface area).
This section describes the feasibility rules that aPriori uses in order to determine when setup requirements render an operation infeasible.
You can influence aPriori’s feasibility determinations in a number of ways, including by by doing one or more of the following:
• Override aPriori’s choice of
principal setups--see
Overriding Principal Setup Axes.
• Add one or more user-specified
activated setups—see
Activating Setup Axes.
• Adjust the cost model variable
fractionalAreaSetupTrigger—see facing and side milling under
Planar Face in
3-Axis Mill.
• Adjust the routings by explicitly user-including an operation—see
Modifying Machining Operation Assignments.
This section contains the information you need for a detailed understanding of how these user actions affect operation assignment.
The section has the following subsections: