Benefits of 2-Model Machining
In addition to the separately-licensed 2-Model Machining group, aPriori also supports costing machined castings and forgings for which only a single CAD model is available. This section describes the difference between the two approaches, and why you may want to consider 2-Model Machining.
When only a single CAD model is available, aPriori uses various configurable heuristics to:
• Determine which features and operations are machined vs. cast or forged.
• Estimate the amount of material removed.
• Compute cycle times and costs.
For example, in Casting, aPriori assumes that holes that are smaller than a specified threshold value are machined rather than cast. For surfaces that are machined, aPriori assumes a certain depth of material has been removed by the machining operation in order to compute machining cycle times. In cases where the aPriori determinations do not match actual practice, you may override operation assignments and other inputs. However, manually selecting individual GCDs and ensuring that override values are correctly entered can be time-consuming and prone to error. The advantage of the 2-Model Machining process group is that the amount of user review and override required is greatly minimized, since comparisons of the raw and machined part eliminates aPriori “guesswork”.
For example, consider the outline of the final part shown in the following illustration:
The starting point for this part might resemble this:
But if you have only one CAD model showing the machined end product, aPriori has no information about what the starting point for the raw casting or forging actually looks like. In this case, aPriori tries to calculate an estimated starting point by adding back some uniform amount of material to surfaces that it determines are machined. (This “material add back” is done in the Casting and Forging process cost models.)
In contrast, when you use 2-Model machining, you supply two CAD models to aPriori, eliminating the need for this potentially inaccurate back-calculation of the starting point.
By using 2-Model Machining, you get a much more accurate costing of the initial model, followed by an accurate costing of the actual machining of the finished details. The 2-Model Process Group allows aPriori to automatically identify:
• GCDs that are produced by the finishing processes rather than the primary processes –eliminating the need for users to manually identify them.
• The actual amount of material that is removed by the finishing processes -- leading to more accurate cycle time and cost calculations.
Note: 2-Model Machining actually uses the same machining cost model that is available in the Casting and Forging process templates as a secondary machining process. However, in 2-Model Machining, the GCDs available to the machining cost model are different because aPriori recognize the differences in geometry between the source and the finished models.