aPriori 2022 R1 provides these enhancements to the 2-Model Machining cost model.
Improved accuracy and comparability of machining estimates in 2-Model Machining process group
Pocket GCDs and Slot GCDs now are extracted in the 2-Model Machining process group, enabling more accurate estimates of machining cycle times and facilitating comparison of different manufacturing scenarios (fully machining the part from billet or bar stock vs. as a machined casting or forging).
The geometry extraction and milling operation and cycle time logic used in the 2-Model Machining process group has been enhanced so that they are effectively equivalent to the algorithms used in the Stock Machining process group. Previously, the 2-Model Machining process group did not recognize features as Pocket or Slot GCDs; instead these types of volumetric material removal features were extracted either as Flat GCDs or included in the Bulk Removal GCD. Pocket and Slot GCDs better characterize the features, enabling aPriori to assign more appropriate machining operations and tool sizes and therefore more accurately estimate machining cycle times.
Note that aPriori recognizes two different ways that Pocket or Slot GCDs may be created:
- By fully machining the pocket or slot feature into the raw casting or forging
- By enlarging (via machining) a smaller or shallower pocket or slot feature which is present in the raw casting or forging
In the 2-Model Machining process group, Pocket and Slot GCDs now have both a Volume property and a Removed Volume property. The Volume property represents the total volume of the finished feature, whether it is fully machined, fully cast or forged, or cast/forged then machined. The Volume Removed property captures just the volume of material that is removed by machining -- that is, the local difference between the "source" and "target" CAD models, in the vicinity of that feature. If the values of Volume and Volume Removed are equal, then the pocket or slot is made entirely by machining; if not, the pocket or slot exists in the "source" (net shape) model but is enlarged by machining. For enlarged pockets and slots, aPriori uses the Removed Volume value to estimate the depth of material that is machined away from the walls of these features, and in turn determines the number and sizes of rough milling tools required. For very shallow estimated cut depths, a finishing pass will suffice and no rough milling tools are required. For larger cut depths and volumes, one roughing tool will be selected for slots, and either one or two roughing tools will be selected for pockets depending on pocket size and corner radius values.
Due to this change, estimates of machining cycle time and cost computed in the 2-Model Machining process group will change when compared to the previous release of aPriori. The amount of change depends on the specific part and feature geometry and may either increase or decrease. Note that extraction of Pocket and Slot GCDs can be controlled with the site variables pocketExtractionEnabled and slotExtractionEnabled, respectively. These are set to true by default but can be set to false, for customers wishing to preserve the behavior of previous releases of aPriori until they have time to review the impact of these changes. Now that similar geometry extraction, milling operation and cycle time logic are applied in the Stock Machining and 2-Model Machining process groups, comparisons of these estimates will be more straightforward and accurate. Note however, there still may be some differences in cycle time estimates for individual pocket and slot features produced by these two process groups, even when a pocket or slot feature is fully machined (so it is present only in the finish-machined CAD model, not in the raw casting or forging CAD model). These cycle time differences generally are due to differences in the tool sizes selected in each process group. In each case, aPriori pre-selects a set of tools to be used to make all features on the part, considering factors including part size and the radii of any concave features. This pre-selected set of tools therefore may vary due to differences between the "fully-machined" CAD model which is analysed in Stock Machining and the "source" net-shape CAD model utilized in 2-Model Machining. Generally these differences will be minor. If needed, users can use process setup options to override tool diameters on a feature-by-feature basis, to ensure an exact comparison.