Machining Enhancements
Fine Finish Milling
Fine Finish Milling extends the functionality of the machining milling processes to provide the ability to achieve better tolerances and surface finishes through additional finishing passes at a reduced feed rate. This allows for higher-quality finishes without the need for a secondary finishing process such as grinding.
This extended functionality was developed in response to customer requests to reflect the capability of modern milling machines and milling strategies to achieve tighter tolerances and superior surfaces finishes. Previously, a grinding operation was applied when the tolerance applied to a GCD exceeded the achievable capability of the standard finish milling operation. Now by default a Fine Finish Milling operation is considered; grinding operations will be evaluated only if the Fine Finish Milling operation cannot achieve the specified tolerance or surface roughness.
Users can change the preference for Fine Finish Milling versus grinding on a per-part basis via the process setup option Disable Fine Finish Milling. Digital Factory managers can set the default behavior for all parts via the cost model variable fineFinishMillingDisabled.
Fine Finish Milling operations are similar to standard surface finish milling operations, but they are performed at a reduced feed rate. The feed rate reduction is calculated dynamically, based on the specified tolerance type and value, and generally is between 40-50%. If desired, Digital Factory managers can increase or decrease the amount of feed rate reduction applied for these operations via the cost model variable fineFinishMillingBaselineFeedFactor (default value of 1.00, indicating no change to the baseline calculated feed rate reduction).
By default a single fine finish milling pass is included, when needed to achieve specified tolerances. If desired, users can increase the number of passes by editing the Number of Occurrences of the Fine Finish Milling node in the Operation Sequence Selection dialog.
Design to Cost (DTC) guidance was added to inform users when a fine finish milling operation was required to meet tight tolerance and surface finish specifications. Users are advised to consider whether the specified value can be relaxed to a recommended threshold that the standard finish milling operations can achieve, in order to eliminate the fine finish milling and its associated cycle time and cost.
Scope and Limitations
This enhancement applies to any milled parts with tight tolerances and high surface finish quality requirements. There is no impact on parts which include no milling operations, that is, parts made on a lathe using only turning operations.
Additional fine finish milling passes are evaluated for the following processes, when tight tolerances are applied to Planar Face, Curved Wall, and/or Curved Surface GCDs:
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3-Axis Bar Feed Lathe
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3-Axis Lathe
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3-Axis Mill
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4-Axis Mill
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5-Axis Mill
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Mill-Turn
Known Limitations: Fine finish milling passes are not evaluated and will not be included for:
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Surfaces that are children of Ring GCDs
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Facing in The Facing and Corner Picking operation sequences
Note: To access fine finish milling, customers either must use the baseline manufacturing cost model available in aPriori 2023 R1 SP2, or upgrade any configured Digital Factories to the latest version (CMV 290).
Impact
As a result of this enhancement, the operations, cycle times, and costs for a tightly-toleranced, machined part may change compared to the previous release. Fewer of these parts will be routed to a secondary grinding process. Part costs generally will decrease due to the elimination of grinding, however milling cycle times and costs will increase due to the additional fine finish milling passes.
It is difficult to quantify the impact of including fine finish milling, as it is highly dependent on:
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Value of the applied tolerance or surface finish requirement
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Area of the milled surface
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Finish operation type (facing, side milling, or contouring)
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Number of tools utilized in the primary finishing operation
For GCDs with a single primary Facing or Side Milling operation, the impact of adding Fine Finish Milling is roughly a 140% increase compared to having no tolerance (and therefore no grinding) applied. The cycle time increase is greater for surfaces assigned Fine Finish Milling contouring operations, due to tool stepover reductions in addition to feed rate reductions. The increase can be even larger in cases where aPriori determines two tools (a larger-diameter and a smaller-diameter tool) are required for standard surface finishing operations. This is because the Fine Finish Milling operation will use the smaller of the two tools to ensure a consistent surface finish quality for the entire surface.