1 © UGS Corp. 2004. All rights reserved. Tool Axis Control in VASC
1© UGS Corp. 2004. All rights reserved.
Tool Axis Control in VASC
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Tool Axis – Relative to Geometry
Elements for calculating LEAD and TILT
V1 = Normal vector of geometry concerned at current contact position
V2 = Vector from current to next drive position
Transform V2 coincide to V1
P1 = Plane form by V1-V2
P2 = Rotate P1 90° about V1
LEAD = V1 lean toward (+) or backward (-) to V2
TILT = V1 tilt right (+) or left (-) on P2
U, V tanget vectors are irrelevant, instead, cut direction is key element
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Dual 4-Axis Relative to Geometry
Only available for Zig-Zag
During step-over, tool axis change from end status of previous movement to start status of next movement
Specify +/- Lead for Zig/Zag can minimize tool axis change during step-over
Side-effect – inconsistent zig zag cutting condition
If Rotation Axis not specified, 5-axis tool path might be generated
If Rotation Axis for Zig and Zag are different, 5-axis tool path might be generated for step-over, with different 4-axis zig and zag
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Relative Dos and Don’ts
Control smooth tool axis change
Avoid sudden change of normal vector
Avoid sudden change of cut direction
If LEAD is specified
Surface Area drive method
Use Zig, or Zig-Zag with Lift
Use Dual 4-axis Relative for Zig-Zag
Boundary drive method
Add fillet to All Passes
Negative LEAD for roughing would cause drilling effect, should be avoided
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Tool Axis Normal or Relative to Part
Tool axis not determined before projection
Longer calculation time
Work well on smooth part geometry
Might cause undesired result on non-smooth part geometry
Relative to Part
Resultant tool axis falls between Max-Min Lead/Tilt
Surface Area drive method, if Tool Position is Tanto, Lead/Tilt are applied on drive geometry to generate drive points
If gouging happen, The resultant tool axis might disregard the Lead/Tilt requirement to avoid gouging the part
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Elements of Seeking Desirable Tool Position
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Calculation Intensive Iteration Process
Move the tool along the projection vector, look for a contact point at which the angle between tool axis and face normal fulfill the lead/tilt angle requirement
If gouging happen, look for a solution …
A time-consuming iteration process !
At each drive point, the CAM processor maintains the tool tip on the projection vector
Try not to use part geometry for tool axis control, unless under the circumstance there is no other better method.
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Normal or Relative to Drive
Only available for Surface Area drive method
Tool axis determined before projection
Why Relative
Improve cutting condition
Ball nose cutter Avoid tool tip cutting
Increase effective tool diameter
Flat end-mill Lean forward (aka Sturz Milling Method) to improve quality and
productivity
Improve machining quality and efficiency
Control contact position
Tilt tool axis to become peripheral cutting
Avoid gouging
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Swarf
Tool peripheral collinear with tangent vector of face ruling, aka Flank Milling Method. Two ruling options:
Grid or Trim – Reparametrized ruling
Base UV – Original untrimmed ruling`
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Flank Milling
Known Issue – Gouging on twisted ruled surface
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Coping with Known Issue
Averaging the gouging by controlling Cut Area percentage
Cut Area
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Other Option
Use Drive Geometry as Part Geometry, set Projection Vector as Nomal to Drive
Get rid of gouge
Some area would remain uncut
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Interpolate
The most flexible tool axis controlling method
Curve or Surface Area drive method
Defining tool axis is not the fun part
Vector or Relative – choose the appropriate method
Prepare point/vector (point/relative) pairs of data
Enough data to control but don’t over-control
Linear or Cubic
Be patient
Key Elements
1. Drive Geometry
2. Tool axis method and data
3. Projection method
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Vector or Relative
Vector
“Hard” method
Easy pre-evaluation by visualizing the vector
Tool axis completely independent from geometry – normal vector and cut direction is not relevant. Transition from one defined vector to another has no relation to geometry
Relative
Low visibilty for pre-evaluation
Equivalent to Relative to Drive/Part with variable Lead/Tilt Angles
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Make Right Choice
Relative
VectorVector
Vector display good for preview, but result not desirable
More locations defined, result still not desirable
Poor visual preview, but generate desirable result
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Linear or Cubic
Linear
Cubic
Notice the slope at each defining location
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Four Axis Rotation Angle
Rotate the tool axis clockwise (-) or counter-clockwise (+) about the Rotation Axis
Similar to Lead Angle, but with no regard to cut direction – always on the same side of projected normal vector
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Projection Vector
Projection Vector
Swarf Ruling – along ruling
Tool Axis
Taper tool – project toward drive geometry along tool axis
Non-taper tool – same effect as Swarf Ruling
Nomal to Drive
Toward Drive
Same as Nomal to Drive, except only take care of geometry on the nomal side of the drive geometry, ignore those on the opposite side
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Cut Step & Max. TA Change
Cut Step
Control maximum distance between two drive points
Smaller cut step to prevent small features from being overlooked
Max. Tool Axis Change
Force to generate more points between two steps
Prevent dramatic tool axis change between two steps that would cause linearization false during post-processing
Max TA Change = 180 Max TA Change = 5
20© UGS Corp. 2004. All rights reserved.
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