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

3

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

5

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.

8

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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