NURBS Based Tool Path Generation for HSM

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NURBS Based Tool Path Generation for HSM

• By
• Rohit Newaskar

Advance Machining Laboratory Mechanical
Engineering Department UNB
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Overview

• High Speed Machining
• Tool Path Generation
• NURBS Interpolation

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High Speed Machining

• High cutting speed machining,
• High rotational speed machining,
• High feed machining,
• High speed and feed machining,
• High productive machining

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Advantages of HSM

• Less Heat Generation on Work-piece
• Improvement in Dimensional Accuracy
• Improved Surface Finish
• Better, More Effective Chip Disposal
• High Production Rates
• Less Machining Time
• Less Post Processing Required
• Can Machine Harder Metals

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Applications of HSM

• Aluminum components for automobile
• Aircraft industry
• Die-mold making industry

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Requirements for HSM

• Spindle speed range gt 40,000 rpm
• Spindle power gt 22 kw
• Rapid traverse lt 90 m/min
• Air Blast/coolant through spindle
• Rigid machine frame with high absorption capacity
  
• Data flow via Ethernet 250 KBPS
• Advanced look ahead function in CNC
• Circular interpolation via NURBS( no linear
  interpolation)

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Importance of Tool Path Technique

• 65 of lead time required for tool path planning
  and NC machining and polishing
• Geometric accuracy
• Surface finish
• Drastically reduce polishing and EDM processes.

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Interpolation Techniques

• Circular Interpolation
• G-code G02 G03
• When radius of curved path is same.
• G03 X2. Y2.75 I.75 J0.0
• X1.25 Y2. I0.0 J.75
• X2. Y1.25 I.75 J0.0
• X2.75 Y2. I0.0 J.75

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Interpolation Techniques ( conti..)

• Linear Interpolation
• G-code G01 G01 X2.626 Y1.697
• Mostly used for machining in straight lines
• Machining of curved parts when radius is not
  constant.

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Components of Tool Path
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NURBS in CAD

• Non uniform rational B spline
• Curves defined by mathematical weight point apart
  from the curve that pull the curve towards to the
  point

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Advantages of NURBS

• Can define any 2 D object
• Easy to manage with few control points
• Easy to edit due to local control

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CAM for HSM

• Cutter path topology
• Helical ramping of tool in to part
• Control of feed rates

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Postprocessor

• Link between CAM system and CNC system
• G code generator or writer

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CNC tool and spindle

• Small tool diameter and low depth of cut
• Air coolant through spindle

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Challenges in Tool Path Generation

• Data starvation
• Surface finish

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NURBS Interpolation-A Breakthrough

• G code 6.2
• Transfer information of weights and control
  points into G code format
• G6.2 P4 K1 X11.9606 Y 1.1554 Z -1.9074 R1

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NURBS interpolation

• Can be archived by transfer of knot points and
  control points from CAD to CAM system.
• Sample program
• N0090 G6.2 P04 K0.0 X0.0 Y0.0 Z0.0
• N0100 K0.0 X.7663 Y1.5085
• N0110 K0.0 X2.343 Y4.3967
• N0120 K0.0 X4.8214 Y7.703
• N0130 K.0946 X7.3075 Y9.6216
• N0140 K.1839 X9.5059 Y10.2069
• N0150 K.2297 X11.2592 Y9.7021
• N0160 K.2685 X13.3658 Y8.4143
• N0170 K.3075 X14.9655 Y6.7408

G-code for NURBS
Order of the Curve
Knot Point
Control point
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How to achieve

• Generic postprocessor

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Advantages of NURBS Interpolation

• More Accurate Parts
• Improved Surface Quality
• Drastically Smaller Part Programs

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Questions andComments