Automatic Generation of Milling Toolpaths with Tool Engagement - - PowerPoint PPT Presentation

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Automatic Generation of Milling Toolpaths with Tool Engagement - - PowerPoint PPT Presentation

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Automatic Generation of Milling Toolpaths with Tool Engagement Control for Complex Part Geometry Alexandru Dumitrache Theodor Borangiu Anamaria Dogar Centre for Research & Training in Industrial Control Robotics and Materials Engineering

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SLIDE 1

Automatic Generation of Milling Toolpaths with Tool Engagement Control for Complex Part Geometry

Alexandru Dumitrache Theodor Borangiu Anamaria Dogar

Centre for Research & Training in Industrial Control Robotics and Materials Engineering University Politehnica of Bucharest

IMS 2010

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 1 / 36

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SLIDE 2

Outline

1

Overview 3D Laser Scanning System CNC milling issues Tool Engagement Angle

2

Related work

3

Proposed algorithm and experimental results Milling parts for algorithm evaluation Traditional toolpaths Proposed algorithm Results

4

Conclusions

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 2 / 36

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SLIDE 3

3D Laser Scanning System Overview

Robot Controller Rotary table controller 4-Axis CNC Milling Machine 1 2 3 4 5 7 6 PC 6-DOF Vertical Robot Arm Laser probe Rotary table Scanned workpiece Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 3 / 36

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SLIDE 4

3D Laser Scanning System Overview

6-DOF Articulated Robot Arm 4-Axis CNC Milling Machine Laser Probe Scanned Workpiece Rotary Table

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 4 / 36

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SLIDE 5

Main issues for CNC milling

CNC milling

Automatic CNC toolpath generation Milling parts with complex geometry Minimizing CNC milling time without overheating the cutting tool

Proposed solution

Depth map modelling of design part and raw stock Natural representation for 2.5D milling operation Can be extended to 4-axis milling

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 5 / 36

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SLIDE 6

Tool Engagement Angle

The amount of sweep subentended by each cutting edge as it engages and leaves the stock Proportional to the cutting forces It is known to increase at internal corners in the toolpath r D 

Milling tool Raw stock Tool engagement

∗

r

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 6 / 36

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SLIDE 7

Tool Engagement Angle ← → Stepover

On straight line toolpaths, TEA (θ) is proportional to stepover (s): s = 1+sin(θ −90◦) 2 , 0 ≤ θ ≤ 180◦ (1) θ = 90◦ +arcsin(2s−1), 0 ≤ s ≤ 1 (2)

37 60 90 120 143 180 0 10% 25% 50% 75% 90% 100% Tool Engagement Angle (deg.) Stepover (%)

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 7 / 36

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SLIDE 8

Related work

Coleman (2006) explains the problem well, with intuitive examples Stori and Wright (2000): modified offset toolpath for convex contours Bieterman (2001) replaced contour-parallel toolpaths with a smooth spiral, nearly circular at pocket center, and slowly morphing into the part shape as it gets closer to the part Ibaraki et al. (2004) removed the convexity requirement from Story and Wright’s approach Wang et al. (2005) defined a set of quantifiable metrics which can be obtained by pixel simulation Uddin et al. (2006) applied the Ibaraki’s approach for improving tolerance on the finishing part by offsetting it nonuniformly, so that the finishing step is done at constant tool engagement Rauch et al. (2009): constraints-based trochoidal toolpaths

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 8 / 36

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SLIDE 9

Milling parts for algorithm evaluation

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 9 / 36

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Milling parts – depth map representation

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 10 / 36

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SLIDE 11

Traditional toolpaths

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle 20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Direction-parallel toolpaths Contour-parallel toolpaths

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 11 / 36

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SLIDE 12

Trochoidal Step (SprutCam v7)

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle 20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Contour-parallel toolpaths Contour-parallel toolpaths with trochoidal step

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 12 / 36

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SLIDE 13

Trochoidal Step (SprutCam v7)

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle 20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Contour-parallel toolpaths Contour-parallel toolpaths with trochoidal step Tool engagement peak

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 12 / 36

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SLIDE 14

Trochoidal Step (SprutCam v7)

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle 20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Contour-parallel toolpaths Contour-parallel toolpaths with trochoidal step Tool engagement peak Tool engagement decreased

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 12 / 36

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SLIDE 15

Trochoidal Step for Complex Geometry (SprutCam v7)

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle 20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Contour-parallel toolpaths Contour-parallel toolpaths with trochoidal step

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 13 / 36

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SLIDE 16

Trochoidal Step for Complex Geometry (SprutCam v7)

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle 20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Contour-parallel toolpaths Contour-parallel toolpaths with trochoidal step Tool engagement peaks are still present!

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 13 / 36

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SLIDE 17

Proposed algorithm

Input

Tool diameter Prescribed tool engagement angle Binary image representing the design part (2D section) Binary image representing the raw stock (2D section) The 2D sections can be obtained by thresholding a 3D depth map

Output

2D milling toolpaths consisting of small linear segments Raw stock shape after the generated milling operation

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 14 / 36

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Proposed algorithm

Contour reached Engagement exceeded Found point

  • utside contour

Contouring

F

  • u

n d p

  • i

n t

  • n

t h e c

  • n

t

  • u

r

N

  • p
  • i

n t s f

  • u

n d

No circumference pixels engaged All contour points visited

Constant Engagement Start Stop Find Starting Point

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 15 / 36

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Constant Engagement Milling

Main section of the algorithm

Milling a raw stock with arbitrary shape The only constraint is the tool engagement angle The raw stock shape is updated at every step

Engagement Milling cutter Previous trajectory Advancing direction Advancing direction for 90o

TEA:

Previous advancing direction: 0o 360o 270o Intersection point

90

  • −ref 

 p 90

climb

90o Raw stock

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 16 / 36

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SLIDE 20

Constant Engagement Milling

Example: toolpath with constant engagement for arbitrary raw stock shape

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 17 / 36

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Contour Milling

Contour Milling

Tool moves along the offset contour Tool is always tangent to the design path Usually, tool engagement angle is much smaller than the prescribed value

Stop conditions

When TEA exceeds the prescribed value with more than a small threshold, the algorithm switches to Constant Engagement mode When all contour points are visited, the algorithm will search for a new starting point

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 18 / 36

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Contour Milling

Example: Contour milling for the test part Direction for constant engagement Direction for contour milling

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 19 / 36

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SLIDE 23

Contour Milling

Tool engagement angle exceeded the prescribed value Direction for constant engagement Direction for contour milling

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 20 / 36

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Contour Milling

The algorithm switched to constant engagement milling Direction for constant engagement

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 21 / 36

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Contour Milling

The algorithm switched to constant engagement milling

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 22 / 36

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Finding Starting Point

The first possibility is chosen from the following:

1

Continue a contouring operation, from the point where the algorithm switched from Contouring to Constant Engagement

2

Enter the raw stock horizontally, from lateral

3

Plunge the cutter into raw stock

Input

Current cutter position: (x0,y0) Current raw stock and part shapes (2D images)

Output

Starting point for next milling operation: (x,y) Milling trajectory for moving the cutter to (x,y):

Cutter retraction moves or tangent / plunge entry toolpaths

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 23 / 36

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SLIDE 27

Example movie

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 24 / 36

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SLIDE 28

Results – 37◦ engagement

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 25 / 36

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SLIDE 29

Results – 60◦ engagement

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 26 / 36

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Results – 90◦ engagement

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 27 / 36

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Results – 120◦ engagement

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 28 / 36

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Results – 60◦ engagement

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 29 / 36

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Results – 90◦ engagement

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 30 / 36

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SLIDE 34

Results – 120◦ engagement

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 31 / 36

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Results – 135◦ engagement

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 32 / 36

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SLIDE 36

Sharp corners

Sharp corners

The generated toolpath may contain external corners These corners do not cause an increase in the tool engagement However, they are not good for machine dynamics Corners are smoothed by the machine controller, with G64

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 33 / 36

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SLIDE 37

Sharp corners

Sharp corners

The generated toolpath may contain external corners These corners do not cause an increase in the tool engagement However, they are not good for machine dynamics Corners are smoothed by the machine controller, with G64

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 33 / 36

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SLIDE 38

Sharp corners

Sharp corners

The generated toolpath may contain external corners These corners do not cause an increase in the tool engagement However, they are not good for machine dynamics Corners are smoothed by the machine controller, with G64

20 40 60 80 100 30 60 90 120 150 180 Tool Engagement Angle

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 33 / 36

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Results

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 34 / 36

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Results

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 35 / 36

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Conclusions

2D toolpath generation with tool engagement control

Prescribed reference value for engagement angle Maximum allowed overshoot (default: 20◦)

Toolpath consists of small linear segments Suitable for arbitrarily complex part and raw stock geometry Raw stock geometry can be digitized with 3D scanning Reduces lubrication requirements and increases tool life Higher feed rates can be used, compared to traditional toolpaths Best results are obtained using this method for roughing, combined with the method from (Uddin et al., 2006) for finishing The algorithm is used for milling complex 3D surfaces on milling machines with 3 or 4 axes

Alexandru Dumitrache (CIMR) Milling Paths with Tool Engagement Control IMS 2010 36 / 36