Improving the accuracy of positioning of work-piece origin using 3D Touch
probe
Abstract:
One of the biggest challenges in the manufacturing industry is to produce highly accurate
work-piece at low cost. The improper positioning of work-piece origin during cutting process
with Abrasive Water Jet machine (AWJ) will lead to dimensional errors, especially while
working on variable heights of work-piece and during the modifications as well.
The purpose of this paper is to present the experimental approach of using 3D Touch probe in
minimizing the inaccuracy of positioning of work-piece during the modification of workpiece. The experiments were conducted on modifying the work-piece using both 3D Touch
probe probe and laser beam for positioning of work-piece origin. The results show that
setting the work-piece origin using 3D Tactile-optical probe is more accurate and efficient
during the modification of work-piece when compared to laser beam.
Keywords: AWJ, 3D Touch probe, laser beam, work-piece origin, accuracy.
Introduction:
Abrasive water jet machines are being widely used by the manufacturing industries.
Producing the highly accurate work-piece at low cost is one of the biggest challenges in the
manufacturing industry. So many of the manufacturing industries are looking for a practical
means to improve the accuracy of cutting process. The principle of AWJ is to use the method
of forcing the highly-pressured water through a small hole (“orifice”) to concentrate on a
small area with an extreme amount of energy. These machines are rapid, efficient, flexible
and precise. The setup and fixture of AWJ machine is simple when compared to CNC lathe
or Milling machines. The setup with water jet is just a matter of loading the part drawing into
the software where setting the material, thickness, positioning of drawing, assigning the
speeds, generation of ISO-file and setting the work-piece origin using laser beam. As setting
the work-piece of origin by means of laser beam is inaccurate, experiments were conducted
on improving the setup of work-piece origin accuracy using 3D Touch probe.
In general during the cutting process, the errors can be classified into
1. Beam Deflection or steam lag
2. Inside corner problems
3. Increased taper
4. Sweeping out of arcs.
5. Fixturing
6. Material Instability
7. Pump issues
8. Water pressure at the nozzle
9. Cutter compensation error
10. Programming error
11. Machine errors
12. Dimensional error
This research has been concerned to the dimensional error.
Tool measurement on the machine shortens non-productive times, increases machining accuracy and reduces
scrapping and reworking of machined parts. With the tactile TT touch probes and the contact-free TL laser
systems, HEIDENHAIN offers two completely different possibilities for tool measurement.
TT touch probes
Probing method
TL Laser System
Physical probing
Non-contacting by laser beam
3-dimensional: ±X, ±Y, +Z
2-dimensional: ±X (or ±Y), +Z
Probing forces
Axial: 8 N, radial 1 N
No forces, operates without contact
Tool materials
Breakage-prone teeth are at
risk
Any
Sensitivity to
unclean tools
Very small
High (tool must be cleaned with blown air before measurement)
Possible measuring
cycles
Length, radius, breakage,
individual teeth
Length, radius, breakage, individual teeth, tooth geometry (also for
combined contours)
Installation effort
Simple connection to NC
control
PLC adaptation in the NC control necessary (6 outputs, 3 inputs),
compressed air connection
Cables
Cables
Probing directions
Signal transmission
Infrared to SE
642
2 σ ≤ 1 µm
2 σ ≤ 0,2 µm
2 σ ≤ 1 µm
Min. tool diameter
3 mm 1)
0,03 mm
0,1 mm
Max. tool diameter
Unlimited
37 mm 2)
Repeatability
Type
TT 140
TT 449
1) Probing force must not result in tool damage
2) With centered measurement.
TL Nano
30 mm 2)
TL Micro 150
80 mm 2)
TL Micro 200
180 mm 2)
TL Micro 300
AWJ
EDM
Laser
Plasma
300
100
20
1
Gas
Cutting
E
D
M
AWJ
Plasma
Laser
er
+/-0.1mm
+/-1mm
+/- 5mm
Reachable accuracy
Gas
Cutting
Fundamental usage of 3D Touch probes:
This paper describes how to obtain the accurate finished parts in the cutting operation on
AWJ machine, a measuring instrument named 3D-Touch probe has been used to position the
work-piece origin instead of laser beam.
This can set the zero points quickly and accurately, thus reducing the setup and dimensional
errors while increasing precision. With the use of 3D stylus precisely touch reference edges
on work-piece and fixtures to set the origin. The accuracy of this kind of probes is 0.01mm.
As this measuring instrument is compact and robust, it’s good enough to use on AWJ
machine.
Experimental setup and procedure:
The experiment was conducted on modifying the work-piece which has been cut from the
long hard steel plate of 10mm thickness. The modification consists of adding two holes to the
finished work-piece with the tolerance of + 0.5mm as shown in the fig. During the
modification process, the work-piece has been placed at the same position approximately on
the plate where it has been cut previously. The work-piece origin has been set with the help
of laser beam and the cutting process is continued with the same machining parameters as
before. The modified work-piece is produced and the results show that the added two holes
are out of tolerance. This is due to inaccurate setting of work-piece origin. As the thickness of
laser beam is 1-2 mm, this can lead to improper positioning and thus dimensional errors.
The above experiment has been repeated with the help of 3D Touch probe instead of laser
beam for setting of work-piece origin. The results show that the added holes are accurately
positioned.