Application of the micro water abrasive injector fine jet for precision machining.

Loeser, Carsten ; Duerr, Holger ; Pilz, Rolf 等

1. INTRODUCTION

The conventional abrasive injector waterjet cutting is proved to be usable for versatile machining tasks since a long time. But it is very limited in its precision and its applicability for precision machining (Loeser et al., 2009b; Miller, 2004; Liu, 2010). This served as a starting point for the research activities carried out in a cooperation between the Chemnitz University of Technology and the ATECH GmbH. Beside the unsatisfactoring kinematic capabilities/accuracy of the leading machines the standard abrasive injector waterjet cutting uses an abrasive waterjet diameter/kerf width of only 1.0 to 0.8 mm. The fine abrasive injector waterjet cutting reaches a kerf width of about 0.5 mm. When the now state of the art kerf width is 0.3 mm (Miller, 2004) or below (Vollrath, 2008), it is called micro abrasive waterjet cutting (Loeser et al., 2010b). Machinable tolerances, attributes or bridges in contours are much smaller than the jet diameter. Table 1 explains this classification for the abrasive injector waterjet in more detail.

Miller (Miller 2004) shows trials of a micromachining with abrasive suspension jets with a strongly reduced suspension jet diameter including the possibilities for an appropriate suspension valve. Among other things Liu (Liu, 2010) explains tests with a preproduction nozzle. Here the potential minimum jet diameter/kerf size is expected to be about 200 um (the same as in: Moriarty, 2009; Loeser, 2010a&b; Vollrath, 2008). At this size the industrial practicability ends (Loeser et al., 2010b). Liu further presents the tentative use of "stencil-aided waterjet stage" for a further reduction of the jet diameter. Under the conditions of a reduced injector jet diameter, the drilling of brittle materials is very challenging, as explained later on. A smaller jet diameter results in a smaller kerf and also reaches new spheres for the accuracy of inner corners and inner outlines. So the micro abrasive injector waterjet cutting achieves a significantly higher precision of the cutted contours. The finer grained abrasive material (commonly used: garnet sand of different groups of sizes between 63 um and max. 125 Um) improves the quality of the cut surface. The micro water abrasive injector fine jet is also better suited for the drilling and cutting of coated, sensible or multilayered materials (Loeser et al., 2010b). The precision machining with the abrasive injector waterjet is far more than only a reduction of the jet diameter. As explained in (Loeser et al., 2010b) e.g. the industrial practicability, a new technology and a stabilization of the cutting process are essential. This is especially important for a precision machining of brittle materials as glass and silicon. It was necessary to develope a new cutting head, different leading machines and the technology (Loeser et al. 2009a).

2. PRECISION DRILLING AND CUTTING OF GLASS AND SILICON

Compared to other materials the cutting and especially drilling of brittle materials like glass and silicon is much more challenging. The drilling is nessecary for the manufacturing of inner contours and done with lower water pressure to reduce the risk of damaging these brittle materials. A special technology and newly developed facilities are required in addition to the equipment (cutting head, leading machine) and technology already used for the developed micro abrasive injector waterjet fine cutting--in particular to stabilize the drilling process under these conditions (Loeser et al. 2010b; Loeser et al. 2009a).

So figure 1 shows main problems, samples of parts and tasks for the realisation of this special application of precision machining with an abrasive injector waterjet in more detail. A lost flow of abrasive material for example could lead to a destruction of the sensitive materials through the kinetic energy of the pure waterjet. As pictured, different work had to be done in the spheres of the processing plant and supplementary facilities as well as in the development of the technological conditions. The next figure (figure 2) presents summarised the important results and parameters of this work at a glance.

3. ACTUAL RESEARCH WORKS

Within a further research project in a partnership between the Chemnitz University of Technology and the ATECH GmbH and based on the experiences of the 2D-precision machining with an abrasive injector waterjet, this technology is used for a new 3D-5axis precision manufacturing with the abrasive injector waterjet. Main aspects for this task field are presented in the next figure (figure 3). Apart from fundamental basic explorations, including the occupational safety, the suitable kinematic concept for the leading machine was specified. Furthermore in connection with the development of necessary machine parts, tests for the 3D-precision machining, especially the determination of the cutting parameters had been successfully executed. The CAM-based modelling of the real micro water abrasive injector fine jet form, including the compensation of deviations, is currently under way.

[FIGURE 3 OMITTED]

4. CONCLUSION

The successfully implemented drilling and cutting of glass and silicon and the ongoing research works for the 3Dmachining had been the key aspects of this article. After the favourable realisation of a 2D-precision machining with the micro water abrasive injector fine jet also the more special application of drilling and cutting of brittle materials as silicon and glass was realized in a reliable and stable manner. Especially the implementation of the challenging drilling (e.g. start holes) with an reduced water pressure and a reduced but nevertheless secure and stable mass flow of the finer grained abrasive material was eminent important. When drilling brittle materials also a circling movement of the jet can be beneficial. As claimed in the result of the presented research works new applications for the abrasive waterjet cutting were opened up. Now the next step is the utilisation of the micro water abrasive injector fine jet for a 3D-5axis precision machining.

5. ACKNOWLEDGEMENTS

The authors thank the Industrial Research Groups Association (AiF, Berlin) for supporting the ATECH GmbH and the Chemnitz University of Technology in the bygone PRO INNO II cooperation project "WAFS/AWFC--Water-abrasive jet fine-cutting; Development, Optimisation and Implementation of a Novel, Process-Secure and Industrially Applicable Technology of Water-Abrasive Jet Fine-Cutting" and the actual ZIM cooperation project "Development and Implementation of Technology and Processing Equipment for the 3D-5Axis-Precision Processing by the Method of Water-Abrasive Injector Jet".

6. REFERENCES

Liu, H.-T. (2010): Waterjet technology for machining fine features pertaining to micromachining, In: Journal of Manufacturing Processes 12, p.8-18, www.elsevier.com/locate/manpro

Loser, C.; Seim, T.; Pilz, R. & Durr, H. (2009a): Prazisionsbearbeitung mit dem Wasserabrasivinjektorstrahl, In: Zeitschrift fur wirtschaftlichen Fabrikbetrieb (ZWF) Jahrg. 104 (2009) 7-8, p. 632-636

Loser, C.; Pilz. R.; Seim. T. & Durr, H. (2009b): Wasserabrasivstrahlfeinschneiden, In: Scientific Reports, Journal of the University of Applied Sciences Mittweida, Prozessentwicklung fur Teilefertigung und Montage, Nr. 3, 2009, p.37-40

Loser, C.; Thehos, K. (2010a): Schneiden- auf den Hundertstelmillimeter genau, Professur Fertigungslehre und ATECH GmbH erhohen Prazision des Wasserabrasivstrahlschneidens, In: TU-Spektrum, Das Magazin der Technischen Universitat Chemnitz, 1/2010, ISSN 0946-1817, p.31

Loser, C.; Pilz, R.; Seim, T. & Durr, H. (2010b): "Abrasive waterjet fine cutting based on the injector principle Technology and processing plant for the precision cutting with the abrasive injector waterjet", In: Proceedings of the 20th International Conference on Flexible Automation and Intelligent Manufacturing, FAIM 2010, California State University East Bay, USA, 12.-14. 07.2010, p. 635-642

Miller, D. S. (2004): Micromachining with abrasive waterjets, In: Journal of Materials Processing Technology 149 (2004), www.elsevier.com/locate/jmatprotec, p. 37-42

Moriarty, T. (2009): World premier showing of new kind of machining centre, www.waterjet.se, Accessed 12.11.2009

Seim, T. (2009): brochure ATECH GmbH Chemnitz, June 2009 Vollrath, K. (2008): Wasserstrahl schneidet gut ab in der Mikroproduktion, VDInachrichten, Nr. 28, 11.07.2008

Tab. 1. Division of the abrasive injector waterjet cutting
(cf. Seim, 2009; Loeser et al., 2010b)

 Standard abrasive Fine-abrasive
 injector waterjet injector waterjet
 cutting cutting

Kerf width ca. 0.8 mm ca. 0.5 mm

Accuracy [+ or -] 0.1...0.5 [+ or -] 0.05...0.2
of contours mm mm

Gauge of 1...100 mm 0.2...50 mm
materials

For items measuring the measuring the
 minimum size minimum size
 of ca. 30 of ca. 10 mm or
 mm or above above

Notes State of the State of the art
 art in the last in the last few
 20 years years

 Micro-abrasive
 injector waterjet
 cutting

Kerf width ca. 0.3 mm or
 below
Accuracy [+ or -] 0.02...0.1 mm
of contours or less

Gauge of 0.1...20 mm
materials

For items measuring the
 minimum size
 of ca. 3 mm or
 above

Notes Reliably
 implemented by
 ATECH in 2009

Fig. 1. Tasks and samples of parts for a precision machining of
brittle materials like silicon and glass

Precision drilling and cutting of brittle materials like glass and
silicon and sensible / filigree items with the abrasive injector
waterjet

Problems

Processing plant/
facility * Technology and basics

* Prevention of a * Brittle materials and * Smaller abrasive
jet reflection to filigree items particles (good for
the backside of accuracy and workpiece
the workpiece * Stabilisation of the surface quality, less
 flow of the abrasive cutting efficiency),
 material especially at challenging for drilling
 low pressures or with a operations under low
 significantly reduced water pressure
 flow of abrasive
 material, * Prevention of a
 blockage of the abrasive
* Clamping of * the pure waterjet material supply,
filigree items could damage the especially for (start)
made of brittle sensible parts drilling with low
materials pressures and finer
 * Prevention of a grained abrasive
 blockage in the mixing material
 chamber/focus nozzle
 especially for (start)
 drilling with low
 pressures and finer
 grained abrasive
 material

Fig.2: Solutions for the drilling and cutting of brittle materials

 Solutions
Processing plant/
facility's Technology and basics

* Pointcatcher * The use of the * Turn on of the
(instead of a grid right water nozzles abrasive material
and water basin) for for carrying away air and water at the
jet receiving, and (injector effect) right time
X-Y machine table

* New clamping system * Supplementary * Turn off the
 facilities for abrasive material
* Optimized geometry stabilisation of the first (the waterjet
of the mixing chamber mass flow of abrasive helps cleaning the
 material by mixing chamber and
 mechanical ways, focus nozzle)
 e.g. shaking

* Very accurate * Supplementary * Supplying the
cutting head for facilities for abrasive material
positioning the water blowing free (with and the water at the
and the focus nozzle the right air right time, e.g. when
 pressure) / cleaning starting the drilling
 the mixing chamber process
 and focusing tube

* Feeding the * Use of suited
abrasive material at process parameters
the right angle and e.g. water pressure,
connection into the feed rate, abrasive
mixing chamber material, particle
 size, type/ size/
 diameter of water
 and focus nozzles,
 length of focus
 nozzle, mass flow of
 abrasive material,
 working distance

Results

* Water abrasive injector jet diameter 0.3 mm ([empty set] 0.2 mm has
lower cutting efficiency (smaller jet and particle size) and a higher
possibility of an unstable flow of the abrasive material (when using
air as carrier), water pressure for drilling 500-600 bar, for cutting
3000 bar is enough, abrasive material: garnet sand, particle size
63-90[micro]m or 90-125[micro]m