Influence of nozzle wear on surface quality at abrasive waterjet cutting.

Hloch, Sergej

Abstract: The paper deals with the evaluation of the focusing tube wear on surface quality created by abrasive waterjet cutting technology. On the purpose of the qualification and quantification of the abrasive focusing tube wear, increasing of the inner diameter influence, it has been provided two experiments. By means of design of experiments where was simulated the influence and the effect of factors at two levels; the increasing of the focusing tube inner diameter with the interaction of three main technological factors: abrasive mass flow rate, traverse rate and pressure on surface profile parameter Ra. From the provided experiments and factorial analysis of selected abrasive waterjet factors results that the focusing tube wear has the negative effect on the number values of the surface profile parameter Ra.

Key words: focusing tube wear, surface quality

1. INTRODUCTION

The manufacture of precision parts emphasizes final finish machining operations which may account for as much as 15 % of the total manufacturing costs. The abrasive waterjet technology process optimization has been accelerated because of the need for improvements in surface quality. Moreover, the process features change drastically with machining factors entering the abrasive waterjet cutting process (Brandt et al., 2000), (Ergura et al., 2000).

2. PROBLEM DEFINITION

Technological process of the cutting by means of abrasive waterjet is provided at production equipment by means of tool--abrasive waterjet, that properties characteristics are not degraded in operation time in contrast to classical cutting tool. But in case of the abrasive waterjet technology, the most wearable part of the AWJ equipment is focusing tube, where the abrasive waterjet stream is formed (Jurisevic et al., 2003), (Jurisevic et al., 2006), (Martinec et al., 2002), (Valicek, et al., 2004), (Hlavae, et al., 2003).

[FIGURE 1 OMITTED]

According to measured deviation of the cutting accuracy have been estimated five degrees of the focusing tube wear, which size of the inner diameter [d.sub.f] are in estimated tolerances:

1. Wear degree--[d.sub.f] = 0,89 to 0,90 mm,

2. Wear degree--[d.sub.f] = 0,91 to 1,00 mm,

3. Wear degree--[d.sub.f] = 1,01 to 1,10 mm,

4. Wear degree--[d.sub.f] = 1,11 to 1,20 mm,

5. Wear degree--[d.sub.f] = 1,21 to 1,30 mm.

In dependence of the abrasive mass flow rate [m.sub.a] and operation time t are degrees of wear different. Following figure 2 illustrates the influence of abrasive mass flow rate and the operation time on focusing tube wear. Surface plot was obtained by empirical observation. Mathematically that dependence can be expressed by following equation (1):

[d.sub.f] = -3,0019+0,0085.[m.sub.a]+0,0419.t (1)

[FIGURE 2 OMITTED]

3. EXPERIMENTAL DESIGN

In order to investigate the influence of evaluated AWJ factors on surface profile parameter the average roughness Ra cutting quality, full factorial design for four independent variables was designed. Full factorial analysis was used to obtain the combination of values that can optimize the response, which allows one to design a minimal number of experimental runs (Montgomery, 2001), (Gombar, 2006). Considering that at two levels of the [x.sub.1], [x.sub.2], [x.sub.3], [x.sub.4], and variables are -1 and 1, the designed matrix is 16-observations for dependent variable Ra. Each cut has been replicated three times; yielding total of 48 cuts. As a cutting an Autoline cutting head from Ingersoll-Rand head has been used. As a target material has been used aluminum alloy. The properties of each sample are: length 35 mm, width 8 mm, and height 12 mm. A digital surftest Mitutoyo 301 has been used to calculate the average roughness with 0.01 mm precision of measurement. The measurement procedure consisted of measure variable dependent Ra in 1, and 9 mm (Hloch & Valicek, 2006).

4. RESULTS AND DISCUSSION

On figure 3 is illustrated the influence of the focusing tube inner diameter raising [d.sub.f] in interaction with abrasive mass flow rate ma and pressure p on surface profile parameter Ra, measured in depth trace of h = 1 mm. According to fig. 3 the significant influence on surface profile parameter Ra has the diameter of the focusing tube [d.sub.f]. With the increasing of the focusing tube inner diameter in wear consequence the values of Ra are raising. The more pronounced influence of the focusing tube with interaction abrasive mass flow rate ma on average roughness Ra was finding out on depth trace of 9 mm. The value of the Ra decreases as the pressure is raising (fig. 4).

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

5. CONCLUSION

Surface profile parameter belongs to the basic microgeometrical characteristics of the surface produced by abrasive waterjet. The values of the average roughness parameter Ra determine the necessity of the further finishing of the surface and the total utilization of the material. It raises the manufacturing costs on production by production process extension, which decrease competitiveness. In the paper it was concerned to study of the focusing tube wear on surface quality produced by abrasive waterjet by means of design of experiments. According to full factorial analysis for the further optimization and the process factors selection it is necessary to take in to account the wear of focusing tube, which has the negative influence on surface profile parameter Ra as a factor at creating of the algorithm for on-line control of abrasive waterjet cutting technology. From the evaluation of statistical and physical-analytical rules between the input and the output quantities, it is possible to proceed to the mathematical generalization of these rules and the deducing of statistical and physical equations for predictive and design calculations of particular cuts.

6. REFERENCES

Brandt, S., Maros, Z., Monno, M. (2000). AWJ parameters selection--a technical and economical evaluation. Jetting Technology, BHR Group.

Ergura., H. S., GOlcU M., Pancara, Y., Dombaycic, A., O. (2006). Analysis of the cutting power on abrasive waterjet system applications. In. Proceedings of 5th International Symposium on Intelligent Manufacturing Systems, 475-483.

Gombar, M. (2006). Creation of statistical model of the produced surface by means of Matlab. In Manufacturing engineering. (pp. 14-17).

Hlavac, L., Kusnerova, M., Dvorsky, R., Madr, V. (2003). Increasing of efficiency of the high-energy water jet rock quarrying by jet pulsation. In. Proceedings of the Mineral Raw Materials and Mining Activity of the 21st Century. VSB-TU Ostrava, Ostrava, pp. 383-392.

Hloch, S., Valicek, J. Estimation of abrasive waterjet technology factors significance at the cutting of aluminum and stainless steel. In: Fine mechanics and optics. vol. 51, no. 11-12 (2006), p. 326-329. ISSN 0447-6441.

Jurisevic B., Kuzman K., Junkar, M. (2006). Water jetting technology: an alternative in incremental sheet metal forming. The International Journal of Advanced Manufacturing Technology. Springer. pp. 18-23. ISSN 1433-3015.

Jurisevic, B., Coray, P. S., Heineger, K. C., Junkar, M. (2003) Tool Formation Process in Abrasive Water Jet Machining. In: Management of Innovative Technologies MIT'2003. Ljubljana: University of Ljubljana. pp. 73-85.

Martinec, P., Foldyna, J., Sitek, L., Seueka, J., Vasek, J. (2002). Abrasives for AWJ cutting. Academy of Sciences, Czech Republic. p. 80.

Montgomery, D., C. (2001). Design and analysis of experiments. 5th. edition, Hamilton Printing Company. ISBN 0-471-31649-0.

Valicek, J., Louis, H., Schenk, A., Drzik, M., Hlavae, L. M., Chlpik, J. (2004). Utilization of the optical methods for analyses of cutting edges. BHR Group, p. 487-501.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the support of Scientific Grant Agency of the Ministry of Education of Slovak Republic, for their contribution to project 1/4157/07.