Nonconventional Technologies Review - no. 4 / 2007

Transcription

1 SIGNIFICANCE OF BARTON GARNET AND OLIVINE EVALUATION AT ABRASIVE WATERJET CUTTING BY FACTOR ANALYSIS Sergej HLOCH 1, Jan VALÍČEK 2 ABSTRACT: The paper deals with experimental investigation of the influence of Barton Garnet and Olivine abrasives with interaction of selected abrasive waterjet factors; stand off, traverse rate and abrasive mass flow rate on surface profile parameter average roughness by means of full factorial analysis. The experiment represents the preliminary test, towards to the optimal factors selection for the effective abrasive wateret on-line control. KEYWORDS: abrasive waterjet, surface roughness 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 [2], [13]. 2. RELATED WORKS AND PROBLEM DEFINITION Technologic process of abrasive machining in real objects is in the most of cases very dynamic and stochastic process [17]. Analytic process identification seems to be no effective and of low practical use. By its application, it is not possible to achieve the completed model of the process the influence of certain parameters are neglected, in some of the factors there are not known the exact values, they are variable in time and most often, the intuition is applied to determine them [4]. For such classic experimental design, some routine is needed and it is not effective from the time point of view. On the other hand, the mathematical statistical methods (Design of Experiments) enable the statistic model design outsourcing from the great amount of independent variables [7]. The abrasive waterjet 25 technology of process factor 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 [12]. Most scientific papers concerning to the evaluation of microgeometrical features of abrasive waterjet cutting are available [1], [2], [4], [5], [16]. The objective is to determine the final shape of the surface quality, which is a function of the geometric characteristics of the abrasive waterjet tool. The roughness of the machined surface is seen through microgeometrical irregularities of the surface (fig. 1). The result of this hydro-mechanical cutting process depends on a large number of process factors such as water pressure, orifice diameter, standoff distance, abrasive and material feed rate etc. The shape of the cutting jet stream is also very important. The waterjet pressure has a great influence on the cut-quality. The evaluation of the quality of machined surface is based on the judgment of its roughness. Theoretical roughness depends exclusively on tools geometry and applied process of machining whereas a real roughness appears as the result of theoretical roughness though with bigger or lesser occasional roughness provoked by the many factors. The surface roughness is influenced by the most important factors (fig. 1) that are divided into two basic groups (fig.2); direct and indirect. These factors create surface as

2 area of trajectory working movement of abrasive waterjet. It is specific way of material machining because there are used particles with more edges; that are random oriented in the liquid phase waterjet [7], [8], [9]. Fig. 1. AWJ tool generation and impact to the target material. Fig. 2. Influential factors on surface roughness. 3. PROBLEM SOLUTION In order to investigate the influence of abrasive waterjet process factors on average roughness Ra cutting quality, full factorial design for six independent variables has been 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 [4], [11], [12]. Among the many process variables that influence the cutting results, four have been selected and considered as factors in the experimental phase. A 2 4 full 26 factorial analysis has been used with 3 replicates at the center point, leading the total number of 16 experiments. Evaluated factors were stand off x [mm], traverse rate v [mm.min -1 ], abrasive mass flow rate m a [g.min -1 ] and different abrasive material olivine and Barton Garnet has been used. Considering that the two levels of the x 1, x 2, x 3, x 4, and variables are -1 and 1, the designed matrix is 16-obsevations for dependent variable Ra. 4. EXPERIMENTAL PROCEDURE

3 According to design of experiments of 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 aluminium 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 µm precision of measurement. The measurement procedure consisted of measure variable dependent Ra in 1, and 11 mm with replicates of 6-times yielding total of 384 measurements. 5. RESULTS AND DISCUSSION The quantitative description of the conditions effects on average roughness was performed. Response surface methodology is an empirical modeling technique used to evaluate the relationship between a set of controllable experimental factors and observed results. The results were analyzed using the analysis of variance as appropriate to the experimental design used. The normality of experimental measured data has been tested according Shapiro-Wilkson test criteria for its good power properties as compared to a wide range of alternative tests. The regression coefficients obtained after ANOVA gives the level of significance of variable parameters tested according Student s t-test. The significance of independent variables is interpreted in the chart that shows the factors significance in percentual expression of regression coefficients. From the statistical factor evaluation of the experiment results that surface profile parameter average roughness level is dominantly influenced by tested abrasives, abrasive mass flow rate, traverse speed, the interaction between abrasive mass flow rate and the traverse rate and the stand off at the h = 1mm (Fig. 3). 27 Fig. 3. Significance of factors influence to Ra in h = 1mm. As can be seen from the pareto analysis influence of the evaluated factors and their significance to Ra is changing as the depth of the cutting material increase. Fig. 4. Significance of factors influence to Ra in h = 11mm. In h = 11 mm the significance of evaluated factor is different. The significant factors which influence the surface profile parameter Ra are abrasive mass flow rate and traverse rate. The kind of abrasive and the stand off the both are not significant. From the pareto analysis results that the significance of the abrasive mass flow rate and the traverse rate increase as the extended depth of the machined target material. Close specification of the factor combination influence are shown on following plots of marginal means for independent variables (Fig. 5), (Fig. 6), (Fig. 7), (Fig. 8).

4 Fig. 5. Plots of marginal means for flow rate m a ; traverse rate v; and kind of abrasive (Aluminium h = 12 mm, Ra measured in 1mm). Fig. 7. Plots of marginal means for flow rate m a ; traverse rate v; and stand off x; (Aluminium h = 12 mm, Ra measured in 1 mm). The high variability of the surface roughness evaluated by surface profile parameter Ra has been find out at the evaluation of the three factors (m a, x, abrasive) at the depth h = 1mm. Fig. 6. Plots of marginal means for flow rate m a ; traverse rate v; and kind of abrasive (Aluminium h = 12 mm, Ra measured in 11mm). 28 Fig. 8. Plots of marginal means for flow rate m a ; traverse rate v; and stand off x; (Aluminium h = 12 mm, Ra measured in 11 mm). At the traverse rate of 100 mm.min -1 (Fig. 7) that confirms the significance of the factors interaction v and m a. For comparison of the same situation at h = 11 mm the hardness of the evaluated abrasives the hardness as a factor is not significant to average roughness of the aluminium (Fig. 6), (Fig. 8). The significance of the abrasive mass flow is high as the traverse speed increase and the h = 11mm. As for the used abrasives (Fig. 6), (Fig. 8), (Olivine and Barton Garnet) the development of the numerical values of the

5 average roughness Ra are the same. In that case the use of the olivine as a abrasive material at the AWJ cutting of the aluminium it is suitable to use for the cutting of the thin material. AWJ as a floppy tool loose the cutting effectiveness a function of stand off distance. The (Fig. 7) and (Fig. 8) shows the influence of the following factor combination; traverse rate, abrasive mass flow rate and stand off). As can be seen stand off significantly influences the average roughness numerical values at initial zone of the workpiece at the traverse rate v = 50 mm.min -1 a v = 100 mm.min -1 in depth h = 1 mm. In h = 11 mm the stand off is significant only at the feed rate v = 50 mm.min -1. As can be seen from the results obtained from the factor analysis distance between the end of the abrasive nozzle and the material is sensitive to operation, that is why the stand off is necessary to investigate as a factor together with others. 6. CONCLUSION From statistical physical and analytical regularity evaluation of the relationship between input and output data, it is possible to proceed to the mathematical generalization of these regularities and derive an equation for prediction and project calculation of the concrete cuts. By that calculation it could be theoretical based technology factors selection that will be optimal for the given machined material on required quality, the performance parameters and the total machining economy. This analysis has pointed out that variable independent factors influence the morphology of the cutting surface in terms micro cutting quality. It has been found that influences of selected factors are variable related to different depth. The analysis using full factorial design reveals that higher values of average roughness are caused with increasing of traverse rate. Material thickness and traverse rate and their interaction as shown previously have most significant effect to average roughness. The most important factors influencing the cutting quality of aluminium are traverse rate and abrasive mass flow rate. From performance analyses results, that smooth cut allows achievement of maximum cutting depth in given target 29 machined material. The results will be systematically updated and statistically and analytically evaluated in order to be fully usable for the prediction of the geometrical surface state and for the project of optimisation of the main AWJ process factors, which covers all kinds of materials used most frequently in technical professions. REFERENCES [1] Annoni, M., Monno M. A lower limit for the feed rate in AWJ precision machining. In. BHR Group 2000 Jetting Technology, p , ISBN [2] Ergüra., H. S., Gölcü M., Pancara, Y., Dombaycıc, A., Ö. Analysis of the cutting power on abrasive waterjet system applications. In. Proceedings of 5th International Symposium on Intelligent Manufacturing Systems, 2006: [3] Hloch, S., Gombár, M. Influence of solid phase distribution in waterjet to quality of surface roughness. In: Scientific Bulletins of Rzeszów University of Technology. Rzeszów : Wydawnicza Politechniki Rzeszowskiej, p ISSN [4] Hashish, M.: Modeling Study of Metal Cutting with Abrasive Waterjets. Trans. of the ASME, Journal of Eng. Mat&Tech, Vol. 106, No. 1, [5] Hashish, M.: Pressure Effect in Abrasive Waterjet (AWJ) Machining. Trans. of the ASME, Journal of Eng. Mat&Tech., Vol. 111, No. 7, [6] Hloch, S. Fabian, S. Rimár, M. Design of Experiments Applied on Abrasive Waterjet Factors Sensitivity Identification. In: Nonconventional Technologies Review [7] Hloch, S: Evaluation of abrasive waterjet factors influencing the surface quality. In: Transactions of the Universities of Košice. č. 2 (2005), s ISSN [8] Jurisevic, B., Coray, P. S., Heiniger, K. C., Junkar, M.: Tool Formation Process in Abrasive Water Jet Machining. In: MIT 2003 University of Ljubljana [9] Lebar, A., Junkar, M. Simulation of abrasive water jet cutting process. Modelling Simul. Mater. Sci. Eng. 12 (2004) [10] Mason, R., L., Gunst, R,. F., Hess, J., L. Statistical design and analysis of experiments. Second edition. Wiley-Iterscience. A John Willey & Sons Publication, New Jersey (2003) ISBN

6 [11] Montgomery, D., C. Design and analysis of experiments. 5th. edition, Hamilton Printing Company, ISBN [12] Radvanska, A. FMEA risk assessment of abrasive waterjet cutting. In. proc. New trends in the operation of production technology FVT TU Kosice with the seat in Presov, ISBN , - p [13] Slattery, T., J. Abrasive Waterjet Carves Out Metalworking Niche, Machine and Tool Blue Book, July 1991, pp [14] Smith, E., A., Slaughter, W., S. Neural Network Modeling of Abrasive Flow Machining, Proceedings of the Advanced Technology Program Motor Vehicle Manufacturing Technology Public Workshop, NIST Document, NISTIR 6079, Ann Arbor, MI, (1997). [15] Valíček, J., et al. Method of the determination of superposition relation of changes in surface geometry to mechanical parameters of material due to corrosion. In. Acta Mechanica Slovaca. 3-A/2005. ISSN p [16] Lupták, M. Study of the measuring and scanning methods in the processes of the cutting and machining with waterjet. In Proc. Metalurgia Junior 05, Deň doktorandov HF Košice, [17] Monka, P.: Computer Aided Design of Fixtures for NC Machine Tools, Buletin Stiintific, Seria C, Volumul XIX, Baia Mare, Rumunsko, 2005, pp , ISSN AUTHORS 1. Ing. Sergej Hloch, PhD., Department of Technology Systems Operation, Faculty of Manufacturing Technologies, Technical University of Košice with the seat in Prešov, Prešov, Slovakia 2. Ing. Jan Valíček, PhD., Institute of Physics, VŠB-Technical University of Ostrava, Ostrava, Czech Republic. ACKNOWLEDGEMENTS The authors would like to acknowledge the support of Scientific Grant Agency of the Ministry of Education of Slovak Republic, Commission of mechanical engineering, metallurgy and material engineering, for their contribution to project 1/4157/07 30