Experimental comparison of conventional and highly abrasive abrading agents.

Moravcikova, Jana ; Lipa, Zdenko

1. INTRODUCTION

Important role in increase of technical level and precision of production is industry, where's a lot of grinding components. To the precision grinding is requirement not only quality grinding machine, dresser wheel but abrading agent, too. Is very important to find the optimally setting of the abrasive and dressing parameters, by which they will be achieved qualitative and economically the best parameters of machined surface work piece. By trend of the most accurate dressing of grinding wheels in small-series production are diamonds CNC forming wheels (Janac et al., 2004). The dressing of abrasive wheels after defined number of period and by using different abrading agents' type has a big influence on quality of machining surface. The criterion is the surface roughness parameter Rz. For realization of experiment is proposed plunge-cut grinding and grinding wheels with conventional and high abrading agent. The dressing period of grinding wheels depend to abrading agent.

2. CONVENTIONAL AND HIGHLY ABRASIVE ABRADING AGENTS

Between conventional abrading agents belong grinding wheels on basis of alumina (Al2O3) Standard alumina and semi-high-grade alumina is made of bauxite. High-grade alumina is made of pure alumina oxide in electric furnace at temperature about 2000[degrees]C (fig. 1). Between conventional abrading agents belong grinding wheels on basis of silicon carbide (SiC), too (Humar, 2005).

Between highly abrasive abrading agents we can to include micro-crystal sintered alumina. Fine crystalline grain structure allows on increasing grain wear only chipping his small particles, and grinding-grain edges stay always sharp (Kolarik, 2005).

Development in field of grinding wheels on basis [Al.sub.2][O.sub.3] arrived to new type of grinding wheels--SG (sol-gel). SG abrasive grain has higher hardness and better toughness. SG abrasive grain consisted from submicron particles. These particles can to drop out from abrasive grains during grinding. This micro-crystal fracturing of SG abrasive grains leads to different wear process of SG grains in comparison with conventional grain. SG abrasive grain is suitable for grinding of hardened steels with hardness above 60 HRC. (Neslusan, 2003)

[FIGURE 1 OMITTED]

3. EXPERIMENTAL RESULTS

For experiment was used CNC machine, by whose we can to regulate abrasive and dressing parameters too. Work pieces used in the experiment were produced from material 100Cr6, hardened and tempered to 58[+ or -]4 HRC (Hazlinger & Moravcik, 2007).

As a conventional abrading agent, with which were compared the results of grinding by highly abrasive abrading agents, is grinding wheel of company TYROLIT 508x22x254 with specification 97A100L6V112.

As a highly abrasive abrading agent, is grinding wheel of company ATLANTIC 508x20x254 with specification EB3120K7VB and grinding wheel of company Hermes with specification 3SK3 100/1 M-N5 V09G (fig. 2).

[FIGURE 2 OMITTED]

3.1 Surface roughness by using conventional abrading agent

Surface roughness specified by drawing documentation [R.sub.Z] = 4 [micro]m. The period of dressing is 25 work pieces. The measuring was realised periodically in 10 consecutively following period of abrasive wheel dressing. Measuring data are in the Table 1.

Average roughness after dressing of grinding wheel: RZ = 2,689 [micro]m. Average roughness before dressing of grinding wheel: [R.sub.Z] = 2,279 [micro]m (fig. 3). By increasing of dressing period on 30 parts--work pieces, incurred the burning on the work piece surface, which were inaccessible for the further processing.

3.2 Surface roughness by using highly abrasive abrading agent Atlantic and Hermes

The period of dressing is 70 parts. Measuring data are in the Table 2.

Atlantic--average roughness after dressing of grinding wheel: [R.sub.Z] = 2,923 [micro]m. Average roughness before dressing of grinding wheel: RZ = 2,043 -m. By increasing of true period on 80 parts appeared the problems with stability of prescribe geometrical dimensions.

Helmes--average roughness after dressing of grinding wheel: [R.sub.Z] = 2,617 [micro]m. Average roughness before dressing of grinding wheel: [R.sub.Z] = 1,937 [micro]m. The stability of prescribe geometrical dimensions was good by observance of dressing period 70 parts. After longer time of grinding were the burnings on the surface of work piece.

[FIGURE 3 OMITTED]

4. CONCLUSION

The contribution deals by experimental comparison of conventional and highly abrasive abrading agent at plunge-cut grinding. During the experiment was found, that the Atlantic grinding wheel is the best for our grinding conditions and a type of machining work piece. This grinding wheel doesn't achieve the best average roughness, but its geometric dimension stability was comparable with Hermes grinding wheel during the whole time period of wheel dressing. The better quality of the surface by reason of burning, which may to arise during grinding, decides for the selection of Atlantic grinding wheel. The major criterion of conventional and highly abrasive abrading agent comparison was the surface roughness and economy of production. The number of work pieces, after which is needs to dress the grinding wheel, was given on 25 by using of conventional abrading agent. The depth of cut at dressing was 35 [micro]m. The number of work pieces, after which is again needs to dress the grinding wheel, was given on 70 by using of highly abrasive abrading agent. The depth of cut at dressing was only 15 [micro]m. We achieved the significant saving of abrading agent and smaller wear of pulley dresser.

ACKNOWLEDGEMENT: This paper was elaborated in the frame of project: VEGA 1/4111/07

5. REFERENCES

Janac, A.; Batora, B.; Baranek, I., LIPA, Z. (2004). Technologia obrabania. Machining technology. STU, ISBN 80-227-2031-3, Bratislava.

Humar, A., (2005). Technologie 1, Technologie obrdbeni 3 cast. Technology 1, Machining technology 3. Brno. Available from:http.//www.sjf.tuke.sk/ktam. Accessed: 2007-05-05.

Kolarik, M. (2005). Nove trendy presneho brusenia a orovndvania. New precision grinding and dressing trend. In Strojarstvo--Strojirenstvi, No. 11, pp. 42-43.

Neslusan, M. (2003). Technicko--ekonomicke aspekty aplikacie SG brusnych kotucov pri bruseni kalenych oceli. Technical and economic aspects of the application SG grinding wheels by grinding of hardened steels. In Strojarstvo--Strojirenstvi,, Vol. 6, No. 7, pp. 54.

Hazlinger, M.; Moravcik, R. (2007). Degradacne procesy a predikcia zivotnosti. Degradation processes and lifetime prediction. Elektronicke skriptum. Trnava: AlumniPress, ISBN 978-80-8096-031-5.

Tab. 1. Surface roughness by using conventional abrading
agent.

Work piece Tyrolit 97 A 100
period of L 6 V 112
 dressing [R.sub.z]
 [[micro]m]

 1 2,61
 25 2,21
 1 2,49
 25 2,23
 1 2,64
 25 2,33
 1 2,44
 25 2,17
 1 2,88
 25 2,45
 1 3,05
 25 2,45
 1 2,88
 25 2,22
 1 2,65
 25 2,28
 1 2,72
 25 2,29
 1 2,53
 25 2,16

Tab. 2. Surface roughness by using highly abrasive abrading
agents Atlantic and Hermes.

 Atlantic Hermes

Work piece period
 of dressing [R.sub.z] [[micro]m]

 1 2,78 2,93
 70 2,12 2,04
 1 2,69 2,71
 70 2,08 2,01
 1 3,33 2,83
 70 2,23 2,10
 1 3,49 2,55
 70 2,29 1,99
 1 2,56 2,58
 70 2,01 2,08
 1 2,42 2,44
 70 1,98 1,73
 1 3,04 2,49
 70 2,11 1,88
 1 2,65 2,37
 70 2,03 1,84
 1 3,10 2,67
 70 1,86 1,96
 1 3,17 2,58
 70 1,72 2,03