Decrease of cutting forces intensity at ceramics grinding by ultrasonic using.

Pechacek, Frantisek ; Javorova, Angela ; Charbulova, Marcela 等

1. INTRODUCTION

One of the factors which are operating technological and economical efficiency of machining process are tool technical parameters and machine parameters. Continues progress brings new materials as technical ceramics, hard metal, fibre optics with substantial mechanical, physics' and chemical properties. Machining these new materials by convectional machining methods is frequently unviable or brings a few technically problems. One of the solving this problem is using progress technology as ultrasonic aided grinding.

2. CERAMICS GRINDING

Quality of finishing surface is increasing by using process with chip formation by plastic deformation. This process is characterized fine chip creation and small stock removal and feed moving. There are a several factors, which permit begin chip by plastic deformation. These factors are: using fine diamond grinding tools, insuring Correct tool rotation, exact adjusting tool spindle. Cutting force at grinding is summation of cutting forces, which are acting to abrasive grains. Radial cutting force is much higher than tangential force at grinding ceramics materials. Resolution of forces at grinding process is illustrated on fig. 1.

[FIGURE 1 OMITTED]

High force is needs to pres grinding tool to ceramics materials. Force to sequential plastic deformation is small in plastic deformation area. High tool rigidity is required to achieve high accuracy considering large contact area between tool and finishing material and large radial force.

3. ULTRASONIC GRINDING TECHNOLOGY

Ultrasonic grinding technology by free abrasive is known and using in mechanical engineering at the present time. This grinding method is most old ultrasonic grinding technology. Fine abrasive suspension (diamond, cubic boron nitride etc.) are used at this process with cutting liquid. This cutting liquid is feed into tool waveguide front, which is vibrant by ultrasonic resonance.

[FIGURE 2 OMITTED]

4. CERAMICS GRINDING BY CONVENTIONAL METHOD AND BY ROTARY ULTRASONIC

Rotary ultrasonic grinding is combination conventional grinding by grinding tool rotation and additional translation by oscillation ultrasonic energy. Cooler liquid is feed to cutting area instead grinding suspension. Ultrasonic grinding is realized without tool-workpiece contact. Rotary ultrasonic grinding is realized by direct contact tool and workpiece. Grinding holes in ceramics experiments was realized at the same technological conditions by conventional method and rotary ultrasonic grinding. The target these experiments was cutting force monitoring both grinding methods. Used tool was diamond, designed based on finishing materials--ceramics. Finishing samples was create from [Al.sub.2][O.sub.3] rings (55,7 x 41 x 6 mm) and SiSiC rings (55 x 48 x 8mm).

High grinding productivity was achieved by recessing feed with radial feed movement. This grinding process was opposed--sense of rotation workpiece and tool was opposite. Grinding process was realized on horizontal grinding machine under the same technological conditions. All finishing sample was centered and fixed on specialized clamping fixture that was clamp in grinding machine chuck (Fig 3.).

[FIGURE 3 OMITTED]

Used technological parameters:

* Tool rotational frequency 16 000 - 20 000 min-1

* Workpiece rotational frequency 120 - 180 min

* Longitudinal feed 0,2 - 1,5 m.min-1

* Depth of cut 0,02 mm

* Performance ultrasonic transducer 1 kW

* Amplitude of ultrasonic oscillations 6 - 12 [micro]m

* Resonant frequency of ultrasonic systems 22,8 kHz

Achieved values of radial and tangential cutting forces were recorded in table and illustrated by graph.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

5. CONCLUSION

Comparing achieved results by both methods bring this conclusion. Tangential and radial parts of cutting force are half as much at rotary ultrasonic grinding. This fact permit increase cutting depth or achieving shorter finishing time. The next important findings are fact that grinding tool with ultrasonic process operate in self sharpening mode. Finishing shape quality and round deviation shows great improvement. Using ultrasonic to hard machining materials grinding process with using suitable tool and technological conditions is great improvement means of grinding process.

This paper was created thanks to the national grant VEGA 1/0090/ 08--Optimalized systems and processes of performance ultrasound.

6. REFERENCES

Holesovsky, F.; Hrala, M. (2004). Grinding of Silicon and Nitride Ceramics, In: Vyrobne inzinierstvo 2004, rocnik 3, cislo 2, 21 - 23s, ISSN 1335-7972

Mankova, I. (2000). Progresivne technologie, Vienala vydavatel'stvo Kosice, ISBN 80-7099-430-4, Kosice

Matusova, M.; Hruskova, E. (2007). Element selection algorithm of modular fixture system. Annals of Faculty of Engineering Hunedoara--Journal of Engineering, Tom V, Fasc 3.,(2007) pp. 36-40, ISSN 1584-2673,

Micietova, A. (2001). Nekonvencne metody obrabania. Edis vydavatel'stvo Zilina, ISBN 80-7100-853-2, Zilina

Vasilko, K. (1990). Nove materialy a technologie ich spracovania, Alfa Bratislava, ISBN 80-05-00661, Bratislava

Tab. 1. Measuring data of cutting force that were achieved at
grinding rings [Al.sub.2][O.sub.3]

 Radial Tangential
 part of part of
Tool Conventional Rotary cutting cutting
rotational grinding ultrasonic force force
frequency method grinding [F.sub.P] [F.sub.S]

16 000 x 24 11
20 000 x 22 10
16 000 x 14 7
20 000 x 12 5

Longitudinal feed f = 0,6 m.min-1 and workpiece rotational
frequency n = 120 min-1

Tab. 2. Measuring data of cutting forces that were achieved at
grinding SiSiC rings

 Radial Tangential
 part of part of
Tool Conventional Rotary cutting cutting
rotational grinding ultrasonic force force
frequency method grinding [F.sub.P] [F.sub.S]

16 000 x 21 10
20 000 x 20 9
16 000 x 12 6
20 000 x 10 4

Longitudinal feed f = 0,6 m.min-1 and workpiece rotational
frequency n = 120 min-1