|Budget Amount *help
¥14,200,000 (Direct Cost : ¥14,200,000)
Fiscal Year 1997 : ¥3,200,000 (Direct Cost : ¥3,200,000)
Fiscal Year 1996 : ¥11,000,000 (Direct Cost : ¥11,000,000)
A high-frequency wheel spindle for an ultra-high speed surface grinding machine was developped. This project aims to achieve a high efficiency grinding of steel with cBN wheels, in which a stock removal rate is over 300 mm^3/(mm・s) at a wheel peripheral speed of 400m/s. At such a speed, the power loss caused by air and coolant friction is larger than grinding power. At first, a theoretical analysis of grinding forces was carried out to estimate the grinding power. From this analysis the wheel diameter of F250mm and motor power of 22 kW at 30000 min^<-1> were decided. Also, an eigenvalue analysis by FEM was carried out to decide the diameter of the spindle shaft that avoids the resonance caused by a heavy wheel. In the spindle unit, a newly developed lubrication reduces the no-load power and the temperature rise of bearings. Furthermore, constant pre-load mechanism was adopted to achieve a high stiffness without burning out the bearings. Finally, the advantage of a small diameter wheel
is confirmed experimentally by measurement of air friction loss, which confirmed to calculated results using the logarithmic law.
Secondly, an ultra-high speed grinding (UHSG) machine which is capable of 400m/s wheel speed was developped. UHSG is one of the high efficiency machining methods. It has reached the stage where it can complete well with respects to machining efficiency even in comparison with a cutting method. Concept of the USHG is not new, however a practical application of the UHSG was difficult due to the manufacturing problems of a grinding wheel and a wheel spindle unit in the ultra-high speed rotation. In the previous work, an ultra-high speed spindle unit (30000 rpm, 22kW,2*10^6 dn-value) was developed. In this paper, a UHSG machine using the spindle unit was designed and manufactured. Vibration, noise and coolant friction loss of the machine were measured and compared with the conventional grinding results. The UHSG tests were performed under the 300m/s wheel speed using the developed machine and a vitrified bonded cBN wheel. The cBN wheel having a CFRP core was specially designed. However, coolant supply was not enough in the region of the UHSG,therefore the development of a low friction supplying method was needed.