Recently screw compressors have been employed in various industries due to their advantages over conventional reciprocating piston-type compressors. They can be operated with various working fluids which are gases, dry vapors, or multi-phase mixtures. Consequently, they are used in air compressors, heat pumps, refrigeration-plants, super chargers of automobiles and etc.
Since screw compressors do not have reciprocating parts, they can be operated at high speed with less noise and vibration. Therefore, the advantages of screw compressors are productivity improvement, low noise and vibration, compact size, long-life reliability, and easiness in maintenance.
The screw compressor is composed of a female rotor and a male rotor which have complex section profiles with helically swept geometric shapes. The performance of the screw compressor is determined by the rotor-shape design and machining accuracy because the dimensional tolerance between the male rotor and the female rotor of efficient screw compressor screw rotors should be less than 10 ㎛ meters.
The male and female rotors of screw compressors are generally manufactured by machining using tools and machines designed exclusively for screw rotor manufacturing. Although the production cost of screw rotors is high due to the cost of tools and machines, screw rotors of various sizes and shapes are in great demand due to their many advantages.
In this work, to obtain the tool profiles from the shapes of helical grooves, the numerical tool design algorithm was investigated to solve the inverse problem without undercutting of screw rotors. the tool design method can be used for the manufacturing of various shapes of screw rotors by simply changing tools and machining parameters of general 4-axis CNC machines.
For the precision machining of screw rotors, the analyses and experiments of cutting operation were performed, from which the optimal cutting condition was proposed. Also, both the female and male screw rotors were machined using a 4-axis general CNC machine with the tools designed by the developed method.
To test the performance of the screw compressors, the test apparatus was also developed. From the tests, it was found that the screw compressors composed of the rotors manufactured in this work was satisfactory both in the accuracy of forms and performance.