# Research Progress on the Manufacturing of Screw-Shaped Parts in Screw Compressors
## 2 Common Manufacturing Process for Screw-Shaped Parts  
### Traditional Cutting Process  
At present, the production mode of complex screw-shaped parts is generally determined based on the complex configuration of the screw surface profile through special manufacturing methods. Besides that, it may use high-price screw machine tools, screw grinders, five-axis machining centres and other special equipment, where the bar material is subject to multiple milling or grinding processes. As shown in Figure 2, the common milling methods for screw-shaped parts mainly include finger-type cutter milling, disc-type cutter milling and whirlwind milling [16; 17; 18; 19]. Among them, whirlwind milling is one of the most widely used cutting processes. The ordinary three-axis machine tool has been replaced by cyclone milling machines in many medium and small enterprises. Four-axis or five-axis machine tools are generally used in large enterprises to complete the milling of complex screw profile parts [19]. As the screw rotor is crucial to the assembly of screw compressors, precision in the machining of the screw rotor directly and significantly influences the compressor performance. Therefore, solving the machining accuracy problem of rotor teeth is the key to improving the compressor performance. [PERSON] [16] used a finger milling cutter to  
Figure 2: Screw milling methods: (**a**) disc-type cutter milling; (**b**) finger-type cutter milling; (**c**) whirlwind milling [16; 17; 18; 19]. mill a screw rotor on a flexible multifunctional machine tool, improving the machining efficiency and manufacturing accuracy of the screw product. [PERSON] et al. [20] suggested an insert-cutting trajectory (ICT) process, which was able to generate a designed profile and the cutting-point surfaces of the rotor by the milling procedure. They reported that generating surface cutting marks on the rotor profile was successfully accomplished by the multiple-inserts method for edge cutting in the milling process. The reliability and practicability of the new ICT method was verified by experiments. [PERSON] et al. [21] introduced the methodology of a computer numerically controlled (CNC) machine method with a five-axis flank, which is named double-flank milling. In this process, the cutting tool tangentially contacts the workpiece at two end surfaces, which is more flexible compared to traditional milling. The results indicated that a high accuracy was obtained in the machining process in cases with different rotor benchmarks with the specially designed tool. [PERSON] [22] proposed a processing methodology for producing a screw rotor with a complex profile that had changes in the tooth pitch by CNC turning. Investigation results from simulations revealed that the proposed process method is effective in flexibly realising the manufacturing of the screw rotor by varying the production of the tooth profile. [PERSON] et al. [23] proposed a new skiving method with internal cylindrical cutters for the precise production of screw rotors with a CNC skiving instrument. It was reported that the error of the screw rotor skived by the proposed methodology was significantly low, even close to zero. [PERSON] et al. [15] used the blade-cutting trajectory method to quickly calculate the profile and cutting path of screw rotors, based on which a new prediction model was established. The reliability and application potential of the cutting trajectory method were verified by the milling results of screw rotors under different cutting conditions. With the progress of screw processing technology, grinding has gradually become a popular method of screw finishing or direct powerful integral machining. The grinding methods of screw-shaped parts can be mainly divided into wheel grinding and abrasive belt grinding. Figure 3 shows the equipment and schematic diagram of the RX120 grinding machine tool produced by KAPP company (Izmir, Turkey) [24]. As shown in Figure 3b, a grinding wheel with cubic boron nitride (CBN) is used in this equipment.