Abstract: A design method of forming wheel edge shape for screw rotors machining is presented when arbitrary rotor profile is given. According to the position relationship of the rotor and the forming wheel during machining process, the geometric mapping of the above two coordinate systems is established by rotation transformation of the rotor profile coordinate system. The contact line equation between the rotor tooth surface and the forming wheel revolving surface is derived based on the meshing theory. On this basis, the calculation method for theoretical edge shape of forming wheel is proposed, which is applicable to both analytical and discrete forms of the rotor profile. The corrected edge shape is gained by offsetting the contact line along the normal vector direction with the given inter-lobe clearance, and the defect of unequal normal inter-lobe clearance in the traditional method can be avoided. The machining results show that the proposed method can satisfy the screw rotor accuracy, which is an effective method to get forming wheel edge shape for screw rotor, and the method also can be popularized to edge shape design of other helicoids forming wheel or disc milling cutter.

Key words: Forming wheel edge shape, Helical surface, Inter-lobe clearance, Machining, Screw rotors