Screw Milling Machine CNC Transformation
Injection molding machines and extruders are specialized equipment used in the production of plastic products, and they are widely utilized across the globe. As a crucial component of both extruders and injection machines, the quality of the screw directly impacts the performance of these systems. Traditional manual methods for machining screws often result in inconsistent outcomes, low efficiency, and unreliable quality. To address these issues, the adoption of numerical control (NC) technology for screw processing has become an inevitable trend.
Currently, CNC milling machines specifically designed for screw machining are expensive and not easily accepted by many users. On the other hand, more affordable CNC screw milling machines converted from lathes using economical numerical control systems and stepper motors tend to have limited functionality, lower reliability, and more operational problems.
Nanjing Sikai Electronic Enterprise Co., Ltd. successfully transformed a lathe into a dedicated CNC screw milling machine by installing the SKY numerical control system at the request of a user in Guangdong. This innovative solution offers cost-effectiveness, strong functionality, high precision, and excellent uniformity in the machined screws. It can easily handle complex requirements such as variable diameter and variable pitch, including segmented and continuous variable pitch screws.
The SKY CNC system features a Chinese interface, full-screen program editing, and large memory capacity—capable of storing up to 10,000 machining programs. The machine tool uses digital AC servo motors, ensuring stability and reliability. This system effectively solves the challenges associated with screw machining.
The SKY CNC screw milling machine was developed based on a standard lathe, as shown in Figure 1. It is equipped with milling heads on the carriage, along with digital AC servo motors that control the spindle rotation and X- and Z-axis movements, enabling three-axis linkage. This allows for the machining of various screw shapes.
The traditional lathe tool holder is replaced with a milling head, which is driven directly by the digital AC servo motor through timing pulleys and belts. The X and Z axes are connected via couplings to ball screws, ensuring precise and efficient movement. This design simplifies the mechanical structure, improves flexibility, and reduces transmission errors.
The SKY CNC system uses an encoder mounted on the motor as a feedback element, paired with a digital AC servo motor to create a closed-loop system. With high-resolution encoders and dual-pulse input control, the system ensures strong anti-jamming capabilities. The SKY series supports both full closed-loop and semi-closed-loop configurations based on user needs.
Built on a universal PC platform, the SKY CNC system allows for custom programming in C language for special screw machining tasks. A built-in parameter programming module simplifies operation, as illustrated in Figure 2. By defining parameters such as pitch, diameter, and lead, users can generate accurate numerical control codes.
Depending on the required screw accuracy, the appropriate increment dt is determined, and corresponding space coordinates (X, Z, A) are calculated and output. Through this CNC transformation, significant improvements in accuracy and consistency have been achieved, leading to substantial social and economic benefits.
With numerous ordinary screw milling machines currently in use, the potential for CNC retrofitting is vast, making it a promising development direction for the industry.
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