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Preliminary Study on System Reform of Import Processing Center
The MC340/TWIN is a twin-spindle machining center manufactured by STAMA GmbH in Germany. Due to severe damage, the original system was irreparable, prompting a comprehensive technical upgrade. The project involved replacing the Japanese FANUC-15M control system with the advanced German SIEMENS-840D system. This transformation required extensive hardware and software modifications, involving multiple axes and complex automation processes.
Originally imported in 1994, the machine suffered significant damage and was nearly scrapped. Beyond repairing mechanical components, the control system was also upgraded. The original system controlled eight axes—two spindles (C-axis), X, Y, Z, A, C2 (rotary table), Q (magazine axis), and V (linear robot axis)—through PLC and custom interfaces. The PLC used 288/192 I/O points, allowing two work areas on the rotary table to operate simultaneously, enabling the processing of up to eight parts per cycle.
The tool change process was highly specialized, involving the Q, V, and Z axes. When a tool change was initiated, the Q axis moved to the correct position, the V axis retrieved the tool from the magazine, and the Z axis facilitated the exchange. The robot then rotated 180°, inserted the new tool, and returned the old one to its place. This complex sequence involved multiple axes, solenoids, and sensors, making it challenging to implement.
After research, the Siemens 840D system was selected for its four-axis linkage capability, offering improved performance. The CNC directly controlled the spindles and axes, reducing the PLC’s I/O requirements from 288/192 to 192/160. The Q and V axes were reconfigured using external encoders, improving positioning accuracy. For the V axis, an absolute encoder was used to ensure precise location, even in confined spaces. The C2 axis was also upgraded to a digital servo motor, with PLC programming adjusted to simulate reference point returns without additional hardware.
The transformation included addressing mechanical and control challenges, such as backlash, elasticity, and coordination between axes. Adjustments were made to gain settings, speed, and detection time to stabilize the system. Special attention was given to the Q and V axes, which had significant gaps and deformation, requiring careful tuning to prevent interference during tool changes.
The final result was a fully restored machine that met all original specifications. It achieved rapid movement speeds of 22 m/min, feed rates up to 10,000 mm/min, and a spindle speed of 6,000 rpm. Positioning accuracy was well within factory limits, and the system proved stable and reliable. The upgrade not only revived the machine but also enhanced its performance and usability, ensuring continued operation for years to come.