Machine tool type: CNC punch press
----Control method: Cam method
Manufacturer: HAAR GmbH, Germany
----Original machine tool control system: SIEMENS industrial computer
----Current machine tool control system: SIEMENS 840D CNC system
----Current drive system: BWS-BBH
The machine tool was purchased from Hong Kong by the container manufacturing company in 1988. It had been in operation for nearly ten years before the modification. Due to the instability of the control system and the lack of spare parts, it was decided to modify it. Both parties agreed to remove the original CNC system and drive system used in the machine tool and adopt the SIEMENS 840D CNC system and BWS-BBH drive system.
This machine tool is used to produce aluminum can lids. It uses aluminum alloy and has three axes: X, Y, and a spindle. The X and Y axes are used to position the aluminum sheet, while the spindle controls the punch. The punch has seven dies, meaning each punch produces seven lids. Because aluminum is thin and light, the control method of this machine tool is unique compared to ordinary punch presses, as summarized below:
The punch position is determined using an absolute position encoder, rather than a mechanical cam or inductive switch. This encoder is used to determine the punch position, the feeding timing, the air blowing time, whether a cover passes through, and the lower die lubrication time.
When the upper and lower molds separate, the air nozzles next to the seven molds must simultaneously blow air to remove the cover. At the same time, the system must confirm that the cover has been blown away; if it hasn't, the machine must stop immediately, otherwise the mold will be damaged. As the spindle speed increases, the requirements for system control timing become more stringent. This function is called the cover-dropping mold protection function.
After the cap is blown out, it enters the next process through the cap receiving groove. Since the cap receiving groove can sometimes become clogged, the system must react promptly to prevent mold damage. This function is called the cap-plugging mold protection function.
The stamping speed is 150-200 times/minute.
The timing and timing of the air blowing must be accurate; otherwise, the cover may not fall into the cover receiving slot or may not be blown out, causing frequent interruptions in machine processing and thus affecting production efficiency.
If a fault occurs in the next process step, the machine tool must automatically stop processing, and when the fault is cleared, the machine tool should be able to automatically restart.
The challenge of this project lay in mold protection. Because the caps were very light, seven caps were produced per stroke. Due to airflow instability, the caps passed the detection area at inconsistent times, and the detection time was limited to approximately 50 milliseconds. To ensure accuracy, a separate PLC unit was used specifically for cap detection, and the results were then fed back to the CNC system. Actual operation demonstrated the project's success, achieving the expected results and providing valuable experience for future modifications to similar machine tools.
