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Setting and Realization of Quick Tool Change for CNC Milling Machine
CNC milling machines are increasingly favored by many manufacturing companies due to their lower purchase, operation, and maintenance costs compared to machining centers. However, one major limitation of CNC milling machines is the absence of a tool magazine, which means they cannot automatically change tools. As a result, only one tool can be used for a single workpiece. To complete multi-tool machining on a CNC milling machine, several methods have been used, but each has its own drawbacks.
One common approach is to use separate programs for each tool. This method is inefficient because it requires frequent program calls, increasing the risk of errors and potentially leading to scrapped parts when too many program segments are involved. Another method involves manually modifying the program at each tool change. This includes pausing the program, moving the spindle to the correct position, and then changing the tool manually. While this allows for some flexibility, it is error-prone and increases the chance of processing accidents.
To address these challenges, after extensive practical experience, the author developed a more efficient solution: combining CAM processing software with macro programs. This method effectively overcomes the limitations of manual tool changes, significantly improving both the safety and speed of the process.
To implement this, the post-processing file in CimatronE was modified. The original "TOOL CHANGE" block contained commands such as "T", "M06", and "G43 H", which are typically used in machining centers with automatic tool changers. These were removed, and instead, the G6 code was added to call a macro program stored in the machine's program register.
The modified post-processing code now looks like this:
```
TOOL CHANGE:
IF (QUALIFIER_NAME == "first")
OUTPUT \J "G90 G57 G6 G0" " X" X_CURPOS " Y" Y_CURPOS;
OUTPUT \J "S"SPIN_SPEED " " SPIN_DIR;
ELSE
OUTPUT \J "M9";
OUTPUT \J "G90 G57 G6 G0" " X" X_CURPOS " Y" Y_CURPOS;
OUTPUT \J "S"SPIN_SPEED " " SPIN_DIR;
END_IF;
```
The G6 command refers to a macro program that handles the actual tool change. The macro program performs several key functions, including saving current coordinates, stopping the spindle, moving it to a safe position, and then resuming the process with the new tool. It also checks and sets the spindle speed and other parameters before returning control to the main program.
This technique was successfully tested on a FANUC system and proved to be highly effective. It eliminated the risks associated with manual tool changes and significantly improved the overall efficiency of the CNC milling process.
For more details, you can refer to the article titled "Tool Change Optimization for CNC Milling Machines" published in *Metalworking (Cold Processing)*, Issue 3, 2013, or explore related content on the Metalworking Online website.