Programming skills in the automatic tool change process of the machining center in the machining center - News - Global IC Trade Starts Here.

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A complete PLC program not only ensures the machine operates smoothly but also makes the control logic clear at a glance, which is essential for self-debugging and helps maintenance personnel quickly identify and resolve issues. This article introduces the programming techniques used in the automatic tool change process of the XH756B series horizontal machining center equipped with the SIEMENS 802D CNC system.

First, let's briefly describe the basic configuration of the tool changer. The tool magazine is a chain-type unit capable of rotating both forward and backward. A robot mounted on the tool changer performs a 15-step operation to exchange tools between the magazine and the spindle, and then returns the old tool to its designated holder. To minimize the time required for tool changes, we implement pre-selection of tools while processing parts, effectively reducing the overall cycle time.

The sequence of the robot’s actions during the tool change is as follows:

Step 1: Move and retract, grab the pre-selected tool from the magazine.
Step 2: Pull out the tool from the magazine.
Step 3: Shift the robot to move away from the tool side and position itself to grasp the spindle tool.
Step 4: Retract the tool and pull it back.
Step 5: Extend the arm and rotate it toward the spindle.
Step 6: Move and grasp the tool in the spindle.
Step 7: Pull the tool out of the spindle.
Step 8: Rotate the robot forward or backward to exchange the tools.
Step 9: Push the new tool into the spindle.
Step 10: Retract the robot from the spindle.
Step 11: Retract the arm and turn it back toward the magazine.
Step 12: Pull the tool out of the spindle and prepare to return it to the magazine.
Step 13: Move the robot toward the tool magazine.
Step 14: Insert the old tool back into the magazine.
Step 15: Move away from the tool side and complete the cycle.

These 15 steps can be divided into four main stages:

Stage 1: Grab the new tool. The Txx code directs the tool magazine to rotate to the position where the selected tool is located. Once the position is confirmed, the robot begins its movement through steps 1 → 2 → 3 → 4, grasping the new tool and waiting for the tool change to occur.

Stage 2: Tool change. When M06 is executed, the tool change canned cycle “TOOL” is activated. This cycle moves all axes to the tool change position and sends an M90 signal to the PLC to initiate the tool change. The PLC then requests the NC to "read inhibit" using the M90 signal and proceeds with steps 5 → 6 → 7 → 8 → 9 → 10 → 11. The in-position signal from step 5 ensures the correct positioning of the tool magazine relative to the spindle.

Stage 3: Return the old tool. After the tool magazine rotates and positions, the robot performs steps 12 → 13 → 14 → 15 to return the old tool to the magazine and update the spindle tool number in memory. Once step 11 is completed, the “read-in inhibit” is canceled, the tool parameters are reactivated, and the machining program resumes alongside the robot operations.

Stage 4: Pre-select the next tool. In the next M06 command, the Txx code indicates the tool number to be used in the next operation. While the current part is being processed, the tool magazine can start the robot’s movement (steps 1 → 2 → 3 → 4) simultaneously. This pre-selection allows the robot to be ready for the next tool change, significantly reducing the total cycle time and improving overall productivity.

By implementing these advanced programming strategies, operators can achieve faster, more efficient, and more reliable tool changes, which is crucial for high-performance machining centers.