Difficult tool unloading in CNC machining centers is one of the common faults, but due to its complicated structure, involving electrical, mechanical, pneumatic, hydraulic, etc., any failure of a loop link will cause machine tool unloading failure. This article takes the maintenance case of a VC1055 CNC machining center as an example, analyzes the common fault characteristics of tool unloading according to the spindle structure and principle of the CNC machining center, and discusses the repair of the faulty CNC machine tool according to the fault characteristics for reference.

1. Fault characteristics

There is a VC1055 CNC machining center, which is very difficult during the tool change process. When changing the tool, you need to use a copper hammer or other metals to impact, and the tool handle can only be removed after vibration. In this way, there is bound to be a safety hazard. Long-term impact will cause damage to the handle and affect the accuracy of the spindle.

2. Working principle of CNC milling machine spindle

The structure of the components is shown in Figure 1. The front end of the spindle has a 7:24 taper hole for clamping the taper shank (see Figure 2). In order to realize automatic tool loading and unloading, an automatic tool clamping device is provided in the spindle. It can be seen from the figure that the machine tool is positioned and clamped by the tensioning mechanism to tighten the journal at the end of the tapered shank tool holder.

• (1) When clamping the tool holder, the hydraulic cylinder B cavity is filled with oil, the spring 6 pushes the piston 3 upward, and is in the position shown in the figure, the lever 5 moves upward under the action of the butterfly spring 4. The spring 6 is driven to move up into the sleeve 1, thereby compressing the spring 6 and clamping the tool holder. The cutter bar is fastened to the spindle by friction.
• (2) When the tool holder is released, the hydraulic cylinder A cavity is connected to the oil inlet, the compression spring 4 and the pull rod 5 move downward, driving the spring 6 and the tool handle downward, the spring leaves the constraint of the sleeve 1, the spring 6 is released, the knife The shank pull nail disengages the sleeve 1 and removes the tool shank.
• (3) Compressed air is blown from the pipe joint through the central through holes on the piston and the rod into the spindle mounting hole to remove chips or dirt to ensure the clamping accuracy of the tool. After the manipulator installs the new knife on the spindle, the hydraulic cylinder A is connected to return oil, and the disc spring tightens the knife holder again, and the knife holder is tightened.