Automatic tool change process of CNC machining center

Automatic tool change process of light-duty gantry machining center machine tool:

Overview of light-duty gantry machining center machine tools

The light gantry machine tool is a gantry machine tool with a movable beam and a fixed beam on the worktable, with or without a tool magazine. The machine tool is composed of a bed, a column and a fixed beam to form a rigid, closed frame.

The worktable moves vertically on the bed rails, which is the X coordinate.

The sliding plate moves laterally on the beam guide rail, that is, the Y coordinate.

The boring head and the milling head move vertically on the slide rail. This is the Z coordinate.

The cnc machine tool adopts the SIEMENS 840DE control system, and the X, Y, and Z axes of the machine tool are all CNC controlled axes. The main shaft is driven by a Siemens AC main shaft motor, and the X, Y, and Z three-direction feeds are driven by a Siemens servo motor. It can realize 3D linear interpolation, 2D arc interpolation, and any 3-axis linkage.

Management requirements for automatic tool change

2.1 Tool magazine control machine tool magazine

It can be a disc tool magazine with a capacity of 20 digits. The spindle and tool changer use robots. There is no robot. Tools are used to find nearby tools and directly change tools on the spot. You can also use a chain magazine with a magazine capacity of 40 tools, robots, tools, and tool changers. The magazine tray is driven by a motor through gear reduction, and has forward, reverse and stop controls. A power-off friction brake is added to the motor output shaft to quickly stop the tool magazine. When the stop signal is sent, the brake electromagnet is turned off and the tool magazine stops rotating. The indexing and positioning of the magazine disc rotation are realized by the Markov mechanism, the zero switch and the counting switch. Each time the magazine is transferred to a position, the count switch will be activated once. When the magazine is reset to zero, the reset switch also works. When the tool magazine moves to the specified position, the count switch or zero switch is activated. At this time, the motor stops, the brake is closed, the tool magazine stops, and the Markov mechanism is accurately positioned at the tool change position. When the tool magazine is stopped, the counting switch or zero reset switch is turned off and an alarm is displayed.

2.2 Pneumatic control

Tools Tool magazine protection Door switch and spindle cone blowing are pneumatically controlled, and the processing gas source gas is supplied to the cylinder. The protection door switch of the tool magazine is driven by the cylinder, and the control is completed by the two-position four-way double electronically controlled reversing valve. The characteristics of the reversing valve are as follows. The two positions of the reversing valve are controlled by two electromagnets, and only a short electric signal is given to the electromagnet (the electric signal standby time is 2 seconds) to complete the rectification. The reversing valve changes to another position only after a short electrical signal is given to the other electromagnet. Spindle cone purge is used to clean the spindle cone. The purge is connected by a 2-position 3-power shut-off valve. When the knife is released, the electromagnet is energized, and the cone hole is blown out. When the knife is released, the electromagnet is closed and the blowing stops.

2.3 Spindle brooch control Spindle

Equipped with an automatic tool tension adjustment mechanism, which is tensioned by a countersunk spring and hydraulically released. The tightening and loosening of the tool is controlled by a 2-position 4-port solenoid valve. The brooch mechanism is divided into knife, knife, and knife, and the three states are monitored by three non-contact induction switches.
The tightening and loosening of tools can be controlled by commands or buttons on the control panel. The release and tension of the tool are displayed on the panel. Spindle rotation and tool tightening and loosening operations are interrelated.

3 Markov engine

The operation process of the tool magazine The tool magazine of the machining center is composed of the tool magazine disk of the Markov mechanism, the zero switch, the counting switch, the magazine door switch valve, the travel switch, and the main shaft. The tool magazine of Markov mechanism automatically changes the tool, moves the spindle to the tool magazine, grabs the tool directly with the loose spindle tool, and sends the tool back to the tool magazine. When approaching and leaving the tool magazine tray, you need to move slowly to avoid collisions with the tool magazine or tool, but in other places, you need to move quickly to save time. … Moving the tool magazine involves three processes: spindle gripper, spindle tool return, and spindle tool change. The multiple points of the spindle movement, S1 to S14, represent the movement process of the slider and the slider. It can graphically analyze the three processes of spindle tool grabbing, spindle tool return, and spindle tool change.

3.1 Spindle

The gripping process spindle clamp is a tool that requires a toolless spindle to grip the tool head. The action is to move the Y axis laterally to the top of the tool magazine, and move the Z axis down to the tool position to grab the tool. The Y axis moves laterally from the tool magazine (the content in parentheses describes the operation of the Y axis and the Z axis).
S1 (Z axis to P0, high speed) → S2 (Y axis to P1, high speed) → Spindle orientation, the first soft limit is enabled, and the magazine door opens → S8 (Y axis to P2, high speed) → Spindle tool release → S7 (Z axis to P3, high speed) → S6 (Z axis to P4, low speed) → Spindle tightening → S12 (Y axis to P5, low speed) → S13 (Y axis to P6, high speed) → S14 (Z axis to P1 , High speed) → The second software limit becomes effective, the spindle orientation is cancelled and the magazine door is closed.

3.2 Back to the spindle process

Spindle tool return is to return the spindle tool to the original position in the tool magazine. The action is to move the Y axis laterally to the tool position and release the tool. The Z axis moves from the tool to the top of the tool magazine, and the Y axis moves away from the tool magazine laterally.
S1 (Z-axis to P0, high-speed) → S2 (Y-axis to P1, high-speed) → Spindle orientation, first soft limit enable → S3 (Z-axis to P6, high-speed) → Open tool magazine door is → S4 (Y Axis turn to P5, high speed) → S5 (Y axis to P4, low speed) → Spindle tool release → S11 (Z axis to P3, low speed) → S10 (Z axis to P2, high speed) → S9 (Y axis from P1, high speed) →The second software restriction is effective, cancel the spindle orientation, tighten the spindle, and close the tool magazine door.

3.3 Spindle tool change process

It is necessary to replace the spindle tool, return the spindle tool to the original tool position in the tool magazine, and grab another tool in the tool magazine. The action is to move the Y axis laterally to reach the tool position and release the tool. Z moves from the tool to the top of the tool magazine, the tool magazine rotates to find the tool, the Z axis moves down to the tool position to grab the tool, and the Y axis moves laterally from the tool magazine.

S1 (Z axis to P0, high speed) → S2 (Y axis to P1, high speed) → Spindle orientation, the first soft limit is valid → S3 (Z axis to P6, high speed) → Knife door open → S4 (Y axis to P5 , High speed) → S5 (Y axis to P4, low speed) → Spindle tool release → S11 (Z axis to P3, low speed) → S10 (Z axis to P2, high speed) → Tool magazine rotation, tool magazine looking for tools. → S7 (Z axis to P3, high speed) → S6 (Z axis to P4, low speed) → Spindle tightening tool → S12 (Y axis to P5, low speed) → S13 (Y axis to P6, high speed) → S14 (Z Axis rotation P6, high speed) P1, high speed) → the second software limit is effective, the spindle orientation is cancelled, and the magazine door is closed.

Explanation of the automatic control program of Markov tool magazine

According to the automatic tool change control requirements and the action process, the PLC is programmed to make the ATC work normally.

1. I/O point arrangement of machining center

1.1 Arrangement of input points I33.2:

In-position knife in-position (up)

• I33.3: Spindle tight-knife in-position switch (neutral position),
• I33.4: The spindle releases the tool in place (bottom position),
• I36.3: Spindle release button switch is pressed, I36.4: Spindle tightening button switch is pressed, I62.0: Tool magazine ATC is enabled,
• I62.1: Tool magazine ATC is disabled.
• I62.2: The magazine is jogging.
• I62.3: The tool magazine returns to zero,
• I62.4: The tool magazine rotates forward.
• I62.5: Tool magazine inverted
• I62.7: Number of tool magazines
• I63.0: Tool magazine zero position I63.1: Tool magazine door
• Open
• I63.2: Tool magazine door closed
• I63.3: Tool magazine motor monitoring,
• I63.4: Tool magazine lock.

1.2 Placement of output points

• Q49.0: Spindle loosening valve,
• Q49.3: The spindle is loose,
• Q56.0: ARC is effective for the tool magazine, but
• Q56.1: Tool magazine jog.
• Q56.2: The tool magazine motor rotates forward.
• Q56.3: The tool magazine motor reverses.
• Q56.4: Tool magazine brake
• Q56.5: Open the tool magazine door
• Q56.6: Tool magazine door closing valve
• Q56.7: Spindle blow valve.

2. Program function block placement instructions

• FC51: Spindle pine needle,
• FC66: Ma tool magazine T code processing,
• FC67: Markov tool library M code processing,
• FC68: Comprehensive processing of Markov tool magazine.

3. PLC program debugging program

When the tool magazine is debugged, each electrical component should be debugged in a single step to ensure that the electrical components function normally. Then perform all actions manually and check the execution of the program according to the actions such as tool setting, tool change, and tool return. Finally, you can use the T and M instructions to perform continuous automatic execution of the program in the automatic mode and make the tool magazine work normally.

Conclusion

Our ATC has achieved excellent control and operation requirements by testing multiple products within the enterprise. As the principles and experience of ATC are similar, each type of CNC machine tool has a specific reference function.