Five-axis Head Key Technology for Mill-Turn Machines
he five-axis head of a turn-mill machine is the heart of the machine. Designs vary significantly due to diverse turn-mill machine forms. The turning and milling five-axis head functions like a boring and milling spindle. It performs milling, drilling, tapping, and boring.
Moreover, it has turning capabilities. For example, it can achieve tool power spindle directional stopping and locking. This feature distinguishes it from the boring and milling five-axis head. Therefore, it is more complex and technically advanced. The following sections discuss key technologies of the turn-mill five-axis head.
1. Several Key Technologies
(1) Power Spindle Locking
ower spindle locking is a special requirement for turning and milling five-axis heads. During turning, the tool does not rotate and must maintain accurate center height. Therefore, the power spindle must restrict its original rotational freedom. This restriction enables precise directional stopping. Due to large forces during turning, the spindle experiences significant resistance. Such restrictions require mechanical solutions. However, mechanical structures inevitably cause over-constraint.
The commonly used locking mechanism is the three-tooth disk. It locates in both axial and radial directions. Thus, it restricts six degrees of freedom. Since the spindle already restricts five degrees of freedom, this causes over-constraint. Its advantage is excellent rigidity. However, it demands very high processing and assembly accuracy. Therefore, it places strict requirements on manufacturing and assembly quality.
The position of the three-tooth disk affects machining performance significantly. Typically, it takes two forms. One mounts at the front end of the main spindle’s front bearing (see Figure 2). This brings the locking point closer to the cutting force center. Consequently, it benefits heavy cutting and vibration-induced cutting. Additionally, its hydraulic clamping mechanism dampens vibration. This helps during long tool shank cutting.
The other type mounts at the rear end of the front spindle bearing (see Figure 3). In this setup, the cutting force point is closer to the front spindle bearing. This is better for milling operations. Moreover, it improves rigidity for boring and milling. It also enhances surface finish quality.
Mounting the three-tooth disk at the front bearing end is easier. However, mounting it at the rear end is more difficult. It is also less favorable for maintenance. Generally, angle recognition mechanisms are too large. Hence, they cannot be used in turning and milling five-axis heads.
(2) Tool clamping mechanism
All turn-mill machines are equipped with an automatic tool changing mechanism (see Figure 2). Since the spindle of the five-axis head is shorter than that of general boring and milling spindles, and the tool clamping and releasing mechanisms are generally longer, this poses challenges for the design of the tool clamping and releasing mechanism.Additionally, the clamping force of the tool clamping mechanism is typically over 1,300 kN and acts instantaneously, generating significant impact forces that can damage the spindle bearings. How to prevent the spindle bearings from being impacted while achieving tool clamping within a limited space is another major challenge for five-axis turning and milling heads.
(3) Oil, water, and air passages
The turning and milling five-axis head requires spindle orientation clamping, external and internal cooling of the tool, air sealing, and automatic lubrication, with eight or more oil, water, and air channels (see Figure 4). The associated actuators must be equipped with detection devices, requiring 6 to 9 wire harnesses. The distribution of oil, water, air, and electricity is prone to failures, and their structural layout significantly impacts the reliability of the turning and milling five-axis head.
(4) B-axis of the turning and milling five-axis head
The B-axis of the turning and milling five-axis head (Figure 5) differs significantly from that of the milling five-axis head in terms of rotational functionality. While the milling five-axis head only requires continuous rotation at any angle, the turning and milling five-axis head not only requires continuous rotation at any angle but also limited angle locking and arbitrary angle locking.
Continuous rotation at any angle is required for machining continuous curved surfaces, with the technical key being the elimination of backlash in the transmission chain and sufficient torque.
Fixed-angle locking is designed to meet the requirements for machining specified-angle planes or oriented structures. Since it is difficult to achieve backlash-free rotation in the B-axis transmission chain, even if transmission stiffness is sufficient, it is not enough. To enable limited-angle locking for heavy-duty cutting, a directional three-tooth disk locking mechanism is generally used. This locking method achieves high stiffness.
Arbitrary angle locking is designed to meet the requirements of arbitrary angle orientation machining. Since the three-tooth disk structure can only achieve limited angle locking, arbitrary angle locking must be achieved using other methods, and each manufacturer has its own proprietary techniques for this.
2. Key Technical Solutions
Turn-Mill Power Spindle Directional Locking and Tool Clamping
Select the directional locking method based on spindle use: turning or milling. Choose the cutting method to use structural advantages and ensure workpiece quality. Moreover, design the tool clamping mechanism to avoid force on the spindle during clamping. Structurally, the clamping/releasing mechanism must transfer forces within the spindle. Also, design oil, water, and air supply systems considering pressure losses from curved pipes. Therefore, increase pipe diameter as much as possible. The key to the B-axis is locking at any angle. Thus, select a solution with high rigidity and reliability. Additionally, eliminate transmission clearance to achieve gap-free or low-clearance transmission in B-axis rotation.
Turn-Mill Five-Axis Head Spindle Types and Technologies
The five-axis turn-mill head can be mechanical or electric spindle. Key technologies discussed apply to both types. Each key technology has multiple practical solutions. The approaches here have successful domestic and international cases. Proper implementation avoids many detours. If these challenges are creatively solved, performance can match or exceed foreign counterparts.
Turn-Mill Rotary Shaft Measurement Procedure
Use a bidirectional alternating rotation sequence for measurement. First, rotate in one direction to measure all target positions (0° to 360°). Then, rotate in the opposite direction to measure once (360° to 0°). Repeat this sequence until completing required measurements. When editing the rotation program, consider 5° overshoot at first and last target positions. This eliminates gaps during direction changes. The system controls rotary axis rotation according to the measurement program. The axis moves sequentially to each target position and dwells long enough.
Turn-Mill Data Collection and Software Monitoring
The RX10 software monitors each target position’s reading stability. It collects data at five measurements per second once stable. The dwell time depends on the “Measurement Period 0” parameter. A computer screen arrow shows data collection progress continuously. When the arrow reaches the end, the software averages data and calculates angular error. The software displays the error in a column and graphs the error trend. As measurements increase, the trend graph updates for clear observation. After five bidirectional cycles, the software saves collected data.
Turn-Mill Data Analysis and Accuracy Evaluation
Launch data analysis software to evaluate rotary axis accuracy. Use standards such as GB 10931-89, ISO 230, and VDI/DGQ 3441. Assess positioning accuracy, repeatability, reverse deviation, and position deviation. Additionally, print original deviation data for each position. Include the trend graph of rotational axis position accuracy deviation. This visualization helps understand actual axis deviation. Use the data to improve assembly processes and apply compensation corrections.