Comparison of Machining Methods: 3+2 Axis, 5-Axis Simultaneous, and Turn-Mill

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1. 3+2 Axis Machining

3+2 axis machining, also known as "orientational machining" or "five-axis positioning machining," involves using two rotary axes (typically the A-axis and C-axis) of a five-axis machine to rotate and tilt the workpiece to a fixed optimal angle. Once in position, the workpiece is locked, and the machining is done with three linear movements (X, Y, Z) as in a traditional three-axis machining center.

Steps: Position → Lock → 3-Axis Milling

Equipment: Any five-axis machine with dual rotary axes can perform 3+2 machining. It does not require the machine to have true five-axis simultaneous control, but it does need hardware that supports rotary axis positioning. This is a very common and cost-effective five-axis application method.

2. 5-Axis Simultaneous Machining

This refers to true "continuous five-axis" machining. During the process, all five axes (X, Y, Z, A, B/C) move simultaneously and continuously, based on instructions from the CNC program. This allows the tool tip to follow complex spatial trajectories while adjusting the tool's orientation in real-time, ensuring the most optimal cutting state relative to the workpiece's surface.

Equipment: A high-end 5-axis simultaneous CNC machine is required. These machines not only feature dual rotary axes but also need a powerful CNC system capable of five-axis interpolation, RTCP (Rotating Tool Center Point), and backlash compensation to maintain the tool tip's correct spatial position.

Common Structures:

  • Dual rotary table (e.g., AC rotary table)
  • Dual swing head (e.g., BA swing head)
  • Hybrid table + head (e.g., A rotary table + B swing head)

3. Turn-Mill Compound Machining

The core concept of turn-mill compound machining is the integration of functions into a single machine, reducing the need for multiple setups. A workpiece is clamped on the spindle (for turning), while one or more high-speed rotating power tools (for milling) and a secondary spindle are integrated into the machine.

During machining, the primary spindle rotates the workpiece for turning; power tools perform milling, drilling, and tapping; and the secondary spindle can take over the workpiece for rear-side machining. All of this happens in a single setup, aiming for "one machine, one complete part." The milling function is often integrated into a five-axis (3+2 or simultaneous) system.

Equipment: A turn-mill compound machining center typically includes:

  • Turning spindle (can function as C-axis indexing or linkage)
  • Power tools (high-speed rotating milling spindles)
  • Second spindle (for part retrieval and rear-side machining)
  • Y-axis (allows the power tool to deviate from the centerline)
  • B-axis (a rotating tool head that tilts, enabling 3+2 or five-axis milling)

Comparison of Key Machining Methods

Feature 3+2 Axis Machining 5-Axis Simultaneous Machining Turn-Mill Compound Machining
Core Principle Lock the rotary axes at an angle, then perform 3-axis milling. Five axes (X, Y, Z, A, B/C) move simultaneously, adjusting the tool orientation in real-time. Integrates turning (rotating) and milling (power tool) functions in one machine with a single setup.
Movement Type Sequential: Position → Lock → 3-axis milling. Synchronous: Five axes coordinate and continuously adjust tool orientation. Combination of turning spindle rotation (C-axis) and milling spindle feed, often with a second spindle, Y-axis, B-axis, for compound movement.
Essence A mode of five-axis machine application, not a standalone machine type. Top-tier five-axis machine functionality. A multifunctional integrated machine, its milling function often based on a five-axis system.
Key Advantages Avoids tool interference, uses shorter, stronger tools, improves surface quality, and reduces setup time. Allows for complex spatial continuous surface machining (e.g., impellers, turbines, precision molds). Minimizes setup times, increases precision and efficiency, and completes highly complex parts in one setup.
Typical Equipment Any five-axis machining center with dual rotary axes (vertical or horizontal). High-end 5-axis machining centers (rotary table type, swing head type, hybrid type). Integrated machine tool with both turning and milling spindles (e.g., turn-mill centers with B-axis and Y-axis).
Analogy "Pose, then sculpt." "Dance and sculpt simultaneously." "A craftsman who can both turn and mill, and never lets go of the part."

Core Differences Summary

Goals:

  • 3+2 and 5-axis Simultaneous: Primarily solve issues of tool orientation and machining of complex surfaces.
  • Turn-Mill Compound: Primarily addresses the integration of processes to reduce setups and improve overall efficiency and accuracy.

Relationships:

  • The milling portion of a turn-mill machine is often a five-axis system, capable of both 3+2 and 5-axis simultaneous machining.
  • A 5-axis machine can perform 3+2 and 5-axis machining but cannot perform turning operations.
  • 3+2 machining is a subset of 5-axis simultaneous machining.

Core Value:

  • 3+2: Strategic value through optimized angles to improve quality, efficiency, and avoid tool interference.
  • 5-Axis Simultaneous: Capability-based value, solving the machining of complex geometries that other methods cannot handle.
  • Turn-Mill Compound: Process-based value, revolutionizing traditional multi-machine and multi-fixture workflows, drastically improving precision and efficiency.

Cost Analysis

3+2 Axis Machining

  • Equipment Cost: Higher than traditional 3-axis machines but much lower than top-end 5-axis and turn-mill compound machines. The most cost-effective way to enter the "five-axis domain."
  • Programming Cost:
    • Software: Requires CAM software with five-axis positioning capabilities (e.g., UG/NX, Mastercam, Hypermill), but without top-tier five-axis simultaneous modules, keeping software costs relatively low.
    • Labor & Time: More complex than 3-axis programming, requiring engineers to understand tool orientation and workpiece positioning, but much simpler than full 5-axis programming.
    • Cycle Time: Though positioning takes up some machine time, total processing time is significantly reduced by minimizing setups and utilizing efficient tools.
    • Fixture Costs: Simplified, often requiring just a simple fixture for multi-face machining.
    • Tool Costs: Longer-lasting, stronger tools can be used, reducing breakage risk and improving tool lifespan.

5-Axis Simultaneous Machining

  • Equipment Cost: Extremely high. True five-axis machines have complex mechanical structures and high CNC system requirements, often costing 3-5 times more than equivalent 3-axis machines.
  • Programming Cost:
    • Software: Requires top-tier, expensive five-axis CAM software licenses.
    • Labor & Time: Programming is highly complex, requiring deep understanding of tool paths, vector control, and collision avoidance.
    • Cycle Time: Highest machine-hour rate, but no alternative for machining complex surfaces (e.g., impellers), making it a necessary investment for certain tasks.
    • Tool Costs: Specialized cutters may be needed to achieve optimal results.

Turn-Mill Compound Machining

  • Equipment Cost: The highest, with integrated turning, milling, and often additional functions like drilling, tapping, and even grinding.
  • Programming Cost:
    • Software: Requires specialized CAM software capable of handling both turning and milling operations, often the most expensive.
    • Labor & Time: The most complex programming, requiring knowledge of both turning and milling techniques and seamless integration of both.
    • Cycle Time: Typically the lowest for complex parts, as multiple processes are combined into one machine cycle.
    • Fixture Costs: Extremely low, almost always requiring only standard chucks and centers.

Cost Comparison Summary

Cost Dimension 3+2 Axis Machining 5-Axis Simultaneous Machining Turn-Mill Compound Machining
Equipment Cost Medium-High Extremely High Extremely High
Software & Programming Medium High Very High
Cycle Time Cost Medium Medium-High Usually Lowest (for complex parts)
Fixture & Setup Costs Low-Medium Low-Medium Extremely Low
Tooling Costs Medium (Standard Tools) Medium Medium (Specialized Systems)
Operator Skills & Labor Medium-High High Very High
Suitable Production Volumes Small-Batch, Prototypes Small-Batch, High-Value Single Pieces Large-Volume, High-Value Products
Cost Core Strategic Savings Capability-Based Costs Efficiency