Three-axis or five-axis? A comprehensive guide from manufacturing processes to costs.
In the workshop, you can often hear young engineers muttering, “Why can some machining centers mill complex impellers, while others can only do simple tasks like planing and drilling?” The answer is actually quite simple—the key lies in the number of axes!
The axes of a machine tool are like its joints. The more axes that can rotate, the greater its flexibility and the more powerful its machining capabilities. From three-axis to five-axis, each additional rotary axis upgrades the machine tool’s machining capacity, essentially transforming it from “only able to work horizontally” to “able to operate flexibly at multiple angles.”
Today, we’ll use real-life scene images and explicit annotations to clearly explain the differences between three-axis, four-axis, and five-axis machine tools. Whether you’re choosing equipment or communicating with colleagues, you won’t have to worry about anything; you’ll easily understand the core logic of machining.
I. Three-Axis Machine Tools: The “Basic Model” for Machining “Single-Sided Parts”
Let’s first thoroughly explain the core logic of three-axis machine tools in plain language, making it easy to understand and remember.
Core Structure: Just three “linear axes,” with obvious division of labor!
Three-axis machine tools use three linear axes. Simply put:
• X-axis: The worktable moves left and right.
• Y-axis: The worktable moves forward and backward.
• Z-axis: The spindle head, which holds the tool, moves up and down.
These three axes together form the most basic “Cartesian coordinate system”—meaning the tool can only move within a “plane + up and down” space; there are no rotational axes, and the movements are significantly “regulated.”
Machining Characteristics: Only works on “one surface,” incapable of complex tasks.
1. Movement: No rotation function; the tool moves almost perpendicular to the worktable, only able to work “horizontally and vertically” within a fixed space.
2. Capabilities: Specifically designed for machining “single surfaces” of parts, such as milling grooves on steel plates or drilling and tapping holes in motor end covers—a true “plane surface expert.”
3. Limitations: Machining sides or backs requires manual disassembly and re-clamping, which is time-consuming and prone to misalignment, potentially leading to misaligned holes and precision issues.
4. Suitable for: A “starter kit” for small and medium-sized factories! Price: 100,000-500,000 RMB; easy to maintain; highly cost-effective for mass production of simple parts.
5. In short: For flat surface work, use it – it’s reliable, accurate, and fast; for complex, multifaceted tasks, don’t bother with it.
Typical applications: These tasks are guaranteed to work well with it:
• Flat surface machining and contour cutting of flat parts
• Drilling and tapping various holes
• Roughing and semi-finishing of simple curved surfaces
• Machining of mold reference surfaces and simple grooves
• Mass production of parts with low precision requirements
Practical tips: Avoid these pitfalls:
• When machining deep grooves and cavities, a tool that is too long will wobble, and insufficient rigidity can easily lead to errors.
• Machining multiple surfaces requires special fixtures or multiple clamping operations, which is time-consuming.
• Machining complex curved surfaces is slow, and the resulting surface is not smooth enough; don’t force it.
II. Four-axis machine tools: An “efficiency model” with an extra “rotation axis.”
Core structure: Based on three-axis machining, it adds a “rotational axis”!
Four-axis machine tools aren’t particularly complex. They’re essentially three-axis machines (X-axis for left/proper movement, Y-axis for forward/backward movement, Z-axis for up/down movement) with an additional “rotational axis.” This axis acts like a “joint,” allowing the part to rotate. There are three common types:
• A-axis: Rotates around the X-axis (commonly used in vertical machine tools), for example, “flipping” the part to machine side holes.
• B-axis: Rotates around the Y-axis (commonly used in horizontal machine tools), adjusting the part’s angle in the forward/backward direction to handle machining different surfaces.
• C-axis: Rotates around the Z-axis (commonly used in milling and turning machines), essentially allowing the part to “rotate around the spindle,” enabling the machining of helical grooves on cylinders.
This single rotational axis significantly expands the machine tool’s machining range, eliminating the need for repeated part disassembly as with three-axis machines.
Machining characteristics: Multiple surfaces can be machined in a single setup, upgrading both efficiency and accuracy!
1. Less disassembly and reassembly for greater precision: After the part is mounted on the machine tool, the angle is adjusted by the rotary axis, allowing multiple surfaces to be machined at once without manual disassembly and reassembly—saving time and avoiding precision deviations caused by misalignment (for example, the problem of misalignment between two surfaces in a three-axis machine can be solved mainly by a four-axis machine).
2. Capable of handling cylindrical tasks: For example, machining cylinders with helical grooves or cylindrical cams. A three-axis machine can only handle flat surfaces, while a four-axis machine uses the rotary axis to allow the tool to follow the cylindrical surface.
3. High efficiency but with a learning curve: While the machining speed of complex parts is faster, programming requires understanding the motion laws of the rotary axis, which is more difficult than with a three-axis machine; moreover, the equipment is significantly more expensive than a three-axis machine, so you need to calculate when you can recoup your investment before purchasing.
4. In short, with the addition of a “rotary joint,” it can handle multifaceted and cylindrical parts, but it requires more learning and investment.
Typical application: For these tasks, a four-axis machine is the way to go!
• Cylindrical cams with helical grooves, and helical groove parts
• Holes on different surfaces of box-type parts (such as motor housings)
• Radial holes and grooves on pipes (such as side holes on water pipes)
• Parts with rotational characteristics, such as impellers and propellers (although 5-axis machining is better, simple impellers can also be handled by 4-axis machining)
• Complex structural parts requiring multi-angle machining (such as parts with inclined holes or inclined surfaces)
Technical Points Analysis: Two machining modes, corresponding to different needs!
Four-axis machining mainly falls into two categories, chosen based on the complexity of the part:
1. “3+1″ Mode: While the three linear axes (X, Y, Z) move, the rotary axis is initially fixed at a fixed angle. After the linear axes finish machining one surface, the rotary axis rotates to its position to machine the next surface. Suitable for multi-face machining, such as drilling holes on the front, back, left, and right sides of a part.
2. Four-Axis Linkage Mode: All four axes (three linear axes + one rotary axis) move simultaneously. For example, when machining a spiral groove, the tool moves up, down, left, and right while the rotary axis rotates with the part, enabling the tool to follow the spiral trajectory precisely. Suitable for complex curved surfaces and spiral parts.
Ⅲ. Five-Axis Machine Tools: The “Ultimate Weapon” for Complex Curved Surfaces
Core Structure: Based on a three-axis system, add two more “rotating axes”!
Five-axis machine tools are essentially the same, adding two rotary axes to the three linear axes (X (left/proper movement), Y (backward/forward movement), and Z (upward/downward movement). Different combinations of these two axes result in three common structures, the core difference being whether the “part moves” or the “spindle moves”:
1. Double Rotary Table Type: The part moves, the spindle remains stationary.
• Like “the part sitting on a double-layered rotary table”: The worktable is double-layered, allowing the part to rotate in two directions (usually A-axis + C-axis). At the same time, the X/Y/Z axes move the entire “rotary table.”
• Motion logic: It’s not the tool moving to the part, but rather “the part actively rotating to move to the tool”—for example, when machining an impeller, the part rotates while moving forward, backward, left, and right with the worktable, allowing the tool to cut into every complex curved surface.
• Suitable for: Small to medium-sized complex parts, such as impellers, artificial joints, and grooves in precision molds.
• How is precision guaranteed? It relies on “RTCP technology,” which means that “no matter how the worktable rotates, the tool tip remains firmly aligned with the point to be machined,” resulting in minimal errors (only 0.005-0.01mm, much thinner than a human hair).
• Cost: Relatively inexpensive of the three types.
2. Rotary Table + Head-Table Type: Both the part and the spindle move slightly.
• Considered a “compromise”: The worktable has a rotary axis (for the part to rotate), and the spindle head, which holds the tool, has an oscillating axis (for the tool to rotate). The two work together to adjust the angle.
• Suitable for what parts: Medium-sized parts; more flexible than a double rotary table setup; can machine multifaceted curved surfaces without overly complex adjustments.
3. Head-to-Head Spindle: Spindle moves, workpiece remains stationary.
• Like a “tool with a universal joint”: The workpiece is fixed to the worktable, the X/Y/Z axes move the worktable, while the spindle head can tilt via two rotary axes (e.g., A-axis + C-axis) – essentially, the tool rotates to reach the workpiece.
• Motion Logic: Specifically designed for situations where “workpieces are too heavy to move,” such as aircraft fuselage frames, ship parts, and heavy machine tool beds. Moving these significant components can easily deform them, allowing for more precise tool movement.
• Cost and Barrier to Entry: Extremely expensive (2-10 million RMB), and requires high-level skills in operation, programming, and machine repair. Generally used only in high-end manufacturing fields such as aerospace and medical.
Machining Characteristics: One-time setup, capable of handling any complex task!
1. “All-rounder”: It can machine all five sides of a part in a single setup, eliminating the need for disassembly and reassembly like a 3-axis machine or repeated angle adjustments like a 4-axis machine. For example, a complex mold can be formed directly from start to finish with a 5-axis machine.
2. “Always in Optimal Tool Position”: The tool angle can be adjusted at any time, ensuring the tool tip always cuts the part at the “most comfortable angle,” resulting in a smooth and precise surface finish without the “harsh tool marks” often found in 3-axis machines.
3. Can Use “Short Tools”:Unlike machining deep cavities, it doesn’t require long tools (which are prone to wobbling). Short tools offer high rigidity, enabling fast, stable machining.
4. High Learning Curve:Programming requires specialized 5-axis CAM software, which isn’t something easily learned. The equipment is also expensive; you need to consider whether you can recoup your investment before purchasing.
5. In short:It’s the perfect choice for complex parts, but learning it requires significant time, money, and effort.
Typical Application:Only it can handle these “high-difficulty” jobs!
• Aerospace: Aircraft engine impellers and blades, complex structural components of the fuselage.
• Automotive Manufacturing: Molds for automotive body panels and bumpers (complex and multifaceted surfaces).
• Medical Field: Precision medical implants (e.g., artificial joints), surgical instruments.
• High-end Manufacturing: High-value-added complex curved surface parts, and deep-cavity molds (e.g., precision molds for mobile phone casings).
Core Technological Advantages: Why is the five-axis machine so powerful?
The key is its ability to “constantly change the angle of the cutting tool”:
• Complex curved surfaces “formed in one go”: No need for multiple machining operations, saving time and reducing errors.
• Machining quality “significantly improved”: Smooth surface, high precision, no need for subsequent grinding.
• Production cycle “significantly shortened”: Less time for clamping and adjustment, resulting in extremely high efficiency in mass production.
IV. Comprehensive Comparison of the Three Machine Tools
1. How can it move?
3-axis: Only has three linear axes (left/right, forward/backward, up/down), cannot rotate.
4-axis: Has one more rotating axis than 3-axis (for example, to rotate a part).
5-axis: Has one more rotary axis, allowing parts or tools to be flexibly adjusted at multiple angles.
2. How complex is programming?
3-axis: Simple; a beginner can learn in 60 days.
4-axis: Medium; requires understanding the motion logic of rotary axes.
5-axis: Complex; requires specialized software and experienced technicians.
3. What can it process?
3-axis: Can only process a single surface of a part (e.g., milling grooves on a flat surface), limited scope.
4-axis: Can process cylindrical parts (e.g., spiral grooves), multifaceted machining, and a broader scope.
5-axis: Can handle all kinds of complex tasks (e.g., impellers, artificial joints), with a vast scope.
4. How consistent is the accuracy?
3-axis: Dependent entirely on clamping accuracy; even one disassembly may cause misalignment.
4-axis: Requires one less clamping operation; better precision than 3-axis.
5-axis: Dedicated technology controls precision; error is finer than a hair’s breadth; exceptionally high precision.
5. How much does it cost?
3-axis: Inexpensive (100,000-500,000 RMB), ideal for entry-level small and medium-sized factories.
4-axis: Mid-range (500,000-2,000,000 RMB), balanced cost-performance.
5-axis: Expensive (starting from 2,000,000 RMB), used only in high-end manufacturing.
Machine Selection Guide: Choose the Right Machine for Your Needs
• Choose 3-axis: For simple parts (e.g., brackets, flanges), only needing to machine planes/drill holes, with a limited budget.
• Choose 4-axis: For machining cylindrical parts (e.g., grooved pipes), parts requiring multiple surfaces, and maintaining high precision.
• Choose 5-axis: For complex curved surfaces (e.g., aircraft blades, artificial joints), pursuing high precision + high efficiency.
V. Key Factors in Selection Decisions
Technical Considerations
1. Part Feature Analysis
• Geometric Complexity
• Precision Requirement Level
• Material Machining Characteristics
2. Process Requirements Assessment
• Machining Efficiency Requirements
• Quality Consistency Requirements
• Process Expansion Potential
Economic Analysis
1. Initial Investment
• Equipment Purchase Cost
• Supporting Facility Investment
2. Operating Costs
• Labor and Technical Costs
• Maintenance and Repair Costs
• Tooling and Fixture Investment
3. Overall Benefits
• Increased Production Efficiency
• Reduced Quality Costs
• Market Response Speed
VI. Development Trends and Practical Suggestions
1. Intelligentization
No need for manual parameter adjustments—the machine tool can automatically avoid collisions (e.g., preventing the tool from hitting the part) and adaptively adjust force and speed according to the machining situation, reducing the error rate.
2. Modularization
Flexible like building blocks—to add a function (e.g., an additional rotary axis) or change the machining method, you don’t need to replace the entire machine tool; expand the modules. This allows for flexible handling of different parts, enabling “flexible manufacturing.”
3. Integration
A single machine tool can perform multiple tasks—for example, it can turn cylinders like a lathe and mill grooves like a machining center (milling-turning hybrid); it can even simultaneously cut away material and 3D print material to add it (additive and subtractive manufacturing integration), reducing the number of parts-transfer steps.
Conclusion
The shift from three-axis to five-axis machining is not just about adding more rotating axes, but a qualitative leap in manufacturing capabilities. As mechanical engineers, we shouldn’t focus solely on the number of axes when choosing machine tools; the key is to consider product characteristics and production requirements—for example, using a five-axis machine tool to machine ordinary flanges is a waste of money and a waste of resources; trying to machine impellers with a three-axis machine tool won’t produce satisfactory results.