Modern manufacturing continues to develop and drives increasingly stringent demands on the precision, complexity, and production efficiency of components.

Aerospace, automotive, and mold manufacturing widely use complex parts.

These parts feature intricate structures and high precision requirements, and traditional machining methods struggle to meet these requirements.

As an advanced manufacturing technology, multi-axis CNC machining enables the coordinated movement of cutting tools and workpieces across multiple degrees of freedom, thereby resolving the challenges associated with machining complex parts.

It has become a key driver of modern manufacturing development.

Consequently, intensifying research into the application and optimization of multi-axis CNC machining technology for complex parts is of great significance for ensuring workpiece quality, reducing production costs, and enhancing corporate market competitiveness.

Overview of Multi-Axis CNC Machining Technology

• Principles of Multi-Axis CNC Machining Technology

The core principle of multi-axis CNC machining technology is to achieve complex spatial relative motion between the tool and the workpiece through the coordinated movement of multiple axes.

This technology overcomes the limitations of traditional 3-axis machining by adding rotational axes such as the A, B, and C axes to flexibly adjust the tool’s orientation.

In a 5-axis machining system, in addition to the three linear axes (X, Y, and Z), two rotary axes can rotate around the linear axes (e.g., the A-axis rotates around the X-axis, and the C-axis rotates around the Z-axis), enabling two motion modes: “3+2” positioning or 5-axis simultaneous motion.

The “3+2” positioning mode fixes the rotary axes at specific angles to perform inclined surface machining, making it suitable for mass production and high-efficiency rough machining;

5-axis simultaneous machining, on the other hand, calculates the motion parameters of each axis in real time, ensuring that the tool remains at the (theoretically) optimal cutting angle during machining, making it particularly suitable for continuous finishing of complex surfaces.

The CNC system uses kinematic models to perform inverse calculations on the displacement of each axis, ensuring the precision of the tool center point (TCP) along its spatial trajectory.

The accuracy of these calculations determines the machining error, with precision reaching the 0.001 mm level.

• Advantages of Multi-Axis CNC Machining Technology

Compared to traditional machining technologies, the advantages of multi-axis CNC machining are primarily reflected in four areas:

(1) Minimization of Clamping Errors.

With multi-axis CNC machining, multiple surfaces of complex parts can be machined in a single setup, thereby avoiding the accumulation of positioning errors caused by repeated clamping.

For example, in impeller machining, 5-axis simultaneous machining can control radial runout to within 0.1 mm.

(2) Improved Tool Accessibility.

The introduction of rotary axes allows tools to reach areas that are difficult to access with traditional 3-axis machining, such as undercuts and deep cavities.

When machining deep grooves in mold cavities, tool overhang is significantly reduced, lowering the risk of chatter.

(3) Optimizing Cutting Conditions.

Automatically adjusting the tool’s rake and clearance angles improves the uniformity of cutting force distribution.

For example, using a side milling method can control cutting fluctuations within 10%, preventing excessive deformation of thin-walled parts.

(4) Enhanced Process Integration.

Operations such as rough milling, semi-finish milling, finish milling, and drilling can be completed on a single platform.

In the machining of automotive cylinder blocks, 5-axis machining centers can integrate processes such as face milling, boring, and tapping, effectively boosting production efficiency.

Applications of Multi-Axis CNC Machining Technology in the Processing of Complex Parts

• Aerospace Industry

Multi-axis CNC machining technology is key to effectively overcoming the bottlenecks in the manufacturing of “high-precision, high-tech” parts.

For example, in the machining of integral aerofoil discs for aircraft engines, the hub and twisted blades (numbering in the dozens) are formed as a single unit.

The blade thickness is approximately 2–3 mm, and the surface tolerance accuracy standard is ±0.03 mm.

Traditional machining processes often result in deformation and cumulative errors due to multiple setups.

However, when using a 5-axis machining center, the dual-turret structure allows the workpiece to rotate 360° and the tool to swing at multiple angles.

Combined with specialized (rigid) fixtures to secure the integral blade disc, the entire machining process—from blank to finished part—can be completed in a single operation.

During machining, the CAM system generates helical toolpaths to ensure normal cutting of the blade surfaces, keeping the cutting action perpendicular to the blade surface at all times and limiting thin-wall deformation to within ±0.01 mm. 5-axis machining effectively improves blade disc machining efficiency and reduces scrap rates.

Additionally, for parts with complex internal cavities and inclined holes (such as missile casings), 5-axis machining utilizes a tilting spindle to perform inclined drilling and boring, achieving hole positioning accuracy of ±0.02 mm—a significant improvement over the accuracy of traditional radial drill presses (which have a maximum accuracy of ±0.1 mm).

• Automotive Manufacturing Sector

Multi-axis CNC machining technology has provided significant support for the transition of automotive components toward “high efficiency and precision.”

In the machining of transmission housings, which contain dozens of intersecting shaft holes and oil passages, traditional 3-axis machining required multiple repositioning and clamping operations, making it prone to reference offset issues.

However, with the adoption of 5-axis horizontal machining centers, the workpiece requires only a single setup.

Engineers rotate the spindle around the Y-axis in conjunction with a high-precision swiveling table.

The machining system performs continuous machining of all hole patterns with extremely high positional accuracy.

This process reduces the production cycle time from an average of 3 minutes per part to 1.5 minutes per part.

In the new energy vehicle sector, 5-axis machining offers distinct advantages for thin-walled, irregularly shaped parts such as motor housings.

Adaptive feed control technology enables real-time adjustment of cutting parameters for different thin-walled areas.

Engineers apply high-speed milling at 12,000 rpm on flange surfaces with a 5 mm wall thickness.

The system reduces the spindle speed to 6,000 rpm in sidewall areas with a 2 mm wall thickness.

This adjustment prevents chatter marks and effectively controls the surface roughness Ra value.

• Mold Manufacturing Sector

For complex cavities, multi-axis machining technology can achieve the goal of “near-net-shape” manufacturing.

In the field of injection molds, cores and cavities often feature deep cavities, undercuts, and microstructures.

While traditional electrical discharge machining (EDM) technology can ensure compliance with precision requirements, it suffers from low manufacturing efficiency.

Using a 3mm-diameter ultra-fine carbide tool on a 5-axis high-speed machining center, undercut cavities with a depth of 20mm can be machined directly via tilt-angle cutting.

This significantly reduces the surface roughness Ra value, eliminates the need for subsequent EDM processes, and effectively shortens the machining cycle.

Engineers machine automotive body panel molds using 5-axis machining centers.

Surface elevation differences in these molds can reach 500 mm, and curvature variations are highly complex.

The machining system applies a “contour line + helical line” composite toolpath.

This toolpath ensures uniform distribution of cutting intervals at 0.1 mm.

This significantly controls surface contour errors, resulting in a marked improvement in machining accuracy compared to 3-axis machining.

For hot-work inserts in casting molds, 5-axis machining combined with high-speed dry cutting using ceramic tools achieves cutting speeds of up to 800 m/min.

Material removal rates can reach approximately three times that of traditional processes, while also avoiding contamination issues associated with cutting fluids, thereby meeting green manufacturing requirements.

Optimization Strategies for Multi-Axis CNC Machining of Complex Parts

The complexity of multi-axis CNC machining is not only reflected in the coordinated control of equipment but also requires systematic optimization to achieve a balance between precision, efficiency, and cost.

Common issues in the machining of complex parts include tool interference, cutting deformation, and low efficiency;

These require optimization across three key areas: toolpaths, cutting parameters, and machining strategies.

• Toolpath Optimization

Toolpath optimization should adhere to the core objectives of “no interference, high efficiency, and low deformation.”

As one of the key elements of multi-axis machining, the rationality of the toolpath directly affects machining quality and efficiency.

Engineers apply a comprehensive optimization strategy for complex curved-surface parts.

CAM software simulates the relative positions of the tool, tool holder, workpiece, and fixture through collision simulation functions.

This simulation dynamically evaluates motion interactions during machining.

Engineers eliminate interference by applying “tool radius compensation” and “swivel angle limitation” algorithms.

Engineers machine integral impellers using multi-axis CNC systems.

The tool approaches the transition zone between the hub and the blade root during machining.

The control system adjusts the A-axis tilt angle from 30° to 25°. The system reduces the tool overhang by 60% of its original length.

This action prevents rigid collisions between the tool holder and the blade.

Interference optimization reduces tool wear during impeller machining and minimizes downtime for adjustments.

Engineers maintain cutting force stability through variable pitch and variable feed rates.

CAM engineers use the “constant residual height” algorithm for path planning in aerospace blade machining.

Engineers set the pitch to 0.3 mm in areas with gentle curvature changes, such as the blade back. Engineers set the pitch to 0.1 mm in areas with abrupt curvature changes, such as the blade root.

This adjustment ensures uniform material removal per tooth.

Combined with finite element simulation to predict peak cutting force parameters, the introduction of “helical feed” in thin-walled areas—replacing traditional vertical plunging—reduces instantaneous cutting forces and significantly minimizes blade deformation.

• Optimization of Cutting Parameters

Engineers select cutting parameters such as cutting speed, feed rate, and depth of cut based on material properties, tool performance, and part precision requirements.

Process planners apply a “layered optimization” strategy to control these parameters precisely.

Machining Strategies for Different Materials

Engineers apply low-temperature, high-speed machining solutions for difficult-to-machine materials such as superalloys and titanium alloys.

Machining Inconel 718 uses ceramic-coated tools (Al₂O₃-TiCN). These tools increase the cutting speed to 300 m/min—approximately three times faster than traditional high-speed steel tools. An internal cooling system controls the cutting zone temperature.

The system keeps the temperature below 800°C. This control prevents workpiece hardening caused by high temperatures.

Manufacturers apply a high-feed, low-cutting-force approach for ductile materials such as aluminum alloys.

Engineers increase the feed rate to 0.3 mm/rev and reduce the cutting depth to 0.5 mm to minimize tool sticking and reduce surface roughness.

Dynamic Parameter Adjustment Across Machining Stages

Dynamically adjust parameters during the machining stage.

For rough machining, use “high-efficiency material removal” as the standard, employing deep cuts (3–5 mm) and medium feed rates (0.2–0.3 mm/z), combined with aggressive cutting methods such as “plunge milling” and “layer milling” to increase material removal rates;

During semi-finishing, the standard is “balanced cutting.”

Reducing the cutting depth to 1–2 mm and adjusting the feed rate to 0.15–0.2 mm/z helps control the residual surface height;

During finishing, with “high precision” as the standard, use a small depth of cut (0.1–0.3 mm) and high spindle speed (8,000–12,000 rpm) to improve surface smoothness using the “side-cutting” method.

Data-Driven Optimization of Cutting Parameters

Engineers combine past machining experience with collected machining data to determine optimal parameter combinations based on different cutting parameters, as shown in Table 1.

Table 1. Data on Different Combinations of Cutting Parameters (Steel Processing Data from a Certain Company)

As shown in Table 1, there are significant variations in surface roughness and tool wear under different cutting combinations, which provides a reference for optimizing cutting parameters.

Compared to traditional fixed machining parameters, analyzing big data and optimizing parameter combinations can extend tool life, improve machining efficiency, and reduce production costs.

Real-Time Monitoring and Adaptive Control

If the cutting force exceeds a threshold, the system automatically reduces the feed rate; if the vibration amplitude exceeds 0.01 mm, the system triggers a spindle speed fine-tuning function to prevent resonance.

• Process Optimization

Process optimization should achieve full-process coordination from “clamping—machining—inspection.”

Engineers design clamping solutions to address deformation issues common in thin-walled parts by employing “multi-point floating support” fixtures.

Manufacturers combine 3 to 6 adjustable support pins with vacuum suction to control workpiece clamping deformation within 0.01 mm.

In machining engine cylinder heads (1.5–2 mm wall thickness), support pins automatically adjust their height to match the shape of the workpiece blank and ensure even distribution of clamping force.

Engineers enforce the standard of “precision and uniformity” for large structural components.

They set machining features of the part as positioning references to avoid errors caused by reference shifts during multiple setups, thereby significantly improving positional accuracy.

Engineers adopt a single-clamping, multi-process composite machining solution in process integration and restructuring.

In automotive cylinder block machining, a 5-axis machining center integrates processes such as face milling, boring of main bearing bores, tapping, and chamfering, which can significantly reduce waiting time between processes and improve the coaxiality of the bore system.

Conclusion

In summary, in the field of modern manufacturing, multi-axis CNC machining technology, as one of the core technologies, plays an irreplaceable role in the machining of complex parts and holds broad application prospects.

Currently, this technology has become a mainstream process in sectors such as aerospace, automotive, and mold manufacturing.

It effectively enhances the machining accuracy, efficiency, and quality of complex parts, meeting the contemporary manufacturing industry’s demands for high precision, high performance, and high efficiency.

To address the existing shortcomings of multi-axis CNC machining technology, continuous optimization of toolpaths, cutting parameters, and machining processes is necessary to fully leverage the advantages of this technology.

In the future, with the continuous advancement of CNC technology, artificial intelligence, the Internet of Things, and other technologies, multi-axis CNC machining will evolve toward high-speed, high-precision, intelligent, and multi-technology integration.

This will provide robust technical support for the development of modern manufacturing and drive the industry toward intelligent, high-end, and personalized production.