How to Ensure High-Quality Aluminium CNC Machining

Aluminium CNC machining is a high-precision and highly stable metal manufacturing process.
The following sections outline each key stage of aluminium CNC machining based on Conco’s actual production workflow, offering a clear and practical view of how we manufacture aluminium parts.

Preparation Stage

Selecting the Right Aluminium Material

Different aluminium grades offer significantly different performance characteristics, so the choice should be based on the application and functional requirements of the final product:

1. 6061: Excellent overall performance with high strength. Commonly used for structural components and machined parts.
2. 6063: Superior surface finishing properties, making it ideal for appearance and decorative parts.
3. 7075: A high-strength aluminium alloy, suitable for products that require high load capacity or tight machining tolerances.

Obtaining the Product Design Drawings

To begin production, we require customers to provide one of the following design files:

1. 2D engineering drawings (PDF / DWG)
2. Or 3D models (STEP / IGES / STL)

If the drawings contain structural issues or potential machining risks, our engineering team will carry out a technical review and provide optimisation recommendations before machining, ensuring a smoother and more reliable production process.

Product Modelling Using CAD Software

In aluminium CNC machining, CAD modelling is not simply about drawing the part. More importantly, it involves considering machining tolerances, machine capabilities, and downstream assembly requirements at the design stage.

During the CAD modelling process, we focus on the following key aspects:

• Defining critical and functional dimensions

Designers clearly define key areas such as assembly holes, mating surfaces, and locating features in both the CAD model and 2D drawings, specifying dimensions and allowable tolerance ranges. This prevents deviations during machining and assembly.

• Designing based on actual machining tolerance capabilities

The engineering team defines tolerances according to real CNC machining capabilities, for example:

1. Standard aluminium milling operations typically achieve tolerances within ±0.15 mm.
2. High-precision turning features can achieve tolerances of up to ±0.02 mm.

By clearly distinguishing between critical tolerances and general tolerances at the design stage, we ensure product performance while avoiding unnecessary machining costs.

• Machinability and structural feasibility assessment

During CAD modelling, we simultaneously evaluate:

1. Whether there are deep cavities or narrow slots
2. Whether the part can be completed in a single setup
3. Whether thin wall sections may cause deformation during machining

Engineers identify potential design features that could affect machining efficiency or accuracy and propose optimisation solutions early.

• Allowances for CAM machining and subsequent processes

The CAD model also takes into account:

1. Finishing allowances
2. Dimensional changes caused by surface treatments (such as anodising)
3. The impact of deburring and chamfering on final dimensions

This ensures a smooth transition from CAD design to CAM programming and later manufacturing processes.

Machine Setup

Selecting the Appropriate CNC Equipment

The choice of CNC machine depends on the part geometry and required machining accuracy:

• 3-axis CNC machines: Suitable for standard planar machining and simple part structures
• 4-axis CNC machines: Ideal for multi-face machining, helping to reduce the number of setups
• 5-axis CNC machines: Used for complex surfaces and high-precision components

Setting Up Workpiece Fixtures and Clamping Methods

Therefore, in aluminium CNC machining, the choice of workpiece clamping method plays a critical role in machining accuracy, process stability, and surface quality.
Based on the part structure, size, and machining requirements, an appropriate fixturing solution is selected. Common workpiece fixing methods include the following:

Machine Vice

A machine vice is the most common and versatile workpiece clamping method, suitable for aluminium parts with regular shapes and simple structures.

Key features:

1. Stable clamping and easy operation
2. Ideal for standard square or regularly shaped workpieces
3. Fast part changeover and low fixturing cost

• Typical applications:

1. General milling and drilling operations
2. Small to medium-sized parts with uncomplicated structures
3. Standardised components in batch production

Custom Fixture

A custom fixture is a purpose-built clamping solution designed specifically for a part’s geometry, providing higher positioning accuracy and more consistent machining results.

Key features:

• Precise positioning with excellent repeatability
• Enables multi-face machining in a single setup
• Minimises clamping errors and the risk of part deformation

Typical applications:

• Parts with complex or irregular shapes
• Products requiring tight dimensional tolerances and high assembly accuracy
• Medium to large batch production where consistent quality is critical

Actual Machining Process

Rough Machining

Rough machining is the first critical step in aluminium CNC machining. Its main objective is to rapidly and efficiently remove the bulk of excess material while maintaining workpiece stability.

During this stage, we typically use:

• Larger cutting depths and feed rates
• High-rigidity tools with optimised tool paths

By optimising rough machining strategies, we can significantly improve overall machining efficiency without compromising the structural stability of the part. At the same time, appropriate material allowances are left for subsequent finishing to prevent dimensional shortages or surface damage.

For aluminium parts with complex structures or thin walls, rough machining is often carried out in staged operations. This reduces the risk of deformation caused by internal stress release and provides a stable foundation for precision finishing.

Finish Machining

Finish machining is the key step that determines the final dimensional accuracy and surface quality of the part.

At this stage, the process involves:

• Smaller cutting depths
• Stable feed rates
• Refined tool paths

This allows for strict control of dimensional tolerances and improves the surface smoothness and consistency of the part. Critical areas such as assembly surfaces, locating faces, and holes receive special attention to ensure that the parts fit accurately and function reliably in assembly.

By setting appropriate finishing parameters, it is possible to achieve high precision while minimising the need for post-processing or secondary corrections.

3. Secondary Operations

After the main machining is complete, a series of secondary operations are performed to ensure the functional integrity and usability of the part. These typically include:

• Drilling: For mounting holes, through-holes, or countersinks, ensuring dimensional and positional accuracy
• Tapping: To produce internal threads, ensuring thread precision and reliable assembly
• Chamfering: To remove sharp edges, facilitating assembly and improving aesthetic quality
• Deburring: To remove burrs generated during machining, preventing scratches or assembly interference

Although these secondary operations may seem minor, they are crucial for the actual performance and perceived quality of the part. A systematic secondary machining workflow effectively enhances the overall finish and consistency of the product.

Inspection and Packaging

Individual Protective Packaging
For parts with high aesthetic requirements or surfaces that have undergone anodising, sandblasting, polishing, or other surface treatments, individual protective packaging is typically used. This may include separate bags, cushioning materials, or protective films, effectively preventing bumps, scratches, or surface damage during transportation.

Bulk Scratch-Resistant Packaging
For products shipped in batches, packaging is designed according to part size and shape, using layering, separators, or padding to prevent parts from rubbing against each other. This approach reduces the risk of scratches and deformation while balancing protection and packing efficiency.

Transport-Specific Packaging Solutions
Packaging plans are customised based on the shipping method, such as sea freight, air freight, or courier delivery. For long-distance transport or multiple handling stages, reinforced outer cartons and internal protection are used to ensure that parts remain stable and secure throughout the logistics process.

Conclusion

In summary, aluminium CNC machining is not only about machine operation, but the result of careful material selection, part design, process planning, and manufacturing experience. By strictly controlling each stage of the process, consistent dimensional accuracy, surface quality, and long-term reliability can be achieved. A well-managed machining workflow ensures that aluminium parts can move smoothly from design to production, delivering stable and dependable solutions for real-world applications.