Why Do Forged Aluminum Parts Still Need CNC Machining?

Key Takeaways

Forging and CNC machining serve different purposes. Forging forms aluminum into strong, near-net-shape components, while CNC machining achieves precise dimensions and complex functional features.

Forging alone cannot always meet final tolerances. Critical holes, mounting surfaces, threads, and mating features often require secondary machining.

CNC machining improves fit and functionality. It ensures that forged components meet assembly requirements and engineering specifications.

Combining forging with CNC can improve production efficiency. For suitable part designs and production volumes, forging reduces the amount of material that must be removed during machining.

Not every aluminum part requires forging. The most suitable manufacturing process depends on the component's geometry, mechanical requirements, tolerances, and production quantity.

Introduction

Aluminum forging is widely used in the manufacture of structural components for the automotive, motorcycle, bicycle, and industrial sectors. By applying compressive force to heated aluminum, the forging process not only shapes the material but also promotes the development of a favorable grain structure and mechanical properties.

However, many aluminum forgings still require CNC machining before they are ready for assembly or use.

Since the parts have already been forged, why is additional machining necessary?

The answer lies in the distinct functions of these two manufacturing processes.

Forging primarily determines the part’s shape and mechanical properties, while CNC machining provides the finished product with the required dimensional accuracy, surface finish, and fine details.

Forging and CNC machining are not competing processes; rather, they are often used in combination to produce high-performance, precision-engineered aluminum components.

1. What Is Aluminum Forging?

Aluminum forging is a manufacturing process that uses specialized dies and forging equipment to shape aluminum under compressive force.

In closed-die forging, the material is pressed between forming dies to produce parts that closely resemble their final geometry.

Compared to manufacturing the same part entirely from a larger solid billet, forging offers the following advantages in applicable scenarios:

-Favorable grain orientation and mechanical properties

-Improved material utilization tailored to specific part geometries

-Efficient mass production of parts with repetitive geometries

-Reduced material removal during subsequent machining processes

-Suitable for structural and load-bearing components

However, the forging process is not suitable for every fine detail or strict tolerance required in the manufacture of precision finished parts.

Features such as precise bearing seats, threaded holes, precision bores, and critical mating surfaces may still need to be achieved through CNC machining.

2. Why Is CNC Machining Necessary After Forging?

Even with meticulously designed forging dies and strict control over the manufacturing process, forgings may still exhibit dimensional deviations due to factors such as material flow, die wear, temperature fluctuations, cooling processes, and heat treatment.

While such deviations might be acceptable for certain non-critical surfaces, they often fail to meet the requirements for precision assembly.

CNC machining can overcome these limitations by removing a specific amount of material from designated areas.

Achieving Tight Dimensional Tolerances

Forging tolerances are generally not as precise as those achievable through CNC (computer numerical control) machining.

For parts requiring precise hole locations, exact diameters, or tightly controlled assembly dimensions, mechanical machining is typically necessary.

Through CNC machining, manufacturers can attain the required dimensional accuracy based on part design, machining setup, and inspection requirements.

Producing Functional Features

Certain features are difficult or impossible to form directly through forging, such as:

- Precision holes and internal bores

- Internal and external threads

- Bearing seats

- Slots and grooves requiring high precision

- Complex mounting interfaces

- Precise mating surfaces

These features are typically produced during subsequent machining operations.

Improving Critical Surface Finish

Forged surfaces may retain die marks, parting lines, or other characteristics associated with the forming process.

Where a smooth or accurately controlled surface is required, CNC machining can remove these features and produce a more consistent finish.

This is particularly important for components with visible surfaces, sealing interfaces, or precision assembly requirements.

3. How Forging and CNC Machining Work Together

A typical forged aluminum component may undergo several manufacturing stages before becoming a finished product.

Step 1: Engineering Review and Die Design

Engineers evaluate the customer's 2D drawings and 3D models to determine whether the component is suitable for forging.

Factors such as part geometry, draft angles, material flow, parting line location, and machining allowances are considered during die development.

Step 2: Aluminum Forging

The aluminum material is formed using a forging press and a specially designed die.

The resulting forging blank approximates the final component geometry while retaining material in areas that require subsequent machining.

Step 3: Trimming and Heat Treatment

Depending on the process and material requirements, excess flash may be removed, and the component may undergo heat treatment to achieve specified mechanical properties.

Step 4: CNC Machining

CNC milling, turning, drilling, and tapping operations are performed as required by the drawing.

Critical dimensions and functional features are machined to meet the final specifications.

Step 5: Surface Treatment and Inspection

Depending on customer requirements, the component may undergo sandblasting, anodizing, or other suitable finishing processes.

Final inspection verifies critical dimensions and product quality before delivery.

This integrated approach allows manufacturers to combine the forming advantages of forging with the precision of CNC machining.

4. Forging + CNC Machining vs. Full CNC Machining

Both manufacturing approaches have advantages, and neither is universally better.

For low-volume prototypes or components with complex geometries, full CNC machining may be the more practical choice.

For suitable structural components produced in larger quantities, forging followed by CNC machining can offer advantages in material utilization, machining efficiency, and mechanical performance.

The final decision should be based on engineering evaluation and total manufacturing cost rather than the manufacturing process alone.

5. Common Applications of Forging + CNC Machining

The combination of aluminum forging and precision CNC machining is widely used for components that require both structural performance and accurate assembly features.

Automotive Components

Forged aluminum components can be used in suspension systems, structural brackets, and other mechanically loaded applications.

CNC machining is used to produce accurate mounting holes, connection surfaces, and assembly features.

Motorcycle Components

Motorcycle triple clamps, brackets, and other structural parts may benefit from forging when their design and production requirements justify the process.

CNC machining ensures accurate fork mounting bores, fastening features, and critical assembly dimensions.

Bicycle and E-Bike Components

Bicycle and electric bicycle components often require a balance of strength, weight, and dimensional precision.

Forging can create suitable structural shapes, while CNC machining completes the interfaces needed for reliable assembly.

Industrial Equipment Components

Forged aluminum parts are also used in machinery and equipment where structural integrity and precision-machined features are required.

The manufacturing process is selected according to loading conditions, geometry, material specifications, and production volume.

6. How to Design Forged Parts for Efficient CNC Machining

The efficiency of forging followed by CNC machining depends heavily on the original part design.

If machining requirements are not considered during forging die development, the component may require unnecessary material removal, complicated setups, or additional processing time.

Several design factors should be evaluated early in the development process.

Machining Allowances

Sufficient material must be reserved on surfaces that require CNC machining. Excessive allowances increase machining time, while insufficient allowances may prevent the final dimensions from being achieved.

Parting Line Placement

Forging parting lines should be positioned with consideration for appearance, machining accessibility, and functional requirements.

Tool Accessibility

Deep cavities, narrow grooves, and difficult-to-reach surfaces can increase machining complexity or make certain operations impractical.

Datum and Clamping Design

Stable positioning and suitable reference surfaces help maintain machining accuracy and repeatability.

Tolerance Optimization

Tight tolerances should be assigned to critical functional features rather than every surface of the component.

Early collaboration between forging engineers and CNC programmers can reduce manufacturing risks and improve overall production efficiency.

7. Integrated Forging and CNC Machining at LCW Manufacturing

At LCW Manufacturing, we provide custom metal forging and precision CNC machining services for customers developing aluminum and other metal components.

With over 20 years of manufacturing experience, in-house tooling development capabilities, multiple forging production lines, and more than 70 CNC machining centers and lathes, we support projects from engineering evaluation to finished component production.

Our manufacturing capabilities include:

Custom aluminum forging

In-house forging die design and development

CNC milling and turning

Multi-axis CNC machining

Secondary machining of forged components

Surface finishing coordination

Dimensional inspection and quality control

We understand that not every component is suitable for forging.

Our engineering team evaluates part geometry, material selection, tolerance requirements, production quantity, and manufacturing feasibility to recommend an appropriate process.

Depending on the project, this may involve forging, full CNC machining, or a combination of both.

Conclusion

Forging and CNC machining are complementary manufacturing processes that address different engineering requirements.

Aluminum forging provides an efficient method for producing suitable structural shapes with favorable mechanical properties, while CNC machining delivers the dimensional precision, detailed features, and surface quality required for final assembly.

By combining these processes, manufacturers can achieve a balance between component performance, production efficiency, and manufacturing cost.

However, the best approach always depends on the specific component design, required quantity, and technical specifications.

Looking for a manufacturing partner for your custom aluminum parts?

LCW Manufacturing offers integrated forging and CNC machining services, from tooling development to finished component production.

Send us your 2D drawings or 3D models for a manufacturing feasibility review and quotation