DFM Analysis for CNC Machining Aluminum Complex Cavity Part

In the manufacturing industry, Design for Manufacturing (DFM) plays an important role in optimizing production processes and minimizing costs. It serves as a pivotal bridge between design and production, ensuring a seamless transition from prototyping to mass production.

Taking a typical aluminum cavity part as an example, this article analyzes its DFM from a machining perspective and discusses how to optimize production efficiency and achieve quality control.

Project Overview

The product is a large cavity part with dimensions of 328×272×87.5mm. Made of AL6061 material, this component features fins on its A-surface for heat dissipation. There are two deep holes (orange hole surfaces) on the front and back as coolant circulation channels, forming a loop through small cavities on the B-surface(orange surface). The internal cavity is hollowed out mainly to provide assembly space for other components. And the threaded holes and pillars distributed on the external and within the cavity serve as fasteners for the assembly of other parts.

In addition, the part uses CNC machining during the prototype and small-batch production stages, while die-casting combined with CNC machining is used for mass production. Below, we will share the design for manufacturability solutions for this part in CNC machining from the perspectives of structural design and tolerances.

Structural Design Analysis

Since mass production of this component involves die-casting combined with CNC machining, the designer’s initial design is based on die-casting. However, During the engineering verification and small-batch production stages, the only use of CNC machining results in some structures not being fully suitable for this method.

Thread Pillars on the A-surface and Tool Limitations

The thread pillars on the B-surface extend to the A-surface, with multiple narrow and deep structures in between. To fully machine these areas, especially slender small-diameter tools are required, but the customization of this tool exceeds the limit of what can be made.

In addition, their rigidity is too weak during machining, leading to issues like tool chatter. Therefore, after communicating with the customer, only general slender small-diameter tools were used for chamfering, and the thread pillars on the surface A are not fully penetrated through to the fins.

Narrow Structures in the B-surface Cavity

The depth dimension of the thread pillars in the B-surface cavity is large, and the gap with adjacent surfaces forms a narrow space, making the machining difficulty similar to that mentioned in point 1. In this way, there are certain differences between the practical machining result and the 3D model.

Internal Corner Radii and Draft Angles in the Cavities

There are many internal corner radii in the B-surface cavity. According to the die-casting process, deep cavity corner radii combined with draft angles can be easily achieved. However, in CNC machining, the size of the R-angle at the corners depends on the diameter of the tool selected for finishing or chamfering.

In common, we recommend controlling the ratio of the limit value of corner radii to depth within 10 times. For this component, the ratio reaches about 40 times at the deepest place. Thus, it is necessary to increase the R-angle during actual machining.

If an extreme ratio design is indeed adopted, it is also recommended to add a draft angle of 3° or more in CNC machining. This can form a structure that is wider at the top and narrower at the bottom, which aids in chip removal and machining rigidity for the CNC cutter.

Fillet Design of Slots

This cavity component features fillet designs at the top and bottom of some slots. Fillet designs are no issues for the die-casting process, but in CNC machining, they belong to 3D machining, which increases machining difficulty and time. For the same structure, if it can be processed into a regular structure, a 2D tool path can be generated, and the machining efficiency will be much higher than that of a 3D-machining. Therefore, we often recommend that designers process such structures as regular structures to improve efficiency.

In conclusion, from the machining perspective and experience, for structure designs that need adjustment, engineers at WayKen will fully communicate with our customers to make necessary optimizations while ensuring that assembly and functionality are not affected.

Define Tolerance Specifications for Production

In the initial design of new products, due to the lack of reference from mature products, designers often specify dimensions and tolerances too strictly. The 2D drawing of this component contains 267 controlled dimensions, spanning five pages.

After careful analysis by WayKen engineers, we fully understand that strict dimensional control is necessary for machined parts, but it is sufficient to reasonably control only the critical dimensions. This ensures quality while also considering it affordable.

Therefore, through in-depth communication with our customer, we all agreed to retain functional dimensions related to assembly as mandatory inspection dimensions and convert about 2/3 of the dimensions into reference dimensions.

Measurement Strategies and Quality Assurance

So, how do we ensure the reliability of quality while simplifying the total number of inspection dimensions?

Determine and Measure Mandatory Inspection Dimensions

Based on dimension categories, we develop an inspection operation specification table, specifying inspection tools and methods for each dimension. When the number of parts is relatively small, the coordinate measuring machine (CMM) is the primary measurement tool and method. They offer comprehensive measurement capabilities and are very suitable for parts with a small quantity and many dimensions.

Simulation and Actual Comparison

CAM software is used for detailed simulation before machining to confirm the absence of overcuts or missing structures. After machining is completed, the physical product is compared to the 3D drawing one by one to verify the structural integrity and spot-check some reference dimensions.

By combining strict mandatory inspections with flexible reference dimension inspections, WayKen ensures quality while improving efficiency for this large and deep cavity part.

Conclusion

This cavity component has a complex structure, with a material removal rate as high as 92%, long machining time, high costs, and numerous dimensions to control. Through professional machining capabilities and experience, WayKen actively communicates with customers and makes some reasonable adjustments to some structural features and measurement dimensions based on the characteristics of CNC machining. It achieves both cost-effectiveness and quality assurance. We hope this article provides insights to you for the bridge between design and manufacturing.