Now market, where user experience has become a top priority, manufacturers of smartphones, laptops, and wearable devices are increasingly turning their attention to the materials used in product casings. In the smartphone sector in particular, casing materials have been evolving from engineering plastics toward metals.
Over the years, various material combinations have been tried—plastic with metal, glass with metal, all-plastic, and all-glass designs. Yet none have managed to rival the popularity of the full-metal body. From the perspective of both look and feel, an all-metal smartphone clearly delivers a more premium and satisfying user experience compared with other options.
And whenever all-metal construction is mentioned, CNC inevitably comes into the picture. Today, virtually all full-metal casings for 3C products (computers, communications, and consumer electronics) are produced through CNC (Computer Numerical Control) machining. With its high efficiency, superior precision, and consistent quality, CNC has become an indispensable technology for casing manufacturers.
The unibody CNC machining process was first pioneered by Apple. The method begins with a solid aluminum block, which is die-cast into a rough billet. This billet is then precisely machined, gradually taking shape as a seamless chassis. As the process continues, intricate elements such as keyboard outlines and other fine details are milled out. In total, nine separate CNC milling steps are required before a flawless unibody casing is achieved.
From initial programming to the finished product, manufacturers must pass through multiple stages—rough machining, semi-finishing, semi-precision machining, and final finishing. In many cases, more than ten workstations are needed before a casing is complete. To achieve acceptable yields, every stage must be tightly controlled.
Step 1: Modeling and Programming
Before machining begins, the first step is 3D modeling and programming. The complexity of the model depends on the product’s structural design. The more intricate the structure, the more challenging the modeling, and the more elaborate the programming requirements.
Programming includes defining the machining sequence, selecting cutting tools, setting spindle speeds, and determining feed rates. Different products also require different clamping methods, with some complex designs even needing custom fixtures.
Because programming dictates the entire production process, it must be handled by highly experienced engineers. While machining itself is automated, a poorly written program can result in costly trial and error, driving up production costs.
Step 2: Core CNC Machining Processes
The production of a full-metal smartphone casing involves several key CNC processes:
- Initial block milling: A high-speed drilling and tapping center mills the aluminum billet into a precise three-dimensional block, ready for subsequent steps.
- Rough milling: After positioning, the inner cavity, fixture connection points, and most of the excess external material are cut away.
- Antenna slot milling: Since all-metal casings interfere with signal transmission, antenna slots must be milled to create pathways for signals while preserving structural integrity.
- Precision finishing: The inner cavity, outer contours, sidewalls, and external surfaces are finely milled for accuracy.
- Polishing: High-speed precision CNC machines polish the surfaces, removing tool marks and preparing them for sandblasting.
- Sandblasting: The metal is treated to achieve a uniform matte texture.
- Anodizing:
- Primary anodizing adds color to the chassis (e.g., turning aluminum into gold) while improving surface stability.
- Secondary anodizing creates a dense oxide film that greatly enhances durability and wear resistance.
Unlike plastic casings, which can be mass-produced with high yield rates through injection molding, full-metal casings are far more complex. Their yield depends heavily on both structural complexity and precision requirements, making it difficult to achieve the same production efficiency.
To offset the higher costs, many manufacturers invest in large fleets of CNC machines, which helps reduce overall production costs and maintain competitiveness in price-driven markets—while still meeting the required output levels.
