The difference between stamping, die-casting and CNC machining parts

Nowadays, even thousands of mobile phones are made of metal, and the cold touch can even stimulate users’ desire to consume. However, although metal mobile phones look the same, their physical structure may be very different. Only by grasping the secrets behind them can we have the opportunity to “really see”.

Cost and attitude

There is no doubt that the texture of metal materials is far superior to plastic (polycarbonate), and it is the only magic weapon to increase the color value of mobile phones. However, there are many processes that give mobile phones metal elements, the most common are stamping, die-casting and integrated numerical control.

  • Stamping: Use a punch to press the metal plate out of the phone casing. Solid to solid belongs to material deformation.
  • Die casting: Molten liquid metal is filled into the mold cavity through pressure, cooling and molding. Liquid to solid belongs to material shaping.
  • CNC: Cutting, drilling and polishing a whole piece of metal through a CNC machine tool, and finally an integrated metal shell is obtained.

In terms of cost, processing difficulty, process time consumption, physical strength and quality, stamping < die-casting < CNC machining. Therefore, the technical solution adopted by the metal mobile phone depends on the manufacturer’s demand for cost and the attitude of the consumer.

Metal sequelae

Although the metal material has a good feel and high strength, it has a fatal flaw: signal shielding. Therefore, 100% (excluding the part of the screen glass) mobile phones made of metal do not exist. In order to achieve signal overflow, the mobile phone must “ventilate” the metal parts, and fill other materials to solve the problem of shielding the signal. At present, the main methods for “ventilating” metal mobile phones are three-stage, window, and nmt nanoinjection. However, the combination of stamping, die-casting, integrated numerical control and three-phase, window, and nmt nano-injection molding has formed the “full-lived phase” of the current metal mobile phone.

Three stages: the choice of entry

The so-called three-stage design refers to a design in which the middle is made of metal, and the upper and lower ends are made of plastic, and then spliced ​​together. Level three is the “cheap commodity” in metal mobile phones, and the stamping process is the best partner for the three-stage program.

Take the Redmi Notepad as an example. Its metal shell is actually just an “iron sheet” punched out. It covers the middle frame and the plastic material made of the skeleton. The metal and plastic parts are painted in a color through the painting process. m makes it look more harmonious and unified, giving the illusion that the entire back cover is metal. In addition, Meilan Notepad also chose the metal stamping process, which is called “Stamping + Structural Parts Combination” by Meizu.

Open window: Advanced selection

The so-called window type refers to “digging” a hollowed out “window” at the top and lower end (or one end) of the integrated metal shell, and then filling it with a material, such as plastic or glass, that can transmit signals. It should be noted that the window scheme can be matched with the die-casting process, and can also be applied to the integrated numerical control process.

Meilan Metal is the representative of die casting process + window program. This mobile phone opens the signal sunroof on the upper and lower ends of the integrated metal back cover, and then fills it through an injection molding process. The high-gloss chamfers, the outer ring of the camera and the edges of the home button are polished by cnc (to improve visual quality). Finally, the metal is covered with colorful paint and spraying process, and finally the metal is made into a plastic feel (this is also sprayed by many players).

Meizu mxne pro series, oppo r7/r9, Huawei mate s8 and other mobile phones are representative of the integrated cnc technology + window solution. Most of them are cut and formed into a whole piece of metal by CNC machine tools, directly drilled out of the window for overflow signal, and then filled and beautified by processes such as injection molding, sandblasting, and coloring.

Nano injection molding: an extreme choice

Although the window solution will not damage the integrated metal structure, the hollowed-out part used for injection molding has a larger area, thereby reducing the value of the metal ratio. At this time, a CNC integrated process + + nmt nano-injection molding program was proposed.

iPhone 6 should be the best speaker for the project. Its metal back cover has been cut into several thin strips by CNC machine tools, and it is filled with nmt nano injection molding process. The filled bars are jokingly called “leucorrhea” by users. And similar “leucorrhea” also appears on mobile phones, such as leucorrhea and living body x6. The good news is that in order to prevent these white stripes from affecting the overall appearance of the phone, how to reduce the number of stripes and the width of the stripes is the direction of competition.


In short, there are still 369 mobile phones selling metal materials. Due to the difference in technology and structure, there will be big differences in cost, firmness and feel. The phone claims to have a metal body, but the technology behind it may not really match the selling price.

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