CNC machining vs. injection molding: Which method is right for plastic parts?

When designing parts, it is best to consider in advance which process to use to manufacture the model and optimize it accordingly.

Among them, the most common processing methods for plastic parts are CNC machining and injection molding. So how do we choose between these two processes?

plastic CNC machining

plastic-parts-cnc-machining
plastic-parts-cnc-machining

CNC machining usually starts from a piece of material, and after removing the material several times, a set shape is obtained.

CNC plastic machining is one of the main ways of rapid prototyping at present, mainly processing ABS, PC, PA, PMMA, POM and other materials into the physical samples we need.

The sample processed by CNC machining has the advantages of large forming size, high strength, good toughness and low cost, and has become the mainstream way of prototype production.

However, for some plastic parts with complex structures, there may be production restrictions or high production costs.

injection molding

Injection-molding-processing-for-low-volume-production
Injection-molding-processing-for-low-volume-production

Injection molding is to dissolve granular plastic, and then press the liquid plastic into the mold under high pressure, and the corresponding parts can be obtained after cooling.

A. Advantages of injection molding

  1. Suitable for mass production
  2. It can process soft materials such as TPE and rubber.

B. Disadvantages of injection molding

  1. The mold cost is relatively high, resulting in high start-up cost. When the production volume reaches a certain quantity, the unit cost of injection molding is low. If the amount is not enough, the cost of the unit is high.
  2. The update cost of parts is high, which is also limited by the cost of molds.
  3. If the mold is composed of multiple parts, bubbles may be generated during injection and defects may occur.

which process to choose

In general, this can be seen as a trade-off between several different characteristics. Speed / quantity, price, material.

  1. Speed/Quantity

If the number of parts is small, CNC machining is relatively fast. If you need 2 parts in 10 weeks, choose CNC machining. If you need 50000 parts in 4 months, injection molding is the best choice.

Injection molding takes time to build the mold and ensure that the part is within tolerance. This can take weeks or months. Once this is done, manufacturing parts using molds is a very quick process.

  1. Price

Which is cheaper depends on the quantity. If you produce a few or hundreds of parts, CNC will be cheaper. When the production quantity reaches a certain amount, injection molding will be cheaper. It should be noted that injection molding needs to share the cost of the mold.

  1. Materials

CNC machining supports more materials, especially some high-performance plastics or specific plastics, but is not good at processing soft materials.

Injection molding has relatively few materials, but injection molding can process soft materials.

As can be seen from the above, the advantages and disadvantages of CNC or injection molding are obvious, and the choice of which processing method is mainly based on the speed / quantity, price, and material to weigh the choice.

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