Plastic CNC VS Plastic Injection Molding

Plastic CNC VS Plastic Injection Molding, which method is better for you?

When designing a part, it's a good idea to think ahead about which process we will use to build the model and optimize it for that production process.

For plastic parts, the most common processes are CNC machining and injection molding. So how do we choose between these two processes?

First CNC machining

CNC machining usually starts from a piece of material, after several times to remove the material, to obtain the set shape, CNC plastic machining is currently one of the main ways of handboard modeling, mainly ABS, PC, PA, PMMA, POM and other materials processed into the physical samples we need.

CNC machining out of the sample has the advantages of large molding size, high strength, good toughness, low cost, etc., has become the mainstream way of handboard production. However, for some complex structure of plastic parts, there may be production restrictions or higher production costs.

Second, injection molding

Injection molding is a granular plastic dissolved, and then through high pressure will be liquid plastic pressed into the mold, after cooling to obtain the corresponding parts.

01. Advantages of injection molding

1.Suitable for mass production

2.It can process soft materials such as TPE and rubber.

02.Disadvantages of injection molding

1.Mold cost is relatively high, resulting in high start-up cost. When the production volume reaches a certain amount, the single piece cost of injection molding is low. If the quantity is not enough, the cost per piece is high.

2.The update cost of the part is high, also limited by the cost of the mold.

3.Molds that consist of more than one part may produce bubbles and defects when injecting.

Third, which process to choose

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

01. Speed/Quantity

CNC machining is faster if the number of parts is small. If you need 10 parts in 2 weeks, go with CNC machining. If you need 50,000 parts in 4 months, injection molding is the best choice.

Injection molding takes time to build the mold and make sure the parts are within tolerance. This can take weeks or months. Once this is done, building the part using a mold is a very quick process.

02. Price

Which is cheaper depends on the quantity. If a few or hundreds of parts are produced, CNC will be cheaper. When a certain quantity is produced, injection molding will be cheaper. It is important to note that injection molding requires sharing the cost of the mold.

03. 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 less materials, but injection molding can process soft materials.

As you can see from the above, the advantages and disadvantages of CNC or injection molding are obvious, and the choice of which processing method to choose is mainly weighed by speed/quantity, price, and material.

Advantages of CNC Machining vs. Injection Molding for Precision Parts

When evaluating injection molding versus CNC machining of plastics, there are four areas to consider:

 QUANTITY: Typically, CNC machining provides faster delivery and lower costs for reduced part quantities. The exact volume threshold for cost reduction in injection molding depends on part size, part complexity and material selection.

 Speed and Cost: CNC machining offers higher speeds for small lot sizes. Or for rapid prototyping or limited part production runs that won't break your development budget, machining offers faster turnaround times at a lower cost. For production runs in the tens or hundreds of thousands, injection molding usually makes more sense.

 Accuracy: Machined parts give you more control and fewer variables when dealing with precision tolerances. Machining focuses on the exact specifications of the part itself, as opposed to injection molding, which considers the tolerances of the mold rather than the part. CNC machining typically provides more accurate results when absolute precision is required in the final product, especially for aerospace, medical and defense applications.

 Performance: For high-performance hard plastics that cannot be molded, manufacturers choose CNC machining. Certain applications require hard plastics that must be machined. The melting and re-hardening of plastics in injection molding may introduce undesired changes in the material properties of the final part.

Difference between the use of cnc machining and injection molding for parts in the pilot stage and mass production stage, respectively

There are some distinct differences in the use of two different manufacturing methods, CNC machining and injection molding, in the pilot and mass production phases:

CNC machining is used in the pilot production stage:

Rapid Prototyping: CNC machining is often used in the pilot production phase to quickly prototype parts to verify design and shape.

Low Manufacturing Costs: For small batches or single samples, CNC machining is usually less expensive because large-scale mold making is not required.

Flexibility: CNC machining is suitable for prototype parts in different materials and complex geometries because it does not require custom tooling.

Accuracy and detail: CNC machining enables high accuracy and intricate detail, making it suitable for manufacturing prototype parts with complex shapes.

Injection molding is used in the mass production stage:

Mass Production: Injection molding is often used in mass production because the cost of manufacturing molds to make large quantities of the same part is relatively high, but more economical in the long run.

Low Unit Costs: Once the molds are made, the unit cost per injection molded part is usually low, especially in high volume production.

High production speeds: Injection molding machines can produce large quantities of parts in a short period of time, making them suitable for high volume requirements.

Consistency: Injection molding ensures that mass-produced parts have consistent dimensions and qualities that meet quality standards.

Material selection: Injection molding allows the use of a wide range of plastic materials to meet specific performance and application requirements.

Overall, CNC machining is suitable for the pilot production stage, where there is limited sample demand and a need to quickly validate the design. Once the design is stabilized and moves into the mass production phase, injection molding is usually the more economical and efficient choice, especially for mass production. The choice of manufacturing method depends on the requirements of the production phase, cost and part design.