CNC Machining vs. Injection Molding: Which technique is Right for Plastic Parts?

The choice of the right production method is inevitable when the matter comes to manufacturing plastic parts. With an appropriate production method, there can be a significant difference in terms of efficiency, quality, and cost. Two of the most renowned techniques used for plastic parts are injection molding and CNC machining as they cater to different needs. It is inevitable to be aware about the effectiveness of these two methods whether you have to create prototypes, produce complex parts in bulk, or deal with small-batch custom designs. Before going in deep on the differences between these methods let’s first get overviews of each of them.

Overview of CNC Machining

CNC (Computer Numerical Control) Machining refers to a process wherein pre-programmed computer software commands the movement of industry tools and machinery. The method involves cutting from a material’s block and facilitates the manufacturing of complex shapes that can’t be achieved with manual machining.

Overview of Injection Molding

This manufacturing method is used for manufacturing plastic parts wherein molten material is injected into a mold. The injection molding manufactures parts for a broad range of industries, ranging from the tiniest components to whole body panels of a car.

Comparison of CNC Machining and Injection Molding for Plastic Parts

1. Choice of material:

   CNC machining can be a good choice for working on plastic parts since it can accommodate a broad range of materials from plastic to metal. For plastic material, the material's hardiness is inevitable. CNC machines can effectively fabricate hard plastic, whereas soft plastic would be deformed. Hence, high precision, tolerance, and workability can be achieved only on hard materials.

   On the contrary, injection molding adopts flexible machinability while working on soft materials. So, this method is a good choice if you wish to work with thermoplastics or some other injection molded materials. These other materials include Polypropylene (PP), Acrylonitrile Butadiene Styrene (ABS), and Polyether Ether Ketone (PEEK). The reason is such materials can be molded without compromising material strength. Note that flexible materials can be forged using this process.

   Norck provides high-quality CNC machining service that fulfills the demanding applications across different industries like robotics, aerospace, industrial, automotive, energy, electronics, defense, etc.

2. Production volumes and cost:

   Both these processes are widely used for mass-production volumes. Rapid prototyping using CNC machining can easily be completed early based on the material. However, the cost reduction when working on mass production volumes is comparatively high and may require a long time for completion.

   On the contrary, injection molding can be useful for swift prototyping for smaller machines. So, it is a better choice for mass production volumes and substantiates cost reduction more efficiently. Time injection molding is only required in designing custom molds. Hence, the injection molding method proves to be more affordable than CNC machining.

3. Design flexibility:

   Manufacturers consider CNC machining service as the best choice for design flexibility. Engineers prioritize the feasibility of post-manufacture changes in plastic parts. So, any additional changes required can be easily incorporated into CNC-based products.

   When an injection molding process is used, a new mold will be required if additional modifications are required. Consequently, it adds up to the cost. So, this limitation suggests that CNC machining is preferred over injection molding when it comes to design flexibility. Norck employs rigorous quality control to ensure excellent accuracy, superior part quality, and tight tolerances.

4. Tolerances:

   It is vital to consider tolerances i.e. what amount of physical variation is acceptable within viable plastic parts. This tolerance ensures that end-use parts perfectly fit together and work as intended. Note that injection molds come with tolerances of 0.005”, whereas CNC machining tools can cut workpieces with very accurate tolerances of 0.001”. But machining molds with very tight tolerances can get costly which eventually makes the plastic injection molding expensive. So, directly machining the plastic parts using the CNC machining method can be more efficient.

5. Performance and strength:

   For plastic parts, injection molding facilitates the creation of parts with unvarying mechanical properties and strength. This process is more suitable for producing plastic parts that have to withstand strain and stress consistently across their surface. Since a wide range of plastic materials are available for the injection molding process, the process gets options with different strength requirements.

   Contrastingly, CNC machining is quite prestigious for its capability to deal with an extensive array of materials –metals, plastics, etc. The performance and strength of CNC machined parts are greatly dependent on the chosen material. Since machined parts are usually stronger than molded parts, they can ensure better performance when working on plastic pieces.

6. Surface finish:

   When the matter comes to the surface finish of a part, the injection molding process utilizes ejector pins to forcefully detach the cooled part. The corresponding process can leave minor cosmetic imperfections on the surface of the product. Essentially, this may not be significant for certain applications but if manufacturers demand smooth finishes then CNC machining may be the perfect choice for plastic parts. Contacting Norck benefits you with custom manufacturing and engineering solutions that are personalized to your needs, across industries.

Conclusion

The in-depth comparison between the two methods as discussed above analyzes aspects like design flexibility, production runs, costs, tolerance, and more. CNC machining service enables more quality control and machinability. So, it is preferred over injection molding for the manufacturing of specific parts that need excellent precision, tolerance, and durability. On the other hand, the injection molding method is more suitable for lightweight, cost-effective, simple to complex, and swift production of plastic parts. The final decision depends on your requirements and project specifications i.e. parts precision, volumes, and dimensional tolerances.