Comparing CNC, MIM, and Additive Techniques: Pros and Cons

Micro CNC Machining

Micro Metal Injection Molding (MIM)

Micro Additive Manufacturing

Complexity

Pros: This method allows the production of complex geometries at small scales, within the limits of the machine tools and configuration.

Cons: The level of complexity is limited by the size of the machine tools. Tool shapes may also affect the possible geometries. Cylindrical tools, for example, will almost always produce rounded internal corners.

Pros: When producing large runs of parts with relatively complex geometry, a MIM process becomes faster than CNC machining.

Cons: The degree of complexity is limited by the physical capacity of the mold. The expense of creating a mold for highly complex parts might not be cost-effective and some designs may not be possible.

Pros: The highest levels of complexity are possible with RIPL at fast production speeds with minimal lead times..

Cons: Some 3D printing technologies have struggled with micro-level tolerances, but RIPL has improved on this greatly to match the quality of CNC machining.

Design flexibility

Pros: CNC machining tends to work best for parts with an established design. It can produce parts with precision and reliability.

Cons: Design changes often require retooling and overhauls to CNC machine configurations.

Pros: Once a mold for a challenging design is completed, many parts can be produced quickly and efficiently. 

Cons: Any design changes require the production of a new mold. This can take months or longer, depending on available lead times.

Pros: Additive manufacturing machines can quickly adapt to design changes. It often only requires updating the digital model. This significantly reduces the time and expense needed to make modifications.

Cons: None.

Prototyping

Pros: CNC machining can produce prototypes faster and at less cost than MIM (although not “fast”) with lead times of 6-12 weeks.

Cons: The cost of prototyping can be high with complex designs. Depending on the materials used, prototyping and end-product production can require changes to the machine and its settings. When converting to a production run, more complex parts become less cost-efficient due to the time required to machine each part).

Pros: Once a prototype is proven, the same MIM mold can easily be re-used for production.

Cons: The prototype mold might not be suitable for a production run, requiring the creation of updated molds. This makes MIM an extremely expensive and time-consuming choice for the prototyping stage of product development (and therefore, virtually never used).

Pros: RIPL produces high-precision prototypes with quick turn times and provides a near-seamless transition between prototyping and production. No equipment changes are necessary. Prototype parts are identical to production parts, enabling engineers to test and validate designs with the real thing, rather than a mockup.

Cons: None.

Surface Finish

Pros: Micro CNC technology has a demonstrated track record of producing native surface finishes within established parameters.

Cons: None.

Pros: MIM is capable of producing parts with surface finishes that approach industry standards.

Cons: Some materials may require additional polishing or other work to achieve the desired surface finish.

Pros: RIPL can attain Ra32 native surface finish without the need for additional work.

Cons: Some other additive manufacturing methods have not been able to produce the desired native surface finish.

Tolerances

Pros: CNC machining has a reputation for precision.

Cons: Tolerances may vary from one shop to another, from one operator to another, and from one day to another depending on how well tooling and fixtures are maintained.

Pros: Mold production provides consistent precision.

Cons: Any error or imperfection in mold design or construction affects all parts produced with that mold. Mold injection physics can also cause issues with tolerances and repeatability.

Pros: RIPL can produce precise parts that match CNC machining and MIM for tolerance. Tolerances are tight and highly repeatable across large volumes.

Cons: Other additive manufacturing methods have not met the same standard, but RIPL has rectified this.

Lead Time

Pros: Actual production time can be quick.

Cons: Lead times can be quite long until machines become available. Preparing a machine for complex micro-components can be time-consuming.

Pros: Actual production time can be quick.

Cons: Lead times can be long for both the production of the mold and the MIM process.

Pros: Lead times are short and enable quick design iteration cycles. 

Cons: None.