Micro-medical manufacturing tolerances: obtaining high-resolution and ultra-precise functionalities

The manufacture of precise miniature plastic parts is the result of precise tooling execution. By understanding the tolerances of micro-tooling and micro-injection molding, it is possible to achieve a high level of repeatability and part precision, even for the most advanced medical micro-devices.


Equipment capacities

The mold is the catalyst for manufacturing success, and precise execution is achieved using state-of-the-art equipment and unconventional tooling methods.

Advances in high precision mold making and casting technology offer more possibilities when miniaturizing medical device components. For example, MTD Micro Molding has invested in equipment (and personalized) for very specific work:

  • Sarix 3D EDM milling machine creates a cavity geometry with an end mill electrode that can be as small as 5μ.
  • Mitsubishi MX600 Wire EDM Machine allows machining operators to use ultra-small wire down to 0.0008 ″ (20μ).

Precision and accuracy

Part accuracy refers to what the actual part looks like coming out of the machine, not what the machine is specified to do. At MTD, our part accuracy target is 0.000042 ″ (approximately 1μ).

Exact tooling

The characteristics and tolerances achievable in plastic depend on the precision and material of the steel. As tolerances decrease, the allowable margin of error for steel precision also decreases. There is essentially no margin for error in micro tooling, but with some materials these rules become more stringent when tight tolerances are required. With tool inserts moving together like intricate tiny puzzle pieces with ultra-precise sequencing, the build accuracy of these pieces is crucial.

If we analyze the types of projects MTD saved from production failure, it was often the lack of precision in the mold that didom the project from the start. The smaller the parts and features, the less errors can be tolerated in a mold. It becomes increasingly difficult, if not impossible, without state-of-the-art micro-tooling equipment, methods and expertise.

Assuming a part feature size of .010 ″, we can compare two commonly used micromolding materials with respect to required steel targets and tolerances based on feature tolerance:

As you can see above, the steel tolerance required to reach a specification tolerance target for polypropylene (PP) is significantly lower than for polycarbonate (PC). This is due to the difference in the shrinkage rate of these materials. It is more difficult to achieve the tolerance of the plastic characteristic when the shrinkage rate is higher.


Room size

Micro components typically fit into a square or 1 ″ diameter, but parts can also be microscopic in size. In terms of weight, MTD made a part where 520 parts were made from a single plastic pellet.

Room characteristics

Any plastic injection molded part can be miniaturized, with some more difficult to manufacture than others due to the complexity and geometry of the design.

When miniaturizing your design, focus on the most critical areas of the design and understand that some features may need to be changed or eliminated to enable successful manufacturing on such a small scale and to avoid excessive costs and delays. .

At MTD, we carry out the following parts characteristics:

Now that we’ve created some boundaries for what a micromolded part fits into, we can talk about what this geometry has allowed medical device OEMs to achieve with their designs. What is possible is quite exceptional

Achievable characteristics and tolerances

  • 5µ / very sharp rays
  • 002 ″ wall thicknesses / taper to edge
  • 250: 1 aspect ratios
  • Zero drafts
  • ± 0.0005 ″ tolerances

MTD’s offerings with wall thicknesses up to 0.002 ″, aspect ratios of 250: 1, rag-free designs and cutting edge radii of 5μ have been a game-changer for medical markets such as endoscopy, drug administration and laparoscopy.

In the photo above, drug delivery devices made of polypropylene (PP). The drug delivery straw (top) has a long distance wall of 0.005 ″, while the cannula design (bottom) has walls as thin as 0.0025 ″. High performance tooling and molding equipment and techniques are required for successful injection molding of thin-walled parts like these.

With the right partner who understands micro-molding and tooling, medical equipment manufacturers can improve the functionality and quality of their micro-medical device.

To learn more, read our free white paper on Advances in Design for Manufacturing: Producing Innovative Micro-medical Devices.

Do you have a question about your medical micro design? Talk to MTD Micro Molding.

Content sponsored by MTD Micro Molding

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About Leona A. Yow

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