Components and devices with micron tolerances can only be manufactured successfully by applying years of tooling and plastics engineering experience. This allows for the accurate estimation of percentage tolerance risks and ways to mitigate such risks at each phase of the Microns MatterTM process. These phases include:
- ULTRA-PRECISION TOOLING
- MATERIAL DRYING
- MATERIAL LOT TO LOT VARIATION
- MICRO INJECTION MOLDING PROCESS
The histogram in Figure 1.1 shows the average percentage error in each of these phases for a molded part with a tolerance of +/- 8 microns (16 microns total) and a process capability index (Cpk) of 1.33.
Figure 1.1 Isometric Micro Molding “Average” Tolerance Risk Assessment Strategy
Tooling. From a risk mitigation standpoint, it is critical to select a micro molding partner with an in-house ultra-precision mold making capability. Tooling is the enabling technology for any micro molded component, and especially those with micron tolerances. For example, Isometric Micro Molding builds in-house micro molds to 20% of tolerance, regardless of how tight the tolerance is. 20% of tooling tolerance requires the steel to be cut to ~3 microns (~0.0001”) tolerance, and each additional micron adds 6% error to the total capability.
From the Microns MatterTM point of view, steel measurements are verified and recorded in the validation- and design-history records. Cutting steel to 20% of tolerance requires the use of EDM, milling, and wire EDM equipment that is capable of one order of magnitude beyond the total tolerance target.
By way of example, if the mold tolerance target of 20% is ~3 microns (~0.0001”), the EDM, milling, and wire EDM equipment requires accuracy of ~0.3 microns (~0.00001”) or 10 millionths of an inch. Measurement of the mold is therefore required to be 10% of that or 0.03 microns or 1 millionth of an inch.
This is where the “rubber hits the road” and is fundamental to the proven Microns MatterTM process. Reviewing each step of the process — including the mold fabrication process — allows a cushion of error for the rest of the micro molding process to withstand. There are very few mold shops that have the measurement, fabrication, and environmental controls necessary to achieve these tolerances. It is for this reason that tooling is the enabling technology for the example in this White Paper, a Class III micro molded device with 16-micron tolerances.