MICRO TOOLING CONSIDERATIONS
5/1/13 Micro tooling enables micro molding, and machining is extremely critical. Since we don’t currently have a “micro” industry standard to go by, we had to create a rough ASTM standard when we make tooling. Example: the industry standard uses an 8” tensile bar, which doesn’t help us in the MICRO world so we had to create a 0.00001” x 0.00002”. In this example we had parts in molds that have 0.00002” gates, with that being a very small gate you end up shearing the material that is going through that small gate. Most conventional sized tools are 0.0002” gate, so you are shearing the material much more than it’s used to, therefore we have to determine what we did with that extra heat/extra shear when it went through an injection mold. We had to make the very small tensile bars to be able to test that polymer to see what happens to the part when subjected to very high shear forces.
Conventional tool making practices, like CNC-EDM-wire EDM, are using extremely small wires (about 0.001”). We have made electrodes for extremely small machined components to be used in the mold.
Unconventional tool making practices are needed in the MICRO world and they include:
- Machining techniques
- Venting
- Core pins 0.0029”
- Ejector pins 0.0049”
- Multi-component micro molding
Acceptable tolerances in conventional sized tools are unacceptable in the micro world. For example: when you have a 0.001” wall thickness and your tool parting line is .02” in Y and 0.03” in X. The 0.03” is 30% of the wall thickness. So what would conventionally happen is when you inject the material down the fat side it will fill very easily but it won’t fill the thin side. It has to be balance filled to fill something using these extremely small parts. What needs to be done in this example is we had to split the 0.03” and 0.02” offset in tooling to create a 0.01” error to be able to fill that part uniformly.
CURRENT MICRO TOOLING METHODS
Top-down methods Bottom-up methods
(removing steel to create the part/tool)
Laser machining genetic code
EDM_WEDM complexity theory
Ultrasonic machining self assembly
Ion machining biological cell
CNC machining proteins
Chemical milling DNA and RNA
Photochemical machining LIGA
Elecrochemical machining