>> Tuesday, 1 September 2009
The second step in validating an injection mold according to injection mold validation flow chart is dry cycle mold. The steps before are:
1. Mold certification
The purpose of the dry cycle mold is to evaluate the mold mechanical actions for any gross problems prior to injecting plastic into the mold. The machine operator at the mold builder or molder should know how to adjust the settings on the injection unit to cycle the mold without injecting plastic into the tool. If at anytime during the dry cycle procedure there is a possibility that damage is being done to the tool or if the mold is not operating as designed, pull the mold from the press and have it examined by an experienced mold builder.
This stage is often carried out prior to the customer being invited to the mold builder for the debug. If there are any machine/mold operation issues it is preferable for the mold builder to remedy this before customer attendance, saving unnecessary travel. If there is a serious mold design flaw (as opposed to a mold assembly issue) it will then be necessary to attend to discuss next steps.
1. Put mold in press. Ensure that the cooling circuits are attached to the mold and that water is circulating through the mold. Also, if there is a hot runner manifold have the controller installed and temperature heaters turned on.
2. Verify water is flowing through the mold at resin manufacturer’s recommended mid-range; check with flow meter indicator or measure flow rate by having the returns empty into a bucket. Ensure heaters are working in the hot runner system by reading the thermocouple outputs.
3. Close the mold at a slow rate and pressure to verify that the mechanical, pneumatic or hydraulic actions of the mold have responded and are moving as designed. Listen for any suspect noises of possible binding of slides or galling.
4. Clamp up on the mold at a low tonnage. Be sure to have mold protection time, pressure and rate properly set so that no major damage can be done to the mold.
5. When the mold is in the press, open the mold at a slow rate to ensure that the mechanical, pneumatic or hydraulic slides are responding and moving as designed. Listen for any suspect noises of possible binding or galling. The slides should move with little resistance.
6. After mold is completely open, cycle the ejector plate manually at a low pressure and low rate, while visually inspecting to verify the ejector plate is performing as designed.
7. Cycle the mold without injecting plastic. Typically this is done by transferring from fill/pack stage to hold stage by position and setting the feed stroke and transfer position to the same position while having the hydraulic pressure set to 0 bar. Keep the clamp open/close rates and pressures to a minimum. Set the hold time to zero. Set cool time to a minimum machine value to decrease the cycle of the mold.
8. Evaluate the mold while it is cycling for any gross mechanical problems. Study the movements of the mold for possible binding or galling of slides, ejector pins and leader pins.
9. Increase the rate and pressure of mold open/close slowly until it replicates the speed and pressures expected during production or sampling. Also do the same with the ejection action.
10. Increase the tonnage slowly until it replicates the tonnage necessary to keep the mold closed during the injection stage of the molding process.
11. Continue cycling the mold until you determine that mechanically there are no fundamental flaws with the production or design of the mold.
The further steps are required in validating a injection mold according to injection mold validation flow chart:
3. Process stability test
4. Gage repeatability & reproducibility (R&R) test
5. Mold viscosity test
6. Balance of fill analysis
7. Gate freeze test
8. Commissioning (multi-cavity analysis)
9. Design of experiments
10. Qualification (process capability study)
11. Mold metal Adjustments - centering process
12. Verification (30-day run)