Injection Molding Process Validation Using Scientific Molding
Developing the process validation around the following four plastic variables allows the flexibility to move the validated mold and process to any comparable molding machine.
Plastic Melt Temperature
Use the material manufactures recommended melt temperature for process development and verify with a calibrated melt probe to check the plastic melt temperature. As a general rule of thumb the heat energy required to melt plastic is 20% from barrel heaters and 80% from mechanical shear. The melt temperature is a combination of many factors and settings. As part of Crescent's start up and shut down procedure the established melt temperature is verified and documented.
Plastic Flow Rate
Inject as fast as possible, consistent with quality, until the cavity is 95 to 99% full. As this point, transfer to pack and hold using machine position transfer. This is the established (plastic flow rate) machine fill time for this mold. The fill time is a combination of many factors and settings. The established fill time for this validated process does not change.
Crescent buys world-class equipment that gives us the confidence of consistent (plastic flow rate) machine fill time through closed loop control. The CNC electric molding machine has pushed that confidence of consistency to an even higher level versus hydraulic machines. As part of our start up and shut down procedure the established fill time is verified and documented.
Plastic Pressure Gradient
Pack the part to finish filling while adding enough plastic to compensate for shrinkage. Establish the hold pressure that gives the part the desired cosmetic look and size. Coupled with the established hold pressure the proper amount of hold time is established. If a post gate cavity pressure sensor is not present, then use the weight method.
Traditionally for Crescent's process development, we are establishing gate seal. We then push the hold pressure to its high and low limits to establish the range for the validated process. As part of our start up and shut down procedure the established hold pressure is verified and documented.
Plastic Cooling Rate and Time
Cooling rate is the difference between melt temperature and mold temperature. The mold temperature is established using the material manufactures recommended ranges and the customers working temperature of the part. Water flow is verified and checked using a calibrated surface probe to measure the temperature difference between the in and the out. The delta T of each water circuit during process development is established at 4 degrees or lower and documented on the process sheet.
A targeted cooling time is already established based on the part and mold design and the material being used. Fine tuning the cooling time during process development is directly related to the customers' expectations of part appearance, size and desired properties. Once established it is documented on the process sheet.
For more information About Crescent Industries Custom injection Molding Services www.crescentind.com/crescent_industries_custom_injection_molding.html, call 1-800-411-3844 or email sales@crescentind.com.
