polymer processing

The fifth step in validating a injection mold with the overall process shown in figure injection mold validation flow chart is mold viscosity test . The steps before: 1. Mold certification 2. Dry cycle mold 3. Process stability test 4. Gage repeatability & reproducibility (R&R) test Purpose: The mold viscosity test was developed to identify the maximum and minimum fill rates permissible for the mold with a specific plastics material. The theory behind using high speed injection rates is to take advantage of the decreased viscosity which results when plastics are subjected to high shear rates. The mold viscosity test should be performed on the correct size press, for which the mold was designed. The injection rate should be recorded in volume per unit time so that the learnings and results of the mold viscosity test can be transferred to another press that may have a different size injection unit. The mold viscosity test could be skipped if mold fill analysis has been perform...

The fourth step in validating a injection mold with the overall process shown in figure injection mold validation flow chart is gage repeatability & reproducibility (R&R) test . The steps before: 1. Mold certification 2. Dry cycle mold 3. Process stability test Purpose: The purpose of the gage R&R analysis is to quantify the magnitude of variation of a measurement system. To ensure the benefit derived from using measurement data is of value and cost effective, attention must be focused on the quality of the measurement data. One of the most common reasons for low-quality data is too much variation in the measurement data. For example, a measurement system with a large amount of variation may not be appropriate for use in analyzing an injection molding process because the measurement system’s variation may mask the variation in the injection molding process. A gage is any device used to obtain measurements. This includes devices like coordinate measurement machines, verni...

The third step in validating an injection mold according to injection mold validation flow chart is dry cycle mold is process stability test . The steps before are: 1. Mold certification 2. Dry cycle mold Purpose: The purpose of the process stability test is to identify any gross mechanical design/construction flaws which will cause part variation over time. In addition, the process stability must be established with no short shots, flash, etc., prior to running designed experiments. The test is run at mid-range resin molding conditions for a period of time to allow thermal expansion equilibrium. In most instances, the mold builder may already have a process where the mold could run comfortably for several hours. During the process stability test the mold must run with one ejection stroke unless it was designed to cycle with multiple strokes. A robust ejection system will be able to eject the part and runner with one ejection stroke. Multiple ejection strokes per molding cycle incr...