More reasons why injection molders fail at scientific molding: Page 3 of 5

  • Material. It is important to understand the effect that material can have on process consistency. Molders need the ability to trust that the materials they are receiving are consistently produced and handled. For instance, we know for a fact that one nylon is not the same as another. They may perform in a similar fashion, but one material’s response may be totally different despite the base similarities. A process is established based on each specific blend. Every time a material change occurs (regardless if the material manufacturer insists they are the same), it is a brand-new material and a brand-new processing approach must be deployed.
  • Changing auxiliary equipment. A thermolator, dryer, hot-runner controller and so forth are not the same when we are making every effort to ensure process consistency. It is highly recommended that molders marry equipment, molds and other systems to the same press. What this means is each component is physically bound to the same production press every time, so that there is no deviation in press and auxiliaries. Remember, every variation that is introduced into a process is a new process. It is also important to note that there are changes that occur to auxiliary equipment itself, which requires historical data to be collected: Thermolator valves stick causing overheating or poor heat dispersion, gallons-per-minute readings change, valve gates stop functioning. Monitor every condition available to you for verification of true process.
  • Mold modification. Mold modification is generally implemented during the engineering stage, not on the production floor. If a mold is modified in any way, the process should be viewed as new until the modification has been revalidated. Never assume that a change to a mold will not affect the process in any way. Instead, consider the mold to be suspect, and review all historical data you have available to ensure that no real change has occurred. Your quality department needs to be fully aware of the modifications and should perform the proper layout inspections and testing, prior to the press being released for normal production.
  • Watering and heating. Molds should be evaluated during the process engineering stage for proper cooling and heating dispersion, allowing base historical data to be established. Setup diagrams should be documented, and frequently updated. Turbulent flow to and from process (supply/return) should be measured in units of gpm/lpm. Steel temperature measurements are also critical components for measuring process changes over time. It is important to note that mold steel temperatures can vary in different areas of the mold due to heat exposure and flow differentials. Measure and record temperatures in multiple mold locations for historical reference.
  • Process monitoring. Once a process has been validated as true and consistent, process monitoring is a primary key for measuring historical change. Fill time, screw rotate time, cushion, peak pressure and all other primary sources of process monitoring data quickly identify changes within the process. Monitoring is a reliable identifier that triggers reaction when the troubleshooting system is enacted. Verify all key monitoring measurables, and if you identify a significant variance, use that change to identify other changes that might have taken place, including the five M—man, mold, machine, material, maintenance—system of troubleshooting.
  • Barrel temperature. Barrel temperature is not limited to set points—temperature actuals should also be monitored. Controller measurements that monitor actual temperature, as well as manual measurements of true barrel temperatures between heater bands, should be recorded and used to identify changes in temperature over time. In addition, watch for signs of worn heater bands, such as poorly heating zones at start up. Historical data of steel temperature data between bands throughout all zones will identify heater bands that are performing poorly, and quickly identify bands that need immediate replacement.

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