Ultra-Precision Injection Molding

MPR Plastics specializes in ultra-precision injection molding of plastic parts

MPR Plastics, Inc specializes in high precision injection molding of plastic parts. The cornerstone of achieving high precision is the minimization of process variation during injection molding. Process variation can be caused by any external variable that causes change in the resulting plastic part’s dimensions or physical properties. Examples of such external variables include the plastic material’s consistency, the molding machine’s accuracy, and the thermodynamic control of the injection mold.

All three of these variables are significantly impacted by the environmental characteristics of the molding plant. Specifically, temperature and humidity variation and elevation can negatively affect process variation.

Material Consistency

Many of the plastics that MPR runs are hydroscopic which means they attract moisture at the molecular level. As such, the materials need to be dried in a drying system prior to molding. Any moisture picked up by the material in the molding plant after drying will negatively affect the material’s consistency and physical properties as the material will succumb to hydrolysis during molding. The higher the plant’s humidity the more difficult it becomes to maintain dried material. This is a significant problem for quality, high precision molding.

To mitigate these effects, MPR’s new plant in Elgin, Illinois is equipped with a new, technologically-advanced, centralized drying system which is capable of drying the most difficult engineering grade resins (even up to 400 degrees Fahrenheit).

Molding Machine Accuracy

High temperatures can affect the viscosity of hydraulic oil in molding machines which may create velocity and pressure deltas in the molding cycle. Such variation causes dimensional inconsistency from shot-to-shot in the molding process.

To mitigate these effects, MPR uses what are widely considered the most precise injection molding machines in the world. All electric molding machines utilize extremely accurate servo motors without any of the variability inherent in hydraulic molding machines to achieve repeatability within microns.

Thermodynamic Control of the Mold

High plant temperatures and temperature variation in general make accurate mold temperature control very difficult. Injection molds are designed with water lines to thermodynamically balance the loss of heat from the plastic material to achieve a specific plastic shrink and, thereby, part dimension. Molds are run with individual water temperature controllers to achieve the desired temperatures. Consistent control of mold temperature and the resulting plastic shrink is absolutely critical to high precision injection molding. Environmental temperature variation undermines the goal of consistency.

Finally, elevated humidity, where the plants dew point exceeds the temperature of a mold (58 degrees F), creates condensation and a rapid chilling affect on molding surfaces as the mold opens and closes. The result is an extremely negative effect on precision molding.

To mitigate these effects, MPR’s new molding plant employs a state-of-the art HVAC system to maintain environmental temperatures in a controlled range of 68 to 82 degrees F and a dew point below 58 degrees F. This control is essential to the efficient execution of MPR’s high precision injection molding business model.