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Injection Molding Process Monitoring Parameters

The only way to run a successful injection molding operation is to have an outstanding process monitoring system to go along with the injection molding machines. There are several parameters that need to be monitored, with the goal to minimize variability in the process itself, which in turn will minimize variability in the product.

Parameters include (not in order): Times (Cycle, Fill, clamp, etc), Pressures (pk hyd, hold, back, in-cavity, etc), Temps (water, oil), Distance (Cushion, etc).

Regarding to in-cavity pressure and temperature. Yes, these are good, but not the "1st" choice, or only choice. Any injection mold shops (that know their real problems, or admit to problems) will tell you that water is 80% of the problem. Temperature, flow, setup, system water, heaters, chillers, hoses, etc). Water is the problem! Process monitoring the water is the first step. It is unbelievable all the problems that you will troubleshoot and root cause all the way down to water!

I am amazed at the number of companies that do not monitor their processes. I think it is because of the variability of the process from job run to job run. This variability is a built in rationalization for non-investment in monitoring hardware, software, etc. One needs to be convinced of the immediate and long term cost savings before an investment will be made.

I am always amazed when the subject of monitoring comes up and water temp is viewed as a priority variable to monitor. I think steel temps (cavities, cores, platens, manifolds, etc.) are a much more important variable to monitor. While water temps need to be monitored, they will not necessarily show a rise in, for instance, core temperature if a water channel in the injection mold becomes clogged. In other words, the time to reach HDT is prolonged without anyone being cognizant of the change in steel temperature. In this scenario, a pin marks show up on the part while the monitoring data is showing a stable process.

I think the sensor industry is missing the boat by not developing sensors for cavity and core steel temperature monitoring. If one knows where the steel temperatures are trending to, then an adjustment to the water temperatures can be made to compensate for this.

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