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In this case, the customer was buying as many parts as the molder can produce. The ejected parts were sub-gated for part removal while the parts are being dropped onto a conveyor belt. Since the material was a TPO, the parts were flexible and needed a 2 second ejection forward delay to ensure the part completely fell off of the ejector pins before the mold closed. Air blasts were previously tried, but the parts were not falling well and the result was part damage and increased inspection.

To speed up the removal process, we replaced the sprue picked with a high-speed robot. Since the robot can move with the ejection system, the part were picked up during ejection, and the ejection was retracted quickly. We were also allowed to reduce the mold opening distance which resulted in an overall cycle time reduction of 1.5 seconds which quickly justified the cost of the high-speed robot.

Don’t overlook the big things when attempting to tweak a process. Sometimes replacing a major component such as a screw, barrel, robot, or even mold will give you a significant ROI. The key is to cover the small details first.

-Andy

Although most bolt manufacturers recommend at least 1.5 times the bolt diameter… I believe threading the eyebolt at least 2 times the diameter will provide a much higher degree of confidence.

Most mold makers will thread the holes to a depth of 2.5 times the diameter or more… but it is always best to check the depth to make sure.

When specifying your tooling, always make sure the eyebolt holes are at threaded at least 2.5 times the diameter of the eyebolt.

-Andy

I was recently asked the question…

You can reduce your cooling time a couple ways. The first way to reduce cooling time is to increase your rate of heat transfer. That means you must increase the thermal conductivity of your mold material The second way to reduce your cooling time is to move your cooling lines closer to the mold cavity surface. By reducing the distance between your cooling lines and cavity surface you effectively reduce the thermal gradient between your cooling fluid and polymer melt.

The amount you should invest into increasing the efficiency of your cooling is dependent on many factors. You must perform a cost analysis on your expected output with different cooling system designs. Use the expected cooling time and cost of each cooling system in your business plan to determine which design is most cost effective for you. 

Be aware that a thermal conductivity value five times greater than steel will not result in a five times greater cooling rate. The cooling rate will become limited by the heat conduction through the plastic and the heat convection to the mold coolant.

-Andy

The material you are processing is a ETPU (engineering thermoplastic polyurethane) which tends to be prone to degradation, especially when the material is not properly dried.

It is critical that you determined the dewpoint of the material at the hopper and compare the melt temperature, dewpoint, and drying recommendations of the material.

Any time you are using a hot runner system, you are adding more heat and residence time to the material. If the hot runner design is not specifically tailored to reduce stagnation and hot spots, it is very likely that hangups and degradation will occur within the hot runner system.

-Andy

As a response to an earlier blog, I received this follow-up question…

There are many additives that can be used with Polypropylene… but it requires research, and significant testing, into the application. I wish I could just recommend an additive, but I have encountered many additives which will either increase or decrease the number and size of semi-crystalline regions within the polymer.

-Andy