Once you have determined the tonnage that should be used on a tool, I recommend you put a plaque on the side of the mold stating the tonnage to be used. If the recommended tonnage is stamped right on each tool, it is hard for a technician or setup person to miss it.

If you are having a problem with a specific issue, such as tonnage, always look for a simplistic way to draw attention to it.

-Andy

Companies who use individual water lines rather than a manifold should color-code everything using blue lines for incoming water, red lines for outgoing water, and extra colors such as yellow for line which exit and re-enter the mold.

Once you have this established, place colored plaques on each connection of the mold. This will ensure that your employees cannot accidentally connect an in-line to an out connector.

-Andy

A good rule of thumb is 10% of the initial shot size. For example, if the overall shot size is 100mm, then the cushion should be about 10mm. This avoids pressure losses from too much material in front of the screw, yet provides enough room in front of the screw for normal variability.

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-Andy

We typically recommend between 1 and 2 hours a week. It is always much better to provide your employees a slow, steady, & consistent stream of information over an extended period of time. One hour a week for 40 weeks can be much more effective than one 40-hour week in altering the behavior and improving the skills of your employees.

There is always a place for multi-day training sessions, but they are most effective in teaching a specific skill rather than relaying general knowledge.

-Andy

Essentially, semi-crystalline polymers with a high degree of crystallinity such as PBT and nylon are not highly affected by temperature. In such a case, you will have to adjust the gates or the hot runner system itself to balance the shear of the mold.

Cold runner systems are the best for these materials. I know many molders who use a press-side low-RPM grinder to effectively grind up the material and re-introduce PBT back into the process.

-Andy

Training is good, but it is critical that you tie the training to each job function through the use of a training plan. Without a structured training plan focused on job title you will not be able to make a change to your workforce. In general, your employees will not go and train unless there is a structure to show them what they are supposed to do when they train.

-Andy

This question points out how complex the interactions between the mold, machine, material, and  injection molding process can become.

-Andy

This is correct because of two reasons. First, the gate begins to freeze the moment the material enters the gate. The shorter time required to fill the mold allows more time for packing. The second reason is because the pressure loss within the mold cavity is decreased, allowing more packing pressure to reach the extremities of the mold during packing.

-Andy

Actually, a higher velocity reduces overall energy consumption during injection even though the injection pressure is increased. Increasing the injection velocity decreases the material viscosity through shear thinning. As a result, the overall energy required to push the final volume of polymer necessary to fill the mold is decreased.

In an actual example performed by one of our trainers, the data from a molding process which was filled at two different times is shown below:

Fast Fill:

Fill time = 0.83sec

Transfer Pressure = 11,910psi

Although the faster fill time has a higher pressure at transfer, the molding machine applied the injection pressure for 27% of the time necessary to fill the mold at the slower speed. When you multiply the fill time by the transfer pressure you get the following effective (or relative) viscosity:

Effective Viscosity = t x psi

Slow Fill = 32,950 psi-s

Fast Fill = 9,890 psi-s

Assuming the pressure profiles are similar in shape, it can be reasonably proposed that the faster fill consumed approximately 30% of the energy necessary to fill the mold at the slower speed.

The additional benefit to filling faster is that the polymer fills the mold and begins to cool faster. In this case the overall cycle time could drop as much as 2 seconds due to the higher injection viscosity.

-Andy

The idea behind this is that you always want to know you are making a change which is important. Too often people will tweak different parameters without any direct knowledge as to the effectiveness of the change.

When you make a change, you want to ensure it is large enough to make a difference. Remember any change to the process can be reversed either completely or partially.

I have seen many molders who make small adjustments with the belief it will improve the situation. A symptom of this behavior is a control panel with a large amount of numbers which do not end in either 5 or 0. For instance, if the injection profile looks like the following... V1=11.1 mm/s, V2=30.3 mm/s, V3=23.4 mm/s, V4=28.4 mm/s, and V5=12.7 mm/s. It is very unlikely that each of those velocities have been optimized and each speed in the profile can be properly justified. This type of profile is almost always the result of someone tinkering with the process until a good part came out of the machine.

-Andy