Tech Tip December 1999

Troubleshooting Basics, part one

In the past, we have covered an extended range of topics and thoughts; the time has come to review some basics on the science of trouble shooting. Note that the word science has come up and that should not scare you away but help to explain the thought process. This process is based on numbers or data as previously discussed in many different ways.
It must be stated that time is money and getting acceptable parts out is the main concern of the floor personnel along with management. Sometimes this leads to what is called the Band-Aid approach in that we worried the parts out and got someone to tweak the knobs or impute on the computer but never solved the problem. In the short term, you may be correct, (some can debate) but in the long term, it costs a lot more, as the problem may always be there. Using a standardized approach or jumping to an approach based on scientific molding can solve problems better in the end, because now we have solved the problem. In addition we create the knowledge of the why and how of the problem.

Step One
Define the problem.  Though as simple as this sounds we, tend to not define the problem at all. The tendency is to define the symptoms and results. For example lets say that the parts are short, not full, the usual reply is that we have short shots.  Yes this is true but the real cause is that we have not put enough material into the mold. The same is true for sinks in the part too, not enough material. By now defining the problem, as we did not put enough material into the cavity we can inspect those areas that effect the placement of material into the cavity. These may include but not be limited to the shot size, screw forward timer, transfer position, melt temperature, mold temperature, injection speed, fill time, injection pressure, delta P, and other factors.
Please remember that this definition of the problem need be specific. Again, back to shorts, if in a multi-cavity tools are all cavities short or only 1 or 2. Does it happen all the time or only after running for a period of time? Again, we are trying to define the
problem as to a specific cavity problem or time function that now allows for an answer or direction to progress.

Thought process to take in defining the problem:
1) What is the problem?
2) When did it start?  Has it always been there and no one noticed, i.e. couldn't see it in the white part but can on the black.  After an hour of running, we notice the problem.
3) Was it at a lot change?  Do we actually document this?
4) Was it at a box or bag change in the same lot?
5) What is the material and are we adding anything to it? If so what and how much? Did we change one of the additive lots or percentage?
6)  Are we drying the material? How, how long, temperature, dryer conditions etc…
7) Is it in all cavities or specific to a few or one?
8) Is it consistent on every shot or varies shot to shot?
9) Does it occur only at specific times during the day?