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In my opinion it is better to have invested in whatever it takes to get your testing tools performing correctly and let the supplier base know that you have the tool and know how to use it correctly. Melt flow index results are not the end all or the be all, but they are a significant indicator that something is not right in the reacting/extruding/pelletizing process, or in the material handling/molding process.

The alternative is to fly mostly blind and react only after a problem develops that could be extremely expensive. I don't know if you have dealt with the automotive industry or not, but if they get a chance to hang all their warranty costs on you, especially if you send them 100,000 defective (5, PPM or more) moldings they will not hesitate to charge you for their full warranty costs, and the costs to keep their assembly lines running during transition to good product. This could, depending upon the situation, bankrupt your company.
The old school understandings around processing are pretty much proven the wrong way to work and knowledge more than 10 or 15 years old is way out of date, get current. There is much written about and many good trainers who can help bring your processing ability to state of the art. I recommend this as I continue to find that too little of good engineering practice is being used to the detriment of everyone involved. Strong and robust methods will bring rewards ten-fold back not to mention a bit of excitement at how the trade is changing.

It's about the plastic not the machine, the true melt temperature is the 30-30 check. The best way to check it is to check the melt after the machine runs a few cycles. This way you get a true melt from the screw running under a full load. If you do it on a purge shot you may not read the true melt. You can also sensor the injection mold with temperature sensors to read the melt of the plastic when it enters the mold cavity. I have found this to be very helpful also. This will show you the shear heat from the barrel into the injection mold as it goes through whatever runner system the mold is equipped with.
I have found that the injection molding process monitoring systems are often taken off of machines and packed into boxes to collect dust.

This even after they have been successful in optimizing a process and served to create 100% bad part containment. It is obvious that many who find success with this technology fail to understand that it is only a "tool" that requires continued training to live beyond one problem mold or project. I know of other molders who literally have e-Darts on every machine in their plant and claim to save hundreds of thousands of dollars every year in gained efficiency.

It is interesting (and sometimes frustrating) to see injection molding companies purchase half-a-million dollar machines, but refuse to invest less than twenty thousand dollars to optimize the process that is paying for the machine and justifying its existence. I truly believe that this scientific approach to injection molding is the only right way to mold. Yet I am surprised at how many molders reject the technology. My intent in starting this conversation is to get a better idea of why some companies fail and others succeed in utilizing this technology.
If you are going to implement proper process control, buying and installing the equipment is just the start. The challenge is this: You must have personnel who know what they are looking at. Unfortunately, there are not a lot of qualified people out there. Secondly, you need to develop the means to correlate the data from the monitoring system to the data your end customer cares about.

Process monitoring is not a silver bullet. If it is to pay off, it requires process discipline and a systematic approach. I have used several of the systems mentioned above and some that were designed for specific applications. If there was process discipline and a systematic approach to interpreting and acting on the data, the payback was quick and dramatic. If those elements did not exist, the project was looked on as a waste of time and money.
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).
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.
The propositions behind injection molding process simulation are very basic. First, that although our plastic materials and processes are very complex they are not special. They obey the same laws of physics as everything else and that means that prediction is possible. Plastic Injection Molding Process

Second, that expert calculation is better than expert estimate. If plastic injection molding had been simple, we would all have been calculating the process since plastic injection molding began. But it was too complex for pencil and paper, slide rule and log table so it had to wait for affordable computing to come along. That is the sole reason why injection molding process simulation by computer seems controversial while rule-of-thumb calculations for locking force seem natural.

Third, that because the materials, processes and geometries are so complex, the computer model must be imperfect but this does not mean it is useless. A law of diminishing returns ensures that beyond an economic point, further gains in model accuracy bring only slight improvements in results. The threshold moves as calculation techniques develop and the cost of computing power drops but the principle remains. Current simulation models are probably close to being as good as they need to be. With them, a plastic injection molding expert can get closer to right-first-time than without them and that's where the benefit lies. Incidentally, when we use a rule of thumb, we are using a very simplified process model. It is a lot further from reality than any computer simulation out there.
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Plastic Injection Molding Process ... Plastic Injection Molding Process SimulationThe propositions behind injection molding process simulation are very basic. First, that although our plastic materials and ...