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Trouble Shooting The Plastic Injection Molding Process | Injection Process Troubleshooting BasicsCustom Plastic Injection Molding - Trouble Shooting Your Injection Molding Process - Now that we have established our basic injection molding process, we can look at a number of the obstacles that plague all of us in the injection molding industry and that the "battle of the defects". This is a fact of life in any injection molding process, and no matter how well we might have our process established, optimized, and refined, we will always be at the mercy of certain process variables that are not within our control.
By now, if you have been reading the previous articles I've written, you realize that there hundreds of injection molding machine settings and variables in an injection molding process, that it becomes a statistical improbability that your process will not experience issues with many of these over it's lifetime in the average production setting. First let's define' what the "process" is because I know when I am teaching newly graduated college students and process staff that are relative newcomers to the injection process arena, that the conception of the injection molding process is the machine and the mold. While these are obviously critical to any injection molding process, they are yet only a portion of it. Let break it down a little bit.
If you are familiar with some of the brainstorming techniques used in problem solving, one of them should be the use of what commonly is referred to as an Ishikawa or "cause and effect a.k.a. fish bone diagram" because of what it looks like on paper. I'm not going to explain the use of this tool in this section but just show it's basic elements to give you an example of how the injection process interacts. The "four M's" of the basic diagram are method, machine, man, & materials. Sometimes "measurement, mother nature, and or management" are also added to these diagrams for troubleshooting purposes.
So, why did I just waste a paragraph on that explanation? Because the injection molding process is a very dynamic and interactive process by nature, and that is a fact that must always be kept in mind when troubleshooting your injection molding processes. If you lose sight of this when you are trying to problem solve an issue you are having, you could quickly becomes lost in your troubleshooting and end up putting a band aide on your process instead of really solving the root of your issue to be able to say that you have implemented a permanent corrective action. You need to understand the entire interaction component of the injection process, so that you find the true "root cause" of your problem and correct that and not just correcting the symptoms of the problem as many will do. Knob turners (process troubleshooters that stab in the dark until they get lucky and never know why) are a dime a dozen in the processing world, but the true process troubleshooters are those who take the time to learn the injection molding process at a whole different level. This doesn't mean your need to understand polymer chemistry (although there are times it doesn't hurt) to be a good process problem solver, but it does mean taking the time to learn and gaining the experience to do it properly.
We will classify the defects with our injection molded parts into two main categories for the purposes of this article and they will be "surface, visual, or cosmetic" and "dimensional or functional". The surface defects are exactly what they sound like, and that is defects that can be "seen" such as knit or weld lines, blush, splay, and sinks, just to name a few. The dimensional or functional defects are a little more difficult to detect, as you most often "can’t see them" and they will require a mating part or a gauge of some type to take measurements, which can be compared against an established standard. This can be as basic as a using calipers, gage pins, or micrometers, all the way to specially designed gauges and check fixtures that are made for one specific part. In the next section will begin to break down the various defects, determining their possible causes and some possible ways of correcting them.
Written by: WM8C, August 25th, 2006. Not for use without written permission
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