There are certain issues no one wants to see when dealing with injection molded products, and one broad category here is a defect of some kind in the final part. Many plastic parts don’t ever make it all the way to market with their originally-intended properties, and defects are one of the largest reasons why – but are these sorts of defects an unavoidable part of the injection molding industry, or issues you can avoid with the right preparation?
At EnviroTech Custom Injection Molders, we’re here to tell you that in the vast majority of cases, the answer falls into the latter category. While certain material or machinery issues may cause extremely rare defects in certain parts, the far more common culprit in part defects is operators or molders who were not taking the proper approach to the job. Our custom injection molding services, which range from bulk molding to slab stock molding, machining, testing and numerous other areas, are carried out exclusively by the best professionals in the business, with years of experience avoiding the risks that lead to part defects – in fact, we even take on business from clients who are sick of finding defects in parts from lower-quality manufacturers.
What are the common causes of defects in injection molded parts, what are some of the most frequent defects that may be seen, and how will working with our team minimize or eliminate these risks entirely? Here’s a primer.
Operators, Not Equipment
We want to really drive this point home: The vast majority of injection molding part defects are created not by problems with the machinery or materials used, but by the operator(s) of said machinery. The most common error here is a lack of understanding of how a given finished part will tolerate its intended environment – an issue that, sadly, traces back to poor training.
Any professional plastic injection molder has to be well aware of the way part properties will be impacted, both during the molding process and after it. This is part of what makes it so important to work with quality pros who have experience avoiding part defects.
Our next few sections will go over some of the most common defects you’ll see if you don’t take these steps.
Cavity Pressure
Within a given plastic injection molding part, cavity pressure and part dimension are directly linked. The less variation in cavity pressure, the tighter the dimensional control or variation – and this means that the higher cavity pressure gets, the less the part will shrink (if all other factors are equal).
However, a common error here among inexperienced plastic injection molders is “experimentation” with machine settings to determine gate freezing timing. This approach often creates a defect in parts due to the fact that other processes in manufacturing will interfere with the finished part – in ways the molder isn’t able to see, as well. This means that the issue won’t even be discovered until the part is being used by the client and breaks or wears down far too quickly, costing both them and the manufacturer time and money.
Injection Rate
Another important factor in any plastic injection mold is the injection rate, which has an impact on several other elements like cooling rate, cavity pressure, melt temperature and the amount of stress the plastic can withstand before cracking or warping.
Once again, the primary issue here for inexperienced molders is experimentation. Trial and error may work in some fields, but it’s not meant for injection molding at all – “learning on the fly” isn’t something that can be done in this industry. While the technical details of injection-related defects are a bit too complex for this blog, the theme is apparent.
Cooling Rate
Cooling rate is often considered alongside injection rate, and has many of the same impacts. Once again, any injection molder who doesn’t know the precise cooling rate needs for a given part – or who wants to “try a few things” with this metric – should not be utilized, and should be cast aside in favor of a molder who knows how to approach these elements properly.
Melt Temperature Problems
Finally, another common processing defect in plastic injection molding comes due to improper melt temperatures for the mold – and this is one of the defect types that most commonly signals a poor molder (all the issues we’ve gone over in this blog signal this, but this one especially). This is because most material suppliers for plastic injection molding materials offer a relatively wide range of acceptable melt temperatures suggested – meaning a molder just has to fall somewhere within that range, not even at a precise number.
If they aren’t able to do so, this is a big red flag that can lead to several different part defects, including some that won’t be noticed until the part is being used by a client. In addition, molders should know how to purge resin out of the nozzle for injection to create a smooth injection process; failure to do so could lead to rough part edges or even defects in some cases.
Working With Quality Injection Molders
If the above information convinces you of anything, it should be the massive value of working with experienced, quality plastic injection molders. Our team is well aware of all the potential defects we just went over, plus several other less common ones, and knows exactly how to avoid them through proper injection molding approaches. Contact us for examples of our prior work or further info on how we prevent defects in your final parts.
For more on this, or to learn about any of our custom molding services, speak to the staff at EnviroTech Custom Injection Molders today.
