All You Need to Know About Plastic Injection Molding Quality Control

Injection Molding Quality Control

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Imagine living in a world where we do not fear quality. What if we all had a fearless reaction to the phrase quality. Imagine what you can do if you took on your work with your perspective of quality.

We have different opinions of quality; to some, it is giving the best products and services. Others will argue that quality is resistance to compromise. In the end, we need to make quality our priority and part of our life. It is time we come to terms with the fact that the smallest actions can birth dire consequences. If we resist the urge to make compromises, success will become local. It is the small things we do that end up affecting us in the future.

Let’s shift our attention back to injection molding quality control. In the plastic industry, quality is undebatable. The automotive industry wants its parts to be precise and accurate. A good thing about injection molding is automation. Machines reduce the chances of errors that lead to poor quality parts. For the plastic industry, there are many methods of quality control. They all cover planning, design, development, assembly, production, and packaging.

Injection Molding Quality Control for Water

Before injection, your resin should have the correct amount of moisture. Molding with wet resins can affect the mechanical properties of the final component. Excess water may make your parts cloudy or even crack.

Some resins draw water from the atmosphere, meaning that you should store it well. Drying resins before molding has the following advantages.

  • Preventing Surface Problems
  • Preventing Hydrolysis
  • Preventing Part Failure

 So, what about injection molding quality control? What is its benefit? Why the emphasis? Stick around if you want answers to all these burning questions.

Importance of Injection molding quality control.

Enforcing quality control measures in an injection molding company will encourage quality consciousness. Workers will learn the importance of quality and incorporate it into their work. This will help you reach the desired level of quality.

Apart from making money, manufacturers are also looking for customer satisfaction. Customer will get satisfied with the quality which you achieve through quality control.

Injection molding quality control reduces the costs of production. The main aim of quality control is to reduce the instances of defects in products. Since all your products are fit for use, your cost of production will be lower.

Injection molding quality control will see to it that you utilize your resources. It will help reduce wastages and inefficiencies.

Good quality will sell out your business. Ensuring that you have quality control measures will increase your sales volume.

Injection molding quality control’s main aim is to prevent defects in parts. Even so, there is still a chance of some defects showing up. You should have measures set up to deal with them.

Plastic injection molding defects and how to fix them

Examples of injection molding defects:

Flow Lines

Sink Marks

Vacuum Voids

Surface Delamination

Weld Lines

Short Shots


Burn Marks


Sink marks

 Sink marks are the result of uneven cooling. When the inside cools slower than the outside layer, a small depression will occur at that point. A sink mark will show up as a small dimple on a part. It occurs if the inner core of a part made from molten material solidifies before the outer surface. For every problem, there exists a solution. How exactly do you deal with sink marks?  


You can opt to increase injection pressure, holding time, and finally reduce the speed. The efficiency will depend on the location of your gates in relation to the thicker walls. Make sure there is ample time to fill up the cavity before the gates close. Although these measures help reduce sink marks, they can induce stress on your parts. This can damage the structural integrity of your final products

Or, you can manipulate the temperatures since the marks come from uneven cooling. Altering the temperatures from the core to the cavity may pull the mark out. It is worth noting that you risk distortion if you are not keen on the temperatures.

Another way to deal with sink marks is by adding up to 0.5% of a blowing agent. The downside with blowing agents is lowering the mechanical strength of the end part.

  Flow lines

Flow lines are visible streaks or lines that appear on a plastic part. It is a result of the physical path and cooling of the resin during the injection. Flow lines are the results of changes in injection speed and wall thickness.  As the molten resin travels, the mold cavity uneven cooling causes physical paths.


To fix flow lines, you can increase the injection speed to an optimum level. Increasing the pressure and temperatures will ensure that the molten resin cools evenly.

You can also round corners in the mold cavity and where the wall thickness changes. In doing so, you will prevent a sudden change in the flow rate of the resin.


Flash appears like a thin lip of excess material on the edges of the parts. Excess flash can impact the final component’s functionality. The main cause of flash is low-quality molds or worn out molds. If the plates in your mold do not fit, they will allow the resin to flow out of the channel. Overheating and high pressure can force the molten resin into the mold plates.


It would help if you retooled your mold to ensure that the plates fit well. If the plates fit well, the probability of pressure leading to flash is low.

You can also increase the plate clamping force to keep the resin in the channel.

  Burn Marks

They appear like scorched sections on a part and result from hot compressed air trapped in the mold. Overheating the resin can also cause burn marks.


Lower the temperatures to an optimum level.

Reducing injection speed will reduce the chances of trapping air in the mold.

Enlarge your mold’s gas vents and gates

Shorten the molding cycle, so air does not overheat.

Emerging Trends in Injection molding Quality control

The joy of technology is new and better inventions. As we strive to make work easier, we should also look at quality assurance. So, what has technology given us in the injection molding quality control sector?

The IdentiPol QA2

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Lacerta Technologies are the minds behind the IdentiPol QA2. They started distributing the machine back in the year 2018. The IdentiPol QA2 allows for straightforward and efficient quality assurance tests. It has taken injection molding quality control to a whole new level.


  • Identifying common plastics
  • Measuring stiffness
  • Measuring polymer melting point

The IdentiPol QA2 is easy to operate and does not need any plastic knowledge. The machine works on a Fail and Pass basis. With the IdentiPol QA2, you will be comparing your resin with known good quality resin. It majors on strength and melting point.

The IdentiPol QA2 will ensure that your production line has quality and consistency.

The machine works with a 0-10 scale, making it easy to use for everyone.  It also bridges the gap between simple testing and complex lab analysis.

  Injection Molding Quality control and Artificial Intelligence


Some of our industries are heavily reliant on thermoplastic injection molding. A good example is a medical industry. -The syringes used for administering injections come from injection molding. During injection molding, you cannot afford to change the dimensions of such products. You may end up messing up dosages in hospitals. To achieve the desired quality, you need to set up stringent quality control systems.  The actual process is sophisticated, making it hard to take care of all changes in the cycle. To make it worse, most of these industries need mass volumes of parts and products. This means that consistency is paramount. Every single part in a batch should have the same dimensions. Incase warping occurs in some parts; you will have a lot of scrap and waste. A sink mark in a hospital syringes means that there is a volume change. We all know how delicate the medical sector is. So, what have we done with technology to ensure quality and consistency? Two letters, AI or rather two words Artificial Intelligence. This is where it all goes down.

You can split the control process into three nested loops. The first one, control of machine parameters, is the most developed. At this juncture, you are dealing with variables like speed, temperature, and pressure. The second loop, process control, has a lot of research going on. It deals with variables like in-mold temperature and pressure. The last one, setpoint control, is the least developed. Research and minor advancements have only started in the last decade. It deals with part quality feedback.

For all three loops to work well, you need complex and reliable quality control systems. We need to work more on this, and a viable add-on is AI.  With the integration of AI and quality control systems, we can achieve consistency. A control system with AI can make adjustments to the cycle on its own. A neural network is a good example of AI.

Post-processing for better surface finishing and quality

Some post-processing activities aim at improving the quality of parts. When some parts come out of molds, they need trimming and shaving. Most of these processes make surface finishing better.  We also have heat treatment, which reduces stress caused by rapid heating and cooling. Uneven cooling can also induce stress, so heat treatment is key to quality control.

A worthy manufacturer in the plastic industry should have the following traits:

Certification. Any manufacturer should provide you with their certifications.

Working with a wide range of products. If a manufacturer is working with a wide array of industries, they must have the best control systems. For them, maintaining consistency and quality may not be a problem.

Work with high precision sectors. If a manufacturer is working with industries that need high precision, try them. They must have some good quality control measures set up.  Look at the feedback from the manufacturer’s customers.

Shops that offer onsite tool designing and repair are an advantage. You can change your mold design fast according to your customer needs.

Industries that rely on injection molding need quality parts and components. To achieve the desired quality, you need to have top-notch quality control systems. Quality control focuses on variables like injection speed, temperature, and pressure.  There are consequences of molding with a wet resin. It would help if you did thorough testing on your resins before injection molding.

Thermoplastic testing is now easier with gadgets such as the IdentiPol QA2. It is easy to use since it grades you resin on a fail and pass basis. It is useful where mass production of the same parts to ensure consistency. It will only get better with Artificial intelligence. Or will Artificial intelligence will take over the world as we see in the movies?                                                                                                                             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