Inline quality control in plastic injection molding

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Infrared cameras with six different views can help injection molding manufacturers find defects in the production line.

Bestech speaks with Manufacturers’ Monthly about providing reliable sensor monitoring systems for plastic injection molding 

The trend in industrial manufacturing demand is forecasted to increase for the foreseeable future. Technological advancement will bring better automation and there will be an increased focus into sustainability and waste handling. 

Injection molding manufacturers offers large-scale production capacity with low waste generation. It has been extensively applied in the medical manufacturing industry. As the world battles to come out of the current pandemic, manufacturing of parts or components in medical devices is expected to increase in demand, prompting the need to ensure for a more efficient and streamlined production technique with 100 per cent of quality control.  

Modern injection molding systems are generally equipped with an automatic handling system for removal and storage of components. During automatic removal of the components, a decision on a “good/bad” component must be made within a short time frame. The purpose is to ensure that corrective measures can be performed immediately to prevent further product wastage. 

Most quality control system relies on batch or periodical testing, as the cost of performing 100 per cent checking are argued to outweigh its benefit. However, with the vast range of sensors currently available in the market, it is possible to design a system that can perform inline monitoring close to 100 per cent checking.   

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Industrial thermal imaging cameras and inline colour measurement sensors can be used at the same time to improve quality during production for injection molding.

Such a system can be developed through combination of different sensors and inspection techniques to enable easy and flawless monitoring. From Bestech’s partnership with global sensor company, MicroEpsilon, the business has the capability to design and supply the afore-mentioned QA system for the injection molding and many other manufacturing industries.  

For the solution, the industrial thermal imaging camera and inline colour measurement sensor are combined to simultaneously measure and inspect the molding quality during production. The sensors and components are positioned in such a way to enable comparison between thermographic images from one video to another. This enables a direct comparison of the measured colour values to a normalised standard. 

Defect detection in injection molding 

The infrared camera has been consistently deployed in the production line for quality control and monitoring. They can capture the thermal profile of a component with up to six different views to allow the users to visually examine them. The data provides a global quality statement about incorrect temperature control of the workpiece, tools malfunction, visible geometry errors and hidden defects. The system can also be easily initiated and operated which minimises start-up rejects following periods of downtime or tool replacements. 

The test results are interpreted based on the difference between the reference image and the image taken at the real time. The identified temperature difference provides the basis for a good/bad decision. This can be freely specified in the software settings. Based on these results, defective components can be removed from the production line without having to stop the production. 

Furthermore, the system also has the capability to store the limit values for different components in the database which can be easily accessed and retrieved. It may produce a warning signal to the operator when extreme differences in results have occurred, which will prompt machine shutdown and production stop before further losses occur. This configuration offers a 100 per cent traceability of data that are integral for continuous improvement in manufacturing. 

Inline colour measurement for enhanced reliability 

For components that pass the thermal imaging test, its colour will then be inspected with the inline colour sensor. In plastic processing, the random fluctuations in temperature, also known as “thermochromism”, cause changes in colour. This problem is even more pronounced for red dyes due to difficulties in differentiating variation in colour shades. A slight error in expected molding temperature may result in colour deviation of more than 2ΔE. The reference data was stored in the system and error limits can be set to distinguish between good/bad products. 

By firstly measuring the temperature profile, followed up by direct measurement of colour values, this system manages to achieve 100 per cent inline quality testing with good reliability and less time-consuming. Both sensors can be directly installed in the production line thus minimising the need for retrofit and process modification. The sensors are also able to deliver fast response to avoid high rejection rates in case of production errors. Customised, engineered solutions for special applications are also possible with minimum costs. 

There are a wide range of colour measurement sensors for accurate measurement on different type of surfaces. Bestech supplies high precision inline colour sensor that can be readily used and integrated for industrial applications.  

The circular sensor is the most suitable for measurement on the highly reflective, shiny and metallic surfaces. It has 24 lighting optics that are arranged in a circular fashion around the receiving optics to provide continuous lighting which produces stable measurement regardless of the objects position. The standard sensor head with integrated transmitter and receiver can be used for measurement on matt and fine-structured materials. For inline applications, the ACS7000 colour sensor offers a separated transmitter and receiver unit for measurements of self-luminous and transparent objects, such as film, glass or Plexiglas. 

The applications of precision sensors and measurement technology is crucial to advance industrial manufacturing capability. Bestech Australia draws its expertise in industrial test and measurement with a wide range of sensors, instrumentation and data acquisition. They pride themselves in not only supplying technology, but also assisting the end-users with full local technical support, from design, testing, commissioning and after-sales support.  

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