Injection Molding Quality Control: Advanced Inspection Techniques

on variousToday’s injection molding quality control processes require that the critical stage of mold manufacturing and products fabricated with them undergo advanced inspection techniques. Components made via injection molding increasingly depend upon various types of measurement technologies that help manufacturers inspect and test molds and molded parts for imperfections or weaknesses. The measuring tools used in these processes range from handheld probes and gauges to integrated, automated systems.

The earlier defects are identified, the less expensive remediation will be, while resolving issues before they become real problems also lowers the overall cost of production. To keep competitive, manufacturers must use the most accurate techniques to maintain superior injection molding quality. Controlling measurements for parts and molds via these new methods involves keeping abreast of the cutting-edge injection molding technologies that will continue to play an essential role in shaping the world well into the future. 

Importance of Injection Molding Quality Control 

These days, injection molding quality control has become more automated and digital, consisting of anything from 3D scanners that calculate a part’s geometry to electronic transducers that use ultrasound to identify defects in denser and heavier components. However, quality control in injection molding is still primarily about ensuring that a product’s various parts fit together to function as designed. Quality control measures ensure that molded components are safe and work as they should.

With plastic injection molding, quality control helps identify mistakes like: 

• Absent or askew holes
• Cavities that are unfilled or only partially filled
• Geometrical measurements that are off from the original designs
• Incongruity in colors and textures

Injection molds must be assembled appropriately to prevent warping, leaks, or other flaws that keep components from aligning precisely and otherwise affecting component quality. After the mold, the raw materials also need to meet specific standards, which is the first point in the production process where quality is addressed in injection molding. Quality control also confirms that the machines have the proper pressure, temperature, and other settings to ensure flawless fabrication processes.

The steps involving the material and machines ensure the resins are suitably liquefied before entering the machine, keeping issues like air bubbles or poor surface finishes from becoming real problems. Quality checks also look for any contaminants within the molten plastic that could cause problems. The final stage of injection molding quality control is often referred to as first article inspection (FAI), which confirms that molded parts have the correct geometries, measurements, strength, tolerances, weights, and other specifications. This is normally the final step in part manufacturing before shipment to the customer.

New Technologies & Techniques for Injection Molding Quality Control 

As technology has advanced other part manufacturing methods, so has it transformed the injection molding process. Quality control methods today have advanced considerably from the past, where visual inspections using manual measuring tools were once the norm. Technology has made injection molding more precise for fabricating parts, which extends to quality control. Since the turn of the century, injection molding quality control has become increasingly refined, embracing new technologies and integrating various systems for real-time monitoring and more accurate measuring methods.

A key technological aspect that’s transforming the sector is the use of automation in injection molding. Quality control in modern parts production can even involve robots that remove and inspect components without direct human intervention. Like other injection molding processes, quality control technologies that aid inspection ensure consistency and precision, while significantly reducing the chance of producing defective parts. These key techniques and technologies include 3D inspection and scanning, coordinate measuring machines, CT scanning, simulation technologies like digital twins, IR thermography, in-process monitoring with sensors, machine vision, statistical process control, and ultrasonic inspections. 

3D Inspection & Scanning 

Using either structured light or lasers, 3D scanners can create exact models of molded components, which in turn allow comparisons with CAD designs to help ensure better dimensional accuracy. Additionally, 3D scanning inspections can identify shrinkage, warping, and other defects. Working on measurements along the X, Y, and Z axes of a component, this technique helps calculate surface measurements and internal geometries more easily.

A 3D scan captures data on a component’s shape and texture, creating images that can be used by manufacturing software for various purposes beyond quality control. This can include comparing CAD or other virtual models, digitizing part geometries, fabricating prototypes, and even reverse engineering components. For a production that involves injection molding, quality control methods that use 3D scanning provide a convenient way to measure complex structures in parts, a task for which conventional measuring tools often struggle.

Coordinate Measuring Machines

A coordinate measuring machine (CMM) precisely measures a part’s geometry by detecting variations in dimensions and probing underneath the surface to ensure the component meets specifications. One primary element of a CMM consists of a platform on which a component is supported in a stable position to provide accurate measurements. A probe touches points across the X, Y, and Z axes, sending signals to a computer that then translates them into exact measurements of the part.

The five primary elements of a modern CMM are: 

• Connected computer for running metrology software
• Controller
• The machine’s platform and other structural elements
• Probe
• Stylus

A scanning probe can compare the finished part to 3D designs by generating a point cloud to check its accuracy.  

Computed Tomography Scanning 

Computed tomography (CT) scanning provides high-resolution images of a component’s external and internal structures. This process aids in the detection of inconsistencies in the material, like cracks or internal spaces, permitting non-destructive inspection of complex parts with multiple mechanisms. Using X-rays, it creates cross-sectional imagery of a component that can then be digitally assembled into a 3D model.

CT scanning can be used for: 

• Accurate assembly
• Analyzing breakdowns
• Comparing parts to CAD models
• Detecting internal voids or porosity
• Identifying defects

CT scanning works especially well for the detection of internal defects.

Digital Twin Software

Digital twin technology has been used to create virtual models for various industries, including injection molding. Quality control processes within the sector can also benefit from simulation software, which can be used to predict defects like sink marks or warping. By determining and correcting problems in the design stage, fewer defective parts will be produced. Such digital simulations have become increasingly common in manufacturing since the turn of the 21^st century, though their use in injection molding quality control is more recent.

Solutions involving digital twins require a significant amount of data, however, so combining this technology with a means to quickly and reliably gather accurate data is important. For example, digital twin technology is often used with 3D scanners. These machines can capture data without making contact with the part, creating a digital blueprint in three component dimensions. However, not every 3D scanner is suitable for making digital twins.

In injection molding, quality control benefits from simulations of various processes, allowing a better understanding of how components fit in real-world situations. Verifying how parts fit together virtually saves both time and money. It’s also better to use data from scanning an actual component than the virtual computer-aided design, which only provides minimal data regarding the actual physical parts.

Infrared Thermography 

With infrared (IR) thermography, it’s possible to capture temperature profiles of components when they come out of the mold or even during the molding process. This helps manufacturers detect inconsistent flow or uneven cooling of material and identify any points of internal stress. Using IR sensors in injection molding, quality control processes can determine temperature by taking readings from the radiant energy emitted by material in a mold.

These IR sensors are neither affected by heat convection nor heat conduction, able to measure temperature quickly and accurately even when the resin within the mold contracts away from the tip of the sensor. IR thermography allows accurate measurements of material during each stage of injection molding. Quality control can thus monitor the entire production process as the mold is filled, held, cooled, and opened to reveal a finished component. However, there are complications with this technique, which depend upon the material’s absorbance of radiant energy, for which a weighted average is often used to accommodate the material’s thickness.

In-Process Monitoring Sensors 

In conjunction with integrated software, in-process monitoring sensors track flow, pressure, temperature, and other parameters during the various injection molding processes. Monitoring molding machines in real time can more easily resolve quality control issues, prevent imperfections, and ensure consistency throughout the process.

Pressure sensors monitor the mold cavity’s holding and injection pressures to ensure it fills and packs as it should. This inhibits sink marks, short shots, and other defects from forming. The temperatures of the cooling, melting, and molding channels are tracked to keep temperatures optimal, which is imperative when fabricating components. With continuous tracking of these parameters throughout the molding process, any issues can be dealt with immediately.

Integrated Machine Vision 

Another real-time system advantageous for injection molding quality control is machine vision. By integrating software with machine vision cameras, aesthetic imperfections, dimensional divergences, and surface flaws can be identified. Additionally, by integrating machine vision with robotic systems, production lines can continuously monitor molding machines as they remove parts from them.

These systems differ in complexity, but many can view parts to show color contrasts to examine design features or present multiple views to provide more in-depth inspection. Machine vision systems are often mounted within the robot, triggering the camera once it reaches a certain position. The machine vision camera processes images and deploys the necessary inspection tools, with the robot acting automatically to separate out flawed components.

Statistical Process Control 

The use of statistical process control (SPC) involves applying statistical methods to the production process and using software to recognize trends and dissimilarities that may cause defects in components. Based on data gathered in real-time from sensors and other devices, SPC tools allow the detection of defects while enabling remedial actions to be implemented immediately to ensure quality further. These statistics are found in control charts that track essential factors like cycle times, pressure, and temperatures.

Ultrasonic Inspection 

Able to detect cracks, voids, and other defects beneath the surface of molded parts, ultrasonic inspection techniques work well for denser and thicker materials. Using an electrically powered transducer to assess how high-frequency soundwaves react to a part’s material, this device notes changes within the material. The ultrasonic inspection process involves placing the plastic part or material in a medium, such as water, into which the transducer emits sound waves. The transducer analyzes the sound waves as they rebound back from the material.   

Ultrasonic inspection can be used to:

• Distinguish defects on and below the surface.
• Provide comprehensive information on defects’ location, shape, and size.
• Test a wide array of materials.

As a nondestructive quality control method, the assessed material is neither damaged nor altered during testing. The soundwaves that pass through the material can provide particularly valuable data on its internal structure.

To learn more about the latest injection molding quality control technologies and techniques, contact the injection molding experts at Spaulding Composites Inc. today.