Inline process monitoring with piezoelectric sensors

Manufacturers need to address short-term measures to move forward with rapid, effective responses to changes in overall conditions and production chains. They also need to take strategic action to adapt to new challenges such as increasing requirements for production performance and product quality. Many manufacturers of disposable medical products, small devices, and plastic components depend on the injection molding process to achieve these goals. They should, as cavity pressure, or mold cavity pressure, is the most informative process variable. It allows total process transparency, enabling users to attain zero-defect production.

Cavity pressure provides a complete picture of the conditions under which a part is produced throughout the injection molding process and is an indicator of the quality of the part being produced. Quality-related characteristics such as dimensional accuracy, surface, weight, and degree of molding can be attributed to the cavity pressure profile during the injection, compression, and holding phases. The cavity pressure profile is the basis for precise statements about optimal process parameters throughout the entire production process. Good parts can already be distinguished from bad ones while production is still in progress.

Meeting demanding requirements

Sensors measuring cavity pressure must be dependable, accurate, and robust. Determining pressure and temperature requires reliable measuring technology with high resolution and no maintenance. Measuring chains must cover a melt temperature range up to 450°C and need to capture and resolve the smallest pressure fluctuations, even under pressure conditions of 2,000 bar. To meet these requirements, Kistler deploys piezoelectric sensors that are partially manufactured from special materials. Alongside the physical measurement principle, location is also a decisive factor, especially for process reliability. Kistler offers an extensive and varied portfolio of sensors to match every part geometry, installation position, injection molding process, and plastic material. The portfolio also encompasses direct and indirect measuring sensors, with diameters ranging from 1mm to 9mm, and sensors allowing the combined measurement of pressure and temperature. A third method besides direct and indirect measurement is contact-free measurement, where measuring pins capture the mold compression caused by the pressure. This portfolio brings benefits for users, such as having an alternative when lack of space in the mold makes direct measurement impossible or when the parts must be completely free of visible marks.

Intelligent process monitoring

Process monitoring systems independent of the machine control that are integrated into the production sequence allow optimal use of the information captured by piezoelectric sensors. This approach delivers a reliable, stable process combined with maximum transparency of the fundamental steps in the process. Suitable systems – such as ComoNeo – can track the progression of cavity pressure in real time. ComoNeo can also use adjustable evaluation objects (EOs) to assess part quality while the cycle is still running, giving users 100% in-process prediction of all quality features. As opposed to machine-integrated solutions, external process monitors can store complete curve profiles for the entire injection molding facility in one database. This way, manufacturers can compare past production runs with the target curve at any time, and the validated process profile can be proven in case of a complaint.

One-stop solutions for medtech manufacturers

Alongside its process monitoring solutions for injection molding, Kistler offers a range of additional sensing and process monitoring solutions, including maXYmos systems for joining and assembly processes as well as testing manufactured parts. These solutions are based on acquisition and analysis of physical variables such as pressure, force, and torque. Integrating the maXYmos system into assembly processes makes process monitoring 100% transparent and reliable, so medtech device manufacturers can boost production efficiency from component design and part assembly through to final product testing. Medtech manufacturers can benefit from the maXYmos TL ML process monitoring system, the first monitoring system for assembly and joining processes that are FDA and EU MDR compliant.

Kistler Instrument Corp.
https://www.kistler.com