INDUSTRY FOCUS Medical Equipment
Value chain transparency
Manufacturers of medtech devices can now boost production efficiency from component design and part assembly through to final product testing, writes Suzanne Graeser Bieri, Head of Marketing, Kistler Group
I
n these challenging times, besides short-term measures, manufacturers 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. And, rightly so: cavity pressure, or mold cavity pressure, is the most informative process variable. It opens up the possibility of 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, in eff ect being 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 profi le during the injection, compression and holding phases. Thus, the cavity pressure profi le 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.
A varied range of sensors The sensors used to measure cavity pressure have to be dependable, accurate and robust. Measurement of pressure and temperature calls for reliable measuring technology with high resolution and no need for maintenance. Measuring chains must cover a melt temperature range of up to 450°C, and must capture and resolve
the smallest pressure fl uctuations, even under pressure conditions of 2,000 bar. To meet these requirements, Kistler uses 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 off ers an extensive and varied portfolio of sensors to match every part geometry, installation position, injection- molding process and plastic material. Also, the portfolio 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. The extensive portfolio brings substantial benefi ts for users – for instance, 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 that are independent of the machine control and are integrated into the production sequence allow optimal use of the information captured by piezoelectric sensors. This approach guarantees a reliable and stable process combined with maximum transparency regarding the fundamental steps in the process. Suitable systems – such as ComoNeo from Kistler – can track the progression of cavity pressure in real time. ComoNeo can also use adjustable evaluation objects (EOs)
The piezoelectric eff ect
• The piezoelectric effect refers to the property of certain crystals to emit a proportional electrical charge when a mechanical load is applied to them.
• The directional deformation of the piezoelectric measuring element creates an electrical charge proportional to the exerted pressure. The charge signal is converted into electrical voltage with the help of a charge amplifier.
• Piezo sensors are ideal when extreme requirements need to be met – especially as regards miniaturisation, temperature and dynamics.
• Walter P. Kistler patented the charge amplifier for piezoelectric signals in 1950 30 March 2021 | Automation
Kistler’s UNISENS 6183D miniature cavity pressure sensor
to assess a part’s quality while the cycle is still running. This gives users 100% in- process prediction of all quality features. As opposed to machine-integrated solutions, external process monitors make it possible to store complete curve profi les for the entire injection-molding facility in one database. In this way, manufacturers can compare past production runs with the target curve at any time, and the validated process profi le can be proven in case of a complaint.
One-stop solutions for medtech Alongside its process-monitoring solutions for injection molding, Kistler off ers a range of additional sensing and process-monitoring solutions, including maXYmos systems for joining and assembly processes, as well as testing of 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 manufacturers of medtech devices can boost production effi ciency from component design and part assembly through to fi nal product testing. And now, medtech manufacturers can benefi t from a special advantage: the maXYmos TL ML process monitoring system launched in 2020 is the fi rst-ever monitoring system for assembly and joining processes that is FDA- and MDR-compliant.
CONTACT:
Kistler
www.kistler.com
automationmagazine.co.uk
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