Serially producing medical plastic components depends on two things: high-quality products that function safely and reliably according to the requirements of their medical application, and an efficient and cost-effective production method.
To facilitate more efficient production, RKT is breaking new ground in quality inspection and part approval in a customer project. We are establishing a largely automated approval procedure based solely on compliance with the specified parameters for the injection molding machine.
Our sophisticated digital documentation system ensures that previous testing processes, such as random sampling during production, are now a thing of the past. Manual testing is a considerable cost factor, as it ties up personnel in defined time windows.
First, the production facility, including all processes and equipment, undergoes extensive calibration and validation. During each injection molding cycle, all relevant parameters are recorded and compared against predefined tolerances. If the recorded data falls within these validated limits, it can be confidently assumed that the entire batch produced during this period is free from defects and can be released without individual part inspection.
The evaluation of the measurement data is fully automated; only the final review and approval of the batch parameters are performed manually by the staff.
Sufficiently large production volumes and long project runtimes are prerequisites for an efficient batch release process that recoups costs for investment in validation and digital documentation systems.
Key parameters that must be monitored and complied with during the injection molding process are:
Depending on the component, the tools must be cooled or tempered and operated at precise temperatures. The flow rate is an essential part of this process because it affects the mold’s heat balance. The component’s dimensions are determined by the mold’s temperature. Even the slightest impurity in the cooling channels of the cavities can affect component quality, as a blocked channel can cause temperature fluctuations. Therefore, temperatures must be monitored and kept constant. To ensure this validated status remains stable, the system components are recalibrated annually. This ensures the necessary comparability of the process, and therefore the parts produced, even years later.
As soon as the temperature or the flow rate deviate from the tolerance values, the corresponding shot is ejected directly. If subsequent faults occur or if a total number of faulty parts is exceeded, the machine stops and issues alarms or error messages so that the operator can search for the cause and rectify the problem.
Injection pressure and residual melt cushion are important indicators of an effective injection molding process. During machine validation, an internal pressure sensor is placed in a cavity of the mold to check the pressure curve when the melt is injected directly into the cavities at the point of injection. The residual melt cushion indicates the volume of plastic melt still present in the screw once the cavity has been filled. Smaller fluctuations in the residual melt cushion indicate more stable pressure conditions, and therefore better process quality.
All measurement data accompanying series production is recorded and transferred to a production data acquisition system and stored per batch. This means that the data remains available if, for example in the case of product recalls, it has to be proven years later which batch was manufactured at which time and with which parameters. After such a production batch is completed, the recorded measurement data is checked and evaluated by a quality manager and released to the customer with a certificate if all parameters are within tolerance. There is no longer any need for final measurement of manufactured parts.
The new release system was developed for a customer project. Thanks to its successful implementation, however, it is now being used for other projects and customers as well. State-of-the-art measurement and documentation technologies provide added value by enabling efficient, automated production processes that save time and money.
Stefan Preis
Head of Project Business
S.Preis@rkt.de
