Injection Molding and Process Validation Why, at Engel, the component sets the pace

Using the production of a multi-well plate as an example, Engel demonstrates how process validation in injection molding can be planned more effectively and completed more quickly. In the described use case, the effort required for qualification and validation decreased, while the cycle time was reduced. The key is an approach that starts with the functional requirements of the part and uses digital assistance systems to evaluate process stability and ensure critical settings are correct.

A multi-well plate is used, among other things, for cell culture. Its lid must allow for adequate gas exchange while minimizing evaporation as much as possible. At first glance, this may seem like a matter of application, but it has direct implications for manufacturing: the dimensions, flatness, and parallelism of the contact surfaces must be precise so that the plate and lid function together as intended.

This is where risk-based validation comes into play. Instead of considering all available machine parameters equally, the approach moves from the requirements for use, through the critical quality attributes of the component, to the process variables that influence these attributes. In technical terminology, this means: from the User Requirements Specification (URS) through Critical Quality Attributes (CQA) to Critical Process Parameters (CPP). Behind these abbreviations lies a simple question: What must be right in the end—and what factors in the process determine that?

When a requirement becomes an inspection characteristic

For the Multi Well Plate, tolerances of ±0.25 mm apply in both the X and Y directions, and ±0.15 mm in the Z direction. The contact surfaces are also inspected. Factors relevant to dimensional accuracy include holding pressure and internal mold pressure; uneven temperature control can cause warpage. Thus, the requirements for the interaction between the plate and the lid translate into a specific testing and monitoring task. Many factors can be measured—what matters most is what influences the function of the molded part.

Qualifying with a Clear Research Question

A targeted validation strategy can be derived from an understanding of the component requirements. Even during Design Qualification (DQ), simulations help to narrow down risks and potential process windows. In this early phase, it is still relatively easy to plan countermeasures—both for the hardware and the software. For example, the Engel iQ weight control system can be incorporated to compensate for material variations between batches during the process and to help ensure compliance with tight molded part tolerances. This can significantly increase process stability in production. However, it is crucial that this be taken into account from the very beginning.

Installation Qualification (IQ) verifies that the production cell is installed as intended and that its components are functioning properly. This includes documentation of sensor calibration and the cell’s operational capability. This documentation lays the foundation for reliably evaluating measurement data later on. The company can also provide ongoing support for such documentation through the everQ service. Operational Qualification (OQ) examines the limits within which the process meets the requirements; Performance Qualification (PQ) demonstrates reproducibility under intended production conditions.

Simulations help prepare experiments but do not replace testing on the actual component. Especially in the case of extensive test series, data analysis can save time and reduce scrap. For the multi-well plate, 60 settings were examined during the OQ as part of a Design of Experiments (DoE) . To ensure sampling is performed only after the process has stabilized, a standard wait time of 30 to 60 minutes is often observed following a process change—without considering whether the process has actually stabilized yet. This results in a waiting time of 30 to 60 hours per validation, which is often unnecessary. This is where the iQ process observer comes into play—it clearly displays measurement data and cell settings and assesses process stability. Instead of waiting for a fixed amount of time, samples can then be taken as soon as the process has stabilized. This allows the OQ to be significantly reduced.

How Driver Assistance Systems Keep the Process on Track

After qualification, the process must remain within the approved range during mass production. In this practical example, the multi-well plate is produced on a fully electric Engel e-motion 280 combi M. The Engel validation assistant links the component requirements with assistance and monitoring functions.

The mold breathing curve recorded using iQ clamp control can reveal changes in injection and holding pressure behavior. If necessary, mold sensors can provide additional data on internal pressure and temperature trends—though this requires a corresponding amount of effort.

Parameter limits allow critical settings—such as the after-pressure profile or cooling time—to be restricted to approved ranges, and changes to be secured on a role-based basis. This ensures that the process—systematically safeguarded by the CC300—always remains within the defined process window. The iQ Process Observer helps identify anomalies in the process data and narrow down their causes. The systems support process control and monitoring; however, product inspection, evaluation, and approval are still required.

The numbers apply here. The method goes further.

In the use case described, the time required for qualification and validation was reduced by approximately 30%. The cycle time dropped from an industry-standard benchmark of 16 seconds to about 11 seconds. The extent of the savings for a different product geometry must be assessed in detail—depending on the geometry, material, tool, initial process, and requirements.

The method is certainly transferable. Those who first understand the product’s function can specifically define quality characteristics, examine their influence on the process, and ensure the qualified range during operation. This knowledge also helps to systematically evaluate subsequent changes or a process transfer. More advanced concepts, such as approval based on process parameters, remain a future prospect that requires specific prerequisites and supporting documentation.

It all started with a multi-well plate and the question of what the finished component needed to be capable of. The result is a process tailored precisely to that purpose—sometimes thinking in reverse is the most direct path to validation. (sl)