Stephen Sanderson, group inspection product manager and Guven Turemen, group metrology product manager, both from manufacturer Vision Engineering, discusses how manufacturers can ensure the quality of plastic components.
Whether you are manufacturing parts for use in class III medical devices or class II products - such as syringes or catheters, it is necessary to have a quality management process in place to ensure your products meet industry standards, customer specifications, and your own quality benchmarks.
A quality control process must be reliable and easily documentable to provide proof of compliance. The detail of the quality management system will be dictated by the customer’s product specification which, in turn, will guide the choice of inspection and measurement systems used within the quality infrastructure.
Visual inspection
Visual inspection checks are undertaken to ensure parts meet specific requirements in terms of colour and surface finish. It also makes sure that there are no residual material fragments left over from the manufacturing process.
In many instances, due to the size of the components, a microscope will be required to conduct the inspection.
Visual inspection checks alone are not always sufficient to assess product compliance. In instances where there are tight-tolerance standards, a series of measurements may be included in the quality management process.
Measuring components
There are varying degrees of accuracy when it comes to measuring components; from basic comparison against a reticule to measuring distance in terms of micrometres.
When creating the protocol for a quality management system, the degree of accuracy will need to be taken into consideration.
Quality managers will also need to review the measurement range which will dictate whether a two or three axis measurement system should be used.
High value, safety critical devices will often be made up on a number of components, all of which will need to be measured for compliance.
These criteria need to be considered carefully when planning an efficient quality control procedure.
An instant Field of View (FOV) measuring system can be used in cases where 2D measurements are acceptable. In addition, multiple small components can be placed within the FOV and accurately measured within moments; ideal for small medical devices.
The use of a telecentric lens will further improve accuracy through the elimination of any distortion in the FOV due to curvature of the lens.
The need to measure a variety of components can make the process more complicated. To maintain accuracy and efficiency a variety of measurement types may need to be incorporated into the quality protocol.
The solution may be to combine an optical measurement system with a video measuring system.
Video measurement offers speed of measurement, making it ideal for components where edges are clearly visible. Where parts are more complex or have difficult to view features, the intricacies are better seen with the aid of an optical system. This is particularly useful in cases where the plastic is black or transparent.
This ability to switch seamlessly from a video to an optical view maintains accuracy whilst offering time saving benefits.
Measurement procedures for complex parts may also require measurements in three axes or measurement of 3D forms, where a mixture of non-contact and contact (touch-probe) measurement methods can be combined.
With such a system, features that can be displayed clearly via the digital camera are measured using the non-contact method and others with poor edge definition or concealed features can be measured with a touch-probe.
Switching between probe and non-contact measurement will reduce measurement time, maintaining accuracy without compromising speed of checks. Inclusion of a motorised zoom lens further optimises the process offering the ability to incorporate magnification changes into the assessment process.
Selecting the appropriate equipment
A successful quality control process is reliant on utilising the appropriate equipment to ensure not only accuracy but efficiency. That said, the variety of available systems, together with keeping up to date with the latest inspection and metrology technology, can be daunting.
The simplest way to select the best system for your business is to share your requirements with the experts. They will then be able to advise you, and tailor the inspection and measurement system in order to deliver the ideal solution for you.