Glue and Sealant Presence Inspection

The visibility of transparent adhesive depends on reflection conditions, and special illumination (low-angle side light, polarization, dark field) is usually needed to make the adhesive outline stand out. Whether it can be imaged consistently must be validated on the actual workpiece and adhesive type, and differences between adhesive batches must also be checked.

The minimum detectable break size depends on the imaging resolution and the contrast between adhesive and background, and must be calibrated with actual workpieces; a single figure cannot be promised in advance. The usual practice is to first verify detection capability with break samples of known size.

The earlier the better. The adhesive changes form before curing (flowing, shrinking), and early detection allows timely interception and reduces the amount of rework. The inspection timing is also constrained by cycle time, and is usually placed immediately after the dispensing process step.

You can try using non-visible differences to enhance contrast, for example a UV fluorescent adhesive combined with UV illumination, or differences in how materials reflect light in specific wavelength bands. This is a matter of optical solution design and must be evaluated for the specific combination.

The threshold design for missing-adhesive detection should take sealing requirements into account: where continuous sealing is required, no break of any size can be accepted; where the adhesive only serves a fixing function, the tolerance can be relaxed. This must be decided by the process, not assumed by the inspection party. The inspection result at the dispensing station has direct feedback value for upstream processes: if missing adhesive concentrates at the same position along the path, it usually points to a problem with the dispensing valve, air pressure, or path parameters.

The visual characteristics of adhesive beads differ greatly between adhesive types: white adhesive usually appears as a bright region, dark adhesive as a dark region, and transparent adhesive may only appear at specific angles due to reflection. Therefore, when multiple adhesive types are handled on the same machine, different inspection recipes usually need to be configured per adhesive type. Trajectory alignment is the key to accuracy. If the workpiece posture is stable, a fixed trajectory can be used directly; if the posture fluctuates, the coordinate system must first be aligned using datum features on the product (edges, hole positions, marks) before unfolding the trajectory, otherwise "broken adhesive" will be widely misreported as position offset.

View the object characteristics, acceptance criteria and optical considerations for each object; it covers 8 common object types including O-ring presence/absence inspection, seal ring presence/absence inspection, gasket presence/absence inspection and label presence/absence inspection.

What visual inspection replaces is repetitive visual judgement, not manual labor for everything. The typical division of labor is: vision performs part-by-part full inspection and judgement, while people handle re-judgement of borderline samples, changeovers and exceptions, and maintenance of the optics and tooling. How many people are actually involved depends on the degree of automation and the re-judgement strategy.

Please provide product samples after dispensing (including good parts and known adhesive break / misalignment parts) as well as the adhesive type and dispensing path requirements; the engineer will assess the imaging visibility and detection capability for the adhesive.