Fixturing for UV Spot Curing — Holding Guide Angle and Standoff Repeatable
A UV spot lamp can only be as consistent as the hardware holding its lightguide. Small shifts in standoff or angle change the dose at the bond line, so the fixture belongs in the cure specification alongside the lamp and the adhesive. Q: Why Does a Few Millimeters of Lightguide Drift Matter in Spot Curing? A: Because Irradiance Changes Steeply With Distance, So Small Movements Change the Delivered Dose Dose equals irradiance multiplied by exposure time. If the exposure timer stays fixed while the guide drifts, the dose changes in direct proportion to the irradiance change. The irradiance curve of a spot lamp is steep, which is why a loose bracket can turn a passing recipe into an under-cure without any alarm on the controller. Reading the Drift in Real Numbers Incure publishes irradiance at the focal point for its L9000™ UV LED spot lamp: 7,500 mW/cm² at 9 mm, 5,000 mW/cm² at 10 mm, 2,300 mW/cm² at 17 mm, 1,200 mW/cm² at 20 mm, and 223 mW/cm² at 30 mm. Simple arithmetic on those figures shows what drift costs: Moving from 9 mm to 10 mm removes one third of the irradiance. Moving from 17 mm to 20 mm removes nearly half (2,300 down to 1,200 mW/cm²). At 30 mm, irradiance is roughly 3% of the 9 mm figure. With a fixed timer, each of those shifts cuts the dose by the same fraction. The practical message is that a fixture tolerance of a couple of millimeters is not a small tolerance for a spot cure. Designing the Guide Holder A good guide holder does three jobs: it clamps the guide without crushing it, it sets the standoff against a hard reference, and it resists being knocked out of position. Useful design features include: A positive stop that the guide seats against, so standoff does not depend on how far an operator pushes it in. A clamp that grips the guide body, not the tip, to avoid damaging the output face. A locating feature tied to the part datum, so the guide references the part rather than the bench. Strain relief on the guide run, so cable movement cannot pull the tip. Incure's L9000™ guide options differ in length, which affects holder design. The Cool Guide uses a 24 mm cube head with an integrated fan and 83 mm total length; the Short Guide is 66 mm; the Long Guide reaches 118 mm for deep positions. The L9000™ reach and working-distance guide explains which geometry suits which fixture. Setting and Holding the Angle Aiming the guide square to the bond face keeps the spot round and its intensity predictable. Tilting it stretches the spot and spreads the light over a larger area, so the bond receives less energy per square centimeter than the straight-on reading suggests. When the bond face sits at an angle to the approach axis, change the beam direction rather than tilting the whole guide. Incure's LGT-Series™ terminators redirect the beam at 90° (LGT-90-5, LGT-90-8) or…