Holding a lens, a connector, or a fiber in perfect alignment for the full length of a cure ties up a costly station on the line. A short UV spot tack, followed by a full cure somewhere else, often breaks that bottleneck.
Q: What Is a Tack-Then-Cure Spot Curing Process?
A: A Brief Spot Exposure Locks Position, and a Flood Lamp or Chamber Finishes the Cure
In a two-stage process, the alignment fixture holds the part while a UV spot lamp delivers only enough light to fix the adhesive in place. The part then leaves the alignment station and moves to a flood lamp, a cure chamber, or a conveyor, where the full dose reaches the entire bond line. The precision fixture is released after seconds instead of waiting on the complete cure.
This works because a UV-curable adhesive does not start curing until light reaches it. Incure’s Optik™ optical adhesive documentation describes working time as effectively unlimited until the operator triggers the lamp, which is what makes active alignment possible without a clock running. If you are new to spot equipment itself, Incure’s UV LED spot curing system explainer covers the hardware basics; this guide focuses only on when to split the cure in two.
Three Signals That a Single Spot Cure Is the Wrong Tool
A single spot exposure is simple and fully adequate for many small bonds. Consider splitting the process when one or more of these conditions applies:
- The alignment station is the bottleneck. If parts queue in front of an active-alignment fixture, every second of cure spent there is lost capacity. Tacking releases the fixture as soon as the part is fixed.
- The bond line is larger than the spot. On the Incure L9000™, spot diameter runs from 3 mm to 12 mm across its 9–30 mm focal range. A seal bead running around a housing perimeter is longer than any spot, so a spot lamp would have to step around it point by point.
- Part of the bond is shadowed. A spot reaches what it can see. Joints that run behind a wall or under a bracket need a dual-cure adhesive or a broader exposure from several angles, and a flood or chamber stage can provide the second.
Choosing the Second Stage
The finishing stage should match the part’s size and the plant’s flow.
Batch chambers suit low-to-medium volume. Incure’s B/C-Series™ chambers pair with specific flood lamps: the C131D, C131C, and C141C with the L-Series™ L11 through L44, the C191C with the L88 through L1414, and the B500 and B201 with F-Series™ arc lamps. Several tacked parts can share one chamber cycle, and a drawer or door interlock cuts UV output when the enclosure opens. Incure’s guide to matching a B/C-Series™ chamber to lamp and part size walks through that pairing.
Open flood lamps suit larger parts or fixtures that will not fit in a chamber. The L-Series™ UV LED flood lamps range from the L11 up to the L1414, so the curing area can be sized to the part rather than the other way around.
Conveyors suit continuous production, where tacked parts flow directly off the alignment station into an inline cure without manual batching.
Email Us with your bond geometry and alignment cycle time, and Incure’s engineers can help decide whether a single spot cure or a two-stage sequence fits the line.
Setting the Tack Exposure
The tack exposure needs to be long enough to hold position through handling and short enough to keep the alignment fixture moving. Because dose equals irradiance multiplied by time, both levers on the spot lamp matter.
As a hypothetical example, suppose an adhesive needs 300 mJ/cm² to hold position and the lightguide sits where irradiance measures 1,200 mW/cm². The tack time is 300 ÷ 1,200, or 0.25 seconds. The L9000™ timer is programmable from 0.1 to 999.9 seconds, so a sub-second tack is within its range. Its intensity can be set from 10% to 100%, which offers a second way to fine-tune the tack. Take the real tack dose from the adhesive supplier or from your own trials, not from this example.
Confirm the tack on real parts by handling them exactly as production will: lifting, transferring, and loading them into the second stage. A tack that survives a gentle bench test but shifts during a conveyor transfer is not a tack.
Qualifying the Two-Stage Sequence
A tacked-then-flooded bond is a different process from a single continuous cure, so qualify the full sequence rather than each step in isolation:
- Confirm alignment is held after transfer, using the same inspection method the finished part will face.
- Confirm the finished bond meets its strength or sealing requirement after the second stage.
- Set a maximum hold time between tack and full cure, and test parts at that limit, so a backed-up line does not produce untested conditions.
- Record both doses in the work instruction, with the radiometer position used for each.
Thermal behavior matters too. Bonds between materials that expand at different rates can be stressed by the full cure in ways the tack never reveals; Incure’s article on how CTE mismatch causes adhesive bond failure explains what to watch for.
When One Spot Exposure Is Still the Right Answer
Two stages add a transfer, a second piece of equipment, and a second dose to control. When the bond is small enough to fall inside one spot, fully visible to the lightguide, and the alignment fixture is not the constraint, a single spot cure is simpler and easier to document. The decision is about where the bottleneck sits, not about which method sounds more advanced.
Final Thoughts
Tack-then-cure turns the spot lamp into a positioning tool and hands the bulk of the curing to equipment built for area coverage. It pays off when alignment time, bond length, or shadowing would otherwise slow a single-stage spot cure. Contact Our Team to plan a tack exposure and a matching second-stage cure for your assembly.
Visit www.incurelab.com for more information.