Formed-in-place gaskets (FIPG) deliver design flexibility and repeatable sealing, but the process is unforgiving of poor setup. Most FIPG defects trace back to a handful of root causes in surface preparation, curing, or dispensing. Knowing those causes is the first step to consistent, leak-free results.

Poor Adhesion and Delamination

When the bead peels away from the flange, a leak path opens even though the gasket itself is intact. Contamination is the usual reason. Oils, grease, mold release, machining fluid, and even fingerprints leave a film that blocks adhesion. Low substrate surface energy, an incompatible pairing of sealant chemistry and flange material, and undercure all weaken the bond as well.

The remedy is a validated cleaning step, typically a solvent wipe or plasma treatment, confirmed on production parts with a peel test. Where the flange is a low-surface-energy plastic, a primer restores adhesion. Confirm the sealant is rated for the substrate material before committing the line.

Incomplete Cure and Soft Spots

Sections of the bead that stay tacky or gel-soft compress permanently under clamp load and lose sealing force. The cause is almost always insufficient cure energy: too little oven time for heat cure, too little UV dose for light cure, or too little ambient moisture for RTV. Off-ratio mixing in two-part systems and UV shadowing behind ribs or bosses produce the same result locally.

Measure the actual cure conditions rather than assuming them. For UV systems, a radiometer confirms dose at the bead, and a dual-cure sealant handles shadowed geometry. Matching lamp output to the material is covered in our guide to selecting a UV lamp for resin and sealant curing. For heat cure, profile the oven with the part loaded rather than empty.

Dispensing Inconsistency

A bead that varies in width or height, skips, contains voids, or lays down too much material points to the dispensing hardware. Worn nozzles, incorrect pressure, and pump wear all shift flow. Sealant viscosity drifts with temperature and with settling in the reservoir, while robot path errors and entrapped air introduce gaps.

Put the dispensing equipment on a preventive maintenance schedule that includes nozzle replacement, temperature-condition the sealant so viscosity stays stable, and switch to a de-aired cartridge where air entrainment causes voids.

Compression Set

If the cured gasket stops rebounding after sustained clamp load, sealing force decays and the joint eventually weeps. This happens when the material has poor compression-set resistance at its service temperature, when assembly applies excessive clamp force, or when the gasket is exposed to chemicals and heat beyond its rating.

Select a sealant with a documented low compression set at the operating temperature, design the flange with a hard stop or bead-height control so assembly cannot over-compress the gasket, and verify compatibility with any fluid the joint contacts.

Material Bleed-Out and Migration

Uncured sealant that flows past the intended sealing zone before it gels can contaminate nearby surfaces or electrical contacts. The drivers are viscosity too low for the dispensing speed, excess pressure or an oversized nozzle, and surface contamination that lowers surface tension and lets the bead spread.

Moving to a thixotropic, non-sag grade solves most cases. Reducing nozzle size and pressure to the minimum that maintains bead continuity, and tightening the cleaning step so the flange surface is uniform, address the rest.

Differential Expansion Stress

A housing and its cover made from different materials expand at different rates, so a bead spanning both is loaded on every temperature cycle. This mechanism is explained in our article on how CTE mismatch causes adhesive and seal failure. A gasket material with adequate elongation moves with the joint instead of cracking.

Detecting Defects Before Assembly

Many FIPG failures can be caught at the dispensing station rather than at final leak test. In-line vision systems check bead continuity, width, and position against a reference and flag skips, thin spots, and path drift in real time. Weighing a sample part before and after dispensing confirms the deposited volume is within tolerance. For cured beads, a quick manual check with a blunt probe reveals soft spots that indicate undercure. Adding these checks upstream keeps defective parts from consuming assembly and test time.

Leak Testing the Finished Joint

Sealed assemblies should be verified with a quantitative method rather than a visual check. Pressure-decay testing pressurizes the cavity and measures the pressure drop over a fixed dwell, with the allowable leak rate set by the application. Where the specification is tighter, tracer-gas methods using helium or forming gas detect leaks well below what pressure decay can resolve. Whichever method is used, test after the sealant has reached full cure, since a green bead can pass and then fail once it finishes curing and shrinks slightly.

Building a Reliable FIPG Process

Prevention beats troubleshooting. Bring FIPG requirements into the design phase: adequate flange rigidity, controlled gap, a clean bead path free of sharp direction changes, and access for the light source or oven airflow. Then validate on production parts, checking adhesion after cleaning, cure completeness in the worst-case shadowed area, and sealed-assembly performance across the full pressure and temperature range.

If a current FIPG line is producing intermittent leaks and you need help isolating the cause, Email Us with your bead specification, cure method, and defect photos.

Most FIPG problems are process problems, not material problems. Systematic control of cleaning, curing, and dispensing, backed by validation on real parts, is what turns formed-in-place sealing into a dependable production method. Contact Our Team to review your sealing process.

Visit www.incurelab.com for more information.