Applications · Seam sealing

Seam Welding for Hermetic Sealing

Continuous seam welding fuses two edges into a single leak-tight line — the process behind welded tube from a strip mill, cylindrical enclosure closures, can end-cap seams, and bellows convolutions. The hard part is not any single spot; it is holding overlap, current density and thermal state constant across the full length of the seam. On the acceptance side, leak-tight means no gap between overlapping fusion spots along the seam, verified by helium-leak, pressure-decay or dye-penetrant testing on the finished part.

Send Sample for Evaluation Compare Processes

Copper roller electrodes running along a metal sheet seam with a glowing orange weld trail behind them during continuous resistance seam welding

Typical joints

Typical seam sealing parts and joints

Seam sealing covers a broader parts universe than diaphragm sealing — anywhere two edges close a cavity and need to hold pressure, vacuum or a controlled internal atmosphere without a mechanical gasket. The recurring joint forms are:

Longitudinal seams on cylindrical enclosures, small tanks and welded tube — tube mills fuse a rolled strip’s edges into a continuous axial seam that becomes the finished pipe or tube
Circumferential end-cap seams on aerosol canisters, small pressure vessels and cylindrical enclosure closures where a cap closes the open end of a formed body
Rectangular and box enclosure corner seams on electronic housings, junction boxes and instrument cases that need water- or dust-tight closure at the case seam line
Bellows convolutions on metal bellows for expansion joints, vacuum feedthroughs and aerospace hermetic couplings, where each convolution is joined edge-to-edge in a repeating pattern
Hermetic package lids sealed to the housing rim on sealed electronic packages — distinct in scope from the diaphragm-to-housing joint on measurement devices, which sits under pressure sensor assemblies
Repair seam welds on fielded enclosures where a leak point has been located and the seam is re-fused locally rather than the whole part replaced

Process fit

Which process fits seam sealing

Resistance seam (workhorse)

Long straight and cylindrical seams in volume

Roller-electrode seam-welding heads roll along the joint line, laying down a continuous overlap-controlled fusion pattern spot by spot. Force, pulse timing and roller speed together lock the overlap distance across thousands of consecutive spots — the setup that carries volume production on can bodies, welded tube from strip mills and cylindrical enclosure closures where the geometry stays predictable across the run. See the resistance spot line →

Laser

Thin-wall enclosures and hermetic package lids

Continuous or overlapping-pulse laser seams sit on thin-wall enclosures where a roller electrode would deform the substrate under mechanical force, and on hermetic package lids where an autogenous weld gives the tightest leak-path control. Precision pulse timing holds heat accumulation within the local seam’s tolerance across long runs. See the laser line →

Pulse arc / Micro TIG

Repair, bellows convolution touch-ups, one-off seams

Pulse arc / micro TIG covers the smaller cross-section repair role — re-fusing a leak point on a fielded enclosure, laying a filler bead across a bellows convolution, or hand-guiding a precision seam on a one-off build where a full production setup would be over-invested. Weld visibility during setup also helps on non-repeat geometry. See the pulse arc line →

Acceptance sits downstream of the weld line — helium-leak, pressure-decay or dye-penetrant testing on the finished part is what confirms overlap consistency held across the full seam, and a sample run through the same test flow is the quickest way to lock the process choice for a given geometry.

What’s hard

Common difficulties in seam sealing

Four difficulties dominate seam-sealing programs, all traceable to one fact — a seam is not a single weld but many welds in sequence with cumulative state carrying forward from spot to spot:

Overlap consistency along the seam — each fusion spot must overlap the previous one by roughly 50% for a continuous leak-tight line. Spacing drift from force variation, roller-speed inconsistency or worn contact geometry opens gap-line leak points that pass every individual spot check but fail the full-part leak test.
Electrode wear on roller heads — as the roller radius wears, contact patch geometry and current density shift, walking the parameter working point mid-run. Scheduled roller dressing and in-process current monitoring hold the drift before it walks the process out of window.
Long-seam thermal accumulation — heat builds cumulatively as the weld progresses down the joint line, so the trailing end can distort or over-melt while the starting end welded cold. Pulse-off intervals, seam-direction planning and clamped heat-sink fixtures manage the buildup so start and finish land in the same window.
Start-stop and closed-loop joining — where a straight seam ends (start-stop weld) or a cylindrical seam closes back onto itself, the joint has to fuse cleanly with neither a gap nor a double-melt zone. Ramp-in / ramp-out parameter profiles and a short overlap-back segment handle this transition without leaving a discontinuity.

Seam-sealing acceptance is decided by the leak test, not by how any single spot looks. The reliable go/no-go is a sample seam on the actual enclosure geometry followed by a leak test — helium-leak, pressure-decay or dye-penetrant — in the same flow the finished part will see. The evaluation itself is free.

Send a sample for free evaluation