Applications · Strain gauges

Strain Gauge Welding

Strain gauge attachment bonds gauge lead wires to a terminal pad on the gauge backing, or the gauge tab directly to a test article, structure or load-cell body. The controlling difficulty is that heat conducted into the substrate shifts the very property the gauge measures — residual stress, temperature history, prior heat treatment — and can cook the polyimide backing before the weld sets, so pulse energy has to stay extremely low and localized.

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Foil strain gauge bonded to a metal substrate with two fine copper lead wires welded at the gauge's solder pads, close-up on a dark surface

Typical joints

Typical strain gauge parts and joints

Strain gauge welding covers a short list of recurring joint forms:

Strain gauge lead wires attached to the terminal pad on the gauge backing
Gauge tab attached directly to a steel or aluminum test article
Load cell body — gauge-to-flexure attachment on strain-gauged load cells
Structural monitoring — long-term gauge attachment on bridges, pressure vessels and aerospace components
Composite structures with a metallized surface layer — attachment through the metal coating rather than to the composite itself
Rosette gauges — multiple gauges arranged geometrically, requiring consistent attach parameters across the pattern

Process fit

Which process fits strain gauge welding

Capacitor-discharge resistance spot

The dominant process for gauge attach

Pulse runs in microseconds to a few milliseconds with tightly bounded total energy, so heat into the substrate stays minimal and localized. CD units built for gauge work dial energy precisely, so the same welder puts a spot on aluminum one hour and stainless the next. See the resistance spot line →

Laser

Selected cases — heat-sensitive substrates, cosmetic surfaces

Where the gauge sits on a heat-sensitive substrate even a CD spot might disturb, or on a part where a residual arc mark is cosmetically unacceptable, laser fits. Same rule: peak pulse energy dominates the choice, not average power. See the laser line →

Pulse arc / Micro TIG

Generally not a fit

Arc heat is too much for a gauge attach; the test article's material state would be disturbed. Only when the gauge sits on a heavy heat sink (a thick weldment for structural monitoring) does pulse arc become marginal-viable, and sample-test on the actual part first. See the pulse arc line →

Because measurement accuracy is the whole point, a sample-attach on the actual test-article material is the only reliable process check.

What’s hard

Common difficulties in strain gauge welding

Four failure modes recur across strain gauge welding programs:

Heat into the test article changes what you are measuring — residual stress state, temperature history and any prior heat treatment can all shift under the weld pulse, so energy has to stay below the disturbance threshold.
Batch consistency drives measurement repeatability — variation in the spot weld from gauge to gauge shows up as variation in the measurement, so parameter stability across a run is not optional.
Substrate material variety — steel, aluminum, titanium and composite-with-metallized-surface show up in the same lab or on the same line, so the machine has to switch parameter recipes cleanly.
Gauge-backing damage — excess heat cooks the polyimide or epoxy backing of the gauge itself before it reaches the weld pad; the fix is lower energy, not more force.

Strain gauge attachment has almost no margin for excess heat, and every combination of gauge type and substrate needs its own energy setting. The most reliable way to lock the setup is a sample attach on the actual test article. The evaluation itself is free.

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