NN
ss_weld_nandini
OP
April 3, 2026
We're using a Fronius TPS 500i with CMT Advanced on a CNC robotic cell welding 304L stainless at 2mm thickness, 1.0mm ER308L wire, 98% Ar / 2% CO2 gas mix. Spatter is excessive — way beyond what CMT should produce. The welds look okay cosmetically but we're spending 20 minutes per part on post-weld cleanup which destroys our cycle time. We've confirmed wire stick-out at 13mm, contact tip recessed 2mm, torch angle 5° push. Everything by the book. Fronius field service visited and said parameters look correct but couldn't explain the spatter. Anyone?

CW
cmt_wizard_tobias
April 4, 2026
For 304L stainless on CMT, your gas mix is the first suspect — 98/2 Ar/CO2 is correct for carbon steel but stainless really wants 98% Ar / 2% O2 (not CO2). The CO2 reacts with the chromium in 304L at the arc interface and creates chromium carbide particles that contribute to both spatter and sensitization of the HAZ. The spatter from CO2 on stainless is small and flies far, which is different from typical carbon steel spatter — it looks like the machine is "perfectly fine" but you find glassy micro-beads all over your part 10 minutes later. Switch to a tri-mix (90% He / 7.5% Ar / 2.5% CO2) or the standard 98/2 Ar-O2, reset your CMT correction value to 0 and retune. This single change has resolved stainless spatter for at least 5 shops I know of.

HG
hi_freq_guenther
April 5, 2026
Also check your CMT correction value and the dynamic correction on the TPS 500i — Fronius CMT Advanced has a "Correction" parameter (−10 to +10) that adjusts the droplet detachment energy. Factory default is 0 but for stainless with its higher surface tension, a correction of −2 to −3 actually reduces spatter significantly by shortening the droplet dip duration. Most TPS 500i users never touch this because the Fronius documentation describes it vaguely, but it's genuinely the most powerful tool for fine-tuning spatter on the machine. Also verify your robot's TCP speed at corners — if there are any < 30° direction changes in your program running at speed > 400 mm/min, the torch hesitates momentarily and CMT's sync with motion breaks down, causing a burst of spatter exactly at that point.

SK
stainless_king_sergio
April 7, 2026
One thing that genuinely surprised me when we audited our Fronius cell — the WeldConnect app logs showed our TPS 500i had been running with a 4% wire feed speed variation because the feeder roller bearings had developed a flat spot. The wire speed variation was below what the machine dashboard displays as an alarm but it was enough to make CMT's droplet-detection algorithm confused, generating false "short circuit detected" signals and triggering unnecessary arc corrections that threw micro-spatter. Fronius TPS feeders on high-duty robotic cells should have their roller bearings inspected every 6 months — it's a 15-minute job and a $12 bearing, but shops skip it because there's no warning light. In 2026, Fronius's WeldConnect cloud dashboard (if you're on a subscription plan) actually tracks feeder motor current signature and can flag bearing wear before it causes production problems — that feature alone is worth the subscription cost if you're running multiple cells.