How to Inspect a Used Welding Robot Before You Buy: A 12-Point Field Checklist
Figure 1. An engineer checking a used welding robot's wrist and cable chain — the areas where hidden wear usually lives.
never appear in photos. A machine can look immaculate in a listing and arrive with a tired servo, a cracked cable chain or a controller that forgets its calibration on a hot afternoon. We know, because we buy hundreds of used robots a year ourselves, and we reject machines on exactly these grounds.
So before you wire money to any seller — including us — run this 12-point checklist. It takes an hour on site, or a 30-minute video call if the supplier is serious about transparency.
Part 1: History (points 1–3)
Point 1: Serial number and age. Cross-check the serial plate, the controller serial and the documentation. In many countries, including Vietnam, used equipment above a certain age cannot be imported at all, so a mismatch here can stop your shipment at customs.
Point 2: Operating hours. Ask for the hour meter and the controller's stored values. A welding robot doing 6,000 hours a year with heavy duty cycles ages faster than a palletizer doing 3,000 light hours.
Point 3: Alarm history. A robot that spent its life throwing servo or battery alarms has a story. Pull the alarm log from the controller if you can — it is the closest thing to a medical record.
Part 2: Mechanics (points 4–6)
Point 4: Axis backlash and play. Jog each axis slowly and feel the transition through zero. Any clunk, grinding or dead band is worn gearing — one of the most expensive repairs on a used robot.
Point 5: Cables and connectors. Inspect the cable chain, the wrist cables and every connector. Cracked insulation and bent pins are the number one source of intermittent faults after shipping.
Point 6: Torch, bracket and dress-out. A welding robot's torch neck, gas hose and torch bracket take constant abuse. Check for leaks, cracks and non-original modifications.
Part 3: Electronics (points 7–9)
Point 7: Controller and teach pendant. Power the system on and watch for error codes at boot. Test the pendant keys, the deadman switch and the screen. A replacement pendant can cost thousands and take weeks to source.
Point 8: Servo drives, fans and power supply. Listen for bearing noise in fans, check for burnt smells, and verify the cabinet's dust and humidity history.
Point 9: Batteries. Encoder backup batteries that are flat or missing mean the robot may need full re-homing and calibration — and sometimes encoder replacement.
Part 4: Validation (points 10–12)
Point 10: Power-on and full-axis jog. Run every axis through its full travel at low speed, then at speed. Watch for vibration, overheating or position drift.
Point 11: Repeatability check. With a dial indicator or a laser tracker, return the wrist to a fixed point 10 times and record the spread. This is the number that decides whether the robot can hold your weld seam tolerance.
Point 12: Safety circuits. Test the emergency stop, the safety gate interface and the brake hold. A robot with failed safety circuits is not a discount — it is a liability.
Can't visit? Ask for the evidence
A supplier that refuses a live video test has a reason. A supplier that sends you a recorded video plus a written test report is showing you how their process works. Every robot ZOTRADE ships is tested on our 12-point standard, and we send the report and a live walk-around video before payment. In 15 years of business we have learned that transparency is cheaper than warranty claims.
How to inspect from 8,000 km away
If you cannot visit the machine, demand a structured video walk-around. Insist it follows a script: serial plate close-up, hour meter on the controller, each axis jogged at slow and fast speed, cable chain and wrist cables inspected end to end, controller boot with the pendant keys tapped, and a repeatability run on camera. A seller who follows the script without hesitation is showing you a machine they are confident about.
One more check that costs nothing and reveals a lot: ask the seller to run the robot through a full working cycle of its intended job — a welding path, a pick-and-place sequence — without editing the video. Watch for hesitation, vibration or position drift near the extremes of the envelope. Latent axis problems show up at the edges of the working range, exactly where a test program that avoids the extremes will hide them.
About ZOTRADE
ZOTRADE is a China-based refurbisher and exporter of used industrial robots, serving 1,200+ factories in 50+ countries since 2010. We rebuild robots from FANUC, ABB, KUKA, Yaskawa, OTC, Nachi, Staubli, Epson and other leading brands through a six-step refurbishment process, test every machine on our 12-point standard, back it with a 60-day warranty, and keep 10,000+ spare parts in stock. From welding to palletizing, painting to machine tending, we deliver tested robots at about 45% of the new price — with the documentation, freight and support to make the whole purchase work end to end.
The bottom line
Inspection is not a step you complete — it is a standard you carry into the negotiation. The seller who shows you the serial, the hours, the alarm history and a live test is telling you the truth about their business. The seller who cannot is telling you something too, and it is worth the same attention. Every robot we buy for our own stock passes the same 12-point standard we describe here, and every robot we sell ships with the report. Use the checklist once and you will know the difference between a machine and a story.
Ask us for the inspection report and live test video of any robot in stock — we will send both the same day you enquire.