How to repair a welding machine

How to repair a welding machine 

By following a regimen of suitable and thorough maintenance procedures, a welding machine can operate in safe condition and dependably for a long time.

Welding machines in poor repair waste money

Outsourcing provides expert maintenance

Because of their durability and long life, welding machines sometimes don’t get maintenance as usual. For some companies, a broken welding machine is a normal interference. For those who are dependent heavily on welding, a broken machine can lead to many headaches. It typically means expensive lost production. Welding machines with erratic arcs also waste energy. Welds that fail to pass x-ray, ultrasonic, or other tests are costly to repair.

Hard failures, such as blown PC boards or electrically “fried” components, are unpredictable. However, owners of welding equipment can directly control “soft failures” by repairing worn items, such as cables, connections, internal wiring, drive roll systems, guns, torches, and consumables. Preventing soft failures also includes removing corrosion and air-borne contaminates from the machine that lead to over-heating and circuit board failure.

Pressing deadlines and other priorities often cause delays in maintenance until it’s too late. If this is the case, strongly consider outsourcing maintenance to a qualified source.

Preventable cost efficiency

The premise behind outsourcing maintenance is that manufacturers may not have the internal resources to perform maintenance, or their internal resources are already over-burdened with more pressing maintenance issues.

While some people may hesitate to outsource work because they perceive it costs more, calculating Preventable Cost Efficiency (PCE) can put actual numbers to the problem. PCE is a factor of the cost of production downtime per hour and the cost of service per hour. The following calculation illustrates the potential savings:

PCE = Cost of Maintenance/Hour

If a service provider charges $75/hour for service and downtime costs $500/hour, then the PCE is 15%. In other words, spend $15 for preventative maintenance now or pay $85 dollars to fix it later. Service experts believe that preventative maintenance generally reduces the chance of hard failures by up to 50%.

System Checklist

Before servicing equipment, unplug it; this includes all 115 V plugs from feeders and water coolers. Always follow established lock-out/tag-out procedures and follow the safety information in the operator’s manual. Contact the manufacturer when in doubt.

The following is a basic list of service actions for most welding systems. For a complete, detailed list, consult the owner’s manual or an authorized service provider.

Fig. 1. Welding machines must be blown out regularly to maintain reliable performance.

Power sources. Approximately every six months use clean, dry air to blow out the inside of the machine. In heavy service conditions, cleaning monthly or weekly may be necessary (Fig. 1). For inverter-type machines, leave the cover on and direct the airflow through the front of the machine. Failing to blow out the machine can lead to overheating, erratic arc performance, board or electrical failure, and premature wear.

Load bank testing. Load test each machine to ensure the welding output is accurate, it is required for ISO compliance.

Cable connections, cables and electrode holders. Poor weld circuit connections can yield any number of problems. This includes excessive resistance in the weld circuit, which in turn leads to arc wandering, an arc that won’t start or an arc that is difficult to start.

Fig. 2. Inspect cables to ensure they are not damaged.

Frequently inspect all parts of the circuit. Tighten loose connections and inspect cables, electrode holders and ground leads for wear, cracks, and damage (Fig. 2). Immediately replace those with excessive wear or damage. Note that excess cable length and coiling cables around ferrous metal, such as a table leg or pipe, also causes erratic arcs and drifting weld parameters. Use quick disconnects to add or subtract cable as needed to avoid these problems.

Guns. A gun is not a hammer, but operators often use it as one. Banging may loosen connections inside the gun and lead to erratic arcs. Inspect guns every six months, tighten loose connections, and blow out any particles.

Cables and liners. Clean the cable assembly after finishing a spool of wire, or about twice a week. Disconnect the cable from the feeder and check for a secure connection. Blow out the cable, directing air into the contact tube end. Tap the cable every few feet to loosen any residue trapped in the liner and blow it out again.

Without regular cleaning, the liner will eventually clog and seize the wire. This causes feeding problems, typically slipping, that can cause the wire to burn back to the contact tube. This may cause a bird’s nest at the drive rolls. If the liner is cleaned and still there still are wire feed problems, the liner is likely worn and needs replacing.

Drive rolls. Inspect the drive rolls when the cable is cleaned. If dirty, remove and clean them with a wire brush. If deformed, replace them. In addition, check the inlet and outlet guides and replace them if they are deformed from wire wear. More pronounced wear on the inlet guide may indicate the need to realign the wire spool hub assembly.

Water coolers. Maintain proper coolant levels. Rather than water, use a blended coolant from the manufacturer. It solves problems related to sludge build-up and foaming.

Gas hoses. Porosity in the weld bead and poor bead color can result from insufficient shielding gas coverage. Examine hoses regularly for leaks, wear, and loose connections. Immerse pressured hose in water to check for leaks. Repair a leaky or worn hose by cutting out the damaged area and splicing. Do not use tape.

Regulators. Remove a faulty regulator from service for repair after closing the cylinder valve. External gas leaks, excessive creep (when delivery pressure continues to rise with the downstream valve closed) and faulty gauges (pointer does not move off the stop pin when pressurized, nor returns to the stop pin after pressure release) indicate a faulty regulator. Do not attempt to repair a faulty regulator; send it to the manufacturer’s designated repair center.

Engines on welding generators. Basic maintenance includes changing the oil, oil filter, air cleaner, and fuel filter. Check the owner’s manual for service intervals, as this varies greatly between gas and diesel engines.

Problem: Welder will not start (Starter not operating)

Cause: Power circuit dead.

Remedy: Check voltage.

Cause: Broken power lead.

Remedy: Repair.

Cause: Wrong supply voltage.

Remedy: Check nameplate against supply.

Cause: Open power switches

Remedy: Close. Cause: Blown fuses. Remedy: Replace.

Cause: Overload relay tripped.

Remedy: Let set cool. Remove cause of overloading.

Cause: Open circuit to starter button.

Remedy: Repair.

Cause: Defective operating coil.

Remedy: Replace.

Cause: Mechanical obstruction in contactor.

Remedy: Remove.

Problem: Welder will not start (Starter operating)

Cause: Wrong motor connections.

Remedy: Check connection diagram.

Cause: Wrong supply voltage.

Remedy: Check nameplate against supply.

Cause: Rotor stuck.

Remedy: Try turning by hand.

Cause: Power circuit single-phased.

Remedy: Replace fuse; repair open line.

Cause: Starter single-phased.

Remedy: Check contact of starter tips.

Cause: Poor motor connection.

Remedy: Tighten.

Cause: Open circuit in windings.

Remedy: Repair.

Problem: Starter operates and blows fuse

Cause: Fuse too small.

Remedy: Should be two to three times rated motor current. Cause: Short circuit in motor connections.

Remedy: Check starter and motor leads for insulation from around and from each other.

– Problem: Welder runs but soon stops

Cause: Wrong relay heaters

Remedy: Renewal part recommendations

Cause: Welder overloaded

Remedy: Considerable overlaod can be carried only for a short time

Cause: Duty cycle too high

Remedy: Do not operate continually at overload currents Cause: Leads too long or too narrow in cross section Remedy: Should be large enough to carry welding current without excessive voltage drop

Cause: Power circuit single-phased

Remedy: Check for one dead fuse or line

Cause: Ambient temperature too high

Remedy: Operate at reduced loads where temperature exceeds 100° F

Cause: Ventilation blocked

Remedy: Check air inlet and exhaust openings

Problem: Welding arc is loud and spatters excessively Cause: Current setting too high

Remedy: Check setting and output with ammeter

Cause: Polarity wrong

Remedy: Check polarity, try reversing, or an electrode of opposite polarity

Problem: Welding arc sluggish

Cause: Current too low

Remedy: Check output, and current recommended for electrode being used

Cause: Poor connections

Remedy: Check all electrode-holder, cable and groundcable connections. Strap iron is poor ground return

Cause: Cable long or too small

Remedy: Check cable voltage drop and change cable Problem: Touching set gives shock

Cause: Frame not grounded

Remedy: Ground solidly

Problem: Generator control fails to vary current

Cause: Any part of field circuit may be short circuited or open circuited

Remedy: Find faulty contact and repair