Inverter-based welding power cuts maintenance costs

If time means money, then an inverter-based welder and plasma cutter may provide the best return on investment using inhouse plant maintenance and repair personnel. If experiencing any of the following problems, inverter-based technology can likely reduce wasted time and lower costs:

• Difficulty moving heavy welders to the work site, such as downtime caused while waiting for a forklift, truck, or crane to move the welder
• Inability to bring a larger welder close to the job site while working in tight spaces
• Difficulty finding useable primary power such as having a 115 V outlet and a 230 V machine
• Difficulty with primary power, such as voltage fluctuations, needing to add more welders but exceeding the capacity of the circuit, or facing additional assessed charges from the utility company for poor power factor
• Problems with finding experienced welding personnel or problems related to improper equipment setup

Inverter-based welders and plasma cutters can solve all of these problems because their advanced technology dramatically lowers machine weight and size, provides primary power management capabilities not possible with conventional welding technology, and delivers unbeatable arc performance.

Today's inverter technology makes machines easier to operate. Their enhanced arc starts and arc performance can turn an average welder into a good welder, leading to improved weld quality and fewer rejects.

All welders transform high voltage, low amperage primary power into low voltage, high amperage power used for welding. The welder does this using a transformer, which is an iron core wrapped with hundreds of turns of copper wire.

Variables that determine the physical size of the transformer include the number of turns of wire, the cross-sectional area of the core, the voltage being applied, and frequency of the primary power.

The key variable that inverters address is frequency. The equation that governs the design of a welder states that increasing the frequency of the primary power allows reducing the size and mass of the transformer.

Inverter technology increases the frequency of the primary power reaching the transformer from 60 Hz up to 20,000 Hz to 100,000 Hz. It does this through the on/off action of high power solid-state switches called IGBTs that turn on or off in as little as one millionth of a second. The on/off action creates ac power, except at a very high frequency and with a rectangular ac waveform (Fig. 1).

By controlling power on the primary or line side of the transformer and boosting frequency, lightweight welding equipment is now produced. Stick/TIG inverters that weigh 10 to 50 lb., all-in-one MIG welders that weigh less than 50 lb., and multiple-process inverters for Stick/TIG/MIG/flux and cored/gouging that weigh about 80 lb. and produce a 425A output.

In an average welding operation, labor accounts for 85% of the cost (Fig. 2). Measuring how much a repair costs includes time spent to bring the welder and the work together, welding equipment setup time, material preparation time, arc-on time, welding cleanup time, any rework time, time spent moving the welder between jobs and time spent returning the welder to the tool crib or storage space.

Today, a four-arc rack for TIG/Stick welding can weigh as little as 340 pounds, rack included, measure a mere 50 inches high, fit in an elevator, and feature wheels for extreme mobility. Rack systems also offer the flexibility of removing individual welders from the rack. The individual inverters are a little larger than a briefcase or carryon suitcase, size varies by output power. One or two people can easily move a small inverter and bring it into a tight space.

Saving time by bringing a lightweight inverter to the work does no good if there isn't anywhere to plug it in. An inverter provides location flexibility through two types of primary power management technology: automatic linking technology and automatic power management technology.

With automatic linking technology, the inverter senses the type of primary power applied, then automatically and physically links to the correct power: 230 V or 460 V, single- or three-phase, 50 Hz or 60 Hz.

The automatic power management circuit eliminates physical linking. The circuit boosts primary power to a higher voltage, and this power then becomes the source voltage for the inverter.

The primary power voltage can vary, but as long as it stays within the machine's operating range, the power at the arc remains steady (Fig. 3). Operators will never see a flicker, and the machine will operate continuously through conditions that cause other machines to shut down for self-protection or trip the circuit breaker.

This benefit pays off on sites with dirty power or when running off generator power. To create a cost-efficient two-arc welding station in the field, pair an engine with a welding generator and use the generator power to run an inverter.

People encountering an inverter for the first time usually cannot believe that such a small machine provides so much welding output. For example, small Stick/TIG inverters weigh less than 14 pounds (Fig. 4), but have enough power to weld with a 1/8-inch Stick electrode. Even an inverter for carbon arc gouging with 3/8-inch carbons at 600A weighs only about 120 lbs.

Inverters also provide outstanding power efficiency, which can lower utility bills, and make good use of the primary power being supplied, which is known as good power factor. Good power factor lowers amperage draw, which may enable adding more welders to existing primary power.

Mechanical contractors working in processing facilities benefit from low primary power draw and primary power management. These job sites are often starved for power and may have generator power that fluctuates. An inverter's low amp draw means that a single generator can power more arcs.

By switching primary power at thousands of Hz/min. and using advanced microprocessor control, an inverter can create optimum arc performance in any given welding mode. Operators can weld at their best and not fight the arc, or they can select the welding process best suited for the job.

Among the inverter benefits:

• Multiple process welding outputs
• Excellent arc starts
• Dig control for Stick welding
• Broad range of inductance control for MIG welding. This allows an operator to create a softer arc with more inductance or a stiffer arc with less. Adding more inductance for better wet-out or to reduce spatter can save hours of post-weld grinding.
• Improved pulsed MIG or pulsed TIG output, the ability to tailor the pulsed wave form. Depending on the application, pulsing can reduce heat input for less warping distortion or burn-through, improve bead aesthetics, reduce spatter, provide out-of-position puddle control, and increase travel speed.
• Output frequency adjustment and extended balance control for ac TIG welding. These functions enable tailoring the weld bead profile to match the application to improve weld quality, minimize post-weld, grinding and substantially increase travel speed
• User-friendly controls. Functions such as last procedure recall remember preferences when changing the polarity, such as starting method and panel or remote control. To account for operator preferences, yet to keep operators out of trouble by making incorrect adjustments, manufacturers try to provide commonality among equipment. The control panel design on an inverter may resemble the control panel used on an engine-driven welding generator the operator used on a previous job.

In addition to user-friendly controls, manufacturers also address the need for user-friendly processes. The welding world generally acknowledges that wire welding, MIG or flux cored, is the easiest process to learn, with Stick being harder and TIG the most difficult.

If a job requires bringing the welder to the work site, multiple process welding, and problems with primary power management, take a closer look at inverter technology. Saving 10 or 20 hours of time, a realistic goal on a single large job, means that an inverter will pay for itself many times over within the two or three years typically allotted for capital investments. And if an inverter helps get a facility up and running in an emergency, it's worth its weight in gold.

The author is available to answer questions about this article. Mr. Borchert can be reached at 920-735-4274, or nborch@millerwelds.com. For general information go to millerwelds.com. Article edited by Joseph L. Foszcz, Senior Editor, 630-288-8776, jfoszcz@redbusiness.com.