At a glance RESEARCH REPORT: TESTED: PLASMA CUTTERS

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1 AUTHOR Josh Giumelli KONDININ GROUP At a glance A plasma cutter uses a combination of electricity and compressed air to cut metal. Tests showed there was a difference in cut quality between cheaper units and more expensive brands. Cutting torches tended to make a difference in cut quality but some higher quality torches had less visibility. Cheaper torches have no electrical isolation, leading to a possible electric shock when disassembling the nozzle. Oxyacetylene sets still may offer a more versatile solution for cutting needs, as they can also heat, braze and weld. Photo: Ben White With the flood of cheaper Chinese-made tools on the market, Kondinin Group engineers Josh Giumelli and Ben White and researcher Chris Warrick investigated plasma cutters, putting low-cost models up against more established brands. 16 Farming Ahead March 2008 No

2 Cutting steel with electricity and compressed air might seem like a magic trick but recent Kondinin Group tests of nine plasma cutters show there is no smoke and mirrors. Plasma cutters are a viable alternative for cutting a range of metals in the workshop, even if only single-phase electricity is available. As with inverter welders (see Farming Ahead No. 181), imports of Chinese-made, inverter-based plasma cutters have seen the price of entrylevel machines fall to levels affordable for many farm workshops. Yet differences in quality and performance remain between cheaper plasma cutters and the more established brands. In particular, Kondinin Group has discovered serious safety concerns with the handpieces used in cheaper plasma cutters. Torch safety concerns Some of the cheaper plasma cutter handpieces were not fitted with a safety cut-out system, which prevents current flow if the handpiece nozzle is stripped. This means that in the situation where the nozzle has been disassembled to replace a cup or electrode, current can flow between the electrode and the workpiece if the trigger is depressed accidentally. This could result in the operator receiving a shock of more than 90 volts. The more expensive units featured lockout switches or contacts which cut current to the handpiece after the nozzle was pulled apart. The BOC and Unimig plasma cutters were the only low-cost units that featured safety cut-outs in the nozzle. The construction quality of the cheaper handpieces was appalling; the trigger switches were cable-tied to the handpiece, which looked like a modified TIG welding torch. But these handpieces did provide adequate visibility when cutting. Plasma cutters shrink in size Just as inverter technology has shrunk the size and weight of arc welders, it has had a similar effect on the design of plasma cutters. A plasma cutter power supply shares much in common with a welder, as it must take a higher voltage, lower current alternating current (AC) supply (240 volts) and change it to a high current, lower voltage, direct current (DC) supply. The inverter power supply allows a much smaller transformer to do the job of traditional larger units, as far less heat is generated during operation. For more information on how inverter power supplies work, see Farming Ahead No Putting the torch to the metal Kondinin Group tested the Bell Carroll Cut-40A, BOC Smoothcut 40, CEA 26i and 46i, Hypertherm 30, Thermal Dynamics 38, Unimig 40, Weldmaster 40 and the Weld Smart LGK 40 plasma cutters (see Table 1, page 18). All are single-phase models and are generally limited to an output of 40 amperes. This means most manufacturers specify a practical cutting thickness in steel of 10 millimetres, or 12mm severance (roughly finished cut). The Bell Carroll was rated to cut a thickness of 16mm, which from Kondinin Group tests it had no hope of achieving. All units were tested on 6mm, 8mm, 10mm and 12mm mild steel, using a machine-controlled travel speed (see Figure 1, page 20). Not all are equal The Hypertherm, Thermal Dynamics and CEA 46i cutters produced excellent results on all thicknesses to 12mm. The CEA 26i produced credible results, despite it being a lower rated machine because it had an internal air compressor. The BOC and Bell Carroll units performed reasonably for lower cost plasma cutters. In contrast, the Weldmaster had the worst cutting performance, as it failed to cut 12mm and only just managed 10mm steel. The Unimig and Weld Smart plasma cutters both struggled on 12mm but still managed severance. Same machine, different colour The Bell Carroll, Unimig, Weld Smart, BOC and Weldmaster were all Chinese-made and virtually identical underneath the casing. But as the results suggest, the performance of these machines was not identical at all. Some of the variations in cutting performance can be attributed to the different torches fitted to the machines. But this does not explain why the Bell Carroll and Weldsmart produced a significant difference in cut quality even though both units had the same handpiece. The Weld Smart initially failed to work until it was discovered a plug had come What is plasma? Plasma cutting nozzle Illustration: Kondinin Group. Plasma is an ionised gas, which means it has free electrons and can conduct electricity. Plasma is created by passing an electrical current through a neutral, dry gas such as compressed air. In a plasma cutter, a hafnium electrode is used to create an arc between the electrode and the work (pictured). Due to the electrical resistance of the ionised gas, heat is created which melts the metal being cut. The compressed air from the nozzle blows the molten metal away and forms the cut. The flow of air also cools the handpiece but some larger units have water-cooled torches. Farming Ahead March 2008 No

3 TABLE 1 How plasma cutters performed in Kondinin Group tests Model Duty cycle Maximum rated Tested average measured Country Insulation Weight Air pressure Performance ratings* at 100% output current 1 current (amperes) of origin rating (kg) (bar) (amperes) (amperes) input output Cutting Ease of use # Bell Carroll Cut-40A China IP BOC Smoothcut China IP CEA 26i Italy IP Internal CEA 46i Italy IP Hypertherm USA IP Not specified Thermal Dynamics 38 Not specified USA IP Unimig China IP Weldmaster China IP Weld Smart LGK China IP Manufacturer specifications (amperes). 2. Has internal air compressor. * Ratings are out of 100%. The higher the rating, the better the performance. # Score is a combination of ease of use, machine set-up and torch quality. The good and the bad: Kondinin Group engineers liked the fact the BOC plasma cutter (pictured top) incorporated an electrical cut-out in the handpiece. The Hypertherm 30 (middle and inset) was praised for its portability, quality handpiece and cutting quality. On the downside, the Weld Smart unit (below) did not work at first during testing and when it did, the arc was intermittent. adrift from a circuit board inside the machine during manufacture or transit. Maintaining air pressure is vital for quality cutting. All plasma cutters tested were supplied with a regulator and pressure gauge, either inbuilt or bolted to the rear of the machine. Benefits of cutting metal with plasma While angle grinders and drop saws are a favourite method for straight cuts through metal, the oxyacetylene set has been the traditional tool for cutting thick steel or producing curved or intricate cuts. The major benefit of plasma cutting is that it consumes only electricity and compressed air, making it a far cheaper option than the oxyacetylene or oxy-lpg cutting, where gas is consumed and cylinder hire is an annual cost. As plasma cutting is a melting process, it can cut any metal, whereas oxyacetylene cutting is an oxidising process and cannot cut metals such as stainless steel and aluminium that do not oxidise readily. See Table 2 for the pros and cons of plasma versus gas cutting. Beware the hidden costs While plasma consumes only electricity and compressed air, the plasma nozzle contains several components that wear out during cutting. These torch consumables can vary in price dramatically and in some instances be difficult to obtain. It was noted during testing that the cheaper Chinese plasma cutters tended to use torch consumables faster than the other machines. One supplier charged $5 per nozzle, cup, diffuser or electrode but these were also sourced from a welding supplier for $3 a piece. The Thermal Dynamics and Hypertherm machines both had stickers on the case showing an exploded view of the cutting nozzle and the associated part numbers. Clean air extends nozzle life The quality of the workshop compressed air supply will have a large bearing on cut quality and how long the nozzle components last. Compressed air often contains moisture, especially in humid conditions, so fit an adequate dryer or water trap to the air line. This should also help remove any oil contamination in the air. Take care when using portable compressors and drain water from the tank daily. The CEA 26i featured an inbuilt compressor which worked well. While the machine was a little heavier and larger as a result, it was more portable as it only required connection to 240V. The major benefit of plasma cutting is that it consumes only electricity and compressed air, making it a far cheaper option than the oxyacetylene or oxy-lpg cutting, where gas is consumed and cylinder hire is an annual cost. Photos: Ben White and Josh Giumelli TABLE 2 Plasma versus oxyacetylene Plasma Oxyacetylene Consumes Electricity, compressed air, nozzle components Oxygen and acetylene (or oxygen and LPG) Cut Any metal including aluminium and stainless steel Steel only Cost of equipment Moderate to high Low but cylinders will need to be rented (except for LPG) and refilled Versatility Low; can only cut and gouge High; can cut, heat, braze, gouge, weld Safety Risk of electrocution, burns, eye injuries Risk of gas explosion, burns, eye injuries Portability Lighter but requires 240V and compressed air supply Very portable but heavy, can use small cylinders Distortion Low Moderate to high 18 Farming Ahead March 2008 No

4 FIGURE 1 Plasma cutter test cuts 12mm mild steel 10mm mild steel 8mm mild steel 6mm mild steel Bell Carroll Cut-40A BOC Smoothcut 40 CEA 26i CEA 46i Hypertherm 30 Thermal Dynamics 38 Unimig 40 Weldmaster 40 Weld Smart LGK 40 Kondinin Group tested each plasma cutter on thicknesses of 12mm, 10mm, 8mm and 6mm mild steel, using a machine-controlled travel speed. Travel direction is from right to left on this page. Source: Kondinin Group. 20 Farming Ahead March 2008 No

5 RESEARCH : REVIEWS PLASMA CUTTERS BELL CARROLL CUT-40A CEA 26i Price: $599 Price: $2310 Cutting performance. Recessed plastic panels protect switches. Earth clamp. Case has a strap handle. Plugs and air hose are difficult to connect. Dodgy quality handpiece and trigger. No electrical cut-out in the handpiece. Built-in air compressor. Excellent cutting performance for low current use. Easy to use and well constructed. Excellent handpiece. Electrical cut-out in handpiece. Slightly larger than other machines. Expensive. BOC SMOOTHCUT 40 CEA 46i Price: $720* Price: $2530 Long leads. Excellent cut quality. Quality handpiece with cutting guide. Electrical cut-out in handpiece. Reasonable cutting performance. Expensive handpiece and lead. Tip shroud obscures cut. * A cutting torch is extra at $341. Stable cutting arc. Quality handpiece features cutting guide. Electrical cut-out in handpiece. Inbuilt pressure gauge, water trap and regulator. Large and heavy unit. Expensive. This space is deliberately blank 22 Farming Ahead March 2008 No

6 PLASMA CUTTERS REVIEWS : RESEARCH HYPERTHERM 30 UNIMIG 40 Price: $2942 Price: $1441 Expensive. Excellent cut quality. Quality handpiece and trigger. Compact, portable unit. Poor cutting performance. Quality handpiece. Electrical cut-out in handpiece. Portable unit. Lightweight earth lead. One plug for main lead. Unstable arc. Electrical cut-out in the handpiece. Air fittings are non-standard. THERMAL DYNAMICS 38 WELDMASTER 40 Price: $3080 Price: $1336 Larger, heavier unit. Expensive. Cut quality. Built-in regulator. Carry handles. Quality handpiece with a convenient trigger. Machine is well-protected and rugged. Poor cutting performance (did not cut 12mm). Three main lead connections are fiddly. Low cost. Portable unit. Simple to use. One connection for the main lead. No electrical cut-out in the torch. Sourcing equipment Kondinin Group sourced plasma cutters for this Research Report from a range of sources. Loan units were provided by Burnback Welding Equipment services (Thermal Dynamics and CEA units), Gentronics (Hypertherm, Unimig and Weldmaster units) and BOC for the BOC Smoothcut 40. The Bell Carroll was bought on-line from Deals Direct and the Weld Smart purchased new via ebay (also available from Universal Industrial Supplies (08) ). BOC Phone: Web site: Burnback Welding Phone: (08) equipment services Web site: CEA Deals Direct Gentronics Phone: (08) Hypertherm Thermal Dynamics Phone: (CIG) Web site: Unimig Phone: (02) Web site: Weldmaster Phone: (02) Web site: WELD SMART LGK 40 Dodgy torch no electrical cut-out. Unit did not work at first. Slightly intermittent arc. Price: $550 Low cost unit. Simple to use. Reasonable cutting performance up to 10mm. Farming Ahead March 2008 No

7 Getting the perfect cut Photos: Josh Giumelli and Ben White For the perfect cut ensure the compressed air supply is dry, well filtered and supplies at least 150 litres per minute at bar (65 87 psi). The earth clamp needs to make effective electrical contact with the work. If necessary, polish off paint or rust with a grinder. For cutting at lower amperage, the tip of the plasma torch can be dragged along the surface. For higher current, use a gap of 1 2 millimetres. Drag the torch when cutting with the tip at 90 degrees to the work. If problems are experienced with the plasma arc extinguishing, check that the travel speed is not too slow or the current is not too high for the thickness being cut. Correct travel speed is achieved when the sparks below the work spray slightly away from the direction of travel (as pictured left) While the Thermal Dynamics was one of the larger machines tested, it featured handy carry handles, which also protected the front and rear panels. The Unimig handpiece had two pins which cut current flow to the electrode if the nozzle is disassembled. This prevented the operator from receiving an electric shock if the trigger was depressed accidentally. 2 4 The Weld Smart plasma cutter did not work when tested by Kondinin Group engineers. A quick look inside the case revealed a plug had become detached from the circuit board. 6 The Thermal Dynamics and Hypertherm (pictured) models both had stickers displaying part numbers for torch consumables. Kondinin Group researcher Chris Warrick used an AC/DC clamp meter to measure input and output current levels. The Bell Carroll and Weld Smart units had a cutting torch of incredibly poor quality the trigger was cable-tied into place and there was no electrical cut-out feature in the nozzle. 24 Farming Ahead March 2008 No

8 7 8 Group research and development manager Ben White monitors the performance of a plasma cutter on the test bench. Kondinin Group engineering manager Josh Giumelli operated the metal lathe carriage feed to provide a constant travel speed for the plasma cutter test bed. ABOUT THE ENGINEERS Josh Giumelli and Ben White are engineers with Kondinin Group and writers for Farming Ahead. Chris Warrick is a researcher with Kondinin Group. Contact: josh@kondinin.com.au or ben@kondinin.com.au Edited and laid out by Anne Cullinan, Farming Ahead. ACKNOWLEDGEMENTS Gentronics, Western Australia; Burnback Welding, WA; BOC. This space is deliberately blank Farming Ahead March 2008 No