FOCUS ON PLASMA CUTTING
An ESAB plasma cutter .
■ Precision electronic torch height control which can maintain the exact pierce and cut height for the process . This needs to be vibration-free , as any movement or vibration in the torch will transmit to the cut profile .
■ Safety breakaway device for the torch . This needs to be ‘ rigid ’ but also able to protect the torch over the life of the machine . These are typically either magnetic or maintenance-free pneumatic systems . Whichever style is selected , the torch needs to maintain rigidity throughout the cutting process .
■ Independent downdraft cutting tables that are not connected in any way to the motion system . By remaining stand-alone , the table ensures that vibration is not introduced into the motion control system whilst cutting .
productive cuts on a variety of different materials . The power supply is a constant current DC power source . The output current ( amperage ) of the power supply determines the speed and cut thickness capability of the system . The main function of the power supply is to provide the correct energy to maintain the plasma arc after ionization .
The arc starting circuit is a high-frequency generator circuit that produces an AC voltage used to create a high-intensity arc inside the torch to ionize the gas , thereby producing the plasma . The torch serves as the holder for the consumable nozzle and electrode , providing cooling ( either gas or water ) to these parts . The nozzle and electrode constrict and maintain the plasma jet .
“ Early CNC profiling machines were fitted with single or multiple oxy-fuel cutting heads . These were built using large heavy castings and / or structural beams and driven around at relatively slow speeds using gearboxes with large motors – and such machine designs are still available today . Modern high-speed precision plasma cutting machines need to be able to accelerate , decelerate and change direction in a smooth , controlled and vibrationfree manner . This requires a more refined machine design that includes a variety of features ,” commented Craig Walsh of Kerf Developments .
He outlined a list of key components to form what he dubbed the ‘ ultimate ’ plasma machine design . This includes :
■ A rigid bridge assembly that is strong but not excessively heavy , as the task of the bridge is to move the torch assembly around the cutting table by precisely following a pre-defined NC toolpath .
■ A reliable and predictable CNC control and motion system which can position the cutting torch exactly where it needs to be in a smooth and controlled manner . The controller must provide feedback to the user and communicate with the plasma unit to set power settings , speed feeds and gas pressures where appropriate .
■ Advanced CAM software that can take base CAD geometry and apply appropriate technology to the part to ensure consistent high-quality cutting . This should include an intelligent selection of cutting speeds for holes , slots and other internal features , together with intelligent strategies to pierce and lead in and lead out of the profile . Failure to do so will impact consumable life and cut quality .
“ While the plasma unit is central to the cutting process , it is the sum of the complementary parts that control , hold and move the plasma cutting torch that will ultimately define cut quality . When investing in this type of CNC technology , you are doing so to decrease your costs and increase your profits . A high-performance plasma cutting machine can reward you with returns of over one hundred pounds per hour if you can
The RUR 2500 plasma cutter from Kerf Developments Ltd .
ISMR July / August 2021 | sheetmetalplus . com | 17