FINISHING TOUCH: INTEGRATED PLASMA CUTTING
By Jim Colt
WHAT IS AN INTEGRATED PLASMA CUTTING SYSTEM?
The latest technology improvement intimately links all of the major CNC cutting machine components. Many of the functions of a plasma cutting system always operated in a sequential order for each cut cycle. On early systems this was due to the simple reason that the older relay logic was limited in its ability to distinguish one cutting operation from a different one that could be possibly more efficiently performed by using some different process sequences.
Later systems, including most CNC plasma machines built today, simply use components from a variety of different manufacturers that do not communicate on a real-time basis with each other. These non-integrated systems cut better and faster than the systems from the 1960s, but there is much room for improvement in the areas of ease of use, cut-to-cut cycle times and fine feature/hole cutting accuracy.
An integrated CNC plasma cutting system utilizes the PC-based control in conjunction with the CAM software to operate all of the major components concurrently. This dramatically cuts down any lost time between cuts. The advanced intelligence and communication between components allows for recognition of features of the metal part to be cut and applies years of expertise (based on the large CAM database) to the part program that is sent to the production floor, thereby taking the majority of the “expert operator” tasks out of the equation for shorter cut-to-cut cycle times and better fine feature/hole cutting accuracy.
COMPARING PROCESS STEPS
A job shop with a machine that does not have fully integrated capability, but does have automatic gas control as well as a high definition class plasma, has a job to cut a variety of parts with holes and features that require a high definition plasma:
(1) .dxf drawing files are imported into the nesting software: The software adds features (lead ins, lead outs, kerf width) and arranges (nests) the parts in their proper quantities on the plate to be used. The job is then sent to the shop floor. It could be sent wirelessly or the file could be manually transferred on a USB drive.
(2) Operator loads the file into the CNC monitor: They take a look at the graphic of the parts to be cut and make sure the correct plate is loaded on the table.
(3) Operator then determines the best process power level: If it is ½ in plate, for example, it could be cut at any power level between 80 amps and 400 amps. The operator chooses which process they want based upon their expertise. The operator puts the consumables in the torch and sets the correct plasma process on the CNC monitor.
(4) Operator also sets cut speeds and height control parameters based on his decision for power level.
(5) Cut process starts: The torch moves into position. The height control starts moving to detect the plate and starts the plasma preflow. The torch finds the plate surface and retracts to pierce height, then fires (after preflow times out, as much as two seconds), then indexes down to the cut height and the X-Y motion starts. At completion of the first cut segment, the torch retracts.
(6) The next segment (if the part has 10 internal holes, each hole is a segment) repeats at step 5 until all segments are complete.
(7) An expert operator will adjust the cut speed manually when cutting holes to a slower speed: This will result in better hole quality, but requires skill as the operator must stay at the control. If he leaves the speed override at the slower speed when the external contour of the cut is done, the cut quality and accuracy will be affected.
(8) Cutting nest done, unload table.
The same cutting job is performed in a shop that has a fully integrated high definition plasma cutting system:
(1) .dxf drawing files are imported into the CAM software: The programmer enters the quantity of each file and chooses the process power based on the suggestion from the expert database in the software. All lead ins and lead outs are automatically placed to avoid plate collisions. All settings for plasma power, gas flow and height control are automatically attached to the cut file. Proper speeds for each hole and contour are built into the cut file automatically based on the expert database. Plate sensing and torch retract is automatically skipped in many areas where cut segments are in close proximity. The torch preflow is started in advance during traverse from segment to segment.
(2) Operator loads the file into the CNC monitor: They take a look at the graphic of the parts to be cut to make sure the correct plate is loaded on the table. The graphic shows the consumables required in the torch (part numbers and picture) and prompts the operator to respond if they are installed.
(3) Operator pushes the start button, then performs other tasks until it is time to unload the table: The CAM database auto controls all power levels, gas flows, changes the process gasses and cut speed on holes to eliminate taper, control the height control to minimize time between cuts, avoid collisions between cuts by smart placement of start and stops so the torch does not traverse over tipped up parts, etc.
(4) Cutting nest done, unload table.
The scenarios above are simplified, but one can clearly see that with an integrated CNC plasma system the expertise comes from the CAM database.
The programmer’s job is simpler because the CAM does the difficult work of choosing the processes and lead in configurations as well as speed changes for critical features and holes. The operator’s role is simpler and quicker. Any operator (in all shifts) can cut with the same productivity and consistency as a seasoned veteran.
While the PC-based components and their digital communications links are the reason that this technology is possible, having this rapid part cutting technology is the result of the years of expert cutting data that is stored in the database in the CAM software. The data is combined knowledge from plasma, CNC motion control and height control information, as well as “seat of the pants” programming and shop floor machine operator knowledge – all gathered and fine-tuned after many years of experience.
Many shops are switching to these integrated systems for cut consistency as well as increased productivity and lower cutting costs. It is the next natural progression in the 50-year evolution of mechanized plasma cutting.
I am still trying to figure out why that plasma cutting nozzle don’t melt on the very first cut, even after 35 years in this business!
Pages: 1 2