A Cut Above the Rest

Plasma cutting aluminum is quick, affordable and easy if done the right way. It also offers significant advantages over laser cutting aluminum, depending on the thickness and volumes needed due to its lower equipment and operating costs.

DOING IT RIGHT: Proper gas selection is key when plasma cutting aluminum. Using different gases, such as nitrogen or argon mixes, will deliver better results. Cutting aluminum with air creates a rough edge coated with aluminum oxide. Modern plasma cutting systems can cut at very high speeds per amp, greatly minimizing the amount of heat input to the cut edge.

One consideration when cutting aluminum is excess hydrogen buildup. If using a water table, caution must be taken to ensure that explosive gases do not build up in the water table. To prevent this you can install a bubbler in the bottom of the water table to agitate the water and release the gas or a downdraft cutting bed.

Plasma cutting is a quick, affordable and easy way to cut stainless steel. Modern plasma systems allow you to select from an expanded range of gases and amperages, to produce optimal cut speeds and deliver the desired cut quality for a variety of needs. The type of stainless steel cutting table and plasma source you use makes a big difference.

FACTORS THAT MATTER:

• The build quality of your cutting machine will make a significant difference in the cut quality in the long run. Specifically, the edge quality (ripples vs no ripples) and angularity of the cut may be impacted by mechanical imperfections of the cutting table. The main difference between a low-cost air plasma system vs an industrial type of plasma cutting systems relate to the types of gases that are used to cut and the pressure at which the plasma gas will come out of the torch. Both of these significantly impact the end-result of the cut.
• You need to assess the stiffness of the gantry (Y-axis that moves over the material to be cut) and whether the construction of the rails can be affected by the heat dissipated by the cut quality.
• Cut quality may look the same when machines are brand new, heat can bow the metal construction of your table over time, which may impact the straightness of the cutting machine.
• Various machine components, like the drives, rails, and gears impact motion. Poorly assembled or poor quality components could lead to motion irregularities.

Downdraft and water tables have advantages and disadvantages. Downdraft tables are more expensive and louder than water tables, but are easier to clean and your only option for cutting aluminum. Water tables are less expensive and quieter, but more difficult to clean and not recommended to cut certain materials. Be sure to weigh the pros and cons for the applications you will be cutting and decide which fits your needs the best.

DOWNDRAFT TABLES-HOW THEY WORK

A blower pulls air out of an enclosed table while a plate is being plasma cut. This works because most of the plasma smoke is pushed below the plate. The smoke flows out of the bottom of the cut and billows outward. As long as enough air is being sucked by the blower, very little of the smoke will escape.

• Single-zone, downdraft tables with one area under the slats are usually used for smaller tables. Up to 5’ x 10’. These are easy to construct and usually feature a single duct connection.
• Zoned downdraft tables are divided into sections, or zones and used for tables larger than 5' x 10'. A duct is built down the length of the table either in the center or into the sides. This duct has openings in each zone with doors or dampeners which open and close according to the position of the gantry. When the gantry is above a zone the door opens in the zone while the remainder stay closed. This allows the blower to pull smoke only from over the zone that is being cut. This reduces the size of the blower needed and greatly increases the efficiency of the zoned table.

WATER TABLES-HOW THEY WORK

Many water tables are simply a tank filled with water. Using a water table with an adjustable water level provides a better level of smoke extraction and noise reduction.

To achieve this, a large chamber is built into the table/tank with openings inside the table along the bottom edge, which allows air to be trapped inside. Adding air into or letting are out of the chamber causes the water level to go up and down, respectively. 

At minimum, the water level controls have an air supply valve and an air release valve, which control the compressed air going into and coming out of the chamber. These valves can be simple ball valves operated by hand, or can be solenoid valves controlled by the CNC.

One of the main reasons for using a water table is for underwater plasma cutting. Some plasma torches are not designed for underwater use. Before submerging any torch verify with the manufacturer, as additional hardware may be needed to be successful. 

Options include Standard Downdraft Worktables, Standard Water Table Work Tables and Heavy Duty Water Work Tables with Slag Removal System.

In addition to unitized systems (where the gantry mounts to the cutting bed), we also offer industrial CNC plasma systems with an independent heavy-duty steel gantry riding on floor-mounted rails and columns. The style offers many options: the rails can be longer or wider than the material table to afford cutting space for hard to cut items like beams, pipe or weldments or a gantry-mounted operator station can be added for long systems.

The gantry rides over a free-standing water table or downdraft cutting bed. We can custom-build systems to work for nearly any size system.

We can build and install the cutting table or provide you with drawings for building one. If you need a custom design and we can work with you to meet your need.

Preventive maintenance can help you get the best performance, longevity and ROI out of your equipment AND avoid costly downtime. Let us help you set up the necessary checks. We also offer emergency troubleshooting support and repair for all major brands.

Learn more about our CUTTING SYSTEM REPAIR & SERVICE.

YOUR PM CHECKLIST: Here is a checklist that serves as a good starting point for a preventive maintenance program.

1. Clean the torch body. Remove the torch parts and examine the inside of the torch. Check for signs of mechanical damage to threads. Clean the inside of the torch with electrical contact cleaner and a cotton swab. Disconnect the torch from its mounting tube and slide the tube back to reveal the torch-lead fittings. Check for leaks or damage to any of the connections. Blow out any accumulated metal dust.
2. Clean the torch leads. Wipe down or blow off the entire length of the torch leads to remove accumulated metal dust and dirt. Metal dust can cause dissipation of the high voltage needed to start the plasma arc. Check for kinked or worn hoses, exposed wires, cracked fittings, or other damage. Check high-frequency shielding for proper connection to earth ground.
3. Clean out the power supply. Blow out any accumulated metal dust using clean, dry, shop air. Metal dust can cause damage to power-supply components, especially PC boards. Contactors, relays, and spark-gap assemblies can also malfunction due to excess buildup of metal dust. Check air filters on the power-supply housing; replace as necessary.
4. Check torch-cooling components. With water-cooled torches, check the coolant stream in the tank for signs of aspirated air or reduced flow. Make sure that the return flow is at the specified gallons per minute. Check that flow switches on the return line function properly—insufficient coolant flow can cause the torch to overheat. Check coolant filters and pump screens and clean or replace as necessary. Check coolant resistivity using a conductivity meter, if available. Resistivity should not exceed 10 micro-ohms for most systems. Flush and replenish coolant every 6 months.
5. Check water quality. Secondary water quality is particularly important with water-injection torches. Water hardness should not exceed 8.5 ppm or 0.5 grains. Hard water causes mineral deposits to build up on nozzles, leading to shortened life. Use a commercial water softener if necessary. Water quality in water tables is also important. If the water in the table is heavily contaminated with slag and metal dust, it can cause hard-starting of the plasma torch. It may also cause rust accumulation on the cut pieces.
6. Check plasma. Gas quality is critical to maintaining good parts life and cut quality. To check air quality, hold a clean paper towel under the torch while purging air through the system in the TEST mode. Check for water, oil mist, or particulate contamination. Check filters weekly; empty moisture traps whenever they begin to accumulate water.
7. Clean machine components— rails, gears, racks, and such.
   Use a degreasing agent and an abrasive pad to remove grease, dirt, and metal dust. Lubricate gears with dry lubricant such as graphite powder. If bearings have grease fittings, lubricate them. Do not lubricate rail sections— lubricants will attract contaminants that lead to excessive wear.
8. Level and align rails. Check joints where rail sections meet with a piece of tool steel or other precision straight edge, feeling for misalignment. Rail alignment will prevent drag on drive motors. Distances between the rails should be constant across the entire length of the system.
9. Align and adjust gears and bearings. Gears should not overlap above or below the rack. Adjust gear alignment to remove play between gears and racks. Make these adjustments for rail and cross drives. Alignment bearings should have minimal play between them and rail or crossrail surfaces. These bearings are usually mounted on an eccentric. Adjust until no light can be seen between bearing and rail surface. Do not over-tighten. With drive gears disengaged, roll the beam across the rails to check for binding. Adjust accordingly until the beam rolls free with minimal vibration and little resistance.
10. Check the squareness of the torch with respect to the table and workpiece.  Collisions can knock the torches out of square with the workpiece.
11. Check torch-mounting device. This can cause vibration that will translate into a wavy cut.
12. Check safety limits, which need to operate properly to ensure operator safety and prevent damage to the machine. Move the machine to each limit to test switches. Make sure the machine stops when each switch is reached. Inspect mechanical stops to make sure that they are in proper working order.
13. Tune the drive motors and control. Drive-motor tuning may be necessary if the motors appear to be out of synch—the torch may not return to its home position, or inaccuracies in cut pieces may develop, particularly in combination moves where both x and y drives are operating. Speeds for each axis need to be equal for proper torch positioning. Motor drift must also be minimized. As these adjustments differ from system to system, consult the manual or an authorized representative for your particular machine to tune the drive package.