Canadian Industrial Machinery asked Mitsubishi Technical Marketing Manager Greg Langenhorst to describe the role proper maintenance plays in wire EDM production.
CIM: What happens when a wire EDM is not properly maintained?
Langenhorst: If machines that are as intricate as a wire EDM are not maintained properly, they will let you down when you need them the most. It never fails that when you’re in a rush with a hot job on a short deadline, something goes down. With such a delicate process, something as seemingly minor as resin particles can lead to much larger machine performance issues.
CIM: Why is dirt such an enemy in EDM cutting?
Langenhorst: There are a lot of moving parts in a wire EDM, many of them small and delicate, and others that need to be clean to sense if things are working properly. Because the machine cuts with a shaped electronic pulse, the cutting technology is tuned to a clean machine and will change as the machine gets dirty and the contact point wears.
The cutting tool on a wire EDM is the brass wire electrode. If anything hinders the smooth operation of that electrode traveling through the machine, accuracy, and performance go down very quickly.
Users expect these machines to hold accuracies of 0.0001 inch and complain when they don’t. What we normally find when checking out these issues is lack of maintenance. All it takes to screw up an auto threading cycle is a dirty contact sensor that no longer lets the machine know that the wire is even there.
CIM: What can be discovered during a routine visual inspection?
Langenhorst: Sometimes we see faint lines on the surface of a multiskimmed part and find it was caused by a rusty bearing in the lower head of the machine. Wire breakage or reduced cutting speeds are generally caused by a lack of attention paid to the power feeders, electrical cables, and possibly water conductivity. All of these items need to be checked regularly to ensure proper operation and performance.
CIM: How can worn parts be recognized?
Langenhorst: Most machines have a maintenance timer screen that coordinates many wear items with an expected life span or maintenance interval. When they count down to zero, do the maintenance.
Other items can be checked visually, such as the depth of a wear groove in a ceramic pinch roller and dirt accumulation in certain areas. Others can be felt by turning a roller and feeling a growling bearing. Power feeder wear can be seen by lost cutting speed, and increased wire breakage tells you the wear groove is too deep and the carbide needs to be indexed.
The auto threader has a maintenance screen that keeps track of where an insert cycle fails, and how many attempts it makes to pinpoint what part needs to be attended to. A back-pressure gauge tracks filter contamination, and when it reaches a set pressure, it needs to be changed. The water conductivity is monitored by a sensor displayed onscreen that lets you know when the DI [deionization] resin needs changing.
CIM: What is happening when a machine is cutting slower than normal?
Langenhorst: That tells me there are many maintenance issues that need to be addressed on that machine. Machines, like people, can run at optimum performance even when they are considered old as long as they are exercised and fed proper consumables, with attention paid to proper upkeep.
CIM: What is an overlooked area of maintenance in EDM machines?
Langenhorst: The first item on this list is the water conductivity sensor. It checks the electrical conductivity of the water and cycles it through the DI resin to maintain a proper level.
The problem is, as this sensor gets dirty, it gives you a reading lower than the water really is, which directly affects the cutting technology, surface finish, and wire breakage. I recommend cleaning it every second filter change, or if you’ve blown a filter and dirt has gotten into the system, several times following installation of new filters to make sure there is no dirt buildup on this sensor. Second on my list is the fluid solenoids as they can accumulate dirt, like when a filter blows, and all of a sudden you aren’t getting proper water flow through the auto threading (AT) jet, suction aspirator, and wire collection system.
CIM: How should cabling be maintained?
Langenhorst: Wire electro-discharge machines cut with the flow of pulsed energy between the wire electrode and a workpiece. The frequencies are very high, peak pulse currents are very high, and any disruption in that shaped pulse causes a drop in performance. A loose feedback cable, a corroded connection, or a small cut in the rubber surface of a cable can all spell doom to your finely tuned machine.
Just as an example, some of our customers make fixtures from aluminum, not understanding that they will work great the first few days, and then oxidation sets in. Dissimilar-metal corrosion builds a resistance layer between the fixture and the grounding points, and then they don’t work anymore. I’ve taken a machine that was cutting poorly and removed, sanded, and replaced every cable connector in the work tank area and saw the performance improve. We recommend replacing the power feed and ground cables every five years to keep the current flowing and maintain new-machine performance.
CIM: What is the ideal approach to EDM maintenance?
Langenhorst: Every machine made has a recommended maintenance cycle printed in the manual. We cannot stress highly enough to follow that to the letter, and if you claim to be a high-end shop holding very high accuracies, you’ll be doing some things even more often.
Regular maintenance time is the best time you can give to your bottom line. Then you have a machine you can depend on when a hot job rolls in the door or you expect it to run through the weekend and have the job done Monday morning and not break the wire 15 minutes after you walk out the door.
MAJOR COMPONENTS OF WIRE EDM SYSTEM
Auto threading/Wire Transport System. The auto threader automatically threads the wire through the workpiece and allows for many unattended hours of operation. Worn parts and dirt in this system can lead to failure.
Fluid System. This system removes ions from the water generated by the cutting process and controls the conductivity of the water. Paper filters and improper deionization (DI) resin levels can lead to failure.
Power Transfer Components. These components bring the cutting current to the machine heads from the power supply. Any defects in the cables can lead to power loss.
Mechanical System. Mechanical components include rollers, bearings, and flush cups. Resistance to movement, dirt, and wear in any of these components can lead to failure. Bad bearings create vibration and can cause lines on the workpiece surface. Flush cups direct the high-pressure flush into the gap to remove sludge quickly. Chipped, cracked, or broken cups allow that water pressure to escape to the sides, resulting in reduced cutting speeds. Dirty components in the wire transport system can lead to clogging or inaccuracies in part quality.
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