Speed and control optimizeEDM

Speed and control optimizeEDM



Mitsubishi's EA 12 sinker EDM partners high-speed jumping with an intelligent, active adaptive control that competes with linear motor EDM

Mitsubishi's MF Adapter function, together with its software reaction system, called Fuzzy Pro 3, optimizes the company's high-speed jump for sinker EDMing.

Machining time comparison between Mitsubishi's system and other competing systems.

In order to improve a sinker EDM's overall performance, machines must have reaction software that is fast enough to keep up with extreme speeds. While many manufacturers have increased the jump speeds of their EDMs, these machines may lack the intelligence that is necessary to optimize machining conditions.

Although linear EDM can reach jump speeds of 50,000 to 70,000 mm/min, this technology tends to put the cart before the horse. Sludge builds up around the top edges of the burn cavity with these types of machines. This forces operators to slow the jump to keep sludge out of the gap, which, in turn, makes a non-linear, high-speed jump with the right adaptive control more effective.

Mitsubishi has introduced an adaptive control with a high-speed jump function that accomplishes jump speeds of 3,000 mm/min. This function, however, is just one advancement made to the company's adaptive control system, which optimizes the EDM process just as effectively as linear technology would. Its MF Adapter is another.

Unattended sinker EDMing requires that the best spark be made at any given moment during any given job. To accomplish this, Mitsubishi's MF Adapter function controls and monitors each individual spark at microsecond speed. It translates spark information into digital signals and passes them to the software-reaction side of the machine's controller. Called Fuzzy Pro 3, this software system adjusts the machining settings in degrees following burn trends to efficiently remove the most material possible.

Another control advancement is a primary function that monitors the initial IP (peak current). This optimizes the steps from startup machining through the first E-condition. Such an advancement improves electrode life.

Plus, electrodes with complex geometries enter smoothly into cavities without extreme wear or current-density problems. Machining area sensors then track the changing surface area of the electrode to gage how much power is necessary for the best efficiency level.

In addition to these benefits, the Mitsubishi control features an upgraded Orbit Pro software that oversees orbits of the electrode within the cavity. This new, orbital movement prevents the electrode from stalling or stopping in problem areas by displacing dielectric oil and freeing sludge that may be trapped in the corners.

As a Mitsubishi EDM removes workpiece material, its adaptive control actively adjusts IP, jump speed/ distance, and off-time based on the level of gap contamination and stability. Such preset levels of adaptive-control activation have been around since the introduction of conventional EDMing, but they were improved by the introduction of CNC EDMs.

Shops with EDMs running on older, passive-type adaptive controls must reduce their machining efficiency by as much as 30 to 40% during unattended operations. This is because the control is undependable running at optimum speed unless supervised by an experienced operator. Today's adaptive controls, however, are more active systems that let machines run at 100% efficiency during unattended hours.

Instead of waiting for conditions to reach a preset unstable point, as with a passive or linear-type adaptive control, Mitsubishi's non-linear system recognizes degrees of instability and makes frequent adjustments. In essence, the Artificial Intelligence database, compiled by the company's experienced operators, joins with the machine's ability to monitor power output, sludge accumulation levels, and jump speed. The result is a system that makes expert decisions to optimize machining efficiency any time the machine is running.

High-speed jump and unattended operation
Flush burning can disrupt the EDM process if a shop's goal is unattended machining. Reason being, a normal flushing setup may require a complicated set of flush lines spraying from different directions and operating from a programmable flushing manifold. Other setups may involve drilling holes through the electrode and flushing through it to control sludge buildup during unattended operations. In addition, adding a toolchanger, which is common for unattended machining, limits the type of flushing used.

Further still, hydraulic forces also work against shops doing unattended sinker EDMing. These forces restrict the dielectric oil as it moves through the cavity to wash away sludge, which has a direct affect on how fast the electrode travels. It's a matter of physics. Liquid does not compress, but must displace.

Working in conjunction with high-speed jump, active adaptive controls monitor the reaction-force sensor that watches the hydraulic force in the gap. This function then compensates for any extreme hydraulic forces being applied to the electrode and workpiece during the jump cycle. These detrimental forces are especially prevalent when machining large cavities.

Most cavities trap fluid, which is then displaced when an electrode plunges back into it. An EDM's powerful servomotor can produce several tons of force during this down-segment of the jump cycle. Jump controls let this necessary displacement occur while the active control's reaction-force sensor makes the necessary adjustments. Without this capability, large electrodes may not burn to the proper depth.

Most shops with sinker EDMs agree that no extra flush makes for a more simple setup and operation. But what happens to speed? In order for no-flush burning to keep up the same speed as flush burning, electrodes must jump in and out of the cavity.

The up-and-down motion of the electrode creates a mechanical flushing motion by pumping the clean dielectric oil through the cavity. Evacuating the electrode from the cavity and returning it quickly pumps out both oil and debris in a short time. This solves sludge problems created in deeper cavities.

High-Speed Jump works well in the machining of ribs where contamination tends to concentrate in the smaller areas. Correct rib machining requires great care, not just brute jump speed. Optimizing a high-speed jump function's speed and distance and combining it with a good decisionmaking software create the ideal conditions for fast, accurate rib burning on a sinker EDM.

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