Wire EDM Cutting: Process, Advantages and Applications
Wire EDM machining is a lesser-known manufacturing process that uses electrical discharge to vaporize metal in a highly controlled way, resulting in some intricate parts with extremely tight fits and dimensions.
As an experienced engineer, I’ve witnessed the evolution of this process firsthand and in the upcoming sections, I’ll share with you the practical knowledge, in-depth insight into the process, and the benefits of using Wire EDM machining. Stay tuned to gain a comprehensive understanding of Wire EDM Cutting.
What is Wire EDM?
Wire EDM or wire electrical discharge machining is a manufacturing process that removes material through a conductive electrode in the shape of a thin wire and a grounded workpiece.
A high discharge voltage passes through the wire that vaporizes metal instantly while being submerged in a dielectric fluid.
Wire EDM machines perform subtractive machining but are different from traditional CNCs as there’s no metal being cut. Instead, wire-cut EDM machines precisely melt material from the conductive workpiece.
How Does Wire EDM Work?
Wire EDM machining process follows the same principle as electrical discharge machining. The wire EDM process involves using a brass wire with a current and high voltage that passes through the workpiece. While the workpiece remains fixed, the cut is guided by the moving wire which produces electric sparks when it gets close enough to the grounded workpiece.
In other words, there’s a very high voltage between the tool electrode and the part and upon getting in contact, the circuit completes generating an electric spark melting tiny bits of metal in the process.
The voltage for wire electrical discharge machining is so high, that the tool electrode (wire) never touches the metal and the charge jumps to the earthed part.
The wire EDM process happens in dielectric fluid which controls the spread of the charge and flushes the eroded metal bits away from the spark gap.
Parts Of A Wire EDM Machine
Wire EDM machines are capable of machining metal pieces identical to conventional CNC machining. However, the parts, machining process, and EDM wire cutting are different from conventional cutting tools.
Here are the machine tools of a Wire EDM machine.
Electrodes
In wire EDM machines there are two electrodes. The cathode is the metallic wire that conducts current and the anode is the fixed workpiece. This is usually done by grounding the workpiece inside the wire EDM machine.
In the industry, they’re called
Tool Electrode or Wire Electrode
Cutting wire made of conductive metal usually brass (Cathode)
Controlled movement by the machine
Workpiece Electrode
Conductive material being cut (Anode)
Material is removed from the workpiece electrode using electrical discharges from the tool electrode.
Wire
Wire is the cutting tool of an EDM machine. There are different diameters of wires available that can cut through different thicknesses of workpiece materials.
Wire EDM machines are capable of cutting complex shapes up to 0.0001” accurately. To put it into perspective, the wire can be 25 times thinner than a human hair. This close accuracy and tolerance is the reason Wire EDM cutting is also called ‘0 tolerance machining’.
The wire material and conductivity affect cutting speed. They can also impact the surface finish and for these reasons, different wire-cut EDM machines have different wires.
Brass Wire
Brass is typically used in wire EDM machines because it is electrically conductive. Brass, an alloy of zinc and copper is also cost effective and works on a wide variety of materials.
Coated Wire
Coated wires have the usual brass or tungsten wire, coated with another metal like zinc. This is mainly done to improve cutting speeds, enhance the tool life in the case of tungsten, and improve the wear resistance for mass production.
Tungsten Wire
Tungsten wire exists for wire cutting because it is a hard and tough electrode. The high tensile strength makes it useful for cutting hard materials of a thicker clearance in wire-cut EDM.
They offer a better surface finish at a higher price compared to brass wires.
Working Table
Working table of a wire EDM machine is designed with careful consideration. The material used is mostly cast-iron or granite. It is the heaviest component in a wire EDM machine to minimize vibrations and unwanted movement.
The working table also houses the vise or fixture where the workpiece is clamped and it also holds the reservoir for deionized water.
In dynamic working tables, the working table can translate in the X, Y, and Z axes using stepper motors that control the movement using numerical control. This results in taper designs and complex shapes.
CNC Control
Wire EDM machines have CNC control built in. The CNC can control axis movements, wire path, and cutting feed. This is similar to any conventional CNC machine control and the process is completely automatic.
Dielectric Medium
The dielectric medium controls the charge spread during electrode contact. This prevents unwanted cuts and unnecessary metal vaporization.
Dielectric liquid also flushes out the tiny metal pieces that are melted and helps with a smooth surface finish. Deionized water is the most common dielectric fluid.
Power Supply
Wire EDM machines have a unique power supply. Since the cutting method primarily relies on current and voltage, the power supply unit of wire electrical discharge machining needs to regulate the voltage, frequency, and the amount of charge that contacts the workpiece.
Conventional power supplies deliver constant power at fixed voltages.
Wire EDM Materials
Despite the high voltage and close precision of wire cutting EDM process, the machining process is only worth the cost and complexity for a few industrial applications. These applications most commonly use the following materials.
Aluminum
Aluminum is a common metal that is machined using wire-cut EDM. It is relatively softer than others on the list, but wire EDM can achieve tight tolerances which is important for aluminum parts in the aerospace industry.
Brass
Brass is essentially a conductive material, made of copper and zinc. It is soft and can be easily cut into the desired shape.
However, using electrical discharge machining on soft metals like brass, and aluminum is not cost-effective. Such metals can be cut into desired shape by conventional machining operations.
Steel
Steel, specifically hardened steel is the most common material machined with wire EDM. Steel is machined using wire electrode because of its use in extrusion dies, injection molding inserts, and precision tools.
Titanium
Titanium is a relatively harder-to-machine material, but because it can conduct electric current, it is often cut using electrical discharge machining EDM. Since spark machining of large titanium workpieces generates considerable heat, proper flushing, and dielectric fluid must be used.
Tolerance of Wire EDM
Wire EDM offers unmatched tolerance when compared to CNC machining, laser cutters, and plasma cutters. This is because wire edm does not apply any mechanical forces to the part, reducing the need for polishing and post-machining surface finishing.
What Tolerance Can Wire EDM Achieve?
Electrical discharge machining is capable of achieving precision tolerances of up to ±0.001 mm and standard tolerances of up to ±0.005 mm.
Such precision allows wire EDM machining to work on complex shapes that are necessary for automobile parts, aircraft components and applications dependent on dimensional accuracy.
Advantages of Wire EDM
There are many reasons manufacturers prefer EDM process.
Cost-effective
Electric discharge machining is an expensive machining process, but it is cost-effective in many applications.
For jobs demanding high precision, intricate geometry and increased production volume, electric discharge machining EDM remains cost-effective, when compared with standard CNC which may require more man hours, machines, and different tool types.
There’s minimal material wastage which can make it cost-effective for medium production runs specifically for machining expensive materials. It offers quick turnaround times and the tooling cost is not significant, since it’s just a conductive wire.
Minimal distortion
Wire EDM works with hard materials and soft materials alike. Since there’s no force exerted on the workpiece (spark eroding machining process) it can cut and shape even the most fragile and thin metal pieces.
High production speed
For prototyping and scaled production wire EDM process delivers quick turnaround times. This is due to
Small setup time and CNC-programmed control
Exceptional surface finish (eliminates grinding and polishing)
Close tolerance (doesn’t require any further tooling.
Extreme accuracy
Accuracy of a machining process is linked to the cutting tool. Since an edm wire can reach diameters of 0.01 mm it can achieve extreme accuracy and precise cuts.
Part complexity
Wire EDM is an extremely modifiable machining process. Wires can be aligned at an angle, the parameters can be adjusted at different stages and it can work in multi-axial planes. This allows wire EDM to reach even the smallest details in designs for applications in aerospace.
Applications of Wire EDM
Aerospace Industry
The aerospace industry is a given for wire edm process application. Since intricate parts with thin walls and tight cavities require soft cutting tools, thin wires with great accuracy offer the best solution.
This is important for applications like turbine blades where even the slightest dimensional or surface discrepancy can ground air operations. Other uses include tiny nozzles and engine components.
Medical Industry
Wire EDM is widely used in manufacturing medical equipment. Dental implants and surgical instruments are just a few uses of wire EDM.
Dental implants employ the majority of EDM process applications since they are already miniature in size and require a cutting tool with the smallest diameter for perfect alignment.
Manufacturing Industry
Wire EDM is highly employable in die-making processes. Plastic injection molding is a technique that fills a negative mold with molten plastic to produce millions of pieces.
Because of the high production, wire EDM offers reliable and accurate machining of injection molding dies of the desired shape.
Electronics Industries
When thinking of electronics we often miss the tiny components inside those devices. Electrical components like connectors, lead-frames, and other micro-components housed inside the casing are often made by wire EDM.
What Is the Difference Between EDM and Wire Cut EDM?
Essentially electrical discharge machining edm process and Wire cut EDM have the same working principle. They both remove material using spark machining and different applications require different EDM manufacturing processes.
Wire EDM offers a free range of motion, better parameter adjustability, control over axes and the ability to machine different shapes using the same tool i.e. the wire. Conventional EDM relies on different shaped tools which are often limited in their range of motion and are slower when working on tapered designs and intricate shapes.
Here are the key differences between EDM and Wire EDM.
Electrode: Normal EDM uses tool electrodes in diamond, round, cylindrical, or disk shape. The electrode translates in 3 axes, sparking as it contacts the workpiece and removing material.
Wire EDM uses a thin wire and the electrode and the workpiece are submerged in dielectric fluid which guides the spark and removes debris.
Accuracy: Conventional EDM is less accurate than wire EDM. This is largely because the disk or diamond-shaped electrode is made on a CNC machine which limits its accuracy to the accuracy of the tool.
Wire EDM can have diameters less than 0.002 mm which gives them an edge in accuracy.
What Other Types Of EDM Processes Are There?
Sinker EDM
Sinker EDM works by eroding conductive metal using a high voltage and in turn, giving the workpiece the desired shape. The electrode in sinker EDM is the positive image of the desired cut which slowly sparks away material and gives it the desired cut and shape.
The electrode is often made of graphite and this EDM process is also called die-sinking.
Hole Popper EDM
Hole drilling EDM or hole EDM has a single designated purpose of eroding accurate holes into the workpiece. Hole EDM uses a tubular electrode that erodes base metal to create holes.
Conclusion
Wire EDM serves as an upgraded, more precise and versatile process of conventional EDM that uses high voltage to erode bits from conductive materials. It uses an EDM wire as an electrode that shapes the workpiece in a dielectric liquid which removes debris from the spark gap and controls the spark.
Wire EDM is mainly used in aerospace and medical equipment manufacturing where precise manufacturing processes are crucial for the accuracy and complexity of the shape. It is one of the most high-tech machining methods available in the market and reduces material wastage making it cost-effective in its applications. The only real con of wire EDM is the wire burning or wire electrode breaking which can also be recycled for further improvement.