Electrical Discharge Machining (EDM) in Contract Manufacturing
Electrical discharge machining (EDM), the application of the electrical discharges under a controlled mechanism to remove metal, has long been a favorite for high accuracy machining applications where conventional metal removal is difficult or impossible.
The early-day EDMs were being used to remove broken taps and drills. The EDMs disintegrated taps with electrodes, burning a hole in the center of the tap or drill, leaving the remaining fragments that could be removed. This saved workpieces and very expensive parts from being scrapped. This process is still used today to make precision cavities primarily for the mold making industry.
Industrial EDM machines are commonly grouped into three categories - Die Sinker, Hole Drilling, and Wire. In this blog we cover some basic knowledge of wire EDMs which are often seen on the production floor of a contract manufacturer.
Wire EDMs for Mold Making in Plastic Injection
Wire EDM technology was developed around the 1960s for making molds from hardened steel. It uses a spool of thin (brass) wire as an electrode that’s continuously moving to present a fresh discharge path.
An electrical current passes between an electrode and a workpiece which are separated by a dielectric liquid. The dielectric fluid acts as an electrical insulator until enough voltage is applied to make it an electrical conductor. The thin wire moves in a carefully controlled pattern, causing sparking to occur between the wire and the workpiece. The heat from a series of electrical sparks, estimated at around 15,000° to 21,000° Fahrenheit, erodes away a tiny bit of material that is vaporized and melted from the workpiece to form a desired final shape for the steel mold.
Wire EDM machines normally use deionized water, into which only the sparking area is immersed. The dielectric fluid serves three critical functions:
1.) It controls the spacing of the sparking gap between the electrode and workpiece.
2.) It prevents heat build-up in the workpiece and preserves finished parts’ dimensions and positional accuracy.
3.) It removes EDM chips from the cut through the flushing nozzles.
Advantages of EDM
There are several advantages of EDM compared to traditional machining technologies such as CNC milling.
• Materials - It can machine anything that is electrically conductive regardless of the hardness, from common materials such as steel, aluminum, copper, and graphite, to exotic alloys such as titanium, carbide, and conductive ceramics.
• Accuracy - The process is capable of producing parts with extremely high accuracy (+/- 0.0005” or +/--0.012mm or finer). This is essential for injection molds with complex geometry that require strictest tolerances.
• Excellent surface treatment - The advantage of EDM is that it produces excellent surface finishes, thus reducing the need for post-processing or surface treatment. The process leaves no residual burrs on the workpiece and so eliminates the need for subsequent finishing operations.
• Increased productivity - EDM machining can be performed unattended, allowing operators to do work in other areas. So the direct labor and manufacturing costs are typically lower for EDM than other machining methods.
• No damage to the workpiece - Since EDM is a non-contact machining process, the fixture requirements for cutting small parts are considerably less burdensome compared to those of a standard CNC mill, thus preventing damage or distortion to the workpiece.
Today there are great demands for higher precision in machining, ease of operation, and increased longevity of both the parts, and the machines that make them. Wire EDM can satisfy and meet these needs. The precision machining of an injection molding with complex geometry can be easily accomplished with minimal operations
In summary, if you are looking for a machining process that’s accurate, precise and stress-free—at least on the workpiece—EDM could be just what you need.