Waterjet technology involves directing a thin stream of high velocity water at a piece of material to make a cut. Water on its own can be used, or an abrasive substance can be added creating a more powerful eroding effect. Electrical Discharge Machining (EDM) on the other hand relies on spark erosion to make cuts in electrically conductive materials. While the methods may appear similar because they both use a form of erosion there remains distinct differences between the two. So what are the differences between the two technologies? Why are many shops that were previously using EDM switching to waterjet technology? The following is a comprehensive comparison of the two:

Waterjet Electrical Discharge Machining (EDM)
How it Cuts The waterjet directs a thin stream of high velocity water at the piece of material. Pure water on its own can be used for softer materials or an abrasive can be added to cut through harder, thicker materials. The abrasive adds erosive power to the stream of water giving it greater cutting capabilities. Electrical discharge machining involves discharging an electrical current between an electrode and a piece of material. The wire is considered negative and the material positive, causing a current to be created between the two. This current essentially vapourizes and erodes the material to create a cut. The particles are then removed by a non-conductive or dielectric solution.
What Can it Cut? The highly versatile waterjet can cut an extremely wide range of material including things such as aluminum, stone, leather, acrylic, Kevlar, ceramic, lexan, mylar, granite, PVC, foam, mild steel, marble, concrete, wood, delrin, copper, brass, rubber, titanium, tempered glass, paper, and the list goes on. EDM can cut only electrically conductive materials such as steel, alloys, graphite, carbide, copper, brass, etc.
Speed Waterjets are very fast machines. They can cut pieces that may take hours to cut on another machine in minutes. The speed will vary however based on the type of material, thickness, and design being cut.

This is one of the main characteristics of the waterjet allowing it to outshine the EDM technology.

EDM works at speeds up to 10 times slower than a waterjet to remove metal and create the cut.
Accuracy The waterjet has a high level of accuracy and repeatability when cutting material. The accuracy of a waterjet ranges from +/-0.0003 to +/-0.015 inches.

In addition waterjet technology creates a very narrow kerf which contributes to its high level of accuracy. Kerf is the amount of material that is removed along the vector design line as the material is cut. This means that the waterjet can very accurately cut along the design lines.

EDM is very precise and accurate. It has a rough cutting accuracy of +/- 0.0015 inches and a precise cutting accuracy of +/- 0.0001. It has an even narrower kerf than the waterjet allowing for accurate cutting at an even higher level and very low levels of material wastage.
Heat Affected Zone (HAZ) With the waterjet technology there is no heat affected zone. A heat affected zone is a portion of the material that has undergone structural changes due to immense heat. This means that with the waterjet, the material being cut will maintain its original properties. With EDM technology there is the possibility of a heat affected zone in the material. This means that in the cutting process the piece of material may undergo changes due to the heat generated.

A heat affected zone is often invisible, but can sometimes cause a tint to appear in the material.

Set-Up Time The set up time for a waterjet is shorter because it mainly just involves weighing down the piece of material. The set up process is longer as it involves more steps and elements. This is due to the complexity of setting up the electrodes because of their high level of sensitivity.

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