EDM vs. EXTRUDE HONE
Electrical Discharge Machining, or EDM for short
According to www.industrial101.com/services/edm.aspx
Electrical discharge machining (EDM) is extensively used in the fine machining of complex forms and shapes in mold and die cutting, and fine hole drilling in injector cups, etc. The process can be used to machine fully-hardened metal components such as tool steel, which would not be possible using ordinary machining processes.
EDM is a thermal process which removes and re-deposits material on the object that is being machined. The area that is recast is usually much harder than the original surface with more resistance to abrasion and corrosion.
In the EDM process, there is an electrical discharge that is formed between the surface of the object and the finishing tool which can create temperatures of between 10,000 and 20,000 degrees centigrade. A dielectric field is formed that continuously removes and re-deposits material to the item's surface. Metal and elemental powders can also be introduced into this dielectric stream which will cause an alloy to be deposited.
Extrude Hone Process
According to www.gethoned.com/process.html
Extrude Hone patented the Abrasive Flow Machining (AFM) process in the 1960's as a method to de burr, polish and radius difficult-to-reach surfaces. One-way AFM systems flow the abrasive media through the work piece in only one direction, allowing the media to exit freely from the part for fast processing, easy cleaning and simple quick-exchange tooling.
A plastic, abrasive-laden polymer media is pushed through a part, such as a nozzle assembly clamped to the processing machine. The media sands away unwanted material, stress risers, and burrs from the internal passage ways creating a smooth, polished surface.
Diesel fuel injector manufacturers rely heavily on this process to improve the performance and fuel efficiency on big rigs, motor homes, and off-road construction equipment.
These two processes have one key element separating them.
1. EDM is recognized as a method to create spray holes and even enlarge pre existing holes.
2. Extrude Hone is a method of de burring and polishing and possibly enlarging preexisting passages to enhance flow characteristics.
EDM can be used as a method to modify or increase the spray hole size in a given nozzle. It is even one of the most relied on methods of forming spray holes in new diesel injector nozzles. It is not however the finish process for a nozzle going directly into service. All EDM nozzles have a by-product of re-deposited metal from the forming or enlarging of the spray holes as noted in the detailed description above. When the re-deposited metal from the forming or enlarging of the spray holes is located on the backside of the hole or inside the nozzle case it may interfere with the needle seat of the injector. That's why the OE manufactures take the extra step to de burr the holes.
How do OE's remove this re-deposited metal? Each OE has their various preferred forms of the final finishing process and all include some form of Abrasive flow, more commonly known as Extrude Hone. What varies is the media used to perform the de burring. Media can range from a liquid almost paint like consistency to the plastic, polymer media containing a special formula of abrasives we use.