Burr Free Electrochemical Grinding
The Burr Free Electrochemical Grinding process is a hybrid method of metal removal combining Abrasive Grinding and Electrochemical Machining (or ECM). ECM is a non-traditional metal removal method developed many years ago based on Michael Faraday’s laws of electrolysis. Faraday found that metal can be dissolved when DC current flows across a small gap in the presence of an electrolyte solution. The current flow between two electrodes, the Anode and the Cathode, cause the Anode to dissolve.
In an Electrochemical Grinding system a conductive grinding wheel is used as a Cathode and the workpiece becomes the Anode. The metal is removed both by mechanical abrasive action and the gentle electrochemical dissolution of the metal. The result is that metal can be cut with very little heat, stress or mechanical deformation. This results in a cut without burrs and eliminates the typical deburring operation required of most other machining operations. Burr Free Tube Cutoff is a typical application
Figure 1 shows a typical Electrochemical Grinding system. The DC (+) is connected to the fixture holding the material, in this case stainless steel tubing. The DC (-) is connected to the grinding spindle via contact brushes and a commutator. The conductive grinding wheel acts as the Cathode and dissolves the Anode material as the abrasives remove the metal oxides. Some amount of mechanical grinding is almost always present. The ratio of mechanical grinding to electrochemical reduction is fully variable by adjusting the system parameters. A common misconception about ECG is that the wheel does not contact the workpiece. The wheel is almost always in contact with the part being cut but the load placed on the wheel will vary depending on many factors.
The electrolyte is a key part of the Electrochemical Grinding process. The electrolyte is pumped from a reservoir tank to the point of the cut through a nozzle much like coolant in conventional grinding. Unlike coolant though, the electrolyte flow will remove some material. The electrolyte must be applied correctly to insure accurate cuts. For most metals a solution of Sodium Nitrate (NaNO3) and other chemical additives is used. Standard table salt (NaCl) is generally too corrosive and is only used on very difficult materials. Sodium Nitrate solutions such as Tridex TX-1 are easy to use and require little operator attention.
The primary variables in the ECG process are voltage, electrolyte flow, feed rate and wheel type. A brief outline of the variables and their influence follows:
Voltage – Low voltage results in less electrochemical action and more abrasive cutting with minimal deburring. Higher voltage will cause more electrochemical and less abrasive action. Too much voltage can cause electrical arcing. A properly designed DC power supply is critical to get accurate cuts and good surface finish. Tridex machines use only the latest Solid State DC power supplies for precise voltage control under all cutting conditions.
Electrolyte Flow – Enough flow must be used to create and electrochemical cell at the point of the cut and complete the process but too much flow may remove metal beyond the desired cut area. Tridex machines have advanced flow controls to provide the correct amount for the cut. Tridex can supply all your Electrolytes for grinding and cutoff.
Feed Rate – Feed rate in ECG is similar to creep feed grinding generally in the 0.5 to 4 inch/minute (13 to 100mm/minute) range depending on size of the cut and cross section of the material. A precise servo driven feed is best for a uniform cut and accuracy. A slow feed will allow more electrochemical action and lower cutting forces. A faster feed will increase the amount of abrasive action in the cut.
Wheel Type – A variety of wheels are used in the ECG process but all must be conductive. The standard ECG wheel is usually Aluminum Oxide and Copper in a resin bond. These are economical, are easily shaped and give very good burr free cuts. Most burr free tube cutoff is done with resin-copper AlOx wheels. Diamond, CBN and Ceramic abrasives are also widely used in conductive resin bonds. . Metal bonded wheels can also be used but are mainly for Tungsten Carbide applications. Wheel life is usually very good with the ECG process. In many cases the wheel will last 30 to 50 times longer than in standard abrasive or creep-feed grinding. Because wheel wear is low, truing and dressing is kept to a minimum and in some cases not needed. ECG wheels can be dressed into complex shapes for form grinding in many applications. Tridex is your best source for all your ECG wheel requirements.