What are the criteria for selecting Electrochemical Grinding (ECG) as a process?
The most common reason customers choose ECG is for the burr-free quality of the cut. If a part is difficult or costly to deburr, then ECG is the best machining option. On materials that are difficult to machine by conventional methods, work harden easily or are subject to heat damage from machining. ECG is the solution. The very low cutting forces in the ECG process make it ideal for thin wall and delicate parts.
How does ECG equipment differ from conventional grinding?
ECG is a combination of electrochemical (anodic) dissolution of material in combination with abrasive action. The metal is decomposed to some degree by the DC current flow between the conductive grinding wheel (cathode) and the work piece (anode) and the presence of an electrolyte solution.
What materials can be cut with ECG equipment?
Almost any conductive metal can cut with ECG equipment. Alloys high in nickel, chrome and cobalt such as stainless steels, Inconel and Hastelloy cut very freely with ECG Equipment. Titanium, nickel/titanium, zirconium and tungsten can also be cut effectively.
What tolerances can be achieved with ECG Equipment?
This depends greatly on the material being cut, the size and depth of cut and the ECG equipment parameters being used. On small cuts, tolerances of .0005″ (.013mm) have been achieved but generally tolerances of less than +/- .001″ (+/-0.05mm) are not practical.
How does ECG equipment compare to EDM, laser, water-jet and other non-traditional technologies?
EDM and laser both cut metal by vaporizing the material at very high temperatures. This results in a recast layer and a heat affected zone on the material surface. ECG is a low temperature process that never results in metallurgical damage. ECG is usually much faster than an EDM cut but typically less accurate. Laser cutting can be very fast and accurate but it is normally limited to thin materials. Water-jet cutting can be quite fast and usually leaves no metallurgical damage but the consumable costs can be very high and the cuts are limited to jigsaw-type shapes, much like Wire EDM. In most cases, ECG is a more accurate process than water-jet.
How long do wheels last?
: The ECG process causes much less wheel wear than conventional abrasive grinding. The actual amount of wheel wear will vary depending on the material being cut and the ECG parameters. Wheel wear is expressed as a ‘G ratio. This is the ratio of material removed divided by the amount of wheel consumed. For example, if 10 cubic inches of material are removed and 2 cubic inches of wheel was consumed then the ‘G ratio is 5. Using a standard aluminum oxide electrolytic wheel cutting stainless steel tubing, a ‘G ratio of 10 to 15 would be typical. A diamond or super-abrasive wheel may give ‘G ratios as high as 100.
What is the composition of the grinding wheel?
ECG wheels are classified as either conventional or super abrasive. A conventional ECG equipment wheel is an abrasive (aluminum oxide, silicon carbide, or combination), copper and a resin bond. Super abrasive ECG equipment wheels are diamond or CBN in a metal bond or conductive resin bond form.
What electrolytes are available for use with various materials and how do you select the correct electrolyte?
Everite has a number of different electrolytes available for different alloys. Most electrolytes will work on a variety of materials but each one has advantages and disadvantages. The main issues are aggressiveness of the cut and the amount of corrosion that can occur on the machine or fixturing. A very aggressive electrolyte can remove metal faster and result in less wheel wear but may cause excess erosion of the fixturing or will not permit close tolerance cutting. A very mild electrolyte may be ideal for close tolerance grinding but may require more frequent wheel dressing.
What are the waste disposal issues with different electrolytes?
Electrolyte is sold as a dry powder and is mixed with water. Once mixed it becomes a waste that can not usually be disposed of in the sewer because of the high salt levels. When electrolyte is used for cutting, the fluid gets contaminated with grinding sludge (metal particles, abrasives and metal hydroxides). Electrolytes with chelating agents will absorb metal into the solution and will produce less sludge. Eventually the electrolyte becomes saturated and must be changed. Non-chelated electrolytes will not absorb metals and will stay clean longer, but require more advanced filtration to handle the increased amount to sludge. In almost all cases, used electrolyte must be treated as a hazardous waste and handled in accordance with the relevant environmental regulations.
Is the ECG process compatible with the recently revised OSHA regulations on airborne hexavalent chrome?
Certain types of electrolytes can produce hexavalent chrome when cutting stainless steels and other metals with chromium as an alloy. The amount of hexavalent chrome in the electrolyte will increase as more metal is cut and the electrolyte becomes more contaminated with metals. As electrolyte is applied to the rotating grinding wheel a mist is created. The mist should be contained within the machine guarding and not allowed to enter the work area. A properly working mist collector is critical to evacuate the machine cabinet and prevent mist from exiting the guard during part loading and unloading. Even when cutting materials that do not produce hexavalent chrome, a mist collector is still required to protect the operator and surrounding equipment from exposure to the high salt level.
Is there information available specific to tube cutoff machine setup and troubleshooting?
Everite application engineers are available for technical help by phone or email.
What is the typical operating voltage during grinding and does material type affect the voltage?
Voltage is typically 4-15v, with 7-10v being the most common. Increasing DC voltage increases the electrochemical activity. When voltage is too high (the spark over point), electrical arcing will occur and the process becomes EDM. This is never recommended. Voltage selection is sometimes material dependent, e.g. copper may require a longer voltage because it is highly conductive, but mostly voltage is adjusted to optimize other cutting parameters.
How does the customer dispose of the used solution?
Spent electrolyte must be disposed of as a hazardous waste because it contains dissolved metals, grinding sludge and oxidizers. Disposal costs can be greatly reduced by distillation or evaporation of the water, thereby reducing disposal volume. Electrolyte life is greatly influenced by the level and type of filtration. Electrolyte can be used for long periods of time if it is kept clean and adjusted for concentration.
Is it true that the material removal is about 90% electrochemical and 10% abrasive?
The 90/10 electrochemical/abrasive rule is a myth. The ratio of electrochemical-to-abrasive cutting is widely variable by parameter settings. Cutting at two volts would give a predominately abrasive cut. However, if it produces the desired result it should be used. A proper and effective ECG equipment setup should focus on maintaining the correct balance of productivity, wheel wear, tolerance, surface finish and metallurgical condition.
Is there a shock hazard when operating the machine?
Since the voltages are low, the risk of shock is minimal but proper procedures should always be followed.
What is wheel conditioning and why is it necessary?
When a copper/resin/abrasive ECG wheel is dressed with a diamond tool, the copper in the wheel gets smeared into the voids on the surface (between the grains of abrasive). This creates a thin film of copper that will short out to the workpiece. This film will naturally burn off during the cut, but the high amperage arcing that occurs could damage a sensitive part such as a thin wall tube. The wheel can be conditioned prior to grinding by shorting the wheel to the fixture using a copper ground cable. Conditioning the wheel with a ground strap basically burns away that film. The cable is sacrificed instead of the work piece. On a deep cut, conditioning may not be necessary. The wheel will short out initially, but by the time the wheel is fully engaged in the cut the wheel is already conditioned.
What is overcut and how does it affect the form and tolerance of a cut?
Overcut is defined as material that is removed beyond the shape of the grinding wheel. The overcut results from the path of the electrolyte around the wheel within the electrical field created in the cut. A higher voltage creates a larger electrical field which allows the electrolyte to remove more material beyond the wheel profile. The electrolyte flow and pressure also have a large impact on the form of the cut. Higher flow will allow the electrolyte to remove more metal within the electrical field than a lower flow. The ideal flow pattern would be a uniform film of electrolyte in the exact shape of the wheel in the cut. However, this can never be fully achieved because of the high wheel speeds and centrifugal force of the electrolyte on the wheel. In addition, the profile of the cut will usually disturb the electrolyte flow to some extent. A correct nozzle can be critical to getting the correct flow pattern on the wheel.
How can I reach Everite?
Everite’s customer service staff is available to answer any questions you may have. We can be reached at 856-330-6700, Monday through Friday from 8:00 a.m. to 5 p.m., Eastern Standard Time, or via email at firstname.lastname@example.org.