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ECM FAQ
Q How is metal removed electrochemically?
Q What is a typical cycle time?
Q Is the cycle time material dependent?
Q Do I need a special shaped 'cathode' (a.k.a. electrode) tool developed for every different part feature?
Q What materials are the 'cathodes' made from?
Q What is the life of a 'cathode'?
Q Do I need a special-shaped 'anode contact' developed for every different part feature?
Q What materials are the 'anode contacts' made from?
Q What is the life of an 'anode contact'?
Q What happens if a burr (anodic + charge) contacts the 'cathode' (- charge)
Q What protection devices are offered to avoid short circuit tooling damage?
Q What is the typical gap between workpiece (burred edge) and 'cathode'?
Q Explain 'triple deck' tooling design
Q Explain 'building block' tooling
Q What would a typical fixture cost?
Q Should customers be encouraged to make their own tooling/fixtures?
Q What tooling methods are offered with the Miniburr product?
Q How critical is electrolyte flow?
Q What happens to the burrs? Are they burned up? Are they dissolved?
Q How does the process/machine know when the burr is gone? Or edge sufficiently radiussed?
Q What kind of edge radius can we expect and is it a 'true radius'?
Q What is the largest burr you can remove?
Q How do we decide if rough mechanical pre-deburring is required?
Q Are there any part size limitations
Q Are there any material limitations? Materials more ideal than others?
Q Are other features/surfaces, nearby to the edges being deburred, adversely or positively affected?
Q What is 'undercutting?'
Q What kind of finish can we expect from ECM Polishing? Give examples.
Q What kind of surface finish can we expect from EC-Micromachining?
Q What kind of tolerances can we hold with ECM and EC-Micromachining?
Q Will a parts exposure to ECD/ECM affect its hardness?
Q Is part hardness a factor in process speed, surface finish, and other results?
Q Will ECM/ECD induce, remove, or otherwise impact part stress?
Q Will ECM/ECD remove a recast layer?
Q Are there other metallurgical issues of concern, e.g. hydrogen embrittlement, intergranular attack, etc.?
Q How important is part surface cleanliness to the process results?
Q How important is electrolyte cleanliness to the process results?
Q How is filtration managed?
Q What is considered normal operating temperature?
Q How important is it to maintain electrolyte temperature?
Q Does the electrolyte require routine replacement?
Q What are the types of electrolytes available?
Q What is a 'power supply?'
Q Are there differences in types of power supplies employed by our various ECM divisions?
Q What are the pros and cons of various types of machine construction (steel welded frame, fiberglass, stainless welded tube frame)?
Q Is ECD/ECM expensive to operate? What are the cost considerations?
Q Is this salt-water process likely to affect surrounding equipment, buildings?
Q The machine produces hydrogen and oxygen gas and electrical charges are present on exposed conductors. Are there any operator health or safety hazards to be aware of?
Q Does the machine operator require special training?
Q What are the general preventative maintenance issues to be considered?
Q What is the expected life of a ECD/ECM machine?
Q Help me put things in perspective; if TEM, AFM, and ECD are all effective for internal deburring, in what circumstances is ECD the process of choice?
Q TEM DISQUALIFIERS
Q ECD DISQUALIFIERS
Q AFM DISQUALIFIERS
   
A
How is metal removed electrochemically?
Electrochemical metal removal is often thought of as 'reverse electroplating.' Instead of applying metal to a part as in electroplating, we are removing metal using the same principles of metal ion transfer found in an electrolytic plating cell. The similarities end there. ECD/ECM is selective metal removal requiring the use of a cathode (a.k.a. tool or negative (-) electrode) that conforms to the edges being deburred or features being machined. The electrolyte is flowed through the gap between part (made (+) anode) and cathode (-) causing the metal to disassociate itself from the edge or surface that is adjacent to the cathode. The underlying metal is unaffected but the metal removed forms a hydroxide when it combines with the water in the saline electrolyte typical of ECD/ECM processes. This hydroxide can be extracted through mechanical means (filter, centrifuge, settling) and the process can continue. A low-voltage, high-amperage power supply provides the electrical input to the anode (part) and cathode (tool).
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A
What is a typical cycle time?
Deburring - 15 to 30 seconds
EC Micromachining - 2-5 sec
EC Polishing - 2 sec - 4 min
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A
Is the cycle time material dependent?
In general no, although there are some slight differences in reaction time depending on the material composition that could have some effect on cycle time.
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A
Do I need a special shaped 'cathode' (a.k.a. electrode) tool developed for every different part feature?
Yes, conformal shaped tooling is a requirement of the process with few exceptions.
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A
What materials are the 'cathodes' made from?
Typically they are made from brass or stainless steel
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A
What is the life of a 'cathode'?
Actually, the cathodes should not wear out from the process. They may become damaged from mishandling or after repeated minor short circuits. Protection circuits built into most machines avoid major, catastrophic, short -circuits.
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A
Do I need a special-shaped 'anode contact' developed for every different part feature?
Not usually. Anode contacts must have sufficient surface area to carry the current and should be placed on smooth surfaces of the part for best contact. Anode contacts are typically one or more per part and are usually round spring-loaded devices.
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A
What materials are the 'anode contacts' made from?
Typically these are made from copper, copper-tungsten, zirconium shaft with platinum tip, or over-molded copper-platinum. These are listed in order from most to least maintenance required and from least to most expensive to produce.
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A
What is the life of an 'anode contact'?
Copper or copper-tungsten anode contacts can be expected to last for tens of thousands of cycles provided they are kept in a dry condition. If they become wet, the life will be very short - perhaps a couple hundred cycles. Copper-platinum anodes will outlast copper and copper-tungsten particularly when coupled with the 'triple-deck' tooling design.
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A
What happens if a burr (anodic + charge) contacts the 'cathode' (- charge)
Minor Short-Circuit
Upon start-up most machines include a precycle short-circuit detection mode. Once the part passes this test the machine goes to full current. If the part does not pass the cycle is interrupted and the operator has the chance to replace the bad part. If a burr or chip moves into the gap during the deburring cycle a minor short circuit may take place. The operator may notice a small spark. This is not dangerous and will often clear itself without shutting the machine down.

Major Short Circuit
In the event that a large chip becomes lodged between the part and tool and is too big to burn up, it will draw a high current and interrupt the machine cycle (not all machines). The speed with which this happens will determine whether or not there is damage done to the part and tool. Machines are different in this respect
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A
What protection devices are offered to avoid short circuit tooling damage?
Precyle short circuit detect and machine interrupt
In-cycle short circuit detect and machine interrupt
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A
What is the typical gap between workpiece (burred edge) and 'cathode'?
Deburring .030'-.040'
Micro Machining .001'-.003'
Polishing .030 - .050'
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A
Explain 'triple deck' tooling design
Machines used in high volume, poor maintenance environments will soon suffer from corroded electrical cable connections. This novel design serves to protect the anode connections from splashing electrolyte and thus the electrolytic action. Consequently fixtures built with this design and also incorporating the unique zirconium/platinum tipped anode will seldom experience downtime due to connection failure.
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A
Explain 'building block' tooling
Extrude Hone devised a system of standard off-the-shelf tooling components to enable the rapid design and construction of deburring fixtures for the valve and fitting industry (primarily). A tool engineer can use off-the-shelf components (base plate, manifold, clamps) and only special build the cathode and mask. This enables quick turn-around and very economical tooling in a business that is known for high tooling cost.

For example if we had to tool up to deburr a "T" fitting the designer can chose to use a standard electrode holder, clamp, and riser plate. Once the designer has chosen the standard components, all that has to be custom designed is the mask and electrode.
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A
What would a typical fixture cost?
ECD fixtures are part specific and depend on geometry, requirements, production rates, number of parts per fixture, etc, Prices can range from $100's to $10,000's.
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A
Should customers be encouraged to make their own tooling/fixtures?
Not without specialized training. Building ECD/ECM tooling is quite different than other tooling and fixture construction a customer may be familiar with. Use of incorrect materials, lack of understanding of electrolyte flow, corrosive properties of electrolyte, etc. will likely result in more cost when it fails and they have to do it over again.
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A
What tooling methods are offered with the Miniburr product?
Simple probe type (brass tubing insulated with heatshrink or a single - twin fixed tooling using building block tooling components. Please note: Extrude Hone no longer offers Miniburr systems.
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A
How critical is electrolyte flow?
This has a very critical function. The electrolyte must remove the hydroxide by-products, bring fresh ions into the reaction, and cool the gap in a very precise way. This is part of the process 'art' and usually must be derived empirically.
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A
What happens to the burrs? Are they burned up? Are they dissolved?
This is a cold process, so the common misconception that the burrs are 'burned off' is incorrect. The burrs are disassociated from the parent metal in a cool electrochemical reaction that leaves the parent material unaffected and the burr converted to a hydrous oxide or 'hydroxide' that is not soluble in the electrolyte. Given time, these hydroxides would settle out but are usually removed by filtration or centrifugal separation.
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A
How does the process/machine know when the burr is gone? Or edge sufficiently radiussed?
Most systems today incorporate a feedback system that monitors time and current. Metal is removed as a function of time and amperage following Faraday's Law. Through trials we determine the amount of time and current that should pass to assure us of a completely deburred part. The machine controller monitors these parameters.
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A
What kind of edge radius can we expect and is it a 'true radius'?
Due to burr geometry and the resulting flow characteristics the process does not usually produce a uniform 'true' radius.
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A
What is the largest burr you can remove?
Seldom will the tool designer provide for a part to cathode gap larger than 0.045 . Since the burr must not come in contact with the cathode, the burrs must be smaller than the gap. Of course, burr orientation plays a role. A burr parallel to the electrode face may allow for a larger burr to be removed. However, ECD is not friendly toward large burrs, drill caps, packed chips, etc. These must usually be pre-deburred mechanically. Small (under 0.020  length and smaller) burrs are preferred for ECD.
There are exceptions however to this rule. Applications have been successfully made for burr as large as 0.030  thick and ?  long! The key to success is consistency. Can the customer provide all parts with a predictable burr size, location, and most important, orientation? If yes, then it is possible to design tooling that will cut off the burr at its root and flush away the undissolved portion of the burr/chip.
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A
How do we decide if rough mechanical pre-deburring is required?
Drill caps (coolie caps) must be knocked off ahead of time.
Burrs larger than 0.020' in length should be predeburred.
Chips packed in holes should be probed and flushed ahead of time.
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A
Are there any part size limitations
Although the standard machines have definite size capacities, fundamentally there is no part size limitation. Parts have been deburred that did not fit in the machine. So, they were set on a platform that provided for return of the electrolyte to the process station and portable electrode probes were clamped onto the part. It is akin to bringing the machine to the part
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A
Are there any material limitations? Materials more ideal than others?
As it turns out most ECD applications turn out to be steel or aluminum parts. This is mainly due to the wide use of ECD and these materials in the automotive market. However, virtually all metals can be deburred with ECD or machined with ECM except some refractory and precious metals.

Problematic Materials - Problem
Aluminum die castings - High silicon content leaves loose black granular particles on surface.
High carbon steel - Carbon does not react - similar to silicon
Powdered metal parts - Depending on p.m. density - may absorb electrolyte and leach out later. The trapped electrolyte may cause corrosion within.

Note: the so-called 'problematic materials' have been electrochemically deburred and machined successfully. However, post-processing steps may be necessary to address the contamination issues.
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A
Are other features/surfaces, nearby to the edges being deburred, adversely or positively affected?
This must be examined on a case-by-case basis. Usually, ECD will leave a gray discoloration (sometimes referred to as 'smut') just beyond the deburred and radiussed region. This coloration represents an oxide firmly attached to the part surface as if it had been plated on. To the extent that this may be unacceptable may determine if ECD can be used at all. If the adjacent surface shows rough tooling marks, the amplitude of these marks may be reduced. If the adjacent surface is extremely polished it is likely that the surface will become rougher. Masking (plugs, pins, plate) is sometimes used to minimize this effect.
If the surface adjacent to the burred edge is a bearing surface how far from the edge will the process stray and to what tolerance can we control the effect?
This is commonly referred to as 'stray attack.' Each case is different but to provide an answer we would not be surprised if the stray effect covered an area 0.100' from the deburred edge and this will vary +/- 0.005'.
Note: Chilled electrolyte and different electrolyte formulations can reduce stray attack. How is masking accomplished, materials used, etc.
Typically a mask is a plug or sleeve placed in a critical bore. The material is usually of some plastic that will not absorb electrolyte and does not break down in the presence of an electric field. Rigid Polyurethane and PVC, are common materials used for masking.
  ^top
 
A
What is 'undercutting?'
This phenomenon usually takes place at the interface of the mask edge and the part surface nearest to the processing area. The surface appears to be an edge due to the presence of the non-conductive mask. The ions concentrate here and cause a high rate of erosion in this region. It can be avoided by use of metallic masks (sacrificial or of tantalum, platinum etc.) or by tapering the mask where it comes in contact with the part surface.
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A
What kind of finish can we expect from ECM Polishing? Give examples.
EC finishes depend on material, roughness, surface geometry, material grain structure as determined by forming process (e.g. casting, forging, etc.) and heat treatment. Our experience has been primarily with stainless steel (i.e. high chrome content materials) with finishes resulting in a 'better than 16 Ra' condition. In some situations, finishes in the 2 - 10 Ra range have been attained (although these typically start with a good finish).
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A
What kind of surface finish can we expect from EC-Micromachining?
Unknown because the features are too small to measure surface finish
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A
What kind of tolerances can we hold with ECM and EC-Micromachining?
Depends on many factors-geometry and area machined, tool design, etc. MicroECM applications (3 to 30 microns) are typically +/- 10% or better
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A
Will a parts exposure to ECD/ECM affect its hardness?
No, ECD/ECM is a cold process and does not adversely affect the underlying metal hardness.
  ^top
 
A
Is part hardness a factor in process speed, surface finish, and other results?
In general, no, but there are examples where hardness has had effect on the results, therefore, heat treatment information is desired on application evaluations.
  ^top
 
A
Will ECM/ECD induce, remove, or otherwise impact part stress?
With electrochemical metal removal no stresses are imparted to the workpiece. However, it is possible for the process to remove desirable stresses in the skin of a part, as that which is provided by shot peening.
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A
Will ECM/ECD remove a recast layer?
Recast layers are heavily oxidized regions usually not so conductive as surrounding material. Sometimes this can lead to inconsistent metal removal or no removal depending on the conditions of conductivity. Therefore, each case must be examined or tested.
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A
Are there other metallurgical issues of concern, e.g. hydrogen embrittlement, intergranular attack, etc.?
On hydrogen embrittlement: not an issue with ECM
On intergranular attack: which is the preferential ECM-ing (or attack) of the grain boundary on the surface of a workpiece, can occur on chrome bearing materials (such as stainless steel) and titanium, if improper parameters are used. The greatest concern of intergranular attack is when sodium chloride electrolyte is used because the chlorine ion can be the cause of grain boundary attack.
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A
How important is part surface cleanliness to the process results?
Oils, grease, other contaminants on a part surface may affect the surface conductivity. Therefore it is recommended that parts be washed free of machining oil prior to ECD/ECM. However, this also depends on the fussiness of the part. Automotive parts processed through ECD have been successfully processed with water-soluble coolant on the parts with little negative impact. However, customers should not be advised to do this as the machine builder has no control over the amount of drag in of contamination nor can they know the long-range impact.
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A
How important is electrolyte cleanliness to the process results?
In the main, this is a very forgiving process in terms of contaminants in the electrolyte. However, with fussy applications, particularly machining applications, the electrolyte cleanliness can be critical. It is wise to have the machine builder's engineering department evaluate the application and recommend the most suitable filtration method.
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A
How is filtration managed?
Extrude Hone offers many different methods of filtration: Bag filter, Dual or single, cartridge filters and membrane filtration. The filter system is sized to the applications and machine.
Extrude Hone offers centrifuges and filter presses.
Extrude Hone's Miniburr (no longer available) does not provide for filtration - contaminated electrolyte is tossed out.
MicroECM uses a combination of multi stage filtering, settling, and filter press.
  ^top
 
A
What is considered normal operating temperature?
for deburring - 62-75F is typical
for machining - 65-95F is typical
for polishing - 65-95F is typical
  ^top
 
A
How important is it to maintain electrolyte temperature?
Electrolyte temperature will affect cycle time and discoloration of the workpiece. Therefore once an appropriate result is derived, the temperature should be maintained within 2 to 5F degrees.
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A
Does the electrolyte require routine replacement?
Rarely. Only in the case of unexpected contamination, failure of the filtration system, or in the case of the Extrude Hone's Miniburr (no longer available) where there is no filtration system.
On systems using bag filters, due to inefficiencies of this low cost filtration method, periodically the concentration of hydroxide will get too high, and affect the deburring process. At this point the electrolyte should be replaced.
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A
What are the types of electrolytes available?
Sodium Nitrate and water - most universally applied electrolyte
Sodium Chloride and water - faster acting than Sodium Nitrate. Excellent for machining annulus in injector tips but can be overly aggressive and so not suitable for many other applications in particular where best finish is desired.
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A
What is a 'power supply?'
The power supply takes the factory supply voltage and reduces it to less than 30 volts and converts the current from AC to DC. The DC output of the 'power supply' is what is connected to the part (+) and the cathode (-).
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A
Are there differences in types of power supplies employed by our various ECM divisions?
Yes. Some DC power supplies have filtered output and others provide little or no filtering. Proprietary pulse power supplies with varying characteristics provide for results not duplicated with more elementary power supplies.
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A
What are the pros and cons of various types of machine construction (steel welded frame, fiberglass, stainless welded tube frame)?
Cost, existing designs, and market preference are the determining factors.
  ^top
 
A
Is ECD/ECM expensive to operate? What are the cost considerations?
There is no one answer to this question. Each application must be evaluated and measured against value and alternative methods to assess if it is relatively expensive or inexpensive to operate.
  ^top
 
A
Is this salt-water process likely to affect surrounding equipment, buildings?
No. Many years ago systems were designed without taking into account atomization of salt-water electrolyte in high-pressure ECM installations. These systems led to contamination and corrosion in the workplace. Modern systems do not have this problem. However, since systems are different with respect to electrolyte exposure potential and evaporation, these details are reviewed when considering installation.
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A
The machine produces hydrogen and oxygen gas and electrical charges are present on exposed conductors. Are there any operator health or safety hazards to be aware of?
Electrical Danger: the conductors are all exposed in ECD systems because the current carried is low voltage direct current. The National Electrical Code permits exposed conductors up to a threshold of 50 vdc. Most ECD/ECM systems operate well under this threshold.

Gas Exposure: the volume of hydrogen and oxygen gas produced at the reaction is very small in most installations. Normal ventilation is sufficient to dissipate the gas and avoid danger. Machines in small confined rooms should be well ventilated and electrolyte tanks and vessels should provide for free exchange of fresh air.

Salt Water Electrolyte: Typically we are using Sodium Chloride (table salt) or Sodium Nitrate (fertilizer) and water. These are no more hazardous to humans (skin contact) than bathing in the ocean. Some may have allergic reactions and therefore it is advised that operators wear gloves and minimize skin exposure as much as possible. Also, since the process releases metal by-products into the electrolyte that have unknown toxicities it is advisable to protect the operators by using appropriate skin protection.
  ^top
 
A
Does the machine operator require special training?
Normal machine operator skills are called for. An operator can be trained to run an ECD machine in a few hours at most. Most of the training will be in learning to observe to head off problems.
  ^top
 
A
What are the general preventative maintenance issues to be considered?
pH adjustment - automatic on some machines
Add salt - conductivity instrument indicates, optional salt feeder available
Add water - monitor fluid level
Filtration - depends on equipment installed
Fixtures - periodically flush to remove any build-up of hydroxides, salt residue
Housekeeping - periodically wipe down area to remove splashed electrolyte
  ^top
 
A
What is the expected life of a ECD/ECM machine?
Ten years
  ^top
 
A
Help me put things in perspective; if TEM, AFM, and ECD are all effective for internal deburring, in what circumstances is ECD the process of choice?
Not an easy question. Maybe we should look at it this way;

CHARACTERISTIC ECD AFM TEM
Deburr Yes
Small to medium 		No
(edge condition)
small		 Yes
Small to large
Improves Surface Finish No / Yes Yes No
Radius Yes Yes (uniform)
Small radii		 Yes (cast iron, zinc, mild steel)
No (copper, brass, s.s., alum.)
Typical Cycle Time 15 - 30 sec. 5 - 30 minutes 30 - 60 sec.
High Volume Yes Not Generally Yes
Low value parts Yes No Yes
Capable of machining Yes No No
Monitors burr removal Yes No No
Adapts to automation Yes Difficult and not
usually cost effective		 Yes


The above table would lead one to believe that ECD and TEM are close equivalents. In general, since TEM is so quick and easy to try out, it does make good sense to attempt this process first. If TEM is disqualified (see below), ECD is the next logical choice. There are few parts that can't be deburred by ECD. And, since there is a wide range of machines available today, there is a machine for every budget. AFM is most often thought of today as a surface and edge finishing process as opposed to a 'deburring' process. In some respects you may find it easier to decide when to use ECD and not TEM or AFM by applying certain disqualifiers.
  ^top
 
A
TEM DISQUALIFIERS
Thin-walled and can't be easily protected with heat sink fixture
Requires specific controlled edge radius
Part too large for available chambers
Insufficient volume to justify large capital investment
Oxide layer cleaning issues - won't accept chemicals, dull appearance
  ^top
 
A
ECD DISQUALIFIERS
Can be effectively and economically deburred by TEM or mass finishing
Burrs are very large - bridge gap between tool and part - pre-qualifying not accepted
Part has microscopic burrs and needs radiussing and surface finish improvement typical of AFM
Volume is very low and edge complexity is high (may only be suitable for manual deburring)
  ^top
 
A
AFM DISQUALIFIERS
Can be effectively and economically deburred by TEM or mass finishing
Burrs are visible and significant
Too many passages making tooling impractical
Radius and surface finish enhancement not valued
  ^top
 
Extrude Hone is dedicated to innovating and providing advanced manufacturing processes to produce some of the highest quality engineered surfaces and edges on the planet. A menu of technologies and equipment for deburring, polishing, and producing controlled radii are available to our customers for improving the strength, performance, and overall reliability of the components they produce.

"The most important aspects of a part are its surfaces and edges."
( The rest of the part is there merely to hold the surfaces and edges together!) 


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