The limitations of what is possible with EDM are constantly being redefined and with this comes the requirement of ensuring that all components, parts and consumables are up to the challenge of modern EDM. To ensure high quality results from the EDM process, operators are required to finely adjust the machining parameters and ensure that high quality materials which are designed for the process are made a priority. Ensuring highly efficient filtration offers a number of benefits including; Higher cutting speeds, high quality surface finish, improved dimensional accuracy, reduced machine wear, stable conductivity, maximising ion exchange resin consumption which all lead to the reduction of maintenance and consumables costs.
The past 10-15 years has seen dramatic improvements in EDM machines capability, especially regarding; machine tool construction, CNC controls, power supplies, the metal removal rate, operator interfaces and the speed at which they cut. As the machines improve their capability, the systems the machine uses need to improve as well - one of these systems is the fluid system. On a wire erosion machine or hole drilling machine it is normally a re-circulating water system and on a spark erosion machine a re-circulating dielectric oil system. For each system, the filters play a very important role in the system. Here, EDM Plus outlines why using the correct EDM filters is imperative to the efficient and profitable running of EDM Machines, explaining that through careful filter selection and use, there are many benefits to be gained. A common mistake made by EDM owners and operators is choosing the cheapest option for filtration - this is understandable as filters require frequent replacement, but often the impact of a good filter is underappreciated.
EDM Filters - The Importance and Types
Filter manufacturers use a variety of different filter material types for particulate retention capabilities. Smaller edm filters commonly use spun polyester and strung wound polyester materials, whilst larger edm filters commonly use pleated paper. The majority of modern large filters use macro pleating technology, with paper and fleece polyester materials, to find the best solution to EDM filtration for that process. There is a balance required between filtration efficiency and cost, although EDM users would argue that because clean dielectric fluid is essential for erosion quality, the ‘cost’ of edm filters should be considered beyond just the unit cost.
To achieve quality filtration for most modern Wire Erosion machines a 1-3 micron rating is required to produce the best dimensional and surface finish requirements on the part being produced. Slightly older machines will require a 5 micron rating, which is perfectly acceptable for the generator capabilities of the machine.
EDM Hole Drilling machines do not need a rating higher than 5 microns to achieve quality filtration due to the slightly more aggressive nature of the EDM process whereby the speed of cut is far more important than the surface finish produced in the majority of cases.
High quality filtration for sink machines can be attained with a 10 micron rating, however there are some machines which require a 5 micron rating due to the generator capability for fine surface finish requirements. On the other hand, Micro EDM machines require a 1 micron rating to deliver the very cleanest fluid to the working area because of the extremely small spark gaps that the machines produce. Very often a 5 micron pre-filter will be used to remove the bulk of the particles before the 1 micron filter, which also helps to extend the life of the most expensive filter.
If a filter is not properly constructed, or any of its parts are below standard, it can cause the filter to fail, sending contaminated fluid back into the system. This causes damage to the system and can also damage any parts being produced.
Modern macro pleated edm filter
Layered paper edm filter
Standard pleated paper edm filter
Strung wound polypropylene edm filter
The Impact of Poor Filtration
Dirty dielectric fluid negatively affects the cut speed (metal removal rate) as well as the part quality during electrical discharge machining. The reason for this is that the fluid is what transfers the charge from the wire or electrode to the work-piece - in the spark gap - with no contact ever being made. It also flushes away the micron-sized particles from the spark gap and away from the work-piece - if the dielectric fluid is unclean or poor flushing conditions are experienced during the process, the particles in the gap can have a detrimental effect. These particles will interfere with the spark causing issues during the process (secondary erosion) and this will produce inaccuracies in the cut and part produced.
Without proper filtration, over time particulates can deposit themselves and accumulate onto other important parts of the machine and begin to slow process productivity, causing slower metal removal rates, poor quality surface finishes as well as rejected parts by Quality Control. It goes without saying that poor quality parts are a significant issue but particulate build-up in the dielectric fluid can be argued to have even more costly detrimental impact as these particles can linger long after a project is complete meaning they may affect future work-pieces.
Poor filtration can cause further significant long term maintenance problems for the EDM machine. Solenoids which power the pumps and circulate the dielectric fluid are easily damaged by particulate build-up, these parts are incredibly delicate and expensive to replace. As if that wasn't enough to convince you of the importance of effective filtration, resin life span is also significantly reduced in cases where poor filtration is present, this is because the resin begins to act as the primary filter in place of the intended filter, all of which results in unnecessary accrued costs.
The Filtration Process in Brief
The main role of EDM filters is to filter out mechanical impurities from the dielectric fluid to maintain the quality of the EDM machines’ working process and to further protect the machine from untimely wear and tear and blockages. So, the clean fluid is delivered from the ‘clean fluid’ tank of the dielectric system into the working area of the machine and the resulting dirty fluid from there then overflows into the ‘dirty tank’ of the dielectric system. This dirty fluid is then pumped through the filter cartridge, via a nipple connector or bore connection and the impurities within the fluid will be blocked by the filter materials. The cleaned fluid is then discharged from the EDM filter back into the ‘clean fluid’ tank, allowing for clean fluid to be pumped back to the working area to facilitate the spark erosion process. Regardless of the specification type of the EDM filter, the working principle is the same.
Filter Efficiency Factors
Ensuring the correct flow rate and capacity of the filter is important for the effective and efficient working of the fluid system delivering clean fluid to the working area. If the edm filters can't keep up with processing, the result may be a loss of fluid supply to the working area of the machine (pump cavitation may occur and air particles may be introduced) which is all detrimental to the efficiency of the process. Most fluid systems will have a filter pump pressure gauge, with a recommendation of the maximum working pressure that the edm filters can take (this indicates how dirty the filters have become) and as the pressure increases (meaning the filters are clogging up) the flow of clean fluid may be restricted into the ‘clean tank’ working area and further to the working area.
Due to the increased size and capacity of modern EDM filters, it is normal to expect filters to be changed after 200-400 hours of operation. The filtration system capacity, the operations being performed by the machine, and the material being eroded all impact the life cycle of the filter so 200-400 hours is not a hard and fast rule.
The characteristics of certain metals such as Aluminium, Inconel alloys and some coppers mean that larger pieces break off during the process and there is a tendency for particles to stick together, making them more challenging to remove from the fluid which may decrease the lifespan of the filter.
It should also be noted that when changing edm filters, if the previous filter had not been performing effectively then the new filter will have to run through remaining debris initially and so this filter may need changing earlier than expected until the fluid is fully cleansed. Once a system of effective filtration is established, a high quality and appropriately selected filter should have a longer lifespan than an economy product.
Increase Your Output with Effective Filter Selection
There are many ways to increase your output with an effective filtration system. The first of which is understanding the work which is being undertaken. By understanding the different wear rates and the erosion differences of materials, wires and electrodes, you can optimise the performance of your machine. For example, the particles which extract from softer metals can be prone to sticking together during the process which clogs the filters faster. Equally, the same result can happen with larger diameter wires and roughing operations. By understanding the difference between the work that different EDM machines do you can understand how this will affect the filtration system and allows the operator to make considerations which will optimise cutting and machinery performance.
This point leads on well to the second consideration. It is a common mistake to directly correlate filter performance with operational hours. It is sometimes reported that 400-450 hours can be achieved with edm filters but you should be wary of looking at this as a benchmark. There are so many factors playing a part in the performance life of a filter, for example 40 hours cutting a thick material will generate far more particulate than the same amount of hours cutting a much thinner workpiece. Similarly, the first pass will produce more particulate than subsequent skim cuts and with spark erosion, electrodes with larger surface areas will produce more particulate than those with a smaller surface area. What all this means is simply that by understanding the work being completed you can ensure that not only the correct filter is being used, but also that maintenance is undertaken in line with the limitations of the filtration system for specific processes rather than using a one-size-fits-all approach.
The third point refers to an often overlooked factor of filtration on a wire erosion machine - resin. Filter and resin work together to deliver clean de-ionised fluid to the working area. It is important not to rely on the resin to enact the filtration process to compensate for an ineffective filter. This is a relatively common practice, thought to increase the lifespan of the filter but ultimately this is a false economy and leads to increased running costs over time.
Our next point promotes forward thinking and the long term maintenance of your machine. Various components of EDM machines are negatively impacted by poor filtration such as; solenoids, sight glasses, valves and general plumbing. By investing in better quality edm filters and thoughtful maintenance processes, considerable costs can be prevented when the inevitable damage to these components requires part replacement and lost production time due to intensive maintenance where routine maintenance could have averted the premature damage.
Finally, you should ensure that your consumables suppliers are ‘Quality Assured’. The primary concern should be with the filter media being used and the quality of this and the best way to guarantee the quality of the product is to check the status of the supplier of your filter to prevent the purchase of poor quality products.
EDM Filters from EDM Plus
Consumables, such as edm filters, are often an afterthought in the busy environment of an EDM machining company. This is not good practice and is something which can cost a company significant money in the long run. It may require a shift in mindset and some forward budget planning, but whatever short-term discomfort this may create is far outweighed by the long term benefits and savings created by enacting an appropriate maintenance plan and investing in quality consumables.
Please give us a call on 02476 678888, we'd be happy to be of service.