EDM Wire - Making the right choice for your business

Electrical Discharge Machining remains at the frontline of metalworking innovation, even with a five decade history in industry. Wire EDM continues to advance, evolve, and revolutionise techniques in numerous industries. Whilst the rudimentary principles of wire EDM have not significantly changed, the process has advanced dramatically in the scope, speed, accuracy and complexity of the metal-cutting it can perform, even as the equipment has become more affordable, more reliable, and easier to operate.

The EDM wire electrodes used in wire EDM are a crucial component and as such, making the right choice is vital. It was once a simple decision as there were far fewer choices; copper or brass. Now, there are many wire options available; economy EDM wires, utility-grade EDM wires, wires for speed, wire for carbides and PCD’s, wires for tapering and fine-wire machining.

A core consideration for engineers utilising an EDM machine is: ‘how can I be most efficient and profitable whilst maintaining the highest level of quality in the machining process’. Due to wear, and an associated decrease of the wire diameter, the wire electrode is a single use consumable and therefore the choice of wire for the work-piece is key to the time taken (cutting speed achieved), accuracy and surface finish of the final product. This is a complicated consideration for the modern engineer and this article considers the various types of wire available, properties of certain wires, and discusses the benefits of utilising high-end products versus lower-cost options. Therefore by ensuring that you are using the correct wire type to maximise your outputs and minimise machine downtime, you can manage the impact of the false economy of cheap consumables.

To begin, it is useful to revisit the properties of EDM Wire, considering the benefits of certain properties in the machining process.

EDM Wire Properties

Tensile Strength

This is the maximum load-bearing capability of the material relating to its ability to resist stretching and fracturing. The measure is determined by the maximum load in pounds per square inch divided by the cross-sectional area of the wire. The benefits of a high tensile EDM wire includes that it provides a better edge straightness which is advantageous for single-pass parts and for small and fine-diameter wires to reduce breakage. High tensile wire aides in geometric accuracy, part straightness and provides a superior skim cut.

Fracture resistance

It is more accurate to refer to fracture resistance as toughness or resilience as there is no standardised index or rating for fracture resistance in EDM wire. When talking of the fracture resistance of EDM wire, it is the ability of the wire to resist the effects of the process of EDM. Having a more resistant wire reduces instances of deviations and breaking, which can significantly impact auto-threading and the overall productivity of an EDM machine.

Conductivity

In EDM, the higher the wires’ conductivity, the more power can be delivered to the workpiece increasing efficiency and cutting speed.

Vaporisation temperature

In machining on a micro scale, space is a commodity. Having a low melting/vaporisation temperature in the EDM wire allows for greater flushability of by-products of the process. It is beneficial that the wire surface vaporises rapidly to avoid contamination of the electrode gap.

Hardness

Not to be confused with tensile strength, the hardness (or temper) of a wire refers to the wires ductility, or its ability to endure elongation. EDM wires are categorised as either soft or hard and are better suited to different machining types. On closed-guard machines, a hard wire threads better than a softer wire but a soft wire may be more suited to a taper-cut, for example. Auto-threading is an important innovation in EDM and hard wires provide higher rates of reliability in auto-threading than its softer counterparts.

EDM Wire Types - which do I choose?

Brass EDM Wire

Various Coated EDM Wires

There are various types of Coated EDM wires on the market today and each has been developed to give different results depending on the application requirements of the finished work-piece or in some cases developed for improved performance on a particular type of machine. Coated wires claim a superior surface finish and better surface integrity than brass wires, particularly against carbides and PCD materials.

Zinc Coated EDM Wire

Diffusion-Annealed & Gamma Phase EDM Wires

Higher Zinc content wires are argued by some to be better EDM electrodes. However, producing EDM wire with zinc percentages approaching 40% is problematic as its crystalline structure changes at this point to a gamma phase which can cause the product to become brittle and difficult to draw if not carefully controlled. Creating wires with a higher surface zinc percentage has been achieved through a heavy coating of pure zinc (18-35 μm) being applied to a copper or brass core, which then undergoes annealing in a unique furnace. This annealing diffuses the pure zinc coating into a combination of brass and zinc, allowing the zinc content to exceed the 40% threshold previously limiting this process, diffusion-annealed wire can contain 45-47% zinc. Tensile strengths can range from 430-900N/mm² and the wire appears with a brown colour-tone at prime condition. This type of wire is suited to finest accuracy and surface finish cutting and also for tall workpieces and fast cutting, volume production and in instances where there are poor flushing conditions available. Furthermore, diffusion-annealed wire can be used against a wide range of materials such as tool steel, aluminium and graphite.

A Product Focus - STAMMCUT® EDM Wires

Having revisited the properties and types of wire electrodes available in EDM Machining, a case study of one of the leading manufacturers of EDM wire - German based company: Stamm - explores some of the high quality wire consumables available on the global market today.

The Heinrich Stamm GmbH was founded in 1815 as a brass wire drawing mill and has remained family owned for seven generations. Since the 1970s, and the emergent need for quality consumables in EDM Machining, Stamm began the manufacture of high quality EDM wires under the label STAMMCUT®.

The STAMMCUT® product line is closely governed by a certified quality management system [that is certified according to DIN ISO 9001:2000] and all the products are 100% recyclable and environmentally friendly. Maintaining this commitment to quality, the development stage and entire product range available under the STAMMCUT® label are completed to meet extremely high standards of quality. This is achieved partly through the use of in-house galvanic facilities as well as raw materials and a commitment to future-orientated, innovative production plant development. Further to the practical aspects, STAMMCUT® manufacturers are internationally renowned for their expertise in the field and for their experience in non-ferrous metallurgy creating a basis for consistently high quality EDM Wire electrodes. STAMMCUT® EDM Wires are made in Germany and distributed worldwide in the following classifications:

• Standard/Brass
• Surface Finish
• Performance
• High Performance
• Fine Wire

This product focus will take six EDM Wire electrodes across the above classifications, and consider the value of investing in higher quality, and ultimately more expensive consumables.

STAMMCUT® - Surface Finish EDM Wires

The products in this category claim; high accuracy and precision, the finest surface conditions of the work-piece, as well as the best geometry and parallelism. These attributes are achieved through the zinc coating of the electrodes and the use of in-house galvanisation lines which allow for consistency across the products and uniformity in the process.

STAMMCUT® TG

STAMMCUT® A950 /A500

STAMMCUT® Performance EDM Wires

The products in this category combine high cutting performance with outstanding precision characteristics. In this group the suitable power electrodes can be found for all machine types. Special core materials, different phase characteristics and metallurgical compositions characterise the STAMMCUT® performance electrodes. This category of products are heat treated and produced using in-house galvanic lines allowing for consistency and uniformity and are monitored extensively for flaw meaning a high quality product is delivered in every batch.

STAMMCUT® TH

STAMMCUT® XP

STAMMCUT® High Performance EDM Wires

The ‘high speed’ range is characterised by a fine-structured wire surface as well as a combination of different metallurgical phases in the coating layer. This feature results in so-called multiphase wire electrodes with a unique surface structure for a broad range of applications. These special features are achieved through innovative production procedures and one-of-a-kind wire alloys. The specific technical characteristics ensure a high cutting performance, even under bad flushing conditions. The fine wire surface reduces the wear of the power supply contacts.

STAMMCUT® TPN

STAMMCUT® Standard/Brass EDM Wires

The STAMMCUT® brass wire electrodes are characterised by their chemical purity. Self-developed casting specifications and close tolerances in the metallurgical wire composition guarantee the fulfillment of all technical requirements. Continuous quality controls in an inhouse laboratory ensure a high and consistent quality level.

STAMMCUT® Brass 950

Which is better for overall economic performance?

This article has explored a selection of the STAMMCUT® EDM Wire product range, giving an example of higher-end consumables. The question remains, are products such as these worth the extra cost? Here we explore whether cheaper products are cost-effective in the wider challenges of business management in the current economy, or whether they represent a false economy.

The evolution of wire EDM has seen improvements in machining rates, precision and accuracy. With the increase of machining speeds, we see an increase in consumable usage and wear parts – all of which amounts to an increased running cost of wire EDM machines. Wire guides, power feed contacts, ion exchange resin and filters are all expended at a faster rate and all of these factors affect the bottom-line. Beyond the cost of consumables used during high-speed machining, it should however be considered that the cost of downtime for maintenance is of higher long-term impact to a business.

It is not only through major issues that the false economy of cheaper wire can be noted. Lower quality products have a lesser dimensional accuracy and poorer quality surface finish meaning that overall quality is sacrificed. Wire made from virgin materials are superior to wires made from recycled materials because impurities in EDM wire can create further issues. Wire EDM is a speciality machining process, developed for its extremely high level of accuracy and ability to work to micron accuracy, poor quality cheap wire can jeopardise this.

The processes involved in creating high quality EDM wires is costly, whether this be for plain brass wire or the more expensive coated wires, therefore the final product is more expensive. This being said, the superior quality wires provide the machine with the ability to be reliable, to keep running and keep earning money.

Faster machining on modern wire erosion machines means threading is a far more frequent necessity. The majority of modern EDM machines on the market have an automatic wire threader (AWT) which supports the unattended operations of wire EDMs. Wire breakage is usually detected through the cessation of wire tension. The AWTs on modern machines respond to this with an approximate 90% threading success rate, however this success rate is greatly decreased when poor-quality wire is used, as flaws in the wires can restrict the AWTs ability to re-thread the wire and keep the machine working.

The earning capacity of a Wire EDM machine is far more valuable to a business than the relatively low-cost consumable that is wire, even if you choose to use a more expensive coated wire. Setting up a job to run overnight only to find that a wire breakage has occurred a few hours into machining, stopping the machine from running because the auto-wire threading failed, triggering a machine shutdown lasting potentially hours, is not only frustrating but incredibly costly to a company's overall annual profits.

Considering these elements, the STAMMCUT® products have been rated against the following criteria:

• Speed
• Surface
• Precision
• Taper
• Threading

See the STAMMCUT® product comparison below for surface finish vs. speed:

Given the importance of wire electrodes in EDM Machining, the issues associated with cheaper products appear to overwrite any initial savings.

Investing in higher quality products may incur an increase in outgoings on consumables in the short term but it is clear that the bigger picture requires deeper consideration at a business level. It may be that risking larger one off outputs and losses due to machine failure is a calculated risk suited to your specific business model. On the whole, the long term savings and potential to increase profits that accompanies the investment in higher quality consumables is far more appropriate for the majority of businesses.

EDM Plus (UK) LTD & STAMMCUT® EDM Wires

EDM Plus (UK) Ltd select their suppliers very carefully to uphold our company policy of providing high quality EDM consumables to their clients and are proud to be the UK sales agents for STAMMCUT® EDM wires. STAMMCUT® has over 45 years experience in manufacturing EDM wires and provides a comprehensive product range of high quality plain brass and speciality coated wires with a variety of diameters and tensile strengths available depending on the application demands.

STAMMCUT® have refined their EDM processes over many years and are committed to quality. It is their belief that investing in higher grade consumables is more cost effective over longer periods. In this business, the money is in uptime and the labour of the process so machine downtime, wasted workpieces and unreliable consumables are problematic and incur unnecessary costs. Although it may be the case that cheaper wire may present a minor frontline saving, their clients and ourselves have found that the initial savings are offset by the costs incurred by wire breakage amounting to machine down time, loss of precision and wasted materials.

What's the right STAMMCUT® EDM wire for your EDM machine?

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