This is part two of a four-part series about buying a wire EDM. For more on Wire EDM, click the links:
For more information, please visit Moly Wire.
Find more insights about acquiring a new machine tool by visiting the Techspex Knowledge Center.
The wire used in the electrical discharge machining (EDM) process may consist of brass, zinc-coated brass, brass-coated copper, tungsten, molybdenum or brass with a steel core, to name a few. Each type has its own purpose, benefit and cost.
EDM wire ranges in diameter from 0.0008 to 0.013 inch. A wire with a diameter of 0.0008 inch will produce a 0.00044-inch radius in a corner, a feature nearly impossible to manufacture any other way. Such precision may be required for openings in dies to produce electrical components, for example. However, wire this fine is rarely used, because of the unusual challenges it creates. Typically, the smaller the wire, the lower the power settings and the slower the cut. Most shops do not want to pay for this lengthy machine time unless the application absolutely requires it.
Plain brass wire 0.010 inches in diameter is used in more than 80 percent of EDM work. Three types of brass wire exist: hard, half-hard and soft. Soft brass is typically used for cutting tapers because a low tensile strength is needed. This type can bend while cutting at an angle without breaking.
Hard brass is best for both roughing and skimming when higher tensile strength is desired. Hard brass withstands aggressive flushing and enables a high voltage to be applied to the wire without breaking. A faster cutting rate is the result.
Brass wire is available with a zinc coating. Because zinc melts at a lower temperature than brass, the zinc absorbs heat as it boils away. Less heat enters the wire, so it retains its strength. Whereas brass wire is very smooth on the outside, zinc-coated brass has a rougher outside finish. This rougher finish improves flushing, resulting in increased speed. Typically, coated wire delivers a 10- to 15-percent improvement in speed.
Wire with a copper core and a defused zinc outer layer is often referred to as a high-speed wire, or stratified wire. The high electrical conductivity of copper enables doubling the cut speed. However, the price of the wire can be double that of other types. A stratified wire is recommended for roughing cuts. Plain copper wire is now rarely used because it is too soft and is too expensive.
No matter which type of wire is selected, it can only be used once. All wire is degraded by the wire EDM process and can be sold for scrap afterward.
Specifying the tensile strength of EDM wire is also important. Even though the wire does not touch the part during cutting, it is stretched by the machine’s wire drive feed mechanism, which consists of wire tensioner, roller guides, and upper and lower feed contacts (where the electric current is applied). Tension is preloaded onto the wire and can then be increased or decreased to accomplish different cutting techniques. Tensile strength determines the ability of the wire to withstand the tension imposed during cutting. The lower the tensile strength, the easier it is to break.
Wire with less tensile strength will cut angles without breaking. By displacing or offsetting the wire guides in the U-V axis, large tapers and angle cuts of up to 45 degrees can be generated. Wire with more tensile strength can be stretched more tightly when using the U-V axis to closely control the perpendicularity of vertical walls for precise cutting.
For more Tungsten Barinformation, please contact us. We will provide professional answers.
For roughing, lower wire tension enables the machine to cut faster without breaking the wire. Skim cuts require higher tension, so slower speeds and less power are applied to achieve maximum surface finish and precision.
EDM wire is sold by the pound and typically comes in an 8-pound spool. Under normal cutting conditions, one spool will last eight to 10 hours of uninterrupted cutting. Most EDM manufacturers offer a large-spool option, which will hold a spool of wire weighing as much as 35 or 50 pounds, making it possible to cut more than 40 hours without interruption. Provided the EDM unit has an auto rethreading system, the machine can operate for a week or more with little attention. However, a robot or automatic workpiece-loading device is needed to support such long run times.
All wire EDM units now come with an automatic wire rethreading system. This feature works exceptionally well with wire as small as 0.002 inches in diameter, but the larger the wire diameter, the better. A high-pressure stream of water guides the wire through the workpiece.
Automatic threading enhances unattended operation by making it possible to produce multiple openings or features within a part in a single setup. Cutting and rethreading of the wire are controlled by codes in the program. If the wire breaks accidentally, the machine senses the break, rethreads the wire and resumes cutting where the wire broke. If wire smaller than 0.004 inches is required, a fine wire kit is available as an option.
Many people have never heard of molybdenum, an element that sits in the middle of the periodic table, with 42 protons, 54 neutrons and the symbol Mo; however, it is in very high demand. Discovered in 1778 by Carl Scheele, it is a silvery-white metal and it features a number of notable properties. For example, molybdenum has one of the highest melting points of all pure elements – hitting 2620°C – and it demonstrates high thermal and electrical conductivity. It is also extremely tough yet ductile and it is very resistant to corrosion from glass and other metals.
The first-ever molybdenum application occurred in the early 20th century when, thanks to its stability and strength at high temperatures, it was used to create wires for incandescent lamps. Since this first application, scientists and engineers have realised that molybdenum’s wide range of remarkable properties makes it an ideal choice for a wide range of other applications. It is now employed in a variety of different industries, both in its pure form or as an alloy or compound, and here we take a look at each of the top five modern-day molybdenum uses in further detail.
This has to be one of the element’s biggest applications, accounting for the largest percentage of its demand and usage. Molybdenum is a highly valuable alloying agent in a variety of structural, high-speed, and stainless steels. Not only does it contribute to their toughness and durability, but it also improves their resistance to corrosion and their ability to be welded into an appropriate shape.
For example, thanks to the addition of molybdenum, stainless steel demonstrates excellent anti-corrosive and rust-resistant properties – thus making it suitable for use in kitchen appliances and common household items, industrial steel pipes and underwater oil and gas pipelines. The addition of molybdenum also significantly improves the strength-to-weight ratio of steel and it is often used to increase the strength, hardness, temperature and pressure tolerance of cast iron, therefore making it suitable for use in the automotive industry.
Compounds that include molybdenum are often used within the chemical industry, either as an effective catalyst or lubricant. Take for example molybdenum sulphide; a compound that is typically employed as a catalyst in the hydro-fertilisation of petroleum. When combined with heat and pressure, this compound successfully removes sulphur from the natural gas and refined petroleum products. Molybdenum compounds can also be used as an effective lubricant, particularly in situations where high temperatures would cause oil-based lubricants to decompose, and it is also used as pigments for plastics, corrosion inhibitors, ceramics, and smoke suppressants.
It goes without saying that when flying a plane, it is vitally important that a pilot has full visibility at all times – regardless of the weather conditions at 35,000 ft, they need to keep passengers. This is where molybdenum comes into play. An electrical current is sent through a molybdenum wire, thus heating up the material, transferring the heat to the windshield and acting as a defrost mechanism. Due to its creep resistance and low coefficient thermal expansion, the molybdenum wire maintains its shape and withstands the high temperatures. The windscreen remains clear at all times and the pilot is able to fly the plane safely and successfully to its destination.
As one of their main trace elements, molybdenum is essential to the normal growth and health of plants. It helps to convert atmospheric nitrogen into ammonia, promotes the absorption of phosphorous, accelerates the formation and transformation of alcohol and generally improves a plant’s resistance to drought, cold, and disease. With these benefits in mind, most countries now produce and use plant fertilisers that include trace amounts of molybdenum powder.
Molybdenum components also have an incredibly important role to play within the medical field. For example, technetium-99m is commonly used in radionuclide medical imaging – such as high-power x-rays and computerised axial tomography (CAT) scanning equipment. This particular isotope is a derivative of molybdenum-98, produced when molybdenum-98 absorbs neutrons.
Here we have highlighted some of the most common modern-day uses of molybdenum, however, others include lighting, sintering trays and boats, charge carriers, plasma spraying nozzles and electrodes, sputtering targets, furnace components, and glass stirrers – to name just a few. Thanks to its remarkable properties, the applications of molybdenum are already very far-reaching, and we predict that – over the next few years – scientists and engineers will continue to find new uses for this versatile and intriguing pure element.
Special Metals Fabrication demonstrate over 120 years’ experience in the specialist metals industry and you could say we know a thing or two when it comes to molybdenum. Call upon our wealth of experience and expert knowledge in this area and, we guarantee, we will find the perfect molybdenum product to meet your exact requirements. From molybdenum wire and rod to molybdenum plates and sheets, we have it all. We offer a range of pre-manufactured goods and we can also make bespoke molybdenum parts to specification. The choice is yours.
So why not take a look at our full range of molybdenum parts and fittings today, and if you have any questions, please feel free to get in touch. Give us a call on 01268 820409 or drop a message using our online contact form. One of our friendly members of staff will be more than happy to help!
Are you interested in learning more about Carbide Bar? Contact us today to secure an expert consultation!