Marc Sanders, EDM Application Specialist at Entegris | POCO Materials, joins Graphel’s Ken Dworznik to discuss the services Entegris POCO can provide to EDM users, the importance of graphite material choice, and answer common EDM application questions.
Jim Norcross of System 3R joins Graphel’s Ken Dworznik to discuss System 3R’s history and tooling abilities, as well as tips for EDM applications.
Rob Fothergill of Entegris | POCO Materials joins Graphel’s Ken Dworznik to discuss the EDM Training available at the Entegris POCO training facility and common graphite application questions.
by Entegris Poco Graphite
Increasing the effectiveness of EDM operations does not come solely with technological improvements in the EDM sinker. This is one of many aspects needing to be considered when working to optimize EDM performance and increase productivity. Other areas of consideration include the type of dielectric fluid, tooling and electrode material used in the EDM applications. One area often overlooked or disregarded is the training required to make the most of the many factors affecting efficient operations.
A competitive company should seriously consider every opportunity to take advantage of technical training being offered by leading suppliers in the industry. This training is often at no charge with the only investment to the company being travel and salary. Even the shortest of training sessions provide the opportunity to recover any costs incurred in a very short time. A case in point includes a company engaged in EDMing – primarily carbide – and experiencing significant electrode wear and slow burn times. The wear and slow burn times demanded an increase in the volume of electrodes produced; therefore, not only adding to material cost, but significantly increased manufacturing costs for machining these electrodes.
The manufacturing cost limited profitability in this application, so the decision was made to send an employee to our EDM technical training session. One of the topics covered in the training included electrode material selection, honing in on the advantages of specific material when EDMing high thermally conductive metals. As it turns out, this company was purchasing the wrong type electrode material for EDMing carbide.
When working with metals of high thermal conductivity, the work-piece absorbs the spark energy almost instantly and limits the effectiveness of the EDM process unless changes are made specific to these type metals. In the case of this example, the electrode material used was a medium grade non-copper impregnated material and was selected primarily on a lower material costs than others available. The student realized during this training that copper impregnated electrode materials exhibit significantly lower electrical resistivity values than a non-copper impregnated material and allows for maximum spark intensity in the EDM cut. This not only increases the metal removal rate, but also allows for reduced electrode wear as well.
Another factor learned during this training session included the need to reduce the on-time to a length approximately equal to when the work metal begins to dissipate the spark energy in the cut. Any longer on-time will only serve to increase wear of the electrode without an effective metal removal rate. Upon the employee’s return, he began to implement the lessons learned during his time at the training. With sample material provided during the training, he began to experience immediate productivity improvements in the EDM. He claims his productivity has increased so much that the company has recovered the cost of the training and much more.
Be sure to contact us for more details on how your company can benefit from attending a training session — with both classroom and laboratory activities for the beginner or the experienced EDM operator — on the products you use in your EDM operations. Look for a program designed to help end users gain a better understanding on how to control the EDM process to achieve predictable results and one that enables you to return with practical information that can immediately be put to use on the shop floor.
FOR MORE INFORMATION
Please call your local distributor to learn what our premium graphite solutions can do for you. Visit poco.entegris.com/distributors for the location nearest you.
Different Types of Milling
There are many different types of tooling, the most common being work holding tools. Work holding tools include jigs and fixtures; cutting tools for milling and grinding machines; dies for cold forming, forging and extrusion machines; and welding and inspection fixtures. In this month’s blog, we are going to look at the basics of milling.
Milling is the machining process of using rotary cutters to remove material from a workpiece by advancing the cutter into the workpiece at a certain direction. The cutter may also be held at an angle relative to the axis of the tool. Milling covers a wide variety of different operations and machines and is one of the most commonly used processes for machining custom parts to precise tolerances.
Milling is a cutting process that uses a milling cutter to remove material from the surface of a workpiece. The milling cutter is a rotary cutting tool, often with multiple cutting points. The cutter in milling is usually moved perpendicular to its axis so that cutting occurs on the circumference of the cutter. As the milling begins, the cutting edges of the tool repeatedly cut into and exit from the material, shaving off chips from the workpiece with each pass. The cutting action is shear deformation; material is pushed off the workpiece in tiny clumps that hang together to a greater or lesser extent to form chips. This makes metal cutting somewhat different from slicing softer materials with a blade.
The milling process removes material by performing many separate, small cuts. This is accomplished by using a cutter with many teeth, spinning the cutter at high speed, or advancing the material through the cutter slowly; most often it is some combination of these three approaches.
There are two major classes of milling process:
In face milling, the cutting action occurs primarily at the end corners of the milling cutter. Face milling is used to cut flat surfaces (faces) into the workpiece, or to cut flat-bottomed cavities.
In peripheral milling, the cutting action occurs primarily along the circumference of the cutter, so that the cross section of the milled surface ends up receiving the shape of the cutter. In this case the blades of the cutter can be seen as scooping out material from the work piece. Peripheral milling is well suited to the cutting of deep slots, threads, and gear teeth.
Many of Graphel Carbon Products’ customers find milling graphite to be very messy and damaging to their equipment. Hence, as our milling supervisor, Jim Hoskins states, “We machine graphite, so you don’t have to.”
There are many different types of tooling, the most common being work holding tools. Work holding tools include jigs and fixtures; cutting tools for milling and grinding machines; dies for cold forming, forging and extrusion machines; and welding and inspection fixtures. In this month’s blog, we are going to look at the basics of grinding.
Grinding, or abrasive machining, is the process of removing metal in the form of minute chips by the action of irregularly shaped abrasive particles. These particles may be in bonded wheels, coated belts, or simply loose.
Grinding wheels are composed of thousands of small abrasive grains held together by a bonding material. Each abrasive grain is a cutting edge. As the grain passes over the work piece it cuts a small chip, leaving a smooth, accurate surface. As each abrasive grain becomes dull, it breaks away from the bonding material.
Two types of abrasives are used in grinding wheels: natural and manufactured. Except for diamonds, manufactured abrasives have almost entirely replaced natural abrasive materials. Even natural diamonds have been replaced in some instances by synthetic diamonds.
The manufactured abrasives most commonly used in grinding wheels are aluminum oxide, silicon carbide, cubic boron nitride, and diamond.
Abrasive grains are held together in a grinding wheel by a bonding material. The bonding material does not cut during grinding operation. Its main function is to hold the grains together with varying degrees of strength. Standard grinding wheel bonds are vitrified, resinoid, silicate, shellac, rubber and metal.
The size of an abrasive grain is important because it influences stock removal rate, chip clearance in the wheel and surface finish obtained.
The grade of a grinding wheel is a measure of the strength of the bonding material holding the individual grains in the wheel. It is used to indicate the relative hardness of a grinding wheel. Grade or hardness refers to the amount of bonding material used in the wheel, not to the hardness of the abrasive.
The structure of a grinding wheel refers to the relative spacing of the abrasive grains; it is the wheel’s density. There are fewer abrasive grains in an open-structure wheel than in a closed-structure wheel. A number from 1 to 15 designates the structure of a wheel. The higher the number, the more open the structure will be; and the lower the number, the denser the structure will be.
All grinding wheels are breakable, and some are extremely fragile. Great care should be taken in handling grinding wheels. New wheels should be closely inspected immediately after receipt to make sure they were not damaged during transit. Grinding wheels should also be inspected prior to being mounted on a machine.
Quality Control in manufacturing is a needed process that ensures customers receive products that are free from defects and meet their needs.
Our customers expect us to deliver quality products in a timely manner. Quality is critical to satisfying our customers and retaining their trust and loyalty. It influences our reputation and helps to control our overall costs.
Recently, Graphel Carbon Products held a Kaizen event to help improve our quality and our on-time performance. One of the main pillars of LEAN methodology, a Kaizen is a specific tool to improve quality. The objective of a Kaizen is to improve productivity, reduce waste, eliminate unnecessary work and humanize the workplace.
Our Kaizen was held over a period of 3 days and included members of our engineering, operations, quality and manufacturing departments. They discussed current methodologies, best practices as well as requirements of all the departments. “In any process there are 3 considerations, the way we plan it to take place, the way we think it takes place, and the way it actually takes place. “ The Kaizen is a great tool for merging the desired and needed attributes of all of these to streamline and enhance a process”, stated Karl Schmidt, Graphel’s Quality Manager.
The results of the Kaizen were very interesting. It was determined that we could utilize our Quality Coaches on the floor much more effectively by intermittently testing with mechanical inspection tools, and complete the final inspection with advanced technologies in our quality department. With the use of micrometers, calipers and gages, time can be freed up on the CMM in the Quality Department for the more complicated quality requirements.
Quality Coaches are a group of certified professionals dedicated to improving quality and productivity. Graphel Carbon Products has over 20 individuals on our production floor who have received additional training and perform some of the functions of quality staff. It was determined that by investing in training, we could reduce the hours in quality by 549, freeing up time and netting a 29% productivity improvement. By furthering the training of the quality coaches and operators, we freed up resources that could be utilized for other jobs, netting a overall productivity improvement of 58%.
By taking the complete responsibility for quality out of the quality department and bringing it to the production floor, our team was able to free up resources and streamline productions.
Quality is part of our culture at Graphel Carbon Products, and we believe it is everyone’s responsibility.
There are many different types of tooling, the most common being work holding tools. Work holding tools include jigs and fixtures; cutting tools for milling and grinding machines; dies for cold forming, forging and extrusion machines; and welding and inspection fixtures. In this month’s blog, we are going to look at turning.
Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates. Turning is a form of machining, a material removal process, which is used to create rotational parts by cutting away unwanted material. The turning process requires a turning machine or lathe, workpiece, fixture, and cutting tool.
Turning is used to create rotational parts by cutting away unwanted material. The workpiece is a piece of pre-shaped material that is secured to the fixture, which itself is attached to the turning machine, and allowed to rotate at high speeds. The cutter is typically a single-point cutting tool that is also secured in the machine, although some operations make use of multi-point tools. The cutting tool feeds into the rotating workpiece and cuts away material in the form of small chips to create the desired shape.
Turning is used to produce rotational, typically axi-symmetric, parts that have many features. Features would include holes, grooves, threads, tapers, various diameter steps, and even contoured surfaces. Parts that are fabricated completely through turning often include components that are used in limited quantities, such as custom designed shafts and fasteners.
Turning is also commonly used as a secondary process to add or refine features on parts that were manufactured using a different process. Due to the high tolerances and surface finishes that turning can offer, it is ideal for adding precision rotational features to a part whose basic shape has already been formed.
The quality of a finished part depends on the precision and characteristics of the tooling. Its’ properties, the speed and accuracy with which it can be produced and the repeatability of manufacture in high volume production runs, all depend on the precision and characteristics of the tooling. So, for the best parts, tooling needs to be designed and engineered to the highest quality.
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EDM Cavity
As the cut progresses through the work metal a cavity starts to form. The deeper this cavity becomes, the harder it is for fresh dielectric fluid to get into the cavity to remove debris and quench the work piece and electrode. In order to get smooth, even flow of dielectric through the gap, flushing becomes an essential part of the EDM process.
Good flushing allows the work piece particles and eroded electrode particles to be removed from the gap. Flushing also allows fresh dielectric into the gap. Both are necessary to maintain stable cutting and to prevent arcing.
It is the volume of oil moving through the gap that performs particle removal. Turbulence in the tank would indicate not enough volume and too much pressure. The ideal pressure is usually between 3 to 5 psi. Flushing at higher pressure may actually prevent the flow of particles out of the gap and the dielectric renewal in the gap. High pressure also tends to wear the electrode.
The balance of volume and pressure is important. Roughing operations where the gap is large would require high volume and low pressure for good oil flow. Finishing operations where the gap is smaller may necessitate higher pressure to improve the oil flow.
The three basic types of flushing are pressure, suction, and external. The choice of flushing method may be limited by the application. The electrode shape and size may prohibit through the electrode flushing.
This is the most common method of flushing. Pressure flushing forces the dielectric fluid through holes in the electrode into the gap between electrode and workpiece. Fluid and particles flow up the sides of the cavity. Pressure flushing through the electrode helps cool the electrode.
This is the opposite of pressure flushing. Fluid and particles are pulled out of the gap through holes in the electrode or workpiece. This method reduces secondary discharge and tapered walls.
Nozzles or tubes may be used to direct streams of fluid into the gap opening. Fluid and particles are pushed out the opposite side. This is the least desirable method of flushing. Poor flushing conditions can trap particles which may cause DC arcing and pitting.
EDM machining is considered by most to be a thermal removal process. The most convincing support for this claim is the removal of material from the electrodes by melting and/or vaporization by a thermal process, along with pressure dynamics established in the spark-gap. The spark gap generates an electrical force on the surface of the electrode that removes material.
Electric discharge machining (EDM), sometimes referred to as spark machining, spark eroding, burning, die sinking or wire erosion is a manufacturing process whereby a desired shape is obtained using electrical discharges (sparks). Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. One of the electrodes is called the tool-electrode, or simply the ‘tool’ or ‘electrode’, while the other is called the workpiece-electrode, or ‘workpiece’.
Electrode gap (spark gap) is the distance between the electrode and the part during the process of EDM. Electro-mechanical or hydraulic systems are used to respond to average gap voltage. To obtain good performance and gap stability a suitable gap should be maintained.
The EDM process is based on the thermoelectric energy. This energy is created between a workpiece and an electrode submerged in a dielectric fluid with the passage of electric current. The workpiece and the electrode are separated by a specific small gap called spark gap. Pulsed arc discharges occur in this gap filled with an insulating medium, preferably a dielectric liquid like hydrocarbon oil or de-ionized (de-mineralized) water. In this process there is no direct contact between the electrode and the workpiece thus eliminating mechanical stresses, chatter and vibration problems during machining.
As an electrode moves toward the workpiece the spark gap is reduced so that the applied voltage is high enough to ionize the dielectric fluid. Short duration discharges are generated in a liquid dielectric gap, which separates electrode and workpiece. The material is removed from tool and workpiece with the erosive effect of the electrical discharges. The dielectric fluid serves the purpose to concentrate the discharge energy into a channel of very small cross sectional areas. It also cools the two electrodes, and flushes away the products of machining from the gap.
Engineering materials having higher thermal conductivity and melting points are used as a tool material for EDM process of machining. Copper, graphite, copper-tungsten, silver-tungsten, copper graphite and brass are used as a tool material (electrode) in EDM. They all have good wear characteristics, better conductivity, and better sparking conditions for machining. Tungsten resists wear better than copper. The factors that affect selection of electrode material include metal removal rate, wear resistance, desired surface finish, cost of electrode material manufacture and material and characteristics of work material to be machined.
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