Micro EDM is an important micro manufacturing process because it is unconstrained by the hardness or material strength of the material being machined. Article by Sodick.
Micro electrical discharge machining is similar with the principals of electrical discharge machining (EDM), a thermal process that uses electrical discharges to erode electrically conductive materials. EDM has a high capability of machining the accurate cavities of dies and mould. It is an effective technique in the production of micro components that are smaller than 100µm.
The main differences between micro EDM and conventional EDM are the size of the electrode used, the power supply (current and voltage), and the resolution of the X-, Y- and Z- axes movement. Micro EDM is a process based on thermoelectric energy between workpiece and electrode. In micro EDM, the pulse generator produces very small pulses within a pulse duration of a few microseconds or nanoseconds. Therefore, micro EDM utilizes low discharge energies to remove small volumes of material.
Micro EDM is an important micro manufacturing process because it is unconstrained by the hardness or material strength of the material being machined. It has a wide implementation because there is no direct contact between the electrode and machined component; hence, no contact forces are induced during the machining process. Which is why it is highly suitable for machining all types of conductive metals and semiconductors.
One example is Sodick’s AP30L linear motor-driven die-sinker EDM, which features ultra-precision machining and achieves high speed and quality surface finish by adopting the stable EDM system Arc-less 4. This series has been developed for the purpose of improving the machining accuracy and productivity of small and miniaturized high precision moulds, such as components for electronic equipment, automobiles, and digital consumer electronics, among others. Various advanced technologies are implemented in this machine in order to achieve ultra-high precision machining in the range of 1μm.
In micro EDM, changes in temperature impact the machining of high precision parts. Sodick’s AP30L will collectively manage all the ambient temperature changes and internal heat generation through the overall temperature control. It is capable of optimum high rigidity mechanical structure by CAE analysis, and built with a fully separate heat source structure integrated with ceramic components and machining-fluid for temperature control. This is the upgraded model of the die-sinker EDM, featuring a newly designed main body, tank, electric discharge power supply and NC unit. The comprehensive temperature control minimizes the effects from the temperature change in the installation environment and the heat generated during high-speed drive, which used to be an issue in high-precision machining.
In order to maintain extremely accurate positioning of the X, Y and Z axis, the machine is installed with Sodick’s in-house developed linear motor, which features high-speed axis motion and quick response, made possible by its ball screw-less design. Conventional drive systems use ball screws to convert the rotational motion of the motor into the linear motion of the axis stroke, leading to the unavoidable deterioration of the high-speed servo motors due to back-lash and mechanical lost motion. However, linear motors directly provide motion to each axis without converting rotational movements of the motor to linear motion. To achieve maximum performance with a linear motor, the K-SMC motor controller is also developed in-house, utilizing Sodick’s control know-how. The feedback from the spark gap is directly fed to the K-SMC board, allowing for instantaneous adaptation of the sparking conditions.
The machine is equipped with a newly developed carbon fibre reinforced polymer (CFRP) compact symmetrical head to achieve low weight and high rigidity. In addition to the fully separate heat source and precise cooling mechanism, a newly developed precise thermal displacement compensation system makes it possible to perform high-precision machining. The system also incorporates artificial intelligence (AI) technologies.
The system’s LP4 power supply NC unit, developed and manufactured in-house, has new discharge circuits and control that significantly improve machining speeds for all processes, from rough machining to finishing. The new Arc-less 4 EDM system offers stable, high-precision machining for all types of materials. The discharge state can be maintained steadily; but speeding up is possible. In addition, it realizes suppression of electrode consumption, achieves a wide variety of processed surface quality ranging from satin finish to mirror finish, and improves the overall performance of electric discharge machining.
As the industry moves toward Industry 4.0, EDM machines are expected to become more intelligent as manufacturers incorporate more and more advanced functionality to enhance the productivity and efficiency of the system. Article by Makino.
The electrical discharge machining (EDM) process utilises short bursts or pulses of electrical energy to erode and machine conductive materials. This process can be thought of as machining with lightning bolts, called sparks. With EDM, the number and power of each spark can be precisely controlled, thus, by modifying the amount and power of the discharge spark energy, the material removal rate, attained surface finish and resulting accuracy can be predictably and repeatedly controlled.
While EDM is commonly thought of as a slower form of metal removal compared to conventional milling and some other processes, recent advancements in EDM technology have led to significant improvements in processing times and finish quality for even the most complex and involved part geometries.
But what has now become an essential process for die/mould shops, aerospace, automotive and other manufacturers humbly began with a failure.
Brief History of EDM
In the early 1940s, two scientists in the former Soviet Union, B.R. Butinzky and N.I. Lazarenko, experimented with methods to prevent erosion of tungsten contacts caused by electrical sparking during welding. Although they didn’t find a better welding method, they discovered how to control metal erosion by immersing the electrodes in oil or water. From their research, Butinzky and Lazarenko built the first electrical discharging machine for processing metals that were difficult to machine with conventional milling, drilling or other mechanical methods such as tool steel and titanium.
Butinzky and Lazarenko drew on ideas developed by English physicist, Joseph Priestley, who wrote about the erosive effects of electricity on certain metals back in the 1770s. The Russians’ early work became known as spark machining because electrical discharges caused sparks that could be controlled to manufacture specific shapes.
Machining with Electricity
In conventional machining, the material is removed by cutting tools that turn or grind against the workpiece with a mechanical force. In the EDM process, sparks of electricity create short bursts of high energy that instantly melt and vaporise the material without making contact. Due to the non-mechanical and non-contact machining process, EDM is referred to as a “non-traditional” type of manufacturing.
The key to EDM machining is the passage of electricity from a tool (electrode) to the workpiece, which must be composed of conductive material like steel or aluminium. The tool, which can either be a small diameter wire, hollow tube, or an electrode mechanically machined into a negative version of the workpiece’s final shape, is then placed and maintained in close proximity to the workpiece during the EDM spark erosion process.
EDM technology has evolved into three distinct machining approaches:
Wire EDM: Wire EDM uses a small diameter copper or brass-alloy wire to cut parts much like a band saw. Traditional uses are to make punches, dies, and inserts from hard metals for die/mold tooling applications. Uses have since expanded to include part production uses over a wide array of industries.
Sinker EDM: Sinker EDM uses electrodes machined from a special graphite or copper material into the shape or contour feature needed on the final workpiece. Typically, uses include the production of small or complex cavities and forms for die/mould tooling, but have also found use in many production applications.
EDM Drilling: EDM drilling uses a small diameter hollow tube electrode made from copper or brass alloys to erode holes into the workpiece. This method is typically used to prepare start holes for the wire EDM process, but have also progressed to producing small hole features found in dedicated production applications such as turbine engine components and medical devices.
Why Use EDM
One of the key advantages in EDMing is the machine’s capability to work on small corners that cannot be cleared by the milling process. Also, when it comes to precision parts, very small work pieces are prone to damage when machined with conventional cutting tools because of the excess cutting pressure. You won’t have this issue with EDM.
With conventional cutting, extremely hard materials will affect the high wear rate of the cutter. This is not the case for EDM. In fact, apart from cutting these hard pieces of materials, the EDM process also provide excellent surface finishes.
Moreover, EDM enables the processing of complex shapes that would otherwise be difficult to produce with conventional cutting tools.
Over the years, many new machine technologies have helped improve the performance of EDM systems, enabling higher cutting speeds to produce parts faster than before.
One example of the latest technologies in EDM is Makino’s U6 H.E.A.T. Extreme wire EDM, which features an industry first 0.4mm (0.016”) coated wire technology that increases rough machining rates up to 300 percent compared to traditional 0.010” brass wire, while maintaining comparable wire consumption rates of 0.6–0.7lbs/hour. As a result, the new machine is able to significantly improve rough machining speed without increasing manufacturing costs.
Addressing the Labour Skills Challenge
Despite the advancements in EDM, there continues to be challenges facing the segment. One issue is labour, in particular, the lack of skilled EDM operators.
As new technologies are being incorporated in EDM, the need for programming skills, and the setting up and operation of more complex machines with more and more functionality are increasing. This, in turn, requires more knowledge and skills needed for ordinary operators.
One way of addressing this is the introduction of Industrial Internet of Things (IIoT) applications for EDMs to reduce the otherwise long learning curve required by the system, enhance user experience and efficiency, and reduce machine downtime.
Makino’s expanded Hyper-i Control family and Remote Monitoring features intuitive, intelligent, and interactive functions that utilise familiar smartphone/tablet functionality that provide operators with a powerful and user-friendly interface.
Its unified control system for both wire and sinker EDM machines provides operators with enhanced functions to improve productivity, regardless of operator skill level. The large 24” class HD touch-screen display provides a commanding view for the operator and utilises intuitive and familiar touch Pinch/Swipe/Drag operations similar to smartphones and tablets.
Straightforward machine operation is accomplished on the Hyper-i Control with a three-step process of Program/Setup/Run flow, and there are many helpful intelligent tools and functions for the operator that provide greater convenience and flexibility, such as the standard full-function advanced Handbox. In addition, digital onboard electronic manuals, instructional training videos, and the advanced E-Tech Doctor help functions provide the operator with practical resources at their fingertips to remain highly productive.
Another EDM technology from Makino is the HyperConnect application, which facilitates machine-to-machine connectivity. HyperConnect is a suite of IIoT applications for EDMs that enhances user experience and efficiency and reduces machine downtime. They are available on all Makino EDMs equipped with Hyper-i control systems. Some of the features of HyperConnect are as follows:
The app enables shop managers and operators to monitor and control EDM processes from any PC, smart device, or other Hyper-i control systems on the network. It has four primary connectivity features for shop personnel to monitor, plan, and troubleshoot EDM operations.
EDM Mail relays machine status information to operators via email during unattended operation to help reduce downtime and support multitasking abilities. It delivers periodic, timed interval updates of a machine’s operating conditions and alerts operators of a machine stoppage.
Machine Viewer is an application that permits networked access to the control’s NC operation screens, which allows operators to remotely view the machine control and process information from any office environment PC or enabled smart device.
Machine-to-Machine Viewer gives operators remote access to view and control a networked EDM from another machine, preventing unnecessary foot traffic across the shop floor.
PC Viewer provides operators with remote access to all software on a networked PC directly via the control and includes accessibility to any CAD/CAM software, specialized shop tracking software, and Microsoft Office applications.
Future of EDM
It’s been a long time since the discovery of EDM for metalworking. As the industry moves toward the fourth industrial revolution, EMD machines are expected to become more intelligent as manufacturers incorporate more and more advanced functionality to enhance the productivity and efficiency of the system.
One way “intelligence” is being added to the machine is through voice-enabled machine interaction. It is just like your iPhone’s Siri—but instead of asking for directions or calling a certain person in your address book, you are giving instructions to a machine regarding the processing or machining of a particular workpiece.
Makino is the first adopter of ATHENA, the first ever voice-operated assistant technology created specifically for manufacturing work. Developed by iTSpeeX, ATHENA is designed to enable operators of all skill levels by simplifying human interactions with industrial machines. For example, with one voice request, ATHENA can search through a machine’s maintenance manual and display the needed information right at the machine.
This will give operators more ease of control and will not just save time in training and onboarding new machinists, but also in giving experienced machinists the information they need when and where they need it.
EDM and ECM processes are advanced manufacturing technologies with unique capabilities due to their non-mechanical material removal principles can be found in different areas of application in industry offering a better alternative or sometimes the only alternative in generating accurate 3D complex shaped macro, micro and nano features and components of difficult-to-machine materials.
Electrochemical Machining (ECM) is a non-traditional machining (NTM) process belonging to Electrochemical category. ECM is opposite of electrochemical or galvanic coating or deposition process. Thus ECM can be thought of a controlled anodic dissolution at atomic level of the work piece that is electrically conductive by a shaped tool due to flow of high current at relatively low potential difference through an electrolyte which is quite often water based neutral salt solution.
On the other hand, Electrical Discharge Machining (EDM) is a controlled metal-removal process that is used to remove metal by means of electric spark erosion. In this process an electric spark is used as the cutting tool to cut (erode) the workpiece to produce the finished part to the desired shape.
Wire EDM beginnings in 1969, the Swiss firm Agie produced the world’s first wire EDM. Image Credit: Pinterest
Challenges Of Machining
The demand for macro- and micro- products and components of difficult-to–machine materials such as tool steel, carbides, super alloys and titanium alloys has been rapidly increasing in automotive, aerospace, electronics, optics, medical devices and communications industries. In spite of their exceptional properties, many of these difficult-to-machine materials seem to have limited applications. These materials pose many challenges to conventional machining processes (such as turning and milling).
For example, titanium alloys are susceptible to work hardening and its low thermal conductivity and higher chemical reactivity result in high cutting temperature and strong adhesion between the tool and work material leading to tool wear. Electrical Discharge Machining (EDM) and Electrochemical Machining (ECM) offer a better alternative or sometimes the only alternative in generating accurate 3D complex shaped features and components of these difficult –to- machine materials.
Advantages of ECM
One of the major advantages of ECM is the scalability of the process with the use of multiple electrodes on the same machining setup. ECM using multiple electrodes machined to machine arrays of micro holes results in increased productivity. Taper induced on the workpiece during ECM drilling is a major concern. Some of the tool designs for the reduction of taper include dual pole tools, insulated tools, and tools with shaped ends.
High conductivity, heat resistance and high melting point are the main desired properties for an EDM tool. The most common materials used in EDM tooling are copper, graphite, tungsten and tungsten carbide. Research is being done on many new materials including composites for EDM tooling.
Typical as well as innovative examples of application for the most important areas of application – die and mold manufacturing, turbomachinery component manufacture, tooling and prototyping and medical engineering. In addition, combined and even hybrid EDM and ECM processes are known with superior overall process performance.
Electro-Chemical Machining (ECM) with up to four Axes. Image Credit: Pinterest
In all areas of application, the final surface integrity defines the later part performance. Therefore, the machining processes have to be designed and executed in such a way that the specific operation demands are fully met by the remaining surface modifications of the machined part. From application point of view different manufacturing processes could only compete with each other when providing at least the same part functionality and therefore similar material modifications.
While EDM incorporates thermal energy dissipation, ECM purely relies on a chemical material removal principle. ECM and EDM technologies have been successfully adapted to produce macro, micro components with complex features and high aspect ratios for biomedical and other applications. These processes are also being attempted at the nano-scale.
Today’s waterjets can cut much faster than CNC mills and wire EDM machines, and with high precision. But it is not only the cutting speeds and tight tolerances that make them so attractive. By Dr John H Olsen, vice president of operations at Omax Corporation.