What to Look for When Selecting a Magnetic Chuck for Sinker EDM

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When consulting EDM shops on work holding solutions, one question that we frequently receive is whether you can use standard magnetic chucks for EDM applications. Unfortunately, this is not the case. Magnetic chucks used in EDM machines are typically specialized for EDM applications. These chucks are sealed differently than magnetic chucks that are used for grinding machines, as the oil and debris from the EDM process can damage and seize-up the typical ON/OFF magnet levers. Several magnetic chuck manufacturers (such as Walker Magnetics, Suburban, Hermann Schmidt) offer EDM specific chucks that have fine pole divisions for improved work holding, magnetic poles that reach to the very edge of the chuck, and a more compact, thinner design to preserve the usable Z-axis stroke of the machine. Be sure that the magnetic chuck you purchase is designed and compatible for use on EDM machines.

EDMmatters 5-25-17

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A Q&A on EDAF Sinker EDM Electrode Discharge Dressing

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Q: Is there a way to perform discharge dressing of the electrode on a Makino EDAF3 machine?

A: Yes, the Hyper-i control does have a dedicated macro program for discharge dressing of electrodes, but the machine should be equipped with the high-speed C-axis spindle (MA C-Axis) and discharge dress macro. The discharge dressing process uses the machine to create its own electrode through the EDM erosion process. Creating small diameter electrodes is the most commonly performed function of EDM dressing, but this process can also be used to create shaped electrodes or remove worn sections of an electrode.

Discharge dressing starts with a larger diameter electrode that is then EDM’ed down to whatever diameter is needed using a dressing block that is setup within the work tank. Depending on the required electrode size, multiple steps can be dressed on the electrode to provide the best possible rigidity for the final diameter. Once an electrode diameter is dressed to size, it is then used to EDM the workpiece feature.

The dressing block can be made from pure tungsten, tungsten carbide, copper tungsten (CuW), or silver tungsten (AgW). The CuW and AgW materials typically provide the best results. The electrode material can be made from copper, tungsten carbide, pure tungsten, copper tungsten, or silver tungsten. Each electrode material type has slightly different characteristics that determine the amount of time that is required to discharge dress. Additionally, each material type provides varying degrees of rigidity for extremely small diameters, but AgW electrode materials are typically recommended for best results.

On the Hyper-i control, there is a dedicated Model Plan and G-Code function associated with the discharge dressing process.

G-code Function:

G105  O9020 N1 X___ Y___ Z___ R___ I___J___ T___ L___ A___ B___ M___

  • Main Functions:
    • X = X-Axis Start Point
    • Y = Y-Axis Start Point
    • Z = Target Dressing Length
    • R = Target Finish Diameter
    • I = Start Process Number
    • J = Finish Process Number
    • L = Dressing Direction [1 = -X (←) | 2 = -Y (↓) | 3 = +X (→) | 4 = +Y (↑)]
    • M = Spindle Rotation Speed (value of 15 is typically used)

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For additional information, please refer to Chapter 12 in the Machining Techniques manual, or contact Makino Technical Support at 1-888-625-4664.

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Selecting the Best Type of Coated/Stratified EDM Wire (Part 3 of 3)

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For first time visitors, this blog entry is part three of a three-part series discussing considerations for selecting coated EDM wires. To get up to speed on previous entries in this series, please check out part one and part two.

Not all coated EDM wires are created equal, making it critical for EDM shops to know and understand the physical and performance-based differences of each coated wire type. In this series, we’ve covered initial planning considerations, impacts on speed, and accuracy capabilities for coated EDM wire. In this final entry, we will look at additional considerations related to surface finish, speed and limitations, that can impact your selection of coated EDM wire.

SURFACE FINSH: If surface finish requirements are priority, it is advised to avoid coated wires that are designed for speed. Coated wires designed for speed may result in the degradation of surface finish, resulting in a rougher surface. Depending on the type of coated EDM wire, 1- or 2-pass skim cut finishing is all that might be achievable, as some high-speed coatings do not work with low power settings. If an incompatible coated EDM wire is used for fine finishing, wire shorting can occur, causing visible wire lines on the final part.

For finer surface finishes, plain zinc-coated wires, the same types used for improved accuracy, will the deliver the required results. The degree to which surface finishes are improved will depend on the make and model of the machine and the machining processes used, but improvements of up to 15% over Plain Brass wire are achievable.

Wire Examples: MegaCut-A, HyperCut, THERMO-A

WIRE BREAKS: If your current processes are challenged by wire breaks, the use of any type of coated EDM wire should provide a higher level of wire break prevention compared to plain brass wire. The outer layer of a coated wire is designed to erode off during machining, preserving the integrity of the inner wire core and making wire breaks less frequent. The outer layer thickness and metallurgical make-up vary between the different types of coated wire, which explains the differences in price and performance characteristic that exist among the available coated EDM wires.

LIMITATIONS: It is important to understand the advantages and disadvantages, as well as the unique performance and capability attributes of each coated wire type compared to traditional plain brass wire. Each coated EDM wire is designed for a specific application, characteristic and price point, so it is important to understand how and when to apply the different types of wire.

The bulk of coated EDM wires are marketed for achieving greater speed, so it is critical to establish specific part requirements for accuracy and surface finish before rushing to apply coated wire to a job. Based on the part requirements and machine being used, some simple test cuts may help to verify a coated wire’s capability and performance gains within a specific application. This may lead to further process optimization, which can also help to justify the higher consumable price paid when using coated wire. Additionally, the use of coated EDM wires may increase the need for machine maintenance, including the cleaning of rollers or more frequent indexing of power contacts, so it is important to take this into consideration when switching to coated wire.

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We hope this series has been helpful to you. If you are interested in learning more about coated EDM wire, please check out our free webinar, “The Selection of EDM Coated Wires”. Thank you for your readership, and happy EDMing!

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Selecting the Best Type of Coated/Stratified EDM Wire (Part 2 of 3)

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As we introduced last week in part one of our series, not all coated EDM wires are created equal, and no single type of coated wire should be considered the BEST for all conditions. The different coated EDM wires available have each been developed to achieve different performance levels at different price points. That challenge is knowing which type is right for your workpieces and processes.

In many ways, selecting a coated EDM wire is similar to purchasing tires for a car. Different tires provide varying levels of traction and braking performance, and they are each available at different price points. For instance, there are specific tires for ice and snow (winter tires), warm/wet weather (summer tires), and tires designed for all conditions (all season tires). These different tires contain specialized rubber compounds and tread patterns, and are available with a range of different tread life, but no one type is the BEST performer for all conditions. Each of these different types of tires has been designed for specific characteristics and conditions… just like coated EDM wire.

In today’s blog update, we will be focused on coated EDM wires that designed for speed and for accuracy:

SPEED: The use of coated EDM wire is most commonly used to achieve faster rough-cut machining speeds. In this case, the coated wire allows additional power to be applied to the wire without breaking, which leads to faster machining. There are variety of coated EDM wires on the market today that are designed for enhanced speed, which fall into two main types: diffusion annealed and gamma-phase. Both types are able to achieve 30% greater speed over plan brass wire; however, the latest generation of gamma-phase coated EDM wires provide the biggest increases in speed, particularly within applications featuring poor flushing conditions.

Wire Examples: MegaCut-D, Topas-Series, Topas HEAT, THERMO-SD, Gamma-D

ACCURACY:  Using a coated EDM wire that is designed for speed might not translate into greater productivity in workpieces where high accuracy (+/-0.0002” or finer) is a key requirement. By design, the high-speed coated EDM wires exhibit more wire electrode wear during machining, which can lead to additional unwanted taper or straightness variation in the final part. These coated EDM wires also show reduced accuracy and greater variations in part alignment pick-up cycles. So if accuracy is the main concern, then coated EDM wires with plain Zinc coating should be considered. These types of coated EDM wire will provide a slight 5-10% increase in machining speed over plain Brass wire, but it is the consistency of the thin outer coating of zinc that maintains and enhances accuracy.

Wire Examples: MegaCut-A, HyperCut, THERMO-A       

What matters most to your workpiece requirements today: speed or accuracy? If surface finish or wire breaks are your biggest concerns, be sure to check back next week for part three in our coated EDM wire series.

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Selecting the Best Type of Coated/Stratified EDM Wire (Part 1 of 3)

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One of the more frequent questions we receive is, “what is the best type of coated or stratified EDM wire?” While seemingly a simple question, a detailed response is required to cover the many different machine and application variables that must be considered. As such, we will be covering this topic in a three-part series over the next several weeks. To begin, we’re going to focus on some of the primary variables to consider:

  • Does your machine have optimized settings for a particular type of coated EDM wire? If your wire EDM machine does not have coated EDM wire settings, you will need to modify the standard brass EDM wire settings.
  • What type of flushing application is on the workpiece? Good flushing conditions would have both heads achieving seal-off on the workpiece, while poor flushing conditions would mean that seal-off on the workpiece cannot be achieved on one or both heads.EDMmatters 4-6-17
  • What is the desired production benefit to using coated EDM wire?
    • Faster machining speed
    • Higher accuracy
    • Finer surface finish
    • Less wire breaks

The two main factors that will help determine which type of coated EDM wire is BEST for a specific application are the flushing type and desired production benefit. Determining which of these variables applies to you is the first step in finding a coated or stratified EDM wire for your applications.

What types of variables are you working with today? Once you’ve identified the status of your setup, check back next week for part two as we dive into recommendations based on each desired production benefit.

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