Achieving the Best Possible Surface Finish for Sinker EDM Machining

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Q: Does high-qualify surface finish (HQSF) technology produce the best possible surface finish on Makino EDMs, and what is added to the machine for this option?

A: For over 20 years, Makino has offered HQSF technology as an option on sinker EDM products. The benefits of this technology are still a valuable and important function for fine-finish applications. When initially released, HQSF was designed with a focus on the improvement of surface finish and finish consistency to eliminate post-machine polishing, but the technology also yields additional benefits.

HQSF technology uses a special proprietary powder (µSc) designed to be neutrally buoyant so that it remains suspended when added to the dielectric oil fluid. During machining, the powder additive evenly distributes the discharge spark energy over the entire electrode contour. This design provides a more controlled and stable EDM process by minimizing any local concentrations of power that can create shortages resulting in “hot spot,” or pin-hole, discharge.

HQSF does not necessarily improve the “best possible surface finish” capability of a machine, as seen with the use of copper electrodes. However, the use of HQSF with copper electrodes does dramatically improve the total cycle time.

When using graphite electrodes, HQSF dramatically impacts and improves the best achievable surface finish. Performing standard EDM processing using graphite electrodes yields a best surface finish of 0.7µRa (27µinRa). Using HQSF with graphite electrode can produce a best surface finish of 0.4µRa (16µinRa), which is a significant improvement of almost 50 percent. Additional cycle time, however, is required to achieve this finer finish with the HQSF special generator settings.

During HQSF machining, the machine filters are bypassed, and the machine tracks the machining hours of the HQSF powder. Once the powder is depleted, the filters are reactivated to collect the material debris from the fluid. Early machines with HQSF technology are equipped with magnetic separators used to filter large metal contaminants from fluids. The magnetic separator system is still an available option, but this system is recommended only for large EDM applications that use 120-amp or higher power settings.

The Makino EDAF-Series machines offer HQSF technology as a retrofit option (except for machines equipped with the fine-hole EDM drilling options), but the larger EDNC-Series machines offer HQSF only as a factory-ordered option.

HQSF Technology Benefits:

  • Faster roughing speeds
  • Faster total cycle time to fine surface finishes using copper electrodes
  • Faster total cycle time to standard surface finishes using graphite electrodes
  • Up to 50 percent finer surface finish with additional cycle time using graphite electrodes
  • Improved metallurgical quality (less recast, HAZ and micro-cracking) that can extend the service life of the part/tooling component
  • Reduction or elimination of polishing time

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Streamlining Electrode Reduction for EDM

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 Q: Is it acceptable to utilize the same electrode reduction undersize amount for all of the electrodes?

A: The real answer is yes and no, as a proper answer requires a detailed look at the overall EDM operation. The practice of using a standard electrode reduction amount is very common. However, depending on specific applications, it may or may not yield the best machining speed or accuracy results.

Benefit of Using a Standard Electrode Undersize:

  • In many shops, the electrodes are machined by milling, and different mill programmers typically have varying levels of EDM knowledge. Using a common or standard electrode reduction amount for all electrodes can help streamline and simplify the process of electrode programming, regardless of the operator.
  • Applying the same electrode reduction amount to all electrodes prevents confusion in EDM setup and tracking. If all electrodes have the same reduction amount, there is no need to mark and/or measure every electrode during EDM setup.
  • Applying the same electrode reduction to all electrodes lends greater EDM process flexibility, as the electrodes can be shuffled around and reused as roughers and finishers when needing to produce multiple cavities of the same contour (for example: cavity #1 finish electrode becomes Cavity #2 roughing electrode).

Downside of Using a Standard Electrode Undersize:

  • Using a standard electrode reduction amount can waste valuable shop machining time. With too small of an electrode reduction amount, the EDM operator is often handicapped into using a lower power discharge setting in order to maintain proper size, which results in slower machining speeds and increased electrode wear.
  • Applying the same electrode reduction amounts between the roughing and finishing electrodes can deteriorate form accuracy, as the finishing electrode is machined further away from the final net shape of the desired cavity and often requires greater optimization. This method can also lead to declines in machining speeds (slower roughing and more required orbiting on finishing).

Intelligent Review on Electrode Preparation:

  • It is paramount that the EDM operator and electrode milling programmer communicate to discuss plans for electrode reduction on each job.
  • Through proper review and planning, shops can significantly improve efficiency and apply optimal electrode reduction amounts that produce the fastest machining speeds (roughing speeds often see the largest improvements).
  • The use of different electrode reduction amounts can be strategically deployed on critical part details that require tighter tolerances.
  • It is important to establish a reliable identification system when manufacturing electrodes with different reduction amounts, such as a marking or color code system on the electrode holder for roughing and finishing.
  • For more open tolerance details, a standard electrode reduction size can be established.

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A Q&A on Optimizing Die Guide Clearances for EDM Drilling Applications

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Welcome back, EDMers! This Q&A post is designed to help inform you on the best die guide clearances for your specific EDM drilling needs and applications.

 Q: What are the typical die guide clearances that Makino recommends for EDM drilling applications?

A: Properly optimizing die guide clearances for specific EDM drilling applications significantly contributes to the overall success in machine shop drilling operations. If not done properly, shop owners can experience continual setback and operational challenges. For example, using a clearance that is too large can give way to poor part quality. On the other hand, using a clearance that is too tight can also result in poor edge quality and reduced tool life.

Makino offers two different types of EDM drilling machines designed for specific applications. Below are the recommended die guide clearances for each:

Fine-Hole EDM Drilling:

Fine-hole EDM drills are designed specifically for ultra-high accuracy. These machines use a standard EDM oil dielectric fluid, and all machining is performed fully submerged. Both standard sinker EDM and EDM drilling operations can be performed using fine-hole EDM drills. Due to high-accuracy requirements, die guide clearances are small and limited to L:D drilling ratios.

Some Makino products that support fine-hole EDM drilling are noted below:

  • EDAF2 / EDAF3 equipped with the fine-hole specification
  • EDGE2 / EDGE3 equipped with the fine-hole specification
  • EDFH-1 machine

Recommended fine-hole die guide clearances are listed below:

  • 0008″ ~ 0.012″ Ø à 0.0002″ clearance
  • 012″ ~ 0.080″ Ø à 0.0003″ clearance
  • 080″ ~ 0.160″ Ø à 0.0006″ clearance

Production EDM Hole Drilling:

Production EDM hole drills are designed primarily for high-speed and high-volume production, as the name implies. These machines use a deionized water dielectric fluid; and like fine-hole EDM drilling machines, all machining is also performed fully submerged. However, unlike fine-hole EDM drills, production EDM hole-drilling machines perform only EDM drilling operations and not standard sinker EDM operations. Due to more open part tolerance, die guide clearance is larger to prevent jamming of the electrode into the die guide on deep L:D ratio holes. Die guides are also available in long/extended lengths to yield deeper access to a workpiece.

Some Makino products that support production EDM hole drilling are noted below:

  • EDBV3
  • EDBV8

Recommended production EDM hole die guide clearances are listed below:

  • 008″ ~ 0.125″ Ø à 0.002″ clearance
  • 125″ ~ 0.250″ Ø à 0.004″ clearance

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Knowing the proper die guide clearance recommendations for your precise EDM drilling applications helps shops not only improve machining performance but also preserve machine and tool life, both of which are guaranteed to deliver value to any machine shop in the long run.

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How to Justify the Higher Purchase Cost of Coated EDM Wire

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How to Justify the Higher Purchase Cost of Coated EDM Wire

For wire EDM operators, selecting the right EDM wire for their machine shop applications is just as important as any other task in the operational cycle. Many times, justifying the cost of consumables can be difficult, and operators often have to consider several criteria in order to make the most cost-effective decision. This week’s post helps inform these decisions to guide you in selecting the most appropriate wire for your EDM shop and applications.

Is making 20 percent greater profit desirable? Well, the most valuable asset a shop has is its hourly billable shop rate (HBSR), which ultimately drives profitability and the bottom line. High-speed coated wires have been available for more than 10 years, and their 20 to 30 percent increase in cutting performance is well documented. Still, many shops limit their productivity by using only standard hard brass wire. A common misconception and false justification for going with coated wire is: “If the wire costs twice the price per pound, but doesn’t cut twice as fast, then it’s not worth using.”

The actual manufacturing cost of the consumed wire is very small when compared to the HBSR, even when using coated wire. For a typical $60/HBSR, the wire consumption costs of brass wire are about 10 percent, compared to about 18 percent for coated wire. The justification for coated wire is that it yields greater profit and productivity in any accounting approach. Below are the two most common justification comparisons between using brass versus coated wires. The comparisons focus on the additional billable shop time and increased machining speed.

Justification of additional billable machine time

  • Cost-benefit analysis between brass wire and coated wire
  • Operation cost model comparison for one year of operation (2,080 hours)
  • Coated wire provides 520 hours of additional billable shop time

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Justification of increased machining speeds/cost per part

  • Cost-benefit analysis between brass wire and coated wire
  • Operation cost model comparison for one year of operation (2,080 hours)
  • Coated wire provides a lower total cost of operation for the same output

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Makino wire EDMs feature a complete machining condition database designed to provide the optimum mix of machining speed, accuracy and low wire consumption. Every condition for all material types and wire sizes on a Makino wire EDM has low wire-consumption technology and takes advantage of Makino’s proprietary BellyWIZARD™ technology to maintain part straightness and accuracy. Below is a cost justification between brass and coated wires reflecting real-world hourly wire consumption values attained by Makino wire EDMs.

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Based on the information presented, wire EDM shoppers can informatively justify higher purchasing costs for coated EDM wire. Whether it is for additional billable machine time or increased machining speeds, having the right information to help justify any material cost can greatly improve machine shop efficiency and utilization.

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A Q&A on Coated EDM Wires for High-Precision Machining Applications

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Q: What is the best type of Coated EDM Wire to use for High Precision machining applications?

A: When researching coated EDM wires online, you’ll probably come across lots of information on different types and the unique benefits of each type. But, did you know that certain types of coated wires, although fast in performance, might cause degradation to a machine’s accuracy output?

It is important to recognize the certain types of coated wires that can degrade a machine’s accuracy output. Part accuracy can be degraded with coated wire as a result of the wire’s outer coating eroding and vaporizing quicker than a standard brass wire. This deviation is often seen as a tapered error in the part from the additional wire electrode wear. Some coated wires have an outer coating that can also affect a machine’s pick-up cycle accuracy. This is either due to an oxide layer or from the flaking rougher surface of the coated wire.

Certain wires are specifically designed for high accuracy applications. These kinds of wires tend to provide less of a machining speed increase than high-speed type coated wires.  One of the oldest and most common coated wire types is the Type-A Wire, which is ideal for high accuracy applications.  A-Wires often have a distinctive bright and shiny silver color. They provide a minimal machining speed increase compared to brass wires, but typically provide a more reliable AWT performance whilst achieving high levels of surface finish and accuracy.

A-Wires are typically produced with a higher tolerance level than traditional plain brass wires, providing an accuracy advantage. Mak1Many machine OEM’s recommend using A-Wires, as they have been the industry’s go-to wire in achieving the highest part quality and the best possible surface finish, especially on carbide materials.

As we continue to explore best practices in using coated EDM wires, be sure to join us next week for an in-depth look at how to achieve best surface finishes.

 

 

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