Techniques for Repeatable Hole Popping

Hole popping  in a variety of materials can have varying results and sometimes becomes very frustrating. There are a couple of things users can do to make this process a little easier:

1). Brass tubes (Electrodes) can be used for steel for 90 % of your applications down to .008 diameter. We found that by going to copper electrodes below .008” wear rate improves and burn rate remains. The wear rate becomes extremely important in small hole applications. For harder material such as Carbide, it is strongly recommended to use Copper tubes as the wear rate using brass is more then double.

Dielectric Influence on Burning Characteristics

Dielectric fluid can influence all kinds of burning characteristics that have a direct effect on the successful outcome of an end users application.

1). Using oil that is a mineral based has a shelf life depending on usage for a period of two years. With mineral based oils each spark causes break down of dielectric strength. Cutting speed can be increased because of this breakdown but finishing speed will be greatly reduced. Pitting or Arcing can also occur causing the possible destruction of your work piece. When observing this situation it will become necessary to completely change your oil

Custom Macro Programming

Custom macro programming can provide for faster and easier machine operations when manufacturing parts or a family of parts with similar features. In certain production instances, a custom macro program can eliminate the need for individual job programming, and the electronic data management of multiple programs. A macro program can be considered the ultimate in custom NC G-code programs. As long as a number of parts and/or operations can be used and controlled by the use of a macro program, time can be saved by reducing the need to generate a dedicated program for each job.

Choosing a Fast Hole Guide

When ordering Fast Hole guides you should be aware that there are two types of guides to choose from. Most fast hole users have no idea that there is a difference between the guides. Guide type A have a very small ceramic land to hold the electrode in place. Where as Guide type B has a land surface that is three times that of Guide type A. Guide type B is used for drilling very tall work pieces or when increased accuracy is desired.

Negative Polarity on Rib or Gate Electrodes

Using Negative polarity on rib or gate electrodes can provide much faster cuttings speeds. The only draw back that you will see is about 40% more electrode wear. Depending on your surface finish you may choose to use negative polarity on the last few power settings where you are not removing a lot of material. Choosing the proper electrode material for this application is also a factor. A graphite material with a grain structure at or below 5 micron would be the best choice.

Inspecting Start Hole Quality

Always inspect all start holes for burrs and heat-treat scale. It is quite common for burrs to exist in start holes due to flat grinding, and a non-conductive scale can result due to some heat treating processes. Both can be removed with a diamond file or lapping procedure. Making sure that start holes are clean and burr free will prevent unwanted wire breaks at the beginning of a program.

Choosing the Proper Electrode for Small Holes

Using the proper electrode can save countless hours of frustration when machining small holes such as .008″ and .010″ . Machining stability and high wear are indications that electrode quality could be a factor. Some manufactures do not have the electrode straightening capability which can result in the product having a slight bend which is a major contributor to a multitude of problems. Please be sure to consult with your vendor as to their products quality and consistency.

Proper Filtration Materials

Proper filtration is the most important aspect to machine with consistent results. You really need to examine what type of work you are doing to maximize your capabilities. There are recommendations from the manufacturer that could actually give you poor results. Some recommend using a staked filter using a cardboard type material. Initially, this filter cleans immediately upon installation but over a very short period the filtration media deteriorates. The customer believes that these filters last a very long time, unfortunately the filter media is doing nothing at all! Dirt is being passed through the media resulting in poor EDMing performance. Using a paper filter will give the customer a much more consistent result.

Using Your Cleaning Agents Properly

Depending on the type of cleaners used, care should be taken when cleaning. Allowing cleaners to sit on some surfaces too long may etch, bleach, or damage surfaces. Avoid getting cleaners on attachment points where power cables connect to the heads, as cleaners can act like a corrosive agent and degrade the power cables.

Significance of Fast Hole EDM Conductivity

Many systems use tap water on their Fast Hole EDM machines. Although this is the case, these machines need to maintain a specific level of conductivity to insure consistent results. When machining and filtering, many systems cannot maintain these levels and poor performance is realized. Please verify these levels with your manufacturer as this can really make a difference in performance.