How to Increase the Process Speed of Die Sinking EDM

Developments in the EDM process and its technology along with improvements in accuracy, automation and micro-mold making technology can pay enormous dividends to the domestic mold making industry.

 

Speed Is Not the Solution

Increasing drive speed is one solution to improving the speed of die sinking EDM. In this way the unproductive times for lifting movements are reduced; however, the gain in speed is limited to small electrodes and very deep cavities. In addition, above a certain speed the electrode wear is considerable and very high axis speeds result in extreme strain on the mechanism, make the machine more expensive and shorten its working life. Therefore, it is wrong to believe that a general increase in the process speed is only to be achieved by rapid lifting movements. The contribution of fast axes to the machining process is just one supplementary aspect to a complex interaction that encompasses the generator, process control, gap width regulation and the mechanism. And die sinking EDM requires intelligent flushing.

 

Potential Lies in the Flushing

You can imagine the EDM process as being a balance between the EDMed and evacuated material in the gap. If this balance is not present, then either you flush the machining area unnecessarily—involving a loss of time and additional instability of the process—or you EDM the same particles several times, which cannot be removed from the gap sufficiently.

 

Die Sinking EDM

Before the material can be evacuated from the gap you must remove it from the workpiece. So how can you achieve more removal? As in the case of all optimization problems, the greatest gain potential lies where the efficiency is smallest. The efficiency of a single discharge with a cathodic poled workpiece is theoretically about 25 percent.1 In addition there are some factors that make the efficiency even worse (e.g., process control problems, non-ideal flushing conditions, small gap width), so that realistically you must reckon with an efficiency of less than 10 percent.

 

Removal and Surface Quality Determine the Time Requirement

In the case of EDM, the objective is always to optimize the removal performance of the machining on one hand, and to achieve the surface quality of the workpiece to be machined on the other hand. The workpiece, when machined, is intended to display a certain final roughness and a certain form precision. In addition, two conditions are called for:

 

  1. As small a thermally influenced area of the workpiece surface as possible
  2. As low an electrode wear as possible.

 

These marginal conditions determine the machining time and costs for workpiece production. In practice, a sequence of technological parameters is used because starting out from the roughing to finishing settings, the pulse energy is gradually reduced until the required technological results are achieved. Once again the law of nature applies: you can quickly achieve results of modest quality, but only slowly results in high quality.

 

Physical Processes Show a Solution

The approach toward an ideal state means moving the characteristic curve in the direction of the arrow. That means faster EDM with the same gap width, roughness and wear. If, up to now, the discharge energy of the EDM pulses was increased, regrettably you also only had greater roughness and a greater gap width so that the gains in speed during roughing were lost again through longer finishing. You will find a way to a solution if you return to the basics of EDM theory—to the physical processes leading to the formation of the spark and metal removal.

 

During the discharge, you can identify three main physical phases in succession:

 

  1. The Build-Up
  2. Discharge
  3. Fade Phases

 

In the first phase the discharge canal is built up. After passing through the working medium, the current flows almost exclusively on the surface area of the discharge canal and the anode is partially evaporated by the electron bombardment. The electrode wear mainly takes place here. Every pulse—whether contributing intensively to removal or not— causes microscopic wear. In the discharge phase, the electrical energy supplied causes melting or evaporation of material mainly on the workpiece. The fade phase begins with the switching off of the power supply. The plasma canal collapses and the partially evaporated, partially liquid material is ejected.

 

When to Interrupt Pulses

During the discharge, a crater forms in the workpiece. Fundamental studies of discharges have shown that the growth of the crater in the workpiece stagnates from a certain time. This is because a balance forms between the energy supplied and the energy lost, as well as energy that is used for the maintenance of the plasma and the heat loss to the workpiece and dielectric. This asymptote of the crater growth can be recorded in real time from the spark voltage and current.

 

However, why is the asymptote of the crater growth so important? Because this is the right moment to interrupt the pulse. It is unnecessary to let a pulse last longer if the target radius of the crater and the required roughness have been achieved. You can begin with the next pulse immediately. The time required by the pulse to reach this state also is not constant, as the speed with which a discharge reaches a certain spark base diameter depends on the macroscopic situation in the gap and the local geometry in the spark discharge area. With this first measure alone, you will optimize the number of discharges per unit of time and increase the removal rate.

 

When to Increase the Current

If you now observe the charge’s fade phase you will see that the removal from the workpiece is caused by the collapse of the plasma canal. The sudden drop in pressure—triggered by switching off the power—causes the evaporation and ejection of superheated material. The plasma canal has a very high temperature and pressure. The gradient of its collapse influences material removal. The more abruptly the energy disappears, the better the crater material will be ejected. In order to enhance this effect, a special trick is employed: before the pulse is interrupted, the current is increased briefly. The idea of increasing the pulse current is not new, the innovation is the definition of the point in time when this increase is to take place. The increase in the pulse current has no consequences for the roughness, wear or gap width, but does increase the removal. In addition, as the removal per pulse is greater, you need fewer pulses for the machining, and therefore the wear sinks.

 

Removal Rate Doubles in Part

This new machining strategy (asymptote detection, current increase and pulse interrupt) is the subject of a patent application for its use in new EDM die sinking systems. The results are in accordance with the theoretical reflections, especially where good flushing is guaranteed (e.g., pre-machined workpieces). For these machining jobs removal rates have doubled.

 

Generator Brings Striking Improvements in Performance

The innovative generator offers an increase in productivity of approximately 30 percent; however, up to 100 percent with pre-milled molds that occur increasingly nowadays through synergies with HSM. This refers to all roughing and finishing using copper and graphite electrodes. The advantages are particularly great with good flushing conditions and pre-milled workpieces. These convincing results explain that it is possible to increase the speed and productivity of die sinking EDM, and the potential for improving this technology is still considerable.

 

If you need more information about die sinking EDM, please try to visit the website of Excetek Technologies Co., Ltd. – the company is the well-known brand for its EDM machines. Get more details about Excetek, welcome to check out their product pages and feel free to send inquiry to them.

 

Article Source: MoldMaking Technology

What is Die Sinking?

Die sinking is a process used to machine or create a specific size or shape cavity or opening in steel blocks. The openings in the steel blocks can then be used to mold plastic into different shapes. Such openings may also be used when doing forging, either hot or cold, or for coining or die-casting.

 

Most often, die sinking is used to place names, numbers, and other sources of information onto metal. It can also be used to place such elements on a piece of wood, leather, or many other materials. The process for die sinking is fairly simple and something that anyone can do with a few simple tools. There are also larger machines that can help with the process, but these machines come with a price tag.

 

The process of die sinking begins by obtaining a piece of sheet metal and cutting out a shape. For instance, the shape may be a shield or name tag. When doing the process of die sinking, it is important to use a piece of sheet metal for the project that is at least 1/64 of an inch (0.4 mm) thick.

 

Once the shape has been placed on the piece of sheet metal, it will need to be cut out. To do this, a chisel and hammer or otherwise special piece of equipment for cutting sheet metal is used. Once the piece has been cut out, it is necessary to file the rough edges down.

 

After the shape has been completely cut out, next begins the process of die sinking to add letters and numbers. An outline must be created containing the information intended to put on the piece letter by letter. This outline can be created with a soft leaded pencil and using a group of 1/8 inch (3.17 mm) steel lettering.

 

Once all the lettering has been applied, it is necessary to sit the steel lettering on top of each of the outlined letters and then pound the letter down into the metal with a hammer. This process will create an indentation in the metal. This process is continued until all the lettering, numbers, and other designs are completed.

 

When done, the process should have created a piece where the indentation of the metal is personalized. It is possible to enhance the lettering by filling the indentations with some type of colored polymer. This permits the indentation to stand out against the metal.

 

Excetek is the professional manufacturer of providing die sinking EDM. Our die sinking EDM series are divided into CNC die sinking machines and ZNC die sinking machines, both series feature high quality and high efficiency. The EDM process becomes a common method of making prototype and production parts, especially in the aerospace, automobile and electronics industries. EXCETEK would be your best choice of die sinking EDM manufacturer. Welcome to visit our website and contact EXCETEK for more specifications.

 

Article Source: http://www.wisegeek.com/what-is-die-sinking.htm