Machining of small holes for cooling ventilation outlets on turbine blades at a very high inclination angle has significant advantages over conventional piercing processes with EDM piercing machines. While conventional machining processes cause problems for grades up to 1mm, mechanical piercing is completely replaced by EDM piercing for diameters ranging from 0.10 to 3.0mm (up to 10mm in special cases). The benefits are significant time and cost savings, as phenomena such as tool breakage, tool passivation and tool resharpening will no longer occur. EDM ensures high precision of the hole diameter, perpendicularity and cylindricity of the holes as well as no burrs and no deflection. Hardened steel can also be subjected to EDM treatment. As a result, the phenomenon of quenching deformation of plates that are traditionally pierced and then hardened can be avoided. Even difficult-to-cut materials such as tungsten, titanium, inconel, nickel-based alloys, stainless steel alloys and molybdenum can be processed. With the Heun EDM machine, it is possible to enter the surface of the workpiece at an extremely steep angle and etch through unknown empty areas. The entire process is precisely controlled without the need to set a precise depth of penetration in advance.
After many years of research and development, a system has been developed to detect the extent of electrode penetration independent of electrode wear and to influence the depth and character of the EDM process through the machine's electronic control unit. Different machining processes have different effects on the degree of electrode wear, which makes it difficult to control the depth of the EDM process with reproducible precision. In addition, the EDM process changes during the etching process, so that even a further 2 to 3 mm of advancement in the etching axis can take as long as the 100 mm drill hole itself. This in turn affects the accuracy of the diameter of the hole and the external dimensions of the electrode in terms of taper and concentricity.
When machining large inclined entry and exit holes in blades, the use of a penetration recognition system ensures that precise electrode depth creativity comes from the machining of turbine blades without damaging the back wall immediately behind it. The penetration recognition system consists of hardware components and a corresponding intelligent software, which, after recognizing the electrode penetration, can realize different measures according to the different requirements of the user.
This penetration recognition technology also offers many benefits under other conditions of use, such as in tool and mold making. The machine operator can eliminate the need to think about electrode wear. He is only responsible for making a rational choice between material, electrode diameter and machining strategy. Everything else is done in an instant by an intelligent control system. Manufacturers, on the other hand, seek to continuously improve the efficiency, flexibility and rationalization of their production. Putting adaptable production equipment into operation not only makes good economic sense, but is also a necessity in the growing competition with today's low manufacturing cost countries. This is true for large companies with complex production equipment, as well as for small companies with only a single piece of equipment.
The control system of a CNC EDM CNC piercing machine can be interfaced with devices such as robots or measuring systems, data collection systems for visualization of components, or bar code scanners, and thanks to customer-specific system interfaces, it can be integrated into the production line, exchange of data with higher-level management systems, and remote maintenance.
The EDM process is useful when machining small holes in hard materials. Smooth, precise and of high quality, the electrodes are increasingly going deeper. During the piercing process, software influences the depth dimension and the characteristics of the EDM.
The EDM process for small holes is particularly suitable for machining hard materials with conductive properties. Drilling depths of up to 700 x D can be achieved by means of EDM machines with electrode tubes of 80 μm to 3 mm (up to 10 mm in special cases) in diameter. For example, with a 1.0 mm diameter electrode, a drilling depth of 700 mm can be achieved. The maximum drilling depth achieved so far in high-alloy hard materials is 1500 mm. At the other extreme, small holes are drilled, which are only about the thickness of a human hair. The maximum drilling speed achieved so far in high-alloy materials is about 70 mm/min.