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August 20, 2010 - High-speed drilling by EDM

Drilling into materials which are difficult to work by stock removal is a challenging process. If, however, drilled holes with a diameter of 1 mm shall be manufactured into high-alloyed steel, up to a depth of 1000 mm, every twist drill will fail. For such process high-speed EDM drilling is applied.
It is not only an enormous process safe technique, but also works very speedy. Even drill holes of 0.08 mm diameter can be manufactured by EDM drilling. In the field of electrical engineering this technique is used to manufacture cooling holes into blades. EDM drilling is a perfect solution for manufacturing of hard material which is electro-conductive. Drill holes from diameter 0.08 up to 10 mm. With electrodes of diameter from 0.080mm = 80 my up to 3mm, in special cases up to 10mm drilling depth, up to 1000xd can be achieved. For example with electrodes of diameter Ø 1.0 mm = drilling depth 1m. The maximum drilling depth already achieved by Heun into high-alloyed, hard material is 1.500 mm. A further extreme are exceeding small drillings, with just about the thickness of a hair. The maximum drilling speed achieved up to now is about 70 mm/min. into high-alloyed material, which is used in aviation and aerospace industry. Into other materials drilling speeds of up to 200 mm/min. have been achieved. Smallest drillings and newest technology is offered to their customers by HEUN. With the machines of the APos series drilling speed up to 200 mm/min. can be achieved. Electrodes with diamater from 0.1 to 6.0 mm can be used.

EDM drilling machines are used in the industrial sectors of tool and mold making, aviation and aerospace, machine building and fixture construction, glass industry, automotive industry as well as in medical engineering. The prevailing ranges of application are start holes, nozzle holes, degassing holes as for example into molds for cast parts in automotive industry, coolant holes for plastic tools, vacuum holes or air cleaning holes, coolant holes into turbine blades for airplanes and aerospace, as well as coolant holes into turbine parts for gas turbines for power plants.

 

In the range of turbine blade manufacturing, well-known manufacturers use machines of Heun GmbH, to insert cooling holes in extremely steep entry- and exit angles into the blades.

High precision possible with EDM drilling

 

In comparison with conventional drilling, the advantages of EDM are in evidence. When using traditional machining, problems arise for diameters below 1 mm. Mechanical drilling is completely displaced within the diameter range from 0.10 to 3.0 mm, exceptionally even up to 10 mm. High time and cost savings are achieved, since breakage of drill bit, blunt drill bits and grinding of drill bits is absolutely unnecessary. EDM machining guarantees highest precision regarding drilling diameter on top and bottom, exact drilling verticality and cylindricity, as well as drilling free of burrs and without deflection. Even hardened metal can be eroded. Thus shape distortion is avoided, which can arise on conventionally drilled and then hardened sheets.

Material of any hardness can be machined

 

Thus shape distortion is avoided, which can arise on conventionally drilled and then hardened sheets. Any kind of material hardness can be machined, even exotic materials like tungsten, titan, inconell, hatelloy, stainless steel alloys, molybdenum. With the EDM drilling machines of Heun, it is possible to accurately control extremely steep immersion into work piece surface as well as breakthrough into unknown empty space, without knowing the exact drilling depth.

 

After a development phase of several years, Heun successfully generated a system to detect the breakthrough of the electrode, independent from the electrode wear and to initiate respective actions via the control system of the machine, to influence depth and eroding characteristics during the further drilling process.
 

Previous problem: varying wear rate

 

It is a well-known, process-related problem, that the electrode is subject to varying wear during eroding and that due to this an exactly repeatable eroding depth is almost impossible. Furthermore the conditions of the eroding process are changing basically during breakthrough. This causes that continuation of drilling during breakthrough process of about 2-3 mm can take as long as the actual drilling of i.e. 100 mm itself. This in turn has influence on the exactness of the diameter of the drilling and the geometry of the electrode regarding cone and concentricity.

   

In addition to energy technique there are various applications in medical engineering, tool- and mold industry, as well as for special machines.

Cooling holes with extremely steep entry- and exit angles

 

Heun company has found a method to eliminate these problems. Originally these problems appeared in the manufacture of turbine blades. Well-known producers are working with the Heun machines to insert coolant holes into turbine blades with an extremely steep entry and exit angle. The task or requirement for Heun was to guarantee the breakthrough of the drilling without damage of the close rear panel, even though the material thickness is not known. These requirements cannot be fulfilled with a normal depth programming, which is used generally.


 

Important: automatic breakthrough detection

 

The breakthrough detection consists of hardware components with a respective intelligent software solution. This software enables several actions after detection of breakthrough of the electrode, also according to specifications of the customer.

 

Also under other conditions, like in tool and mould making industry, this special breakthrough detection offers considerable ease and advantages. The operator has not to take care for the observance of the wear of the electrode any more. He only chooses one of the selectable materials, electrode diameters and strategies. Everything else is executed by the control system within a split second

The task and requirement for the EDM specialists was, to guarantee continuity of drilled hole, without damaging of rear panel, even though material thickness is not known. The specialists of Heun have solved this problem.



Interface for integration into flow of production

 

Of course, all data can also be taken over from the CAD system. Drilling coordinates up to 5 axes, work piece height, drilling depth, detailed generator data or activation of the automatic generator, as well as extensive M-functions (help functions).

 

In manufacturing industry it is important to increase productivity, flexibility and efficiency permanently. The application of flexible assembly lines is not only profitable, but also essential because of the steadily growing competition with low-wage countries. This applies to big branches of production as well as to small companies with single machines.

 

The control system of our EDM machines of the APos series enable connection to robot systems, measuring systems, visual data recording systems or bar code scanners. A user-specific interface configuration allows integration into a production line, data exchange with superior control systems as well as remote maintenance by remote access.

 

We give you advice for planning of a new production line or integration of a machine into an already existing system. We are able to solve your problems because of our long lasting and global experience and our qualified team.

 

Visit us in our demonstration centre in Kahl/Main and see the advantages of our manufacturing technique at your work piece. The slogan of Heun is: Your requirement is our challenge.

S
hort interview:

„Essential for turbine blades“

SMM: Within this paper high precision is mentioned. Is it possible to quantify which precision and surface roughness can be achieved?

 

Rüdiger Heun: Within this article we talk about a deviation between entry and exit of drilling. Here we achieve an accuracy of a few hundreths of millimeters or professionally spoken +/- 10 bis 20 µm. With EDM drilling, the surface of the work piece is multiple better than with mechanical drilling. Because of several millions of sparks the structure is very equal. This also means it is very plane. It does not show any drilling grooves. Surface roughness required up to now is within the range of Ra 2µm. We have received statements from customers saying that a roughness of Ra 1µm was achieved on their materials with machines from Heun.

 

SMM: Your machines are so-called high-speed EDM drilling machines. Which speeds are achieved in drilling process und does the feed rate have any influence on precision?

 

Rüdiger Heun: Within this article it is already stated, that drilling speeds up to 70 mm/min can be achieved into especially high-alloyed and very ductile materials, which are used for turbine blades, like „Inconel“, „Hastelloy“, and so on. The drilling speed is independent from entry angle to surface of work piece. That means that it does not matter whether drill hole is required straight (right angle to surface) or extremely slant to the surface of the work piece.

 

SMM: In which range of power engineering is EDM drilling applied?

 

Rüdiger Heun: The method of EDM drilling is used everywhere, where drill holes with the diameters stated above are required. For turbine blades, which are used for production of electricity, cooling of the respective individual components is essential. For example for blades, vanes, combustors, and so on. For your understanding: The component parts which are placed within the so-called „hot area“ of a turbine, have to be cooled by an air stream, which flows without any breakaway over the components. No alloy has the ability to resist these combustion temperatures without cooling. In order to assure that it is an optimum air stream, the drill holes are machined within a very special angle. However, the experts of turbine blade industry can surely explain this much better.

 

SMM: To what extent is EDM drilling already known on the market?

 

Rüdiger Heun: Our machining by EDM drilling and mainly our technique and quality is known world-wide and is also approved. Anyway there are still new requirements again and again and still there are too many who do not know about our technique – not yet. With this publication you contribute your part to increase the degree of awareness.

HEUN Werkzeugmaschinen

& Industriebedarf GmbH

Lange Hecke 4

DE-63796 Kahl

Tel.: +49(0)6188 – 910 510

Fax: +49(0)6188 – 910 540

 


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