04/30/2019

High tensile steel surfaces with spark erosion

The strength of the material is the decisive criterion for many applications in engine or tool construction. However, the harder the material, the harder its machining. Nevertheless, steel is usually used. Despite its high strength, it is one of the most versatile construction materials and can be recycled indefinitely.

EDT process and spark erosion

Spark erosion is often used to provide steel or metal surfaces with defined surface textures. This process is also called Electro Discharge Texturing (EDM). "As a rule, the electrically conductive workpiece to be machined (often metals) is processed in a non-conductive liquid (dielectric), usually deionized water or special oil. For this purpose, a likewise electrically conductive tool is brought into the vicinity of the material, which has a negative electrical voltage (typ. 40 to 150 V) compared to the workpiece. This leads to numerous small discharges between the tool and the workpiece. This leads to recurring sparks which primarily remove material from the workpiece."(wikipedia.org) This material removal roughens the material.

This roughening process is used e.g. for the following components:

- Cylinder surfaces in the automotive industry,

- Etching dies for minting plastic surfaces or coins

- Structuring of the surfaces of sheet metal or rolls

In contrast to the conventional roughening process, the EDT process results in a rougher surface with a higher number of peaks. A minor disadvantage is that the surface tends to absorb dirt and foreign particles due to the higher number of tips. These can in turn be removed in a cleaning process. The particles are cleaned by light brushing with the roller brushing machine, whereby the roughness peaks are also slightly ground off. (wikipedia.org)

Analysis of mechanical and functional properties with modern surface measurement technology

With the surface measuring tools such structures are quantitatively measured to determine roughness, texture and morphology of the surface. This is already necessary during the manufacturing process in order to guarantee the desired process reliability.

By analyzing the three-dimensional parameters roughness, structure and bearing curve, the mechanical and functional properties of such a structure, which is used, for example, in deflection pulleys, can be permanently optimized during the production process. The degree of contamination respectively the degree of cleaning of the used steel surfaces is also controlled in this way.

Finally, the wear or destruction of structured functional surfaces can also be quantified in operation. In addition to calculable wear, unexpected damage can also destroy the surface, for example due to the influence of foreign materials during operation. Of course, the defects can also be precisely quantified by evaluating the roughness, the structural heights and the profiles. Among other things, critical limit values for the performance of components can be found.

The MicroProf® series

Various sensors and measuring tools from the MicroProf® series are used for these applications. The selection depends on the customer's requirements, for example whether the measurement is to take place in the laboratory, during the process or in the production line. The results are completely integrated into the usual documentation and traceability within the scope of quality assurance.

The measuring tools of the MicroProf® series offer the option of double-sided sample inspection. This allows simultaneous measurement of the top and bottom of the sample and determination of the sample thickness. This makes it possible to determine the total thickness variation (TTV) of the sample together with surface parameters, e.g. roughness and flatness of both sides.

The advantages of optical measurements

Another big advantage of optical surface metrology is its short measuring time. Measurements can be made with optical sensors in a few minutes, where tactile systems often require several hours. Finally, the optical measurement is non-destructive and non-contact and can be fully automatically integrated into production processes.

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