Title

ROLL TEXTURING BY ELECTRONIC DISCHARGE TEXTURING MACHINES “EDT“ AND SUPERFINISHING UNIT

ROLL TEXTURING BY ELECTRONIC DISCHARGE TEXTURING MACHINES “EDT“ AND SUPERFINISHING UNIT

Authorship

Tscherche, Stefan; Nitschke., Mike

Tscherche, Stefan

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Nitschke., Mike

I am this author

DOI

10.5151/2594-5297-22577

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Abstract

Automobile manufacturers demand a certain surface roughness on the sheet in order to have smooth deep-drawing and painting operation. Deep-drawing requires a coarse structure whereby oil pockets are formed to prevent the metal sheet from ‘cold welding’ to the die shoe tool. Painting requires a fine structure to achieve a surface finish with a high quality; on the other hand lacquering requires a defined roughness to have an excellent cling to the sheet. In addition to these requirements the costs for rolls are increasing but with the Superfinishing Unit it is possible to increase the life time of the rolls and to improve the surface quality as well as to reduce the cost due to a longer life time of the rolls. A generator switches on the erosion impulse. The conducting particles in the dielectric oil form a dipolar bridge which produces intermittent charge of current to be passed onto the roll. A bowl shaped particle is brought to its melting point and a gaseous by product bubble is formed at the discharge duct area. After the erosion impulse is completed, the discharge duct collapses and the melted particle is expelled. A through-shaped surface structure remains. Comparing the shot blasting and EDT methods with regard to the distance of peaks from one another, EDT is significantly higher. Furthermore the Superfinishing Unit, which does not change the geometry of the roll, cut off only the highest peaks. This process based on the honing process and the stock removal is only a few microns. The texturing process results can be programmed and reproduced with great regularity and narrow tolerances. Comparing the shot blasting and EDT methods with regard to the distance of peaks from one another, EDT is significantly higher. The texturing tolerance of the preselected roughness is: From 0.5 Ra to 3.5 Ra ± 4 %; From 3.5 Ra to 8.0 Ra ± 5 %; From 8.0 Ra to 15 Ra ± 5 %. Surface qualities with an average coefficient of roughness Ra between 0.5 and 15.0 micrometers and 240 to 25 peaks per cm (Pc) can be achieved. In combination with the Superfinishing Unit the EDT-machine allows particularly the reduction of roll changes in the mill as well as constant roughness of the sheet during the rolling process.

Automobile manufacturers demand a certain surface roughness on the sheet in order to have smooth deep-drawing and painting operation. Deep-drawing requires a coarse structure whereby oil pockets are formed to prevent the metal sheet from ‘cold welding’ to the die shoe tool. Painting requires a fine structure to achieve a surface finish with a high quality; on the other hand lacquering requires a defined roughness to have an excellent cling to the sheet. In addition to these requirements the costs for rolls are increasing but with the Superfinishing Unit it is possible to increase the life time of the rolls and to improve the surface quality as well as to reduce the cost due to a longer life time of the rolls. A generator switches on the erosion impulse. The conducting particles in the dielectric oil form a dipolar bridge which produces intermittent charge of current to be passed onto the roll. A bowl shaped particle is brought to its melting point and a gaseous by product bubble is formed at the discharge duct area. After the erosion impulse is completed, the discharge duct collapses and the melted particle is expelled. A through-shaped surface structure remains. Comparing the shot blasting and EDT methods with regard to the distance of peaks from one another, EDT is significantly higher. Furthermore the Superfinishing Unit, which does not change the geometry of the roll, cut off only the highest peaks. This process based on the honing process and the stock removal is only a few microns. The texturing process results can be programmed and reproduced with great regularity and narrow tolerances. Comparing the shot blasting and EDT methods with regard to the distance of peaks from one another, EDT is significantly higher. The texturing tolerance of the preselected roughness is: From 0.5 Ra to 3.5 Ra ± 4 %; From 3.5 Ra to 8.0 Ra ± 5 %; From 8.0 Ra to 15 Ra ± 5 %. Surface qualities with an average coefficient of roughness Ra between 0.5 and 15.0 micrometers and 240 to 25 peaks per cm (Pc) can be achieved. In combination with the Superfinishing Unit the EDT-machine allows particularly the reduction of roll changes in the mill as well as constant roughness of the sheet during the rolling process.

Keywords

Texturing; Superfinishing; Surface; EDT.

Texturing; Superfinishing; Surface; EDT.