Electro-optical deflectors (EOD) and acousto-optical deflectors (AOD) are based on deflection of laser light within a solid state medium. As they do not contain any moving parts, they yield advantages compared to mechanical scanners which are conventionally used for laser beam deflection. Even for arbitrary scan paths high feed rates can be achieved. In this work the principles of operation and characteristic properties of EOD and AOD are presented. Additionally, a comparison to mirror based mechanical deflectors regarding deflection angles, speed and accuracy is made in terms of resolvable spots and the rate of resolvable spots. Especially, the latter one is up to one order of magnitude higher for EOD and AOD systems compared to conventional systems. Further characteristic properties such as response time, damage threshold, efficiency and beam distortions are discussed. Solid state laser beam deflectors are usually characterized by small deflection angles but high angular deflection velocities. As mechanical deflectors exhibit opposite properties an arrangement of a mechanical scanner combined with a solid state deflector provides a solution with the benefits of both systems. As ultrashort pulsed lasers with average power above 100 W and repetition rates in the MHz range have been available for several years this approach can be applied to fully exploit their capabilities. Thereby, pulse overlap can be reduced and by this means heat affected zones are prevented to provide proper processing results.

Electro-optic and acousto-optic laser beam scanners

Growing ambitions for efficient resource utilization and improving environmental standards stimulate the abandonment of environmentally harmful lubricants. However, dry forming leads to direct contact between tool and workpiece surface which causes increasing friction and wear. This paper presents a methodology for realization of lubricant free deep drawing processes. Dry deep drawing of a rectangular cup is investigated by a numerical simulation. First numerical results reveal the necessity of modifying the tribological system in order to realize dry deep drawing. Basic tribological investigations reveal increasing friction and intensive wear under dry conditions. Therefore, tailored surfaces are developed to improve the tribological properties without lubrication. By laser structuring various micro features were fabricated on the tool surface. Furthermore, tungsten doped hydrogenated amorphous carbon coatings (a-C:H:W) were deposited on the tool using unbalanced magnetron sputtering. The tribological behavior of these surface modifications were researched by a ring-on-disc-tribometer. The wear mechanisms during the dry sliding process are discussed depending on the micro features and coatings. The obtained test results help building the basic concept for generating tailored surfaces and subsequently to realize lubricant free deep drawing.

Investigation of Tribological Systems for Dry Deep Drawing by Tailored Surfaces

Evaluation and Calibration of LCoS SLM for Direct Laser Structuring with Tailored Intensity Distributions

In deep drawing processes sustainability can be increased and processing steps can be omitted by abolishing any lubricants. Tailored tools with locally textured surfaces offer a possibility to compensate higher strains caused by the changed tribological system. Ultrashort pulsed laser machining is an advantageous approach to generate surface features. Thus, very hard and brittle materials can be processed inducing negligible heat affected zones so that the surrounding tool material keeps its initial properties. The material-dependent process parameters for efficient picosecond laser structuring are applied. The effects of features with single feature sizes in the range of 100 µm to 500 µm on friction of the tribological pairing are presented. The dependencies of the friction coefficient on the properties of the micro features - the geometry, the shape, the density and the orientation - are investigated by using a ring-on-disc-tribometer. The ring representing the tool is made out of the cold work steel 1.2379. The zinc-coated deep-drawing steel DC04 is used as disc respectively workpiece material. During the ring-on-disc-tests a constant contact pressure of 2.1 MPa and a mean sliding velocity of 100 mm/s are applied. To obtain the significant influences of micro features on friction, screening tests by varying the parameters according to the Shainin method are carried out. Because of the stochastically occurring high wear observed in reference experiments a changed methodology of ring-on-disc-tests is proposed. Applying this method the effects of textured ring surfaces on friction coefficient of steel-zinc-sliding are evaluated and compared to untextured rings. The latter are tested non-lubricated as well as with lubrication. The screening tests show that the feature orientation is the significant parameter influencing the friction. Selecting this parameter together with the feature density the friction coefficient can be adjusted with regard to untextured surfaces.

Friction Adjustment within Dry Deep Drawing by Locally Laser Textured Tool Surfaces

In addition to coatings, microstructures can increase abrasion-resisting quality of sheet bulk metal forming tools by influencing friction conditions. The use of ultrashort pulsed lasers offers a possibility for manufacturing flexible microstructures with very high precision. Thus the processing with picosecond laser allows the generation of structures with dimensions down to the range of single microns. Because of the characteristic ablation process temperature sensitive materials can be structured without any heat transfer into the material. Applying appropriate processing parameters avoids complex post-finishing processes because of the achieved good structure qualities without any melt and any material throw-up. For implemention of a fast structuring process with high ablation rates it is shown, that only fluences near the ablation threshold allow a processing result of high quality and with the maximum ablation efficiency.

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H. Hetzner

Papers

Microstructuring Tools for Sheet Bulk Metal Forming - A Designated Application for Picosecond Laser