Marco Teller

Bio: Marco Teller is an academic researcher from RWTH Aachen University. The author has contributed to research in topics: Forming processes & Tribology. The author has an hindex of 6, co-authored 29 publications receiving 84 citations.

Investigation of the Suitability of Surface Treatments for Dry Cold Extrusion by Process-Oriented Tribological Testing

Abstract: In cold extrusion of aluminum alloys adhesive wear can be prevented by an excessive lubrication of the process. While this causes additional process steps also environmental risks have to be addressed. Hence, dry metal forming, i.e. avoiding lubrication by means of coatings and topography modifications is highly desirable. In this paper first results concerning the behavior of tailored surfaces under dry metal forming conditions for pure aluminum are presented. Different surface treatments (laser polishing and Mo2BC coating) of the tool steel AISI H11 are tested in a compression-torsion-tribometer under conditions adapted from cold extrusion. Normal stresses six times higher than the initial yield stress of the tested workpiece material pure aluminum (AA1050-O) are applied. Furthermore, a strategy for the characterization of aluminum adhesions to the tool is introduced. The influences of different topographies and the presence of a coating on the loss of material due to adhesive wear are investigated.

A New Compression-Torsion-Tribometer with Scalable Contact Pressure for Characterization of Tool Wear during Plastic Deformation

Abstract: A contact pressure which reaches up to ten times the yield stress of the workpiece material is characteristic for cold extrusion processes. Common tests for friction and wear are limited to rather low contact pressures. Thus, the aim of this paper is to present a new compression-torsion-tribometer which is able to scale the contact pressure to a multiple of the yield stress of the workpiece. In order to enable a contact pressure that greatly exceeds the yield stress of the workpiece material, the workpiece specimen is encapsulated laterally. As main parameters, contact pressure, glide length, and relative velocity can be adjusted independently, thus allowing for multiple load cycles. The resulting torque is measured continuously as an indicator for wear. Afterwards wear can be also quantified by examination of surfaces. Hence, the developed setup enables a comparison of tool surfaces and coatings and a characterization of wear behaviour under high contact pressure.

Decreasing friction during Al cold forming using a nanomolecular layer

Abstract: The authors demonstrate that functionalizing tool steel die surfaces with an octadecylphosphonic acid molecular monolayer decreases friction during Al cold forming. Specifically, molecular functionalization leads to a 1.9-fold decrease in time-averaged torque during tribological compression-torsion wear tests. Electron spectroscopy suggests that weak van der Waals interaction between aluminum and the distal CH3 termini of the phosphonic acid molecules anchored to the steel surface via P–O bridges lubricate the aluminum–steel interface. The observation of this effect at contact-pressures of ≥75 MPa underscores the tremendous potential of molecular functionalization for devising industrial metal forming processes without the use of liquid lubricants.

How dry is dry? - A critical analysis of surface conditions used in dry metal forming

Abstract: In the present study, the surface conditions of workpieces used for dry-metal forming experiments were analyzed. Specifically, the effectiveness of different cleaning approaches was evaluated using x-ray photoelectron spectroscopy, infrared spectroscopy and wetting experiments. The best cleaning results were obtained using a CO2-based approach. CO2 acts as an effective solvent and as a result of the mechanical impact, it removes material from the surface. In fact, cleaning results were similar to those achieved by plasma cleaning. However, even simple cleaning with a towel and acetone left only a surface film of less than 100 nm. A residual oil film thickness below 100 nm on the work piece appears sufficient to mimic true dry-forming conditions in most cases. In order to determine cleanliness of surfaces used in drymetal forming, an infrared spectroscopy-based oil film gauge along with a customized extended calibration curve turned out to provide for sufficiently accurate data.

Assessment of steel surface roughness and waviness in relation with paint appearance.

Abstract: Paint appearance is an important factor in the overall product quality of steel sheet, especially in the automotive industry. The present paper deals with the functional behaviour of the surface texture according to paint appearance. The main results on the improvement of paint appearance of outer car body panels, obtained with coated and uncoated cold rolled steel, textured with EBT-rolls, is reviewed. There are different methods to relate steel sheet surface texture to the appearance after painting. From the literature it is found that waviness has a detrimental effect on the surface appearance after painting. Different roughness and waviness parameters are compared in order to find a good relation with paint appearance. The following surface texture parameters are evaluated in this study: roughness parameters Ra, peak count Pc, waviness parameters Wca and amplitude between 0.5 – 5mm (Fourier analysis) and envelope parameters motif W and Ra-macro, measured with a spherical stylus of radius 1.5mm. Classical parameters such as Ra and Pc are only able to evaluate paint appearance for one single texturing process, and within very limited range. The ability to predict paint appearance by Ra-macro and Wca also seems to be limited, because of their dependency on the roll texturing technique. Based on extensive testing, it is suggested that Fourier analysis might be the best approach to predict the appearance after painting, and this independently of the texturing process. The results clearly show the improved appearance of Sibetex textured sheets compared to conventional textured sheets. This is due to the fact that, with Sibetex sheet, a reduction in waviness can be achieved.

A soft pneumatic bistable reinforced actuator bioinspired by Venus Flytrap with enhanced grasping capability.

Abstract: Soft actuators, as an important part of soft robotics, have attracted significant attention due to their inherent compliance, flexibility and safety However, low capacity in force and load limits their applications Prestored elastic energy can improve the capacity in output force and load of soft actuators This work introduces a soft pneumatic bistable reinforced actuator inspired by the Venus Flytrap's bistable mechanism that allows for the storage of elastic energy The proposed actuator consists of two separated 3D-printed actuation chambers that are attached to a central prestressed steel shell to achieve bistability The pressure triggering the pneumatic bistable reinforced actuator from one stable state to the other is derived and validated by experiments Further experimental comparisons between the proposed actuator and a dual chamber actuator show that the proposed design significantly improves the block tip force, load capacity and stiffness The pneumatic bistable reinforced actuator also demonstrates superior performance in the actuation speed and bending angle under the same input pressure Finally, a two-finger gripper is developed using the proposed actuator, which is demonstrated to grasp and hold various objects