An der University 2

Neustadt an der Weinstraße, Germany

An der University 2

Neustadt an der Weinstraße, Germany
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Gottwik L.,CeramTec GmbH | Wippermann A.,An der University 2 | Kuntz M.,CeramTec GmbH | Denkena B.,An der University 2
Ceramics International | Year: 2017

A detailed and systematic comparison of the residual strength, after indentation and grinding, of three different zirconia-based materials is reported. The materials analyzed were: yttria-stabilized zirconia (Y-TZP "MZ111"), alumina-toughened zirconia (ATZ "TZ-3Y20AB"), and a newly-developed strontium hexaaluminate-toughened zirconia ("HTZ500"). HTZ500 showed higher residual strength after indentation and grinding than the reference materials MZ111 and TZ-3Y20AB. HTZ500 combines an initial strength exceeding 1700. MPa, fracture toughness of 8.6. MPa·√m, and an elastic modulus of 213. GPa. The strain to failure was 1.7 times that of the reference materials. These features make the newly-developed material a desirable alternative to the commonly-used materials Y-TZP and ATZ, for example for use in medical implants. The damage tolerance, in particular, may be attributed to the strengthening mechanisms applied. Beside the phase transformation, the addition of dispersed strontium hexaaluminate platelets into the zirconia microstructure provides a supplementary strengthening mechanism. © 2017.

Akin M.,An der University 2 | Rissing L.,An der University 2
Proceedings - Electronic Components and Technology Conference | Year: 2015

Driven by low-cost, resource abundance and distinct material properties, the use of paper in electronics, optics and fluidics is under investigation. In order to realize a dense coverage of sensor networks as part of the roadmap of the internet-of-things, achieving lower manufacturing cost of the aforementioned sensors is required. Considering microelectro-mechanical systems based on magneto-resistance principles (anisotropic, giant, tunnel) that are conventionally manufactured onto inorganic semiconductor materials, we propose the use of paper substrates for cost reduction purposes primarily. In particular, we studied the magneto-resistance sensitivity of permalloy (Py:Ni81Fe19) onto paper substrates utilized in various daily applications. Here, the Py:Ni81Fe19 coating was developed by means of, but not limited to, sputter deposition, and spans an area of 10x10 mm2 and a thickness of 70 nm. In this research, we investigated several paper materials covering a range of grammage of [80, 350] g/m2, surface roughness of [0.21, 3.462] μm given by the root mean squared Rims, various impregnations, porosity levels and surface macro-structures. Yet, in this paper, we focus on our findings with clean room paper (80 g/m2, Rrms = 2.877 μm, 23% surface porosity, latex impregnation, no embossed macro-structure). Employing a four-point-probe resistivity measurement setup, we investigated the change of electrical resistance of Py:Ni81Fe19 under the presence of an oriented external magnetic field. Compared to the theoretical limit of 2.5% of Py:Ni81Fe19 on smooth surfaces, we have obtained large and positive magneto-resistive changes (2.5 - 14%) for these aforementioned systems. Principally, we analyzed the effect of surface topology of the clean room paper on the magneto-resistance sensitivity of Py:Ni81Fe19. We concluded that the occurrence of such magnetic behavior is most probably due to tunneling of electron waves through the asperities and porosity of the paper surface and subsequent scattering of electrons at pinned domain walls. © 2015 IEEE.

Denkena B.,An der University 2 | Grove T.,An der University 2 | Maiss O.,An der University 2
Procedia CIRP | Year: 2016

The endurance of highly loaded parts such as bearings is influenced by their surface integrity. Low surface roughness and high compressive residual stresses lead to an increased lifetime. In contrast to grinding and honing, the processes hard turning and deep rolling can induce compressive residual stresses up to σ = -1000 MPa with depths of d0 = 500 μm in combination with surface roughness values of Rz < 0.8 μm. Combining both processes to the innovative hybrid turn-rolling exhibits benefits with respect to topography and residual stress stability. Developing this process, the interactions of the single processes are analyzed in this paper. © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license.

Denkena B.,An der University 2 | Bickel W.,An der University 2 | Sellmeier V.,An der University 2
Production Engineering | Year: 2012

The use of chamfered tools is widely spread in cutting processes. Prior investigation show, that a chamfer on the rake face of a milling tool can increase the stability of cutting processes significantly due to a contact between the chamfer surface and the workpiece and the resulting damping forces. In addition to higher process stability, it is possible that the chamfer shows positive effects on the machined surface as well. A sufficient chamfer length can cut off the feed marks on the machined surface, but also damping effects on the process vibrations can lead to a better flank surface when milling compliant parts or tools as well. This paper describes an approach of simulation of machining of the flank surface with consideration of the chamfer geometry. In the experimental and simulative investigations it was found that by the reduction of extensive workpiece vibrations, the chamfer does have positive effect on the flank surface quality due to a contact between the chamfer and the workpiece. Furthermore, this contact does apparently occur earlier than a theoretical consideration would predict from the kinematics of the process. With increase of the chamfer length on the other hand, also augmented appearance of smearing effects on the surface, which decrease the surface quality, was observed. © 2012 German Academic Society for Production Engineering (WGP).

Denkena B.,An der University 2 | Kohler J.,An der University 2 | Woiwode S.,An der University 2
Production Engineering | Year: 2014

Profile accuracy, high surface quality and compressive residual stress in the tooth root and flank are necessary for a high durability of heavy stressed gears. This article shows the advantages of vitrified bonded cubic boron nitride (CBN) tools in comparison to corundum tools relating producible compressive residual stress. In this context, especially the relationship between the dressing strategy for vitrified CBN tools and the workpiece surface and subsurface was investigated in detail. © 2014, German Academic Society for Production Engineering (WGP).

Von Witzendorff P.,Laser Zentrum Hannover e.V. | Stompe M.,An der University 2 | Moalem A.,Laser Zentrum Hannover e.V. | Cvetkovic S.,An der University 2 | And 3 more authors.
Precision Engineering | Year: 2014

The ultra-precision dicing of hard and brittle materials causes high wear on the abrasive tool which results in the deterioration of blade cross section as well as the decrease of diamond grain exposure. Resin-bonded diamond blades are used due to their in-process self-sharpening capability. Nevertheless, the shape of the blade cross section generated by self-sharpening is random which leads to poor accuracy when precise grooves need to be produced. Metal-bonded diamond blades feature higher tool lifetime and shape accuracy compared to resin-bonded blades, but are not capable of performing self-sharpening. In this study, the laser dressing of metal-bonded diamond blades is investigated to enable their use in the ultra-precision dicing of hard and brittle materials by continuous laser dressing. We investigated laser dressing with and without the presence of cooling water. The sharpness (grain exposure) after dressing is measured by the cutting face surface roughness. The dicing performance is evaluated by observing the dicing results in terms of cutting depth consistency and by monitoring the spindle power during dicing. Dicing blades which have been laser dressed in an environment with coolant feature less grain exposure than dicing blades which have been laser dressed in dry condition. The dicing results show an improvement in the sharpness and durability of laser-dressed dicing blades in comparison with new or conventionally dressed blades. The ability to apply and perform laser dressing on a dicing machine in an environment with coolant shows the feasibility of laser technology for continuous dressing.© 2013 Elsevier Inc. All rights reserved.

Gaebel C.M.,An der University 2
Advanced Materials Research | Year: 2013

The application of ground and satin stainless steel sheet metal with anti-fingerprint coating is well established in the household appliance industry. In essence, they reduce the adhesion and visibility of fingerprints on satin stainless steel surfaces and improve the cleaning characteristics. The thickness of these imperceptible clear coatings amounts to a few micrometers. They are applied by the stainless steel manufacturer in a coil coating process. The required high hardness and scratch resistance is achieved by an ultraviolet radiation curing procedure and a nanoparticle reinforced coating system. The final painted sheets are further processed e.g. to covering panels of white goods. During forming operations a damage of the clear coating results in the form of crack formation and delamination. But due to the optical properties of the coating systems specifically adjusted to ground stainless steel surfaces, the damage in the clear coating is difficult to identify. This paper deals with the identification of the deformation induced coating damage on the bending edges of a typical covering panel geometry. The experiments show an influence on the coating damages resulting from the grinding direction and the use of a deep drawing foil. Furthermore, panels are formed at higher temperatures with an effect on the coating damages. In addition, mandrel bending specimens are formed. Due to different bending radii and orientations of the grinding direction the damage varies. These specimens are also examined in a salt spray test to analyze the influence of the coating damage degree on the corrosion resistance. © (2013) Trans Tech Publications, Switzerland.

Nywlt J.,An der University 2 | Grigutsch M.,An der University 2
Advanced Materials Research | Year: 2013

Nowadays, for customers the logistical performance of industrial companies is as important as the price and quality when buying decisions have to be made. It can be observed that considering the KPIs of logistical performance as quality figures, similar to the product quality, becomes quite popular within national and international markets. Two logistical performance key figures that can be pointed out in that context are short lead times and high schedule reliability. The delivery times demanded by markets often are shorter than the realizable lead times of products or the replenishment time of raw materials or purchased parts. In order to deliver the products in time, companies have the opportunity to implement so called order penetration points (OPP) within their productions. The OPP specifies the point within a production which connects upstream processes linked with work orders and downstream processes link with costumer orders. The OPP is often built up as a stock of unfinished goods. Currently companies position their OPP only with the goal to satisfy the demand of short lead times set by the market. Other logistical targets such as a low work-in-process (WIP), high schedule reliability or a high utilization are usually not taken into account. Hence, due to the complexity of positioning the OPP companies underestimate the logistical potentials that can be achieved by positioning the OPP optimally. In this publication the fundamental determining factors which both influence the position of the OPP and are influenced by the selected position of the OPP are presented. In particular the dependencies between the four logistical targets, lead time, WIP, schedule reliability and the grade of utilization, and the position of the OPP are discussed. Exemplarily the correlation between the position of OPPs and the schedule adherence at the end of the supply chain are presented. It can be assumed that the schedule adherence increases by moving the OPP towards the end of the supply chain. Possible reasons that explain this particular effect, like the reduction of lead time variation, will be discussed in detail. © (2013) Trans Tech Publications, Switzerland.

Denkena B.,An der University 2 | Koehler J.,An der University 2 | Moral A.,An der University 2 | Moral A.,Leibniz University of Hanover
Journal of Materials Processing Technology | Year: 2010

Nacre is a composite material found in the inner layer of sea shells. It consists of soft organic and hard inorganic components arranged in a complex hierarchical structure. Due to this arrangement, nacre exhibits outstanding mechanical properties (elastic modulus: 64.70 ± 3.50 GPa, hardness: 4.41 ± 0.45 GPa, density: 2.6 g/cm3). Therefore, nacreous implant materials have a high potential in many fields. In medical science, these materials might be used for bone replacement. This article provides an insight into the material removal mechanisms occurring in the scratching of natural nacre. Scratch tests are a simplification of the grinding process and are used to investigate the influence of single input parameters on the material removal. Different scratch tool geometries and varying processing parameters are applied, so that the material removal efficiency can be evaluated by analyzing the process forces. Additionally, the scratch geometry is examined by using a scanning electron microscope (SEM) and optical profilometer images as well as photomicrographs. The results of these examinations provide knowledge on the machinability of nacre and also on the machinability of new nacreous materials. © 2010 Elsevier B.V. All rights reserved.

Denkena B.,An der University 2 | Koehler J.,An der University 2 | Rehe M.,An der University 2
Procedia CIRP | Year: 2012

The cutting edge microgeometry has a significant influence on the wear behavior of cutting tools and therefore on the machining performance. To investigate the effect of tailored cutting edge microgeometries, a detailed geometrical description of different cutting edge designs is necessary. The cutting edge profile is analyzed with respect to the machining conditions as well as the cutting edge segments S? and S?. Furthermore, this paper presents the influence of tailored cutting edges on tool wear, burr formation and residual stresses in slot milling of 42CrMo4 steel regarding the normalized ploughing zone in front of the cutting edge. © 2012 The Authors.

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