Current Projects
Friction Stir Welding Equipment for Joining Large Steel Structures - FSW Steel
Joint Project supported by the Ministry of Economy and Technology (BMWi)
Subproject: "Development of Efficient Tools for Friction Stir Welding of Steel"
Support Code: VP2095003PK9
Duration: Dec. 1st, 2009 - Oct. 31st, 2011
associate partners: SLV Berlin-Brandenburg, Ingenieurtechnik und Maschinenbau GmbH, Lippold Hydraulik und Wälzlager GmbH, Helmholtz-Zentrum Geesthacht, Materion GmbH, H.Loitz - Robotik GbR
Abstract:
The objective of this project is the development of efficient tools and production equipment for friction stir welding of large, thin steel sheets, aiming at an economic application of this innovative joining technology.
Starting by determining process parameters for joining thin steel structures on experimental welding machines, the necessary parameters for future equipment and welding tools are identified. Concurrent to the development of new tools (materials, design, surface treatment), the concept for a production facility for joining large steel structures of a thickness of 3 to 4 mm is created. Solutions for the main components for clamping, process control and tool fixture are developed, prototypes are produced, integrated into the equipment and tested on lab scale.
The outcome of this project will be efficient friction stir welding tools as well as a functioning example for a production facility. Those will be the basis for the following design, construction and commercialisation of production facilities for friction stir welding of thin steel sheets.
Research area: Tooling
Contact: M. Sc. Stefanie Hanke
website: www.innowelding.de
Fatigue behaviour of Cu-based single and stranded wires
associate partner: Deutsches Kupferinstitut Berufsverband e.V. & International Copper Association
Abstract:
Dimensioning of technical components in order to reach endurance strength makes the use of mechanical values necessary. For many technical materials this values can be found in standards or guidelines as minimum or standard values. The determination of mechanical values for Cu-base materials in thin single wire or stranded wire shape under cycling loading is the aim of this project. The test and investigation methods for this material shape may differ compared to usually known since the microstructure is oligocrystalline due to the grain size/wire diameter ratio in this small profiles. Here the use of adequate or adapted investigation methods is necessary. Beside the wire surface and stranded wire structure the anisotropic properties need to be considered. In a first approach the mechanical behaviour of single wire samples is investigated and statistically secured under bending load.
Research area: Material Science
Contact: Dipl.-Ing. Michael Schymura
Metal Friction Surface Welding
Project: Ford- University Research Program
Abstract:
The demands on production tools of one car line with approximately 600.000 cars per year over the running period of app. 6 years or more are extremely high. Stamping tools areas with high tool wear are e.g. die radii or draw beads. The use of low cost tool materials with enhanced wear resistance will support both cost reduction and quality improvement. For mild steels, low cost tools like globular grey iron castings (GGG70L or GG25) are used as tool material for stamping tools. Today, coatings are used to reduce wear, which make fast and flexible tool and die changes in production impossible.
Friction Surfacing opens up new possibilities for the repair of worn and damaged components. This process is also potentially useful as an alternative surfacing process as it allows for a compromise between the bulk substrate, which can be dictated by strength or economic constraint, and that of the surface, which can be altered by the application of selective materials to form a protective barrier against wear and corrosion.
The possibility of forming a high quality and regular layer onto a substrate by Friction Surfacing process depends of the selection of appropriate welding parameters. The reproducibility of the weld however, depends of the controllability of the machines used for this purpose.
The Friction Surfacing Process can be divided in two Phases: Pre-heating Phase and Welding Phase. During the Pre-heating stage the rotating stud is pressed onto the substrate, the heat is developed due to the energy generated by friction between the substrate and the rotating stud. The temperature rises just below the melting point of the material, where the yielding strength of the material decreases and the shear stress produced in the stud is high enough to enable plastic deformation in the material.
The welding phase of the process is responsible for the production of the coating layer onto the plate by start of the transversal motion of the rotating rod. In this phase a quasi-steady thermal condition is reached influencing the properties of the HAZ formed. At this point the dimensional properties and the quality of the layer formed are significantly influenced by the transversal speed, rotational speed and the load applied.
When the weld length required is reached, the transversal and rotation motion is stopped and the axial load is maintained, assuring the high bonding quality of the end of the layer.
The projected benefits from this project are cost reduction due to reduced maintenance time and enabling low cost tool material. Further, an improved quality due to reduced tool wear and scratches is expected. The implementation of this advanced technology, which can be used on machines which are already available (milling) with low investment costs is regarded as new solution for well known challenges.
Research area: Tooling
Contact: M.Sc. Stefanie Hanke
Completed Projects
Nanocrystalline Composite Coatings with nano textured surface for Cylinder Running Surfaces of highly stressed Gasoline and Diesel Engines - NaCoLab
Support Code: BMBF 03X0003K
Duration: Jun. 1st, 2005 - Mai 31th, 2008
Abstract:
The aim of this research project is to replace grey cast iron liners in aluminium crank cases by a new coating material. By thermal spraying of a newly invented iron based filler wire feedstock alloyed with chromium, carbon and boron a hard, wear resistant and low friction coating is generated. The microstructure of these coating is an amorphous matrix with nanocrystalline precipitates. Increasing pressures during ignition (200 bar and higher) demand coatings which for all that ensure a good reliability and low wear rate.
Within this project a complete, innovative manufacturing chain for coating aluminium crank cases with this nanocrystalline material is developed. It includes the mechanical roughening of the substrate, thermal spraying of the filler wire feedstock and finally the surface finish by honing.
The institute of product engineering, materials science and engineering, advances the furthering of knowledge and understanding of the tribosystem piston ring - cylinder running surface by investigating the acting wear mechanisms. Running-in and wear influence the formation of the lubrication oil film in the contact zone. This results in differing friction losses, emissions and oil consumption which are significantly related to the durability of the motor. Advancing simulation tools to predict running-in and wear within the highly stressed positions top and bottom dead center is an additional objective within this project.
Research area: Automotive
Contact: Dipl.-Ing. Mareike Hahn
Solving Steel Welding Problems by the use of Friction Stir (SOLVSTIR)
Project: EU-Projekt
Support Code: RFS-PR-03077
Abstract:
Conventional fusion welding processes are reaching their applicability limits as far as the weldability of thin gauge, modern high alloy steels (i.e. UHSS, TRIP, CP, MS, DP and IF steels) is concerned. Weldability issues are also a matter of concern in Cr-containing steels employed in the energy sector (i.e. 9Cr1MoNbVN, 12Cr1MoV, etc) due to microstructural control, embitterment and particularly environmental concerns. The Friction Stir Welding (FSW) process, a low heat input, solid state joining method, offers a number of advantages likely overcome weldability problems in difficult-to-weld steel grades. Moreover, FSW has also shown to be able to produce multi-material joints between steel and non-ferrous alloys. Starting from the present state of art in FSW of steels this project intends to focus on two lines of development: process technology and application to relevant steel grades and multi-material joints. The process technology focus will aim at alternative tool materials and geometry, their respective process parameter fields as well as pre- and post-weld heat treatment methods viewing increased tool life and the cost effectiveness of the process. The suitability of the process to different steel grades will be investigated on modern high alloy and Cr-alloyed materials with emphasis on the microstructure development and joint perfromance. This development work will be supported by modelling (temperature and deformation) and by an economic evaluation and concluded with the manufacturing of demonstration structures from the automotive, shipbuilding and energy sectors. In summary, the main objective of this project is to define the merits of FSW when applied to steels based on the achievable joint performance, applicability to structures and economics.
Research area: Tooling
Contact: Dr.-Ing. Christian Zietsch
Reducing the Emission of Wear Debris in Metal on Metal Hip Joints by Means of Microstructured Surfaces.
Project: industrial project
Duration:
Jan. 1st, 2007 - Dec. 31th, 2008
associate partner: Zimmer GmbH
Abstract:
For years surface texturing is known to be an effective method to improve the properties of certain tribological systems. One approach is to create lubricant reservoirs by non-corresponding dimples in the surface of one of the articulating surfaces. In MEMS devices, surface texturing is used to reduce the contact area in order to overcome adhesion and friction. Another interesting beneficial effect of a textured micro-topography is its function as a wear particle trap. By eliminating particles from the tribological system, third-body-wear is prevented. The metal-on-metal (MOM) artificial hip joint is a system which does not suffer third body wear by means of abrasion. Nevertheless, wear particles are suspected to be responsible for implant failure due to osteolysis, a bone degrading disease that causes implant loosening. A major improvement would be the elimination of wear particles, in particular, during the run-in of the artificial joint. In order to apply a micro-topography different techniques can be performed like machining, ion beam texturing, laser texturing, and etching. For this study an electrochemical etching process is used. The advantage of this process is the homogeneity of the material. Furthermore, this process is a less expensive application than, for example, laser texturing. In order to observe whether an electrochemically textured surface is beneficial for wear performance in a first step, a reciprocating sliding wear test rig has been established. The characterization of the textured surfaces will be performed by means of confocal white light microscopy.
Research area: Biomedical Engineering
Contact: Dipl.-Ing. Robin Pourzal
Projekt: Microstructure and Deformation Behavior of Coronary Stents under Fatigue
Projekt: öffentlich gefördertes Forschungsprojekt
Förderkennzeichen: DFG FI495/9-1, DFG FI495/9-2, DFG WE2671/1-3
Laufzeit:
Description:
Stents are metal vessel scaffolds which are inserted to prevent vessel walls from collapsing. During implantation these stents have to tolerate a distinctly inhomogeneous plastic deformation due to crimping and dilation. Subsequently the implant has to sustain up to 700 million cycles induced by the cyclic diameter change of coronary arteries. During this time biofunctionality as well as biocompatibility have to be guaranteed. Because of the oligocrystalline structure of stents and the type of deformation the structure of the stent undergoes inhomogeneous plastic deformation. This results in local differences in chemical and mechanical load. This research project focuses on the experimental investigation and additional simulation of deformation mechanisms of oligocrystalline stents. Further, the development of a quantitative model for the deformation under static and cyclic load will be established. The diameter of one strut of a stent is generally about 100 µm. Therefore, depending on the grain size, there are not more than five to ten grains within the cross section of a stent strut. Thus the microstructure of only very few or even just one grain can be responsible for the behavior of the entire stent structure. Oligocrystalline structures like stents can in fact neither be described as multi-crystalline materials like fatigue specimens nor can they be treated as single crystals. In crystalline samples a size effect of mechanical properties can be observed if the grain size approaches the dimension of the specimen itself. Therefore mechanical investigations (tension and bending fatigue) are carried out using oligocrystalline wires of commercially used stent materials. The analysis of the deformation behavior will give a more comprehensive understanding of the structure property relationship in such thin structures with focus on the deformation behavior of coronary stents. The present study will help to develop a model based on experimental data to reach a better prediction for the endurance of coronary stents.
Forschungsbereich: Biomedical Technology
Ansprechpartner: Priv.-Doz. Dr.-Ing. Sabine Weiß