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Eco-efficient stamping process of sheet metal parts by development of innovative coatings for self-lubricating dies


Based on the definition of die materials, sheet materials and coatings to be studied, testing apparatuses werde developed and/or adapted for characterization and evaluation purpose. The apparatuses will be used for: - Strip drawing test and drawbead test. - Swift Cup test and semi-industrial test. - Test on real stamping conditions with dies for automotive parts.
PVD (Closed Field Unbalanced Magnetron Sputter Ion Plating - CFUBMSIP) and Plasma Spray (PS) coating equipments were utilised within the ECOSTAMP project by the coating partners (Teer Coatings Limited - TCL - and Centro S Materiali - CSM, respectively). This enabled the equipment and its operation to be further refined to meet the needs of the project's end users, and more generally for the treatment of cold forming tools.
Low Friction and Wear PVD Coatings IPN deposited further examples of the optimised W-Ti-N coatings (i.e. V=-70V with the relative pressures of the deposition gases, pN2/pAr, in the range 1/3-1/5, resulting in a chemical composition WxTiyNz=(35-40) at.% (x+y+z=100%)) for evaluation in WP 8. Development of PVD Coatings - TCL During year 3, in addition to depositing the standard MoST and Graphit-iC coatings for evaluation in WP 7, TCL carried out some limited additional development of the coatings in an effort to extend the available range of operating characteristics. MoST/TiB2. One MoS2 target was substituted with a TiB2 target. The investigation focused mainly on a multilayer approach. The TiB2 sputtering power was varied, relative to the MoS2 target power, to produce multi-layers with different thickness, typically 20-30nm for each individual layer. The TiB2 magnetron current was set at 1.0, 1.4, and 1.8 amps. Glancing angle XRD was used to evaluate the resulting structures. An SEM investigation showed no columnar features in the cross section of the multilayer coating. The back-scattered image in the SEM enabled the multi-layers to be seen (for thicker multi-layers). The thickness of the coating was varied in the range 1'Ým to 2'Ým. It was possible to reduce the wear rate further to 10-18 m3/Nmm. There was no increase in hardness. Adhesion, as evidenced in the Rockwell test, was worse if layer thickness was increased. At much higher thickness (e.g. 3'Ým) adhesion scratch test results also degraded, although wear rates, as measured by pin on disc were still very good. Try to control the sputtering of TiB2 by a more gradual change V can maintain high wear resistance and low friction. The advantages of the combined coatings, compared to the standard MoST, were that thicker coatings could be used, with a higher temperature capability and reduced humidity sensitivity (e.g. very good results were still obtained when testing at 45% RH). MoST/ Carbon coatings One MoS2 target was substituted by a carbon (i.e. graphite) target. Both MoST with carbon additions as a composite coating, and MoST/C multi-layers were investigated. The objective was to minimize the resulting friction coefficient (and therefore the investigation did not focus on pin on disc performance at high applied load). Because both carbon and MoS2 were sputtered the Ti target was unavoidably ¡§poisoned¡¨ and would normally have required cleaning between coating runs. To save time the intermediate cleaning run was been omitted for the preliminary series of experiments. With C addition to the MoST there was no obvious decrease in friction coefficient. With the multilayer approach, an attempt was made to increase the coatings wear resistance, reducing the MoS2 coating content gradually. However, overall there was no significant improvement compared to the standard MoST coating. MoST in combination with hard coatings The self-lubricating coatings are often used in combination with a hard underlayer. The effect of different hard coatings in combination with MoST was evaluated: MoST, TiN+MoST (4x increase in wear life), CrTiAlN+MoST (5x wear life), Graphit-iC+MoST (14.5x wear life) It was clear that, in combination with MoST, a Graphit-iC underlayer is more than just a mechanical support ¡V the whole coating can work as a lubricant. For CrTiAlN+MoST, when the top layer was worn through the friction increases dramatically. For Graphit-iC, tested at 40N & 80N load it was possible to detect an increase in friction when the G-iC layer was exposed. When testing a pure Gi-C the starting values of the friction was higher ¡V ie the Graphit-iC exhibited a ¡§running in¡¨ effect, but a MoST top-coat changed this behaviour significantly. In summary, the low friction coatings have been shown to be potentially beneficial in their intended applications.
Stamping dies surfaces with dry lubrication properties have been obtained by thermal spraying of composite coatings containing solid lubricant materials. Graphite was selected as lubricant phase; it was mixed with a cermet powder containing a fine dispersion of Chromium Carbide particles in a Nichel-Chrome metallic matrix. Mixtures with different amounts of the two powders were prepared by mechanical mixing before thermal spraying. The coatings materials were deposited by Atmospheric Plasma Spray on steel substrates. Results showed a negligible wear and low friction coefficient which decreases with increasing graphite content. In particular, friction coefficient as low as 0.34 were measured in tribological tests carried out in dry conditions. Graphite content of 35 vol% gave optimal results in terms of wear resistance.
The Database for PVD coating, die materials and lubricants result is a task 2.3 of WorkPackage2 (WP2): Specifications of Coatings and Design of Test Apparatus. The WP 2 represents the starting point for most of the technical activities carried on during the first year of project. In fact, this WP concerns all the selection and preparation of material and data needed during project, together with critical decisions on thin films demands to support the necessary stamping efforts and provide the requested surface properties. The base decisions concerning the several issues included: selection of die materials, sheet materials, lubricant oils, and a several practical tests, in this WP partners understand needs and limitations, keeping in the scope of the project work programme and objectives. The Database is really a data collection exercise to take a snapshot of the present situation in industrial use (and constantly update by partners according to the needs), for comparison at the project end, for use in implementation across groups, and for marketing. IPN design and producing a useable and useful database, with an emphasis on eventual industrial usefulness. These involve a creation of a Database using Microsoft® Office Access 2003 software, where a large quantity of data has been uploaded. And during the project, all partners are responsible to upload appropriate information. For production a Database, a systematic investigation on the materials currently used for stamping dies, the wear resistance performance of these die materials, the usage of sheet metal forming lubricants and their disposal (for a better understanding on their functional performance and environmental impacts). The collected information will be put into a database to be used for economical, ecological and technical evaluation in project end. Searching and reporting features have also been considered and the constant update. The access to this data can be made by any of the project partners as well as the upload of new data.