Lubricant free forming with tailored tribological conditions
Third Party Funds Group - Sub project
Start date : 01.10.2013
End date : 28.11.2019
Extension date: 31.07.2020
Website: https://www.trockenumformen.de/
Overall project details
Overall project
SPP 1676: Nachhaltige Produktion durch Trockenbearbeitung in der Umformtechnik
Project details
Short description
Short description
Changed ecological and economic situations motivate research into environmentally friendly and efficient manufacturing processes. Forming without lubricant has the potential to meet both requirements by avoiding the usage of environmentally harmful lubricants and shortening the process chain by omitting lubricant application and component cleaning. Within the scope of the research project, an increase in friction and adhesive wear were identified as major challenges. As a result, the components fail due to cracking. Therefore, this project focused on the investigation of measures to meet these challenges. Amorphous carbon coatings, the reduction of roughness and the application of discrete microtextures were considered as potential measures. Hydrogen-containing amorphous carbon coating systems (a‑C:H) fabricated by reactive physical vapor deposition (PVD), plasma-enhanced chemical vapor deposition (PECVD) and PVD/PECVD hybrid techniques, as well as a PVD-generated tetrahedral hydrogen-free amorphous carbon coating (ta‑C) were investigated with respect to their properties and tribological performance Three specific profile requirements – a dopant free carbon network, smooth and defect-free surfaces and a high coating adhesion to substrate – are identified as requirements, in order to prolonger the service life of the coated tools. Moreover, to enable the steering of the material flow the creation of laser based micro textures to tailor the tribology were investigated. Various ultrafast laser based approaches for modification (i.e. smoothing and texturing) were analyzed. To increase the efficiency of the process, several beam shaping approaches based on liquid crystal on silicon spatial light modulators were evaluated providing a homogeneous beam profile to enable a flat and uniform modification. By applying ta‑C and a‑C:H coatings in forming tests, the findings of the laboratory tests were validated and the feasibility of lubricant free deep drawing was proven. In order to benefit from the forming-process-specific advantages, high quantities and therefore high durability of the measures are required. An application-oriented wear test rig has been designed to investigate their durability. By this, it was proven that 3 000 components can be produced from DC04 without wear with both a‑C:H and ta‑C coatings, and thus increasing tool life by a factor of 15 compared to unmodified tools. Even in the case of wear-critical AA5182, 3 000 parts were produced without wear using ta‑C. Within the scope of the project, a fundamental understanding of lubricant free deep drawing processes and measures was created and proof of feasibility in form of a high number of components was achieved.
Scientific Abstract
Within lubricant free forming an intensive interaction of workpiece and tool surface occurs. The aim of this research project is the realization of dry forming processes by developing and applying innovative tribological systems. The challenges of dry forming such as increased friction accompanied by increased wear are met by tool based surface modifications in a tailored tool approach. In the first period of the project forming of steel sheets is investigated in a lubricant-free deep drawing process. In order to test the transferability of derived correlations to other workpiece material classes also an aluminum alloy is tested. In basic experiments under laboratory conditions the fundamental understanding of lubricant free forming is generated by the analysis and description of the occurring tribological effects. At the same time the test results serve as input values for the simulation based design of the segmented tool for manufacturing the demonstrator cup. In the FE simulation tribological relevant tool areas are identified. Subsequently, required surface properties for each tool segment are derived in an inverse approach. The requirements represent the targets for the development of tailored surface modifications. In order to guarantee reasonable wear resistance the suitability of DLC coating systems for lubricant free deep drawing is assessed. In some tool areas lubricant free forming requires an extraordinary high wear resistance of the coatings. In this regard the laser induced heat treatment of DLC coatings is investigated for the local enhancement of wear resistance. Furthermore, for the purpose of controlling the material flow tool based surface structures will be developed and applied by laser ablation. While developing the surface coatings and structures the frictional and wear behavior of the different modification types are investigated by carrying out model tests under laboratory conditions. In particular, the influences of the factors tool material, surface structure and coating on the tool behavior are quantified. For determination of the limits of dry forming process the interactions of tool behavior and occurring process loads are investigated in the laboratory tests. The derived correlations between the process loads, the surface modifications and the resulting tool behavior are used for the local adjustment of the tribological conditions within the lubricant free model process. In order to validate these correlations the friction and wear behavior of the segmented tool is determined in the deep drawing process for the investigated steel and aluminum grade. The results of the first period of the project represent the basis for qualification of tailored tribological systems for the application in lubricant free forming processes.
