Final Report Summary - SIREN (Stability Islands: Performance Revolution in Machining)
Cutting has been considered as primary machining operation for centuries and likely to remain dominant in the future. Cutting went through a revolution in the 1990s when high-speed milling (HSM) was introduced. This has been followed by an incremental development when not just the cutting speeds, but depths of cut and feed rates are also pushed to limits. Cutting is subject to a special vibration called chatter, which is originated in a time delay: the cutting edge interferes with its own past oscillation recorded on the wavy surface cut of the work-piece. In 1907, the 3rd president of ASME, Taylor wrote: “Chatter is the most obscure and delicate of all problems facing the machinist”.
In spite of the development of the theory of delay-differential equations and nonlinear dynamics, Taylor’s statement remained valid 100 years later when HSM appeared together with a new kind of chatter problem. The grantee has been among those leading researchers who predicted these phenomena; the experimental/numerical techniques developed in his group are widely used to find parameters where milling tools with serrated edges or with varying helix angles are advantageous.
The SIREN project was constructed for a transition from standalone empirical models to experimentally validated theoretical models: 1. revolutionary cutting tools, 2. radically improved machine tool dynamics identification, and 3. sophisticated cutting parameter selection help to reach chatter-free stable parameter islands. The research work was performed in three work packages (WP) establishing new mechanical models for chip removal (WP1), for tool/tool holder/spindle contacts (WP2), and for main spindle contacts at bearings (WP3), while the implementation was carried out in WP4.
The progress in the project lines up with the workplan. Essential progress was achieved in the in situ evaluation of mechanical contacts between machine parts. The SIREN procedure is useful for the characterization of both mechanical and electrical contact properties in any situation when metallic bodies are in contact.
The Hardware-in-the-Loop (HIL) approach developed as a part of WP3 is also a promising new approach in HSM; it is already in the centre of international interest after its first publications in conferences and prototype presentations at exhibitions. As side-results, exceptional non-contact exciters and position detectors were developed and built. One of these is the target of a granted ERC PoC project proposal with submitted patent application.
Together with the results of WP1, the implementation part of the project in WP4 was successful in three aspects. A newly designed milling tool provided an order of magnitude improved efficiency of chatter-free milling of alumina workpiece at high speeds with about seven times larger axial depth of cut than standard tools, and three times larger axial depth of cut than the tool designed with the actual accepted theory of pitch angle optimization. While this was demonstrated in laboratory circumstances, another demonstration of the results was implemented in industrial environment for the milling of a difficult-to-cut material for the aeronautic industry, where the strictly prescribed cutting speed gave room for efficiency increase only by the non-uniform pitch angle distribution. Finally, a tuneable worpiece fixing table was designed and constructed with submitted patent application, which is used for chatter suppression and for generating stable cutting parameter islands.
The scientific achievements of project lead to publications: 45 papers in journals with high impact factor, 39 peer reviewed conference papers in proceedings of leading international conferences, 74 conference poster/oral presentations, and 2 patent applications were authored by the PI and his team members. The concept of the project and the results were presented at the annual meetings of CIRP, the most prestigious scientific organization of manufacturing, and a keynote paper in CIRP Annals is already Highly Cited in WoS with lead authorship and 3/7 participation co-authored with leading experts in chatter suppression.
In spite of the development of the theory of delay-differential equations and nonlinear dynamics, Taylor’s statement remained valid 100 years later when HSM appeared together with a new kind of chatter problem. The grantee has been among those leading researchers who predicted these phenomena; the experimental/numerical techniques developed in his group are widely used to find parameters where milling tools with serrated edges or with varying helix angles are advantageous.
The SIREN project was constructed for a transition from standalone empirical models to experimentally validated theoretical models: 1. revolutionary cutting tools, 2. radically improved machine tool dynamics identification, and 3. sophisticated cutting parameter selection help to reach chatter-free stable parameter islands. The research work was performed in three work packages (WP) establishing new mechanical models for chip removal (WP1), for tool/tool holder/spindle contacts (WP2), and for main spindle contacts at bearings (WP3), while the implementation was carried out in WP4.
The progress in the project lines up with the workplan. Essential progress was achieved in the in situ evaluation of mechanical contacts between machine parts. The SIREN procedure is useful for the characterization of both mechanical and electrical contact properties in any situation when metallic bodies are in contact.
The Hardware-in-the-Loop (HIL) approach developed as a part of WP3 is also a promising new approach in HSM; it is already in the centre of international interest after its first publications in conferences and prototype presentations at exhibitions. As side-results, exceptional non-contact exciters and position detectors were developed and built. One of these is the target of a granted ERC PoC project proposal with submitted patent application.
Together with the results of WP1, the implementation part of the project in WP4 was successful in three aspects. A newly designed milling tool provided an order of magnitude improved efficiency of chatter-free milling of alumina workpiece at high speeds with about seven times larger axial depth of cut than standard tools, and three times larger axial depth of cut than the tool designed with the actual accepted theory of pitch angle optimization. While this was demonstrated in laboratory circumstances, another demonstration of the results was implemented in industrial environment for the milling of a difficult-to-cut material for the aeronautic industry, where the strictly prescribed cutting speed gave room for efficiency increase only by the non-uniform pitch angle distribution. Finally, a tuneable worpiece fixing table was designed and constructed with submitted patent application, which is used for chatter suppression and for generating stable cutting parameter islands.
The scientific achievements of project lead to publications: 45 papers in journals with high impact factor, 39 peer reviewed conference papers in proceedings of leading international conferences, 74 conference poster/oral presentations, and 2 patent applications were authored by the PI and his team members. The concept of the project and the results were presented at the annual meetings of CIRP, the most prestigious scientific organization of manufacturing, and a keynote paper in CIRP Annals is already Highly Cited in WoS with lead authorship and 3/7 participation co-authored with leading experts in chatter suppression.