This paper presents an overview of the recent advances in high performance cutting of aerospace alloys and composite currently used in aeroengine and aerostructure applications. Progress in cutting tool development and its effect on tool wear and surface integrity characteristics of difficult to machine materials such as nickel based alloys, titanium and composites is presented. Further, advances in cutting technologies are discussed, focusing on the role of hybrid machining processes and cooling strategies (MQL, high pressure coolant, cryogenic) on machining performance. Finally, industrial perspectives are provided in the context of machining specific components where future challenges are discussed.

High performance cutting of advanced aerospace alloys and composite materials

Cryogenically assisted manufacturing processes are emerging as environmentally-benign, toxic-free, hazardless operations, producing functionally superior products. This paper presents an overview of major cryogenic manufacturing processes, summarizing the state-of-the-art and significant developments during the last few decades. It begins with a summary of historic perspectives, including definitions, scope, and proceeds to analysis of process mechanics and material performance covering tribological and thermo-mechanical interactions, followed by surface integrity, product quality and performance in cryogenic manufacturing. Process analysis and applications includes machining, forming and grinding. Economic, safety and health issues are then discussed. Finally, progress in developing predictive performance models and future outlook are presented.

Cryogenic manufacturing processes

http://publications.lib.chalmers.se/records/fulltext/241311/local_241311.pdf

Influence of Coolant Flow Rate on Tool Life and Wear Development in Cryogenic and Wet Milling of Ti-6Al-4V

Energy efficient machine tools

Titanium alloys are one of the most important design materials for the aircraft industry. The high strength-to-density-ratio and the compatibility with carbon fibre reinforced plastic are the reasons for a raising application in this field. The outstanding properties lead to challenging machining processes. High strength and low heat conductivity affect high mechanical and thermal loads for the cutting edge. Thus, the machining process is characterized by a rapid development of tool wear even at low cutting parameter. To reach a sufficient productivity it is necessary to dissipate the resulting heat from the cutting edge by a coolant. Therefore the cryogenic machining of two different titanium alloys is investigated in this work. The results point out the different behavior of the machining processes under cryogenic conditions because of the reduced thermal load for the cutting tool. According to this investigation, the cryogenic cooling with CO2 enables an increase of the tool life in comparison to emulsion based cooling principles when machining the α+β-titanium alloy Ti-6Al-4V. The machining process of the high strength titanium alloy Ti-6Al-2Sn-4Zr-6Mo requires an additional lubrication realized by a minimum quantity lubrication (MQL) with oil. This combined cooling leads to a smoother chip underside and to slender shear bands between the different chip segments.

Experimental investigation of tool wear and chip formation in cryogenic machining of titanium alloys

Besides developments in the area of dry machining and minimum quantity lubrication, the use of coolant lubricants is still essential when machining high alloyed steels or heat resistant materials like titanium and nickel based alloys. Experts agree that this fact will not change in the next decade. For this reason it is necessary to use coolant lubricants as effectively as possible to maximise their positive effect on productivity and process stability. High-performance cooling strategies like high-pressure cooling and cooling with cold gases (cryogenic cooling) have received increased attention in the last years. Through the targeted supply of coolant lubricants to the cutting site it is possible to decrease tool wear, increase cutting speeds, guarantee defined chip breakage and chip transport and – in terms of cryogenic cooling – waive part cleaning. This paper shows current research results in the above mentioned field. Since the performance of a high-pressure coolant lubricant supply in turning difficult to cut materials has been shown in many previous papers, this paper focuses on the quantification of the potential in turning different steels, namely quenched and tempered but also stainless steel in comparison to the conventional flood cooling. Since energy efficiency is very crucial, pressure and flow rate have to be adjusted carefully and in accordance with the cutting parameters to guarantee best results with less energy. Moreover the effects of cryogenic cooling will be evaluated in comparison to high-pressure cooling and conventional flood cooling. In latter field, cutting tests were carried out under variation of the flow rate in order to find the minimum required value for a certain machining task with the overall aim to prevent waste of the media used. Especially in cryogenic cooling technologies, many fundamental research regarding the working mechanisms but also further developments in cutting tool and machine tool technology are still necessary to make this technology ready for industrial use.

Potential of Modern Lubricoolant Strategies on Cutting Performance

In the field of machining difficult-to-cut materials like titanium or nickel-based alloys, the use of high-pressure cooling lubricant supply (HPCLS) offers huge potential to significantly increase productivity and process stability. Due to enhanced cooling and lubrication of the cutting zone, tool wear can be decreased which allows higher applicable cutting speeds. Furthermore, process stability can be increased through effective chip breaking and evacuation. Increasing energy prices and legislative framework conditions, require energy efficient machine tools and processes. Since additional energy is required to run the high-pressure pump, it has to be determined if the overall process is still energy-efficient due to the increase in productivity resulting in shorter cycle times. In this paper the overall aim is to evaluate the conventional-flood-cooling and HPCLS in terms of economics and energy efficiency. Therefore a case study has been performed in which the energy consumption and production times for machining a rotationally symmetric jet engine part made of Inconel 718 were compared for both conventional and HPCLS. Furthermore, an ecological evaluation has been conducted to determine the advantageousness of the HPCLS. Due to the rising necessity of suppliers to provide a product carbon footprint, a methodology for assessing the footprint has been applied.

Evaluation of Energy Efficiency in Cutting Aerospace Materials with High-Pressure Cooling Lubricant Supply

Increasing Energy Efficiency in Turning of Aerospace Materials with High-Pressure Coolant Supply

w ith H ig hPr es su re C oo la nt S up pl y In the field of machining difficult-to-cut materials, the high-pressure coolant supply represents a promising technology for increasing productivity and process stability. The distinctive characteristic is the targeted supply of the coolant at elevated pressure (> 80 bar) into the wedge between the chip bottom and the tool rake face. In the industrial application, the high-pressure coolant supply is mainly used in turning of difficult-to-cut materials under roughing conditions. Despite the technological advantages, the application is prevented in turning operations under finishing conditions as the coolant jet force accelerates the broken chips to high velocities, which then collide with the workpiece surface. The high-dynamic impact of the chips on the surface significantly affects the surface quality and may reduce the lifetime of the final component. Hence, the technological and scientific motivation of the thesis was to analyse the underlying mechanisms for the occurrence of surface anomalies.

Surface Anomalies in Turning of Difficult-to-Cut Materials with High-Pressure Coolant Supply

In the field of machining difficult-to-cut materials like titanium or nickel-based alloys, the use of a high-pressure lubricoolant supply may result in a significant increase of productivity and process stability. Due to enhanced cooling and lubrication of the cutting zone and thus reduced thermal tool load, tool wear can be decreased which allows higher applicable cutting speeds. Furthermore, the process stability can be increased as a result of effective chip breaking and chip evacuation. Since energy efficiency is very crucial, pressure and flow rate have to be adjusted carefully and in accordance with the cutting parameters to guarantee best results with less energy. For this purpose, experimental investigations were carried out under variation of the flow rate in order to find the minimum required value for a certain machining task with the overall aim to prevent waste of the media used. To maximize the positive effect of high pressure lubricoolant supply strategy on productivity and process stability, specially designed lubricoolant jet guidance geometry on the rake face was also investigated and compared to conventional turning inserts. To study the effect of high-pressure lubricoolant supply on tool temperature, reference tests also carried out using conventional overflood cooling (CoC). The results suggest that the tool temperature can be significantly decreased compared to CoC by applying the high pressure lubricoolant supply and using specially designed jet guidance geometry in turning the investigated aerospace materials TiAl6V4 and Inconel 718.

Tolga Cayli

Papers

Potential of Modern Lubricoolant Strategies on Cutting Performance

Evaluation of Energy Efficiency in Cutting Aerospace Materials with High-Pressure Cooling Lubricant Supply

Increasing Energy Efficiency in Turning of Aerospace Materials with High-Pressure Coolant Supply

Surface Anomalies in Turning of Difficult-to-Cut Materials with High-Pressure Coolant Supply

Increasing Productivity and Process Stability in Turning of Aerospace Materials with High Pressure Lubricoolant Supply