High Performance Cutting Research Articles

Analiza stabilności skrawania z dużą prędkością stopów aluminium

Progress in the production of cutting tools, CNC machine tools, and CAM software has contributed to improvement in subtractive machining processes, including milling, the so-called high speed cutting (HSC) and high performance cutting (HPC) machining. The cutting parameters that define the boundaries between the aforementioned technologies and conventional machining are not clearly defined. This is due to the close correlation between the process conditions and the types of processed material. High speed cutting and high performance cutting can be used for processing such as: machining of materials in the hardened state, machining without cutting fluid and with minimal lubrication, and thin-wall integral aerospace structures. The study examined complex analyses of HSC machining due to the process stability. The test results prove the dominant influence of cutting speed changes on a method’s effectiveness for spindle speeds up to 80,000 rpm.

Preload Control of Spindle Bearings by Means of Shape Memory Alloys

Commercial, motor-driven spindles for applications in machine tools are generally developed for specific machining operations. Spindles can be distinguished between spindles for HPC (High Performance Cutting) and spindles for HSC (High Speed Cutting). HPC and HSC require opposing specifications concerning motor configuration and the preload of the spindle bearings. To realize a universal machine tool spindle, changeable motor configuration and preload of the spindle bearings are necessary. In this paper, a new approach for an adaptive preload element is presented to control the preload of a spindle bearing arrangement. The adaptive preload element consists of actuators based on shape memory alloys in combination with Peltier elements. By controlling the current through the Peltier elements the temperature of shape memory alloys bending springs is controlled. Thus, the preload force of the bending springs can be variated. Experimental tests reveal the properties of the preload element and its suitability for preload modification. Within these tests, the adaptive preload element enables a preload modification of about 850 N.

Pre-Machining of Rolled Plates as an Element of Minimising the Post-Machining Deformations.

The paper presents the influence of the milling strategy, the relation between the cutting tool feed direction and the rolling direction, as well as the pre-machining consisting of the removal of the textured surface layer of rolled plates in the rolling process on the thin-walled elements deformations made of the EN AW-2024 T351 wrought aluminium alloy, after milling. The research used strategies such as: high-performance cutting (HPC), high-speed cutting (HSC) and conventional milling (CM), as well as their combinations. Another tested variable was the relation between the tool feed direction and the rolling direction. In addition, the tests were carried out in the following versions: leaving the textured surface layer created after plastic working and with its removal with technological parameters corresponding to HSC and CM. Based on the obtained results, it was found that the post-machining deformation of thin-walled elements can be minimised owing to the use of a selected milling strategy and its combination with pre-machining (or lack thereof). It was also observed that larger deformations were obtained for samples after milling in the direction perpendicular to the rolling direction.

Analysis and simulation of process damping in HPC milling

The use of tools with chamfered cutting edges is an essential part of high performance cutting (HPC) as a rough milling process strategy for manufacturing structural components in the aerospace industry. Due to an interaction between the chamfer and the undulated workpiece surface, tool vibrations can be damped allowing high depths of cut without the occurrence of harmful dynamic effects. Hence, a significant increase in efficiency is possible. As a result of process damping, the stability boundary predicted by linear stability analysis provided for instance by analytical or geometric physically-based simulations will generally underestimate the experimentally determined one. Consequently, the object of this procedure, namely to reduce the number of test runs until sufficient process parameter values are determined, could not be met. Therefore, the damping effect induced by chamfered tools was analysed in this paper. It is shown that the use of chamfered cutting edges leads to a significant limitation of chatter amplitudes when exceeding the stability limit. The strength of this effect depends on the cutting speed and the engagement situation, which influence the intensity and number of interactions between the chamfer and the workpiece surface and, thus, the resulting process damping. Moreover, a dynamic process damping model presented in the literature was chosen and implemented in a geometric physically-based milling simulation. An evaluation of its validity points out the challenges regarding the simulation of process damping.

Influence of pre-machining on post-machining deformation of thin-walled elements made of aluminium alloy EN AW-2024

The paper presents analysis of influence of pre-machining, consisting of removing the textured surface layer of the semi-finished product formed after plastic working, on deformation of thin-walled elements made of EN AW-2024 alloy after milling. The textured layer was removed from surface opposite to the machined surface. During tests, the influence on thin-walled elements deformation of the following machining strategies was analysed: High Speed Cutting (HSC), High Performance Cutting (HPC), and hybrid strategies HPC + HSC, HPC + CM, and HPC + CM (CM – Conventional Machining). On the basis of received results it was determined that residual stresses stored in subsurface, rolled, and unmachined surface layer have significant influence on value and character of deformations of thin-walled elements. Removing the textured surface layer formed after rolling changes character and value of the deformations of thin-walled elements. The largest difference between samples with initially removed textured layer and samples without such machining was determined for HPC + CM milling strategy. For this strategy, deformations without pre-machining were much larger than in the case of samples with removed textured surface layer.

Evaluation of the impact of the natural seasoning process on post-machining deformation of thin-walled elements made of aluminium alloy EN AW-2024

The study attempts to evaluate the impact of short-term natural seasoning process on the state of post-machining deformations of thin-walled elements made of the EN AW-2024 aluminium alloy. Analyses were made of the impact of the technological history of the semi-finished product, in this case – the rolling direction of the plate (perpendicular and parallel to the feed direction) as well as high-performance machining strategies, such as High Speed Cutting (HSC) and High Performance Cutting (HPC) on the value of deformations of thin-walled samples, directly after machining and after seasoning. Application of natural seasoning at reducing deformations of thin-walled elements made of aluminium alloys may prove an alternative to the difficult intermediate heat treatment. The expected reduction of deformations is a result of reducing residual stresses in the material, in the course of the relaxation process. The dynamics of the natural relaxation is highly correlated with the properties of materials. The study includes an analysis of the effects of a short-term relaxation, accepted in industrial conditions (up to 1 month since the end of machining) for the EN AW-2024 alloy. If the proposed solution gives positive effects, it can bring measurable economic benefits in industrial applications. The study is completed with general and practical conclusions.

Hybrid Spindle – An approach for a milling machine tool spindle with extended working range for HSC and HPC

Commercial motor-driven spindles for milling machine tools are generally developed for specific machining operations, such as HPC (High Performance Cutting) or HSC (High Speed Cutting). HPC and HSC require significantly different working ranges regarding spindle speed and torque. E.g. in HPC operations, high torque at low spindle speeds is needed. The two working ranges are covered only limited by a conventional spindle so far. However, a spindle system that can switch the working range allows cost-effective manufacturing of a wider range of materials within the same machine tool. The spindle bearings and the power electronics supply are challenges, when switching between both working ranges. HPC operation requires high bearing stiffness in order to transmit high forces occurring during the cutting process. However, the associated high bearing preload leads to high frictional losses at high speeds for HSC operations. Furthermore, the wide operating range generates contrary requirements for the motor winding. To increase the spindle speeds with a winding being assembled for high torques, the current has to be increased. For this purpose, expensive and non-standardized motor inverters are required. This paper introduces a concept to overcome these challenges. Firstly, an approach to adjust the bearing preload is presented, using a compact, electrically controlled bearing preload element, which is suitable for industrial applications. Next, an approach for a reconfigurable winding design of the spindle motor is shown. This allows electrical switching between the working ranges using conventional motor inverters. Finally, an analysis of the conditions of use of the hybrid spindles is presented.

Automated microfluidic balancing system for high speed air-bearing spindles

The precision balancing of high speed air-bearing spindles is a delicate process. Due to the low bearing stiffness and the quadratic correlation between angular velocity and centrifugal force, the balancing is usually done manually. In order to prevent damage of the air bearings, multiple iterations for different spindle speeds, up to the working rotational speed have to be conducted, resulting in a time-consuming manual balancing procedure with a loss of accuracy for ultraprecision High Performance Cutting (HPC). In this paper, a novel precision balancing system for automatic balancing of high speed aerostatic spindles based on microfluidic valves is presented. In comparison to manual balancing, the system enables a reduction of balancing time to one third and a rise in balancing accuracy. Due to the remotely controlled microvalves, shifts of the center of mass up to two orders of magnitude more precisely than those achieved with conventional manual balancing operations can be attained.

High Performance Cutting (HPC) in the New Era of Digital Manufacturing – A Roadmap

We are rapidly moving into the new era of digitisation, into an era of the Massive Internet of Things - towards the Gigabit Society and towards 5G Technology. The implications are truly far reaching. Rapid transformation through the implementation of INDUSTRY 4.0 is becoming visible in industries all over the world. Disruption to the more traditional industrial practices and processes is inevitable. High Performance Cutting is no exception. Developments in the Internet of Things (IoT) opens up new and extremely powerful capabilities to help us gain a significantly deeper understanding of the fundamentals of cutting processes and offers entirely new connectivity possibilities at all interfaces, some old and some new, “between the Chip Root and the Cloud”. This supports us in our attempts since the foundation of CIRP in 1951 to remove technological roadblocks and can lead on a new journey towards new and unprecedented scientific/technological developments as well as new business models for companies involved in the various elements of the supply chain for cutting processes (DIN 8580). “Performance” will take on a new and unanticipated meaning over what was originally meant when we established this CIRP-HPC Conference back in the early 2000's. In this paper a critical review of a previous roadmap is undertaken for cutting processes presented in a CIRP Keynote Paper in 2003 by Byrne, Dornfeld and Denkena [1] and new thoughts and ideas are presented on a vision for a 2020 skeleton Roadmap for High Performance Cutting in the new age of Digitisation.

Development of a Cutting Tool for High-performance Cutting of Railway Rolling Components

High performance cutting (HPC) is used in machining railway parts like wheel sets or axes with large depth of cut and high feeds). The process is accompanied by increased thermal loads causing high concentration of stresses in the contact areas with the tool. This paper presents a set of methods to reduce thermal stress in machining zone in HPC conditions through the use of a special tool system, consisting of carbide cutting inserts with nano-structured multilayer composite coatings and a special scheme for mounting such inserts on tool holder with the use of high heat-conducting ceramic-polymer pads. The study has revealed that the developed tool system can significantly accelerate heat transfer from the insert and increase efficiency. Production tests show that the tool and the new coating in machining rolling stock (of railway) components can improve performance by 80-100%.

Microfluidic Balancing Concepts for Ultraprecision High Speed Applications

High-speed, ultraprecise air-bearing spindles require accurate balancing in order to minimize vibrations and achieve an optimum surface quality in diamond machining. In this paper, novel concepts for balancing of aerostatic spindles based on microfluidic pumps and valves are being investigated. Conventional, manual balancing methods are usually time-consuming and lack the required accuracy for ultraprecision High Performance Cutting (HPC). Using remotely controlled micropumps and -valves, minimum amounts of a few nanoliters of a fluid (e.g. water, oil) can be handled, allowing shifts of the center of mass two orders of magnitude more precise than those achieved with conventional balancing operations. Thus, a remote-controlled and automated balancing process is possible.

Design and Test Rig Experiments of a High Speed Tapered Roller Bearing for Main Spindle Applications

A new design of tapered roller bearings (TRB) for main spindles for high-performance cutting (HPC) or heavy roughing applications is presented. The bearing's key features to increase the speed rating are an outer ring rib, additional means of lubrication and ceramic rollers. First results of test rig experiments show that its speed rating is considerably higher than that of standard TRBs while calculations indicate that its stiffness and load rating are superior to conventional spindle bearings (SPB). Measured runout values of the new TRB and a reference SPB indicate that regarding accuracy the new TRB concept can be applicable for main spindles.

Constant Depth Scoring of Fibre Reinforced Plastic Structures to Prevent Delamination

Scoring of the outer layers of a workpiece with small engagement (ae) using circular saws is a well known method to avoid unwanted delamination of these layers, such as coatings of wooden particle boards. In edge milling fibre reinforced plastics (FRP), delamination also occurs in the top or bottom layer of the component and requires time intensive rework or scrapping of material. A combined process of scoring and milling is presented in this paper as a means to avoid delamination during machining of FRP structures such as aircraft carbon FRP parts. For the scoring process a diamond electroplated circular wheel is used. To guarantee a constant width of the scored slot, a constant depth of engagement is needed due to the shape of the grinding wheel. Therefore the profile of the scoring path on the workpiece surface is measured with respect to the machine coordinate system to correct a variation in the workpiece thickness and to compensate for uneven clamping. Next, the workpiece is scored with constant depth of engagement (ae,s < 0.5mm) and a high feed velocity of up to 16 m/min. Subsequently, the scored component is machined with a conventional polycrystalline diamond (PCD) milling tool. From experiments it is proven that a delamination-free edge is achievable even with a worn tool (cutting edge radius rn > 50μm) at an increased feed velocity (vf,m = 4.5 m/min). Without scoring, flawed workpiece edges have been obtained with cutting edge radii beyond rn > 23μm (progressive uniform wear stage) and a feed velocity of vf,m = 1.5 m/min. Hence, high performance cutting (HPC) edge milling of composites may be realized by an initial scoring step to fulfil quality requirements of the machined edges and simultaneously increase the tool life of the milling tool.

COMPARISON OF MECHANICAL PROPERTIES AND CALCULATION OF CUTTING FORCE BETWEEN UNCOATED TUNGSTEN CARBIDE &amp; Ti COATED TIP TUNGSTEN CARBIDE WITH THE HELP OF LATHE TOOL DYNAMOMETER

The keyword for manufacturers of cutting tools and coatings for cutting tools is productivity: a 30%; reduction of tool costs, or a 50%; increase in tool lifetime results only in a 1%; reduction of manufacturing costs. But an increase in cutting data by 20%; reduces manufacturing costs by 15%;. In order to achieve higher productivity different approaches – High Performance Cutting (HPC) and High Speed Cutting (HSC) can be chosen. The performance of Carbide tools was studied to investigate the tool life and wear behavior at various machining parameters. This study presents tool wear characterization of carbide cutting tool inserts coated with titanium nitride (TiN) on a single point turning operation on copper, aluminum. A set of experiments with conditions of cutting speed, depth of cut and feed rate were performed on a lathe machine. Force analysis is done on Lathe Tool Dynamometer. From the result, cutting speed was found to be the main factor to have significant effect on surface roughness. At the end of this study, optimization was made by suggesting the most suitable sets of parameter settings to produce minimum surface roughness. Suggestion on parameter settings to obtain minimum surface roughness made.

Oxygen-Improved Hard Coatings for High Performance Cutting Processes

Conventional hard coatings can be used to improve the properties of tools and machine parts, e.g. to reduce wear and to increase the tool life in cutting processes. In HPC (High Performance Cutting) machining, tools and tool coatings have to show a better thermal and chemical stability due to the higher process temperatures and the higher load of the tools. With oxygen-improved coating systems the thermal or the chemical stability of the used coatings at higher process temperatures can be improved. Therefore, the cutting process can be stabilized. The combination of stable oxidic and oxynitridic structures with conventional hard coatings was used to develop coatings with higher strength and higher hardness as well as an improved stability at higher temperatures. These oxygen-improved hard coatings were produced with the material systems Al-Cr-O-N or Zr-O-N and deposit with an arc-PVD process by use of an oxygen-nitrogen gaseous mixture. According to the analyses, the formation of the cubic and oxidic phases could be verified. These structural elements lead to the improvement of coating properties like hardness and elasticity and optimized thermodynamic properties. The application tests of difficult machinable materials with high strength like ADI (austempered ductile iron) or stainless steel show the great potential of the oxygen-improved hard coatings. In various cutting analyses a strong increase in tool life of oxygenimproved hard coated tools could be proven. This shows the applicability of the developed oxynitridic coating systems for high performance cutting processes to improve the efficiency of cutting processes.

Resource and Energy Efficiency in Machining Using High-Performance and Hybrid Processes

The main goal in manufacturing is to minimize production time, cost, energy and resources while maintaining or even improving performance. The main influence on process efficiency in metal cutting can be related to the machining parameters, while performance also depends on the material behavior such as strain rate, machining temperature and cutting forces. In the past, industry was searching for higher efficiency mainly by using higher production rates, achieved with higher cutting conditions. However, during the last decade the production process chain has been controlled more and more by the near-net-shape of semi-finished components and the use of high performance processes. This paper presents established and new applications of process modifications, substitutions, optimizations as well as the use of hybrid processes. In high performance cutting (HPC) additional elements play an important role, for example tool design and tool material, wear and tool life, coolant strategies, including dry cutting, MQL, cryogenic and high pressure flushing as well as the machine tool properties. Furthermore, this paper presents and discusses examples of the influence of process parameters in turning, milling, drilling, grinding and impact cutting under HPC conditions on the energy and resources efficiency in the automotive, aerospace, dies and moulds, micromachining and heavy duty industries.

THE ATOMIC FINITE ELEMENT METHOD AS A BRIDGE BETWEEN MOLECULAR DYNAMICS AND CONTINUUM MECHANICS

On cutting tools for high performance cutting (HPC) processes or for hard-to-cut materials, there is an increased importance in so-called superlattice coatings with hundreds of layers each of which is only a few nanometers in thickness. Homogeneity or average material properties based on the properties of single layers are not valid in these dimensions any more. Consequently, continuum mechanical material models cannot be used for modeling the behavior of nanolayers. Therefore, the interaction potentials between the single atoms should be considered. A new, so-called atomic finite element method (AFEM) is presented. In the AFEM the interatomic bonds are modeled as nonlinear spring elements. The AFEM is the connection between the molecular dynamics (MD) method and the crystal plasticity FEM (CPFEM). The MD simulates the atomic deposition process. The CPFEM considers the behavior of anisotropic crystals using the continuum mechanical FEM. On one side, the atomic structure data simulated by MD defines the interface to AFEM. On the other side, the boundary conditions (displacements and tractions) of the AFEM model are interpolated from the CPFEM simulations. In AFEM, the lattice deformation, the crack and dislocation behavior can be simulated and calculated at the nanometer scale.

SIMULATION OF THE PROCESS STABILITY OF HPC MILLING OPERATIONS

The optimisation of high-performance cutting (HPC) processes under technological and economical aspects often proves to be extremely difficult due to the appearance of process instabilities, so-called “chatter”. The identification of ideal process parameters often involves the systematic testing with varied cutting parameters. Simulation of the process stability offers a less costly way of optimising processes prior to production. However, the predictions for the stability of high performance milling processes exhibit great deviation from experimental results. The objective is to analyse and to prevent errors within the simulation methods to make stability simulation a reliable tool in process planning. In order to improve the quality of stability simulation, the interacting Systems “Machine Tool” and “Cutting Process” are analysed individually. Methods for the coupled simulation of both systems are implemented to identify stable working conditions. As a result of this work, a time domain simulation environment for the investigation of high performance milling operations is presented. It considers the complex behaviour of the cutting process as well as the speed dependent machine tool dynamics. Cutting tests have been conducted to verify the benefit of the enhanced simulation method.

New approaches to plasma enhanced sputtering of advanced hard coatings

PVD coatings and cutting tool materials experienced a rapid development in the past due to the increased demands of modern, innovative HPC (High Performance Cutting) production processes. The development of new materials progressed so rapidly that it is partly not known, how these materials can be economically processed with respect to measures of reducing costs and thus increasing productivity. In order to meet the different requirements a range of developments have been brought forward in the area of coating technology. Al 2O 3 was and still is an important component of conventional coatings. Especially the different crystalline modifications synthesized by CVD have gained considerable economic significance. Distinct chemical resistance, higher hot hardness and less interaction with almost all production relevant materials than most hard coatings are the main success factors of Al 2O 3 films. Within the first step the plasma enhanced PVD technology for the deposition of ternary coatings with higher aluminum content was developed. These films continuously generate a protective crystalline alumina layer at elevated temperatures. In addition to RF- and DC-sputter sources, pulsed plasma sources are gaining increased attention in sputter technology. This interest is driven by the significantly enhanced ionization of pulsed plasmas as compared to conventional DC and RF techniques. Using highly ionized plasmas the High Ionization Sputtering (H.I.S.) and the High Ionization Pulsing (H.I.P.) processes have been developed to deposit a novel grade of high performance hard coatings, the supernitrides. The present paper provides a survey of latest approaches to plasma enhanced sputtering and related coating systems, with regard to the demands of high performance applications.

Workpiece and Tool Handling in Metal Cutting Machines

Recently many researchers have focused substantial efforts on understanding the cutting process in mechanics, capability and design. Advances in machine performance with research towards high performance cutting (HPC) and high speed cutting (HSC) have led to improved tool properties and application of advanced materials. Because of that, primary processing time has been successfully reduced, which leads to the need for re-focusing on reduction of secondary processing time. Minimizing the time for workpiece and tool changing, re-positioning, workpiece handling, and tool handling systems shift attention towards improvement of these systems which are currently installed in various metal cutting machine tools. This paper presents an approach for the assessment of the technological effectiveness of workpiece and tool handling systems for metal cutting machine tools, gives an overview of the state of the art of these systems, surveys recent developments and elaborates requirements for future systems.