Thermal Tool Load Research Articles

Internal coolant supply in circular sawing

The internal coolant supply (ICS) allows a cooling lubricant to be used efficiently in terms of quantity and application. Especially in processes in which access to the cutting zone is impeded by the workpiece and the tool, an ICS can deliver cooling lubricant to the cutting zone. While an ICS has already been successfully implemented in numerous machining processes, there is a lack of fundamental research regarding its use in circular sawing. In this paper, an analysis of an ICS in circular sawing is presented. It showed that an ICS with a significantly reduced amount of coolant improved the thermal tool load, the chip form as well as the workpiece surface quality.

Influence of dressing strategy on tool wear and performance behavior in grinding of forming tools with toric grinding pins

The performance of grinding tools in grinding processes and the resulting surface and subsurface properties depend on various factors. The condition of the grinding tool after dressing is one of these factors. However, the influence of the dressing process on the condition of the grinding tool depends on the selected process parameters and is difficult to predict. Therefore, this paper presents an approach to describe the influence of the dressing process on tool wear of toric grinding pins and the resulting subsurface modification. For this purpose, toric grinding pins with a vitrified bond were dressed with two different strategies and the wear and operational behavior were investigated when grinding AISI M3:2 tool steel with two different grinding strategies. In general, the investigations have shown that the dressing process influences the performance and wear behavior differently depending on the grinding strategy used. The degree of clogging is influenced by the geometric contact sizes. In the case of small engagement cross sections with simultaneously large contact lengths the thermal tool load is distributed over a small annular area of the tool and favors clogging. Crushing and additional transverse loading of the grains result in an almost clog-free tool surface. This also leads to a lower G-ratio. Crushing leads to an intensified decrease of the torus radii. The influence of the dressing strategy can also be observed in the induced residual stresses. Toric grinding pins dressed by crushing induce lower compressive residual stresses into the workpiece, which can be attributed to the self-sharpening effect. This effect reduces the mechanical and thermomechanical load of the workpiece during machining.

Numerical and experimental analysis of thermal and mechanical tool load when turning AISI 52100 with ground cutting edge microgeometries

Tools made of polycrystalline cubic boron nitride (PcBN) are usually prepared with a rake face chamfer to increase the performance in hard turning. This chamfer is produced by a tool grinding process. The preparation of the cutting edge itself considering the process and material properties offers further potential for increasing tool performance. In this paper, the rounding of the cutting edge is produced by the already established and highly productive tool grinding process instead of using conventionally processes such as brushing or drag finishing. Therefore, the rounding is approximated by multiple ground chamfers. The influence of the cutting edge microgeometry on the thermomechanical load is investigated by finite element method. By enlarging the microgeometry, the mechanical stress on the tool is significantly reduced. However, an increase in the size of the cutting edge rounding is also linked to an increase in the thermal tool load.

Performance increase by process parameter variation during turning of AISI 4140

Usually, constant process parameters are used for turning. These process parameters result in a thermomechanical load of the tool, which leads to a specific wear pattern. Varying the process parameters along the toolpath, e.g. linear or sinusoidal, can extend tool life by distributing wear over a wider area and reducing the thermal tool load. In this paper, a method for designing process parameter variations during turning is presented. It is shown that tool wear can be reduced using process parameter variation. This reduction in wear is due to a decrease in thermal tool load. In addition, a method for designing processes with modulated process parameters is being developed.

Correlation between Coating Properties and Thermal Load of Craln-Coated Cutting Tools during Machining of AISI4140

In this study a novel inverse hybrid experimental-simulative approach to the determination of the thermal tool load as a function of the coating properties during orthogonal turning of AISI4140 with Cr1-xAlxN-coated cemented carbide tools is presented. The approach consists of an experimental determination of the internal tool temperatures by means of fiber-optic pyrometry as input for an inverse FEM-based simulation algorithm to calculate the surface temperatures. Based on a parameter study, the coating thicknesssand the thermal conductivity of the coating λcwere identified as the main factors influencing the thermal tool load. The combined influence of these properties was described via the thermal resistanceR. It could be shown that the average thermal load on the tool surface increases with increasing thermal resistanceR.

Milling of Ti6Al4V with carbon dioxide as carrier medium for minimum quantity lubrication with different oils

Machining of difficult-to-cut materials such as nickel-based or titanium alloys lead to high static, dynamic and thermal tool loads. A crucial role is given to the used cooling lubricant. Here, the cryogenic cooling with liquid nitrogen or carbon dioxide has been investigated in recent years as a possible alternative to conventional flood cooling.The following article deals with the further development of CO2-based cryogenic cooling combined with a minimum quantity lubrication (MQL) injected directly into the liquid CO2 phase. The focus of the investigation is the experimental selection of MQL oils for this application. For this purpose, the potential of various base oils and additivated lubricants for the CO2 assisted milling of Ti6Al4V has been investigated. The suitability assessment of the lubricants has been based on the optical measurement of wear progress along the cutting edge, recording the effective cutting forces and surface roughness. Furthermore, a mathematical compensation method is presented for the compensation of the measured value drift caused by low temperatures. The results show that the potential of cryogenic MQL is largely determined by the base oil being used. It has also been demonstrated that the use of bio-based ester oils for the present process is an alternative to mineral oil-based lubricants.

Experimentally validated calculation of the cutting edge temperature during dry milling of Ti6Al4V

Abstract In service, milling tools have to cope with severe levels of thermal and mechanical load. Especially temperature influences the damage behavior of a tool’s cutting edge by influencing material properties and thermally induced stresses. It is therefore of relevance to gain quantitative information on the thermal tool load situation. Information on temperatures in milling tools is not readily available today. Therefore, extensive experimental effort was necessary to determine temperatures in-situ during milling in the axial center of a rotating end mill and in a Ti6Al4V workpiece near the milled surface. The used end mill was a WC-Co hard metal tool protected by a TiAlN coating. Since the damage-relevant cutting edge temperature is not directly accessible by experimental means, a simulation was employed. The transient temperature field in the tool was calculated by an iterative and synergetic use of two-dimensional finite element cutting models, three-dimensional finite element end mill models and two-dimensional workpiece models. The simulation allows for the description of the time-dependent temperature distribution from the chip formation site at the cutting edge to the axial tool center and into the workpiece, where thermocouples were placed in experiments. Validation of the calculated cutting edge temperatures was performed for 5000 individual consecutive cuts via comparison of results for tool core temperature in experiment and simulation. The model yields a very pronounced concentration of the thermal load maximum of T>650 °C near the cutting edges in a very small volume of only 1 ppm of the tool’s volume. In particular, the model’s spatial discretization is able to resolve the gradient of temperature in the hard coating towards the coating/substrate interface, showing temperature shielding effects of the hard coating.

Application of Carbon Dioxide Snow in Machining of CGI using an Additively Manufactured Turning Tool

The application of conventional cooling lubricants for the tribological conditioning of machining processes involves high additional costs and health risks. The application of a cryogenic carbon dioxide (CO2) snow cooling strategy is an economical and environmentally sound alternative for oily cooling emulsions since it has a high cooling effect as well as a residue-free sublimation. This article introduces a laser additive manufactured tool holder with an integrated dual nozzle which enables CO2-snow jet application. Initially this work focuses on the characterization and the selection of a suitable nozzle geometry. The modular tool body features an adapted channel structure for process-reliable and targeted CO2-snow cooling for turning processes. This enables the simultaneous cooling of the rake and flank face with CO2-snow, as well as the application of cryogenic multi-component cooling of the rake face. In the context of this study, the focus lies on the technological evaluation of three different supply strategies during the continuous turning of compacted graphite iron CGI-450 at increased cutting speed. It was established that an efficient rake face cooling is indispensable to achieve a low thermal tool load, and thus lower crater wear behavior. Therefore, this study contributes to an improvement in cryogenic machining processes regarding the design of additively manufactured tool bodies for process-reliable CO2-snow cooling, as well as for the selection of supply strategies to minimize the thermomechanical tool load.

Model of tool loads in dry diamond wire grinding of steel

Dry diamond wire grinding of steel is associated with high tool wear restricting productivity as well as tool life. Therefore, the process has to be designed properly to ensure an economic cut. This paper introduces a process model for the dry diamond wire grinding of steel based on analytical and experimental results. The model describes fundamental influences of input parameters on mechanical and thermal tool loads by means of process kinematics and undeformed chip parameters. It is shown that tool temperatures are directly related to tangential grinding forces. The model is verified by experimental results showing high correlation of calculated and measured values.

Suitability of the full body ceramic end milling tools for high speed machining of nickel based alloy Inconel 718

Sustainability of machining processes is becoming increasingly important today. Therefore, the use of conventional machining with oil based cooling lubrication fluids (oil CLF) is becoming insufficient. On the other hand, dry machining, as the cleanest and most environmentally friendly machining process, lacks in cooling and lubrication. This can shorten tool life and decrease productivity, especially when machining difficult-to-cut materials. Machining these materials is often affected via high mechanical and thermal tool loads. Workpiece material characteristics like low thermal conductivity, strain hardening, etc. are causing high temperatures in the cutting zone and consequently high wear tendency of carbide tools, even at relatively low cutting speeds. Therefore, to increase productivity, as an alternative to carbide tools, full body ceramic milling tools are proposed. Ceramic, as a cutting material, is stable even at high temperatures, which are present when machining difficult-to-cut materials, such as nickel based alloy Inconel 718. Hardness retaining (high compressive strength), good wear resistance and chemical stability at high temperatures are other pros of ceramic tools.In this paper, high speed milling process using full body ceramic end milling tools is analyzed in parallel to carbide tools. Tool life of ceramic end mills is compared with tool life of more widely used carbide end mills when milling difficult-to-cut nickel based alloy Inconel 718. The results show that ceramic milling tools are offering an increase in productivity, however, the overall efficiency, in comparisons to carbide tools, is still questionable.

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

In the field of machining difficult-to-cut materials like titanium or nickel-based alloys, the application of high-pressure coolant supply may result in a significant increase in 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 with variation of the coolant flow rate for a given coolant pressure 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 maximise the positive effect of high-pressure coolant supply strategy on productivity and process stability, specially designed coolant jet guidance geometry on the rake face was also investigated and compared to conventional tools in turning aerospace materials TiAl6V4 and Inconel 718.

Modeling of process forces with respect to technology parameters and tool wear in milling Ti6Al4V

The usage and importance of titanium materials is increasing worldwide. Titanium is particularly suitable for use in turbines and lightweight construction due to its high heat resistance and low density. However, its low thermal conductivity results in machining problems and short tool life due to the associated high mechanical and thermal tool loads. Knowledge about the mechanical tool load during the milling process is of vital importance to process design and modeling. This paper presents multivariate regression method to model the process forces involved in the titanium milling process with respect to various technology parameters. In particular, the resulting tool wear and its relationships with these process forces is analyzed.

A Mechanical Model of Diamond Wire Sawing of Steel Structures

Wire sawing with diamond tools is a highly flexible cut-off grinding process with regard to machinable component structure and composition. Nowadays, it is deployed in many fields of application e.g. the dismantling of nuclear or industrial plants. Here, steel has to be cut which results in lower productivity and tool life compared to the conventional processing of natural stone. To ensure a properly designed process the mechanical and thermal tool loads have to be known in advance. This paper presents an analytical model that predicts the mechanical load as a function of the process parameters.

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

High performance cutting of gamma titanium aluminides: Influence of lubricoolant strategy on tool wear and surface integrity

Heat resistant gamma titanium aluminides are intermetallic alloys planned to be widely used in high-performance aircraft engines within the next few years. This application field is ascribed to the exceptional material properties, especially the low density and a unique strength-to-weight ratio for titanium-based alloys, good oxidation behaviour and thermal stability, limited ductility and fracture toughness below brittle-to-ductile transition, and good creep resistance.The demanding machinability of gamma titanium aluminides can be traced back to these desirable material properties. Consequently, cutting process adaptation is essential to obtain components suitable to satisfy strong regulations regarding surface integrity, without neglecting an economical production. Previous research activities confirmed that thermal material softening during cutting due to the high speed machining is a key to reach high quality surfaces, but tool wear was identified as the limiting factor.The relatively high cutting speed results in high temperatures in the shear zone and the low thermal conductivity of the γ-TiAl workpiece material leads to an extreme thermal tool load. Furthermore, in combination with the formation of saw-tooth chips and the discontinuous flow of the chip along the rake face, adhesive wear is caused.The influence of conventional flood cooling and high pressure lubricoolant supply (wet conditions), cryogenic cooling with liquid nitrogen, and minimum quantity lubrication (MQL) were investigated in longitudinal external turning operations. Tool wear, cutting forces, chip morphology and surface roughness were evaluated. Surface integrity was analysed in terms of machined surface defects and sub-surface alterations.The investigations indicate that cryogenic cooling is the most promising lubrication strategy, meaning that the thermodynamical impact of the expanding liquid nitrogen applied directly close to the cutting zone successfully counteract the huge thermal load on the tool cutting edges, providing potentially enormous benefits in terms of tool wear reduction and consequent surface quality improvement.

Influence of a High-Pressure Lubricoolant Supply on Thermo-Mechanical Tool Load and Tool Wear Behaviour in the Turning of Aerospace Materials

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. The present paper investigates the effect of high-pressure lubricoolant jets, directed into the tool—chip interface, in a longitudinal turning process with cemented carbide tools. For this type of lubricoolant supply the reduction of the contact length between tool and chip is an important detail. In turning of Inconel 718 and Ti6Al4V, the cutting tool temperature, tool wear, and resulting chip forms as well as the ratio of cutting forces and tool—chip contact area were analysed as a function of the lubricoolant supply pressure and flowrate (up to 300 bar, 55 l/min). To study the effect of the high-pressure lubricoolant supply, reference tests were carried out using conventional flood cooling. The results suggest that the tool temperature can be decreased by almost 25 per cent by the use of a high-pressure lubricoolant supply for both machined workpiece materials. However, due to the different tool wear mechanisms of the presented materials and the change in the specific load on the cutting edge during machining, the resulting tool wear was influenced differently. In the best case, tool wear could be reduced in an order of magnitude of 50 per cent, while in other cases tool wear even increased significantly due to the use of a high-pressure lubricoolant supply.

Analysis of the High Performance Drilling Process: Influence of Shape and Profile of the Cutting Edge of Twist Drills

The aims of the investigations presented in this paper were to measure the tool load under conditions of high performance drilling and to analyze if changes of the tool edge shape as well as the edge profile significantly influence the edge stresses. The described methods to analyze the influences of edge shape modifications will contribute to the optimization of drilling tools. Based on a specific cutting edge shape of a drilling tool, systematic changes to the tool’s chamfer and the transition from the chisel edge to the cutting edge were made. Forces and temperatures on the cutting edge were measured as well as the heat flow into the chips and the workpiece. Using a quick-stop device, chip roots of the different drill tools under conditions of high performance machining were made in order to analyze the chip formation. The contact between chip and rake face could be made visible by a so called contact area analysis. It could be shown that the modification of the transition from the chisel to the cutting edge influences the orientation of the forces on the drill. Machining with a rounded cutting edge shape compared to a chamfered edge reduces the mechanical and thermal tool load. This is confirmed by the fact that the deformation zone in front of the cutting edge is smaller as shown by the crosssections of the chip roots. The presented experimental methods show the possibility of determining influences of modified cutting edge shapes and to adapt the drill to the needs of the high performance drilling.