Cooling approaches and cutting temperatures in cryogenic machining of Ti-6Al-4V

Cryogenic machining is an environmentally safe alternative to conventional emulsion cooling. In this study, liquid nitrogen (LN2) is applied to cutting Ti-6Al-4V, a difficult-to-machine but widely used material in aerospace industry. With the goal of identifying the cooling approach for most effectively and economically using cryogenic machining, this study evaluated cutting temperatures obtained under various cooling conditions. In addition to analyzing cooling approaches reported in previous cryogenic machining literatures (i.e., precooling the workpiece and conductive remote cooling), this paper introduces an innovative and economical dispensing method that directs LN2 through micro jets to the flank, the rake, or both near the cutting edge. The cutting temperatures were theoretically estimated by finite element method and the influence of cutting speed was analyzed. They were experimentally verified using the thermocouple imbedded at the carbide insert. Temperatures in cryogenic machining were compared with conventional dry cutting and emulsion cooling. Findings showed that a small amount of liquid nitrogen applied locally to the cutting edge is superior to emulsion cutting in lowering the cutting temperature. The study found that cooling approaches in order of effectiveness (worst to best) to be: dry cutting, cryogenic tool back cooling, emulsion cooling, precooling the workpiece, cryogenic flank cooling, cryogenic rake cooling, and simultaneous rake and flank cooling.     

On the effects of cutting speed and cooling methodologies in grooving operation of various tempers of β-titanium alloy

High strength and its retention at elevated temperatures render titanium alloys highly difficult to cut. Of commonly used titanium alloys, β-alloys are the ones possessing highest values of strength. Higher productivity in machining demands higher cutting speed and its implementation generates even more heat at primary and secondary shear zones. Poor thermal conductivity of titanium causes concentration of excessive heat near the cutting edge, which in turn, leads to rapid damage of cutting tool. The situation, thus, demands application of an innovative cooling methodology that would cause effective removal of heat in order to make implementation of higher cutting speeds viable. The paper describes an experimental investigation carried out to quantify the effects of high levels of cutting speed and the influence of carbon dioxide snow (CO₂-snow) as an innovative cooling methodologies in machining of three tempers of β-titanium alloy. A comparison was made among various cooling techniques, which consisted of following: conventional flood emulsion; impingement of jet of CO₂-snow at the rake face, the flank face, the rake and flank faces together; and the combination of the CO₂-jet and MQL. The comparative effectiveness of each methodology was evaluated in terms of cutting forces, tool wear, and acoustic emission as an indicator to measure differences in terms of the chip morphology.     

The Effect of the Heat Treatment on the Dust Emission During Machining of an Al-7Si-Mg Cast Alloys

This paper reports on the effect of artificial aging on the machinability of Al-7Si-Mg (A356) cast alloys for the as-received alloy, solution heat-treated (SHT) alloy and then aged SHT alloy at 155, 180, and 220 °C, respectively. The influence of heat treatment on the machinability of the alloys studied was considered using innovative criteria such as dust emission. The effect of various lubrication modes including dry, mist, and wet process, as well as cutting speed and feed rate, was also investigated. The results obtained from the statistically designed experiments indicate that at the same cutting conditions, the A356-T7 heat treatment generates less dust emission level compared to other various heat treatments (there is 32% less airborne swarf produced than with A356-T6). Aging at low temperature was observed to produce the greatest level of the dust emission while the aging at higher temperatures is accompanied by a reduction in the dust emission level. Fracture surface analysis using scanning electron microscope, has shown that dust emission levels were strongly dependent on the nature of the fracture surface of the alloys studied, with different heat treatments. A change in chip formation was also found to be a function of age hardening and dust emission during machining of the tested aluminum alloy. A correlation was established between the cutting speed, the feed rate, and the dust emission, which is useful for determining the conditions required for minimal dust emission.     

Investigation of coated tools’ cutting performance in milling Ti6Al4V and its correlation to the temperature dependent impact resistance of the film

Based on analytical and experimental test methods, an evaluation of coated tools efficiency in milling Ti6Al4V with coated cemented carbide inserts is introduced. The stress-strain curves and the fatigue critical loads of the investigated coating were determined at various temperatures by nanoindentations and impact tests respectively, employing FEM-supported algorithms for results evaluation. The stress and temperature fields in the cutting wedge region were obtained by force measurements and FEM calculations of the milling process at various cutting conditions. A sufficient correlation of the coating’s impact resistance at various temperatures with their cutting performance at corresponding cutting conditions is revealed.     

Development of temperature sensor thin films to monitor turning processes

Increasing demands on the cutting process require a fundamental analysis concerning the design as well as the material selection for cutting insert and its wear protection. Apart from monitoring the wear and the cutting forces, the knowledge of the developed temperatures during cutting process is essential and necessary.In this work, an innovative technology was employed to measure in situ the temperature development during cutting process. The measurement was based on the Seebeck-effect. Coating adhesion was systematically analyzed and optimized by varying the pretreatment conditions. Furthermore, the design of masks was enhanced and finally turning experiments were carried out to scrutinize the efficiency of deposited temperature sensors in cutting tests.     

Influence of cryogenic heat-treatment soaking period and temperature on performance of sintered carbide cutting tools in milling of Inconel 718

Cryogenic heat treatment is an innovative heat treatment applied to improve the mechanical properties of sintered carbide cutting tools. In this study, the effect of cryogenic heat treatment used at different temperatures and soaking periods on the mechanical properties of carbide cutting tools was investigated. Cryogenic heat treatment was applied at two different temperatures, −145 °C and − 196 °C, for 24 and 36 h soaking periods. The microstructure of the cryogenic heat-treated cutting tool was investigated as microhardness and grain size. As a result of microstructure analysis, heat treatment soaking period was found to be more effective than heat treatment temperature. Milling tests of the Inconel 718 superalloy were performed under dry conditions using cryogenic heat-treated cutting tools and non-heat treated tools. The effect of heat treatment on cutting tool performance was studied in terms of the amount of tool wear, cutting force, surface roughness values. According to the results obtained, the cryogenic heat treatment applied to the cutting tools has a positive effect on cutting performance. In addition, in the examinations carried out on worn cutting tools, effective wear mechanisms were found to be oxidation, adhesion and abrasion.     

Development and parametric study of a water-jet assisted underwater laser cutting process

The conventional underwater laser cutting process usually utilizes a high pressure gas jet along with the laser beam to create a dry condition in the cutting zone and eject out the molten material. This causes a lot of gas bubbles and turbulence in water, and produces aerosols and waste gas. This may cause contamination in the surrounding atmosphere, while cutting the radioactive components. In order to minimize this effect, a water-jet assisted underwater laser cutting technique has been developed using a high power fiber laser. A high velocity coaxial water-jet has been employed in place of gas-jet to remove the molten material through the kerf. Some amount of water vapour bubbles is formed at the laser–metal–water interface; however, they tend to condense as they rise up through the surrounding water. AISI 304 stainless steel sheet of maximum 1.5 mm thickness was cut at 1.4 m/min cutting speed with the present setup at 1800 W CW laser power, and the resulting average kerf-width was about 0.75 mm. The heat convection by water jet and the scattering of laser beam by vapour were found to influence significantly the energy efficiency of the cutting process. The effects of various processing parameters on the cutting performance were investigated. The energy efficiency improved at higher cutting speeds. An energy balance model with various loss mechanisms included has been also developed.     

The reliability analysis of a thin-edge blade wear in the glass fiber cutting process

This study shows that the reliability analysis of a thin-edge blade plays an important role in cutting glass fiber and explores the main effect of three cutting factors: the cutting speed, the cutting load, and the cutting volume. The effect of each cutting factor on the thin-edge blade wear, as determined by long glass fiber weight, and exceeding a value of 1%, as specified in the customer's requirements, was investigated. According to the experimental results, the thin-edge blade wear distribution approximated to a Weibull distribution, and the cumulative probability could be determined after nine iterations. This study also finds that there is a large positive correlation among the various thin-edge blade-wear values at different cutting speeds. However, the correlation is negative for the various thin-edge blade-wear values when cutting at load, and when cutting at different cutting volumes. It was observed also that the optimum cutting speed with minimum thin-edge blade wear is 1.9 m/s. The successful deployment of this study will be a significant factor in improving the cutting process and cutting quality.     

Development of a modular dynamometer for triaxial cutting force measurement in turning

Accurate and reliable measurement of cutting forces in turning is essential for tool geometry, tool trajectory and cutting parameters optimization, as well as for tool condition monitoring and machinabilty testing. In this work, an innovative dynamometer for triaxial cutting force measurement in turning, specifically designed to be applied at a milling-turning CNC machine tool endowed with an indexable head, is presented. The device is based on a piezoelectric force ring integrated into a commercial toolshank, and its modular design allows the easy change of the cutting insert without altering sensor preload. The prototype device was assembled and experimentally tested by means of static calibration and dynamic identification, which evidenced good static and dynamic characteristics. Eventually, the sensor was tested in operating conditions by machining a benchmark workpiece.     

Performance of electrical discharge textured cutting tools

Tool face friction adversely affects chip formation and consumes about 25% of the total cutting energy. Friction in cutting can be controlled by introducing a lubricant into the tool-chip interface, the effectiveness of which may be enhanced by surface texturing the tool. This paper details the innovative application of electrical discharge machining for generating an isotropic texture on the tool rake face, with a view to facilitating lubricant penetration and retention. A significant reduction in feed and cutting forces that ensues from said texturing is demonstrated, followed by a presentation of the features and application areas of the technology.     

Prediction of the cutting forces for chamfered main cutting edge tools

A new cutting model of various tool geometries for tools with a chamfered main cutting edge has been built. Theoretical values of cutting forces were calculated and compared with the experimental results; the forces predicted by this model were consistent with the experimental values. Special tool holders were designed and manufactured to obtain various tool geometries. Cutting experiments were conducted on a carbon steel to examine the mechanism of secondary chip formation; the relationship between the shapes of secondary chips and tool geometries was observed.     

Microstructuring of functional surfaces by means of cutting processes

Microstructuring of mechanically and thermally highly stressed surfaces offers an innovative alternative for adjusting tribological properties and thus reducing friction losses and wear. At the Institute of Production Engineering and Machine Tools (IFW) functional surfaces are structured via cutting. This paper introduces to the basic principles of manufacturing microstructures in ductile materials foccussing cutting tool- and process-dimensioning. Scratch tests are carried out at planar surfaces to describe the basic chacacteristics when producing structures in micron range. Due to the small structure depths, size effects have to be considered. On this account, influences and interrelations of cutting edge microgeometry, material properties, as well as cutting parameters are investigated. In order to avoid further finishing operations, sharp structures with tolerable burr formation have to be achieved. The investigations presented in this paper are supported by the German Research Foundation (DFG) within the project “Microstructuring of Thermomechanically High Stressed Surfaces”.     

Development of a reliable grinding procedure for ceramic medical instruments

Surgical instruments have to meet strict requirements on functionality and stable performance. The functional properties of scalpels, for example, are mainly dependent on a precise cutting edge geometry and high blade sharpness. To achieve a reliable production of scalpels, it is necessary to establish a holistic understanding of the process chain as well as the interactions of all machining processes. An innovative zirconium oxide offers high toughness and high wear resistance, leading to its use in ophthalmic scalpels. A cooperative project has been conducted by two universities and two industrial partners, funded by the German Federal Ministry of Economics and Technology (BMWi).The project focuses particularly on the grinding process as a controlling factor for the scalpel’s functionality and sharpness. The complex process chain with various interactions of kinematics, vibrations and tool micro-topography was developed for high reliability and efficiency. The performance of in-machine dressing of diamond wheels with diamond form rollers was decisive for scalpel quality.     

Development of freeform grinding methods for complex drill flank surfaces and cutting edge contours

This paper details the development of an innovative freeform grinding method that enables the generation of complex drill flank surfaces and cutting edge contours that are non-quadratic model based. This method allows a direct and independent design of drill cutting angle distributions—normal rake angle (γ_n) and relief angle (α_f). Mathematical formulations were first developed for γ_n and α_f in terms of drill geometric parameters such as helix angle, flute contour, and cutting edge contour. The developed freeform grinding methods enhance the flexibility of the grinding process by enabling the production of drills with convex and concave flank surfaces and complex cutting edge contours with standard wheel sets, eliminating the need to manufacture specially designed form grinding wheels.     

Dry machining of Inconel 718, workpiece surface integrity

In the machining of Inconel 718, nickel based heat resistant superalloy and classified difficult-to-cut material, the consumption of cooling lubricant is very important. To reduce the costs of production and to make the processes environmentally safe, the goal is to move toward dry cutting by eliminating cutting fluids. This goal can be achieved by using coated carbide tool and by increasing cutting speed.The present paper firstly reviews the main works on surface integrity and especially residual stresses when machining Inconel 718 superalloy. It focuses then on the effect of dry machining on surface integrity. Wet and dry turning tests were performed at various cutting speeds, with semi-finishing conditions (0.5 mm depth of cut and 0.1 mm/rev feed rate) and using a coated carbide tool. For each cutting test, cutting force was measured, machined surface was observed, and residual stress profiles were determined. An optimal cutting speed of 60 m/min was determined, and additional measurements and observations were performed. Microhardness increment and the microstructure alteration beneath the machined surface were analysed. It is demonstrated that dry machining with a coated carbide tool leads to potentially acceptable surface quality with residual stresses and microhardness values in the machining affected zone of the same order than those obtained in wet conditions when using the optimised cutting speed value; in addition, no severe microstructure alteration was depicted.     

Increasing tool life by adjusting the milling cutting conditions according to PVD films’ properties

The coated tools cutting performance in up and down milling depends significantly on the PVD film material properties. The related wear mechanisms at various cutting speeds can be sufficiently explained considering the developed tool loads and the non-linear coating impact resistance versus temperature. Various PVD coated cemented carbide inserts were tested at different cutting conditions. The corresponding cutting loads and temperatures were determined by FEM simulations and the films’ impact resistance by impact tests. A correlation between the impact resistance and the cutting performance at corresponding temperatures contributed to the optimum adjustment of the cutting parameters to the film properties.     

Properties and performances of innovative coated tools for turning inconel

Three innovative nanostructured coatings have been developed to be applied on cutting tools for continuous cutting of nickel-based super-alloys, in Minimum Quantity Lubrication (MQL) or dry conditions.The coatings, TiN+AlTiN, TiN+AlTiN+MoS₂ and CrN+CrN:C+C, were applied by PVD techniques on WC-Co inserts, developing nanostructured layers, characterised by superior performances, as confirmed both by laboratory tests and machining experiments.Coatings surface qualification included SEM observations with EDS analysis, ball erosion test, nanoindentation and scratch tests, classic tribological evaluation by ball-on-disc set-up, surface texture analysis.Results were analysed in light of the outcome of machining experiments performed mainly in dry and MQL turning of Inconel 718. Ball-on-disc and scratch tests, as well as machining experiments, agreed in classifying the coatings in the following decreasing performance order: TiN+AlTiN+MoS₂, followed by TiN+AlTiN, and by CrN+CrN:C+C.     

Manufacturing of cylindrical gears by generating cutting processes: A critical synthesis of analysis methods

The eternal goal achieving optimum gear manufacturing results in a quick and flexible way can be obtained by efficient machine tools and thorough processes know how. Gear manufacturing is associated with complicated generating kinematics, chip formation and tool wear mechanisms. To capture quantitatively the tool wear progress and the cutting loads, empirical, analytical, numerical as well as FEM-based methods describing the chip geometry and predicting the tool life and cutting forces have been developed. The application of innovative tool materials and coatings, optimized tool geometries and appropriate conduct of reconditioning procedures contribute to the significant reducing of the manufacturing cost.     

滑动齿套拨叉槽的立方氮化硼刀具切削工艺试验研究

为了确定硬态切削代替磨削加工滑动齿套拨叉槽时各参数对其表面质量的影响,采用立方氮化硼刀具对20CrMnTi棒料进行切削,利用正交试验法对加工表面粗糙度进行了直观分析和方差分析,得出切削速度、进给量、背吃刀量对拨叉槽表面粗糙度的影响规律,并给出拨叉槽加工时合理的切削用量;同时也对加工过程中刀具的磨损进行分析,为滑动齿套拨叉槽的立方氮化硼切削工艺参数的选取提供了依据。     

Investigation of the effect of rake angle and approaching angle on main cutting force and tool tip temperature

This paper deals with the comparison of measured and calculated results of cutting force components and temperature variation generated on the tool tip in turning for different cutting parameters and different tools having various tool geometries while machining AISI 1040 steel hardened at HRc 40. The geometric variables (approaching angle and rake angle) of the tool were changed using selected cutting parameters; thus, the cutting force components and temperature variations on tool face (in secondary shear zone) were determined. The selected cutting variables and the tools in different geometries were tested practically under workshop conditions. In this way, the essential information about the validity of selected values was obtained. During the tests, the depth of cut and cutting speed were kept constant and each test was conducted with a sharp uncoated tool insert. For making a comparison, the main cutting force/tangential force component for different cutting parameters and tool geometries were calculated by Kienzle approach and the temperature values were calculated based on orthogonal cutting mechanism. Finally, the effects of cutting parameters and tool geometry on cutting forces and tool tip temperature were analysed. The average deviation between measured and calculated force results were found as 0.37%. The cutting force signals and temperature values provided extensive data to analyse the orthogonal cutting process.