Chip Formation Process Research Articles

On the Physics of Machining Titanium Alloys: Interactions between Cutting Parameters, Microstructure and Tool Wear

The current work deals with the analysis of mechanisms involved during the machining process of titanium alloys. Two different materials were chosen for the study: Ti-6Al-4V and Ti-55531. The objective was to understand the effect of all cutting parameters on the tool wear behavior and stability of the cutting process. The investigations were focused on the mechanisms of the chip formation process and their interaction with tool wear. At the microstructure scale, the analysis confirms the intense deformation of the machined surface and shows a texture modification. As the cutting speed increases, cutting forces and temperature show different progressions depending on the considered microstructure (Ti-6Al-4V or Ti-55531 alloy). Results show for both materials that the wear process is facilitated by the high cutting temperature and the generation of high stresses. The analysis at the chip-tool interface of friction and contact nature (sliding or sticking contact) shows that machining Ti55531 often exhibits an abrasion wear process on the tool surface, while the adhesion and diffusion modes followed by the coating delamination process are the main wear modes when machining the usual Ti-6Al-4V alloy.

A novel method for chip formation analyses in deep hole drilling with small diameters

Recent trends of downsizing and miniaturization of components, e.g. in the automotive industry for the manufacturing of fuel injectors or in the medical industry for the production of bone screws or surgical instruments, increase the importance of mechanical deep hole drilling with small diameters. Unfortunately, there are still some open challenges regarding this process. In addition to the unfavorable ratio of the cutting edge rounding to the achievable feed rates and undeformed chip thicknesses which results in significant mechanical tool loads, the control of the chip formation and the removal constitutes a major difficulty. The slender tool dimensions, especially the small cross sections of the chip flutes, necessitate a favorable chip formation to achieve the required process safety and productivity. Therefore, analyses of the chip formation, when machining difficult-to-cut materials provide the means for an effective process design. This analysis, however, is particularly difficult due to the closed operating zone. Quick-stop devices used for the chip formation analyses so far are limited in the tool diameter respectively the revolution speed. Furthermore the informative value is limited, because a quick-stop test takes a significant time to stop and thus the instantaneous cutting conditions during the tool retraction are altered. To overcome these restrictions, a new method for the analysis of the chip formation in small diameter deep hole drilling is presented in this paper. It is based on the utilization of a high-speed camera and tailored material samples. The experimental set-up and the results of first analyses conducted under minimum quantity lubrication are presented. The chip formation process is analyzed for the single-lip gun drilling of the nickel-based alloy Inconel718 and the bainitic steel 20MnCrMo7.

Investigation of Chip Morphology in High-Speed Milling of Nickel-Based Superalloy GH706

This paper analyzed the serrated chip formation process and mechanism in high-speed milling of nickel-based superalloy GH706. Firstly, analyzed two theories of serrated chip formation: cyclical fracture theory and adiabatic shear theory. Secondly, used the simulation of chip formation in high-speed milling of GH706 process, and concluded that the two major theories have achieved dialectical unity when machining for such difficult machining materials. Finally experiments for serrated chip, when cutting speed exceeded 200/min, serrated chips became more obvious. Research has shown that for nickel-based superalloy, adiabatic shear instability of the unstable thermoplastic in the first deformation zoon become the leader of formation of serrated chip, followed as the speed increases, fracture aggravate the degree of serrated chip.

Chip Formation in High-Speed Milling of Titanium Alloy with PCD Tools

This paper presents a detailed analysis of chip morphology through an experimental study of high-speed milling of Ti-6Al-4V alloy with PCD tools. Milling tests were conducted for cutting speed range from 125 m/min to 2000 m/min with water-soluble cutting fluid. The collected chips were firstly examined with a digital cameras and the free surface of the chips was analyzed by a scanning electron microscope (SEM). Geographical parameters of chip morphologies were described in saw-tooth/lamella frequency on the free surface and chip width. Experimental results show that the variation of chips in high-speed end milling of Ti-6Al-4V alloy is as follows, long and straight-shaped → spiral-shaped → curly-shaped → irregular-shaped. The free surface of chips exhibits saw-tooth lamella structures. The lamella becomes clearer and more obvious at higher cutting speeds. Within the same measurement distance, there is a sharp decrease in the lamella number within same measuring range. This should be attributed to the enhancement of the thermal mechanical coupled field applied to the chip formation processes.

Method of immediately cutting process stoppage

The paper dealt with method of immediately cutting process stoppage, process of chip formation and the non-linear finite element analysis. To be able to follow the process of chip formation and machined surface during machining, it is necessary to stop this process immediately, if it is possible. The paper provides results of non-linear numerical experiment for presented method. The state of plastic deformation in machined material and in front of the tool cutting edge enables to follow the intensity of deformation, friction process between the tool, chip and workpiece, sources of heat in the machining zone. Knowing these processes enables to select optimal tool geometry, cutting conditions, mainly cutting speed, cutting environment, tool material so that cutting process could run with minimal energy consumption and required quality of machined surface could be reached. To understand the process of chip formation is important for the theory and practice of machining of materials.

An explicit finite element model to study the influence of rake angle and friction during orthogonal metal cutting

A fundamental understanding of the tribology aspects of machining processes is essential for increasing the dimensional accuracy and surface integrity of finished products. To this end, the present investigation simulates an orthogonal metal cutting using an explicit finite element code, LS-DYNA. In the simulations, a rigid cutting tool of variable rake angle was moved at different velocities against an aluminum workpiece. A damage material model was utilized for the workpiece to capture the chip separation behavior and the simultaneous breakage of the chip into multiple fragments. The friction factor at the cutting tool–workpiece interface was varied through a contact model to predict cutting forces and dynamic chip formation. Overall, the results showed that the explicit finite element is a powerful tool for simulating metal cutting and discontinuous chip formation. The separation of the chip from the workpiece was accurately predicted. Numerical results found that rake angle and friction factor have a significantly influence on the discontinuous chip formation process, chip morphology, chip size, and cutting forces when compared to the cutting velocity during metal cutting. The model was validated against the experimental and numerical results obtained in the literature, and a good agreement with the current numerical results was found.

Research on Chip Formation Mechanism in Mold Processing of Large Diameter Fresnel Lens

This paper describes the analysis of the chip formation mechanism in mold machining process of large diameter Fresnel lens based on the ABAQUS finite element simulation software and modal test methods. Combined with the material constitutive relation and material failure criteria etc, a two-dimensional orthogonal cutting model was established and the chip derived from the simulation was compared with the chip from modal test, with a consequent verification of the feasibility of simulation chip model. The simulation contributes to an investigation into the effects of the cutting speed on chip formation process. The results show that: the material strength and plastic brittle have significant impact on chip morphology in the H62 brass mold processing, and material strength will improve with the increase of strain rate, the evolution process of the chip of material plastic reduction can be divided into: ribbon cuttings, serrated chips, cell chips.

Improvement of surface conditions of 36 Cr Ni Mo 6 steel by ball burnishing process

Ball burnishing, a mechanical surface treatment, is becoming more popular as a finishing process. As results ball burnishing is noticed as a very simple way of surface mirror finishing and surface work-hardening. Applying the optimal input parameters, a pre-machined surface roughness Ra about of 3.01 μm can be finished to approximately 0.30 μm, whereas an initial hardness HRA about 66.35 can be increased to 71.33. A metallographic observation and some measurement of micro-hardness show that the depth of penetration strengthened by plastic surface deformation (PSD) reaches 100 μm. Results analysis show that burnishing force, burnishing ball radius and number of ball burnishing tool passes have the most significant effects on both surface responses (Ra and HRA). For the generating of high surface qualities and strengthening superficial layers, an alternative to chip-forming process and heat treatments can be given by ball PSD process.

Research on chip formation parameters of aluminum alloy 6061-T6 based on high-speed orthogonal cutting model

Chip formation, an important aspect of the high-speed cutting (HSC) mechanism, is generally accepted as the result of shear deformation in the shear zone and tool-chip friction. In order to accurately study chip formation process in HSC, a theoretical model for the high-speed orthogonal cutting of aluminum alloy 6061-T6 was built, which can be used to calculate the important parameters of chip formation, such as shear angle, friction angle, length of shear plane, tool-chip contact length, and width of the first shear zone. A series of orthogonal cutting experiments, with the YG6 carbide tool and on a wide range of cutting speed (100–1,900 m/min) and feed (0.06–0.15 mm/r), were performed in order to obtain the parameters required in the model, including the cutting forces, the chip thickness, and the shear slip distance. Seven kinds of chip formation parameters were obtained with different cutting parameters in the experiment, and the built theoretical model can well explain the formation process and the morphology characteristics of these chips, which proves that the combined method of theoretical model and orthogonal cutting experiment is an effective and easy approach to obtain the parameters of chip formation in HSC, avoiding the cutting speed limitation and the safety risk in quick-stop test. Within the range of parameters set in the experiments, the chip mainly appears to be continuous chip, curling chip, or discontinuous chip. And the chip thickness, friction angle, length of shear plane, and width of the first shear zone decrease with the increase of the cutting speed; meanwhile, the shear slide distance and shear angle increase.

Research on the Chip Formation Mechanism during the high-speed milling of hardened steel

An easy-to-produce sawtooth chip is the main feature of the high-speed milling process for hardened steel. This chip may lead to a high-frequency periodic fluctuation of the cutting force and accelerate the tool׳s wear rate. This study investigated the process of chip formation and the change in chip morphology during the high-speed milling of hardened steel (51, 62HRC). The formation condition of continuous and sawtooth chips and various characteristics of the sawtooth chip, such as cutting speed, feed rate, axial depth of cut, and others, were also studied. The results showed that the chip of materials with different hardnesses could be controlled as a continuous chip through the optimisation of a combination of cutting speed, feed per tooth, and cutting depth. If the feed per tooth and axial depth of the cut were too large within the range of proper cutting speeds generated by a continuous chip, the chip morphology turned into a sawtooth. Increasing the cutting speed during the cutting process not only strengthened the material׳s hardness but also increased the local temperature of the shear band rapidly and aggravated the material׳s heat softness. When these parameters became balanced, the shear deformation became highly localised in the shear band and resulted in adiabatic shear. A quantitative evaluation of the sawtooth-shaped chip׳s deformation degree was performed using the cross-sectional area and angle of the sawtooth chip. By establishing a geometric model of the sawtooth chip formation during the high-speed milling of hardened steel, that was used to predict the shear strain and strain rate during chip formation, the range of shear angles generating a sawtooth chip was calculated to be 40–60°.

Chip morphology and surface roughness in high-speed milling of nickel-based superalloy Inconel 718

Chip formation process can lead to the fluctuation of cutting force and result in cutting vibration during high-speed milling, which makes serious impact on surface quality. In this paper, chip formation process is analysed and experiments are carried out to investigate the evolution of chip morphology and its effect on surface roughness in high-speed milling of nickel-based superalloy. It is found that, as the cutting speed increases from 25 to 200 m/min, the value of chip burrs firstly decreases and then increases. Chip morphology is gradually transformed from ribbon to serration. At the critical cutting speed of 75 m/min, both pitch and height of chip burrs reach the lowest value and serrated chips begin to appear. The variation tendency of surface roughness values agrees well with the evolution of chip morphology. The experimental results have a great significance for improving the surface quality in high-speed milling of nickel-based superalloy.

Analysis of the Surface Integrity in Ultra-precision Cutting of Cp-titanium by Investigating the Chip Formation

The microstructuring of component surfaces is a method to optimize the adhesion of cells in biological systems. Ultra-precision cutting represents a technology to manufacture microstructured surfaces. When compared to conventional cutting processes additional effects influencing the material surface have to be considered, such as the size effect between the cutting edge of the tool and the depth of cut or the inhomogeneous structure with anisotropic properties. The aim of the presented research is to investigate the surface integrity in ultra-precision cutting of cp-titanium in the micro- and nanoscale. Quick-stop tests were conducted in orthogonal cutting using an ultra-precision turning lathe in order to understand the chip formation process. These investigations of the chip formation process allow to understand the resulting surface integrity. The analysis of the surface integrity concentrated on the burr formation and the surface topography.

Chip Root Analysis after Machining Carbon Fiber Reinforced Plastics (CFRP) at Different Fiber Orientations

Machining carbon fiber reinforced plastics (CFRP) is currently being heavily investigated. The main drivers come from the aviation and automotive industry. Current drilling and milling tool geometries exhibit immense wear resulting in the damage of the work piece. Detailed understanding of chip formation mechanisms when machining CFRP is paramount and enables the optimization of tool geometries in terms of tool lifetime and work piece quality. Current knowledge about CFRP chip formation mechanisms is insufficient. Chip root experiments help understanding chip formation along the cutting edge and are well understood for the machining of metals [1,2]. Insufficient research has been performed in the field of chip formation processes when machining CFRP, especially on chip roots [3–5]. Unlike when machining metals, when machining CFRP micro-particles are generated as opposed to macro chips [4]. This fact makes it difficult to observe the CFRP chipping process, compared to metal machining. Furthermore CFRP is an anisotropic and inhomogeneous material causing machining properties to be highly dependent on the fiber orientation. This paper introduces an extensive study on CFRP chip roots for five different unidirectional fiber orientations using an orthogonal cutting test rig. Intentionally weakened work pieces have been produced. These work pieces enable truly representative cutting conditions due to a continuous cut and constant but wide range adaptable cutting speeds. Analyses of the chip roots are based on light microscopy (i), scanning electron microscopy (SEM) (ii) and micrographs (iii). In combination with previous studies in-house it qualifies to understand the wear mechanisms when machining CFRP. As a result fracture orientations, adhering abrasion particles, chip formation and chip movement allow for the understanding of CFRP chip formation.

High-Speed Photographic Study of Chip Formation during End Milling of GFRP Composites

The chip forming process during end milling of glass fibre reinforced composites has been investigated in this study. The qualitative results from a high speed video camera has showed that discontinuous and fracturing of chips has been created due to the heterogeneity and insufficient ductility of the composite materials. The high-speed photography footage has also disclosed that a layer of delaminated chip can be formed as the tool cutting edge fractured the workpiece along the fibre orientation. The fracture of chips into smaller segments accelerated as the cutting speed increases. Likewise, shorter fragment of chips were created as the tool cut at different fibre orientation or angle. This makes it difficult to denote any chip formation processes during the end milling experiments.

Finite Element Modeling of Cutting Force and Chip Formation During Thermally Assisted Machining of Ti6Al4V Alloy

The improvement in machinability during thermally assisted turning of the Ti-6Al-4V alloy has been investigated using finite element modeling. A 2D thermally assisted turning model was developed and validated by comparing the simulation results with experimental results. The effect of workpiece temperature on the cutting force and chip formation process was examined. The predicted cutting forces and chip morphologies from the simulation strongly correlated with the experimental results. It was observed from the simulation that the chip forms after the coalescence of two deformed regions in the shear band and that the cyclic cutting forces are strongly related to this chip formation process.

Investigation on the chip formation concerning tool inclination angles in ball end milling of H13 die steel

Widespread application of ball end milling operation is an outstanding characteristic in the field of manufacturing of die and molds. Tool inclination angles, which could improve the cutting performance of ball end mill, are critical factor in the ball end milling process, and also chip formation is one of the most important phenomena in the machining process. Numerical simulation, geometric analysis, observation by optical microscope and scanning electron microscope, and energy-dispersive spectroscopy analysis were adopted to study the chip formation during ball end milling of H13 die steels involving tool inclination angles in this work. The theoretical uncut chip geometry and tool–work contact zone were analyzed by computer-aided modeling technology. Finite element modeling of chip formation process involving tool inclination angles was performed, and variations of the maximum chip temperature which could provide assistant understanding of practical chip formation were analyzed. This article also investigated the practical chip morphologies, chip color, and the cutting characteristics under different process conditions and tool inclination angles. The optical microscope and scanning electronic microscope were used to capture the micro-photos of the chips under different process parameters, and the chip color and chip morphologies were discussed together with the cutting characteristics with regard to various process parameters. Energy-dispersive spectroscopy analysis of the chip free surface and back surface was also carried out for some special tool inclination angles. Deep understanding of the chip formation in multi-axis milling process was enhanced, and the research work could provide support for the selection of process parameters to some extent.

Influence of Magnetic Field on Chip Serration Frequency for Turning Stainless Steel AISI 304

In this research, respond surface methodology (RSM) model was developed for the investigation and prediction in order to study the effect of cutting parameters and chip serration frequency during machining stainless steel AISI 304. The model can be used for analysis and prediction for complex relationship between cutting parameters and chip serration frequency on metal cutting process. Tin coated carbide insert is used with 120mm tool overhang to investigate the process. Permanent magnet with the 4500 Gauss power is compared in this experiment with the natural frequency to obtain the required data during machining. Chatter is found to appear as a resonance phenomenon when the frequency of chip serration is equal to or integer multiple of the prominent natural frequency/frequencies of the system component (s). Hence, it is important to study the chip serration frequency. At lower cutting speeds the chip is often discontinuous, while it becomes serrated as the cutting speed is increased. It has been identified that the chip formation process at higher speeds also has a discrete nature, associated with the periodic shearing process of the chip. In this paper a statistical technique is proposed to predict the frequency of chip serration as a function of cutting parameters in turning of stainless steel AISI 304 using Response Surface Methodology (RSM). 95% confident level was predicted using analysis of variance (ANOVA).

Chip Morphology in High Speed Precision Turning Process of Hardened Steel GCr15

The main characteristic of hard turning process is easy to produce serrated chip. The chip deformation will impact greatly turning process. It is very important to analysis the chip formation and morphology during precision turning process of hardened steel. The deformation mechanism of serrated chip formation process and its chip morphology of chips produced during precision turning process of the hardened steel GCr15 is studied in hard cutting experiment by the methods such as numerical simulation of two-dimensional finite element analysis of turning, chip cross-sectional microscopic analysis and other methods .High speed precision turning of hardened steel GCr15 produces morphology of continuous chip and serrated chip; Serrated chip has the typical characteristics of the adiabatic shear slip after section such as apical surface of the serrated chip is composed of multilayer rolling dentate shear plane, a single surface of one tooth is not smooth, but no crack. Extrusion grooves is produced from tooth root to tip; Intensive slip line on serrated chip cross-section can be saw by microscopic observation; Fracture surface of the serrated chip presents small tumor tissues. The results show that the reason of hardened GCr15 steel forming serrated chip is periodic adiabatic shear fracture, and the research provides a theoretical reference application of hard turning technology.

Cutting of Nickel-Based Superalloys with Rotating Indexable Inserts

In this paper the technological basics of machining the nickel-based superalloy Inconel 718 with a self-propelled rotary tool and an actively driven rotary tool are presented. The advantages compared to conventional machining with fixed round indexable inserts are discussed. In a series of experiments the influence of the tool rotation and modification of the process parameters to the chip formation process and characterization of the surface area of the workpiece are investigated. By using a multitasking lathe with a milling spindle further experiments are conducted. Thereby the influence of the direction of the tool rotation, the relative speed between tool and workpiece and the variation of the penetration angles are analysed.

Quantitative Microstructural Analysis of Nanocrystalline Surface Layer Induced by a Modified Cutting Process

Present work analyzes the influence of process and modified geometry parameters of an orthogonal final machining process (finishing) on the nanocrystalline surface layers generation by quantitative microstructural analysis. Thereby, AISI 4140 (German Steel 42CrMo4) in a state quenched and tempered at 450°C is used as workpiece material. Metallic materials used in technical applications are polycrystalline in nature and are composed of a large number of grains which are separated by grain boundaries. The grain size has a strong influence on the mechanical material properties. Metallic parts with a severe nanocrystalline grain refinement in the near-surface area show many beneficial properties. Such surface layers considerably influence the friction and wear characteristics of the workpiece in a subsequent usage as design elements working under tribological loads due to their extreme superplastic properties. The tribologically induced surface layers formation already starts during the manufacturing of the components, by leading to a change of workpiece material near the surface. Particularly when the depth of cut h becomes of the same order as the cutting edge radius rß, the ploughing process becomes increasingly important and strongly influences the chip formation process. The plastic zone depth within the surface layer is especially influenced by the design of the microgeometry of the cutting tools and increases almost linearly with the ratio of cutting edge radius rß to depth of cut h. The plastic zone is hereby approximately of the same order of magnitude as the cutting edge radius rß. Parameters that are studied and taken into account in the manufacturing process are cutting edge radius rß, depth of cut h and cutting velocity vc. Variations of cutting depth h are performed in a range of 30 to 100 µm and variations of cutting edge radius rß are executed in a range of 30 to 150 µm. The microgeometries of the tools are preconditioned by abrasive grinding with a drag finishing machine and observed by a confocal light microscope. A cutting velocity vc of 25 and 150 m/min is applied. The evaluation of the manufacturing process is carried out by detailed analyses of the microstructural conditions in the surface layer after processing using a Focused Ion Beam system. These material characterizations provide information about the surface engineering concerning the microstructural changes in the workpiece surface layer due to machining. Hereby, the grain size analysis is investigated by a line method based on the characterization of portions of several test-lines positioned across the two dimensional Focused Ion Beam images.