Material Side Flow Research Articles

Statistical analysis of different machining characteristics of EN-24 alloy steel during dry hard turning with multilayer coated cermet inserts

This research article describes the experimental and statistical analysis of flank wear, material removal rate, tool tip temperature, surface roughness parameters (i.e. Ra, Rz and Rt), chip morphology, chip thickness and dimensional deviations (i.e. circularity and cylindricity). Taguchi's L27 orthogonal array has been selected for experimental design and ANOVA (analysis of variance) has been used to study the significance of cutting parameters on the responses. The experimental study exhibits that depth of cut is the predominant machining parameter influencing surface roughness followed by feed rate and cutting speed. Similar result was found for flank wear and dimensional deviations. However, cutting speed was found to be the most crucial input parameter for tool the tip temperature whereas feed rate was the most notable input variable for material removal rate (MRR). Abrasion and chipping are two major wear mechanisms found for flank wear in this study. During chip morphology study using scanning electron microscope material side flow, serrations, shear band, shear cracks, smooth and rough surfaces are observed. Further, the effect of flank wear on surface roughness parameters, dimensional deviations and effect of MRR on different patterns of crater wear were studied. For each response, mathematical model was developed with regression analysis and the models having higher R-Sq values show favorable relationship between predicted and experimented values. Finally, the optimal combination of machining parameters has been obtained using neuro-genetic algorithm.

Tribology assessment of surface-contact sliding pairs with streak defect under dynamic harmonic excitation loading

PurposeStreak defect and dynamic harmonic excitation (DHE) loading play important roles in machine operating conditions. The purpose of this paper was to assess the effects of streak defect and DHE loading on the tribological properties of surface-contact friction pairs, for example the differential gear end-face on the washer, via experimental investigation.Design/methodology/approachStreak defect was artificially introduced into the washer surface, which was loaded with DHE loads produced by a spring-connecting weight system. The wear scar of the washers and the monitored friction force signals were respectively scanned using scanning electron microscope (SEM) and analyzed using wavelet simulation.FindingsThe friction force curves, SEM images and discrete wavelet transform results indicate that DHE loading tends to increase friction force, to accelerate plowing damages and result in side-flow of material and plastic deformation on the surfaces of the washer. Whereas, streak oil-channel textures on washer specimen can be machined to modify the lubrication condition in the running-in stage so as to improve the tribological properties of the sliding pairs which were even subjected to DHE loading.Originality/valueOn the basis of this thesis research, the effect of streak defect and DHE loading on tribological performance of surface-contact sliding pairs is discussed. The results of wear form and friction state with the effect of streak defect and DHE loading facilitate to optimize the operating condition of mechanical parts.

Stochastic Kinematic Process Model with an Implemented Wear Model for High Feed Dry Grinding

This paper considers heavy duty grinding with resin bonded corundum grinding wheels and without lubrication and cooling. A vertical turning machine redesigned to a grinding machine test bench with a power controlled grinding spindle is used in all of the experiments, allowing high tangential table feed rates up to 480 m/min. This special test-rig emulates the railway grinding usually done by a railway grinding train. The main test-rig components are presented and the resulting kinematics of the experimental set-up is described. A stochastic kinematic grinding model is presented. A wear model that is based on the kinematic description of the grinding process is set up. Grain breakage is identified as the main wear phenomenon, initiated by grain flattening and micro-splintering. The wear model is implemented into the stochastic kinematic modelling. The workpiece material side flow and spring back are considered. The simulation results are validated experimentally. The workpiece surface roughness is compared and a good agreement between simulation and experiment can be found, where the deviation between the experiment and the simulation is less than 15% for single-sided contact between the grinding wheel and the workpiece. Higher deviations between simulation and experiment, up to 24%, for double-sided contact is observed.

Influence of asymmetric cutting edge roundings on surface topography

For finishing operations in machining, hardened steel hard turning can compete with grinding operations by means of accuracy and productivity. In the past research focussed on the effect of process parameters and tool macro geometry on the resulting surface roughness. Recent investigations show, that the cutting edge micro geometry is an important factor to influence surface quality. The knowledge generated by new methods displays the importance of asymmetric cutting edge roundings on cutting forces, chip formation and tool life. It is known, that chip formation also affects the resulting surface quality. Therefore, this paper investigates the effect of asymmetric cutting edge roundings on the resulting surface roughness in hard turning of roller bearing inner rings. Cutting tests with differently shaped cutting edges and two different feed values are conducted. The resulting surface roughness is measured. The consequent surface quality is explained by geometric coherences between uncut chip thickness and stresses along the cutting edge and the effect of material side flow. It is found, that the cutting edge geometry and the resulting stress distribution around the cutting edge affects the generated surface quality.

Side Flow Effect on Surface Generation in Nano Cutting

The side flow of material in nano cutting is one of the most important factors that deteriorate the machined surface quality. The effects of the crystallographic orientation, feed, and the cutting tool geometry, including tool edge radius, rake angle and inclination angle, on the side flow are investigated employing molecular dynamics simulation. The results show that the stagnation region is formed in front of tool edge and it is characterized by the stagnation radius Rs and stagnation height hs. The side flow is formed because the material at or under the stagnation region is extruded by the tool edge to flow to the side of the tool edge. Higher stagnation height would increase the size of the side flow. The anisotropic nature of the material which partly determines the stagnation region also influences the side flow due to the different deformation mechanism under the action of the tool edge. At different cutting directions, the size of the side flow has a great difference which would finally affect the machined surface quality. The cutting directions of {100} < 011>, {110} < 001>, and {110} < 1-10 > are beneficial to obtain a better surface quality with small side flow. Besides that, the side flow could be suppressed by reducing the feed and optimizing the cutting tool geometry. Cutting tool with small edge radius, large positive rake angle, and inclination angle would decrease the side flow and consequently improve the machined surface quality.

Investigation on the burr formation mechanism in micro cutting

It is desirable to minimize burr formation for improving part quality. This paper presents an investigation on the burr formation mechanism in micro cutting by taking into consideration the stress distribution around the cutting edge arc. The influences of the uncut chip thickness and the cutting edge radius on burr formation were investigated. Poisson burr is attributed to the side flow of the stagnation material at the bottom of the cutting edge arc. The stress distribution at the cutting edge arc has great influence on Poisson burr formation. The burr height decreases to the minimum value and then increases with reducing the uncut chip thickness due to the change of the maximum stress distribution. An optimum machining strategy also is suggested in micro milling of snake-shaped groove microstructure.

Tool damage and machined-surface quality using hot-pressed sintering Ti(C7N3)/WC/TaC cermet cutting inserts for high-speed turning stainless steels

A Ti(C7N3)/WC/TaC cermet cutting tool was developed using a hot-pressed technology. A standard orthogonal array was used to investigate the cutting performance of this newly developed insert in the high-speed turning of 17-4PH martensitic and 321 austenitic stainless steels. The effects of the cutting parameters on the tool life and surface quality were analysed to examine the performance of the inserts based on Taguchi method. The mechanisms of tool damage and machined-surface generation and their relationships were also thoroughly discussed to understand the machinability of different stainless steels. The used cutting parameters are as follows: a cutting speed of 350∼400 m/min for 17-4PH steel and 300∼350 m/min for 321 steel and a feed of 0.10 mm/r and a depth of cut of 0.30∼0.35 mm, which is considered to be a notably efficient parameter for machining stainless steel. The crater wear and flank wear prevailed in the machining of 17-4PH martensitic stainless steel, whereas the flank wear was serious and edge chipping occurred in the machining of 321 austenitic stainless steel. There were some pits on the machined-surfaces of 17-4PH steel and some material side flow on the machined-surface of 321 steel, which is related with the e material properties of these two stainless steels.

Performance and wear mechanisms of whisker-reinforced alumina, coated and uncoated PCBN tools when high-speed turning aged Inconel 718

Inconel 718, an efficient superalloy for energy and aerospace applications, is currently machined with cemented carbide tools at low speed (vc ≈ 60 m/min) due to its unfavorable mechanical and thermal properties. The article presents results of a study of superalloy machinability with whisker-reinforced alumina, uncoated and coated polycrystalline cubic boron nitride (PCBN) tools. Turning of age-hardened Inconel 718 (45 HRC) was done under high-speed machining conditions (vc = 250…350 m/min). Aspects of tool life, tool wear, and generated surface quality were studied. Application of uncoated PCBN tools resulted in surface quality and force level superior to other tool materials. Considerable sideflow of workpiece material was found to affect surface quality, especially for coated PCBN and ceramic tools. It was found that protective function of the coating, which increases the tool life up to 20 %, is limited only to low cutting speed range. EDX and AFM analyses suggested dominance of chemical and abrasive wear mechanisms. EDX mapping of worn tools pointed absence of diffusional wear for PCBN tools and intensive degradation of whisker reinforcement in ceramic tools due to diffusion of Ni, Fe, and Cr.

Distribution of unit forces on the tool nose rounding in the case of constrained turning

The development of force models is important in understanding the effects of tool edge geometry where the tool edge radius is of similar value to the depth of cut. In this paper it is demonstrated that both the rounding of the tool edge and the rounding of the tool nose affect the chip formation process and the quality of the machined surface.The distribution of unit forces on the nose of a tool is presented in detail. The main assumption in all the considerations was constant temperature conditions in the cutting zone, maintaining the thermo-mechanical properties of the work material at a constant level. The experiment was conducted for free and non-free turning, and in both cases the temperatures and forces were measured.For free cutting the distribution of unit forces on the tool edge rounding was investigated—the minimal thickness of cut and characteristic equations for forces Fc and Ff were determined. Then the unit forces distribution was recalculated for the case of non-free turning with rounded tool nose. The summed forces for non-free turning were compared with measured values, for verification of the cutting force model.The distribution of unit forces along the tool nose revealed nonlinearities influencing tool and machined surface integrities. The unit forces acting on the rake face were established to determine the length of the active part of the tool where the conditions for chip formation were favorable. Distribution of unit forces acting on the rake face in the reverse direction indicated the conditions in which a chip was pushed away from the transient surface.The distribution of unit forces acting on the flank face in the feed direction was found to determine the machined surface quality. The range of negative values of unit forces defined the conditions for moving away of the non-machined material (under the condition hj<hmin) in a direction opposite to the feed. This work material was found to be responsible for the effect of material side flow.

Experimental Study on High-Speed Milling of SiC&lt;sub&gt;P&lt;/sub&gt;/Al Composites

Tool life and tool wear, cutting forces and cutting temperature, surface finish, chip formation and surface generation were investigated when milling SiCp/2009Al composites at the cutting speed of 1200m/min using PCD tools. The results showed that PCD tool life was 150min when the 0.1mm tool wear criterion was chosen. PCD tool mainly suffered from tool grain breaking-off, chipping, abrasive wear, micro cracks and adhesive wear due to he very high-frequency impact and scrape of SiC particles. The peak value of the cutting force Fy (the radial direction) was over 1300N and the cutting vibration was very severe. The cutting temperature was 523.7°C. Pits, voids, matrix tearing and scratch were the main defects on the machined surface. The deformation layer thickness was about 20-35μm. The chip for the vol.20%SiCp/2009Al composite took the form of flow type and the mechanisms of the chip formation were the combination of dynamic behavior of voids/micro-cracks and adiabatic shear. For the vol.35%SiCp/2009Al composite, the chip was non-continuous and had the tendency of saw-toothed type. Material swelling and side flow, tool-workpiece relative vibration, feed rate and tool nose radius, removal mode of SiC particles were the main mechanisms of surface generation.

Analytical and Experimental Determination of the Ra Surface Roughness during Turning

In this article an analytical equation for calculating the theoretical arithmetic mean surface roughness, Ra, in the case of turning using a tool with a circular nose radius is presented. The deviation that often occurs between the expected and the obtained surface roughness during these machining operations is investigated. Influence of the minimum chip thickness is discussed especially in regards to the related phenomenon of so called side flow of material on the machined surface. Three different kinds of workpiece materials have been investigated in order to gain a better understanding of their influence on the obtained surface roughness. The obtained results show that the surface roughness could be considered as being inside an interval of two analytically determined Ra-values.

A study on the surface integrity aspects of superalloy Inconel 718 under minimum quantity lubrication in high speed turning

This paper addresses effects of the minimum quantity lubrication (MQL) in pulsed jet mode on the surface integrity aspects of superalloy Inconel 718 when subjected to high speed machining. Investigation done in this study, consider different cutting conditions with respect to the surface roughness, topography and microhardness of the machined surfaces. From the experimental study, it was observed that application of cutting fluid under pulsed jet mode results into better surface finish and minimum material side flow. Moreover, the work hardening rate of the machined surface is reduced considerably compared to dry high speed turning.

Surface Generation and Chip Formation when Ultra-Precision Turning of SiC&lt;sub&gt;p&lt;/sub&gt;/Al Composites

Chip formation and surface generation were investigated when ultra-precision turning of SiCp/2009Al and SiCp/ZL101A composites using Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) tools. The results showed that the machined surfaces took on many defects of pits, voids, microcracks, grooves, protuberance, matrix tearing etc. It was noticed that most of these defects had an intimate relationship with the removal process of SiC particle. The surface finish was much better when the SiC particles were removed by cut through or in-situ pressed into mechanisms. Material swelling and side flow, tool-workpiece relative vibration, feed rate and tool nose radius, removal mode of SiC particles were these main mechanisms of surface generation. Generally, a saw-toothed chip was formed when ultra-precision turning this kind of material and the mechanisms of this type of chip were dynamic microcrack behavior and strain concentration, which induced by the non-uniform deformation of the workpiece material.

Investigation on minimum quantity lubricant-MQL grinding of 100Cr6 hardened steel using different abrasive and coolant–lubricant types

Large quantities of coolant–lubricants are still widely used in the metal working industry, generating high consumption and discard costs and impacting the environment. Alternatives to current practices are getting more serious consideration in response to environmental and operational cost pressures. In the grinding process, promising alternatives to conventional dry and fluid coolant applications are minimum quantity lubrication (MQL) or near dry grinding process. Despite several researches, there have been a few investigations about the influence of different types of coolant–lubricants and grinding wheels on the process results. The current study aims to show the effects of the above parameters on grinding performance such as grinding forces and surface quality. The tests have been performed in presence of fluid, air jet and eleven types of coolant–lubricants, as well as, in dry condition. The grinding wheels employed in this study were vitrified bond corundum, resin bond corundum and vitrified bond SG wheels. The results indicate that SG wheels and MQL oils have potential for the development of the MQL process in comparison to vitrified and resin bond corundums and water miscible oils. Also, the lowest thermal damages, material side flow on the ground surface and wheel loading were generated by using the SG grinding wheel in MQL grinding process.

Studies on minimum quantity lubrication (MQL) and air cooling at drilling

In the recent years a lot has been done to avoid the cutting fluids from the production. Dry cutting and semi-dry cutting such as Minimum Quantity Lubrication (MQL) have been favored by the industry. However, one of the main limitations in the application of MQL is that the full mechanism has not yet been fully understood. This paper deals with the results obtained at cutting with MQL at different oil amounts, dry compressed air and emulsion. The results are discussed in terms of wear, chip contact, forces/torques and surface finish. The short hole drilling tests with indexable inserts showed that MQL and compressed air usage have resulted lower wear both on the center and periphery insert compared to drilling with emulsion. The surface finish values have shown that; cutting with compressed air resulted in side flow and sticking of the work piece material on the walls of the hole that gave bad surface finish. The longer chips were evidenced for emulsion in comparison to MQL and air assisted drilling.

Modelling of Material Side Flow in Hard Turning

In this paper an attempt has been made to model the material side flow generated during hard turning operation. A three dimensional thermo elasto-viscoplastic finite element model is presented. The model incorporates cutting tools with different nose radii and cutting conditions. The model was also used to investigate the effect of different process parameters on the extent of material side flow. The predicted results revealed that more side flow is generated when higher nose radius is used. A similar observation is noted when lower feed is used. The simulated results agreed well with the experimentally examined machined surface, viewed with a scanning electron microscope.

A study on ultra–high-speed cutting of aluminium alloy:: Formation of welded metal on the secondary cutting edge of the tool and its effects on the quality of finished surface

To investigate the mechanism of ultra–high-speed cutting for aluminium alloy, cutting experiments by using a machine tool equipped with an active magnetic bearing spindle were performed over a range of cutting speeds from 20 to 260 m/s. On the whole, the finished surface tends to improve with an increase in cutting speed. However, the formation of welded metal on the tool edge in the speed range from 100 to 200 m/s promotes the material side flow on the finished surface, which causes the surface roughness to increase.

Effects of process parameters on material side flow during hard turning

The phenomenon of material side flow represents an important aspect of machined surface quality during hard turning. In this paper, an experimental study was performed to investigate the main features of this phenomenon. The effects of process parameters including edge preparation, nose radius, feed and tool wear on material side flow were examined. Two possible mechanisms for material side flow were investigated. In the first one, the material is squeezed between the tool flank face and the machined surface when chip thickness is less than a minimum value. In the second mechanism, the plastified material in the cutting zone flows through the worn trailing edge to the side of the tool. Both of these mechanisms can exist simultaneously. The results obtained from surface examination showed a strong correlation between edge preparation and material side flow. An increase in the tool nose radius resulted in a remarkable increase of material side flow. Feed had an indirect effect on material side flow. In addition, tool wear significantly affected the existence of material side flow on the machined surface. An increase in tool wear promoted the occurrence of material side flow.

PHENOMENOLOGICAL ANALYSIS OF MATERIAL SIDE FLOW IN HARD TURNING: CAUSES, MODELING, AND ELIMINATION

ABSTRACT Material side flow causes surface damage that has been observed and partly investigated over a period of several years. This paper presents a phenomenological analysis of material side flow in hard turning. First, material side flow is identified, characterized, and its causes classified. Then, the dependence of the material side flow on different process parameters is analyzed using the results of a comprehensive experimental investigation. Tool nose radius, tool wear, and feed are considered as the primary factors that initiate the occurrence of material side flow in finish turning of hardened steel. A new concept for modeling material side flow is then proposed. This model predicts the minimum chip thickness that allows the workpiece material in the vicinity of cutting to plastically flow at the side of the tool, instead of shearing. The value of the minimum chip thickness affects the size of material side flow on the feed marks. Based on the results obtained from the model, the feed and tool nose radius that eliminates/minimizes material side flow in hard turning are specified.

A Study of Metal Flow Ahead of Tool Face With Large Negative Rake Angle

Although the chip formation mechanism by a tool having a large negative rake angle is not well known, it is very important to make the process clear in order to get high quality in finished surfaces. In this paper, the behavior of material ahead of a tool face with a large negative rake angle is examined by means of low speed machining on lead. The deformation process of the material is investigated by the deformation study combining a finite element method with a grid line method. During cutting, the deformation process of grid lines which were drawn on the sides of testpieces was observed through a side glass which restricted the side flow of material. Cutting force was measured by a dynamometer consisting of an elongated octagonal ring with strain wire gages. As a result it was found that the shear stress on the slip line of maximum increment of shear strain is nearly constant, but the compressive stress changes along the line. It was concave near the top of cutting edge and convex near the surface of the test piece. The position of the change of polarity in the slope shifted depending on the rake angle of the tool. This phenomenon is considered to have close relation with the stagnant tip, which decides not only the size of chip, but also whether or not a chip will be formed. Flow lines of material and the deformed region ahead of tool faces with different negative rake angles were also obtained and they were compared with each other.