Workpiece Contact Research Articles

Numerical Study of Coolant Flow Phenomena and Heat Transfer at the Cutting-Edge of Twist Drill

Cutting tool coolant channels play a pivotal role in machining processes, facilitating the efficient supply of cooling agents to high-stress areas and effective heat dissipation. Achieving optimal cooling at the tool’s cutting-edge is essential for enhancing production processes. Experimental investigations into tribological stress analysis can be limited in accessing complex tool–workpiece contact zones, prompting the use of numerical modelling to explore fluid dynamics and tribology. In this study, the coolant flow dynamics and heat dissipation in drilling operations were comprehensively investigated through computational fluid dynamics (CFD) modelling. Four twist drill models with varying coolant channel arrangements were studied: standard model drill, standard model drill with notch, profile model drill, and profile model drill with notch. Two distinct approaches are applied to the coolant inlet to assess the impact of operating conditions on fluid flow and heat dissipation at the cutting-edge. The findings emphasize that cutting-edge zones have insufficient coolant supply, particularly in modified drill models such as the standard model drill with notch and profile model drills with and without notch. Moreover, enhanced coolant supply at the cutting-edge is achieved under high-pressure inlet conditions. The standard model drill with a notch exhibited exceptional performance in reducing thermal load, facilitating efficient coolant escape to the flute for improved heat dissipation at the cutting-edge. Despite challenges like dead zones in profile models, the standard-with-notch model yielded the most promising results. Further analyses under constant pressure conditions at 40 and 60 bar exhibited enhanced fluid flow rates, particularly at the cutting-edge, leading to improved heat dissipation. The temperature distribution along the cutting-edge and outer corner demonstrated a decrease as the pressure increased. This study underscores the critical role of both coolant channel design and inlet pressure in optimizing coolant flow dynamics and heat transfer during drilling operations. The findings provide valuable insights for designing and enhancing coolant systems in machining processes, emphasizing the significance of not only coolant channel geometry but also inlet pressure for effective heat dissipation and enhanced tool performance.

Control of Tool–Workpiece Contact in Belt Grinding

Control of Tool–Workpiece Contact in Belt Grinding

Dynamic Modeling and Stability Prediction of Robot Milling Considering the Influence of Force-Induced Deformation on Regenerative Effect and Process Damping

Undesirable chatter is one of the key problems that restrict the improvement of robot milling quality and efficiency. The prediction of chatter stability, which is used to guide the selection of process parameters, is an effective method to avoid chatter in robot milling. Due to the weak stiffness of the robot, deformation caused by milling forces becomes an unavoidable problem, which will change the tool–workpiece contact area and affect the stability prediction. However, it is often simplified and neglected. In this paper, a multipoint contact dynamic model of robot milling is established, which considers the influence of force-induced deformation on the regenerative effect and process damping. The tool–workpiece contact area is discretized into a finite number of nodes along the axial direction so that the force and deformation at each node can be calculated separately. The different contact forms of the tool–workpiece under different process parameters are discussed in different cases, and the interaction process between cutting force and force-induced deformation is analyzed in detail. An iterative strategy is used to calculate the deformation of each node and the result of the tool–workpiece contact boundary. Finally, chatter stability of robot milling is predicted by a fully discrete method. Robot milling experiments were carried out to verify the predicted results. The results show that force-induced deformation is an important factor improving the stability prediction accuracy of robot milling, and a more accurate prediction result can be obtained by simultaneously considering force-induced deformation and process damping.

A tribological characterisation of Ti-48Al-2Cr-2Nb and Ti-6Al-4V alloys with dry, flood, and MQL lubricants

The development of cutting tools requires the knowledge of tribological phenomena at the tool – workpiece contact area. This knowledge is in dearth particularly for difficult-to-cut alloys like gamma titanium aluminide (gamma – TiAl alloys). Therefore, this article is an attempt to plug the gap and aid the development of cutting tools for gamma – TiAl alloys. To this end, friction, adhesion, and coating wear between AlTiSiN coated cemented carbide tool and Ti-48Al-2Cr-2Nb (Near lamellar), Ti-48Al-2Cr-2Nb (Duplex), and the most used titanium alloy of Ti-6Al-4V (alpha – beta) were experimentally derived. A Pin-on-Cylinder (PoC) tribometer with contact conditions corresponding to commercial machining conditions was used with dry, flood(EML), and two MQL lubricants. Additionally, the heat generated and partitioned between the pin and workpiece was quantified to assess the thermal exposure to the coatings. The results showed that Ti-6Al-4V had approximately 50% higher apparent friction coefficient than the Ti-48Al-2Cr-2Nb alloys. Interestingly, the friction coefficients of Ti-48Al-2Cr-2Nb alloys were nearly consistent across the entire test matrix. Notably, the change in the microstructure from near lamellar to duplex did not elicit any qualitative or quantitative change in the friction profile of Ti-48Al-2Cr-2Nb alloys. The contact pressure proved to be the statistically significant property influencing friction evolution inversely for Ti-6Al-4V alloy and directly for Ti-48Al-2Cr-2Nb alloys. The results showed higher probability of coating wear in dry conditions as opposed to the flood and MQL lubricants.

Evaluating die wear-induced edge quality degradation in trimmed DP980 steel sheets from in situ force response monitoring

Assessing trimmed part quality involves periodic examinations of cut edges and shear affected zones to characterize rollover, burnish, fracture and burr formation. Established techniques are thorough and reliable but inherently time consuming. This study correlated die wear-induced force response evolutions and the observed transitions between shear-induced deformation zones for DP980 (C-0.15 wt%Mn-1.5 wt%Si-0.31 wt%) steel sheets subjected to trimming with AISI D2 steel dies. The findings are useful for peripheral assessment of part quality and tool wear via in situ trimming force/displacement response monitoring. Measurements were collected from a load cell and a non-contact laser displacement transducer embedded within the instrumented trimming press. The sliding wear damage and failure processes induced by die–workpiece interactions were correlated to force/displacement response phases. Trimming tests were conducted for 20,000 cycles to observe and assess transformations between rollover and burnish zones with increasing tool wear after the initial contact and at every subsequent 5000 cycle interval. The mean trimming force and maximum die penetration increased, primarily due to die edge blunting, by 1.33 kN (44.3%) and 194 μm (32.2%), respectively. An enlarged die–workpiece contact area increased the resistance force and delayed the onset of fracture with increased sliding damage between sheared surfaces and nearly doubled burnish zone depths. Quantitative attributes of the trimming force/displacement responses were linked to die impact and sliding contact induced damage features of trimmed parts, demonstrating the potential for straightforward, rapid and detailed in-field monitoring of acceptable limits to sheared edge quality.

Investigation of the microstructure evolution during the broaching in step-wedge strikers by computer modeling in the deform software package

In this work the forging process in step-wedge strikers by commercial FE-code Deform was simulated. For microstructure evolution the Cellular Automata method was used. The influence of technological and geometric parameters of the forging process on the microstructure evolution was studied. Models with different values of the joint angle of the wedge and depression faces, the friction coefficient at the contact of workpiece and tool, the upper striker movement speed and the workpiece temperature were considered. As a result, the following optimal geometric and technological parameters were determined: the junction angle of wedge and depression faces is 160°; the friction coefficient is 0.7; the upper striker movement speed is 1 mm/s; the workpiece heating temperature is 1000°C.

Material removal and surface generation in longitudinal-torsional ultrasonic assisted milling

Ultrasonic Machining (UM) is extensively used in processing of difficult to cut materials due to its superior performance. However, the mechanics of this process is still not fully understood when superimposed on other machining operations. In this paper, Longitudinal-Torsional Ultrasonic Assisted Milling (LTUAM) is introduced for machining of a high strength titanium alloy Ti-6Al-4V. The separation geometrical characteristics between the tool and workpiece are studied analytically. Moreover, the texturing generation mechanism of LTUAM is analyzed through a theoretical model. The proposed method considers the influence of 3D tool topography, which can accurately simulate the ultrasonic surface topography. Related experiments of the generated cutting force and the surface topography were conducted to investigate the machining characteristics. The results showed that compared with Conventional Milling (CM), a noticeable decrease of the cutting force was observed in LTUAM. This can be explained from the perspective of tool workpiece contact rate model. Micro dimpled surface textures were successfully fabricated on Ti-Al6-4V using LTUAM technique. The surface test results indicated that the surface micro-hardness was enhanced between 6.34% and 13.22% compared with CM. This research provides guidance for applications of ultrasonic machining to textured surfaces.

Prediction of Surface Roughness Using Machine Learning Approach in MQL Turning of AISI 304 Steel by Varying Nanoparticle Size in the Cutting Fluid

Surface roughness is considered as an important measuring parameter in the machining industry that aids in ensuring the quality of the finished product. In turning operations, the tool and workpiece contact develop friction and cause heat generation, which in turn affects the machined surface. The use of cutting fluid in the machining zone helps to minimize the heat generation. In this paper, minimum quantity lubrication is used in turning of AISI 304 steel for determining the surface roughness. The cutting fluid is enriched with alumina nanoparticles of two different average particle sizes of 30 and 40 nm. Among the input parameters chosen for investigation are cutting speed, depth of cut, feed rate, and nanoparticle concentration. The response surface approach is used in the design of the experiment (RSM). For the purpose of estimating the surface roughness and comparing the experimental value to the predicted values, three machine learning-based models, including linear regression (LR), random forest (RF), and support vector machine (SVM), are utilized in addition. For the purpose of evaluating the accuracy of the predicted values, the coefficient of determination (R2), mean absolute percentage error (MAPE), and mean square error (MSE) were all used. Random forest outperformed the other two models in both the particle sizes of 30 and 40 nm, with R-squared of 0.8176 and 0.7231, respectively. Thus, this study provides a novel approach in predicting the surface roughness by varying the particle size in the cutting fluid using machine learning, which can save time and wastage of material and energy.

Impact of Process Variables of Acetone Vapor Jet Drilling on Surface Roughness and Circularity of 3D-Printed ABS Parts: Fabrication and Studies on Thermal, Morphological, and Chemical Characterizations.

Ever since the introduction of 3D printing, industries have seen an exponential growth in production and efficiency. Three-dimensional printing is the process of additive manufacturing (AM) in which the conventional method of material removal is challenged. Layer-on-layer deposition is the basic principle of the AM. Additive manufacturing technologies are used to create 3D-printed objects. An object is built in an additive technique by laying down successive layers of material until the object is complete. Each of these layers can be viewed as a cross-section of the item that has been lightly cut. When compared to traditional production methods, 3D printing allows the creation of complicated shapes with less material. In conventional methods, the materials go through several damages due to the tool–workpiece contact creating friction between them and the dissipated heat that damages the material. Overcoming the conventional method of machining with the help of 3D printing is a new advancement in the industries. The process involves using non-conventional methods for the machining of the parts. This research was oriented towards the chemical vapor jet drilling of the acrylonitrile–butadiene–styrene (ABS) materials. ABS materials are highly machinable and can be recycled for further usage. This paper focused on the usage of acetone as the chemical for drilling. The surface roughness and circularity of the drilled hole was taken into account for this research paper. We set up a manual experiment to run tests and get results. A vapor jet machine was designed with acetone as the core for the vapor. Various analyses were also formulated and conducted during experimentations. Surface roughness analysis provided the insight of roughness after the machining with the help of acetone vapor jet spray. SEM and micro-image parameters were also considered for more clear and advanced reports. In this research paper, DSC and FTIR analysis were performed to understand changes in the internal structure and the material properties of the ABS. Moreover, the research aimed to investigate the effect of various inputs processing parameters such as pressure, flow rate, and stand-off distance on the surface roughness and circularity of ABS workpiece material. The Taguchi L9 orthogonal array design was utilized to conduct tests by chemical vapor jet drilling using acetone and to evaluate the performance of the set-up while reducing the influence of interfering factors in order to provide reliable surface finish and circularity results. The results and conclusion of the research paper aimed to determine the most suitable parameters for the non-conventional acetone vapor jet drilling of the ABS material. The theoretical calculations predicted 1.64432 and 0.3289080 values of surface roughness and circularity, respectively. On the other hand, the experimental values were recorded as 1.598 for surface roughness and 0.322 for circularity. Therefore, a negligible error of 0.046 for surface roughness and 0.0031 for circularity, respectively, was noted which validate the statistical equations and the consistency of the combined vapor jet drilling process.

ПОГРЕШНОСТЬ БАЗИРОВАНИЯ ЗАГОТОВОК ПРИ УСТАНОВКЕ НА ОПОРНЫЕ ПРИЗМЫ С УЧЕТОМ МАКРООТКЛОНЕНИЙ

Work objective: development of devices for high-precision machining of machine parts.
 The problem to which the paper is devoted is to analyze the accuracy of devices with location vees.
 Research methods: modelling of the contact of the workpiece contact with the location vee by means of the theory of dimensional connections, analysis of some model parameter influence using sensitivity analysis, regression analysis of the results of modeling the workpiece fixing in the location vees.
 The novelty of the work: the influence of form tolerances and the relative location of the base surfaces are established when calculating the accuracy of fixing workpieces in location vees; the features of forming basing error in the worst case (by maximum-minimum method) and taking into account the probability of size distribution within the tolerances (by the probabilistic method) are revealed.
 The results of the study: a model is developed for installing the workpiece into a vee, taking into account misalignment and deviations from roundness, dependencies are obtained for estimating the error of basing the workpiece in the location vees, taking into account these macro-displacements.
 Conclusions: the error of basing the workpiece in the vee is influenced by the tolerances of the form and location of the base surfaces; taking into account the errors of the form and location of the workpiece base surfaces make it possible to form the error of the base in the horizontal plane.

Problems encountered in underwater welding and remedies- a review

Wet underwater welding has proved to be the most suitable solution for underwater repairs and fabrication works. However, number of difficulties are faced that are specifically depicted in the testing and analysis of welds obtained while welded underwater. Major issues that are faced include immediate contact of workpiece with water leading to severe quenching effect, hydrogen diffusion due to dissociation of water which causes hydrogen induced cracking, arc instability, porosity in welds due to infused gases, loss of alloying elements leading to degradation of mechanical properties and microstructure of weld metal, increased hardness of HAZ and associated cracking. Since its inception during world war I, number of researchers have worked on finding the way out to control the harmful effects due to problems encountered during underwater welding. This paper discusses the experimental works conducted for detailing the problems encountered and the solutions suggested by researchers to overcome them. Controlling the input parameters during welding, addition of alloying elements into the electrode coating and multipass welding are the suggested solutions for obtaining desired characteristics in the welds.

Investigation of vibratory bed effect on abrasive drag finishing: a DEM study

Purpose The purpose of this paper is to investigate the effect of a vibratory bed, as an assistant agent, on the improvement of the drag finishing process. The dynamics and kinematic of the process were surveyed in microscale for different frequencies and amplitudes and the results were compared to the basic process. Design/methodology/approach The discrete element tool was used to find out the effect of the vibratory bed on the drag finishing process. To this end, the Hertz-Mindlin model was used to investigate the contact of abrasive particles and workpiece. At the first stage, the numerical model was validated with the experimental results, and then the effect of different parameters on the finishing process was evaluated and compared with the basic case. Findings The chosen numerical model was in good agreement with the results measured in the previous literature. Moreover, the results show that not only vibrated bed enhances the contacts of abrasive particles to the workpiece, but it also increases the uniformity of the finished surface. Originality/value In comparison to the experiments, the discrete element technique consumes lower cost and time to estimate the optimum conditions of the finishing process, as well as it provides a good understanding of this phenomenon on the micro-scale.

Numerically modelled study of the plunge stage in friction stir spot welding using multi-tiered mesh partitions

Friction stir spot welding is a solid-state joining process that has attracted significant attention particularly in the field of joining of lightweight, low melting alloys. These materials include alloys of Aluminium and Magnesium amongst many others which are of great importance to the aerospace and the automobile industries. The friction stir spot welding is a complex thermo-mechanical multiphysics phenomenon and is currently a field of intense research. The motivation of the current study is to understand this complex behaviour of the joining process by simulating it in the ABAQUS CAE environment. In the friction stir spot joining technique, the plunge stage is identified as the critical stage of operation as it involves a highly transient and dynamic zone for material and temperature flows. The plunge stage was studied in detail using the finite element based model. The plasticity of the material was simulated by the Johnson-Cook material model while the frictional heat generation was captured by applying a penalty-based frictional contact between the rotating tool and the workpiece contact surfaces. Considering the reasonable assumptions made, the results obtained by the numerical simulation model were found to agree with the past experimental and numerically modelled studies.

Analytical Modeling of Machining Forces and Friction Characteristics in Ultrasonic-Assisted Turning Process

Abstract Intermittent cutting characteristics of ultrasonic-assisted turning (UAT), compared with conventional turning (CT), has shown a significant enhancement in the machinability of hard-to-cut materials. The enhancement in machinability is associated with machining forces and friction characteristics of the process. The present article covers an analytical approach to predict the output responses such as machining forces and friction characteristics in UAT and CT processes. Specific cutting energy (SCE) for a particular work-piece material was considered to predict the output responses. The predictions were made by considering the conventional machining theories. Experiments for the UAT and the CT of SS 304 were carried out to validate the predicted model. The results from the analytical model showed that the shear angle increases and the tool work-piece contact ratio (TWCR) decrease with an increase in amplitude and frequency of vibration. The results obtained from the analytical model were found to be in close agreement with the experimental ones, with an approximate error of 2–20%.

Identification of rake and flank face engagement parameters using a dexel-based material removal simulation with an oriented sweep volume

This paper presents an approach for the simulation of cutting processes with a dexel based-simulation considering process damping. The approach allows an independent modeling of engagement parameters for both rake and flank faces of arbitrary tool and workpiece geometries including dynamic behavior for the first time. A method is introduced for calculating the indentation volume of the flank face independently of the rake face. Therefore, the oriented sweep volume is introduced. The indentation volume of the flank face is used to model process damping for improving stability and dimensional form error prediction. For verification, experimental milling tests are carried out to create stability charts and surfaces. Both, the stability and surface prediction of the approach are analyzed for a chamfered tool, where a flank face - workpiece contact occurs, and an unchamfered tool, where no flank face - workpiece contact occurs. Even though the prediction accuracy of the stability limit can be improved compared to different approaches, there are significant differences between simulation and experiment. Thus, there is still a high need for a more accurate modelling of the process damping effect.

Influence of biodegradable lubricant on the ecology, lubrication, and machining process in minimum quantity lubrication

In minimum quantity lubrication (MQL) processing, lubricating oil is passed through the air flow field in the form of oil droplets. The oil droplets penetrate the field and are adsorbed by it to form a film in the capillary tube at the workpiece–tool interface. Therefore, the type, atomization, penetration, and adsorption of the lubricating oil have crucial influences on the lubrication quality. Three types of lubricant—trimethylolpropane trioleate, vegetable oil, and polyethylene glycol—were used in this research. To protect the environment and meet application requirements, the biodegradability, oxidation stability, and placement stability of the aforementioned three oils were tested in accordance with the relevant national standard. The biodegradation rate and storage stability of vegetable oil 6000 were high; however, its oxidation stability was poor. A three-dimensional particle dynamic analyzer was used to measure the atomization of oil droplets, and the amount of oil penetrating the tool–workpiece contact area was quantitatively evaluated using a specially designed penetration sampling device. The contact angles of the droplets on AISI 1045 carbon steel and TiN coating were measured, and experiments were performed on the MQL machining of AISI 1045 carbon steel. According to the experimental results, the main cutting force, coefficient of friction, surface morphology, and roughness obtained using vegetable oil 6000 were superior to those obtained using polyethylene glycol 400 and trimethylolpropane trioleate, because a more focused oil drop distribution, higher amount of penetrated oil, and higher wettability were obtained with vegetable oil 6000.

Artificial aging heat treatment post-effect on profile and mechanical properties of the AA 6061 friction welding joint

Friction welding is a solution for metal joint problems that are difficult to joint with fusion welding. The quality results of friction welding are highly dependent on process parameters such as friction pressure, friction time, forging pressure, forging time, and rotating speed. There is often excessive softening, hardening of the metal grains, and formation of an intermetallic phase at the weld interface due to too high friction temperatures and too high forging pressures on the alloy. Several studies on AA 6061 concludes artificial aging heat treatment can provide positive changes on the tensile strength and microstructure of AA 6061. The purpose of this study is to find out the effect of post artificial aging treatment toward profile and mechanical properties of AA 6061 friction welding joint. The varied parameters are forging pressure in friction welding of 325 bar, 350 bar, 375 bar and artificial aging heating temperature post-welding of 100 °C, 150 °C and 200 °C. The fixed parameters observed are the connection profile, microstructure, hardness distribution and tensile strength of the joint. Controlled variables include: 1600 rpm spindle rotation, 65 bar or 65 kg cm−2 friction pressure, friction time tf = 6 seconds, time forging pressure tu = 60 seconds, workpiece contact diameter 15 mm and 15 degrees workpiece chamfer angle. The results are specimens with forging pressures of 325 bar, 350 bar and 375 bar without artificial aging treatment still show clearly interface of Zpl and Zpd zone; whereas in specimens treated with artificial aging, the Zpd and Zpl interface are getting faded which indicating that there is structures homogenization in the Zpd and Zpl zone. The hardness of the joint area increased significantly after artificial aging heat treatment because formed Mg2Si precipitates were dispersed in the Zpl, Zpd and Zud zones. The post-weld artificial aging heat treatment also resulted in a more even distribution of hardness in the joint area. The highest distribution of joint area hardness occurred in specimens with a forging pressure of 350 bar and artificial aging treatment at 200 °C. Artificial aging treatment with a temperature of 200 °C will form Mg2Si (black) precipitation and Fe3SiAl12 (gray) particles which are evenly dispersed in the Al matrix in the Zpd and Zpl zones so that their hardness is high. By applying artificial aging heat treatment, the tensile strength of the specimens increases until the artificial aging temperature is 150 °C; when the artificial aging temperature is raised to 200 °C, the tensile strength tends to drop back.

Skew Rolling of Bimetallic Rods.

The present article reports selected results of a preliminary study of the process of skew rolling of bimetallic rods. The experiments were conducted using a numerically controlled three-roller skew rolling mill. During the tests, bimetallic rods were rolled from billets whose cores and outer sleeves (bushings) were made of different types of steel. The results demonstrate that the proposed method can be successfully used in the production of bimetallic rods. However, proper fastening of the two materials depends on the geometrical parameters of the billets, and the quality of bimetallic rods depends on the heating method used. When the rods are heated without protective atmospheres, the surface layer of the core gets decarburized and the surfaces of the materials being joined together are oxidized, which hinders the welding process and adversely affects the physical and chemical properties of such products. The results of numerical modeling indicate that the material near the surface tends to flow, which may have a negative impact on the welding process. In addition, the distribution of stress in the tool–workpiece contact zone may make welding of the materials difficult. The results reported in this paper are preliminary and constitute a prelude to a more detailed analysis of bimetallic rod rolling.

Influence of contact form on mechanical wear characteristics of single diamond scratching on Ta12W

Purpose Mechanical wear is the main wear form of abrasive single crystal diamond (SCD) grit. The mechanical wear of SCD grit has a significant influence on the tool life and machining quality. This paper aims to investigate the influence of grit–workpiece contact form on the mechanical wear characteristics of SCD grit. Design/methodology/approach Three different grit–workpiece contact forms, which involved point/line/face contact forms, are investigated to reveal the wear mechanism of SCD grit scratching on Ta12W. The wear morphology, wear volume and scratching forces are measured, and the stress models of different contact forms are analyzed. Findings The results show that mechanical wear mainly occurs in the grit–workpiece contact area and increases gradually from contact area to entire SCD grit. The scratching forces vary with the mechanical wear progress of SCD grits. The SCD grit with point contact form is the most prone to produce wear. The SCD grit with face contact form can remove more material volume than the other two SCD grits, and it is the most wear resistant. The stress state is closely related with the mechanical wear of SCD grit. The contact form has a significant influence on the mechanical wear of SCD grit. Originality/value The results of this study can provide a theoretical basis for the fabrication of abrasive tools.

Discrete-time sliding mode control and observation via an adjustable accuracy disturbance estimation

Across the industrial sector, precision engineering represents a set of technologies that are the key to successful international competitive development. Ultra precision machine tools demand to control the point of contact of tool and workpiece within the range 100 nm to 0.1 nm. This work presents the novel Adjustable Accuracy (AA) approximation of a DT function based on user-defined previous steps values. Three control and observation problems are addressed with this novel AA Disturbance Estimation that allows to achieve an adjustable accuracy boundary layer of order O(Tβ) of the corresponding sliding manifold of the closed loop system in the presence of disturbances while avoiding the undesired chattering phenomenon with an ultimate bound that decay exponentially w.r.t. the used number of previous steps for the disturbance approximation. The corresponding simulations show the effectiveness of each scheme.