Problems in laser repair cladding a surface AISI D2 heat-treated tool steel

The aim of the present work is to establish the relationship between laser cladding (LC) process parameters (power, process speed, and powder feed rate) and AISI D2 tool steel metallurgical transformations, with the objective of optimizing the processing conditions during real reparation. It has been deposited H13 tool steel powder on some steel substrates with different initial metallurgical status (annealed or tempered) using a coaxial LC system. The microstructure of the laser clad layer and substrate heat-affected zone (HAZ) was characterized by optical microscopy, scanning electron microscopy, and electron backscattered diffraction. Results show that the process parameters (power, process speed, feed rate, etc.) determine the dimensions of the clad layer and are related to the microstructure formation. Although it is simple to obtain geometrically acceptable clads (with the right shape and dimensions) in many cases some harmful effects occur, such as carbide dilution and non-equilibrium phase formation, which modify the mechanical properties of the coating. Specifically, the presence of retained austenite in the substrate–coating interface is directly related to the cooling rate and implies a hardness diminution that must be avoided. It has been verified that initial metallurgical state of the substrate has a big influence in the final result of the deposition. Tempered substrates imply higher laser absorption and heat accumulation than the ones in annealed condition. This produces a bigger HAZ. For this reason, it is necessary to optimize the process conditions for each repair in order to improve the working behaviour of the component.     

A 3D modeling strategy to predict efficiently cutting tool wear in longitudinal turning of AISI 1045 steel

This work presents a numerical strategy to predict efficiently cutting tool wear in longitudinal turning. The full 3D cutting tool is discretized in elementary 2D sections. A FE based procedure is developed to compute in parallel the local contact pressure and sliding velocity along each section and update the tool profiles based on a tribologically identified wear equation. Results are merged to generate the 3D worn tool geometry while an iterative scheme is applied to achieve long simulated cutting time. Experimental cutting tests shown that a good agreement can be achieved in a reasonable computation time without any tuning parameter.     

A study of micropool lubricated cutting tool in machining of mild steel

This paper presents an experimental study of the performance of micropool lubricated cutting tool in machining mild steel. Microholes are made using femtosecond laser on the rake face of uncoated tungsten carbide (WC) cutting inserts. Finite element analysis is conducted to assess the effect of microholes on the mechanical integrity of the cutting inserts. Liquid (oil) and solid (tungsten disulfide) lubricants are used to fill the microholes to form micropools. A comparative study is conducted between micropool lubricated (surface-textured) cutting tools and dry/flood-cooled conventional (untextured) cutting tools. Three cutting force components are measured and compared. Tool–chip contact length and chip morphology are examined using optical microscope. It is found that the mean cutting forces (F_f, F_t, and F_c) are reduced by 10–30% with micropool lubrication. The chip–tool contact length is reduced by about 30%. Coiling chips are produced with micropool lubricated cutting tool while long and straight chips are formed with the conventional cutting tool. Liquid and solid lubricants are found to be equally effective in reducing the contact length and coefficient of friction at the chip–tool interface. There is no adverse effect on the performance of the insert with microholes on the rake face.     

Estimating the effect of cutting parameters on surface finish and power consumption during high speed machining of AISI 1045 steel using Taguchi design and ANOVA

The present paper outlines an experimental study to investigate the effects of cutting parameters on finish and power consumption by employing Taguchi techniques. The high speed machining of AISI 1045 using coated carbide tools was investigated. A combined technique using orthogonal array and analysis of variance was employed to investigate the contribution and effects of cutting speed, feed rate and depth of cut on three surface roughness parameters and power consumption. The results showed a significant effect of cutting speed on the surface roughness and power consumption, while the other parameters did not substantially affect the responses. Thereafter, optimal cutting parameters were obtained.     

Influence of the direction and flow rate of the cutting fluid on tool life in turning process of AISI 1045 steel

High-pressure coolant (HPC) delivery is an emerging technology that delivers a high-pressure fluid to the tool and machined material. The high fluid pressure allows a better penetration of the fluid into the tool–workpiece and tool–chip contact regions, thus providing a better cooling effect and decreasing tool wear through lubrication of the contact areas.The main objective of this work is to understand how the tool wear mechanisms are influenced by fluid pressure, flow rate and direction of application in finish turning of AISI 1045 steel using coated carbide tools.The main finding was that when cutting fluid was applied to the tool rake face, the adhesion between chip and tool was very strong, causing the removal of tool particles and large crater wear when the adhered chip material was removed from the tool by the chip flow. When cutting fluid was not applied to the rake face, adhesion of chip material to the face did occur, but was not strong enough to remove tool particles as it moved across the face, and therefore crater wear did not increase.     

Determining the influence of cutting fluids on tool wear and surface roughness during turning of AISI 304 austenitic stainless steel

Knowledge of the performance of cutting fluids in machining different work materials is of critical importance in order to improve the efficiency of any machining process. The efficiency can be evaluated based on certain process parameters such as flank wear, surface roughness on the work piece, cutting forces developed, temperature developed at the tool chip interface, etc. The objective of this work is to determine the influence of cutting fluids on tool wear and surface roughness during turning of AISI 304 with carbide tool. Further an attempt has been made to identify the influence of coconut oil in reducing the tool wear and surface roughness during turning process. The performance of coconut oil is also being compared with another two cutting fluids namely an emulsion and a neat cutting oil (immiscible with water). The results indicated that in general, coconut oil performed better than the other two cutting fluids in reducing the tool wear and improving the surface finish. Coconut oil has been used as one of the cutting fluids in this work because of its thermal and oxidative stability which is being comparable to other vegetable-based cutting fluids used in the metal cutting industry.     

TWEM, a method based on cutting forces—monitoring tool wear in face milling

One of the most important objectives in manufacturing is the intelligent machining system. To come to such a solution, the tool wear has to be determined on-line during the cutting process on unmanned machining systems. This contribution discusses the results experimentally obtained in face milling with a new rotating dynamometer. The paper introduces the concept of tool wear indicators which can be determined by simple analysis of the feature parameters of cutting force signals. The disturbance of the cutting force signals obtained by using the rotating dynamometer can be solved by applying tool wear indicators such as Normalized Cutting Force indicator (NCF) and Torque-Force Distance indicator (TFD). The Method for Tool Wear Estimation—TWEM is proposed.     

Statistical analysis of surface roughness and cutting forces using response surface methodology in hard turning of AISI 52100 bearing steel with CBN tool

The present work concerns an experimental study of hard turning with CBN tool of AISI 52100 bearing steel, hardened at 64 HRC. The main objectives are firstly focused on delimiting the hard turning domain and investigating tool wear and forces behaviour evolution versus variations of workpiece hardness and cutting speed. Secondly, the relationship between cutting parameters (cutting speed, feed rate and depth of cut) and machining output variables (surface roughness, cutting forces) through the response surface methodology (RSM) are analysed and modeled. The combined effects of the cutting parameters on machining output variables are investigated while employing the analysis of variance (ANOVA). The quadratic model of RSM associated with response optimization technique and composite desirability was used to find optimum values of machining parameters with respect to objectives (surface roughness and cutting force values). Results show how much surface roughness is mainly influenced by feed rate and cutting speed. Also, it is underlined that the thrust force is the highest of cutting force components, and it is highly sensitive to workpiece hardness, negative rake angle and tool wear evolution. Finally, the depth of cut exhibits maximum influence on cutting forces as compared to the feed rate and cutting speed.     

Identification of a friction model—Application to the context of dry cutting of an AISI 316L austenitic stainless steel with a TiN coated carbide tool

The characterization of frictional phenomena at the tool–chip-workpiece interface remains an issue. This paper aims to identify a friction model able to describe the friction coefficient at this interface during the dry cutting of an AISI316L austenitic stainless steel with TiN coated carbide tools. A new tribometer has been designed in order to reach relevant values of pressures, temperatures and sliding velocities. This set-up is based on a modified pin-on-ring system. Additionally, a numerical model simulating the frictional test has been associated in order to identify local phenomena around the spherical pin, from the standard macroscopic data provided by the experimental system. A range of cutting speeds and pressures have been investigated. It has been shown that the friction coefficient is mainly dependant on the sliding velocity, whereas the pressure has a secondary importance. Moreover, a new key parameter has been revealed, i.e. the average local sliding velocity at the contact. Finally, a new friction model has been identified based on this local sliding velocity.     

Prediction of the cutting conditions giving plastic deformation of the tool in oblique machining

A method is described for predicting cutting conditions at which the cutting edge starts to deform plastically when machining with oblique nose radius tools. It is shown how tool stresses and temperatures determined from machining theory can be used together with experimental high temperature compressive strength data for the tool material to make these predictions. A comparison made between predicted and experimental results for two plain carbon steel work materials and a range of cutting conditions shows good agreement.     

Tribology of nitriding layer, TiN coatings and their complex on AISI D2 steel

The sliding wear and impact wear resistances of D2 steel with nitriding layer, PVD titanium nitride coating and their duplex treatment were investigated. The experimental results suggest that the duplex treatment has the best sliding and impact wear resistances under experimental conditions. And the wear resistance of PVD titanium nitride is better than that of nitriding. The impact wear resistance and wear mechanism of all three surface layers remain unchanged under impact load of 0.2 J or 1 J. All samples end with the same symptom of flaking.     

Identification of a friction model at tool/chip/workpiece interfaces in dry machining of AISI4142 treated steels

The characterization of frictional phenomena at the tool–chip–workpiece interface remains an issue. This paper aims to identify a friction model able to describe the friction coefficient at this interface during the dry cutting of a AISI4142 treated steel with TiN coated carbide tools. A new tribometer has been designed in order to reach relevant values of pressures, temperatures and sliding velocities. This set-up is based on a modified pin-on-ring system. Additionally a numerical model simulating the frictional test has been associated in order to identify local phenomena around the spherical pin, from the standard macroscopic data provided by the experimental system. A range of cutting speeds and pressures has been investigated. It has been shown that the friction coefficient is mainly dependant on the sliding velocity, whereas the pressure has a secondary importance. Moreover a new key parameter has been revealed, i.e. the average local sliding velocity at the contact. Finally a new friction model has been identified based on this local sliding velocity.     

PCBN刀具干车淬硬钢时倒棱前角对切削力和刀具磨损的影响

PCBN刀具磨出负倒棱是为了加强刀具的刃口强度，以减少刀具加工时可能出现的破损情况。本文通过对PCBN刀具加工淬硬轴承钢GCr15的一系列试验数据加以分析，得出倒棱前角和切削力、刀具磨损之间的关系，进而得出在实际加工情况下应该采用的最佳倒棱前角值。试验表明：当倒棱前角取15度且切削速度为125m／s时，刀具具有最好的加工效果，不但切削力可以达到最小值，刀具磨损最轻，而且刀具寿命也达到了最大值。     

Sintering behaviour and fracture toughness characterization of D2 matrix tool steel,comparison with wrought and PM D2

A steel based on D2 tool steel without primary carbides (designated as D2 matrix steel) has been produced by several PM densification routes. Its toughness has been tested together with wrought and HIPed D2 with different microstructural characteristics. The presence of primary carbides is responsible for a dramatic decrease in the toughness of D2 steels compared with D2 matrix steel.     

The investigation on the prediction of tool wear and the determination of optimum cutting conditions in machining 17-4PH stainless steel

The purpose of this paper is to develop a predictive model for the prediction of tool flank wear and an optimization model for the determination of optimum cutting conditions in machining 17-4PH stainless steel. The back-propagation neural network (BPN) was used to construct the predictive model. The genetic algorithm (GA) was used in the optimization model. The Taguchi method (TM) was used to find the optimum parameters for both models, respectively. Two steps of experiments have been carried out by machining 6 mm length and 90 mm length of the workpiece, respectively. The experimental scheme was arranged by using an orthogonal array of TM. It has been shown that the predictive model is capable of predicting the tool flank wear in an agreement behavior. The optimization model has also been proved that it is a convenient and efficient method to find the optimum cutting conditions associated with the maximum metal removal rate (MMRR) under different constraints. The constraint is the tool flank wear that can be determined from the predictive model. Furthermore, the systematic procedure to develop the models in this paper can be applied to the usage of the predictive or optimized problems in metal cutting.     

Fatigue failure of coated carbide tool and its influence on cutting performance in face milling SKD11 hardened steel

Failure patterns of coated carbide tool were investigated by high-speed face milling of the hardened steel SKD11. Tool failure surface morphology, cutting force and machined surface roughness were also analyzed to reveal the failure mechanisms. The results indicated that the dominant failure pattern of coated carbide tool was breakage. The primary mechanism of tool breakage was fatigue fracture. Under different cutting speeds, the distinctive morphologies of fatigue fracture were presented on the failure surfaces. At low cutting speeds, many fatigue sources were observed on the rake face. The distance between fatigue sources and tool nose was approximately two times of the depth of cut. With the increase of cutting speed, the fatigue striations and riven patterns were observed at the fracture surface. In addition, the fatigue steps and crack deflection were found under high cutting speeds. The main fracture mode was intergranular fracture at lower cutting speeds. However, it was transgranular fracture at higher cutting speeds. Furthermore, the irregular fracture surfaces at low cutting speeds and at high cutting speeds contribute to a larger cutting force increment compared with the medium cutting speeds. The increment of surface roughness in the initial and severe wear stages was lower than that in the steady wear stage, while the deviation of surface roughness was relatively large.     

Analysis of the influence of tool type, coatings, and machinability on the thermal fields in orthogonal machining of AISI 4140 steels

Micro-thermal imaging was used to determine the amount of heat flowing into the tool, chip and workpiece during orthogonal cutting at speeds up to 400 m min⁻¹. Two AISI 4140 steels with different machinability ratings and three types of tools were compared: (i) uncoated with 0° rake angle, (ii) coated with −6° rake angle and (iii) coated with chip breaker. A control volume approach was used to estimate the energy partition from thermal images and energy outflow was compared to direct measurement of the cutting power. This provides a new physical tool for examining machinability, tool wear and subsurface damage.     

Chip morphology of normalized steel when machining in different atmospheres with ceramic composite tool

Dry cutting tests in air and nitrogen atmospheres with a ceramic cutting tool were carried out on normalized AISI 1045 steel. SEM and EDX techniques are employed to observe the chip morphology and tribological mechanisms are simultaneously discussed. The finite element model of chip formation was created to determine the effective stress and strain distributions in the chip and workpiece. Compared in nitrogen, the friction coefficient in air was reduced when the cutting speed is at 160 m/min and the feed rate is 0.1 mm/r. Experimental data and observation revealed the formation of a lubricating film at the tool-chip interface, which related to the difference chip morphology in air and nitrogen.