A Note on Interpreting Tool Temperature Measurements from Thermography

Thermography (thermal imaging) is a well-established experimental method for studying cutting tool temperature distributions. In one form, cutting edge temperatures within the chip / tool contact area are deduced from thermal images of tool faces normal to the cutting edge but offset from the contact region. In general practice, the offset is made as small as possible (<< 1 mm) and it is assumed that the observed temperature is the same as that within the contact. In this short communication an approximate analytical model is developed for the influence of the offset on the observed temperature. The predictions from the model are compared with previously unpublished existing results on the machining of Ti alloys (Ti6Al4V and Ti5Al4V) and on steel (AISI 4140). It is shown that ignoring the offset may introduce underestimates of cutting edge temperature of ≈ 30% or more. This is large compared to the usually considered uncertainties of ± 5% from camera and tool emissivity calibration. There is a need for a dedicated study of this effect

Effect of heat Treatment Conditions on the Machinability of Ti64 and Ti54 M Alloys

Orthogonal tests on cylindrical workpieces were carried out to analyze the effect of heat treatment on the machinability of newly developed Ti54M titanium alloy in comparison with Ti64. This paper focuses on the comparison of forces and temperature of the tool during dry orthogonal cuttings of Ti64 and three different heat treated Ti54M alloys. Forces and temperature are mainly affected by variation in cutting speed and feed, therefore, the depth of cut is maintained constant while cutting speed and feed are varied. Forces and temperature have been measured and chips are analyzed to establish a direct relationship between machinability and the different heat treatment conditions

Metal cutting experiments and modelling for improved determination of chip/tool contact temperature by infrared thermography

Temperature measurement in metal cutting at the chip and work contact is of central importance due to temperature dependence of tool wear and surface integrity. Infrared thermography is commonly employed to determine the tool side face temperature in orthogonal cutting but temperature needs to be estimated at the tool chip contact area. This experimental and modelling study of AISI 4140 steel and Ti6Al4V titanium alloy cut respectively by P and K grade cemented carbide tools at practical cutting speeds and feeds shows the relationship between side face and in-contact temperature, for the more certain use of the infra-red thermography method

Microstructural aspects of the transition between two regimes in orthogonal cutting of AISI 1045 steel

In depth understanding of tool-chip friction behavior is a significant aspect for tool wear performance in steels. In the present work attention has been paid to the strain mode of the chip section in contact with the rake surface of the tool, and its influence on the mechanics of material removal. There is a multitude of evidence for the existence of qualitatively different cutting regimes in orthogonal machining of annealed AISI-1045 steel with uncoated P15 carbide cutting tools in dry conditions at cutting speeds between 5 and 200 m/min. The evaluation of chip morphology and microstructure, and cutting and feed forces, revealed an abrupt step-like transition at a cutting speed in the range of 50–60 m/min, which was attributed to the transition from built-up edge (BUE) mode developed at low cutting speed, to the mode at which the chip slides directly over the tool surface. These qualitatively distinct mechanisms of tool-chip interaction are determined by two different microstructural effects: work hardening by severe plastic deformation and microstructural softening by dynamic recrystallization (DRX). It is argued that the onset of DRX is the reason for further instability of BUE and thus is the main cause of change of the cutting regime

Experimental investigation of contact forces and temperatures in rubbing interactions of honeycomb interstate seals

The new architecture of high velocity aircraft engines includes labyrinth-honeycomb interstate seals to improve the engine’s stability. To increase these engines capacity a commonly used strategy is to reduce the clearance between the blades and the sealing system. However, this reduction causes non-desired contacts (rubbing) between the rotating and static components of the engine. This rubbing interaction has an adverse effect on the engine life (wear and thermal cracking) and efficiency. In this work, experimental tests were carried out to recreate the rub between an F110 steel fin and a Hastelloy X honeycomb seal. A conventional CNC machine controlled the sliding and penetration velocities, and the interaction forces and fin tip temperatures were measured during the rub. Results demonstrate the dependence that both, interaction forces and tip temperatures, have with sliding and penetration velocities. However, it is clear that this influence is more pronounced in relation to the sliding velocity

Mechanical properties of friction induced nanocrystalline pearlitic steel

Nanocrystalline structured variants of commercially available alloys have shown potential for boosting the mechanical properties of these materials, leading to a reduction in waste and thereby retaining feasible supply chains. One approach towards achieving these nanostructures resides in frictional treatments on manufactured parts, leading to differential refinement of the surface structure as compared to the bulk material. In this work the machining method is considered to be a testing platform for the formation and study of frictional nanostructured steel, assembly of which is stabilized by fast cooling of the produced chip. Analysis of the mechanical properties has shown extraordinary results at the surface, over 2000 MPa of strength on AISI1045 steel, more than three times the strength of the base material, demonstrating at the same time a reduction of 15% in the elastic modulus. The microscopic analysis suggests a reassembly of the elements in a new lattice of carbon supersaturated nano-ferrite

Uncertainty of Temperature Measurements in Dry Orthogonal Cutting of Titanium Alloys

Infrared radiation thermometer is used to measure the temperature of tool during dry orthogonal cutting of titanium alloys. The accuracy of measured temperature depends on several parameters such as the experimental set-up, physical acquisition data system and physical characteristic of the tool. These parameters are identified, their uncertainty estimated and the way they influence the final temperature discussed

Prediction of Surface Roughness of SLM Built Parts after Finishing Processes Using an Artificial Neural Network

A known problem of additive manufactured parts is their poor surface quality, which influences product performance. There are different surface treatments to improve surface quality: blasting is commonly employed to improve mechanical properties and reduce surface roughness, and electropolishing to clean shot peened surfaces and improve the surface roughness. However, the final surface roughness is conditioned by multiple parameters related to these techniques. This paper presents a prediction model of surface roughness (Ra) using an Artificial Neural Network considering two parameters of the SLM manufacturing process and seven blasting and electropolishing processes. This model is proven to be in agreement with 429 experimental results. Moreover, this model is then used to find the optimal conditions to be applied during the blasting and the electropolishing in order to improve the surface roughness by roughly 60%

Inverse Identification of the Ductile Failure Law for Ti6Al4V Based on Orthogonal Cutting Experimental Outcomes

Despite the prevalence of machining, tools and cutting conditions are often chosen based on empirical databases, which are hard to be made, and they are only valid in the range of conditions tested to develop it. Predictive numerical models have thus emerged as a promising approach. To function correctly, they require accurate data related to appropriate material properties (e.g., constitutive models, ductile failure law). Nevertheless, material characterization is usually carried out through thermomechanical tests, under conditions far different from those encountered in machining. In addition, segmented chips observed when cutting titanium alloys make it a challenge to develop an accurate model. At low cutting speeds, chip segmentation is assumed to be due to lack of ductility of the material. In this work, orthogonal cutting tests of Ti6Al4V alloy were carried out, varying the uncut chip thickness from 0.2 to 0.4 mm and the cutting speed from 2.5 to 7.5 m/min. The temperature in the shear zone was measured through infrared measurements with high resolution. It was observed experimentally, and in the FEM, that chip segmentation causes oscillations in the workpiece temperature, chip thickness and cutting forces. Moreover, workpiece temperature and cutting force signals were observed to be in counterphase, which was predicted by the ductile failure model. Oscillation frequency was employed in order to improve the ductile failure law by using inverse simulation, reducing the prediction error of segmentation frequency from more than 100% to an average error lower than 10%

Evaluation of different flow stress laws coupled with a physical based ductile failure criterion for the modelling of the chip formation process of Ti-6Al-4V under broaching conditions

During the machining of Ti-6Al-4V the changing deformation mechanisms produce a complex microstructure of segmented chips, which directly influenced tool-wear and process stability. Numerical simulation could give an insight into the physical phenomena involved in chip segmentation, but its accuracy is directly related to the reliability of the input parameters. In this work, therefore, three different flow stress law were evaluated coupled with a physical based ductile failure criterion, which depends on stress triaxiality and temperature. To this end, the flow stress laws were implemented in the finite element software AdvantEdge by programming user-defined subroutines. The resulting FEM models were compared with orthogonal cutting experimental tests (tubular/linear), analyzing different fundamental outputs (machining forces, temperatures in the workpiece and chip morphology). All the FEM models showed good agreement with the experimental results