This work presents an analysis of transient conduction heat transfer in a semi-infinite solid with uniform surface heating of intensity varying as a Gaussian, without a physically meaningful start. Practical and accurate explicit, closed-form expressions for the characteristic values of the temperature profile are presented. Exact solutions were obtained for the surface temperature and its heating or cooling rate, while approximate solutions were obtained for the subsurface temperature profile. Explicit expressions are presented for surface temperature, surface heating or cooling rate, maximum surface temperature and the time at which it is attained, maximum distribution parameter of the heat source which guarantees the attainment of a target temperature and its asymptotic behavior at early and late times, maximum heating and cooling rates and the times and temperatures at which they happen, asymptotic behavior of surface heating and cooling rate at early, late, and intermediate times, maximum penetration of a target temperature and their associated times and a function for intermediate cases of maximum temperature penetration, temperature profile for the entire time domain. The expressions presented do not require numerical methods or specialized software, and their computational time is negligible compared to numerical models.

The thermal and mechanical behavior of SLM-fabricated Invar 36 was investigated as a function of process parameters and post-processing heat treatments commonly applied in aerospace applications. Density exhibits a non-monotonic dependence on volumetric energy density (VED), reaching a maximum at 52.08 J mm−3, with deviations leading to increased porosity. Yield strength, ultimate tensile strength, and elongation at break are largely insensitive to process parameters, although elongation shows a weak maximum near the optimal VED. The coefficient of thermal expansion (CTE) increases by over an order of magnitude from 20 to 350 °C. One heat treatment was found to optimize CTE, producing nearly identical behavior to the as-built specimens, while the other two treatments result in systematically higher CTE, on average 65

In this study, a 3D thermo-mechanical finite element model was developed in Abaqus/Explicit to simulate the friction stir welding (FSW) of AA7075-T6 aluminium alloy, incorporating a Johnson–Cook constitutive law to represent the material’s viscoplastic behaviour. The model was validated against experimental temperature measurements and microstructural observations. Two tool geometries, a flat-shouldered tool and a scrolled-shoulder threaded tool, were compared under rotational speeds ranging from 1100 to 1700 rpm and welding speeds between 70 and 120 mm/min. The simulations revealed that rotational speed is the dominant parameter influencing heat generation, with the peak temperature rising by approximately 250°C as the rotational speed increased from 1100 to 1700 rpm. Conversely, increasing the welding speed from 70 to 120 mm/min reduced the peak temperature by about 100–130°C, due to shorter tool–workpiece interaction times and reduced frictional heat input. At 1320 rpm and 70 mm/min, the maximum temperature reached 253°C numerically and 187°C experimentally, showing good qualitative agreement between model and experiment. The use of a scrolled-shoulder tool produced higher and more uniformly distributed temperatures, improving material flow and reducing surface defects compared with the flat-shouldered design. Overall, the validated model accurately captured the thermal behaviour of FSW, demonstrating that optimised tool geometry and process parameters can significantly enhance joint quality, refine the stir zone microstructure, and minimise thermal gradients in high-strength aluminium alloys.

Incremental sheet forming is a viable method for manufacturing highly customized components from non-conventional materials. Among these, niobium is a metal of growing interest due to its potential in various technological applications. In this experimental study, the incremental forming of high-purity annealed niobium sheets was investigated, with particular attention given to the surface finish of the formed parts. To this end, the surface morphology of the components, specifically fixed wall conical frusta, and the forming forces were analyzed. The results indicate that, despite the material’s notable formability, the incrementally formed niobium surfaces exhibit poor quality. This is attributed to the unique properties of niobium, suggesting that the development of surface treatment strategies is advisable to improve this aspect.

Explicit closed-form expressions for the velocity, depth of ablation front, and penetration of the thermal profile valid up to a Stefan number of 30 (the vast majority of technological materials have a value below 10) and for all times in the problem of ablation under a constant heat flux are derived. The analysis is based on the blending of the asymptotic, transient, and steady-state, regimes of the above-mentioned quantities. Expressions to estimate the characteristic values representative of intermediate behaviors are also proposed. The prediction of depth and velocity of penetration calculated with the expressions proposed resulted in a maximum absolute error below 8% in comparison to the numerical solution. This model assumes a thick substrate and a criterion for minimum thickness is also proposed. Equations to predict the thickness of the heat-affected zone and of the mushy zone in ablation are also derived. The ultimate aim of this work is to provide simple and accurate expressions to predict the progress of the ablation or to select optimal process parameters in case ablation is used in manufacturing.

In recent years, polymer sheets have been formed by a relatively innovative technology, born for metals and in line with the layered manufacturing principle of rapid prototyping, the incremental sheet forming. This process guarantees high customization and cost-effectiveness but, at the same time, activates some peculiar defects like the twisting phenomenon. To reduce the risk of twisting and the occurrence of failures, it is preferable to reduce the forming forces and one of the solutions is the choice of opportune toolpath strategies. Concerning this, the present experimental research is along the same lines as recent numerical works of the authors; thermoplastic sheets were worked by incremental forming by varying the toolpath strategy. Following the realization of cone frusta, the forming forces and the deformation of the sheets were monitored, to investigate a toolpath strategy capable of reducing the risk of failures and defects for incrementally formed polymer sheets.

Metals and alloys continue to play a crucial role in the design and construction of load-bearing structures and mechanical components [...]

A novel empirical equation is presented to evaluate the Specific Energy Consumption (SEC) in face milling of steel. The proposed approach introduces a corrective factor to estimate the softening of work materials due to thermal effects at large cutting velocity. An experimental campaign on AISI 304 was carried out to investigate the predictive capability of the proposed model. A complete design matrix varying cutting velocity, radial depth of cut and feed rate was performed while measuring the average power consumed as response variable. Experimental results show that SEC reaches a maximum with the increase in the cutting speed. It is demonstrated that the SEC reduction observed at high cutting speeds is due to thermal softening induced by the higher temperatures attained in the work material. The formula proposed aims at providing a simple and accurate expression to select the process parameters in an energy saving perspective, especially in high-speed milling.

Lap joints were friction stir welded in AA 7075-T6 at 1320 rpm and using two welding speeds: 70 mm/min and 120 mm/min. The temperature profiles of the weld zone were registered during the process; furthermore, the microhardness, tensile strength, and microstructure of the joints produced were examined. This study brings new insights into the thermomechanical behavior of the material during the process. The peak temperature obtained with the lower welding speed (70 mm/min) is 10% higher than that obtained with the higher speed (120 mm/min). Moreover, a 5% increase in microhardness and a 6% increase in tensile strength were were observed increasing the welding speed. Addition-ally, the microstructure examination demonstrated that, by decreasing the welding speed, the larger interaction between the tool and the material results in a deeper stir zone due to the increased heat diffusion downwards to the material. This heat flow affects the thermal profile and influences the resulting mechanical properties of the welded joints.

This study shows that the progressive adhesion of weld material to the tool in friction stir welding AA 2024-T3, up to tool saturation, brings about a decrease in power consumption until a plateau is reached. The cause of this behavior is the hindering of the stirring action of the tool due to the material accumulated on it. The built-up material changes the nature of the tool/material interaction and then the friction condition at their interface. The direct consequence is a decrease in the shearing strain and therefore in the heat generated by friction. Bits of this adhering material break off from the tool at intervals. Macro and micro detachments are identified. Micro-detachments happen continuously at small periodic intervals and produce vibrations. The amplitude of these vibrations increases in all their characteristic spectral components up to tool saturation. Macro-detachments generate oscillations in power consumption and leave galling on the weld bead.

The lap joints of AA 7075-T6 aluminum alloy were assembled using the friction stir welding (FSW) technique. Experimental studies were performed to characterize the thermomechanical properties of these welds. The main goal of this research was to comprehensively assess the thermomechanical behavior of AA 7075-T6 aluminum alloy under FSW conditions. Tests were carried out at a tool rotational speed of 1320 rpm and at two advancing speeds of 70 mm/min and 120 mm/min, selected based on a previous study aiming to optimize the heat input during the FSW process. The experimental investigations involved the characterization of temperature profiles during welding, mechanical properties such as microhardness and tensile strength, and microstructure examination at the two advancing speed conditions. This study revealed that the welding speed has an obvious influence on the material thermal behavior during the FSW process. Indeed, the peak temperature obtained with a lower welding speed (70 mm/min) was higher by almost 10% compared to that obtained with a higher speed (120 mm/min). Moreover, by increasing the welding speed, the mechanical characteristics, such as microhardness and tensile strength, were increased by almost 5% for the mean microhardness and 6% for the ultimate tensile strength. Additionally, the microstructure examination demonstrated that, by decreasing the welding speed, more interaction between the tool and the material is observed, resulting in a deeper stir zone due to increased heat dissipation downwards into the material, affecting the thermal profile and influencing the resulting mechanical properties of the welded joint.

A novel semi-empirical equation in explicit form is presented for the estimation of weld penetration in high productivity Gas Tungsten Arc Welding (GTAW). The approach followed in developing the final expression is based on the methodology of scaling analysis applied to the description of the process according to the heat transfer theory. The equation developed is applicable under the condition of gouging penetration usually encountered in arc welding processes and accounts for heat absorbed by phase change, heat carried away by the molten metal, heat lost by conduction in the substrate, and the effect of penetration on arc length. The equation proposed requires as inputs: specific and latent heat, density, and solidus temperature of the substrate and welding speed, current, voltage, and stand-off distance. Welding experiments on five classes of materials (ASTM A36 structural steel, AISI 304 stainless steel, CP aluminium, AA 5083, and CP titanium) were performed to validate the model proposed under welding speed ranging from 3.9 to 19 mm/s and current going from 240 to 700 A. Predictions of penetrations calculated by the final model result in an mean percentage error of −0.87% with a standard deviation of 9.52%. The ultimate purpose of this model is to provide a simple and accurate expression useful for the selection of process parameters when using high productivity GTAW, especially to join novel alloys.

A novel semi-empirical equation in explicit form is presented for the estimation of weld penetration in high productivity Gas Tungsten Arc Welding (GTAW). The approach followed in developing the final expression is based on the methodology of scaling analysis applied to the complete description of the process according to the heat transfer theory. The equation developed is applicable under the condition of gouging penetration usually encountered in arc welding processes and it accounts for heat absorbed by phase hange, heat carried away by the molten metal, heat lost by conduction in the substrate, and the effect of penetration on arc length. The ultimate purpose of this model is to provide a simple and accurate expression useful for the selection of process parameters when using high productivity GTAW, especially to join novel alloys.

A new dimensionless form of the solution to the problem of a Gaussian heat source in steady state on a semi-infinite solid is presented. Applying dimensional analysis, it is shown that dimensionless expressions of all characteristic values associated to an isotherm, as its maximum width or depth, are function only of the Rykalin number, Ry, and the dimensionless distribution parameter of the source, σ∗. Maps delimiting domains of Ry and σ∗ that give specific regimes of the solution are developed. Using these maps, it is possible to know a priori the regime expected for the solution without solving the equation. The proposed expressions can be useful to predict the behaviour of the weld width and depth as function of process parameters in a number of processes involving a Gaussian heat source.

The cold wiredrawing process constitutes a classical-tribological system in which a stationary tribe-element (die) is in contact with a tribe-element in relative motion (wire) and both interacting with the interfacial tribe-element (lubricant). This condition is reflected in the effect of friction as a function of the drawing speed and temperature, and directly affects the wearing of the surface into the die and the final quality on the drawn wire. The aim of this work has been to determine the best conditions to process ETP-copper using two different types of oil/water emulsion lubricants. For this purpose, six different die geometries have been proposed and a set of tests have been carried out at different speeds (between 1 and 21 m/s) to determine those combinations that give a lower value in the required drawing force ( F d ). The experiments allowed to know the friction coefficient ( µ) , the temperature profile inside the drawing die and in the lubricant and also the mean roughness (Ra) in the drawn product. The results have shown that drawing speeds above 10 m/s significantly decrease the drawing force and, as a consequence, the friction effect on the interface. The best results have been achieved in the combinations of the lower die angle (2 β = 14°) with drawing speeds between 17 and 18 m/s with both types of lubricants used, obtaining the lower values of the friction coefficient between µ = 0.10–0.15 with the lubricant type D (Agip S234-60 oil at 7% concentration). It has been found that those tests carried out with dies with a smaller approach angle have generally made it possible to obtain better qualities in the final product. Additionally, FEM simulations have been done to analyse those cases with the lower values of µ , throwing values of F d that are consistent with those measured in the experimental setting and allowing to better understand the behavior of the material as it passes through the die.

The efforts to increase the operating speed of the wire drawing process play a crucial role regarding the industrial productivity. The problem is closely related to various features such as heat generation, material plastic deformation, as well as the friction at the wire/die interface. For instance, the introduction of specific lubricants at the interface between the die and the wire may efficiently reduce the friction or in another context, induce a difference in friction among different regimes, as for the case of hydrodynamic lubrication. The present study systematically explores various aspects concerning the drawing process of an electrolytic tough pitch copper wire. To be specific, the drawing speed, drawing force, die temperature, lubricant temperature, and stress distributions are analysed by using experimental as well as numerical approaches. The obtained results demonstrate how the drawing stress and temperature are affected by the variation of the friction coefficient, die geometry, and drawing speed. It is argued that such a study might help in optimizing the operational parameters of the wire drawing process, which further leads to the improvement of the lubrication conditions and product quality while minimizing the energy consumption during the process.

An experimental campaign of wire drawing was carried out under different conditions of average die pressure. Experiments were carried out measuring the drawing force and the temperature at the exit of the deformation zone with the use of a thermocouple closely located to the wire-die interface. Dies of three different semi-angles (6°, 7° and 9°), were employed to obtain different values of die pressure, while different lubrication regimes were achieved varying the drawing speed in the range 1–22 m/s. It was demonstrated that lubricating regimes of lower friction coefficient are achieved at smaller values of the drawing speed with increasing the die pressure. Likewise, the hydrodynamic regime arises at lower drawing speeds by increasing the die semi-angle. For example, it was observed that the hydrodynamic regimes developed at 19 m/s for the 6° die but at 15 m/s for the 9° die. This behaviour was correlated to the response of the lubricant viscosity to the die pressure by means of the Hersey analysis. The consequences of this finding on the problem of optimizing the die angle with the objective to reduce the drawing stress are discussed. On this basis, it is shown that the optimum die angle decreases as the drawing speed increases, other things being equal.

The selective laser melting of mechanically mixed Inconel 718 and copper powders is studied by processing feedstocks of different Cu content at various energy inputs. It was observed that with the increase of the Cu content the width of the molten pools decreases while the porosity of the samples increases. Lower values of energy input enhance the effects brought about by the addition of Cu. Decreasing the Cu weight fraction or, inversely, increasing the energy input, the tensile and yield strengths progressively increase due both to the reduced content of the softer component, such as the Cu powder, and to the decrease in porosity. Because of the porosity increase, the decrease in hardness and increase in thermal conductivity, registered on incrementing the copper content in the feedstock, are, respectively, greater and lower than expected. The obtained results show the possibility of manufacturing dense part by SLM using Cu-Inconel 718 mixed powders.

The effect of tool wear on dimensional and geometrical accuracy of holes machined by peck drilling in carbon fibre reinforced plastic (CRFP) and titanium (Ti) stacks is studied. Coated and uncoated tungsten carbide drills of both fine and ultra-fine microstructures are employed to assess the importance of grain size and coating on hole accuracy. Hole profiles show two maxima: one at the hole entry and the other at the CFRP/Ti interface. Hole cylindricity as function of tool wear shows a minimum. It firstly decreases due to flank wear and subsequent reduction of the drill diameter. Then the rise of tool instability prevails with the result that an increase of the cylindricity with tool wear is brought about. Less wear-resistant drills attain this minimum in a shorter time of cutting.

The effect of heat input rate, hatch spacing, and focus offset upon microstructure, hardness, and roughness of EBM-manufactured Ti - 6Al-4V titanium alloy was studied via a factorial experiment. It had been found that a coarser microstructure is generated for high heat input and low line offset. Increasing the heat input or conversely decreasing the line offset leads to a higher lath thickness with consequent lower hardness. The roughness of the top surfaces decreases with the increase of the heat input and the focus offset or with the decrease of the line offset. On the other side, the roughness of the side surfaces is dependent only on the heat input and it is proportional to the latter.