Surface integrity

Titanium and nickel alloys represent a significant metal portion of the aircraft structural and engine components. When these critical structural components in aerospace industry are manufactured with the objective to reach high reliability levels, surface integrity is one of the most relevant parameters used for evaluating the quality of finish machined surfaces. The residual stresses and surface alteration (white etch layer and depth of work hardening) induced by machining of titanium alloys and nickel-based alloys are very critical due to safety and sustainability concerns. This review paper provides an overview of machining induced surface integrity in titanium and nickel alloys. There are many different types of surface integrity problems reported in literature, and among these, residual stresses, white layer and work hardening layers, as well as microstructural alterations can be studied in order to improve surface qualities of end products. Many parameters affect the surface quality of workpieces, and cutting speed, feed rate, depth of cut, tool geometry and preparation, tool wear, and workpiece properties are among the most important ones worth to investigate. Experimental and empirical studies as well as analytical and Finite Element modeling based approaches are offered in order to better understand machining induced surface integrity. In the current state-of-the-art however, a comprehensive and systematic modeling approach based on the process physics and applicable to the industrial processes is still missing. It is concluded that further modeling studies are needed to create predictive physics-based models that is in good agreement with reliable experiments, while explaining the effects of many parameters, for machining of titanium alloys and nickel-based alloys.

The process of cryogenic machining, due to increased demand for environmentally friendly manufacturing processes, has seen a growing interest in the machining community. This article presents an overview of cryogenic machining and its induced surface integrity characteristics such as surface roughness, topography, grain refinement and machining-induced layer, microhardness, phase transformation, residual stress and fatigue life in machining of various materials including difficult-to-machine materials, aerospace alloys, lightweight materials, etc. The effect of cryogenic machining on surface integrity characteristics is discussed, and compared with dry, Minimum Quantity Lubrication (MQL), and flood-cooled machining processes. In addition to being an environmentally friendly process, this study shows that cryogenic machining significantly contributes to improved functional performance of machined components through its superior and more desirable surface integrity characteristics.

With the demand of hig
automobile industries, the focus of machining is t
of the machined part with a less tool wear and cost. Aluminium and Al
best suitable material for these purposes, because of its peculiar proper
phase of Al has an important role in case of surface roughness of machined part as
well as the tool wear of the tools.
parameters as well as the chemical nature of tool and
depends upon the hardness and strength of workpiece and tool material.
an attempt has been made by dry turning of pure aluminium with advanced tools like
uncoated WC, WC+TiN, WC+Ti
speed range of 400 to 700 m/min wi
measured using highly précised
formation were observed using SEM
SEM and Elemental mapping technique

Magnesium-Calcium (Mg-Ca) alloy has received considerable attention as an emerging biodegradable implant material in orthopedic fixation applications. The biodegradable Mg-Ca alloys avoid stress shielding and secondary surgery inherent with permanent metallic implant materials. They also provide sufficient mechanical strength in load carrying applications as opposed to biopolymers. However, the key issue facing a biodegradable Mg-Ca implant is the fast corrosion in the human body environment. The ability to adjust degradation rate of Mg-Ca alloys is critical for the successful development of biodegradable orthopedic implants. This paper focuses on the functions and requirements of bone implants and critical issues of current implant biomaterials. Microstructures and mechanical properties of Mg-Ca alloys, and the unique properties of novel magnesium-calcium implant materials have been reviewed. Various manufacturing techniques to process Mg-Ca based alloys have been analyzed regarding their impacts on implant performance. Corrosion performance of Mg-Ca alloys processed by different manufacturing techniques was compared. In addition, the societal and economical impacts of developing biodegradable orthopedic implants have been emphasized.

This paper presents the detailed investigation of surface integrity when end milling AISI H13 tool steels using P10 TiN coated carbide and P20 uncoated cermets tools. The machining parameters studied were cutting speed (224 m/min-355 m/min), feed rate (0.1 mm/tooth-0.25 mm/tooth) and depth of cut (0.3 mm-0.8 mm). The detailed microstructure analysis shows that worn out tools caused over heated of the machined surface and changed the microstructure of the work material. That change increased the hardness of the work material's machined surface, which is very hard and brittle, and generally referred as a white layer. The width formation of microstructure changes, increased with the increase in wear land and feed rate. A maximum of 550 HV was measured directly underneath the generated surface, i.e. 30% more as compared to the hardness of the basic material. This information is useful for the die and mould maker to select the best cutting condition to avoid such increase in hardness.

http://umrefjournal.um.edu.my/public/article-view.php?id=5162

300M steel is widely used in the aerospace industry to manufacture landing gears due to its ultrahigh strength and high fracture toughness. Surface integrity in the hard turning process (one of the final manufacturing processes in making landing gears) can be influenced by tool geometries and cutting conditions. An experimental study is conducted on 300M steel to understand the role of cutting tool geometry and cutting conditions on surface integrity (surface roughness and residual stresses). Cutting tool geometries are varied along the nose edge region (chamfer, hone, and chamfer-hone). These varied geometries are tested at different cutting conditions to highlight the combinational complexity of cutting edges and cutting conditions in producing surface roughness and residual stresses. The results show the necessity of edge preparation in improving machining surface integrity in such a material.

Surface integrity of machined components has a critical impact on their performance. Magnesium alloys are lightweight materials used in the transportation industry and are also emerging as a potential material for biodegradable medical implants. Surface integrity factors, such as grain size, crystallographic orientation and residual stress, have been proved to remarkably influence the functional performance of magnesium alloys, including corrosion/wear resistance and fatigue life. In this study, the influence of dry and cryogenic machining (liquid nitrogen was sprayed on the machined surface during machining) using different cutting edge radius tools on surface integrity was investigated. Compared with the initial material, cryogenic machining when using a large edge radius tool led to enhanced surface integrity in terms of the following: (1) improved surface finish; (2) significant grain refinement from 12 mm to 31 nm in the featureless surface layer; (3) large intensity of (0002) basal plane on the machined surface; (4) 10 times larger compressive areas in residual stress profiles; these changes should notably improve the functional performance of machined AZ31B Mg alloy. In addition to the frequently reported benefits on tool life, this study suggests that cryogenic machining may also enhance the surface integrity of the workpiece and improve the performance of machined components.

Poor corrosion resistance is one of the major disadvantages of magnesium alloys that inhibits their wide application. It was reported frequently that the alloys' microstructure has a significant influence on their corrosion resistance. In this study, cryogenic machining is used as a severe plastic deformation tool to modify the surface and subsurface microstructures of an AZ31 Mg alloy. Liquid nitrogen is applied to suppress grain growth caused by large heat generation during machining. "White layers", where grain boundaries were invisible, were shown to form on the surface and subsurface after machining. The hardness of this layer was about 60% larger than the bulk material. The tool edge radius and the cutting speed have profound influence on the microstructures. Preliminary results from immersion tests in simulated body fluid showed that the corrosion resistance of the AZ31 Mg alloy was enhanced due to the formation of white layer.

Shape memory alloys (SMAs) are unique class of smart materials with excellent physical, mechanical and biomedical properties, which have wide applications in several fields such as aerospace, robotics, biomedical, and dental etc. These alloys are well known for exhibiting shape memory effect (SME) and pseudoelasticity (PE), it is a well-established fact that they are required to be processed into functioning parts. The conventional machining affects the internal properties of shape memory alloys and hence, it is reported that nonconventional machining techniques are more suitable. Wire electro discharge machining (WEDM) is one of the nonconventional machining processes for machining complicated shapes without hampering the internal properties of such type of materials. In the present experimental investigation, wire electro discharge machining of Ti 50 Ni 40 Co 10 shape memory alloy (SMA) has been carried out and machining performances such as surface roughness (SR), and material removal rate (MRR) have been evaluated. Experimental results exposed that pulse on time, pulse off time and servo voltages are most influential process parameters on the responses. The machined surface has been charac-terised with respect to microstructure, microhardness, and phases formed.

An ultrafine-grained surface layer was produced on Mg-Al-Zn alloy by a new severe plastic deformation process, cryogenic burnishing. The total burnishing-influenced zone was found to be over 3.4 mm thick. A large increase in hardness from 0.86 to 1.35 GPa was obtained near the topmost surface, where grains were refined from 12 lm down to 263 nm. The corrosion resistance was significantly enhanced, which may due to the combined effects of grain refinement and strong basal texture.

Poor corrosion resistance is limiting applications of Mg alloys. However, the corrosion performance of an Mg alloy can be enhanced through modification of its microstructure. It has been reported in the literature that the microstructure, especially grain size of AZ31 Mg alloy, has a significant influence on its corrosion resistance. In this study, AZ31B discs were subjected to a novel mechanical processing method-cryogenic burnishing; the surface of AZ31B workpiece was burnished with a custom tool under a liquid nitrogen spraying condition. The processing led to a more than 3 mm thick surface layer with remarkably changed microstructures formed on the disc surface. Significant grain refinement occurred within this surface layer due to dynamic recrystallization induced by severe plastic deformation and effective cooling by liquid nitrogen. Both electrochemical method and hydrogen evolution method indicate that the corrosion resistance of the burnished surface was significantly improved.

This paper presents the detailed investigation of surface integrity when end milling AISI H13 tool steels using P10 TiN coated carbide and P20 uncoated cermets tools. The machining parameters studied were cutting speed (224 m/min-355 m/min), feed rate (0.1 mm/tooth-0.25 mm/tooth) and depth of cut (0.3 mm-0.8 mm). The detailed microstructure analysis shows that worn out tools caused over heated of the machined surface and changed the microstructure of the work material. That change increased the hardness of the work material's machined surface, which is very hard and brittle, and generally referred as a white layer. The width formation of microstructure changes, increased with the increase in wear land and feed rate. A maximum of 550 HV was measured directly underneath the generated surface, i.e. 30% more as compared to the hardness of the basic material. This information is useful for the die and mould maker to select the best cutting condition to avoid such increase in hardness.

http://ejum.fsktm.um.edu.my/ArticleInformation.aspx?ArticleID=762 
http://umrefjournal.um.edu.my/public/article-view.php?id=5162

This study presents experimental results of machined surface integrity of die material (AISI D2 hardened steel) when hot machining (induction heating) assisted end milling using coated carbide is applied. The aim of this work was to study the influence of induction heating temperature, cutting speed, and feed on the effects induced by hard milling on surface integrity (microhardness and work-hardening). Microhardness was measured to observe the distribution of the hardness beneath the surface and to determine the effect of induction heating on the micro-hardness distribution and work-hardening phenomena. The behaviour of microhardness induced in the subsurface region when end milling under room and induction heating cutting conditions using coated carbide inserts was also investigated. The surface integrity and subsurface alteration have been investigated by employing scanning electron microscope (SEM) and Vickers microhardness tester.

In this study, the feasibility of predicting surface integrity and residual stresses by using elastoviscoplastic finite element simulations and temperature-dependent flow softening constitutive material modeling is investigated. A friction determination method is proposed to identify friction coefficients in presence of tool flank wear. Serrated and cyclical chip formation has been simulated for using tools with and without flank wear. The predicted residual stresses and surface integrity is compared against experimental results from literature. Effect of friction on the residual stress profiles is also investigated. These results are highly essential in predicting machining induced microstructure alterations that are detrimental to fatigue life of nickel and titanium alloy components.

Nickel-based superalloy Inconel 718 is one of the hardest materials owing to its high hardness and additional physical properties. It is the most commonly used superalloy in gas turbine, aerospace, and automobile sectors. Micro-milling is generally employed for precision manufacturing of tiny structures, but it is difficult to obtain good surface quality with micro-milling Inconel 718 because of its excellent mechanical properties like high strength and hardness. Atmospheric pressure cold plasma jet can effectively improve surface wettability without changing surface micromorphology, which is expected to have positive lubricating effects in micro-machining of difficult-to-cut materials. In addition, minimum quantity lubrication can induce coolants into the machining area more efficiently, and is especially appropriate for micro-machining. In this paper, we propose a composite micro-milling method combining plasma jet and minimum quantity lubrication to machine Inconel 718. The effect of plasma jet on machinability is investigated by performing micro-milling experiments under different atmospheres (dry, nitrogen jet, plasma jet, minimum quantity lubrication, and plasma + minimum quantity lubrication). Surface roughness, cutting forces, and residual stress are the measures using corresponding techniques. The results indicate that the atmospheric pressure cold plasma jet can efficiently improve surface quality and reduce cutting forces of Inconel 718.

This paper investigates the 3D surface topography, 2D roughness profiles and micrographs were analyzed in the abrasive water jet (AWJ) cutting of AISI D2 steel kerf wall cut surfaces by varying water jet pressures and jet impact angles. In 3D surface topography, roughness parameters such as Sq, Ssk, Sp, Sv, Sku, Sz and Sa were improved
by various jet impact angles with different water jet pressures. However, the roughness parameters Ssk and Sku strongly depend on the water jet pressure and jet impact angle.This is confirmed by kerf wall cut profile structures. Fine irregularities of peaks and valleys are found on the AWJ cut surfaces, as evident from 2D roughness profiles. The SEM micrographs confirm production of an upper zone not very much damaged and a lower striation free bottom zone, by using the jet impact angle of 70o with a water jet pressure of 200 MPa. Finally, the results indicate a jet impact angle of 70o maintaining the surface integrity of D2 steel better than normal jet impact angle of 90o. The results are
useful in mating applications subjected to wear and friction. This has resulted in enhancement of the functionality of the AWJ machined D2 steel components.

Electrical Discharge Machining (EDM) is a commonly used process to manufacture of die and molds, due to the capacity of generating deep and complex cavities. The removal of material occurs from a series of discharges between electrode and workpiece. Discharges melt and vaporize material in form of debris, flushed away by the dielectric flow. This work presents AISI H13 steel surface integrity study, machined by EDM process using constant parameters and a copper electrode with different depths of cavity and pulse times. Textures, crack density, roughness and affected layer were investigated. The collected data was submitted to an ANOVA statistical test. The study showed cavity depth as the only significant factor in roughness. Affected layer thickness is not affected by cavity depth and pulse time. Cracks depth and concentration rise with the increase of pulse time and depth of the cavity.

Electrical discharging machining is a process that uses high-frequency electrical discharges to generate heat, melting and vaporising the workpiece material. Melted material is flushed away by dielectric flushing. However, only part of the molten material is removed, the remaining material resolidifies discharge craters, which affects the integrity of the workpiece. This paper discusses how the flushing flow and the radii of electrode under different machining conditions can affect the roughness and affected layer. Rectangular cavities were machined with a copper electrode in AISI H13 steel. Unilateral side flushing with an immersion flushing was used. An analysis of variance was used to verify the statistical relevance of the results. The obtained data appointed that, under the flushing condition used, independent of the electrode radii, some significant differences were found in roughness and scanning electron microscope (SEM) images. No difference was found in affected layer thickness in different analysed positions of flushing path.

Abstract Electrical discharging machining is a process that uses high-frequency electrical discharges to generate heat, melting and vaporising the workpiece material. Melted material is flushed away by dielectric flushing. However, only part of the molten material is removed, the remaining material resolidifies discharge craters, which affects the integrity of the workpiece. This paper discusses how the flushing flow and the radii of electrode under different machining conditions can affect the roughness and affected layer. Rectangular cavities were machined with a copper electrode in AISI H13 steel. Unilateral side flushing with an immersion flushing was used. An analysis of variance was used to verify the statistical relevance of the results. The obtained data appointed that, under the flushing condition used, independent of the electrode radii, some significant differences were found in roughness and scanning electron microscope (SEM) images. No difference was found in affected layer thickness in different analysed positions of flushing path.

In this study, the surface integrity of nickel-titanium (NiTi) shape memory alloys (SMAs) was investigated after face milling processes with cryogenically treated/untreated cemented carbide cutting tools at the conditions of dry cutting and minimum quantity lubrication (MQL) of cutting fluids depending on the changing cutting parameters. The integrity of surface layer of the workpiece material was evaluated according to the mean surface roughness, microstructure and hardness, as well as according to the resultant cutting force and flank wear of inserts. Cutting tests were carried out at three different cutting speeds (20, 35 and 50 m/min), feed rates (0.03, 0.07 and 0.14 mm/tooth) and a constant axial cutting depth (0.7 mm). The influence of these parameters on the surface integrity was extensively investigated. The face milling tests of NiTi SMA at optimal cutting parameters show that the surface integrity enhanced at a cutting speed of 50 m/min and feed rate of 0.03 mm/tooth using boron-added cutting fluid (EG + %5BX) with deep cryogenic heat treated (2 196°C) CVD coated S40T grade cutting tool. Under MQL conditions, the minimum mean surface roughness (0.278 lm), resultant cutting force (268.2 N) and flank wear (0.18 mm) were obtained due to the high thermal conductivity and lubrication property of EG + %5BX cutting fluid. The highest hardness values (343 HV) were measured at the zone subjected to the highest deformation, while the lowest one (316 HV) was measured at the zone at the least deformation.

SAILMA350 has strong tensile strength and fatigue resistance. WEDM is also Applied in the mold and die field manufacturing pressure vessels and the automotive industry complex shape machining. These properties determine the form and shape of the material. A main Cut followed by a cut of trim improved the surface quality of the material of the SAILMA350. The result revealed surface topography with a dominant, the area affected by heat and white layer, and a pulse (on time and off time) during trim cuts at high micro cracks. Using SEM micrographs, topography and microstructural changes were reported.

300 M steel is widely used in the aerospace industry to manufacture landing gears due to its ultrahigh strength and high fracture toughness. Surface integrity in the hard turning process (one of the final manufacturing processes in making landing gears) can be influenced by tool geometries and cutting conditions. An experimental study is conducted on 300 M steel to understand the role of cutting tool geometry and cutting conditions on surface integrity (surface roughness and residual stresses). Cutting tool geometries are varied along the nose edge region (chamfer, hone, and chamfer-hone). These varied geometries are tested at different cutting conditions to highlight the combinational complexity of cutting edges and cutting conditions in producing surface roughness and residual stresses. The results show the necessity of edge preparation in improving machining surface integrity in such a material.

Nickel-based superalloy Inconel 718 is one of the hardest materials owing to its high hardness and additional physical properties. It is the most commonly used superalloy in gas turbine, aerospace, and automobile sectors. Micro-milling is generally employed for precision manufacturing of tiny structures, but it is difficult to obtain good surface quality with micro-milling Inconel 718 because of its excellent mechanical properties like high strength and hardness. Atmospheric pressure cold plasma jet can effectively improve surface wettability without changing surface micromorphology, which is expected to have positive lubricating effects in micro-machining of difficult-to-cut materials. In addition, minimum quantity lubrication can induce coolants into the machining area more efficiently, and is especially appropriate for micro-machining. In this paper, we propose a composite micro-milling method combining plasma jet and minimum quantity lubrication to machine Inconel 718. The effec...

Metal matrix composite is composite material that combines the metallic properties of matrix alloys and additional element to reinforce the product. This paper evaluates the machining performance of uncoated carbide and coated carbide in terms of surface integrity during end milling of LM6 aluminium MMC. The parameter of cutting speed, feed rate and axial depth of cut were kept constant at 3000 rpm spindle speed, 60 mm/min feed rate and 0.5 axial dept of cut. The radial depth of cut were varied from 0.01mm to 0.1 mm. The results indicated that uncoated carbide show the better performance in terms of surface roughness and surface profile, as compared to coated carbide. On the other hand, coated carbide cutting tools suffered with built-up-edge formation at the tool edge, hence caused shearing effect and deterioration at the tool-chip interface. This study is expected to provide understanding of machining metal matrix composites based materials.

This study presents experimental results of machined surface integrity of die material (AISI D2 hardened steel) when hot machining (induction heating) assisted end milling using coated carbide is applied. The aim of this work was to study the influence of induction heating temperature, cutting speed, and feed on the effects induced by hard milling on surface integrity (microhardness and work-hardening). Microhardness was measured to observe the distribution of the hardness beneath the surface and to determine the effect of induction heating on the micro-hardness distribution and work-hardening phenomena. The behaviour of microhardness induced in the subsurface region when end milling under room and induction heating cutting conditions using coated carbide inserts was also investigated. The surface integrity and subsurface alteration have been investigated by employing scanning electron microscope (SEM) and Vickers microhardness tester.