Built-up Layer Formation Research Articles

The Influence of nc-AlCrTiN/α-BN Coatings on Increasing the Durability of WC/Co Cutting Inserts in the Inconel Alloy Machining Process.

Anti-wear coatings obtained through PVD methods may significantly increase the durability of cutting tools by impacting their wear mechanisms. This study presents and discusses the results of studies on the impact of the thermal conductivity of PVD coatings on the intensity of the built-up edge (BUE) and built-up layer (BUL) formation in Inconel 600 alloy machining processes. The authors determine the microstructure, phase structure, mechanical properties (hardness, Young's modulus, and adhesion), and thermal conductivity of different PVD coatings selected for the purpose of the study and varying in terms of conductivity-i.e., AlCrTiN and AlCrTiN/BN. Machining processes were carried out under controlled conditions using VBGT160404-M3 cutting inserts with AlCrTiN and AlCrTiN/BN coatings deposited on their surface. The authors prove that the adjustment of the thermal conductivity of PVD coatings to the thermal conductivity of the tool and machined materials can help change the direction of heat flow to cool the cutting zone more effectively. The study results presented in this article show that the deposition of the AlCrTiN/BN coating reduces the friction wear on the tool flank by over 70% and lowers the intensity of BUE and BUL formation processes on the face by 10%, compared to the AlCrTiN coating.

Machinability investigations of AZ31 magnesium alloy via submerged convective cooling in turning process

Magnesium alloys are lightweight materials which exhibit high specific strength and is broadly used in aerospace, automotive, electronics, and biomedical. Dry cutting is a common practice in machining this material which always results to an excessive rise in temperature due to the absence of cooling at the cutting zone. The low melting point of AZ31 magnesium alloy always puts the process to the inevitable built-up edge (BUE) and built-up layer (BUL) formation. This study implemented a novel work in turning AZ31 magnesium alloy via an internal cooling technique, known as submerged convective cooling (SCC), to compensate for the absence of cooling in dry cutting. The experimental result revealed that SCC outperformed dry cutting in adhesion wear mechanism, cutting force and temperature due to the cooling induced. SCC recorded up to 15% reduction in cutting temperature with 6% and 12% reduction in cutting and feed force, respectively. In addition, SCC significantly reduced BUE and BUL formation, consequently restrained cutting force fluctuation, owing to the cooling effect of SCC. This research provides an insight into the potential of implementing internal cooling in the severe plastic deformation process, especially in cutting ductile materials like magnesium alloy.

Dry Machining Performance of AA7075-T6 Alloy Using Uncoated Carbide and MT-CVD TiCN-Al2O3-Coated Carbide Inserts

The present study examines dry machining performance of AA7075 T6 alloy using uncoated and MT-CVD TiCN–Al2O3-coated carbide inserts. Machining performance is assessed with regard to tangential cutting force, tool tip temperature and depth of flank wear. The performance of coated tool is compared to that of uncoated insert. In addition, different modes of tool wear and chip morphology are studied in detail. It is experienced that coated tool causes lower tool tip temperature and lesser flank wear than untreated counterpart. Apart from abrasion, adhesion and built-up layer formation; attrition wear is distinctly visible in case of uncoated tool. On the contrary, in addition to common wear modes, coated tool also experiences diffusion wear.

Experimental study on the effects of cold chamber die casting parameters on high-speed drilling machinability of casted AZ91 alloy

Abstract In this study, the effects of the cold chamber die casting parameters on high-speed drilling machinability of AZ91 Magnesium alloys were experimentally investigated. The influence of different casting parameters (casting temperature, molding pressure, and gate speed) on microstructure, mechanical properties and machinability characteristics (thrust force, tool wear, built-up edge, built-up layer formation, surface topography, chip morphology, and burr formation) were examined. The experimental results showed that the grain size of the conventional casting sample was around 50 microns, while in other cold chamber die casting tests, it varied depending on temperature, pressure, and gate speed. It was observed that the tensile strength values ​​of the samples produced with 1000 bar mold pressure were higher than those of other samples. In the formation of thrust force, the feed rate is more effective than the cutting speed. The least tool wear occurred in the drilling of the As-cast sample, while the highest tool wear occurred in the drilling of the sample which was produced with low pressure and low gate speed combination. As a result of the drilling tests, depending on casting and cutting parameters, three different types of chips were formed: fan, spiral cone, and long ribbon type. Furthermore, uniform and transient burrs in different sizes were observed.

On the turning of electron beam melted gamma-TiAl with coated and uncoated tools: A machinability analysis

Abstract Electron beam melting (EBM) is one of the promising technologies with the capability of producing complex near-net shapes from difficult to process materials such as titanium alloys. However, the parts produced from the EBM process suffer from the poor surface quality and machining is required to finish the EBM parts to achieve the necessary surface quality. Unlike the reported studies in the literature, the current study employs both uncoated, and PVD multi-coated (TiAlN/Al2O3/ZrCN) carbide inserts for the finishing of the electron beam melted γ-TiAl (Ti-48Al-2Cr-2Nb) and compares the machinability performance to identify the suitable type of the tool and the corresponding machining conditions. The obtained results indicate that the performance of the uncoated inserts is far superior as compared to the coated inserts in terms of producing lower tool wear and cutting forces, improved surface finish and morphology, and less subsurface microstructural and hardness alterations. The poor performance of the coated inserts is due to the high-temperature accumulation at the tool-workpiece interface due to the thermal shielding effect of the coatings, leading to severe built-up layer formation resulting in cascading effect of higher cutting forces, tool wear and oxidation, and poor workpiece surface integrity.

Investigating the influences of coatings on the built-up layer formation during cutting of Ti-6Al-4V

Investigating the influences of coatings on the built-up layer formation during cutting of Ti-6Al-4V

The effect of material microstructure on the built-up layer formation in dry cutting of Inconel 718

The effect of material microstructure on the built-up layer formation in dry cutting of Inconel 718

Formation of Built-Up Layer on the Tool in Turning Operation of Magnesium Alloys

The present work highlights some factors which affect formation of a protective built-up layer (BUL) on the rake face of the cutting tool when cutting magnesium alloys. This work suggests that BUL can positively affect tool life, surface roughness, cutting speed and tool forces. The BUL is formed in cutting magnesium alloys with the PCD tool inserts at cutting speed range from 500 to 2500 m/min and at the carbide tool inserts at lower cutting speed range around 550 m/min. It has been found that deposit layers primarily have similar chemical composition as MnAl inclusions which are incorporated in the structure of the examined AZ91 magnesium alloys.

Effects of initial surface topography and contact regimes on tribological behavior of AISI-52100/AA5083 materials’ pair when reciprocating sliding

This paper discusses the effect of surface topography and lubrication on the tribological behavior of AA5083 alloy for wide range of average roughness, Ra. Reciprocating sliding tests were conducted under lubricated and dry regimes over different pre-textured surfaces using AISI-52100 steel ball under two contact pressures. Scanning Electron Microscope (SEM) and profilometer were employed for characterizing wear land and type. Particularly, the effect of the mean absolute profile slope Δa of AA5083 plates on friction and wear was investigated within an early repetitive sliding stage. Experimental results show that a close correlation was found between the tribological behavior and the mean absolute slope, Δa, contrary to the average roughness, Ra, which shows a partial link. From SEM inspections, dry sliding correlates with the generation of ploughing over aluminum topographies, and with the formation of Built-Up Layer (BUL) due to adhesion over steel ball. However, lubrication, transforms material removal process over the ball from adhesion to abrasion which affects inevitably the initial topography. The evolution of crater area S − reflects high sensitivity to Δa. In order to predict the wear evolution, a mathematical model taking into account the impact of Δa and the number of sliding cycles (N) was developed using Response Surface Method (RSM).

Investigating the influences of coatings on the Built-up layer formation during cutting of Ti-6Al-4V

Investigating the influences of coatings on the Built-up layer formation during cutting of Ti-6Al-4V

Experimental study of Built-Up Layer formation during machining of high strength free-cutting steel

Machinability of high-strength steels can be improved without degrading the mechanical properties using metallurgical solutions to create or retain non-metallic inclusions. Such a metallurgical treatment usually leads, during machining, to the appearance of so-called Built-Up Layers (BULs) or transfer layers on the cutting tool. These BULs protect the tool against wear, and longer tool life or better productivity is achieved. Formation of such BULs on the cutting tool depends on many parameters i.e. tool geometry, tool material, cutting conditions. This paper proposes an experimental methodology to identify and describe BUL occurring on the tool rake face. Machining tests were carried out with a high strength free-cutting steel using an untested AlSiTiN coated carbide tool. BULs morphology and composition were determined for various cutting conditions. Temperature distributions at the tool-chip interface were measured during the cutting tests using an infrared camera. BUL appearance was then linked to the thermo-mechanical conditions at the tool-chip interface.

The influence of built-up layer formation on cutting performance of GG25 grey cast iron

Abstract The success of high speed machining of grey cast iron relates to the protective built-up layer (BUL) that forms on the tool. The present work investigates BUL formation on pcBN tools for dry, high speed machining of GG25 grey cast iron (up to vc = 750 m/min). This work suggests that the BUL distribution on the tool at high cutting speed (vc = 750 m/min) is key to tool protection. Protection in the area of maximum cutting temperature is critical in preventing thermally driven wear modes, such as crater wear, found at low cutting speeds (vc = 250 m/min).

Analysis of the evolution of the Built-Up Edge and Built-Up Layer formation mechanisms in the dry turning of aeronautical aluminium alloys

Tool wear is one of the main parameters employed for evaluating tool life, due to its influence in the loss of quality of the manufactured parts. So, minimising tool wear is possible to maximise tool life and to optimise the manufacturing performance. Different mechanisms can cause the tool wear in a specific machining process. Adhesion wear is one of the tool wear mechanisms that can be present in a wider range of cutting temperatures. This type of tool wear can be produced by two different ways. On the one hand, direct adhesion wear is caused by the incorporation of tool particles to the chips. On the other hand, secondary adhesion wear is caused by the incorporation of fragment of the workpiece material to the tool. This affects to the tool wear in two ways. First, tool geometry changes by the material incorporation. In a second place, when these fragments are removed, they can drag out tool particles causing tool wear. Indirect adhesion can be located in the tool edge, giving rise to the Built-Up Edge (BUE) and/or in the tool rake face giving rise to the Built-Up Layer (BUL). BUL and BUE formation and their evolutions affects to the workpiece quality. In this paper a study of the BUL and BUE formation mechanisms, their evolution and their influence on the dry turned aeronautical workpieces surface quality has been achieved. In particular, this study has been developed using aerospace aluminium alloys such as UNS A92024 (Al–Cu) and UNS A97050 (Al–Zn). Results have shown that BUE is formed by mechanical adhesion mechanism. On the other hand, BUL is initially formed by thermo-mechanical causes. However, a secondary BUL has been detected as a consequence of the extrusion process of the BUE. Changes in BUL and BUE have been related with the changes observed in the roughness profile of the machined pieces and evaluated through the average surface roughness, Ra. So, a first relationship between the adhesion effects and the surface finish of the worked samples has been found. Obtained results have confirmed that BUE changes the tool position angle giving rise to a reduction of Ra.

An XPS Study of the Stratified Built-up Layers Developed onto the Tool Surface in the Dry Drilling of Ti Alloys

Secondary tool adhesion wear is commonly provoked by two effects, whose nature depends on the placement of the adhered material. The so-called Built-Up Layer (BUL) is formed on the tool rake face and the Built-Up Edge (BUE) is developed on the cutting tool edge. These effects can be developed by different causes depending on both the cutting conditions and the material to be machined. In this work, X-Ray Photoelectron Spectroscopy (XPS) has been used to analyze the built-up layers formed during the dry drilling processes of aeronautical Ti-6Al-4V alloy. Changes in the Ti oxidation state in each layer have allowed proposing a BUL formation mechanism based on chemical reactions of the workpiece material during the drilling process. Effects of these reactions have been contrasted through the XPS analysis of the chip generated in the process. In parallel, SEM and EDS have been used as complementary techniques for obtaining further information about the BUL nature.

EFFECT OF CUTTING SPEED AND SURFACE CHEMISTRY OF CUTTING TOOLS ON THE FORMATION OF BUL OR BUE AND SURFACE QUALITY OF THE GENERATED SURFACE IN DRY TURNING OF AA6005 ALUMINIUM ALLOY

In the present investigation, AA6005 (ISO: AlSiMg) alloy was machined in turning operation with different cutting tools, such as uncoated cemented carbide insert, PVD TiN coated, CVD diamond coated and PCD insert, under dry environment. Effect of cutting speed was studied for each of the cutting tools with regard to the formation of built-up layer (BUL) or built-up edge (BUE). The rake surface of the tools was characterized by optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopic microanalysis. Particular emphasis was given on wear mechanism of PVD TiN coated insert, conventionally used in machining ferrous alloys, during dry turning of AA6005 alloy. It has been observed that increase of cutting speed from 200 m/min to as high as 1000 m/min could not substantially reduce formation of BUL over tool rake surface during dry machining of AA6005 alloy with uncoated or PVD TiN coated cemented carbide inserts. The potential of diamond-based tools in dry machining of aluminium alloy was also studied. Finally, the effect of cutting speed on surface finish of the workpiece machined with different cutting tools was studied during dry turning of AA6005 alloy.

Coating-workpiece optimization of free cutting steels: turning with TiCN-, ZrO 2-, and ZrN-coated cemented carbide tools

The mechanism of selective transfer of non-metallic inclusions from a steel wotkpiece to the rake face of the cutting tool, occurring under specific conditions of simultaneous optimization of workpiece material and tool surface chemical composition, is studied by means of inclusion control of the workpiece steel and by deliberate modifications of the chemical composition at the tool surface. Two resulphurized, free cutting steels, one of which has been newly developed with special inclusion control, are selected as workpiece materials. We present metallographic evidence on protective transfer layer (built-up layer (BUL)) formation enhancement for TiCN-, ZrO 2- and ZrN-coated K20-type, cemented carbide cutting tools. BUL formation and stability are shown to be dominated by the nature and continuity of the chemically active element on the tool surface. Among the coatings selected in this study, Zr-based coatings are found to be most favourable for tool life enhancement. The sulphide formation enthalpy of the active transition element on the tool surface is concluded to be the major driving force for BUL formation.

Mechanisms of built-up layer formation on turning tools: Influence of tool and workpiece

Built-up layer (BUL) formation on tools in turning has been studied for two resulphurized free-machining steels with slightly different inclusionary states and three different types of uncoated and ZrO 2-coated cemented carbide tools. In addition to tool surface topography, crystallography and surface chemical analysis have been carried out. Transfer layers are mostly composed of crystalline MnS. Their chemical compositions have been mapped on the rake face and across the tool-layer interface. The relative proportions of MnS and iron are shown to depend on the chemical nature of the inclusions in the machined steel and on the tool surface as well as on the cutting speed Vc. A minor oxide content in the inclusions appears to be necessary for stable transfer layer formation. For such steels the stability region extends from Vc = 100 to 600 m min −1, with a maximum layer thickness at 400 m min −1.