Machining Chips Research Articles

Steel machining chips as reinforcements to improve sliding wear resistance of metal alloys: Study of a model Zn-based alloy system

Two new steel-reinforced, metal-matrix composites (MMCs), Kirksite+1080 and Kirksite+M2 are developed by adding 25wt% of AISI 1080/AISI M2 steel machining chips to a zinc-based alloy, Kirksite (4% Al and 3% Cu). The sliding wear resistance of the Zn alloy and the two MMCs, against AISI 52100 steel, is determined under increasing normal load (1–10N) and temperature (25–150°C), using a pin-on-disc configuration. The MMCs are found to exhibit superior wear performance under all test conditions. At room temperature, a maximum wear reduction in excess of 70% is obtained for the composites relative to the Zn-alloy at the highest load of 10N. This reduction is as much as 86% at 150°C and 1N for the Kirksite+M2. The wear-reducing ability of the steel reinforcements is generally greater at the more severe contact conditions. The stability of the MMC matrices and recommended limits to the MMC operating temperatures are established using deformation measurements made via dynamic mechanical analysis. The principal wear mechanisms are analysed based on the sliding wear measurements, complemented by optical microscopy and SEM observations, and EDX microanalysis. The results show that the steel chip reinforcements are effective in improving the wear resistance of Zn alloys under severe conditions. Implications for use of low-cost machining chips as reinforcements to create MMCs for improved wear performance, and for recycling/reuse of these chips in advanced structural material systems are discussed.

Effect of die design on the welding quality during solid state recycling of AA6060 chips by hot extrusion

Solid state recycling of aluminum chips by hot extrusion is a novel processing technique, which utilizes remarkably lower energies compared to conventional recycling by remelting. The mechanical properties of the extruded profiles can be improved by optimizing the effect of extrusion die design on the welding quality of machining chips. The chips were extruded through two dies of different design to produce solid rectangular profiles. One of the dies was a flat-face die, which represents a conventional extrusion die design for production of solid aluminum profiles. The second die was a porthole die typically used for complex hollow and semi hollow aluminum profiles. AA6060 chips were compacted at room temperature into billets and hot-extruded at approximately 500°C to aluminum profiles. The microstructure and the mechanical properties of the profiles extruded through the flat-face and porthole dies were compared. The extrusion through the porthole die resulted in a much better welding of the chips and revealed more than 80% higher ductility compared to the profiles extruded through a flat-face die. The welding quality of the chips was studied using a two-step analytical approach: a criterion for the breaking of the oxide layers and an index for the welding quality. These analytical approaches were implemented with the help of subroutines in the FEM code, in which the results of the simulations were compared and confirmed by the experimental results.

Mechanical properties and corrosion resistance of Mg–10Gd–2Y–0.5Zr alloy by hot extrusion solid-state recycling

A solid-recycled Mg–10Gd–2Y–0.5Zr alloy is fabricated by hot deforming of machined chips and conventional hot extrusion. All the recycled specimens exhibit higher yield strength compared with the extruded reference ingots under the same extrusion condition, which is mainly ascribed to fine-grain size, dispersive distribution of oxide and the second phase of recycled specimens. When extruded at 450°C, the ultimate tensile strength and elongation of solid-recycled specimen are higher than reference specimen. As for the corrosion resistance, the corrosion rate of 450°C solid-recycled specimen is slightly higher than reference specimen extruded at the same condition. The 400 and 450°C recycled specimens are corroded uniformly, which is better than the pitting of reference specimens. In 450°C recycled specimen, the dispersive distribution of oxide induces that the corrosion products could hinder the progress of corrosion effectively. Meanwhile, the second phase precipitates easily concentrate along the grain boundary in the reference specimens. The aggregates of precipitates induce the appearance of pitting and deep etch pits.

A Quantified Complex Strengthening Mechanism in Solid-State Recycled Titanium

Machining chips of commercially pure titanium (ASTM Grade 2) were recycled into fully dense bulk material by equal channel angular pressing (ECAP). The morphology of the oxide layer derived from chip surfaces was characterized by focused ion beam miller and transmission electron microscopy. Electron backscatter diffraction and chemical analysis were used to propose quantitatively a complex strengthening mechanism considering interstitials, ultrafine grains (with misorientation ≥15 deg), and subgrains (<15 deg) substantially in existence after ECAP.

Microstructure and mechanical properties of a spray formed and extruded AA7050 recycled alloy

This paper presents the results of the evaluation of the microstructure and mechanical properties of an aerospace alloy recycled from machining chips by spray forming. The machining chips are produced during the manufacturing of machined aircraft parts and represent a high percentage of the initial rolled plate weight. Basically, the idea that guides the development of this work translates into adding value to the use of aerospace alloy machining chips, since these are incorporated in the recycling chain of the casting industry, without adding value. For this purpose, the material AA7050 was collected from an airframe machining facility and spray formed using nitrogen as the atomizing gas at pressure of 6 bar. The deposit was then hot extruded at 425 °C with a 10:1 reduction. Subsequently, samples were solution heat treated (4 h at 420 °C and 8 h at 470 °C) and age hardened at three different conditions. For the best age hardening condition, the results of tensile tests at room temperature were 623 MPa tensile strength, 563 MPa yield strength, and 12% elongation. Comparing these results with the specification data for the AA7050 material, it is possible to conclude that the mechanical properties of the spray formed material, to same extent, exceeded the standard data.

Recent developments in modelling of microhardness saturation during SPD processing of metals and alloys

Ultrafine-grained and even nanostructured materials can be fabricated using severe plastic deformation to ultra-high strains in equal-channel angular pressing (ECAP), high-pressure torsion (HPT), machining and their combinations, such as machining of ECAP specimens, HPT of ECAP billets and HPT of machining chips. This report presents recent results of investigations of the microstructures and microtextures of pure copper, nickel and aluminium subjected to different deformation processes to ultimately high imposed strains. A comparison of the microstructure, dislocation density and microhardness developed during combinations of different strain paths is performed. All characteristics were analysed by X-ray, transmission and scanning electron microscopy, and electron backscatter diffraction (EBSD). The influence of different processing routes is discussed in terms of the accumulated strain and microstructure refinement. The saturation in grain refinement is examined with reference to the recovery taking place during ultra-high strain deformation. A phenomenological model based on the Voce equation is applied for fitting parameters based on the experimental data and this is suggested for a prediction of microhardness evolution for pure metals (Ag, Au) and Cu-based (Zn, Al) alloys.

Numerical and experimental analysis of machining of Al (20 vol% SiC) composite by the use of ABAQUS software

AbstractIn this study two‐dimensional finite element model of Al/SiC metal matrix composites (MMC) are investigated by the use of ABAQUS/Explicit software. Chip formations and machining forces during machining of MMC have been studied and compared to experimental data. It was found that the resulted chips in simulation and the generated chips in experiments both have saw‐tooth in appearance. On the other hand, the obtained cutting forces diagrams from simulation and experimental conditions have considerable fluctuating with passing cutting time. This is due to the interaction between tool and SiC particles during chip formation.

Microstructures of Machined Chips in Pure Titanium, Pure Iron and 0.83%C Steel

Microstructures of Machined Chips in Pure Titanium, Pure Iron and 0.83%C Steel

Ultrafine-grained pure Ti recycled by equal channel angular pressing with high strength and good ductility

Machining chips of commercially pure Ti (ASTM grade 2) were consolidated into full density by equal channel angular pressing (ECAP) with an average grain size as low as 0.8μm, yield strength up to 650MPa, and ductility of ∼16%. Effect of recycling condition on the microstructure and mechanical properties were investigated in terms of ECAP temperature, number of passes and chemical composition. Using electron backscatter diffraction it is evident that continuous dynamic recrystallization (however, which is purely a phenomenological terminology) plays a significant role in grain (with misorientation ≥15°) formation, whilst benefitting from high stacking fault energy, this continuous conversion of subgrain (<15°) into grain can be essentially considered as an extended recovery with a substantial presence of low angle grain boundaries in the recycled Ti. The Hall–Petch relationship is adapted to explain the strengthening of the recycled Ti. Additionally, using scanning electron microscopy fractography, the ductility was analyzed by a modified Griffith criterion. Last, superior energy efficiency of ECAP reduces environmental impact when comparing to conventional melting/casting. ECAP develops an innovative solid-state process for improving the recycling value of waste Ti.

Foaming of Aluminum Alloys Derived From Scrap

AbstractAluminum alloys made from machining chips that have been heat treated and re‐melted, have been successfully foamed (after the addition of TiH2) using processes analogous to both the “Alporas” and “Formgrip” methods. The high oxygen contents associated with the swarf (0.11 wt% for the as‐received material, increasing to &gt;0.5 wt% after conditioning) results in large fractions of both clustered and dispersed oxide films in the melt. It is these films that enhance the “foamability” of this material. Through additional alloying with Mg and holding in the liquid state to allow reaction to take place, fragmentation and wetting of the oxides occurs and foams with low densities (&lt;0.3 g cm−3), good pore structures, and good stability were obtained. The use of scrap material, without costly or embrittling additives, offers a low cost route to the manufacture of high quality foams.

A Non-Dimensional Analysis of Tool Edge Radius Effect on the Mechanics of Micromachining

The effect of tool edge radius on the mechanics of micromachining, both in terms of plasticity and tribology is significant. Through an experimental study, the responses of normalized process variables namely tool-chip contact length, deformed chip thickness and machining force were evaluated for varying relative tool sharpness. A non-dimensional analysis of the interrelationship among the process variables indicate a transformation in chip formation mechanism under an extreme condition is reported.

Laser clad corrosion protection for mild and harsh environments

Corrosion of one type or another occurs in almost every environment and high performance corrosion protection methods are often too expensive to be economically viable. This work examines the performance of protective layers of Inconel 617, laser clad in the form of salvaged machining chips, to protect a corrosive substrate from both mild and harsh environments. The clad layers are investigated for microstructure and phase composition and polarisation measurements used to determine their corrosion resistance in neutral and acidified NaCl electrolyte solutions. The clad microstructure was discovered to be columnar dendritic, with an atypical upper layer. However, neither this nor any dilution by the substrate compromised the corrosion resistance of the Inconel 617, and the clad layer provided very good corrosion protection. The results confirm the viability of using this method as a low cost corrosion protection method for both mild and harsh environments.

Chemistry and tensile properties of a recycled AA7050 via spray forming and ECAP/E

The aim of this work is to evaluate the conjugation of advanced processing techniques, such as spray forming, extrusion and ECAP as a processing route for reuse of machining chips generated during aircrafts manufacturing parts from AA7050-T7451 raw material plates supplied according to AMS 4050H1. In this way, the sprayforming process was used for remelting, and billet production, followed by extrusion and ECAP. At the end of the process, an artificial aging according to AMS 2772E 2 was conducted. An assessment of chemical composition, microstructure, and mechanical properties evolution throughout the process were performed. The results have showed that this proposed route may be used as a potential technological route for secondary aluminum source. For extrusion route for overaged condition, 144 MPa yield strength and 14% of elongation was attained. Beside this, at this stage of work, was verified that the hot extrusion process is more effective for reduction of porosity and microstructure development than ECAP, but on the other hand this one has reduced porosity dispersion significantly for the extrusion parameters adopted. The adopted homogenization schedule, followed by artificial aging after has resulted in excessive grain growth.

Ti-6Al-4V Recycled from Machining Chips by Equal Channel Angular Pressing

Ti-6Al-4V machining chips have been recycled into fully dense material by a solid-state process based on equal channel angular pressing (ECAP). The as-recycled material possessed a refined microstructure and contained a series of oxide layers associated with the boundary of each machining chip. The chip boundaries were observed to dissolve into interstitial solid solution following static annealing. A series of static heat treatments within the temperature range 700 to 1000°C, for durations of between 1 and 20 hours, were performed. The effect of thermomechanical processing on microstructure and mechanical properties is discussed and compared to the as-recycled and commercially available materials.

Recycling of Zircaloy Machining Chips by VAR Remelting and Powder Metallurgy Techniques

In the fabrication of nuclear reactor core parts, machining chips of Zircaloy are generated. These alloys are strategic for nuclear technology and cannot be discarded. In the present work are presented two methods for recycling of Zircaloy chips. One of the methods is by melting in VAR furnace and the other by powder metallurgy method. By this method the Zircaloy was submitted to hydriding process and milled in a high-energy ball mill. The powder was cold isostatically pressed and vacuum sintered. The elemental composition of the samples obtained by both ways was determined by XRF and compared to the specifications. The phase composition was determined by XRD. The microstructures resulting of both processing methods, before and after rolling were characterized using optical and scanning electron microscopy. The good results of the powder metallurgy method suggest the possibility of producing small parts, like cladding cap-ends, using near net shape sintering.

Investigation of Reinforced Sic Particles Percentage on Machining Force of Metal Matrix Composite

In this study two-dimensional finite element models of Al/SiC metal matrix composites (MMC) by using of ABAQUS Explicit software are investigated. Chip formations and machining forces for three types of MMC with 5, 15 and 20% of SiC reinforcement particles were studied and compared with experimental data. The resulted chips in simulation and the generated chips in experiments have both continuous and saw tooth in appearance. On the other hand, the variation of the cutting forces with the cutting time in simulation and experiment have fluctuating diagram. This is due to the interaction between cutting tool and SiC particles during chip formation. ABAQUS explicit software was used for simulation; it was found that there are good agreements with simulation and experimental data.

Experimental and Finite Element Analysis on Chip Formation Mechanism in Machining of Elastomers

Computer simulation of metal cutting processes using the Finite Element Analysis (FEA) method are routinely practiced in today's industry. It is known from the theory of metal cutting that an examination of machined chips provides the cheapest and the most effective way of understanding the machining characteristics of a material. This paper discusses experimental work and finite element analysis to investigate the mechanism of chip formation during machining of Elastomer. Focus of this study is on understanding the influence of different cutting parameters on chip formation mechanism. From the experimental tests, it has been concluded that the morphology of rubber chips can be categorized into continuous ribbon-like chips with a smooth machined surface, segmented chips with a rough machined surface, and discontinuous chips with an even worse surface finish. Continuous ribbon-like chips are associated with a smooth surface finish, which occurs with large rake angle tools. Further from Finite Element Analysis it was observed that at lower rake angle, discontinuous chips are formed and Continuous ribbon-like chip occurs with large rake angle.

Analytical and experimental study on formation of concentrated shear band of saw tooth chip in high-speed machining

Saw tooth chip is a typical characteristic encountered in high-speed machining. It consists of nearly undeformed segments and highly sheared concentrated shear bands. However, no consensus on the formation of the concentrated shear band has been reached though several saw tooth chip formation models have been built. In this paper, the concentrated shear band formation procedure is analyzed based on a new proposed saw tooth chip formation model. Cutting experiments have been conducted to validate the proposed mode. It shows that the plastic side flow and elastic compression of the uncut chip are crucial for the concentrated shear band formation. The localized shear at the inner end (tool tip side) of the primary shear plane firstly takes place under the indentation of cutting tool. Then, the second localized shear is produced at the outer end (free surface side) of the primary shear plane due to stress concentration there, after which the whole concentrated shear band forms. The stress transition at the outer end of the primary shear plane makes the second localized shear easier evolve into cracks. Influences of material brittleness and cutting speed on initiation and propagation of the concentrated shear band are also analyzed.

Improving minimum quantity lubrication in CBN grinding using compressed air wheel cleaning

The application of minimum quantity lubrication (MQL) in grinding has emerged as an alternative for reducing the abundant flow of cutting fluids, thus achieving cleaner production. Although considered an innovative technique in grinding operations, its widespread application is hindered due primarily to the high heat generation and wheel pore clogging caused by machined chips, harming the final product quality and increasing tool wear on the machine. This study sought to improve MQL use in grinding. In addition to the conventional MQL injected at the wheel/workpiece interface, a compressed air jet was used to clean the mixture of MQL oil and machined chips from clogged wheel pores. Experiments were conducted using external cylindrical plunge grinding on AISI 4340 quenched and tempered steel, and a vitrified cubic boron nitrite (CBN) wheel. The cooling-lubrication methods employed were the conventional flood coolant application, MQL (without cleaning), and MQL with a cleaning jet directed at the wheel surface at different angles of incidence. The main goal of these experiments was to verify the viability of replacing the traditional abundant flow of cutting fluid with MQL and wheel cleaning. The analyses were conducted by measuring the following output variables of the process: workpiece surface roughness and roundness errors, diametrical wheel wear, acoustic emission generated by the process, and metallographic images of the ground surface and subsurface. Results show the positive effects of implementing the cleaning jet technique as a technological improvement of minimum quantity lubrication in grinding in order to reduce the usage of cutting fluids. The MQL technique with cleaning compressed air jet, for a specific angle of incidence (30°), proved to be extremely efficient in the improvement of the surface quality and accurate workpiece shape; it also reduced wheel wear when compared to the other cooling-lubrication methods that were tested (without a cleaning jet).

Experimental Analysis on Spherical Chips in High-Speed Machining of Hardened AerMet100

Spherical chip appears frequently in high speed grinding of metals. It is attributed to the melt or oxidation of the small chips in grinding. Spherical chip in machining of steels is observed when the cutting speed is high enough. To clarify the formation mechanism of spherical chip in metal cutting, high speed machining of AerMet100 at cutting speeds from 40 m/min to 3000m/min was investigated. Spherical chip of AerMet100 was obtained at cutting speed range 2000-3000m/min. Optical and SEM (Scanning Electron Microscope) observations of the spherical chip was carried out. The chemical composition of the spherical ship was analyzed through X-ray energy dispersive spectroscopy (XEDS) analysis. The formation mechanism of the spherical chip was proposed. The results showed that the spherical shape of chip is due to the intense reaction between Fe of workpiece and O2 in the air accompanying which large mount of heat is released to melt the oxide into small spheres. The formation of the spherical chip is highly influenced by cutting speed and the size of the chip (surface-volume ratio).