Machining Chips Research Articles

Enhanced tensile, hardness and wear behaviors of pure aluminum matrix reinforced with steel chips via powder metallurgy technique

The mechanical properties and wear behavior of aluminum matrix reinforced with steel machining chips was investigated. Pure aluminum was reinforced with 5, 7.5, and 10 wt% steel chips with an average size of 100 μm using powder metallurgy technique. Aluminum reinforced with 5 and 10 Wt.% SiC particles were manufactured for comparison. The investigation showed clear evidence that the addition of steel machining chips resulted in significantly low porosity levels in the aluminum matrix composites compared with the use of SiC as reinforcement. The mechanical properties (tensile and hardness) as well as the wear resistance were also observed to improve with the use of the steel machining chips as reinforcement. The results demonstrate the capability of steel machining chips to act as efficient reinforcing material and a reliable cost effective candidate in the development of aluminum matrix composites.

A microstructure sensitive grain boundary sliding and slip based constitutive model for machining of Ti-6Al-4V

A composite dual phase internal state variable constitutive model was developed for Ti-6Al-4V. The proposed model includes diffusion assisted grain boundary sliding based physics in addition to a traditional slip-based plasticity. Influence of microstructure on the flow stress is introduced via dislocation density and mean grain size internal state variables. The dislocation density evolves according to a physics based law that considers dislocation nucleation and annihilation processes. Grain refinement is driven by dynamic recrystallization, which is modeled phenomenologically. The model is calibrated with uniaxial stress–strain data that ranges between quasi-static and dynamic rates across a wide range of temperatures. Validation against machining data shows that the model predicts chip segmentation frequency, machining forces, and tool temperatures reasonably well. The newly introduced grain boundary sliding physics was found to dominate deformation following sufficient grain refinement. This deformation mode provides softening at the constitutive level without the need for invoking damage based softening mechanisms. This physical interpretation is something that has not previously been explored in the machining literature.

Production of CuSn10 bronze powder from machining chips using jet milling

In this study, an experimental target plate jet mill was designed and used to produce CuSn10 bronze powder from its machining chips. Taguchi method with an L9 orthogonal array was used as experimental design to determine the optimum conditions for the pulverization of the machining chips via jet milling. The effect of process variables including nozzle to target distance, impact angle, and air pressure were investigated. The optimum conditions were found to be 8 cm for nozzle to target distance, a 90° angle between nozzle and target, and an air pressure of 7 bar. Repeated impact cycles lead to the production of finer and more rounded particles, although the rate of size reduction was reduced. The jet-milled powder did not contain any contamination, and the amount of the surface oxide of the jet-milled powder was even lower than that of the initial machining chips. Investigation of the fragmentation of particles revealed that the initial machining cracks were the main sites for breakage during pulverization. In addition, the delta phase in the microstructure of the bronze alloy plays an important role in the propagation of pre-existing cracks as well as creating new cracks.

Towards criteria for sustainable process selection: On the modelling of pure subtractive versus additive/subtractive integrated manufacturing approaches

Additive Manufacturing (AM) processes can be counted among the disruptive technologies that are capable of transforming conventional manufacturing routes. The ability to create complex geometries, the reduction in material scraps during manufacturing, and the light-weighting due to the think-additive redesign of the components represent the main points of strength of AM. However, for some applications (such as the production of metal components for the automotive and aerospace industries), the surface finishing and dimensional/geometrical part tolerancing that can be achieved via AM processes might not be adequate to satisfy the imposed product specifications, and finish machining operations are often required. A machining approach and an integrated production route, based on an additive manufacturing process plus finish machining, have been compared in this paper. The primary energy demand and the CO2 emissions have been modelled for all the life cycle stages within a sustainable development context. The main result of the research work is a criterion for the selection of the most environmentally friendly manufacturing approach, while varying the productive scenario (i.e., the masses of the process scraps, the machined chips, and the support structures). The application of such a tool to the production of metal components made of either Ti-6Al-4V or stainless steel is discussed.

Low-temperature machining in a fully submerged cryogenic environment

ABSTRACTThe role of an immersive cryogenic environment in affecting material response in machining was explored using dynamometry, calorimetry, electron microscopy, and microindentation. Effects of tool rake angle on energy dissipation, stored energy of cold work, deformed microstructure, and hardening were evaluated for machining under a fully submerged cryogenic cutting environment and a dry cutting environment. Sustained immersion of the cutting zone in liquid nitrogen resulted in greater energy dissipation and hardening in the work and machined subsurface. This increased hardening at low temperature was directly linked to greater microstructure refinement and a lower fraction of dissipated energy stored in the form of added defects and grain boundaries. Various microstructure types with domain sizes from microscale to nanoscale were developed in the machined chips, depending on the rake angle and temperature used.

An Investigation of Side Flow during Chip Formation in Orthogonal Cutting

Orthogonal cutting is a simplified two-dimensional model that neglects many geometric complexities, which describes complicated three-dimensional cutting process quite well in most cases. The orthogonal cutting should satisfy the plane strain assumption to prevent the extensive deformation perpendicularly to the cutting direction due to the pressure between the cutting tool and the workpiece, which is named as the side flow. To satisfy this assumption, the depth of cut (the uncut chip width) needs to be much greater than the feed (the uncut chip thickness) with a certain ratio. However, this criterion is not valid all the time. This paper presents an experimental study of the side flow with different cutting conditions by comparing the profiles of the cross section of the machined chip in machining of aluminum alloy. It is shown that the higher ratio between the uncut chip width and the uncut chip thickness (chip width-to-thickness ratio) and the lower cutting speed can prevent the side flow during chip formation. A new criterion for plane strain assumption has been proposed in this study as well.

Mechanical Performance and Fracture Behavior of Recycled AA6061-T6 Alloy Melted from Aluminium Chips

Aluminium chips were re-melted under the molten bath in a gas fired reverberatory furnace and superior quality recycled AA6061-T6 alloy was synthesized. The chips were added 5 to 20% by weight in the recycled alloy. The furnace charge included clean scrap of the same alloy (AA6061) along with the machining chips or tunings of mixed nature. The chips used in this study were mostly generated from lath/bore operations carried on homogenized billets. The fabricated alloy of each heat was characterized for microstructures, mechanical properties and fracture behavior. The results showed that the metallurgical and mechanical performance of the recycled alloy was comparable to the primary alloy. However, SEM analysis of the recycled alloy revealed a sizeable amount of Fe and Si containing intermetallic compounds such as AlFeSi, AlFeMg, and AlSiMg phases.

Effect of Equal Channel Angular Pressing on the Surface Roughness of Solid State Recycled Aluminum Alloy 6061 Chips

Solid state recycling through hot extrusion is a promising technique to recycle machining chips without remelting. Furthermore, equal channel angular pressing (ECAP) technique coupled with the extruded recycled billet is introduced to enhance the mechanical properties of recycled samples. In this paper, the surface roughness of solid state recycled aluminum alloy 6061 turning chips was investigated. Aluminum chips were cold compacted and hot extruded under an extrusion ratio (ER) of 5.2 at an extrusion temperature (ET) of 425°C. In order to improve the properties of the extruded samples, they were subjected to ECAP up to three passes at room temperature using an ECAP die with a channel die angle(Φ)of 90°. Surface roughness (RaandRz) of the processed recycled billets machined by turning was investigated. Box-Behnken experimental design was used to investigate the effect of three machining parameters (cutting speed, feed rate, and depth of cut) on the surface roughness of the machined specimens for four materials conditions, namely, extruded billet and postextrusion ECAP processed billets to one, two, and three passes. Quadratic models were developed to relate the machining parameters to surface roughness, and a multiobjective optimization scheme was conducted to maximize material removal rate while maintaining the roughness below a preset practical value.

Al-SiC Metal Matrix Composite production through Friction Stir Extrusion of aluminum chips

Abstract The production of most mechanical component requires machining operation, thus usually implying the cut material to be wasted as scrap. Traditional recycling techniques are not able to efficiently recycle metal chips because of some critical aspects that characterize such kind of scraps (shape, oxide layers, contaminating residues, etc). Friction Stir Extrusion is an innovative solid state direct-recycling technique for metal machining chips. During the process, a rotating tool is plunged into a hollows matrix to compact, stir and finally, back extrudes the chips to be recycled in a full dense rod. This process results to be particularly relevant since no preliminary treatment of the scrap is required. Experimental campaigns have been carried out in order to investigate the effects on process mechanics of the introduction of silicon carbide micro powders.

Verification of New Method of Determining the Roughness Parameters for Rotational Turning with Non-linear Cutting Edge

Technology of rotational turning is a progressive chip machining technology with a defined tool geometry, which in some cases can replace conventional finishing technologies with undefined geometry of the cutting tools.The paper deals with the influence of the cutting parameters of the rotational turning on the surface roughness after machining and comparing the roughness parameters with the theoretical roughness calculation. Since this is a new machining technology with new kinematic structure with atypical geometry of the cutting tool, the paper deals with the measurement methodology of the certain roughness parameters on machined surface after rotary turning with nonlinear cutting edge.Executed experimental tests and their evaluation are verified with the method of roughness parameters determination and results show, how the real process correlate with implementation of empirical relations.

Micro-mechanical and tribological properties of aluminum-magnesium nanocomposites processed by high-pressure torsion

High-pressure torsion (HPT) is one of the major severe plastic deformation (SPD) procedures where bulk metals, in the shape of a disk, achieve exceptional grain refinement at ambient temperatures. HPT has been applied for the consolidation of metallic powders and the bonding of machining chips whereas there are very limited reports examining the application of HPT for the production of new metal systems and the formation of nanocomposites. Accordingly, this investigation was initiated to evaluate the potential for the formation of a metal matrix nanocomposite (MMNC) by processing two commercial metal disks of an Al-1050 alloy and a ZK60 magnesium alloy through HPT under 6.0GPa for 20 turns at room temperature. Evolutions in microstructure, mechanical properties including hardness and plasticity and the tribological properties were examined in the MMNC region of the processed Al-Mg system. The significance of post-deformation annealing (PDA) at 573K for 1h was investigated by the change in microstructure and the enhancement in mechanical properties and wear resistance of the HPT-processed MMNC. This study demonstrates the promising feasibility of using HPT to fabricate a wide range of hybrid MMNCs from simple metals and for applying PDA for further improvement of the essential mechanical and tribological properties in the synthesized alloy systems.

Effects of SiC Nanoparticle Content on the Microstructure and Tensile Mechanical Properties of Ultrafine Grained AA6063-SiCnp Nanocomposites Fabricated by Powder Metallurgy

Ultrafine grained AA6063-SiCnp nanocomposites with 1, 5 and 10 vol.% SiCnp have been fabricated by a novel powder metallurgy process. This process combines high energy ball milling of a mixture of 6063 alloy granules made from machining chips and SiC nanoparticles and thermomechanical powder consolidation by spark plasma sintering and hot extrusion. The microstructure and tensile mechanical properties of the samples were investigated in detail. Increasing the SiC nanoparticle content from 1 to 10 vol.%, the yield strength and ultimate tensile strength increased from 296 and 343 MPa to 545 and 603 MPa respectively, and the elongation to fracture decreased from 10.0%, to 2.3%. As expected, a higher SiC nanoparticle content generates a stronger inhibiting effect to grain growth during the thermomechanical powder consolidation process. Analysis of the contributions of various strengthening mechanisms shows that a higher SiC nanoparticle content leads to a higher contribution from nanoparticle strengthening, but grain boundary strengthening still makes the largest contribution to the strength of the nanocomposite. When the SiC nanoparticle content increased to 10 vol.%, the failure of the nanocomposite was initiated at weakly-bonded interparticle boundaries (IPBs), indicating that with a high flow stress during tensile deformation, the failure of the material is more sensitive to the presence of weakly-bonded IPBs.

Mechanical Behavior of a Metal Matrix Nanocomposite Synthesized by High-Pressure Torsion via Diffusion Bonding

High-pressure torsion (HPT) is one of the major severe plastic deformation (SPD) procedures where disk metals generally achieve exceptional grain refinement at ambient temperatures. HPT has been applied for the consolidation of metallic powders and bonding of machining chips whereas very limited reports examined the application of HPT for the fabrication of nanocomposites. An investigation was initiated to evaluate the potential for the formation of a metal matrix nanocomposite (MMNC) by processing two commercial metal disks of Al-1050 and ZK60 magnesium alloy through HPT at room temperature. Evolutions in microstructure and mechanical properties including hardness and plasticity were examined in the processed disks with increasing numbers of HPT turns up to 5. This study demonstrates the promising possibility for using HPT to fabricate a wide range of hybrid MMNCs from simple metals.

Effect of microstructure on the breakage of tin bronze machining chips during pulverization via jet milling

In this study, jet milling was used to recycle tin bronze machining chips into powder. The main purpose of this study was to assess the effect of the microstructure of tin bronze machining chips on their breakage behavior. An experimental target jet mill was used to pulverize machining chips of three different tin bronze alloys containing 7wt%, 10wt%, and 12wt% of tin. Optical and electron microscopy, as well as sieve analysis, were used to follow the trend of pulverization. Each alloy exhibited a distinct rate of size reduction, particle size distribution, and fracture surface appearance. The results showed that the degree of pulverization substantially increased with increasing tin content. This behavior was attributed to the higher number of machining cracks as well as the increased volume fraction of brittle δ phase in the alloys with higher tin contents. The δ phase was observed to strongly influence the creation of machining cracks as well as the nucleation and propagation of cracks during jet milling. In addition, a direct relationship was observed between the mean δ-phase spacing and the mean size of the jet-milled product; i.e., a decrease in the δ-phase spacing resulted in smaller particles.

Influence of Process Parameters on the Product Integrity in Friction Stir Extrusion of Magnesium Alloys

Friction Stir Extrusion is an innovative direct-recycling technology for metal machining chips. During the process a specifically designed rotating tool is plunged into a cylindrical matrix containing the scraps to be recycled. The stirring action of the tool prompts solid bonding related phenomena allowing the back extrusion of a full dense rod. This process results to be particularly relevant because allows the reuse of the scrap without any previous treatment. Experiments have been carried out in order to investigate the influence of the process parameters on the extrudes quality and a numerical model has been developed in order to simulate the evolution of the material flow.

Aluminium Machining Chips Formation, Treatment & Recycling: A Review

The recycling of alumium alloys has been growing in interest and applications during the last fourthy years and has become a cost effective, ecological and reliable way to produce aluminium parts. The aluminium scraps that can be recycled include cans and machining chips. The machining processes produce chips of various sizes and shapes, wet or dry, oxidised or not, depending on type of process and the machining conditions, parameters and tools used. Some processes produce metallic dusts and fine chips while other produce large or medium size chips. In some industries such as mould making and aeronautic industries, the chip removal can easily represent 80% of the initial workpiece mass. The type of chips produced during machining can have a great impact on chip management, on part quality, on machine and tool reliability and on part manufacturing costs. The machining chips can be recycled using casting, sintering or pressing and extrusion processes depending on the goal targeted. The selection of the recycling process must take into account the targeted applications, the chip (composition, sizes and cleanliness) and its mechanical properties. Depending on the nature of process to be used and the machining chip generation conditions, some treatments might be necessary prior to transportation and recycling. Parts made with recycled chips can either be bi-phase metal matrix composites materials or usual one phase material with mechanical properties and wear properties comparable or not to the parent alloys. Over the last decades, several chip recycling processes have been proposed for aluminium alloys. This article review the aluminium chips formation, treatement methods, the recycling processes and their impact on recomposed parts’ performance: strength, ductility, corosion and wear resistances.

Effect of Machining on Shear-Zone Microstructure in Ti-15V-3Cr-3Al-3Sn: Conventional and Ultrasonically Assisted Turning

This work systematically studied morphology of nano- and microstructures in primary and secondary shear zones of machining chips produced with two different machining methods: conventional and ultrasonically assisted turning. Electron backscatter diffraction and transmission electron microscopy showed that chips had similar microstructures for both machining techniques. The nanostructure in secondary shear zones was less homogeneous than that in primary shear zones. In addition, a heavily deformed layer was formed in a subsurface of Ti-15V-3Cr-3Al-3Sn work-pieces, replicating the microstructure of secondary shear zones of the machining chips, and elongated nanocrystalline grains in this layer were aligned with a tangential direction of turning.

Solid state recycling of pure Mg and AZ31 Mg machining chips via spark plasma sintering

This work investigates the applicability of spark plasma sintering (SPS) as a solid state recycling technique for magnesium alloy scrap. In this respect, machining chips from pure Mg and AZ31 Mg alloy ingots are chemically cleaned, cold compacted and SPSed directly into bulk specimens. It is found that SPS can successfully establish full densification and effective metallurgical bonding between chips without altering compositional constituents. This is attributed to the dynamic compaction during sintering as well as to the disruption of the chips' surface oxide film due to SPS electric current based joule heating. Apart from the successful consolidation, microstructural analysis of the initial Mg ingots, chips and SPS recycled material reveals that the SPS microstructure was finer than that of the original ingots due to significant deformation induced grain refinement during machining. As a result, the recycled materials had a higher compression and shear strength than that of the starting ingot material. The findings indicate that SPS is an effective alternative method for solid state recycling of magnesium alloy scrap.

Effects of chip conditions on the solid state recycling of Ti-6Al-4V machining chips

Five different types of Ti-6Al-4V machining chips were recycled in their solid state using equal channel angular pressing (ECAP). The chips were produced by either turning or milling with or without the application of a coolant. All the as-recycled materials achieved full density but their microstructures, including the prior chip boundary spacing and grain size, are dependent on the starting chip morphologies and dimensions. The differences, however, were largely removed in the subsequent mill-annealing processing consisting of β homogenisation, hot deformation and final annealing, leading to near-identical mill-annealed microstructures for all different types of chips consisting of equiaxed α+β grains with lamellar α, typical following such a treatment. The recycled and mill-annealed materials possess high yield strengths of >900MPa and satisfactory tensile ductility of >11%, comparable or superior to the original commercial mill-annealed Ti-6Al-4V and independent of the initial chip conditions.

Mechanical properties, wear and corrosion behavior of copper matrix composites reinforced with steel machining chips

The mechanical properties, wear and corrosion behavior of copper matrix composites reinforced with steel machining chips was investigated in this research. Steel machining chips with chip size range of 105μm and below were utilized to develop stir cast copper matrix composites having 5, 7.5 and 10wt% of the chips as reinforcement. Unreinforced copper and 10wt% alumina reinforced copper matrix composites were also prepared for control experimentation. Hardness and tensile properties evaluation, wear test, potentiodynamic polarization corrosion tests, and optical microscopy; were used as basis to characterize the composites produced. The results show that the addition of steel machining chips in copper resulted in significantly low porosity levels in the copper matrix composites compared with the use of alumina as reinforcement. The mechanical properties (hardness and tensile properties) and wear resistance were also observed to improve with the use of the steel machining chips as reinforcement. The corrosion susceptibility in 3.5wt% NaCl solution were observed to be more intense for the unreinforced copper and the alumina reinforced composite grade compared with the steel chips reinforced copper matrix composites. But in 0.3M H2SO4 solution, no consistent corrosion trend was observed although the corrosion resistances of all the composite grades produced were superior to the unreinforced copper. The results demonstrate the capacity of steel machining chips to serve as a reliable cost effective and technically efficient reinforcement material for the development of copper matrix composites.