Burr Formation Research Articles

Statistical Analysis of Machining Parameters on Burr Formation, Surface Roughness and Energy Consumption during Milling of Aluminium Alloy Al 6061-T6.

Due to the increasing demand for higher production rates in the manufacturing sector, there is a need to manufacture finished or near-finished parts. Burrs and surface roughness are the two most important indicators of the surface quality of any machined parts. In addition to this, there is a constant need to reduce energy consumption during the machining operation in order to reduce the carbon footprint. Milling is one of the most extensively used cutting processes in the manufacturing industry. This research was conducted to investigate the effect of machining parameters on surface roughness, burr width, and specific energy consumption. In the present research, the machining parameters were varied using the Taguchi L9 array design of experiments, and their influence on the response parameters, including specific cutting energy, surface finish, and burr width, was ascertained. The response trends of burr width, energy consumption, and surface roughness with respect to the input parameters were analyzed using the main effect plots. Analysis of variance indicated that the cutting speed has contribution ratios of 55% and 47.98% of the specific cutting energy and burr width on the down-milling side, respectively. On the other hand, the number of inserts was found to be the influential member, with contribution ratios of 68.74% and 35% of the surface roughness and burr width on the up-milling side. The validation of the current design of the experiments was carried out using confirmatory tests in the best and worst conditions of the output parameters.

Micro-milling of Ti-6Al-4 V with controlled burr formation

• A methodology is proposed to suppress the burr generation by tailoring compressive residual stress on the workpiece during the micro-milling process. • The burr formation is reduced by 63% by incorporating compressive surface residual stress of 589 MPa at the material surface. • The cutting marks at the machined side-wall are investigated and found to depend on the frictional behaviour between the tool and the workpiece. • Dynamic recrystallization is captured by EBSD on the micro-milled slot. • User-defined constitutive flow and friction models are proposed to capture the mechanism of the burr formation and morphology of the chip. Burr generation is expected to be a function of the state of stress and microstructure of the material before micro-milling. Burr formation may be hindered by cold working process such as peening, as peening leads to grain refinement and the induction of residual stress at the material surface. The novelty of the present work is the numerical modelling and experimental verification of control of burr formation in micro-milling of Ti-6Al-4 V by introducing compressive residual stress on the surface of the workpiece. The practical significance of the current study is that the compressive residual stress suppresses the burr generation by up to 63% in terms of burr width and height. The resultant cutting forces are found to be 13% higher for pre-stressed material, compared to the ones without pre-stress. As the cutting-edge radius and grain size of the material are of comparable magnitude in the case of micro-milling, a strain gradient-based dynamic recrystallization constitutive flow model is developed and incorporated into a finite element model in Abaqus. In addition, the cut marks at the machined wall of the material, are modelled with a proposed friction model and verified with experiments. The results of the FEM model are found to agree with the experimental finding by up to 12%.

Sharpening mechanism of extremely sharp edges for diamond micro mills

• This study explores the sharpening mechanism of extremely sharp edges for PCD micro mills. • The transient temperature model of laser cutting PCD is constructed for studying the material removal mechanism . • The uniform graphitisation , micro abrasion , and smaller material stress near edge contribute to the extremely sharp edges. • The PCD micro mills with cutting edge radius of r β = 0.21 μm are fabricated indicating better sharpness compared with r β = 1–5 μm reported hitherto. The fabrication of extremely sharp cutting edges for ultra-hard micro mills is crucial for suppressing the severe size effect, restraining burr formation, and improving the surface quality of widely used micro components in micro milling. In this study, a hybrid machining technique, laser-assisted precision grinding, is proposed to improve the grinding efficiency and increase the sharpness of the cutting edges of polycrystalline diamond (PCD) micro end mills. A transient heat model of laser ablation was constructed to investigate the laser-cutting mechanism of PCD with a cobalt binder. Facilitated by suitable heat conduction, cobalt absorbs photon energy to heat itself and transmits thermal energy to the surrounding diamond, resulting in uniform graphitisation and cobalt oxidation on the cut section. Hence, the affected layer on the cut section can be easily ground using a low grinding load. Moreover, the subsequent grinding mechanism of the laser-cut section was demonstrated. The diamond was removed via micro-abrasion without any intercrystalline cracks or grain dislodgement, and the abrasive grain size was optimised to achieve superior ground surface quality. Thus, the uniform graphitization, micro abrasion, and smaller material stress near edge contributed to the extremely sharp edges. Furthermore, PCD micro end mills with a diameter of 400 μm, aspect ratio of 2, and cutting-edge radius of approximately 0.2 μm were fabricated, showing a superior sharpness compared with that of the end mills with an edge radius of 1–5 μm reported hitherto. Subsequently, micro-milling experiments were conducted on oxygen-free high-conductivity copper (OFHC) using the self-fabricated PCD micro end mills. Almost no burrs were observed, and the surface roughness of the machined groove was 19.8 nm, indicating the superior cutting performance of the fabricated PCD micro end mills.

Analysis of drilling-induced geometrical damages in basalt and carbon fibre-reinforced polymer (BFRP and CFRP) composites

Basalt fibre-reinforced polymer (BFRP) composites probably tend to replace some carbon fibre-reinforced polymer (CFRP) applications due to their excellent specific strengths and sustainability. Despite the published early promising results concerning the material properties of BFRP, their application is not widespread, and their machinability is not supported widely by published experiences. The main aim of the present study is to experimentally investigate the drilling-induced geometrical damages of BFRP and CFRP composites. Drilling experiments were conducted at various feed and cutting speed levels using a solid carbide twist drill. The drilling-induced burr was analysed by a Mitutoyo 361–804 digital microscope, a Mitutoyo SJ400 surface tester recorded the surface roughness, and the microstructure was analysed by a Zeiss Evo MA 10 scanning electron microscope. The measured data were evaluated through digital image processing (DIP), response surface methodology (RSM), and analysis of variances (ANOVA). The experimental results show that drilling-induced burr is more severe and surface roughness is worse in BFRP than in CFRP. The composite type influenced the geometrical damages primarily, followed by the feed in the case of burrs and by the cutting speed in the case of surface roughness. The present experimental study suggests that the drilling of BFRP is even more challenging than drilling CFRP from the point of view of burr formation and micro geometrical properties.

Thermal Pulse Processing of Blanks of Small-Sized Parts Made of Beryllium Bronze and 29 NK Alloy.

The presence of burrs on parts is not allowed in high-tech industries; there is a tendency to improve accuracy and quality and to reduce overall dimensions. A high proportion of operations are aimed at removing burrs in the labor intensity of release. Thermal pulse deburring machines are being developed and are applicable for deburring small-sized high-precision parts while providing additional processing conditions. A significant part of the electronic component base—coaxial radio components—is produced from beryllium bronze and the 29 NK alloy. It is not possible to prevent burr formation when cutting these materials. The conditions for deburring by the thermal pulse method are established in compliance with the requirements for deviations in the geometry of parts, for surface roughness and for ensuring maximum processing performance. These are restrictions on the thickness of the burr root, a variant of the arrangement of parts in the chamber of thermal impulse installation, which ensures the prevention of damage to parts during processing. Additionally, it provides access to a combustible mixture of all the surfaces of the parts; there is also a pressure value of the combustible mixture, depending on the characteristics of the thermal pulse installation, the total area of the treated surface, and the thermal conductivity of the materials for workpieces.

Machinability and surface integrity investigation during helical hole milling in AZ31 magnesium alloy

Conventional drilling has been widely used for making holes in structural materials. However, drawbacks like high cutting forces, poor surface finish, high cutting temperatures, excessive tool wear, and undesirable burr formation while drilling magnesium alloys have necessitated the development of alternative hole-making methods. Lately, the helical milling process has attracted interest in facilitating hole-making for assembly applications. However, the machinability of magnesium alloys using the helical milling process needs more investigation. Therefore, the presented work analyzed the influence of axial pitch, tangential feed, and spindle speed on cutting forces and surface integrity while milling AZ31 magnesium alloy. Axial feed was the most crucial factor contributing to the thrust force (71.8%), followed by tangential feed (13.2%). All three process variables impacted the radial force. Spindle speed was the most influential variable affecting the surface roughness (48.7%), followed by axial pitch (31.4%) and tangential feed (12.5%). Microhardness closer to the free surface of the hole was higher than the subsurface hardness. Moreover, microhardness showed an upward trend with the rise in axial pitch and tangential feed; however, it reduced with increased spindle speed.

Investigation of Top Burr Formation in Micromilling for Surface Quality Improvement

Investigation of Top Burr Formation in Micromilling for Surface Quality Improvement

A Review on Drilling of Multilayer Fiber-Reinforced Polymer Composites and Aluminum Stacks: Optimization of Strategies for Improving the Drilling Performance of Aerospace Assemblies

In recent years, the use of hybrid composite stacks, particularly CFRP/Al assemblies, and fiber metal laminates (FMLs) has progressively become a convincing alternative to fiber-reinforced polymers (FRPs) and conventional metal alloys to meet the requirements of structural weight reduction in the modern aerospace industry. These new structural materials, which combine greater mechanical properties with low specific mass, are commonly assembled by riveted and bolted joints. The drilling operation, which represents the essential hole-making process used in the aerospace industry, proves particularly challenging when it comes to achieving damage-free holes with tight tolerances for CFRP/Al stacks in one-shot operations under dry conditions due to the dissimilar mechanical and thermal behavior of each constituent. Rapid and severe tool wear, heat damage, oversized drilled holes and the formation of metal burrs are among the major issues induced by the drilling of multi-material stacks. This paper provides an in-depth review of recent advancements concerning the selection of optimized strategies for high-performance drilling of multi-material stacks by focusing on the significant conclusions of experimental investigations of the effects of drilling parameters and cutting tool characteristics on the drilling performance of aerospace assemblies with CFRP/Al stacks and FML materials. The feasibility of alternative drilling processes for improving the hole quality of hybrid composite stacks is also discussed.

Numerical modeling and simulation of machining of 3D printed CFRP composite

Carbon Fiber Reinforced Polymer (CFRP) composites are gaining popularity in recent years for their high specific strength and superior performance under extreme conditions. Additive manufacturing (AM) or 3D printing of CFRP composites has added a new dimension to the existing research of CFRP composites. However, one of the caveats of 3D printed CFRP composites is that the dimensional accuracy and the surface finish achieved fail to meet the standard tolerance requirement. To achieve the desired accuracy further post-process machining is required. However, machining an anisotropic material such as 3D printed CFRP composites impose challenges. This study aims at investigating the machining behavior and post-processing capability of 3D printed CFRP using numerical modeling and simulation using ABAQUS/Explicit, a commercially available powerful finite element analysis (FEA) software package. Influence of machining parameters, such as feed and depth of cut (DOC) and 3D printing parameter, such as percentage of overlap between adjacent passes have been studied. The post-processing capability or machining behavior of 3D printed CFRP has been evaluated by dependent parameters, such as, cutting forces, strain, chip and burr formation, and the resultant surface topology. With the use of proper damage parameters, such as, ductile and shear damage and Johnson-Cook criterion for plasticity, a 3D model was developed in the FEA. Eight layers were stacked with the orientation of 45°-135°-45°-135°. The layers were joined using cohesive properties. Damage in the cohesive bonds was also defined using the quadratic damage criterion to model delamination. To capture the changes in elemental level, linear tetrahedral elements C3D4T, were used. A reference point on the bottom layer was used to capture the history of cutting forces. The cutting and thrust forces increased with the increase of DOC and feed. The rigidity, shape of the flutes and print direction influenced chip formation. Finally, the proposed model was used to observe the quality of surface finish.

Suppression Mechanism and Prediction Model of Top Burr in Metal Milling Under Ice Boundary Constraint

Abstract During metal milling, top burrs will inevitably appear on the edge of the workpiece, which seriously reduces the edge quality and assembly accuracy of the workpiece, thereby reducing the service performance of the product. This study innovatively proposes an ice boundary constraint (IBC) method to avoid top burrs formation during cutting. First, the formation mechanism of the top burrs is analyzed, and the principle of IBC is interpreted. Then, an analytical model is established to realize the cutting analysis, obtain the stress distribution during cutting, and explore the plastic deformation process of the workpiece edge, thus revealing top burrs suppression mechanism and predicting top burrs height. Afterwards, based on the proposed analytical model, finite element method (FEM) is used to simulate the stress distribution at the top edge to verify the stress analysis results of the analytical model. Finally, the effectiveness of IBC method and the prediction accuracy of the analytical model are verified by aluminum alloy 2024 (AA2024) milling experiments. The experimental results show that IBC method can reduce the top burrs height by 54.62% on average, and the percentage of average prediction error of the analytical model is limited to 16.66%. Moreover, the milling experiments of carbon steel and aluminum alloy 6061 (AA6061) are carried out under the same process parameters, and the results show that IBC method can realize the suppression of top burrs of different materials. This study can provide valuable theoretical and practical reference for the minimization of burrs formation during cutting.

Performance evaluation of DLC and NCD coatings in micro-milling of Al7075-T6 alloy

The main problem in machining of aluminum alloys is the adhesion of chips to the cutting tool. In micro milling, chip adhesion causes a decrease in surface quality and contributes to micro burr formation. There are several ways to minimize chip adhesion, one of which is to coat the tool with the appropriate material. Carbon-based coatings are coating materials that can minimize chip adhesion. In this study, the performances of Diamond-Like Carbon (DLC) and Nano-Crystalline Diamond (NCD) coating materials in the micro-milling process of Al7075-T6 alloy were investigated in all aspects. The tests are performed under dry cutting conditions using various cutting parameters. Experimental results show that DLC and NCD coated tools produce approximately 20 % and 40 % lower forces, respectively. For fz ≤ 0.5 μm/tooth, no decisive influence of the coating material on the cutting forces is observed. For fz ≤ 0.5 μm/tooth, surface roughness and burr width increase significantly in uncoated and NCD coated tools due to size effect. A strong size effect was observed at feed values less than approximately 36 % of the tool edge radius in terms of surface roughness and <18 % of the tool edge radius in terms of burr width.

Micro-drill on Al/SiC composite by EDD process: An RSM-MOGOA based hybrid approach

The development in technology developed new materials such as composites. These composites can be developed by different techniques. But the processing of these composites exhibits many challenges due to hard reinforcements. The recent work used the stir casting technique to develop the Al/SiC composite. After that, the machinability of the developed composite was checked with the electric discharge drilling. The microholes of diameter 1.5 mm were made on the developed composite. The experiments were designed using Response Surface Methodology based Box-Behnken design. According to the available drilling parameters (discharge current, pulse on-time, and pulse off-time) and their level, for each experiment overall, fifteen experiments were performed, and the tool wear rate (TWR) and material removal rate (MRR) were evaluated. After that, empirical models were developed for MRR and TWR, which were further solved by the Multi-objective Grasshopper Optimization Algorithm (MOGOA). It was observed that the predicted solutions suggested by MOGOA produce excellent results reproducibility. A small amount of burr formation was observed at the optimized setting. Energy dispersive spectroscopy (EDS) has been performed to determine the elements in the drilled composite.

Cutting Force in Drilling with Flat Bottom Drill

Flat bottom drills at a point angle of 180 deg. have recently been applied to not only drilling on inclined surfaces but also flat bottom holes in terms of the dimensional accuracy and the process efficiency. Controlling the cutting force, the tool damage, and the surface finish, the corner shape is a critical parameter in the design of the flat bottom drill. The paper discusses the effect of the corner radius on the cutting forces and the surface finish in drilling with flat bottom drills. The typical differences in the cutting force are confirmed during the edge engagement. Then, the cutting force is simulated with a chip flow model, in which the chip flow angle is determined to minimize the cutting energy. The cylinder surface finishes and the burr formations are associated with the chip flow direction and the uncut chip thickness at the end of the lip.

Hybrid laser and micro milling methods for higher depth microchannel fabrication

The performance of microchannels is dependent on the geometry, dimensions and surface quality. The most widely used methods for manufacturing microchannels are laser micro-milling (LMM), conventional micro-milling (CMM), micro-forming, and chemical etching. The main challenges in manufacturing microchannels with LMM are non-uniform dimensions, tapering effect, and low aspect ratio. In addition to that, tool wear and burrs formation on the top surface of channels are common challenges in conventional micro milling (CMM) techniques. In the present study, Hybrid micro milling techniques have been proposed to manufacture the better quality of micro-channels. The proposed methods include the application of laser and conventional micro milling in two approaches; laser pre-channel micro milling (LPCMM) and laser assisted sequential micro milling (LASMM). In the LPCMM approach, a pre-channel was fabricated by LMM followed by CMM, whereas in LASMM, the material was removed layer by layer by LMM followed by CMM. The proposed methods were compared with CMM considering cutting forces, surface finish, top burrs, tool morphology and flank wear as responses. As compared to CMM, results revealed that the hybrid methodologies mean down burr width decreased by 75 % and 20 %; mean up burr width reduced by 81 % and 20 %; and cutting force decreased by 24 % and 60 % in LASMM and LPCMM, respectively. However, surface roughness (Sa) increased by 7.5 % and 32 % in LASMM and LPCMM, respectively, because of the thermal effect of the laser beam on the fabricated channels.

Study of deformation and fracture of high strength steel sheet during conventional and robust trimming by conducting partial trimming tests

An instrumented trimming press equipped with D2 grade steel die inserts with sharp edges was used to conduct trimming tests on DP980 sheets with clearances of 10%, 20%, and 30% of the sheet thickness. Trimming tests were conducted either with or without a support pad placed under the scrap piece and the trimming force was measured as a function of penetration distance of the upper die. The progression of plastic deformation and fracture processes that occurred in the shear affected zone (SAZ) of DP980 were observed on the polished cross-sections of the sheet by performing partial trimming tests. During conventional trimming with 10% clearance, cracks propagated simultaneously from the upper and lower surfaces of the sheet toward each other. However, when the clearance was increased to 30%, the main crack was initiated from the upper surface and propagated toward the lower surface resulting in the formation of a tensile-type burr. At 30% clearance, the trimming test conducted with a support pad prevented bending of the scrap piece, resulting in a uniform damage distribution within the SAZ. Thus, an improved sheared edge quality is achieved at larger clearances.

Thin Wire Casting Using Twin Wheel Caster Equipped with Horizontal Wheels

solidification, process shortening and energy saving. A twin-wheel caster equipped with two additional horizontal wheels was proposed to cast thin aluminum alloy wire at higher speed. In the proposed twin-wheel caster, a groove was machined on the lower wheel. Two small horizontal wheels were positioned between the molten-metal-pouring launder and the upper wheel to assist the solidification of poured molten metal and to prevent burr formation. The alignment of the horizontal wheel sensitively affected the occurrence of wire defects. An Al-1.2%Fe wire with a cross section of 6.2 mm2 was cast at 15 m/min. Thinner wires without burring could be cast at a speed higher than that of the twin-wheel caster without the horizontal wheels. The surface condition of the as-cast wire cast by the twin-wheel caster equipped with horizontal wheels was worse than that of the casting using the twin-wheel caster without horizontal wheels.

Investigation on burr formation characteristics in micro milling of Ω-shaped reentrant microchannels

Reentrant microchannels show excellent heat dissipation capabilities and are promising for microchannel cooling systems in a variety of application areas. This study developed a micro milling method to fabricate a unique type of Ω-shaped reentrant microchannels in pure copper. The critical issues in micromilling, i.e., formations of side burr, entrance burr and exit burr in reentrant microchannels and their mechanisms, were comprehensively investigated with experiments and finite element (FE) simulations. It was found that side burrs in reentrant microchannels were mainly formed on the up-milling side, and some of them extended from the sidewall of circular cavity to the top exit slot. The restriction of top exit slot of reentrant microchannels played a significant role on the extrusion, squeezing and thrusting of deformed materials and chips, which contributed to the formation of side burrs. Moreover, the effects of spindle speed and feed rate on the side burr formation and their sizes were also explored. The side burr size firstly increased, reached the maximum, and then decreased with increasing spindle speed. Besides, it firstly increased, then decreased to be the minimum and finally increased with increasing feed rate. The ratio between the feed per tooth and cutting edge radius (fz/re), which combined both spindle speed and feed rate, is believed to be the critical factor for burr formation. The minimum uncut chip thickness seemed to be of 0.25 fold of the tool edge radius in micromilling reentrant microchannels. The fz/re of 0.42 with a spindle speed of 15,000 r/min and feed rate of 25 mm/min was suggested to be the optimal machining parameter to minimize the side burrs of reentrant microchannels.

A robust digital image processing method for measuring the planar burr length at milling

The burr formation is one of the difficulties at the cutting processes; moreover, its size and characteristics show changes along the edge; therefore, it is hard to measure. The main aim of the paper is to develop a novel algorithm that is suitable for measuring the planar burr length of such contours that cannot be scanned below. The proposed method uses a digital microscope attached to a machine tool and using existing image processing algorithms in combination with novel approaches. The advantage of the current method is that, it allows collecting the height of burr along the workpiece automatically since it is able to handle and avoid interruptions, branches and provide uniform thickness for the determined contour. Another advantage is the extended measurement ability for workpieces which contains inner contours and cannot be illuminated from below. The method was tested with sample images and also with face milling experiments, and the results were validated with the data originating from a coordinate measurement machine. The result shows a good agreement at the validation. The available accuracy mainly depends on the applied measuring equipment (resolution and magnification of camera) and set up. The theoretical accuracy of the proposed method can even approximate the magnitude of the pixels. In this research work, the achieved accuracy was ±0.06 mm in the best case, and ±0.1 mm in the worst case with the used experimental device.

Investigation of deviation and surface topography in ultrasonic vibration-assisted milling

Thin-walled structures have many applications in the aerospace industry. An important feature of them is their high strength to weight. When milling the thin-walled part, the thickness decreases step by step by cutting, which causes the process to be complex and dependent on process parameters. In the present study, thin-walled aluminum structures are investigated using conventional and ultrasonic milling processes, and distortion, surface roughness, surface texture, and average thin-wall forces are also investigated. Therefore, 18 tests are performed on parts made of 7075T6 aluminum alloy using various feeds, spindle speeds, and machining modes. The results showed that the machining type and spindle speed had 47% and 33% effect on distortion, respectively. In addition, the results showed that by applying vibrations to the milling, the amount of distortion can be reduced by up to 30% and effectively optimized. This technique is suitable for manufacturing industries that require high dimensional accuracy. Also, the surface texture and burr formation are investigated. In particular, the surface roughness in ultrasonic milling decreased compared to conventional milling.

Manufacturability and surface characterisation of polymeric microfluidic devices for biomedical applications

Generally, machining of polymeric microfluidic devices is a one-step manufacturing process. It is economical compared to lithography and can be used for batch production and rapid prototyping. However, surface properties are modified during machining due to the viscoelasticity property of polymers and the mechanical nature of fractures. In this present work, the manufacturing capability of the mechanical micromachining process of polymers has been explored. Surface characteristics like surface roughness, surface energy, and burr formation are investigated. Surface quality is chosen as a contributing factor for defining the manufacturing capability as it is one of the significant factors influencing the physics of fluid flow in microchannels. In the present work, several manufacturing methods, such as 3D printing, hot embossing, photolithography, and mechanical micromachining, were considered. The surface energy of various surfaces machined using the abovementioned methods is evaluated and compared. It has been observed that mechanical micromachining is the most suitable methods as they have less wettability with lower surface energy. Further investigations are carried out by machining microfluidic devices using polymethylmethacrylate (PMMA) and polycarbonate (PC) materials, as they are extensively used in biomedical applications. Surface roughness was measured on the PMMA and PC surfaces after milling. The surface roughness values and surface energies are used for evaluating the suitability of the machining process to fabricate microfluidic devices. Microfluidic devices with serpentine channels were machined on PMMA with a depth of 50 µm and width of 200 µm for evaluating inertial focusing in the channels. These devices were further evaluated for blood cell separation at different dilution rates. It is observed that PMMA is the preferable choice for fabricating microfluidic devices using mechanical micro-milling.