Larger Feed Rate Research Articles

Investigation on tearing damage of CFRP circular cell honeycomb in end-face grinding

CFRP circular cell honeycomb has promising applications in the aerospace field due to its excellent mechanical properties. However, a large number of periodically distributed tearing damages severely restrict the high-quality machining of CFRP circular cell honeycomb. This paper investigates the formation mechanism of tearing damages during end-face grinding of CFRP circular cell honeycomb and proposes suppression strategies. In this paper, a maximum undeformed chip thickness model considering tearing damage distribution is developed, and the evolution behavior of tearing damage is studied by combining the material removal process and grinding force. The grinding force and maximum tearing damage depth in different grinding conditions are analyzed. The results show that the formation of tearing damage in the cut-in stage is related to the weak stiffness of thin walls and the radial grinding force. The radial grinding force and maximum tearing depth can be altered by changing the maximum undeformed chip thickness which can be adjusted for different grinding speeds, feed rates, and offset ratios. The low-damage machining of CFRP circular cell honeycomb can be achieved by using a large offset ratio and variable feed rate.

Theoretical and experimental study of 3D ultrasonic vibration-assisted turning driven by two actuators

Ultrasonic vibration-assisted turning techniques can be used to reduce the roughness of the output surface and also to obtain special texture structures. This paper introduced an adjustable 3D ultrasonic vibration-assisted turning device, which has two operating modes, one for reducing the roughness of the output surface, and the other for constructing special textures with hydrophobic properties. Theoretical calculations, geometric modeling, finite element simulation and harmonic response analysis were used to guide the design process, and finally experimental verification was performed. The amplitude calibration results show that a 3D spatial elliptical vibration pattern of the turning tool can be realized. The experimental results indicate that a small cutting speed and a low feed rate help to reduce the roughness of the finished surface, while a large cutting speed and a large feed rate are good for increasing the contact angle of the output surface.

Effects of cutting parameter on microstructure and corrosion behavior of 304 stainless steel in simulated primary water

• Cutting can induce a gradient surface microstructure with a several microns deep fine-grain layer on top, followed by several tens or hundreds of micrometers deep plastic deformation region. • Even with the similar surface roughness, the deformation microstructure can be very different due to the different cutting parameters. • The effect degree on the depth of machining-affected zone (MAZ) is feed rate > cutting depth > cutting speed. • At the same depth of MAZ, the localized corrosion rate along the deformation bands is higher than that along the grain boundaries. The influence of surface conditions on the corrosion behavior of engineering structures has been paid more attention. However, there is still a lack of systematic research on the effect of cutting parameters on material's microstructure and performance in service. In this paper, the effect of cutting parameters on microstructure and corrosion behaviors of 304 stainless steel in simulated primary water is well investigated. The results show that different cutting parameters can cause the superficial layer a gradient microstructure with nanocrystalized layer on top and deformation band structures underneath. With the similar surface roughness, the deformation microstructure can be very different due to the different cutting parameters. The effect degree on the depth of deformation zone is feed rate > cutting depth > cutting speed. The larger feed rate, lower cutting depth, lower cutting rate may induce a deeper deformation zone. With the increasing depth away from the machined surface, the localized corrosion rate is decreased, and at the same depth the localized corrosion rate along the deformation bands is higher than that along the grain boundaries (GBs). The nanocrystalized surface has a smallest general corrosion rate due to the quick formation of Cr rich oxide film. However, once the corrosion penetrates through this nanocrystalized layer, subsequent preferential corrosion at deformation bands and GBs will dominate and may lead to the significant increase of corrosion rate of the component in high temperature pressurized water.

Energy consumption, carbon emissions, product cost, and process time in incremental sheet forming process: A holistic review from sustainability perspective

Due to continuous worsening of the environment and depletion of natural resources, concept of sustainability in manufacturing sector is gaining an increasing attention. New processes and strategies characterized by efficient use of energy and materials, low processing time and zero or nearly zero green-house emissions are being explored. Incremental sheet forming (ISF) is a comparatively new sheet forming process with high economic payoff for small production runs and customized orders. The current study presents a comprehensive review on the sustainability aspects of the process. The process performance in terms of power demand, energy consumption, cost, CO2 emissions, processing time, and material wastage/usage is analyzed on the basis of published literature, and important conclusions and recommendations are drawn to utilize the process for cleaner, economical and time efficient production. The review establishes that ISF is more sustainable process than conventional forming methods for small production runs. Further, its sustainability performance can be further enhanced by choosing optimum process conditions especially lower spindle rotation, larger feed rate and step size. Shorter tool paths and advent of energy efficient machines is likely to further elevate the process performance. The review also identifies future work and presents fundamental guidelines and recommendations for establishing the sustainable ISF process.

Selecting process parameters of crack-free Ni60A alloy coating prepared by coaxial laser cladding

Ni60A alloy coating prepared by laser cladding is limited by the high cracking susceptibility. In this study, the crack-free Ni60A coating is obtained by selecting suitable process parameters. In order to avoid size effect on heat dissipation and stress evolution, the width and height models of cladding track are established to obtain same size track with different process parameters. These two models divide the three main parameters laser power, powder feed rate and scanning speed into two groups, namely line energy (the ratio of laser power to scanning speed) and powder feed rate, and determine their experimental values. Then the influence of determined line energy and powder feed rate on cracking are tested, which significantly reduces the amount of tests compared with common optimization methods. The results show that large line energy and low powder feed rate are helpful to prevent crack, but lead to low microhardness. In order to obtain crack-free Ni60A coating with higher microhardness, the combination method of preheating to 300 °C and adding insulating plate under the substrate is further studied, which can not only reduce thermal damage to the substrate but also improve the microhardness up to 510–553 HV.

Elliptic vibration assisted cutting of metal matrix composite reinforced by silicon carbide: an investigation of machining mechanisms and surface integrity

This paper aims to investigate the deformation mechanisms and surface integrity of SiCp/Al composites machined by elliptic vibration assisted cutting (EVAC). Self-designed EVAC device was applied to generate the elliptical trajectory on tool tip, which is driven by three piezoelectric actuators along different directions with phase difference. A two-dimensional (2D) microstructure-based finite element (FE) model of SiCp/Al composites was also established to research the deformation mechanisms and surface integrity in the process of EVAC, including material removal mechanisms, cutting force, surface roughness and microstructure. Systematic orthogonal cutting experiments shown that the relative position of tool-particles are changed by the time-varying cutting thickness in EVAC, leading to more obvious particle fracture during SiC particles removal process. Particle fracture appears in the area of particle clusters affected by chip lifting of tool. The intermittent cutting effect not only reduces the average cutting force, but also eliminates the scratch on machined surface caused by SiC particles entering the flank face–workpiece interface, improving the machined surface quality. Limited by the volume of material removal, 2D FE model has a high prediction accuracy for the micro-removal process of composite materials. The application of elliptical vibration is able to create the special functional surfaces. In order to increase the hydrophobicity of machined surface, larger feed rate and smaller cutting depth should be selected as far as possible.

Surface Finishing of FDM-Fabricated Amorphous Polyetheretherketone and Its Carbon-Fiber-Reinforced Composite by Dry Milling.

In recent years, many investigations have been devoted to fused deposition modeling (FDM) of high-performance polymer-polyetheretherketone (PEEK) and carbon-fiber-reinforced PEEK (CF/PEEK) for biomedical and aerospace applications. However, the staircase effect naturally brought about by FDM restricts further applications of 3D-printed PEEK and its composites in high-temperature molds, medical implants, and precision components, which require better or customized surface qualities. Hence, this work aimed to reduce the staircase effect and improve the surface quality of 3D-printed PEEK and CF/PEEK parts by dry milling of the fluctuant exterior surface. The co-dependency between 3D printing parameters (raster angle and layer thickness) and milling parameters (depth of cut, spindle speed, and feed rate per tooth) were investigated through experiments. The difference in removal mechanisms for PEEK and CF/PEEK was revealed. It was confirmed that the smearing effect enhanced the surface quality based on the morphology analysis and the simulation model. Both the raster angle of +45°/−45° and the small layer thickness could improve the surface quality of these 3D-printed polymers after dry milling. A large depth of cut and a large feed rate per tooth were likely to deteriorate the finished polymer surface. The spindle speed could influence the morphologies without significant changes in roughness values. Finally, a demonstration was performed to verify that dry milling of 3D-printed amorphous PEEK and CF/PEEK parts could lead to a high surface quality for critical requirements.

Surface quality of cemented tungsten carbide finished by direct cutting using diamond-coated carbide end mill

• Superiority of direct cutting of cemented carbide with diamond-coated tool was shown. • Surface quality in direct cutting, electrical machining, and polishing was compared. • Specularity of finished surface similar to polishing was obtained via direct cutting. • Large compressive residual stress can also be obtained via direct cutting. • Higher transverse rupture strength can be achieved compared with polishing. This study addresses the finished surface quality of cemented tungsten carbide obtained via direct cutting with a diamond-coated carbide end mill under ultrasmall feed rates. The surface appearance, composition distribution, profile, roughness, residual stress, and transverse rupture strength were experimentally investigated. The finished surfaces obtained via electric discharge machining with two types of machining conditions and mechanical polishing processes were also evaluated to compare the surface quality. Two types of cemented tungsten carbide materials, TAS VC-70 and VM-40, were applied as the workpiece materials. A mirror surface can be obtained via direct cutting and mechanical polishing with both materials. The microstructure morphologies of the finished surface obtained via direct cutting were different from those obtained via mechanical polishing. In the case of VC-70 which has larger tungsten carbide grain size and higher cobalt content, the flat cross-section of the tungsten carbide grain under ductile mode cutting was conspicuous in direct cutting under small feed rate and depth of cut. In contrast, an extremely thin layer composed of fine grains of tungsten carbide and cobalt was observed on the finished surface in direct cutting under comparatively large feed rate and depth of cut. The surface roughness and profile of the finished surface resulting from direct cutting were comparatively rougher than those resulting from mechanical polishing, although the finished surface was significantly smoother than that resulting from electric discharge machining. The residual stress of the subsurface obtained via direct cutting showed larger compressive stress than that obtained via electric discharge machining and mechanical polishing under all cutting conditions and materials. Moreover, satisfactory transverse rupture strength can be obtained via direct cutting in both materials compared with other processes, and two times more transverse rupture strength can be achieved via direct cutting compared with the case of electric discharge machining in VM-40 cutting.

Effects of spinning parameters on microstructures of ellipsoidal heads during marginal-restraint mandrel-free spinning

Marginal-restraint mandrel-free spinning is an advanced technology for manufacturing ellipsoidal heads with large diameter-thickness ratios. The effects of spinning parameters on the forming accuracy of ellipsoidal heads have been studied, and optimized spinning parameters have been obtained. The microstructure evolution of a workpiece is usually very complicated in the spinning process. In this work, the influence of spinning parameters on the microstructures of two-pass spun ellipsoidal heads is studied. It is found that the forming angle and feed rate of the first pass, angle between passes, and feed rate of the second pass significantly affect the microstructures. Meanwhile, the evolution rule of the microstructures near the inner and outer surfaces of the spun parts is almost consistent. A large forming angle, large angle between passes, or large feed rate of the second pass are beneficial to obtain uniform microstructures. A small or large feed rate of the first pass reduces the microstructure uniformity. To improve the microstructure uniformity between the inner and outer surfaces, the optimized spinning parameters are determined.

Experimental investigation on the performance of novel double cone integrated tool in one-shot drilling of metal stacks

In order to reduce misalignment, enhance tight tolerance, and improve machining efficiency, a novel double cone integrated tool was developed and experimentally investigated during one-shot drilling of aluminum and aluminum alloy stacks in this paper. This special tool geometry can finish drilling, reaming, and countersinking processes at the same time. Its machining properties were comparatively evaluated with a standard twist drill (reference drill) by means of a series of experiments. Experimental results highlighted the influence of tool geometry on cutting force and vibration signals for drilling, reaming, and countersinking processes, respectively. The results indicated that the double cone integrated drill can induce a little larger thrust force than a reference drill due to its longer cutting edge. In addition, the chip morphologies generated by different processes and cutting variations also have been comparatively analyzed. The double cone drill under a larger feed rate was prone to produce smaller chips. Furthermore, the double cone drill can achieve smaller burrs, better surface integrity, and lighter tool wear compared with reference drill. The information obtained from this study can provide a better understanding of the one-shot drilling process and guidance for achieving higher efficiency and better hole quality.

Experimental study on the incremental forming limit of the aluminum alloy AA2024 sheet

Aluminum alloy AA2024 has superior characteristics, including high specific strength, excellent corrosion resistance, and remarkable mechanical properties. Moreover, it has an undeniable role in the aerospace and automotive industries, which originates from its lightweight. As an advanced sheet metal in the 3D printing technology, the incremental forming process also has unique advantages in the rapid and small batch production of components in aerospace and automotive industries. The present study investigates the mechanical characteristics of AA2024 sheets at different heat treatment conditions. Moreover, effects of different process parameters on the incremental forming limit are studied through tensile and warm incremental forming experiments. It is intended to provide a guideline for aluminum alloy AA2024 sheet forming. Obtained results from tensile strength experiments indicate that the elevated temperature can reduce the tensile strength of AA2024-T4 by 26.14% and increase its uniform elongation by 28.29%. Incremental forming experiments show that as the temperature increases, the forming angle limit of AA2024-T4 increases by 21.98%. However, it is still lower than the forming angle limit of AA2024-O by 18.38% at the room temperature. It is found that a variable-angle busbar shape, larger feed rate, and lower pitch value can make a component with a greater forming limit. Compared with the stamping process, the incremental forming process can significantly increase the forming limit of the AA2024 sheet, indicating that the incremental forming process is a good choice for AA2024 sheet forming.

A thermo-mechanical model of drill margin-borehole surface interface contact conditions in dry drilling of thick CFRP laminates

Dry drilling of thick carbon fiber reinforced polymer (CFRP) laminates requires careful selection of process parameters in order to obtain acceptable borehole surface quality. Complex contact conditions between the drill margin and the borehole surface determine the integrity of the borehole surface depending on the process parameters and temperature-dependent viscoelastic material properties. Temperature rise during dry drilling reduces the elastic modulus of the CFRP and causes thermal expansion of the drill, resulting in considerable contact length at the drill margin and borehole surface interface. Manufacturers need a better understanding of the interaction among contact pressure, sliding velocity, temperature at the interface, and temperature-dependent material properties to develop predictive models for drilling CFRPs. To examine this complex interaction, this study develops a novel, hybrid model that combines a time-based analytical modeling of drilling process with a finite element-based modeling of temperature rise. Drilling experiments were performed in which thrust force, torque, and temperature were measured as a function of feed, and these measurements were used to identify unknown hybrid model parameters. The results revealed that a significant change in friction conditions occurs when increased temperatures at the margin and borehole surface interface approach and exceed the glass transition temperature of the CFRP laminate at a large feed rate. These findings show the benefit of increasing feed during dry drilling, which is nonetheless limited by the temperature-dependent material properties of the work material.

Cutting performance and wear mechanism of spark plasma–sintered silicon nitride ceramics tool in dry turning of 41Cr4 hardened steel

Cutting performance and wear mechanism of spark plasma-sintered Si3N4 (SN91) and Si3N4/WC (SW10) ceramic tools in the dry turning of 41Cr4 hardened steel are studied. SN91 tool shows better wear resistance than SW10 tool and commercial ceramic tool SW500 and cemented carbide tool YG8 under the same cutting conditions. The better cutting performance of SN91 can be attributed to its excellent high-temperature flexural strength. The most significant factor affecting the tool life of SN91 is the cutting speed. A higher material removal volume can be achieved at a low cutting speed, large depth of cut, and large feed rate. A long cutting distance/time can be achieved at a low cutting speed, small depth of cut, and feed rate. At a cutting speed of 103.62 m/min (ap = 0.1 mm, and f = 0.05 mm/rev), the wear mechanisms of SN91 are adhesion, oxidation, and diffusion, and no crater wear is observed on the rake face. At a cutting speed of 214.31 (ap = 0.3 mm and f = 0.05 mm/rev) and 314 m/min (ap = 0.2 mm and f = 0.05 mm/rev), the failure forms of SN91 tool are mainly rake face crater wear and flank wear; the wear mechanisms of rake face are diffusion, abrasion, and oxidation; and the wear mechanisms of flank face are abrasion, adhesion, and oxidation. The failure forms of SW10 tool are mainly rake face crater wear and flank wear, and the wear mechanisms are diffusion, abrasion, adhesion, and oxidation.

Effects of Different Cooling Methods on the Specific Energy Consumption when Drilling CFRP/Ti6Al4V Stacks

As the current trend in the manufacturing industry is moving toward cleaner production and sustainable manufacturing, selecting a proper cooling method is of vital importance to reduce the environmental and economical impacts of machining processes. Thus, one of the biggest challenges a manufacturer faces when machining titanium-composite stacks is whether or not to use coolant, and, if so, how to apply it effectively. Therefore, it is important to know how the application of coolants to machined composite stack surfaces affects the kinetics of cutting and how the cut surfaces interact with the coolant. The aim of this paper is to study the cutting energy distribution in drilling CFRP/Ti6Al4V stacks under different cooling conditions and to optimize the machining process in order to reduce the energy consumption. A series of drilling tests using TiAlN-coated drill bits under dry and MQL conditions were conducted to quantify the specific cutting energy consumption of each stacked phase. The results indicate that the use of vegetable-based lubricating oil can effectively reduce the energy consumed on the the friction work between the drill bit and the machined hole wall, which leads to a decrease in drilling torque and specific cutting energy. To achieve better hole quality and energy efficiency, large feed rates under MQL conditions are recommended.

Effect of cutting parameters on tool wear under minimum quantity cooling lubrication (MQCL) conditions

This paper presents the effect of cutting parameters on tool wear under minimum quantity cooling lubrication (MQCL) conditions. Turning AISI 304 stainless steel was carried out using VAMF-1 environmentally friendly cutting fluid under MQCL conditions, for which 27 groups of all-factor experiments were utilized. The tool wear results showed that the most effective parameter was the cutting speed (relative contribution of 46.725%), followed by the feed rate (relative contribution of 28.120%). According to the tool vibration results, the cutting speed was the most important parameter, followed by the feed rate and the cutting depth. During low-speed cutting, a larger feed rate and cutting depth could be selected, for which adhesive wear is the prevailing mechanism. As the cutting speed increased, the built-up edge (BUE) near the cutting edge disappeared and the adhesives fell off; diffusion wear was the main mechanism in this case. In addition, a prediction model was constructed with the objective of surface finish and tool wear, and the results were optimized by an improved fruit fly optimization algorithm (FOA). The verification experiment results showed that the prediction errors of VB and Ra were 2.15% and 6.48%, respectively. Moreover, MQCL achieved better surface quality and lower tool wear than minimum quantity lubrication (MQL) and dry cutting under the optimized parameters.

A precise direct parametric interpolation method for NURBS-toolpath generation

Non-uniform rational B-spline (NURBS) interpolator has many advantages over conventional linear/circular interpolator. However, as there is a nonlinear corresponding relation between the curve parameter and the arc displacement of the NURBS curve, it is hard to accurately calculate the parameter of the next interpolation point, thus resulting in a deviation between the desired and the actual feed rate, i.e., feed rate fluctuation. A large feed rate fluctuation may cause machine-tool vibration, which is bad for the cutter life and the machining quality. Therefore, aiming at reducing the feed rate fluctuation, this paper presents a high-precision parametric interpolation method, which features a second-order Runge-Kutta algorithm with parameter compensation. First, a second-order Runge-Kutta method is employed to compute the initial interpolation-point parameter. After that, the parameter is compensated using first-order Taylor's expansion of the feed rate-fluctuation function, thus enhancing the calculation precision of the next interpolation point parameter. Experimental results demonstrate the advantage of the presented method.

An investigation in the ultra-precision fly cutting of freeform surfaces on brittle materials with high machining efficiency and low tool wear

In diamond machining of freeform surface on brittle materials, very small machining parameters are necessarily adopted to suppress the brittle fractures, which inevitably leads to low processing efficiency as well as fast tool wear. In the present study, ultra-precision fly cutting is first adopted in processing brittle materials for freeform surfaces to improve machining efficiency and reduce tool wear. In fly cutting, a large swing radius (over 40 mm) is configured between the diamond tool tip and the rotation axis of the spindle, so the workpiece material is intermittently removed by the periodical cut-in and cut-out movement of the diamond tool. The theoretical results show that this unique process generates a very small chip thickness (80 nm) even under large feed rates (9 μm/r) and cutting depths (70 μm), which accordingly improves the machining efficiency without generating brittle fractures. The experimental results show that only 200 min is needed in fly cutting of an F-theta lens with height variation over 50 μm on single-crystal silicon, while over doubled time is needed for conventional slow tool servo. The generated surface is very smooth and uniform with a roughness of only 6 nm Sa. Besides, only micro-ruggedness of diamond tool is formed in fly cutting without the premature appearance of the micro-chips, which enhances tool life and reduces the re-sharpening cost of diamond tools in processing brittle materials.

Mechanisms and FEM Simulation of Chip Formation in Orthogonal Cutting In-Situ TiB₂/7050Al MMC.

The in-situ TiB2/7050Al composite is a new kind of Al-based metal matrix composite (MMC) with super properties, such as low density, improved strength, and wear resistance. This paper, for a deep insight into its cutting performance, involves a study of the chip formation process and finite element simulation during orthogonal cutting in-situ TiB2/7050Al MMC. With chips, material properties, cutting forces, and tool geometry parameters, the Johnson–Cook (J–C) constitutive equation of in-situ TiB2/7050Al composite was established. Then, the cutting simulation model was established by applying the Abaqus–Explicit method, and the serrated chip, shear plane, strain rate, and temperature were analyzed. The experimental and simulation results showed that the obtained material’s constitutive equation was of high reliability, and the saw-tooth chips occurred commonly under either low or high cutting speed and small or large feed rate. From result analysis, it was found that the mechanisms of chip formation included plastic deformation, adiabatic shear, shearing slip, and crack extension. In addition, it was found that the existence of small, hard particles reduced the ductility of the MMC and resulted in segmental chips.

Flank wear mechanism and tool endurance of (Ti,W)C-Mo2C-Co cermets during dry turning

Flank wear and tool endurance of (Ti,W)C-Mo2C-Co cermets during dry cutting of hardened steel were investigated in present work. The results indicated that the boundary between core and rim in the (Ti,W)C-based cermets was less corrosion-resistant for its composition inhomogeneity. The intergranular fracture of ceramic phases was the dominant mode in the fractograph due to generally rounded ceramic grains with isotropic surface energy at the boundary. Regarding to flank wear of (Ti,W)C-based cermets during dry turning, the diffusive wearing played increasingly significant role with the cutting speed or depth of cut increased. In contrast, the abrasive wearing and adhesive wearing were still main factors leading to flank wear when the feed rate was enlarged. Large depth of cut caused likely cutting edge abnormal breakage such as chipping due to increased cutting stress. To enhance the machining efficiency without excessively decreasing tool endurance, large feed rate is taken in consideration first as far as the (Ti,W)C-based cermets.

An investigation of the influence of phases’ removal ways on surface quality in micro milling SiCp/Al composites

SiC particle-reinforced aluminum matrix (SiCp/Al) composites are widely employed due to their outstanding performance. However, since they are composed of brittle SiC and ductile aluminum, the different removal mechanisms of the two phases may affect the surface quality in micro milling. In this paper, an experimental investigation of micro milling a kind of 45% SiCp/Al composites is presented. Using different values of the feed rate, the changes of the removal ways of the two phases are shown by 3D surface roughness and surface morphology. The results indicate that the surface roughness decreases firstly and increases later with the feed rate growing, which may be caused by the change of the removal way of the particle. A criterion for that is built. SEM pictures show that the surface is significantly coated by aluminum matrix when the feed rate is small; as the feed rate increases, the coating effect of the matrix weakens, and the removal ways of the particle changes from ductile regime machining to brittle fracture. Smaller feed rate may lead to the incompletely removing (plowing) of the Al and make the soft matrix coat the surface, while larger feed rate may result in the particle fracture, producing large numbers of cracks and damaging the surface integrity. Using suitable feed rate, the Al matrix can be removed efficiently and the SiC particle can be cut in its ductile regime. The unit of the suitable removal ways of Al matrix and SiC particle in machining process can produce a better surface.