Ratio Of Uncut Chip Thickness Research Articles

Experimental investigation on extrinsic size effect in micro-orthogonal cutting of commercial aluminium alloy

The achievable precision in micro-machining is constrained by a phenomenon known as the size effect. The edge radius of the tool significantly influences the size effect leading to non-proportional scaling of process performance. The process becomes unscalable below a certain ratio of uncut chip thickness to edge radius termed as critical relative tool sharpness (RTS). Despite extensive studies on the size effect associated with non-linear process performance, very limited studies have focused on the critical RTS range. In the present study, orthogonal cutting experiments were conducted on a commercial aluminium alloy (Al6060) with different cutting-edge radiuses in the RTS range of 0.5 to 0.01. Extensive analysis of the morphology of the chips and tool-work material adherence has been carried out and correlated with the observed size effect on surface integrity. One of the key findings in this study was the size effect in the chips with respect to the chip curl radius and pitch. Between RTS 0.5 and 0.09, an increase in chip curl and pitch is observed, followed by a sharp fall up to RTS 0.07. In addition, another notable phenomenon was the formation of dual-layered chips with deformed layer on the rake side and lamellae like features on the free side. Furthermore, size effect was observed in surface roughness, surface hardness and flank adherence. In summary, the present investigation offers a comprehensive understanding of the size effect within the critical RTS range elucidating its multifaceted impact on micro-cutting.

Comparison of different 3Y-TZP substrates for the manufacture of all-ceramic micro end mills with respect to the cutting edge radius and the tool wear

In micro milling, size effects such as the ratio of uncut chip thickness to cutting edge radius result to high mechanical stresses. The tools need to be able to withstand these, with as little tool wear as possible. Cemented carbides are currently the tool substrates of choice. Technical ceramics are highly wear resistant as well, but they are not yet used in micro milling. To utilize their potential in micro cutting processes, we previously identified Y-TZP as the best ceramic for this purpose. Compared to cemented carbide, they exhibit only marginal tool wear when micro milling PMMA.To investigate whether the 3Y-TZP characteristics influence the performance of all-ceramic micro end mills, three different substrate materials were used to manufacture tools that were tested by micro milling of PMMA. Further varied factors were the feed per tooth and the spindle speed. The initial cutting edge sharpness of the tools and the tool wear were used to quantify the results. One substrate was found to result in lower cutting edge radii and a more stable manufacturing process than the others. Also, a feed per tooth dependent wear behavior was observed.

Semi-analytic modelling of cutting forces in micro ball-end milling of NAK80 steel with wear-varying cutting edge and associated nonlinear process characteristics

Cutting edge of miniature ball-end mill is one of decisive importance for the machining performance by affecting the thermal and mechanical load in cutting process. In this paper, a semi-analytic model is proposed to estimate the cutting forces in micro ball-end milling of NAK80 steel considering wear-varying cutting edge and the associated nonlinear process characteristics. The wear-varying cutting edge geometry under the different wear stage is obtained by 3D optical profilometer. The measured results indicate that cutting edge of miniature ball-end mill under the different wear stage includes not only the enlarged cutting edge radius but also the extended flank wear land, which can be described by a combination of edge radius and flank wear land width. The influence laws of the edge radius and flank wear land width on tangential and feed force coefficients are investigated, and the enlarged edge radius and extended flank wear land under different wear stage could be separated from each other by utilizing the cutting force coefficients data based on their different sensitivity on cutting forces. A semi-analytic method is developed to predict the shearing/plowing/friction forces in primary and tertiary shear zones based on classical oblique cutting and slip-line field model. The nonlinear tool-chip friction behavior with the phenomenon that the ratio of tool-chip contact length to uncut chip thickness and friction factor nonlinearly change with the ratio of uncut chip thickness to edge radius are investigated and employed to estimate rake/shear/friction angles, and the nonlinear strain gradient plasticity effect with the fact that effective strain gradient is affected by not only rake angle and shear angle, but also primary shear zone thickness that obviously increases with reduce of the ratio of uncut chip thickness to edge radius are considered to estimate the shear flow stress. The nonlinear behavior derived from the tool-chip/workpiece friction and material constitutive affects the contribution level of size effect on cutting forces in micro ball-end milling. Finally, to calibrate and validate the effectiveness of the proposed cutting forces model, a set of micro ball-end milling of NAK80 steel experiments are performed on a three axis ultra-precision machine by using same solid carbide tool with wear-varying cutting edge under different wear stage. The comparisons between the predicted and measured results show that the proposed model can provide higher accuracy and better understanding for micro ball-end milling of NAK80 steel.

Revisiting size effect due to work of new surface formation in mechanical micro-machining using FEM

Finite element simulations of chip formation have been carried out for uncut chip thickness of 4 µm to 24 µm by incorporating Johnson-Cook fracture model to study the energy spent in new surface formation in metal cutting. The plastic dissipation and the damage dissipation energy of the chip formation are analyzed for the orthogonal machining simulations carried out. From the analysis it has been shown that the damage dissipation energy in machining is negligible compared to the plastic dissipation energy and it increases with the enhancement in the ratio of uncut chip thickness to edge radius of the cutting tool.

Plastic deformation and critical condition for orthogonal machining two-layered materials with laser cladded Cr-Ni-based stainless steel onto AISI 1045

Laser cladding has been widely used to repair some high value-added parts for remanufacturing or sustainable production. Additional machining is necessary when the repaired parts require high precision and high quality. However, using conventional cutting theory to machine cladding workpiece is always a challenging work. The depth of cut in machining cladding workpiece is restricted in a shallow range and exhibits comparable to the thickness of cladding. It is meaningful to explore the critical conditions for orthogonal machining two-layered workpiece formed by laser cladding. The critical condition was defined as an initiation of plastic deformation in substrate while elastic deformation still occurring in the bottom of cladding. These different deformation mechanisms attributed to the inferior physical-mechanical characteristics of the substrate compared to the cladding. The stresses induced by machining can reach the cladding-substrate interface and result in a premature plastic deformation in substrate. As a result, discontinuous plastic deformation zones generated in both subsurface and substrate. For this reason, a coupled thermo-mechanical model was developed to predict the plastic deformation behaviors in subsurface and substrate materials. It was found that the ratio of uncut chip thickness to critical cladded thickness ranged from 0 to 0.678 with increase of uncut chip thickness. It meant that the thicker the cladding was, the more difficult it would be to induce a premature plastic deformation in the substrate. Lower cutting force but higher specific cutting energy was found under lower uncut chip thickness. Thinner cladding was not recommended for purpose of repairing. The results are expected to provide fundamentals to weigh pre-cladded thickness and cutting parameters in a post machining process for manufacturing sustainability.

Investigation on size effect of specific cutting energy in mechanical micro-cutting

Mechanical micro-cutting is one of advanced processes to manufacture the miniature parts. The uncut chip thickness is one of the two important parameters in mechanical cutting. The uncut chip thickness and the cutting edge radius are at the same length scale, and the cutting tool extrudes and shears the workpiece with the round cutting edge during micro-cutting process. Size effect of specific cutting energy in micro-cutting is significant in comparison with that in macro cutting. A slip-field model is proposed in this paper to analyze the deformation process of workpiece material in micro-cutting. Johnson–Cook constitutive model, which includes shear strain hardening, shear strain rate hardening, shear temperature softening, and plasticity strain gradient (PSG) effects, is applied to the calculation of the shear flow stress at the primary shear zone (PSZ). Predicted cutting force using the shear flow stress is validated by the micro-orthogonal cutting experiments. The specific cutting energy is also calculated. It shows that the size effect on specific cutting energy in micro-cutting is influenced greatly by the shear strain hardening, shear strain rate hardening, shear temperature softening, and relative cutting length due to the ratio of uncut chip thickness to cutting edge radius. The plasticity strain gradient has effect on the specific cutting energy when the uncut chip thickness is smaller than 25 μm for micro-orthogonal cutting AISI 1045 steel.

Experimental investigation of specific cutting energy and surface quality based on negative effective rake angle in micro turning

Since the uncut chip thickness is comparable to the cutting edge radius, in fact, micro cutting is a negative rake angle cutting process. The minimum chip thickness has great effect on the cutting process. This paper presents an experimental investigation of specific cutting energy and surface quality based on the negative effective rake angle in micro turning. A new model is developed to calculate the negative effective rake angle in micro cutting. The effective rake angle is found to be more negative with the decreasing ratio of uncut chip thickness to cutting edge radius. The minimum chip thickness is calculated to be about 0.2–0.3 times of cutting edge radius based on the critical negative rake angle. The turn point of the nonlinear increase of specific cutting energy is observed to be at the critical negative rake angle. The minimum surface roughness also is found to be achieved near the critical negative rake angle.

Investigation on Mechanism of Ultra-Smoothed Surface with a Micro Slot on the Flank Face in Micro Cutting

Micro cutting is a promising manufacturing method to obtain good surface integrity. Surface roughness shows size effect when the uncut chip thickness is smaller than the cutting edge radius. A special micro slot on the flank face of cutting tools was manufactured with discharge. Two groups of micro orthogonal cutting were conducted. The surface roughness of machined surface was measured and compared to each other. The results show that surface roughness decreases first and then increases with the ratio of uncut chip thickness to cutting edge radius. The surface machined with micro slot is better than that of without micro slot due to the micro slot restrain the back side flow of work piece based on the finite element model.

Investigation of Size Effect on Micro Hardness of Machined Surface in Micro Cutting

Micro cutting is a promising way for manufacturing micro parts, especially micro three dimension parts. Micro hardness is an important character to evaluate surface integrity of machined surface. Micro cutting is different from macro cutting due to size effect of specific cutting energy because of the influence of the ratio of uncut chip thickness to cutting edge radius. A group of micro cutting experiments were conducted to investigate the cutting parameters on the micro hardness of machined surface. The micro hardness of machines surface decreases with the ratio of uncut chip thickness to cutting edge radius first, and then increase when the uncut chip thickness is smaller than the cutting edge radius. The micro hardness shows size effect due to the machined surface compressed twice with the round cutting edge. The micro hardness decreases with the distance increasing far away from the machined surface.

Experimental Investigations of Size Effect on Cutting Force, Specific Cutting Energy, and Surface Integrity during Micro Cutting

Micro cutting is a promising technology to manufacture the micro parts. The shear mechanism of micro cutting is different from the conventional cutting due to the round cutting edge. The ratio of uncut chip thickness to cutting edge radius plays an important role on the micro cutting process. This paper investigates the size effect phenomena of micro cutting. Firstly, the cutting force and size effect of specific cutting energy depending on the ratio of uncut chip thickness to cutting edge radius are analyzed according to the experimental results. Then, the size effect of surface roughness due to the size effect of specific cutting energy is explored. Lastly, the size effect of the exit burr height is depicted and the potential reason is analyzed. The paper supplies a good understanding of how to get the best surface integrity and minimize the exit burr height for micro cutting.

Process simulations for 3D turning using uniform and variable microgeometry PCBN tools

In this paper, uniform and variable edge microgeometry design inserts are utilised and tested for 3D turning process. In 3D tool engagement with workpiece, thickness of the chip varies from a maximum equal to the feed rate (at primary cutting edge) to a minimum on the tool's corner radius (at trailing cutting edge). The ideal tool edge preparation should posses a variable configuration which has larger edge radius at the primary cutting edge than at the trailing cutting edge. Here the key parameter is the ratio of uncut chip thickness to edge radius. If a proper ratio is chosen for given cutting conditions, a variable cutting edge along the corner radius can be designed or 'engineered'. In this study, Finite Element Modelling (FEM)-based 3D process simulations are utilised to predict forces and temperatures on various uniform and variable edge microgeometry tools. Predicted forces are compared with experiments. The temperature distributions on the tool demonstrate the advantages of variable edge microgeometry design.