Chip Thickness Effect Research Articles

Influences of size effect and workpiece temperature during cryogenic micro milling of soft viscoelastic polymer: an experimental assessment

Application of tool-based micromachining in soft polymer has been limited due to high adhesion and low elastic modulus of this material at room temperature. This study aims to evaluate the machinability of a typical viscoelastic soft polymer and understand the effect of material and process parameters on machining performances. In this study, a micro-milling process using cryogenic-assisted cooling is proposed and the importance of temperature control toward glass transition zone was particularly addressed. To identify insight of machinability in micro domain, this article also determines minimum uncut chip thickness (MUCT) and size effects by considering the variations of cutting force and surface integrity with the ratio of h/re (uncut chip thickness (h) to cutting edge radius (re)). The experimental results reveal that consideration of size effect during micromilling of soft viscoelastic polymer helps in reduction of machined surface roughness (Sa) value. Based on the cutting force pattern, it is evaluated that higher machining stability can be achieved during cryogenic machining by reduction of specific cutting force value. Moreover, temperature range around glass transition zone yields more promising experimental outcomes, outperforming other cooling zones.

Effects of feed direction on material removal behavior in belt grinding of titanium alloys

For abrasive belt grinding, although machine processing selection has been well studied to achieve good machinability, there is still a lack of understanding regarding the influence of feed direction and its mechanism, even though it is a common matter. This paper investigates the differences between up- and down-grinding in belt grinding of TC4, where the grinding forces, material removal performance, surface quality, and chip morphology are captured for the grinding process evaluation and mechanistic analysis In up grinding, it was observed that approximately 21.1 % more material removal can be achieved due to the larger penetration depth of scratching grains when maintaining a constant normal grinding force. Furthermore, the higher tangential grinding force resulting from increased cutting behavior and an additional sliding phase leads to more severe abrasive belt wear, as evidenced by a 22.7 % higher grinding ratio. Comparatively, down grinding mode generates a machined surface with lower roughness in the transverse and longitudinal direction, which can be explained by the minimum chip thickness effect and undeformed chip thickness model. The microscopic characteristics of chips and ground surface provide more evidence on the different chip formation mechanisms between two grinding modes.

Effect of chip thickness, wood cross-sections, and cutting speed on surface roughness and cutting power during up-milling of beech wood

The aim of the conducted experiments was to determine the effect of selected machining parameters on power consumption and surface quality obtained during the milling of beech wood using a computerized numerical control woodworking machine. Surface roughness was tested using the contact roughness measurement method, while roughness parameters Ra and Rz were recorded and cutting energy was determined. Tests were conducted for two variants of cutting speed (7.5 and 15 m·s-1) as well as three variants of chip thickness (0.10, 0.06, and 0.02 mm); additionally, the tests examined different cross-sections of wood. It was found that greater chip thickness and feed speed caused an increase in surface roughness and cutting power. In turn, cutting speed had no effect on surface roughness, whereas its increase resulted in increased cutting power. Surface roughness at the radial and tangential cross-sections was comparable, while it was greater at the transverse cross-section. It was also found that cutting power was lowest at the radial cross-section, while it was greater at the tangential and the greatest at the transverse cross-section.

Introduction of non-linear fracture mechanics in the modelling of a flip-chip component under drop impact

PurposeThis study aims to contribute to the numerical modelling of drop impact on a flip-chip component assembled on printed circuit boards using solder micro-bumps. This contribution is based on the introduction of non-linear fracture mechanics in the numerical approach.Design/methodology/approachThe integration of non-linear fracture mechanics into the numerical approach requires the proposal and validation of several simplifying assumptions. Initially, a dynamic 3D model was simplified to a dynamic 2D model. Subsequently, the dynamic 2D model is replaced with an equivalent static 2D model. The equivalent static 2D model was used to perform calculations considering the non-linear fracture mechanics. A crack was modelled in the critical bump. The J-integral was used as a comparative parameter to study the effects of crack length, crack position and chip thickness on the fracture toughness of the solder bump.FindingsThe different simplifying assumptions were validated by comparing the results obtained by the various models. Numerical results showed a high risk of failure at the critical solder bump in a zone close to the intermetallic layer. The obtained results were in agreement with the post-test observations using the “Dye and Pry” methods.Originality/valueThe originality of this study lies in the introduction of non-linear fracture mechanics to model the mechanical response of solder bumps during drop impact. This study led to some interesting conclusions, highlighting the advantage of introducing non-linear fracture mechanics into the numerical simulations of microelectronic components during a drop impact.

Effects of tool angles and uncut chip thickness on consumption of plastic deformation energy during machining process

Research on the underlying mechanism that controls the chip deformation and energy consumption is a basis to instruct the cutting process planning and improve the machining efficiency. The metal cutting process can be treated as purposeful separation of workpiece material, and the stress state located at the tool tip has great effect on the fracture of material being removed. Through studying the relationship between the stress triaxiality and chip formation process, this paper aims to reveal the effects of tool rake angle, inclination angle and uncut chip thickness on chip deformation behavior and associated energy consumption during machining of 1045 steel based on finite element method (FEM). A two-dimensional FEM model for orthogonal cutting is developed to study the effect of tool rake angle and uncut chip thickness on chip deformation, while a three-dimensional FEM model for oblique cutting is developed to investigate the effect of tool inclination angle. The parameter of chip compression ratio (CCR) is adopted to assess the chip plastic deformation and energy consumption under varied machining conditions. The cutting force component calculated based on CCR is compared with the total cutting force to demonstrate the dominant role of chip plastic deformation in cutting energy consumption. The results indicate that larger rake angle and smaller inclination angle of cutting tools as well as larger uncut chip thickness lead to increase of stress triaxiality near the tool tip, which can reduce the material fracture strain and be beneficial for the separation of material being removed from the bulk workpiece. This paper will be attractive from both practical and fundamental perspectives devoted to instructing the optimization of cutting parameters to improve the processing efficiency and reduce the energy consumption.

Investigation on minimum uncut chip thickness and size effect in micro milling of glow discharge polymer (GDP)

Glow discharge polymer (GDP) is used as the ablator material in inertial confinement fusion (ICF) applications. Its machining surface quality and geometric accuracy directly affect its high energy performance. Minimum uncut chip thickness (MUCT) and size effect are the keys to obtain higher surface quality during micro cutting. In this work, a hybrid analytical model of MUCT using cutting forces and effective rake angle based on minimum energy method (Model A), and micro milling experiment are applied to determine the MUCT of GDP. Furthermore, a specific cutting energy-based model (Model B), considering the mechanical properties, strain evolution, and tool geometry, is established to verify model A. Additionally, the material removal mechanism and size effect are also studied. It is found that the MUCT value of GDP determined by model A is between 0.268 and 0.532 μm, and the normalized MUCT value is between 0.148 and 0.295. These results are verified by the specific cutting energy obtained from model B. It is also proved that model B could preliminarily evaluate the MUCT value of GDP without conducting milling experiment. Moreover, below the MUCT threshold, the severe size effect and ploughing effect cause nonlinearly increase of specific cutting energy, and the random variation of cutting force and surface roughness. When the ratio of feed per tooth to cutting edge radius is larger than 0.61, the size effect could be ignored since the cutting mode is shearing.

Effects of minimum uncut chip thickness on tungsten nano-cutting mechanism

Tungsten is considered as the preferred material for plasma-oriented materials in fusion reactors, and its ultra-precision machining is a concern at present. However, the critical cutting depth for chip generation is an important parameter affecting the surface formation and removal behavior of materials in ultra-precision machining. Herein, the simulation analysis of nano-cutting tungsten using molecular dynamics (MD) was performed, and a new method to determine the minimum uncut chip thickness hmin by identifying the atomic trajectory and calculating the relative coordinate value was proposed. Then, the effects rarely reported of the chip formation on the removal mechanism of tungsten were studied. The research showed that when the cutting depth h was 0.253 times of the cutting edge radius r, the critical cutting depth without chip was reached, namely hmin. The increasing cutting temperature and stress led to the decrease of machined surface quality and the increase of subsurface damage with the rising in h/r. Meanwhile, the dislocation slip dominated by the direction of 1/2<111> was the main plastic deformation mechanism during cutting without chip, but the dislocation slip dominated by direction of <100> was main plastic deformation mechanism during processing with chip. The plastic deformation dominated by dislocation slip was also accompanied by the amorphization. The dislocation reaction from 1/2<111> dislocation to <100> dislocation occurred under both energy and geometry conditions. Moreover, the dislocations had more energy to expand and evolve as a result of thermal-activated effect induced by elevated cutting force and temperature, which increased the dislocation density, depth of subsurface damage layer, and the stress variation degree of the machined area with the enhancement of hmin during cutting. This research provides a reference method for determining the minimum uncut chip thickness during material removal and is of significance for mastering the microscopic removal mechanism of tungsten.

Kraft pulping of softwood chips with mild hot water pre-hydrolysis to understand the effects of wood chip thickness

Hemicelluloses consume alkali during kraft pulping and dissolve in the black liquor as a low energy fuel. Acidic pre-hydrolysis of softwood chips removes hemicelluloses but preserves cellulose content prior to pulping. This study compared mild pre-hydrolysis (140 °C) kraft pulping with conventional kraft pulping of commercial softwood chips at two H-factors for wood chips with thickness ranging from less than 2 mm to over 6 mm. The chip thickness less than 2 mm increased hemicelluloses oligomer yield and showed little influence on pulp fiber yield. However, the kraft pulp fiber length decreased 5.6%. Kappa number and fiber reject increased dramatically when chip thickness was greater than 6 mm. The detailed compositional analysis of kraft pulp and fiber quality analysis indicate that pre-hydrolysis followed by kraft pulping enhanced delignification with limited reduction of fiber length and width, and increased kinks. Strategic considerations for the integration of pre-hydrolysis into kraft pulping for future biorefineries were outlined.

Machining sound analysis for the effects of fiber bending on cutting mechanisms during carbon fiber reinforced plastic composite milling

Fiber bending during carbon fiber reinforced plastic (CFRP) milling is an important factor on the machined surface quality. During milling, the fiber first contacts the rake face instead of the tool edge at a certain cutting angle, and then the fiber is bent instead of being cut by the tool, causing the matrix and the fiber to fall out. The fiber is then broken from inside the machined surface and subsequently pulled out as the tool rotates, which are known as pull-out fibers. The machining defect is the main cause of deteriorating the surface quality. To reduce such machining defects, it is important to predict the fiber bending during CFRP milling. However, it is difficult to determine where fiber bending occurs because the fiber cutting angle changes every moment as the tool rotates. This study analyzed the fiber cutting mechanism considering bent fibers during CFRP milling and proposed a method to identify the type of machining mechanism through machining sound analysis. Moreover, CFRP milling simulation was performed to numerically analyze the machining parameters such as fiber cutting angle, fiber length, and the magnitude of fiber bending at different milling conditions. Through experiments, it was verified that fiber bending or defects can be identified through sound analysis of machining in the high-frequency range between 7500 and 14,800 Hz. The effect of chip thickness in up-milling and down-milling on fiber bending was investigated by analyzing simulation and sound signal, and their effects on cutting force and machining quality was experimentally verified.

Influence of Circular Saw Blade Design on Reducing Energy Consumption of a Circular Saw in the Cutting Process

Optimal cutting conditions, which lead to a high quality of the machined surface and low energy consumption, are crucial for wood processing. This paper describes the effect of feed speed, cutting speed and mean chip thickness on energy consumption and saw blade surface temperature during the spruce (Picea excelsa) cutting process. In the experiment, the energy consumption and the surface temperature of the saw blades were measured to find the optimal cutting conditions for the energy-efficient cutting process. The surface temperature of the circular saw blade was monitored online using a non-contact infrared sensor connected directly to a PC via a USB connector. The results show that the cutting power and the surface temperature of the circular saw blade increased with increasing feed speed. The lowest values of cutting power were shown by the saw blade CSB3. Compared to the classic CSB1 circular saw blade, the values were lower by 8%. The surface temperature of the circular saw blade is highest at the outer edge (area of the heel of the teeth), and decreases towards the center of the circular saw blade. For an identical mean chip thickness, energy-efficient cutting was achieved at a feed speed of 21 m/min. There must be a trade-off between machine productivity and energy consumption. Monitoring the cutting process of circular saws using intelligent sensors is the way to adaptive control systems that ensure higher quality of the machined surface and cost-effective machining.

Numerical investigations on residual stresses in orthogonal cutting of Ti-6A1-4V

Titanium is widely employed in aerospace space, where the surface integrity plays an important role in part quality. This paper presents the numerical and experimental results of residual stress when machining Titanium based on a CEL (Coupled Eulerian-Lagrangian) method. The performance of proposed model is compared with LAG (Lagrangian) and ALE (Arbitrary Lagrangian-Eulerian) methods regarding segment chip formation and residual stress. The correctness of simulation results is validated by orthogonal cutting experiments of Ti-6Al-4V as well as the experimental data given in recent published literature. The effects of uncut chip thickness, cutting velocity and edge radius on residual stress are discussed through simulation results.

Prediction of Nonlinear Micro-Milling Force with a Novel Minimum Uncut Chip Thickness Model.

The minimum uncut chip thickness (MUCT), dividing the cutting zone into the shear region and the ploughing region, has a strong nonlinear effect on the cutting force of micro-milling. Determining the MUCT value is fundamental in order to predict the micro-milling force. In this study, based on the assumption that the normal shear force and the normal ploughing force are equivalent at the MUCT point, a novel analytical MUCT model considering the comprehensive effect of shear stress, friction angle, ploughing coefficient and cutting-edge radius is constructed to determine the MUCT. Nonlinear piecewise cutting force coefficient functions with the novel MUCT as the break point are constructed to represent the distribution of the shear/ploughing force under the effect of the minimum uncut chip thickness. By integrating the cutting force coefficient function, the nonlinear micro-milling force is predicted. Theoretical analysis shows that the nonlinear cutting force coefficient function embedded with the novel MUCT is absolutely integrable, making the micro-milling force model more stable and accurate than the conventional models. Moreover, by considering different factors in the MUCT model, the proposed micro-milling force model is more flexible than the traditional models. Micro-milling experiments under different cutting conditions have verified the efficiency and improvement of the proposed micro-milling force model.

Numerical simulation on the warpage of reconstructed wafer during encapsulation process

Abstract At present, the general fan-out package generally uses the molding process and uses epoxy molding compound (EMC) material to complete the reconstruction of wafer, but it is not friendly to small-size chips and high fan-out ratio packaging types. In order to solve the problem of small size and high fan-out ratio and other fan-out packaging, JCET ADVANCED PACKAGING CO., LTD. introduced a new kind of encapsulation material, and the wafer reconstruction process in the fan out package is accomplished through three basic processes, such as the lamination process, the leveling process and the silicon support process. However, it also faces warpage problems after curing. Excessive warpage poses a significant challenge to subsequent RDL fabrication, mid-testing and process automation. In this paper, the actual process is reasonably assumed and finite element methods are used to study the effects of chip thickness, fan-out area, the encapsulation material properties and support silicon wafer on the warpage after curing. The lamination process is that an airbag slowly squeezes the encapsulation material into the fan-out area, and the pressure of the airbag can be adjusted by the gas in and out. The wafer surface is uneven after the lamination process, so it needs to be leveled by the leveling process. Leveling process is to make the uneven surface smooth by a heavy and proper amount of steel plate. The encapsulation material is soft, so it is necessary to support the silicon wafer in order to enhance the strength of the structure. In this paper, the curing process is divided into two processes: pre curing process and post curing process. The main function of pre curing is to shape the encapsulation material, and then post curing can make the encapsulation material, chip and supporting silicon have a better combination. The lamination, leveling, and silicon support processes do not involve higher temperatures, so it can be assumed that the reconstructed wafer has no residual stress and warpage. In order to save computer resources and shorten the verification period, the geometric model of simulation is simplified under the condition of ensuring accuracy. Through the finite element method to explore the influence of structural characteristics and material characteristics on the wafer warpage, the selection of parameters is determined according to the actual situation, so as to meet the manufacturability of the structure. The results indicate that with the increase of the thickness of the encapsulated material the encapsulation, wafer warpage is gradually increasing, while the encapsulation material with low modulus and small CTE can improve warpage performance. High modulus, thicker support silicon has a significant effect on reducing warpage, and larger CTE support silicon can also effectively reduce wafer warpage because the larger CTE support silicon reduces the degree of mismatch with the encapsulation CTE. Thinner chips and high fan-out areas tend to increase the warpage of the reconstituted wafer. The study of warpage of package structure and material properties can provide theoretical basis for predicting and improving warpage during the design and evaluation phase of the product.

Establishment of instantaneous milling force prediction model for multi-directional CFRP laminate

Carbon fiber reinforced polymer (CFRP) is widely used in the aerospace field due to its light weight and high strength. The CFRP milling process is prone to damage such as burrs and tears. The cutting force is closely related to the damage of CFRP and tool wear. In this paper, a back propagation (BP) neural network model of cutting force and edge force coefficients was established. The model considers the effects of instantaneous uncut chip thickness, fiber cutting angle, spindle speed, and axial depth of cut. The unidirectional CFRP laminate instantaneous milling model considering the cutting edge force was further established. The instantaneous milling force prediction model was extended to multi-directional CFRP laminates. And the relationship between the damage mechanism of CFRP and the instantaneous milling force was analyzed. Experiments have proved that the instantaneous milling force prediction model built in this paper has high accuracy.

Analysis of the Effect of Tool Posture on Stability Considering the Nonlinear Dynamic Cutting Force Coefficient

Abstract In aviation and navigation, complicated parts are milled with high-speed low-feed-per-tooth milling to decrease tool vibration for high quality. Because the nonlinearity of the cutting force coefficient (CFC) is more evident with the relatively smaller instantaneous uncut chip thickness, the stable critical cutting depth and its distribution against different tool postures are affected. Considering the nonlinearity, a nonlinear dynamic CFC model that reveals the effect of the dynamic instantaneous uncut chip thickness on the dynamic cutting force is derived based on the Taylor expansion. A five-axis bull-nose end milling dynamics model is established with the nonlinear dynamic CFC model. The stable critical cutting depth distribution with respect to tool posture is analyzed. The stability results predicted with the dynamic CFC model are compared with those from the static CFC model and the constant CFC model. The effects of tool posture and feed per tooth on stable critical cutting depth were also analyzed, and the proposed model was validated by cutting experiments. The maximal stable critical cutting depths that can be achieved under different tool postures by feed per tooth adjustment were calculated, and corresponding distribution diagrams are proposed for milling parameter optimization.

Modelling and analysis of cutting forces while micro end milling of Ti-alloy using finite element method

Micromilling is one of the preferable micro-manufacturing process, as it exhibits the flexibility to produce complex 3D micro-parts. The cutting forces generated in micro end milling can be attributed for tool vibration and process instability. If cutting forces are not controlled below critical limits, it may lead to catastrophic failure of tool. Cutting force has a significant role to decide the surface roughness. Therefore accurate prediction of cutting forces and selection of suitable cutting parameters mainly feed, is important while micro end milling. In present study, finite element method (FEM) based model has been developed by using ABAQUAS/Explicit 6.12 software. Von-Misses stresses and cutting forces are predicted while micro end milling of Ti-6Al-4V. Further, cutting forces were measured during experimentation using dynamometer mounted on micro-milling test bed. Cutting forces predicted by FEM model are in good agreement with the experimental force values. Obtained FEM results have been used to study the size effect in micro end milling process. Moreover, the effect of uncut chip thickness to cutting edge radius ratio (h/rc) on surface roughness (Ra) has been studied. It is found the feed 2.5 µm/tooth is suitable value to produce optimum surface roughness and cutting forces.

Experimental Study on the Minimum Undeformed Chip Thickness Based on Effective Rake Angle in Micro Milling.

Micro milling is widely used to manufacture micro parts due to its obvious advantages. The minimum undeformed chip thickness, the effective rake angle, and size effect are the typical characteristics and closely related to each other in micro milling. In this paper, the averaging method is proposed to quantitatively estimate the effective rake angle in the cutting process. The minimum undeformed chip thickness is explained based on the effective rake angle and determined to be 0.17 rn (tool cutting edge radius). Then, micro milling experiment was conducted to study the effect of the minimum undeformed chip thickness. It is found that the minimum undeformed chip thickness results in the unstable cutting process, the uneven peaks on cutting force signal, and the dense characteristic frequency distribution on frequency domain signal. The dominant ploughing effect induces the great specific cutting energy and the deteriorated surface roughness due to the minimum undeformed chip thickness.

Investigation of effect of uncut chip thickness to edge radius ratio on nanoscale cutting behavior of single crystal copper: MD simulation approach

Extremely small cutting depths in nanoscale cutting makes it very difficult to measure the thermodynamic properties and understand the underlying mechanism and behavior of workpiece material. Highly precise single-crystal Cu is popularly employed in optical and electronics industries. This study, therefore, implements the molecular dynamics technique to analyze the cutting behavior and surface and subsurface phenomenon in the nanoscale cutting of copper workpieces with a diamond tool. Molecular dynamics simulation is carried out for different ratios of uncut chip thickness ( a) to cutting edge radius ( r) to investigate material removal mechanism, cutting forces, surface and subsurface defects, material removal rate (MRR), and stresses involved during the nanoscale cutting process. Calculation of forces and amount of plowing indicate that a/ r = 0.5 is the critical ratio for which the average values of both increase to maximum. Material deformation mechanism changes from shear slip to shear zone deformation and then to plowing and elastic rubbing as the cutting depth/uncut chip thickness is reduced. The deformation during nano-cutting in terms of dislocation density changes with respect to cutting time. During the cutting process, it is observed that various subsurface defects like point defects, dislocations and dislocation loops, stacking faults, and stair-rod dislocation take place.

An investigation on material removal mechanism in ultra-high-speed grinding of nickel-based superalloy: three-dimensional simulation and experimental verification

Ultra-high-speed grinding is a significant method for the advanced manufacturing of the difficult-to-machine material components, e.g., nickel-based superalloy. However, unclear mechanism of material removal behavior is still the main problem. The present work intends to establish the three-dimensional (3D) finite element simulation model of ultra-high-speed grinding with single abrasive grain. The effects of undeformed chip thickness and grinding speed on the morphology of grinding traces and chips are investigated. The parameters, such as pile-up ratio and shear slip frequency, are characterized experimentally, and the mechanism of material removal behavior in the process of ultra-high-speed grinding has been accordingly researched deeply. The results indicate that the pile-up ratio decreases firstly and then increases with an increase of undeformed chip thickness; the lowest pile-up ratio would be obtained when the undeformed chip thickness is 0.8~1 μm. When the grinding speed is below 240 m/s, with the increase of grinding speed, the distance between the sawtooth of the grinding chips is reduced, while the sawtooth degree is increased. When the grinding speed exceeds 400 m/s, the chip shape changes from serrated fracture to banded continuity, and the frequency of adiabatic shear slip goes up with the increase of grinding speed, which helps to reduce the grinding force, making the grinding process more stable and decreasing the difficult machinability of Inconel 718 nickel-based superalloy.

Determination of minimum uncut chip thickness and size effects in micro-milling of P-20 die steel using surface quality and process signal parameters

Prior to a critical value of uncut chip thickness (UCT) or the so-called minimum uncut chip thickness (MUCT), the micro milling process is affected by ploughing which causes deterioration of surface quality and reduction of tool life. Stringent surface quality is the major concern during micro milling of P-20 die steel as it has wide application in preparation of micro injection mould. Again, this MUCT value depends upon the workpiece, cutting tool material and its geometry. In this article, we tried to determine MUCT and size effects by considering the variations of surface quality parameters and process signals with the ratio of h/re (UCT (h) to edge radius(re)). MUCT value was determined to be 0.75–1 μm or critical h/re value was found to be in the range of 0.25–0.33. Comprehensive analysis of tool wear and chip morphology with size effect have been instituted those were lacking in the earlier literatures. Curled and helical chips were obtained at feed rate higher than MUCT value, whereas the chips with arbitrary shapes were noticed at feed rates below MUCT. Lamellar structures were observed at the free surface of the chip having both inclined and vertical orientation. Edge rounding, coating delamination and built-up edge formation were observed due to size effect at feed value below MUCT.