Modeling of minimum uncut chip thickness in micro machining of aluminum

Micro mechanical machining operations can fabricate miniaturized components from a wide range of engineering materials; however, there are several challenges during the operations that can cause dimensional inaccuracies and low productivity. In order to select optimal machining parameters, the material removal behavior during micro machining operations needs to be understood and implemented in models. The presence of the tool edge radius in micro machining, which is comparable in size to the uncut chip thickness, introduces a minimum uncut chip thickness (MUCT) under which the material is not removed but ploughed, resulting in increased machining forces that affect the surface integrity of the workpiece. This paper investigates the MUCT of rounded-edge tools. Analytical models based on identifying the stagnant point of the workpiece material during the machining have been proposed. Based on the models, the MUCT is found to be functions of the edge radius and friction coefficient, which is dependent on the tool geometry and properties of the workpiece material. The necessary parameters for the model are obtained experimentally from orthogonal cutting tests using a rounded-edge tool. The minimum uncut chip thickness (MUCT) is then verified with experimental tests using an aluminum workpiece.     

Phase width analysis of cutting forces considering bottom edge cutting and cutter runout calibration in flat end milling of titanium alloy

This paper is concerned with the combined cutting effects of both flank and bottom edges based on a systematic study of the cutting force in flat end milling of the titanium alloy. Besides the flank edge, the bottom edge of the cutter is also found to be an important factor influencing the cutting force distributions and can lead to uniform phase widths for non-zero cutting forces even under considerable cutter runout. One such phenomenon of uniform phase width induced by the bottom edge for the cutting force is deeply revealed. To do this, the models for characterizing the cutting force coefficients related to both edges are established based on the measured instantaneous cutting forces, and cutter runout is considered in the computation of process geometry parameters such as cutter/workpiece engagements and instantaneous uncut chip geometry parameters. Novel algorithms for identifying the cutter runout parameters and the bottom uncut chip width are also developed. Results definitely show that the flank cutting force coefficients can be treated as constants and that size effect obviously exists in the bottom cutting force coefficients that can be characterized by a power function of the bottom uncut chip width.The proposed model is validated through a comparative study with the existing model and experiments. From the outcomes of the current work, it is clearly seen that the prediction of cutting forces for titanium alloy can resort to the proposed model instead of traditional ones.     

Analytical modeling and experimental validation of micro end-milling cutting forces considering edge radius and material strengthening effects

This paper presents a novel micro end-milling cutting forces prediction methodology including the edge radius, material strengthening, varying sliding friction coefficient and run-out together. A new iterative algorithm is proposed to evaluate the effective rake angle, shear angle and friction angle, which takes into account the effects of edge radius as well as varying sliding friction coefficient. A modified Johnson–Cook constitutive model is introduced to estimate the shear flow stress. This model considers not only the strain-hardening, strain-rate and temperature but also the material strengthening. Furthermore, a generalized algorithm is presented to calculate uncut chip thickness considering run-out. The cutting forces model is calibrated and validated by NAK80 steel, and the relevant micro slot end-milling experiments are carried out on a 3-axis ultra-precision micro-milling machine. The comparison of the predicted and measured cutting forces shows that the proposed model can provide very accurate predicted results. Finally, the effects of material strengthening, edge radius and cutting speed on the cutting forces are investigated by the proposed model and some conclusions are given as follows: (1) the material strengthening behavior has significant effect on micro end-milling process at the micron level. (2) Cutting forces predicted increase with the increase of edge radius. (3) Considering varying sliding friction coefficient can enhance the sensitivity of the predicted cutting forces to cutting speed.     

Effect of cutter runout on process geometry and forces in peripheral milling of curved surfaces with variable curvature

This paper presents a novel method for cutting force modeling related to peripheral milling of curved surfaces including the effect of cutter runout, which often changes the rotation radii of cutting points. Emphasis is put on how to efficiently incorporate the continuously changing workpiece geometry along the tool path into the calculation procedure of tool position, feed direction, instantaneous uncut chip thickness (IUCT) and entry/exit angles, which are required in the calculation of cutting force. Mathematical models are derived in detail to calculate these process parameters in occurrence of cutter runout. On the basis of developed models, some key techniques related to the prediction of the instantaneous cutting forces in peripheral milling of curved surfaces are suggested together with a whole simulation procedure. Experiments are performed to verify the predicted cutting forces; meanwhile, the efficiency of the proposed method is highlighted by a comparative study of the existing method taken from the literature.     

Characterization of the transition from ploughing to cutting in micro machining and evaluation of the minimum thickness of cut

When the machining process is miniaturized two process mechanisms, ploughing and chip formation, are essential and a critical cutting thickness needs to be exceeded so that not only ploughing will occur but chips will also be formed. The ploughing effect thereby influences the chip formation process, workpiece surface roughness, burr formation and residual stress state after processing and is therefore of great interest. In order to optimize the machining process a better understanding of the minimum thickness of cut is crucial.The changes in surface topography along the cutting track occurring during machining with a constant feed rate of the cutting tool were analyzed. The influence of the built-up edge phenomena on the micro machining process was investigated for normalized AISI 1045 using confocal white light microscopy and scanning electron microscopy. Furthermore the sin²ψ-method was applied in order to study the residual stress state in the workpiece surface induced by the machining process. Both surface layer properties investigated, surface roughness and residual stresses, show a characteristic transition indicating a change in the dominating process mechanisms. Based on these results a model is developed to determine the minimum thickness of cut. The minimum thickness of cut is found to significantly decrease with higher cutting velocities and to moderately increase with higher cutting edge radii. In addition a propagation of error for the values obtained with the model was performed, proving the quality of the model developed.     

冷轧304不锈带钢边鳞缺陷的成因分析及其改进措施

针对冷轧304不锈带钢表面的边鳞缺陷，采用扫描电镜对带钢表面及横截面缺陷形貌和成分进行了分析，并对实际生产数据进行了统计，分析了冶炼化学成分、连铸二冷比水量、板坯加热工艺参数与边鳞缺陷降级率的关系。结果表明，冷轧304不锈带钢边鳞缺陷的产生是板坯高温塑性不佳及其加热工艺不合理造成的。为此提出了针对性的改进措施：严格控制钢液化学成分，N质量分数小于0.045%，Cu质量分数小于0.15%，并加入适量的B（0.001 5%~0.003 5%）；同时保证连铸二冷比水量控制在0.60~0.75 L/kg；优化加热工艺，控制板坯在炉加热时间小于220 min，均热段温度不高于1 220 ℃。采用上述改进措施，冷轧304不锈带钢边鳞缺陷降级率显著降低，从8.5%降至1.2%以下。     

冷轧304不锈带钢边鳞缺陷的成因分析及其改进措施

针对冷轧304不锈带钢表面的边鳞缺陷，采用扫描电镜对带钢表面及横截面缺陷形貌和成分进行了分析，并对实际生产数据进行了统计，分析了冶炼化学成分、连铸二冷比水量、板坯加热工艺参数与边鳞缺陷降级率的关系。结果表明，冷轧304不锈带钢边鳞缺陷的产生是板坯高温塑性不佳及其加热工艺不合理造成的。为此提出了针对性的改进措施：严格控制钢液化学成分，N质量分数小于0.045%，Cu质量分数小于0.15%，并加入适量的B（0.001 5%~0.003 5%）；同时保证连铸二冷比水量控制在0.60~0.75 L/kg；优化加热工艺，控制板坯在炉加热时间小于220 min，均热段温度不高于1 220 ℃。采用上述改进措施，冷轧304不锈带钢边鳞缺陷降级率显著降低，从8.5%降至1.2%以下。