Kuan-Ming Li

Modeling of Cutting Temperature in Near Dry Machining

Near dry machining refers to the condition of applying cutting fluid at relatively low flow rates, on the order of 2-100 ml/h, as opposed to the conventional way of using either a large quantity, typically of about 10 1/min, as in wet machining; or no fluid at all, as in dry machining. One important expectation of applying fluids is to control the cutting temperature, which is an important parameter for tool life and part dimensional accuracy in machining processes. In this context, the understanding of cutting temperature variation corresponding to the near dry cooling and lubrication is of interest. This paper models the temperature distributions in the cutting zone under through-the-tool near dry cooling condition. The heat source method is implemented to estimate the cutting temperatures on the tool-chip interface and the tool-workpiece interface. For the temperature rise in the chip, the effects of the primary heat source and the secondary heat source were modeled as moving heat sources. For the temperature rise in the tool, the effects of the secondary heat source, the heat loss due to cooling, and the rubbing heat source due to the tool flank wear, were modeled as stationary heat sources. For the temperature rise in the workpiece, the primary heat source, the heat loss due to cooling, and the rubbing heat source due to the tool flank wear were modeled as moving heat sources. The model describes the dual effects of air-oil mixture in near dry machining in terms of the reduction of cutting temperature through the cooling effect, as well as the reduction of heat generation through the lubricating effect. To pursue model calibration and validation, embedded thermocouple temperature measurement in cutting medium carbon steels with uncorted carbide insets were carried out. The model predictions and experimental measurements show reasonable agreement and results suggest that the combination of the cooling and the lubricating effects in near dry machining reduces the cutting temperatures on the tool-chip interface by about 8% with respect to dry machining. Moreover, the cutting speed remains a dominant factor in cutting temperature compared with the feed and the depth of cut in near dry machining processes.

Innovative through-silicon-via formation approach for wafer-level packaging applications

Through-silicon via (TSV) is an emerging technology for three-dimensional integrated circuit, system-in-packaging and wafer-level packaging applications. Among several available TSV formation methods, Bosch deep reactive ion etching (DRIE) is widely used because it enables the fabrication of TSVs with almost any diameter, from the submicrometer level to hundreds of micrometers. However, the high cost of Bosch DRIE makes it uneconomical for industrial production. We present a novel wafer-level TSV formation approach that is effective and cost-efficient. The proposed method integrates a diode-pumped solid-state ultraviolet nanosecond pulsed laser and rapid wet chemical etching. The former is effective in drilling through 400 ?m thick silicon wafers and the latter is used for removing the unwanted heat-affected zone, recast layer and debris left after drilling. Experimental results demonstrate that the combined approach effectively eliminates the unwanted material formed by nanosecond laser pulses. Furthermore, this approach has a significant cost advantage over Bosch DRIE. In summary, the proposed approach affords superior TSV quality, higher TSV throughput and lower cost of process ownership than Bosch DRIE. These advantages could provide the necessary impetus for rapid commercialization of the several high-density fabrication methodologies that depend on TSVs.

Effect of tool wear in ultrasonic vibration-assisted micro-milling

This article presents an experimental study on how tool wear affects tool life, surface roughness, and burr formation in ultrasonic vibration-assisted micro-milling. Small amplitude of vibration (2 µm) is applied to the micro-tools to evaluate the cutting performance influenced by tool flank wear as the cutting lengths increase. Compared to conventional milling, lower tool wear and better surface quality are recorded when cutting speed is much less than the maximum vibration speed. It is found that the use of minimum quantity lubrication in ultrasonic vibration-assisted micro-milling can further improve cutting performance due to reduction in tool wear.

Effect of Minimum Quantity Lubrication on Tool Wear and Surface Roughness in Micro-Milling

Micro-milling is a suitable technique for manufacturing of microstructures with high aspect ratios and intricate geometries. The application of the micro-milling process in cutting hardened tool steel is particularly challenging. The low strength of the miniaturized end mills implies accurate control of the chip load in order to prevent the tool break and product dimension errors, which requires high positioning accuracy. It is known that the application of cutting fluids can improve the performance of machining operations. However, the supply of cutting fluids in a conventional way is not appropriate for miniature machine tools due to the plentiful electronic components used to construct micro-scale machine tools. Minimum quantity lubrication (MQL) presents itself as a possible alternative for micro-cutting with respect to the minimum impact on the electronic components as well as low tool wear, better heat dissipation, and machined surface quality in metal cutting. This study compares the mechanical performance of MQL to completely dry condition for the micro-milling of SKD 61 steel based on experimental measurements of tool wears and surface finish. The effect of MQL on the burr formation is also observed. Results indicate that the use of MQL leads to reduced tool wears, better surface roughness, and less burr formation.Copyright

Predictive Models for Flank Wear in Near Dry Machining

The objective of this paper is to present a methodology to analytically model the tool flank wear rate in near-dry turning. The resulting models can serve as a basis to minimize time-consuming machining tests in predicting tool life. Analytical models, including cutting force model, cutting temperature model, and tool wear model, are presented. The cutting force model was established based on Oxley’s model with modifications for lubricating and cooling effect due to the air-oil mixture in near-dry machining. The cutting temperature was obtained by considering a moving or stationary heat source in the tool. The tool wear model contained abrasive mechanism, adhesion mechanism, and diffusion mechanism. The important factors related to this model were contact stresses and temperatures that were obtained from the cutting force model and the cutting temperature model. To develop these models, a set of cutting experiments using carbide tools on AISI 1045 steels were performed to calibrate the coefficients in the models and to verify the proposed flank wear mechanisms. The comparisons between the model-predictive flank wear and experimental results showed that the flank wear in near dry machining can be estimated well by the proposed models. It was also found that the cutting velocity was a dominant factor among the cutting conditions.Copyright

Improving the dielectric breakdown field of silicon light-emitting-diode sub-mount by a hybrid nanosecond laser drilling strategy

Abstract This study investigated the feasibility of conventional nanosecond (ns) laser drilling strategy and a new hybrid ns laser drilling strategy for the formation of through-silicon via (TSV), adopted in light-emitting-diode (LED) sub-mount application. In this research work, the most widely known technique, namely, the voltage ramp, was applied to measure the dielectric breakdown voltage of LED sub-mount with 1-μm-thick silicon dioxide deposited on TSV surface and sidewall. The greater value of dielectric breakdown field indicates the performance of better dielectric step coverage on TSV and better reliability of LED sub-mount. Experimental results show that the hybrid TSV drilling strategy represents an improvement of 623% dielectric breakdown field over conventional ns laser drilling method with the same oxidation process condition. The improved breakdown voltage relies on the obtained of smooth TSV sidewall and without wafer surface debris fabricated with the new drilling strategy. The mechanism of how the hybrid drilling strategy achieves smooth TSV sidewalls is also explained. Through this study, it has been demonstrated that with the new hybrid ns laser drilling strategy, it is feasible to achieve a spike-free TSV sidewall to ensure good dielectric step coverage by subsequent oxidation process.

Predictive Modeling of Flank Wear in Turning Under Flood Cooling

The objective of this paper is to present physical and quantitative models for the rate of tool flank wear in turning under flood cooling conditions. The resulting models can serve as a basis to predict tool life and to plan for optimal machining process parameters. Analytical models including cutting force analysis, cutting temperature prediction, and tool wear mechanics are presented in order to achieve a thermo-mechanical understanding of the tool wear process. The cutting force analysis leverages upon Oxleys model with modifications for lubricating and cooling effect of overhead fluid application. The cutting temperature was obtained by considering workpiece shear deformation, friction, and heat loss along with a moving or stationary heat source in the tool. The tool wear mechanics incorporate the considerations of abrasive, adhesion, and diffusion mechanisms as governed by contact stresses and temperatures. A model of built-up edge formation due to dynamic strain aging has been included to quantify its effects on the wear mechanisms. A set of cutting experiments using carbide tools on AISI 1045 steels were performed to calibrate the material-dependent coefficients in the models. Experimental cutting data were also used to validate the predictive models by comparing cutting forces, cutting temperatures, and tool lives under various process conditions. The results showed that the predicted tool lives were close to the experimental data when the built-up edge formation model appropriately captured this phenomenon in metal cutting.

Development of on-line laser power monitoring system

Since the laser was invented, laser has been applied in many fields such as material processing, communication, measurement, biomedical engineering, defense industries and etc. Laser power is an important parameter in laser material processing, i.e. laser cutting, and laser drilling. However, the laser power is easily affected by the environment temperature, we tend to monitor the laser power status, ensuring there is an effective material processing. Besides, the response time of current laser power meters is too long, they cannot measure laser power accurately in a short time. To be more precisely, we can know the status of laser power and help us to achieve an effective material processing at the same time. To monitor the laser power, this study utilize a CMOS (Complementary metal-oxide-semiconductor) camera to develop an on-line laser power monitoring system. The CMOS camera captures images of incident laser beam after it is split and attenuated by beam splitter and neutral density filter. By comparing the average brightness of the beam spots and measurement results from laser power meter, laser power can be estimated. Under continuous measuring mode, the average measuring error is about 3%, and the response time is at least 3.6 second shorter than thermopile power meters; under trigger measuring mode which enables the CMOS camera to synchronize with intermittent laser output, the average measuring error is less than 3%, and the shortest response time is 20 millisecond.

Enhancement of through Silicon via Sidewall Quality by Nanosecond Laser Pulses with Chemical Etching Process

Through-silicon via (TSV) is an emerging technology for three-dimensional integrated circuit, system in package, and wafer level packaging applications. In this study, a wet chemical etching (WCE) process has been employed to enhance the sidewall quality of TSVs fabricated using nanosecond (ns) laser pulses. Experimental results show that the TSV sidewall roughness can be markedly reduced, from micrometer scale to nanometer scale. We concluded that the proposed method would enable semiconductor manufactures to use ns laser drilling for industrial TSV fabrication as the desired TSV sidewall quality can be achieved by incorporating the WCE process, which is suitable for mass production.

Tool condition monitoring with current signals for a low-power spindle

Micro-milling, which is one of the mechanical micromachining methods, shows the potential to make very small parts with three dimensional microstructures. However, micro-milling is usually carried out on a traditional machine tool, which has a spindle with several kilowatts. For micro-milling on a traditional machine tool, most power is consumed by friction, not cutting, resulting in waste of energy. In this study, a miniature machine tool with a low-power spindle is used to improve the energy efficiency. The objective of this study is to investigate the feasibility of using current signal from a low-power spindle to estimate the tool life of a micro-milling tool. If signals regarding tool wear can be identified, product quality can be assured. Experimental results show that the current signal is effective to identify the tool wear in micro-milling with a low-power spindle.