Advances in Laser Drilling of Structural Ceramics

The high-quality, high-efficiency micro-hole drilling of structural ceramics to improve the thermal conductivity of hot-end parts or achieve high-density electronic packaging is still a technical challenge for conventional processing techniques. Recently, the laser drilling method (LDM) has become the preferred processing tool for structural ceramics, and it plays an irreplaceable role in the industrialized processing of group holes on structural ceramic surfaces. A variety of LDMs such as long pulsed laser drilling, short pulsed laser drilling, ultrafast pulsed laser drilling, liquid-assisted laser drilling, combined pulse laser drilling have been developed to achieved high-quality and high-efficiency micro-hole drilling through controlling the laser–matter interaction. This article reviews the characteristics of different LDMs and systematically compares the morphology, diameter, circularity, taper angle, cross-section, heat affect zone, recast layer, cracks, roughness, micro–nano structure, photothermal effect and photochemical reaction of the drilling. Additionally, exactly what processing parameters and ambient environments are optimal for precise and efficient laser drilling and their recent advancements were analyzed. Finally, a summary and outlook of the LDM technology are also highlighted.

Study on Fe-Based Metallic Glass Micro Hole Machining by Using Micro-EDM Combined with Electrophoretic Deposition Polishing

Fe-based metallic glass possesses high hardness and brittleness. It is a hard-to-cut metal material and difficult to machine by conventional methods. Although electrical discharge machining (EDM) has advantages in machining hard-to-cut metal materials, recast layer, pores, and micro cracks will form on the machined surface after machining. The study used a helical tool for the micro electrical discharge drilling (µ-EDD) process on Fe-based metallic glass. The influence of processing parameters, including the pulse on time, gap voltage, duty factor, and spindle rotational speed on the micro hole machining quality characteristics was investigated. The helical tool with SiC electrophoretic deposited (EPD) film was used to polish the inner surface of the electrical discharged micro hole. The findings show that the best micro hole accuracy, tool wear length, and inner surface were obtained at the spindle rotation speed of 1150 rpm, pulse on time of 5 μs, gap voltage of 30 V, and duty factor of 40%. The inner surface roughness can be reduced to 0.018 µm by using EPD tool. The inner surface was polished up to form a mirror surface.

Effect of Fungus, Aspergillus sp. F1-1, on the Corrosion Behavior of PCB-HASL in Humid Atmospheric Environment

Fungi, as one of the serious factors causing microbiologically influenced corrosion (MIC), can shorten the service life of electronic materials which are wildly used in the atmospheric environment. In this study, the effect of Aspergillus sp. F1-1 (A. F1-1) isolated from PCB samples after the exposure test in Xishuang Banna on the corrosion behavior of PCB-HASL was investigated. The presence of the A. F1-1 posed a threat of local corrosion on PCB-HASLs. An obvious decrease of pH was observed in PCB with A. F1-1 due to the various organic acids secreted by A. F1-1. The presence of the fungi also led to serious surface cracking and delamination. Creep corrosion and micro-hole corrosion were accelerated in the presence of A. F1-1 compared to the control. Additionally, the metabolic activities of A. F1-1 were associated with enrichment of Cu-containing corrosion products under the hypha.

Application of TOPSIS Method for Prediction of Optimum Design Parameters of Micro Hole Textured Cutting Inserts in Turning of Al-MMC

Metal Matrix Composite (MMC) has better mechanical properties and it is possible to produce near net shape. Aluminum-based MMC (Al-MMC) has challenges in terms of machinability studies and estimation of its optimum process parameters. Alternative cutting fluid research is a challenging area in machining. To avoid, existing hydrocarbon oil-based cutting fluid, textured inserts embedded with a solid lubricant are one of the alternative solutions. Micro hole textured inserts make a hole on the rake face of the cutting tool inserts. Texture includes various important design parameters namely hole diameter, hole depth and pitch between the holes. These optimum parameters influence the machining process. In this work, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method is used to find the optimum design parameters (hole diameter, hole depth and pitch between holes) during turning of Al- MMC. The objective parameters considered are minimization of surface roughness, power consumption and tool flank wear. The optimum combination of these design parameters is obtained by the higher relative closeness value of the TOPSIS method. The result of the investigation revealed that these design parameters are important to obtain improved machining performance. Also, it is understood that the TOPSIS method has an appropriate procedure to solve multiple objective optimization problems in manufacturing industries.

Characterization of micro hole on super alloy GH4037 and stainless steel 304 by millisecond-pulsed Nd:YAG laser processing

In this study, both super alloy GH4037 and stainless steel 304 were selected as experimental materials to be processed by LASERTEC 80 PowerDrill three-dimensional solid laser machining center. The structure of the micro hole was researched by 3D Laser Scanning Confocal Microscope and Scanning Electron Microscope (SEM). Meanwhile, The holes taper, entrance and exit ends diameter, microcrack, recast layer, orifice deposits and the heat affected zone (HAZ) were also investigated. The single factor experimental method was used to research the influences of defocusing amount, pulse energy, repetition frequency, and pulse duration on quality of micro holes. Experimental results indicated that the holes entrance and exit ends diameter enlarged with increased pulse energy from 3.4 J to 4.2 J. The entrance and exit ends diameter of holes decreased with increased pulse duration from 0.5 ms to 2.5 ms. Besides, the variation of holes diameter and taper were more obvious with repetition frequency changing from 10 Hz to 30 Hz, and variation range for the entrance and exit ends diameters and taper were not obvious with increased defocusing amount from −2 mm to 2 mm. The herein results indicated that pulse energy was one of the most significant influencing elements, and higher pulse energy could bring about lower hole taper within a certain range. Meanwhile, shorter pulse duration reduced splash and debris of holes surface. The recast layer, micro crack and HAZ were existed in the both kinds of experimental materials. Moreover, the microcrack and recast layer on holes wall of GH4037 were less than those of 304, and the HAZ in drilling hole for GH4037 was more than that of 304. The experimental results for the holes size were compared with corresponding simulation results under different defocusing amount respectively, which verified the accuracy of simulation results. Combining the above factors, the quality of micro holes drilling on super alloy GH4037 was better than stainless steel 304.

A method to optimize the length of flexible hose of the radial jet drilling technology

Radial jet drilling (RJD) technology has been applied to enhance the recovery of difficult-to-produce reserves by multiple horizontal micro-holes. The micro-hole length drilled by high-pressure water jets is of vital importance for the oil and gas recovery effect and is usually tens of meters long for applications in maturing oil fields in China. The water jets are generated by multiple orifices nozzle generally. Many studies focused on improving the self-propelled force generated by water jets to increase the micro-hole length. However, there are few researches on improving the micro-hole extension capacity in terms of optimizing the flexible hose that acts as the drill pipe in conventional drilling technology. This paper firstly studied the relationship between the flexible hose length and the micro-hole extension limit according to the analytical model to calculate the micro-hole extension limit. Then, the method to optimize the flexible hose length and the flow rate was developed aiming to obtain maximum micro-hole extension limit. The results show that the micro-hole extension limit decreases logarithmically with the increase in the flexible hose length under the condition that the takes the maximum value. The optimization model is applied by a field case and is proved to be effective to increase the micro-hole extension limit. This study is significant to improve the micro-hole extension capacity. Moreover, it provides a reference for the design of the hydraulics and selection of flexible hose for the RJD.