NEW MACHINING CONCEPT FOR MANUFACTURING MICROSTRUCTURES WITH EXCIMER LASERS

Abstract

The manufacturing of microcomponents with excimer lasers, especially for small series and batch production, is an alternative to other established micromanufacturing methods associated with etch-technology. To avoid long nonproductive times, a general and flexible machining concept is presented, which is based on the mask projection of the excimer laser beam. Beginning the process chain with the workpiece design, a developed preprocessor is able to calculate the overall removal volume from computer-aided design (CAD) data and to break down into elementary volumes that are able to be processed with single laser pulses. Moreover, based on the restrictions of the excimer laser process, a set of NC data is generated to automatically start the production process. The reliability of the system is proven with different geometries such as micro-gear wheels and microlenses.     

Laser removal of TiN from coated carbide substrate

Sustainable manufacturing requires the extended usage of materials and reuse of hard metal tooling. In general, titanium nitride (TiN) coating gives enhanced hardness and wear resistance to the surfaces of engineering tools. However, the high hardness makes it difficult to re-grind or refurbish TiN-coated materials, especially TiN-coated cutting tools. This paper presents the results of laser decoating of TiN from TiN-coated tungsten carbide (WC) substrates. Laser decoating was performed using a KrF excimer laser. The effect of laser fluence, number of pulses, frequency, scanning speed and beam overlap on the decoating performance was investigated in detail. A two-dimensional symmetric finite element model (FEM) was established to elucidate the temperature and stress fields created during the laser decoating process. Successful laser decoating of TiN coating from the WC substrate was demonstrated. It was found that decoating with a laser fluence of 4 J/cm², scanning speed of 2 mm/s, frequency of 25 Hz and a beam overlap of 91% gives best results for removing an area of TiN coating to its 3 μm thickness. The surface roughness of the best samples was found to be in the order of 0.8–0.9 μm Ra. The experimental and FEM investigation suggested that the decoating of TiN follows combined explosion and evaporation mechanism.     

248 nm excimer laser drilling PI film for nozzle plate application

In this study, drilling of polyimide (PI) film by using a 248 nm excimer laser through photomask projection is presented. The parameter effects of laser fluence, shot number and repetition rate on the processing results are realized. A high-quality of microhole array with 50 μm thick PI film has been fabricated. When the projection process is carried out, differences in the diameters of the microhole in the front and back sides of the PI are observed, which cause a conical shape in the kerf. The formation of this conical shape in terms of laser process parameters is discussed. Besides, to improve the laser machining quality of PI microholes, the effects of the process parameters are investigated and characterized. In addition, before excimer laser drilling PI is conducted, the PI surface is pre-coated with, or left without, a thin film material to observe the formation of debris. The results shows that the formation of debris can be reduced significantly when a pre-coated thin film is applied on the PI surface.     

Effect of process parameters in nanosecond pulsed laser micromachining of PMMA-based microchannels at near-infrared and ultraviolet wavelengths

This paper presents investigations on the effects of nanosecond laser processing parameters on depth and width of microchannels fabricated from polymethylmethacrylate (PMMA) polymer. A neodymium-doped yttrium aluminium garnet pulsed laser with a fundamental wavelength of 1,064 nm and a third harmonic wavelength of 355 nm with pulse duration of 5 ns is utilized. Hence, experiments are conducted at near-infrared (NIR) and ultraviolet (UV) wavelengths. The laser processing parameters of pulse energy (402–415 mJ at NIR and 35–73 mJ at UV wavelengths), pulse frequency (8–11 Hz), focal spot size (140–190 μm at NIR and 75 μm at UV wavelengths) and scanning rate (400–800 pulse/mm at NIR and 101–263 pulse/mm at UV wavelengths) are varied to obtain a wide range of fluence and processing rate. Microchannel width and depth profile are measured, and main effects plots are obtained to identify the effects of process parameters on channel geometry (width and depth) and material removal rate. The relationship between process variables (width and depth of laser-ablated microchannels) and process parameters is investigated. It is observed that channel width (140–430 μm at NIR and 100–150 μm at UV wavelengths) and depth (30–120 μm at NIR and 35–75 μm at UV wavelengths) decreased linearly with increasing fluence and increased non-linearly with increasing scanning rate. It is also observed that laser processing at UV wavelength provided more consistent channel profiles at lower fluences due to higher laser absorption of PMMA at this wavelength. Mathematical modeling for predicting microchannel profile was developed and validated with experimental results obtained with pulsed laser micromachining at NIR and UV wavelengths.     

准分子激光刻蚀技术在微机械中的应用研究

准分子激光刻蚀技术在微机械领域有着十分广泛的应用前景,用该技术制作的聚合物微结构深宽比大、精度高,并且工艺简单。我们分析了准分子激光刻蚀原理,探索了这种技术的工艺方法和技术条件,特别对掩膜的结构和制作工艺进行了较为深入的研究。本文采用简易的实验装置,用自行研制的三种结构掩膜进行了准分子激光刻蚀实验,得到了50μm 深的聚合物材料微机械构件。     

光纤石英玻璃基板微V槽阵列的精密磨削

针对脆性石英玻璃的微加工,利用自主研发的金刚石砂轮微尖端修整工艺,研发了光纤阵列石英玻璃微V槽磨削技术。分析了60°的微V槽形状偏差对光纤耦合损耗的影响,然后,研究了砂轮微尖端的误差补偿修整工艺。最后,实验分析了微V槽的磨削精度。理论分析显示:微V槽角度、间距和宽度的偏差分别控制在±0.42°、±1.04μm和±1.2μm以内时,耦合损耗小于0.5dB。实验结果表明:开发的数控磨削工艺可加工高精度的60°微V槽阵列;采用数控轨迹和角度补偿修整后,砂轮微尖端半径可平均达到10.46μm,角度精度为(60±0.22)°;对石英玻璃进行微磨削后,微V槽的角度偏差达到0.4°,尖端半径为10.5μm,宽度偏差为0.3μm,间距偏差为0.5μm,可保证光纤阵列的精密对接。     

Effect of slice thickness on the profile accuracy of model maker rapid prototyping measured by a circular triangulation laser probe

The objective of this research is to investigate the effect of slice thickness on the profile accuracy of the model maker (MM) rapid prototyping (RP) system, layer by layer, through non-contact laser probe measurement. A circular triangulation laser probe, model OTM-3A20, made by Wolf & Beck Co., was mounted on a coordinate measuring machine (CMM), as the non-contact sensor. An adjustment device for the laser probe was designed to minimise the cosine error caused by assembly inaccuracy. The alignment test of the measuring laser beam was carried out using a calibrated specimen. The systematic accuracy of the circular triangulation laser probe with respect to the surface roughness and the surface slope of the RP workpiece was investigated using a HP5529A laser interferometer system. The maximum error of 21/2D RP part profile accuracy can be improved from 220 μm to 131 μm, and the average error can be improved from 78 μm to 46 μm as the slice thickness changed from 0.127 mm (0.005 in.) to 0.0127 μm (0.0005 in). However, the machining time increases by about seven fold based on the experimental results. An overall error of 197 μm as measured by the laser probe is attainable using the finest slice thickness 0.0127 mm (0.0005 in.) for the 3D profile accuracy. To verify the accuracy of non-contact laser probe measurement, the 3D profile of the RP part was also measured by a CNC CMM, with good consistency.     

Design of a servo motion system and an image sampling and processing system on a 3D laser scanner

A three-dimensional (3D) laser scanning system is the main part of reverse engineering. It is a comprehensive technological system, including numerical control (NC), a laser, computer-aided design/manufacturing (CAD/CAM), precision mechanisms, computing image sampling, and image processing. Generally, it consists of a motion control system, an image sampling system, and an image processing system, etc. This paper focuses on introducing control principles, hardware constitutions, and software algorithms of the servo motion system, and analyzes and presents the hardware constitutions, software algorithms, and experimental results of the image sampling and processing system in great detail. Finally, the authors come to the conclusion that the errors all occur within the range ±0.1 mm.     

自聚焦伺服的激光测微技术

以激光ＣＤ 光学头为基础,提出新颖的自聚焦伺服测微工作原理,并以此原理试制测微仪。利用半导体激光器作光源,ＣＤ 光学头作高精度位移检测传感器,并利用高分辨率、高动态响应的压电晶体作微位移驱动源,建立实时闭环反馈的自聚焦伺服系统,由单片机进行控制,实现自动跟踪测量。系统首先在±５００μｍ 范围内进行寻焦搜索,实现光学头聚焦于被测表面,随后立即进入闭环聚焦伺服状态,对微位移进行检测。可获得±０．１μｍ 以上的测量精度,测量范围±１０μｍ ,测量形式为非接触测量。同时,该测微仪还有成本低、体积小、使用方便等优点,是一种值得推广的新方法。     

面向对象的CAD／CAM集成技术的研究

将面向对象方法应用于ＣＡＤ／ＣＡＭ集成的研究，提出面向对象的ＣＡＤ／ＣＡＭ集成的思想和方法；利用面向对象方法建立够集成产品设计和制造信息的产品定义模型－面向对象的产品定义模型，集成表达零件的设计，工艺规划，数控编程等活动所需信息，在此基础上开发ＣＡＤ／ＣＡＭ集成系统。介绍利用该思想方法所开发的回转类零件ＣＡＤ／ＣＡＭ集成系统。     

ICAPP: A process planning system for the CIM environment

This paper describes an approach to the integration of process planning with computer aided design. The link is established through IGES, which is used to transfer the geometric data from the CAD system to the process planning system. The process planning system can subsequently use this data in generating a detailed process plan as well as an NC part program for the manufacture of the part.     

基于MasterCAM＆VERICUT的数控加工仿真及优化

分析总结了虚拟数控仿真加工软件如何结合CAD／CAM软件使用。在MasterCAMX中,进行烟灰缸零件三维造型、制定数控加工工艺、生成数控程序、进行刀轨模拟仿真;基于VERICUT7．0构建了机床仿真环境,通过调用数控程序仿真整个加工过程。验证了数控加工程序正确性;通过优化数控加工程序,提高了加工效率,从而缩短产品生产周期,降低成本。     

基于UG的复杂曲面零件的数控加工

以一个复杂曲面零件模型为例,论述了UG CAO/CAM系统在数控加工中的应用过程：利用UG的建模模块对其进行曲面造型设计,并根据该零件结构特点进行工艺分析,使用UG的CAM加工模块设置加工参数实现自动编程,由程序后处理自动生成NC代码,最后将NC代码导入数控机床加工出实体零件,从而达到缩短编程时间,提高工作效率和编程质量的目的,有效地保证了零件的加工精度。     

A laser sensor with multiple detectors for freeform surface digitization

An integrated laser scanning sensor for freeform surface digitization is presented. The sensor consists of a diode laser light source and four position-sensitive device (PSD) detectors. The stand-off distance of the sensor is 180 mm and the measurable range is 90 mm. The Lambert model is applied to calculate the displacement between the sensor and the measured point on the object surface along the optical axis, under the assumption of a diffusive surface. The inclination angle of the measured point from the vertical plane of the laser beam is calculated by mathematical inference. Those data are used in error compensation to improve system precision. The new design of multiple detectors could increase the measurable angle and could solve the dead space problem in single point laser of triangulation measurement. The computer simulation and actual measurements show that the displacement resolution reaches 50 μm, and the system performs well in regards to stability and repeatability. The sensor system could be mounted on the NC machine orX-Y platform for freeform surface digitization.     

A precision CNC turn-mill machining center with gear hobbing capability

With ever increasing demand for small parts with complex shapes and high dimensional accuracy, many traditional machine tools have become ineffective for machining these miniature components. Typical examples include dental implants, parts used in mechanical watch movements, and parts used in medical endoscopes. This paper introduces our PC-controlled CNC turn-mill machining center. It has 5 axes, an automatic bar feeder, an automatic part collection tray, and a tool changer. It features a special control algorithm for the synchronization of its axes that produces not only higher accuracy but also makes the machine easier to use. In addition, a volumetric error compensation algorithm is implemented to improve accuracy. Based on experiments, the machining error is ±3 μm for turning, ±7 μm for milling and the maximum profile error is less than ±7.5 μm for gear hobbing.     

Experimental analysis of applicability of a picosecond laser for micro-polishing of micromilled Inconel 718 superalloy

An increasing number of recent technological advancement is linked to the widespread adoptions of ultra-short picosecond (ps) pulsed laser in various applications of material processing. The superior capability of this laser is associated with the precise control of laser–material interaction as an outcome of extremely short interaction times resulting in almost-negligible heat affected zones. In this context, the present study explores the applicability of a picosecond laser in laser micro-polishing (LμP) of Ni-based superalloy Inconel 718 (IN718). The specific research goals of the present study constitute determination of melting regime—a mandatory phase for LμP, establishing the concept of polishability of the spatial contents of the initial surface topography and experimental demonstration of the process capability of a ps laser for potential micro-polishing applications. The initial surface topography was prepared by micromilling operation with a step-over of 50 μm and scallop height of 2 μm. The LμP experiments were performed at five different levels of fluence associated with the melting regime by changing the focal offset, a parameter denoting the working distance between workpiece surface and focusing lens focal plane. The LμP performance was evaluated based on the line profiling average surface roughness (R _a) spectrum distributed at different spatial wavelength intervals along the laser path trajectory. Furthermore, additional statistical metrics such as material ratio and power spectral density functions were analyzed in order to establish the process parameters associated with best achievable surface finish. The applicability of ps LμP was demonstrated in two regimes—1D (line) and 2D (area) polishing. During 1D LμP, significant (～52 %) improvement of the surface quality was achieved by reducing an R _a value from 0.50 μm before polishing to an R _a value of 0.24 μm across the laser path trajectory on initially ground surface. In addition, an initially micromilled area of 4.5?×?4.5 mm was LμPed resulting in the reduction of an areal topography surface roughness (S _a) value from 0.435 to 0.127 μm (70.8 % surface quality improvement).     

简单零件的三维造型

介绍了一种简单零件的三维造型和数控加工仿真的方法。采用这一方法 ,用户可对所要加工的零件毛坯进行造型 ,并可对零件的数控铣削加工进行仿真检验。本程序可作为加工仿真软件单独使用 ,也可作为 CAD/ CAM系统中的一个模块。     

Non-contact measurement methods for micro- and meso-scale tool positioning

The demand for manufacturing microscale components for applications in electronic, biological, and microtool industries has resulted in a reduction in the overall size of machine tools. This trend has motivated the development of new measurement techniques to accurately determine the position of the tool. In this study, two noncontact methods to control the initial position of micro- and meso-scale tools and trace the tool position are described: a laser-based measurement system and a halogen lamp-based measurement system. To evaluate the feasibility of these measurement systems, the prototype per each measurement has been constructed. The laser-based measurement system had a positioning error of ±4.5 μm and the halogen lamp-based measurement system had a positioning error of ±2 μm. Several experiments and simulations were performed to identify the effects of a range of factors likely to be encountered in real-world situations.     

基于Auto CAD与数控机床的联接

数控加工系统中,传统的NC代码手工编程不仅效率低,而且易出错;采用APT语言的自动编程虽然语句简洁,功能较强,但语言与规则一旦出错又不易发现。笔者讨论在Auto CAD2006环境下,以模切刀为案例,开发一个数控自动编程系统,可以完成零件的数控编程工作,实现CAD与NC系统的连接,显著提高工作效率。     

双盘式渐开线测量装置误差的计算机补偿方法

以双盘式渐开线测量装置为研究对象,研究了对此装置的微机误差补偿方法。从众多的误差源中选出最大的三种误差进行补偿,使装置不确定度由原来的≤±0.7μm下降到≤±0.5μm.