Kai Leung Yung

Laser Induced Forward Transfer

In this paper, we demonstrate using laser induced forward transfer (LIFT) technology to deposit Ti/Ni alloy on a glass substrate with high precision. Here the photonic feature of laser energy is used to move the Ti/Ni particles forward and deposit them on the glass, while the wave feature of laser is used to turn part of the Ti/Ni particles into ions. The characteristics of deposited films and their relations with the processing conditions are studied. A new method of depositing materials using photons instead of electrons in electric field may bring about a series of new technologies on surface deposition, which can be used to produce shape memory alloys.

Laser Drilling on Elastomeric Polymers

Elastomeric polymers have been used as moulds for fabricating micro structures in the soft lithography technology due to their elastic features and unstickiness to polymer features. Previously, the micro moulds were normally produced by imprinting on micro prototypes, which are fabricated using deep reactive etching or photolithography. In this paper, we introduce a direct mould fabrication method, which uses pulsed laser drilling technology to directly generate high aspect ratio patterns in elastomeric polymers. The effects of laser parameters such as pulse repetition rate and average power on the drilling qualities are systematically studied. The techniques presented in this paper would provide a more flexible way to fabricate high aspect ratio micro features on elastomer mould efficiently.

Target Tracking in Micro Injection Molding

The precision control of the injection process in micro injection molding demands precise tracking of the moment that melt front passes through the nozzle so that accurate prediction of the amount of melt being injected into the mould can be achieved. The tracking accuracy, to large extent, depends on the processing of pressure signals followed by the identification of the critical moment that melt front reaches the nozzle. A new adaptive Kalman filter was introduced in this study to calculate and predict the amount of melt injected. The filter eliminated the delay error and was more robust than other filters. The adaptive Kalman filter switches between two Qs for steadystate and transient estimations, allowing resetting of the Kalman gain so that convergence is speeded up in calculations. Experimental and simulation results prove the effectiveness of the method proposed.

Melt Pressure Signature Tracking Using an Adaptive Kalman Filter in Microinjection Molding

In order to manufacture high quality microproducts, the precision control of injected plastic melt in the injection chamber during a microinjection process requires real-time tracking of the melt pressure when the melt passes through the nozzle. A novel type of adaptive Kalman filter algorithm based on F-distribution is proposed in this paper. This adaptive Kalman filter can switch the system between the steady state and transient state by comparing the differences of input data in F-distribution. By resetting the Kalman gain and other relevant parameters, the adaptive function guarantees the convergence of the filtered signal during the tracking process and tracks the moments which sudden changes occur in the pressure signature. The simulation experiment results show that the method can reduce the effect of measurement noise more quickly and effectively. The method is proven to be effective for microinjection molding applications.

Active Scalable Elastomer Mold to Ease Demolding of High Aspect Ratio Micro Features

To fabricate high aspect ratio micro/nano features, demolding is more challenging than filling of melt into micro mold as solidified micro features can be easily peeled off when demolding resistance is high. Besides using anti-stick agent, using deformable mold is a new solution proposed by the authors. This paper presents a setup for testing the deformable active mold. Experimental results on micro thermal molding with the developed mold deforming system prove that the new system can successfully demold high aspect ratio micro features that can not be produced with traditional metal mold.

Comparisons of Different Elastomer Micro Molds

This paper demonstrates the comparisons of molding with micro molds made of different elastomeric polymers. Micro molds made of pure polydimethylsiloxane (PDMS), 0.3% carbon nanotube (CNT) enforced polydimethylsiloxane (PDMS), 2% carbon nanotube (CNT) enforced polydimethylsiloxane (PDMS) and commercial available high temperature silicon rubber sheet (Avon Group) were studied. Micro moldings using different molding pressures were performed. By comparing the dimensions of micro features produced with different molding pressures, molding accuracies of using micro molds made of different elastomeric polymers are obtained. Results of this study provide valuable information for the development of elastomer micro mold insert for micro injection molding.

Alignment of Carbon Nanotubes in Polystyrene Using Vibration and Electric Field

The most apparent advantages of thermoplastics are the recyclability and processibility. To obtain recyclable and injectable conductive polymer, this paper studied the filling of carbon nanotubes (CNT) in polystyrene(PS) and the aligning of CNT in PS under high frequency electric field and ultrasonic vibration using an experimental set up developed in our laboratory. Results of these studies would be very useful to the development of a new generation of micro fabrication method for producing integrated micro electronic products using micro injection molding that is the most cost effective way to produce micro products massively.

The Interface Behavior of Micro Overmolding

Micro overmolding is becoming more important with the rapid development and applications of microproducts in bioengineering, electronics and other areas in recent years. This paper presents our findings in studying polymer interfaces in micro channels of a micro mold during overmolding process. The bonding strengths between polycarbonate (PC) and thermoplastic polyurethanes (TPU) were examined and compared under different overmolding conditions. Results show bonding behaviors in micro channels are not only affected by temperatures, they are also influenced by surface roughness.

Rapidly Identify the Critical Parameter of MEMS Device Based on Element Model Library

The purpose of this paper is to introduce a simplified yet efficient method to identify the critical parameter of MEMS device based on rapid computer experiments instead of expensive physical experiments. The prototype model of MEMS device is rapidly established by connecting reusable and parameterized element models based on developed element model library. Critical parameters are identified and optimal parameter assemblies are obtained using Taguchi method based on computational experiments of the prototype model. A typical MEMS device--micro resonator is used for demonstrating the design methodology. The method enables the designer to rapidly identify critical parameter of a new MEMS device in early stage of design.

Fabrication of Nanotemplate and Nanowires from Bulk Aluminum at Room Temperature

A method of fabricating nanotemplate and nanowires by the anodization of bulk aluminum at room temperature is reported in this paper. Details of manufacturing processes as well as some in-depth discussions on the formation mechanism of nano pores with reference to the phenomena observed in experiments are presented. Effects of fabricating conditions such as the anodization time, temperature, current intensity, voltage and features of solutions, were studied in the experiments.