Proceedings of the 1st IEEE InternationalConference on Nano/Micro Engineered and Molecular Systems

January 18 - 21, 2006, Zhuhai, China

Micro Fabrication with Selective Laser Micro Sintering

Jimin Chen*, Jianhua Yang, Tiechuan Zuo

Na tional Center ofLaser Technology, Beijing University ofTechnology, China

Abstract-Silicon-based MEMS techniques are very popular forthe manufacture of micro parts. Only a limited number ofmaterials can be processed by these techniques. As the rapiddevelopment of Selective Laser Sintering(SLS) in laser rapidprototyping field almost any material can be used. Laser MicroSintering(LMS) was recently introduced in the fabrication of 3DMEMS parts. The main difference between SLS and LMStechnology is the powder feeding method and laser system. In thispaper a newly developed powder feeding system has beenreported. The sysete makes use of ultrasonic device to depositmicron powder particles to form thin pattern on the substrate.The powder can be micro sintered selectively by a micro-sizedfiber laser beam. After optimization of experimental parameterswe can finally sinter 3D micro parts with micron metallic powder.This electronic document is a "live" template. The variouscomponents of your paper [title, text, heads, etc.] are alreadydefined on the style sheet, as illustrated by the portions given inthis document. Please limit your abstract to 250 words.

Keywords-Micro parts; powderfeeding;Micro laser sinteringt

I. INTRODUCTION

Silicon-based MEMS techniques are two-dimensional (2-D) processes with multiple steps and require complexprocessing procedures in a clean room environment. Only alimited number of materials can be processed by thesetechniques. MEMS should not only be built in three-dimensions (3-D), but should also use a wider selection ofmaterials, including alloys, polymers, ceramics, andheterogeneous materials. In laser rapid prototyping fieldSelective Laser Sintering (SLS) is one of the most potentialrapid prototyping techniques as it can be used to directlyproduce objects according to the concept of layeredmanufacturing[1][2]. The technology can use various powdermaterials and manufacture complex geometrical parts that werepreviously impossible to form by any other conventionalmanufacturing process. As the unrelenting demand ofdownsizing the miniature components in the micro domain isgrowing the micro SLS has been adopted to manufacture themicro parts directly. However current SLS equipment is notsuitable for micro part fabrication for the powder feedingsystem influences the sintered part easily. In this paper a newpowder feeding system is developed and experiments haveproved this system is successful in laser sintering micro part. [

II. MICRO SLS SYSTEM

A general micro SLS system is schematically presented inFigure 1. A device for micro SLS with powder depositionreplaces the powder rolling device of traditional SLS system.Figure 2 shows the detail schematic of the Ultrasonic micro

powder feeding device. The device mainly consists ofaluminum block with a powder hopper inside, a powder-feeding needle, a piezoelectric ceramic actuator and a powersupply. In the middle of the cuboid aluminum block is powderhopper. A columnar hole with a diameter of 8mm and a lengthof 50mm is used to load powder. At the both end of the hole,two taper holes are made for the powder's loading andoutflow. Below the powder hopper a powder-feeding needle ofdifferent sizes is assembled into the aluminum block. Theneedles are composed of a hopper structure and a feedcapillary with an inner diameter from 100 um to 1mm and alength of 5mm to 10mm. A piezoelectric ceramic actuator wasfixed on top of the cuboid aluminum block as the source ofultrasonic vibration. It can generate vertical ultrasonicvibrations. A function generator and a power amplifier wereused to control the frequency and amplitude of the ultrasonicwave which was generated by the piezoelectric ceramicactuator. This ultrasonic micro powder-feeding device wasfixed on a trestle table. The height of the ultrasonic micropowder-feeding device can be adjusted to a propriety positionunder the control of computer. It also can be moved to theexpectant position with the CNC work table. During lasersintering the device deposits very small amount of powder toform a thin pattern with micron particles material. With thismethod the powder was sintered together to build a micro partlayer by layer directly from a CAD model. This novelmanufacturing technology enables the building of micro partsthat traditional SLS has been impossible to fabricate.

Figure 1. Schematic of the laser micro-sintering

This project wasfunded by the Chinese Nature and Science foundationunder grants No.50575005 and No.50335050

*Contact author: jimini@bjut.edu.cn.

1-4244-0140-2/06/$20.00 C)2006 IEEE

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Powder hopperPi6ezelectfic ceramic actuator

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Figure 2. Schematic of the Ultrasonic micro powder feeding device

Figure 3 Different type ofpowderdeposition under same parameters

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Figure 4 The deposition rate and vibrating currentfor Fe powder

III. EXPERIMENT RESULTSMany papers and experiments have approved the theory of

anti-friction of ultrasonic vibration[3-5] . The friction betweentwo relative locomotors contact surfaces will be decreasedunder the condition of ultrasonic vibration. For differentmaterial the deposition is different. Figure 4 shows the resultof metal (Fe powder ) and non-metal ( ABS powder )powder deposition with same parameters. The density of themetal material (Fe Powder) is bigger than the non-metal(ABS Powder) . The deposition rate is quicker at the same

time. Figure 4 is the result of the relation between depositionrate(g/s) and vibrating current(A) for Fe powder. For ABSpowder the similar result was achieved. It shows whenincreasing vibrating current the deposition rate will increase atthe beginning stage. However when current reaches a certainlevel the depositing rate will decrease. The reason is analysedbelow. The anti-friction of ultrasonic vibration can be dividedinto two aspects:. No. one is the dynamics. When the powersupply is working the ultrasonic vibration wave is generatedby the piezoelectric ceramic actuator. The wave in the mannerof stress is transmitted in the vertical direction in the cuboidaluminum block. Some of the vibration energy is absorbed bythe powder-feeding device and the other energy is absorbedby the micro powder in the powder hopper. Both of them willcovert the energy to the exterior movements of the powderparticles. However, because of the different property ofmaterials, the energy that the powder and the inner surface ofthe powder-feeding device have absorbed are not equal at thesame time, so their movements is not synchronous. Relativemovements generate between the contact surfaces. Thedirection of friction is changed, and the friction decreasegreatly. Two friction surfaces are in a dynamic state of awayand close. No. two is hydrokinetics. The micro powder in thepowder hopper transform some of the vibration energy tofriction heat ,accelerate the softening of friction surface of thepowder, induce the inner surface of the powder in the powderhopper to be more smooth. The surface roughness betweencontact surfaces decreased. Thereby, this condition is favor tothe flow of micro powder. On the other hand the powderabsorbs enough energy to movement then the agglomerate aredispersed, and the adhesion forces between powder becomeweak.. From above analyzing the energy of vibrating wasmainly absorbed by powder at a early stage. When the valueof vibrating energy exceeds the maximum the energy will gointo aluminum block. The deposition rate will then decreaseMore deposition rate means the wider of the thin pattern. Thiswill lead thicker wall when sintering with laser beam. From alot of tests we can also conclude that the powder granularityhas little influence on the width and depth of deposited patternwhile the powder type has a great impact. Other parameterssuch as driving voltages of ultrasonic power, frequency, thespeed of working table, and inner diameter of feeding needlewere investigated. The main conclusions list below: (I)Withthe increasing width of the deposited powder line thethickness of the line will decrease.(2)With the increase ofdrive voltage of ultrasonic powder the width of the micropowder lines increased.(3)With the increase of work

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frequency the deposited powder line is changed from thin tothick. When the work frequency exceeded a value, the widthof the powder lines decreased. There exists a best workfrequency in the system.(4) The speed of work tabledetermines the amount of the powder that deposited on thesubstrate. With the increase of speed of work table the widthof the powder lines decreases and the thickness of depositedpowder will decrease simultaneously. (5) With the increase ofthe inner diameter of needle, the width of the depositedpowder lines will increased. In order to obtain a thin anduniform deposition we must select the optimized parameters todeposit powder. Besides powder feeding system the microsintering work should be conducted in an inert gas box toprotect from oxidation during sintering. The laser in microsintering system employs a fiber laser which has a very goodbeam quality. The beam can be focused to about 10um. Thetiny focus spot will benefit to sintering in a very small areawith a low laser power. Under computer control the lasersinters the powder layer by layer. The powder of each layerwas deposited by ultrasonic micro powder feeding device.Fig.5-Fig.7 show some micro sintered parts with laser withoutpost treatment.

Figure 5 Sintered Chinese Character(lOOum thick wall)

Figure 6 Sintered micro rings with Fe powder

Figure7 Three assembled micro rings in Fig.6

The micro Chinese character was sintered with Fe powderusing 20W fiber laser in Fig.5. Next to the sintered character isthe head of a match. The thickness of wall is about 100 micronmeters. The height of the character is 2 mm with 10 layers.Four sintered rings were shown in Fig. 6. The diameter of thesmallest ring(No.3) is less than 1mm. The different diametersof the rings(No.1,No.2 No.4) were able to be assembledtogether(Fig.7). They were sintered with 35W fiber laser atsame time. The height of the rings is 2mm and the wallthickness is less than 1mm with 3 layers of Fe powder.

CONCLUSIONIn order to sinter micro part Micro SLS was investigated.

The new powder feeder device was developed to feed powderinstead of rolling powder. The ultrasonic micro powder-feeding device can delivery many kinds of micro powdercontinuously and uniformly., Some work parametersdetermine the performance of the powder-feeding device, suchas work deposition rate, drive current, powder granularity andcategory.

The ultrasonic micro powder-feeding device is easy to beintegrated into the selective laser sintering system and haveno powder and noise pollution to the environment. From theexperiment the device can be used in micro laser sintering tofabricate micro part without limitation of material. It isprospective method to fabricate 3D micro part in MEMS field.

ACKNOWLEDGMENTSThe authors are grateful to the support from Chinese Nature

and Science Foundation under grants No.50575005 and No.50335050.

REFERENCES

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[1] Xiaochun Li,Hongseok Choi, Yong Yang "Rapid prototyping system formicro components" Thin Solid Films 2002(420-421) 515-523

[2] Chen Jimin ,Zuo Tiechuan "Laser Mcirofabrication with metallicpowder" Journal of Laser Application 2004.Vol.16. No.4.1-3

[3] ADACHIK,KATOK,SASATANIY. The micro-mechanism of frictiondrive with ultrasonic wave .Wear,1996,194:137-142.

[4] Zeng Ping Li Jun Cheng Guangming Yang Zhigang, The Study ofRotary Ultrasonic Vibration Anti-friction Experimental Mechanism,PIEZOELECTRICS & ACOUSTOOPTICS (Dec.1998) pp.393-394

[5] Cheng Guangming Zeng Ping, Study on Ultrasonic VibrationAntifriction Phenomenon PIEZOELECTRICS & ACOUSTOOPTICS(Oct.1998), pp323-32

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