Rapid prototyping use in manufacturing components of a medical laser device.

Iliescu, Mihaiela ; Comanescu, Brindus ; Nutu, Emil 等

1. INTRODUCTION

The nowadays competition, both in industry, medicine, education etc. resulted into the development of several technologies, known as Rapid Manufacturing, whose main objective is (http://www.efunda.com, 2008) to shorten the design and production cycle. Many times, a prototype is often required for testing the product's manufacturing specifications or for an evaluation of its characteristics. So, Rapid Prototyping is worth to be used.

Rapid Prototyping represents (http://en.wikipedia, 2008) the automatic construction of physical object using solid freeform fabrication. It "takes" virtual design from computer aided design or animation modeling software, transforms it into thin, virtual, horizontal cross-sections and then, creates each cross-section in physical space, one after the next, until the model is finished. The virtual model and the physical one correspond almost identically.

In medicine, laser treatment has known a high extent and, thus, specific laser devices had to be designed and manufactured. This paper presents the application of ink jet printing rapid prototyping technology in designing and manufacturing components of a laser device used in urology for splitting kidney stones and in surgery--for fixing damaged bones. As it is an innovative laser device, rapid prototyping is of great help, specially because of the fact that the real components' materials are very expensive ones and the least designing and/or manufacturing mistake costs a lot--money, effort, material, time.

2. EXPERIMENTAL RESEARCH

2.1 Experimental System

The drawing of the laser device studied is presented in figure 1 and the parts to be prototyped are indicated by an arrow. The laser involved is solid state holmium one, with a THC:YAG rod emitting at 2100 nanometer, with 20 watts power and 250^350 microseconds pulse duration.

[FIGURE 1 OMITTED]

One of the rapid prototyping technologies is the 3D printing, meaning (http://www.csa.com, 2008) layers of fine powder are selectively bonded by printing an adhesive from the inkjet print-head in the shape of each cross-section, as determined by a CAD file.

The technological system used consists in: ZPrinter 310 Plus (Z Corporation)--printing machine; a compressed air cleaning enclosure; an electric oven and the materials used for rapid prototyping are: zp[R]131 powder (high performance composites for tough parts and very good resolution); zb60--binder solution and z-max--high strength epoxy.

2.2 Experiments

The experiments--meaning obtaining the prototypes were carried out according to the above mentioned aspects. The ZPrint software was set for 0.01 mm layer thickness and the time for prototype printing was about 21 minutes.

Some images, taken while ink-jet prototyping are shown in figure 2 (a, b)--as computer print screen and in figure 3 (a, b)--as real process, on ZPrinter.

[FIGURE 2 OMITTED]

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When the printing process was over (as mentioned by the software), the parts were removed from the printing machine. They were cleaned off the remaining powder and, after a little dry into the oven, were impregnated with epoxy strength then, finally dried into the oven. These above mentioned facts are illustrated by figure 4 (a, b).

An image of the final prototypes is shown in figure 5, where it can be noticed that finally, there were obtained two prototypes of each part--needed for the laser device (as seen in figure 1). It is worth mentioning the fact that the parts are joined together by thread assembly type but, the thread could not be obtained in rapid prototyping (it was almost impossible to extract the models out of the powder without damaging the threaded part). So, the threading operations, to join the parts together, were carried out on a drilling machine.

2.3 Experimental Results

Similarly, by ink-jet printing rapid prototyping, there were obtained all the components of the laser device. When assembling them together, there could be noticed some problems, most of them dealing with parts' design.

So, through each of side cap's main central holes there is special glass tube that isolates the laser flash and, respectively, active medium (Holmium) from the other components. Through the connecting piece there is the entrance/exit of a cooling fluid--unionized water, that maintains the appropriate temperature of laser body.

The major problem, while joining the prototyped parts, was that the cooling fluid could not "get" into both of the glass tubes, as they were too long and their end restricted the fluid access. Another problem was that the shape of the parts "flushed" by the cooling water did not fit tight so, there was fluid spread away. Thus, there was pointed out the need of using special insulating elements, such as O-rings.

3. TEMPERATURE SIMULATION

Considering the fact that all the rapid prototyping process was done in order to discover eventual mistakes in device's designing, it has been considered useful to simulate temperature within the side cap, knowing that the cooling fluid's temperature, into the exit connecting piece must not exceed a specific value, for example, 37[degrees]C.

Thus, it was carried out a simulation of the temperature field (Sushil et al., 2006), with ANSYS software. The model digitization was a 10 nodal tetrahedron and the considered heat transfer types were convection (from cooling fluid to metal) and conduction (from metal to metal).

[FIGURE 6 OMITTED]

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The temperature into the main holes of the side cap (around the special glass tubes--flash and active medium) were considered to be of 75[degrees]C and 80[degrees]C, while the cooling water entrance temperature was considered to be 27[degrees]C--as shown in figure 6. The ANSYS simulation's results are presented in figure 7--noticing that exit fluid's temperature was below 37[degrees]C

4. CONCLUSION

Using 3D printing technology of Rapid Prototyping it was possible to discover some errors in components' designing of a laser device. So, it was possible to save time (about one month) and money but, more important, not to waste very expensive special materials.

The temperature simulation, with ANSYS software, pointed out the need to reduce entrance cooling fluid's temperature below 27[degrees]C so that, the laser system be able to work well.

Further research and use of other (than ink-jet printing) Rapid Prototyping technique, could be done if several changes in component parts would be required. Thus, Rapid prototyping should be used for reducing product development cycle.

5. REFERENCES

Wang, C.; Park H. S. Rapid Manufacturing, Available from: http://www.csa. com/discoveryguides/rapidman/overview Accessed: 2008-03-08.

Rapid Prototyping, Available from: http://en.wikipedia.org/wiki/Rapid_prototyping Accessed: 2008-03-07.

3D Printing, Available from: http://en.wikipedia.org/wiki/3D_prototyping Accessed: 2008-03-07.

Rapid Prototyping, Available from: http://www.efunda.com/processes/rapid_prototyping/intro.c fm Accessed: 2008-03-10.

Z CORPORATION, Available from: http://www.zcorp.com/Products/3D-Printers Accessed: 2008-03-13.

Sushil Sharma, Bijaya Adak, Brian Rusthoven (2006), Long-Term High-Velocity Erosion of Glidcop in DI Water, APS, Argonne National Laboratory, USA.