Technical Paper: PIM International, Vol.1 No. 1 March 2007, pages 53-58, 3103 words

Authors: Roshan Urval [1], Carl Wu [1], Sundar V. Atre [1], Seong-Jin Park [2] and Randall M. German [2]

[1] Oregon Nanoscience and Microtechnologies Institute, Oregon State University, 106 Covell Hall, Corvallis, OR 97331, USA
[2] Center for Advanced Vehicular Systems, Mississippi State University, 200 Research Blvd., Starkville, MS 39759, USA

Abstract

Design issues related to PIM for fabrication of thin-walled, high-aspect ratio geometries were investigated in this study. These types of geometries are typical to the field of microtechnology-based energy and chemical systems (MECS). MECS are microfluidic devices working on the principle of heat and mass transfer through embedded micro and nanoscale features. 316L stainless steel was the material chosen for the present investigations because of its high-temperature resistivity and chemical inertness necessary for typical microfluidic applications. The investigations for the study were performed using the state-of-the-art computer aided engineering (CAE) design tool, PIMSolver®. The effects of material and geometry, on various process parameters during the mould-filling stage of the injection moulding cycle were investigated using a design of experiments approach based on the Taguchi method. The process variability generally increased with reduction in part thickness. Mould temperature played the most significant role in controlling the mould filling behaviour as the part thickness reduced. The operating range in which the mould cavity was completely filled was greatly reduced as the part thickness decreased. The presence of microchannel features on the part surface increased the possibility of forming defects like short shots and weld-lines when compared to a featureless part. Experiments were performed to study the mould-filling behaviour of a thin, high aspect ratio component and also to study the effect of varying processing conditions on the mould-filling behaviour. These experiments corresponded to the mould filling behaviour simulated using PIMSolver®, showing good agreement.

Introduction

Microfluidic technologies are of importance in diverse fields such as portable energy production, distributed chemical processes, microelectonic devices, and biomedical treatments, as shown in Fig. 1. Multi- scale systems have feature sizes in at least two or more different length-scale regimes with integrated micro-scale mechanical, optic, fluidic and electronic components and macro-scale interfaces and packaging. Microtechnology based energy and chemical and systems (MECS) are highly-paralleled, spatially-intensified micro-macro systems for the bulk processing of mass and energy [1,2]. For the economic and practical success of multi-scale systems, the primary challenge is the availability of suitable mass-fabrication techniques. Injection moulding shows great promise in this area [3]. But most typical, thermal and chemical applications of multi-scale components demand much better material properties than polymers can offer. Hence PIM offers an attractive combination of solutions with respect to material, shape complexity, and......

Further sections of this article include:

- Simulation methods
- Results and discussion
- Results from ANOVA
- Defect formation
- Effect of microfluidic features
- Verification of simulation with experiment
- Conclusions

Figures and Tables:

Fig. 1 Application areas of microsystem technologies.

Fig. 2 A single layer of a microchannel biomedical component, shown as an example of a MECS device component, (a) and an exploded view of a parallel flow microfluidic device, (b).

Fig. 3 Problem statement: establishing a quantitative framework for understanding the material-process-geometry interactions during mould-filling of a thin-walled, microfluidic geometry.

Fig. 4 Four typical MECS geometries investigated in the present study that were created using the PIMsolver® drawing and meshing tools. Plain plates with 3 mm, 2 mm and 1 mm thickness were used for simulations combining the Taguchi method and ANOVA analysis.

Fig. 5 Maximum injection pressure: (a) all cases and (b) results from the ANOVA study.

Fig. 6 The variation in melt-front temperature difference as a function of part thickness, (a) and results from the ANOVA study (b).

Fig. 7 Maximum shear rate; (a) all cases and (b) ANOVA analysis.

Fig. 8 Effect of filling time on short-shot formation in the 1mm plain plate.

Fig. 9 Effect of part thickness on short-shot formation at the mould temperature of 35°C, and melt temperature of 130°C.

Fig. 10 Change in process windows as a function of thickness of the plain plate geometry.

Fig. 11 Effect of microfluidic features on short-shot formation.

Fig. 12 Verification of simulations with experiments.

Table 1 Input data for material properties

Table 2 A 34 design of experiments matrix with 4 factors with 3 levels

Table 3 An orthogonal array (L9) representing the 9 cases considered in the present study