Reinforcement of micro injection molded weld line strength with ultrasonic oscillation

Weld lines are the unfavorable defect not only in normal injection molding process but in micro injection molding process. In this study, polypropylene (PP) was chosen as the processing material and a micro dog-bone tensile test sample was selected as the objective part. The micro tensile part was prepared by the double gate injection mold. An ultrasonic generator was integrated in this mold in order to investigate the effect of ultrasonic oscillation on the micro injection molded weld line strength. The experiments were carried out for studying how the ultrasonic output power and the oscillation inducing time affect the weld line strength. Three output power levels (400, 600 and 800 W) and two inducing mode (Mode 1. the oscillation is induced from injecting moment to ejection moment; Mode 2. the oscillation is induced from injecting moment to packing procedure finishing) were set. The results show that ultrasonic oscillation has obvious influence on the weld line strength; Mode 2 always has better performance than Mode 1 for reinforcing the weld line strength; and when output power is 400 W the weld line strength is the highest. The mechanism of ultrasonic oscillation affecting the micro injection molded weld line was also analyzed by AFM (atomic force microscope) and polarized microscope.     

Design and fabrication of a micro Alvarez lens array with a variable focal length

A 5 × 5 micro Alvarez lens array mold was fabricated using a 5-axis ultraprecision diamond machine and an Alvarez lens array was manufactured by injection molding process. Unlike conventional processes for asymmetrical element fabrication such as small tool grinding, this research demonstrates slow tool servo broaching process that allows the entire Alvarez lens array to be accurately machined on a metal mold in a single operation. To further reduce manufacturing cost, injection molding was used to fabricate the Alvarez lens arrays. The mold and molded lenses were both measured using an optical profiler. All measured profiles showed a good agreement with design and surface roughness also indicated an optical surface finish. The functionality of the molded polymeric lens arrays was achieved when the focal lengths were varied by laterally translating the molded Alvarez lens array pair. This research is a demonstration of the capability of fabricating complex optics using the same approach.     

Integration of polystyrene microlenses with both convex and concave profiles in a polymer-based microfluidic system

This paper reports a new technique of fabricating polystyrene microlenses with both convex and concave profiles that are integrated in polymer-based microfluidic system. The polystyrene microlenses, or microlens array, are fabricated using the free-surface thermal compression molding method. The laser fabricated poly(methyl methacrylate) (PMMA) sheet is used as the mold for the thermal compression molding process. With different surface treatment methods of the PMMA mold, microlenses with either convex or concave profiles could be achieved during the thermal molding process. By integrating the microlenses in the microfluidic systems, observing the flow inside the microchannels is easier. This new technique is rapid, low cost, and it does not require cleanroom facilities. Microlenses with both convex and concave profiles can be easily fabricated and integrated in microfluidic system with this technique.     

Development of an injection molding tool for complex microfluidic geometries

This paper will track the design and results of an injection molding tool developed to manufacture microfluidic chips. The mold design and injection molding process was complicated by the presence of integrated capillary fluidic interconnects. We determined that design of the runner and gate system responsible for delivering molten plastic to the cavity had a significant impact on the quality of parts produced by the mold and the size of the process window. Numerical results confirm our findings that reducing gate lengths and increasing part thickness dramatically improved the filling profile and lowered injection pressures by 37%. Finally, the influence of gate location on part shrinkage is analyzed and discussed.     

Manufacture of a micro-sized piezoelectric ceramic structure using a sacrificial polymer mold insert

There have been technical limitations to manufacture microstructures due to difficulty of demolding during replication process of high aspect ratio microstructure in mass production technologies. In the present study, the fabrication of a novel sacrificial micro mold insert and powder injection molding process using such a micro mold insert is proposed and developed. It utilizes a synchrotron radiation to fabricate the shape of polymer based sacrificial mold inserts and then these mold inserts were exposed at X-ray once more to adjust its solubility. This second X-ray exposure facilitates dissolving of mold inserts instead of demolding process which have difficulties like pattern collapses or defects in case of precise replication process. In this manner, severe problems of demolding process in conventional mass production technologies can be efficiently overcome. To verify the usefulness of the proposed technique, polymer based micro mold inserts with several tens of micrometer sized structure for piezoelectric sensor applications were fabricated using X-ray micromachining process radiated synchrotron. The solubility of mold inserts were optimized by the second X-ray exposure without an X-ray mask and then subsequent powder injection molding process was utilized with a piezoelectric based material. Finally, piezoelectric ceramics with micrometer-scale and high aspect ratio of 5 were successfully fabricated, verifying that the present sacrificial mold system is useful for the precise replication process such as the fabrication of microstructure with high aspect ratio or complicated structure.     

Fabrication method of two-level polymeric microstructure with the help of deep X-ray lithography

Two- or multi-level microstructures are getting more important in several applications such as multi-component micro optical elements and various microfluidic systems. In the present study, a simple and efficient method is newly proposed for a fabrication of the two-level polymeric microstructures. Making a mother two-level microstructure consists of two processes: (1) the hot embossing process for a fabrication of microstructures on a PMMA substrate, and (2) the deep X-ray lithography using the hot embossed substrate for a high aspect ratio microstructure fabrication, resulting in a high aspect ratio microstructure containing smaller microstructures on its surface. Making use of so fabricated two-level microstructures as a mother structure, one could achieve a mass replication of the same microstructures via injection molding process with a metallic mold insert obtained by a nickel electroforming onto the mother microstructure. In order to demonstrate the proposed method, a polymeric high aspect ratio microstructure having smaller square microstructures on its top surface was fabricated. The fabricated two-level microstructure shows fine vertical sidewalls, which is a characteristic feature of the deep X-ray lithography. In addition, a metallic mold insert for a mass replication was fabricated by a nickel electroforming process.     

A visual mold with variotherm system for weld line study in micro injection molding

In order to study the weld line developing process and its influence on mechanical properties in micro injection molding, a visual mold with variotherm system mold was designed and fabricated. In this mold, a visualization design and a rapid heating/cooling system were integrated, and specimens with different cross section shape and micro dimensions could be molded for weld line study. The building process for the visual and variotherm mold was presented and the experiments were executed. The specimens for weld line study of micro injection molding were produced applying different processing parameters. A problem of flash in molded specimens needs to be solved.     

The effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio of chips

Injection molding PMMA microfluidic chips can significantly improve the efficiency of chips forming. However, due to the coexistence of macro and micro effects in the injection molding process, the thickness uniformity of molding substrates is poor, which will seriously affect the thermal bonding quality of chips. In this paper, the effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio and the quality of micro-channels was studied by experiments and simulations. The results show that when the following three conditions were satisfied during injection molding process, chips bonding ratio reaches to 93.9?% and the distortions of micro-channels caused by thermal bonding were acceptable. Firstly, the cover plates flatness error is smaller than 50–60?μm and substrates flatness error is smaller than 80–90?μm. Secondly, the maximum thickness difference of stack chips (cover plate stack with substrate) is smaller than 70–80?μm. Thirdly, chips thickness of the middle is larger than that of the two ends along their length direction and chips thickness distribute evenly along their width direction. These conclusions can be used for the parameters selection and moulds design during injection molding process of PMMA microfluidic chips.     

Nickel stamp fabrication and hot embossing for mass-production of micro/nano combined structures using anodic aluminum oxide

Recently, “micro/nano combined structure” has attracted many researchers’ attentions due to its high potential in various research fields and applications such as biomimetics, tissue engineering, micro systems for biochemical analysis and so forth. The present paper proposes a simple and promising method for mass-production of the micro/nano combined structure, in particular, nano dimple array with micro structures with cost-effective procedures. Three major procedures of (a) master template fabrication; (b) nickel electroforming onto the master template; (c) replication by hot embossing process, are employed: the master template is fabricated by utilizing an anodic aluminium oxide (AAO) process and UV lithography technique; nickel stamp is then obtained by means of electroforming onto the master template; finally, micro/nano combined structures are moulded on a polymethyl methacrylate (PMMA) substrate using the nickel stamp via hot embossing. So replicated micro/nano combined structures turns out to be quite successful according to experimental observation via scanning electron microscope (SEM) and atomic force microscope (AFM).     

Replication of high-aspect-ratio nanopillar array for biomimetic gecko foot-hair prototype by UV nano embossing with anodic aluminum oxide mold

In this paper, we present a simple and cost-effective replication method of high-aspect-ratio polymer nanopillar array as a biomimetic gecko’s foot hair prototype. A UV nano embossing process was applied for the replication of polymer nanopillar arrays. Highly ordered straight nanoporous AAO (anodic aluminum oxide) templates were utilized as reusable master molds. Densely arranged high-aspect-ratio nanopillar arrays have been successfully fabricated by means of the UV nano embossing process with the AAO mold. Pull-off force measurements were carried out to characterize the adhesive force of the replicated nanopillar arrays on the polymer substrates based on the force–distance curves obtained from the atomic force microscope (AFM) with a modified AFM cantilever. The force measurement results showed that the larger diameter and the taller height of the nanopillars result in the larger adhesive force.     

Micro molding for double-sided micro structuring of SU-8 resist

Advances in micro and nano fabrication technologies for MEMS require high-level measurement techniques with regard to sampling and sensitivity. For this purpose at the Institute of Microtechnology (IMT) highly sensitive piezoresistive 3D force sensors based on SU-8 polymer have been developed. In this paper we present an improved micro fabrication process for a double-sided micro structured design. The sensors are produced by multilayer processing techniques such as UV lithography and coating methods. The double-sided micro structured design demands a photoresist application method which simultaneously features a top side structuring and a casting from a mold. We use a new micro molding process to meet the demands. The micro fabrication technology is described, focusing on the development of the molding structure for shaping of the bottom side and a capable release process for the detachment of the molded structures. The fabrication process of the SU-8 mold layer is optimized to fabricate molding structures with heights from a few μm up to 350 μm. Therefore different SU-8 formulations, namely with classification numbers 5, 25, 50, and 100, have been used. The fundamental limitations for the mold design result from the lithography process, which defines the smallest lateral resolution, and from the characteristics of a molding process, e.g. the impossibility to realize an undercut. To allow for reliable release, the molding structures have to be coated with a sacrificial layer. Silicon nitride is deposited onto the substrate with accompanying monitoring of the deposition temperature during the PECVD process.     

Hot embossing of micro and sub-micro structured inserts for polymer replication

Today replication of microstructured parts is state of the art in laboratory and commercial use. Beside the process of injection molding hot embossing enables the accurate replication of polymer structures in a broad variety of thermoplastic polymers even in the nanometer range. Characteristic for the most replication processes dealing with thermoplastic polymers is the use of microstructured mold inserts based on metals. In this paper we describe an alternative to the established mold inserts––the use of so called interstage mold inserts. These interstage mold inserts are replicated in high performance polymers and technical thermoplastics and can be fabricated many times by a previous replication step from a master even in the sub-micro range. Aspects like suitable material combinations, demolding behaviour, long time stability, production rate, and the quality of structures will be discussed. Because of the high flexibility the process of hot embossing is used for the fabrication of the microstructured interstage mold inserts and their replications.     

具有3D微纳结构PDMS阵列免疫传感芯片研制

介绍了一种简便快速加工微阵列免疫传感芯片的新方法。采用化学刻蚀技术加工具有μm级山脉状起伏和nm级表面粗糙度结构(简称为3D微纳表面)的玻璃阳模,以该阳模为模板浇注法制得表面具有3D微纳表面结构的PDMS基片,再借助于物理吸附,将抗体直接固定于该PDMS表面,形成具有3D微纳结构的PDMS微阵列免疫传感器。利用光学显微镜和原子力显微镜对玻璃阳模和PDMS基片表面形貌进行表征,研究了PDMS表面微纳结构化处理对抗体吸附能力的影响。结果表明:3D微纳结构的PDMS由于具有大的比表面积,能显著增强抗体的吸附能力。将研制所得的3D微纳表面结构的PDMS芯片用于微阵列荧光免疫分析,其灵敏度是平板PDMS的5倍。     

Hot embossing of thermoplastic multilayered stacks

The combination of different polymer materials during replication offers additional opportunities for fabrication and functionality of microsystems. Different surface and structural properties of polymers allow for improvements in microsystems for example by means of hydrophilic and hydrophobic combinations in microfluidic devices. Due to its high flexibility and precision hot embossing as one of the established micro replication processes facilitates processing of several polymer layers in one single process step. By this multi-component process micro structured systems consisting of thin layers of different polymers with adapted surface properties are fabricated. In this paper we describe the challenge of molding different types of polymers and some applications for multi-component micro systems.     

Ceramic micro parts produced by micro injection molding: latest developments

Powder injection molding is a preferred technology for the production of micro parts or microstructured parts. Derived from the well known thermoplastic injection molding technique it is suitable for a large-scale production of ceramic and metallic parts without final machining. To achieve good surface quality and control the part size and distortions is an important goal to allow mass production. This means that all process steps like part design adjusted for MIM/CIM-technology, appropriate choice of powder and binder components and injection molding simulation to design the sprue are required. Concerning the injection molding itself high quality mold inserts, high-precision injection molding with suitable molding machines like Battenfeld Microsystem50 or standard machine with special equipment like variotherm or evacuation of the molding tool and an adjusted debinding and sintering process have to be available. Results of producing micro parts by powder injection molding of ceramic feedstock will be presented.     

Miniaturized plastic micro plates for applications in HTS

This paper is focused on the development of plastic nano titer plates for applications in high throughput screening (HTS). For screening systems with integrated confocal microscopes plastic chips have been fabricated by injection molding and injection compression molding which contain micro wells with volumes of 0.9 μl and 1.4 μl and bottom plates with thicknesses of 120 μm and 200 μm. In addition, plastic chips with through holes have been joined with 160 μm glass plates by an adhesive printing process. First fluorescence correlation spectroscopy (FCS) measurements show that the plastic plates with glass bottoms are qualified as screening grade FCS nano titer plates. Received: 15 May 1999 / Accepted: 19 May 1999     

Fabrication of micro gear by micro powder injection molding

Micro components made from polymers can be easily processed but they may not be suitable for all applications. One example is where good mechanical properties are required. Thus, the fabrication of micro components from non-polymeric materials such as metals and ceramics is essential. In this paper, the fabrication of 316L stainless steel micro gear by micro powder injection molding is reported. The specifications of the green micro gear were: 10 teeth, module of 0.08, outer diameter of 1 mm and a length of 1 mm. Injection molding was conducted on a conventional injection molding machine with a small screw diameter of 14 mm. The green micro gear was well replicated. The debound micro gear retained its shape and the teeth were well defined. After sintering, the shape was also retained but with some surface irregularities. The process differences between μPIM and PIM, such as the use of smaller particle size and higher mold temperature are also highlighted.     

Fabrication of barrier ribs of PDP via powder injection molding

In this paper, an attempt was made to explore a possibility of powder micro injection molding process in manufacturing ceramic microstructures such as barrier ribs of plasma display panel. The barrier ribs are glass matrix composites with ceramic powder (alumina and/or titania) filler. In this molding process, a thermosetting paste was molded into polydimethlsilosane soft molds prepared by replication of thick film resist (SU-8) molds. The SU-8 mold was patterned with UV-lithography. The effects of powder content in the paste on paste viscosity and sintering characteristics of molded samples were examined. In addition, effect of molding speed on pore trapping in the microstructure was studied. These results indicated that the powder micro injection molding process at ambient temperature has merits of low-pressure injection molding process with superior mold release characteristics.     

Visualizing analysis for weld line forming in micro injection molding by experimental method

In micro injection molding, the melt flow behavior is important for the final product quality. However, the current process monitoring and measurement technology are not adequate enough to provide a direct analysis access. In the presented study, a glass insert mold designed for performing the direct visual analysis for melt flow phenomena in micro injection molding is introduced. The micro tensile specimen with 0.1 × 0.4 mm² (depth × width) cross section dimension is chosen as the objective part. The correlation between processing parameters (injection pressure, injection speed, mold temperature) and flow behavior was investigated and analyzed. The results show that the injection pressure put an obvious effect on the filling speed through micro cavity. Injection speed can influence the filling time dramatically also. Higher mold temperature brings positive influence with the flowing speed, due to the lower viscosity of polymers in higher mold temperature.