Ultrasonic Embossing Research Articles

Ultrasonic welding of continuous carbon fiber reinforced PEEK with embossed energy directors

Ultrasonic plastic welding (UPW) is an efficient and environmentally friendly method for joining carbon fiber reinforced thermoplastic (CFRTP). A crucial aspect of UPW is the design of the energy director (ED). In this study, ultrasonic embossing technology was used to process flat EDs to obtain a new type of ED, named embossed ED. The effect of embossed EDs on the joint formation in ultrasonic welding of continuous carbon fiber reinforced PEEK was investigated in terms of tensile shear properties, macro and micro-morphologies, and fracture morphology. The results show that the use of embossed EDs makes a more homogeneous temperature distribution at the welding interface which significantly reduces defects in the joint. The use of embossed EDs increases the failure load of welded joints by about 50 % (up to 39.6 MPa) and reduces the variation of the joint quality compared with the use of flat EDs. In the optimal condition, the joints made with embossed EDs experiences interlaminar failure of the base material.

Coupled thermomechanical finite element analysis of ultrasonic hot embossing process

Ultrasonic Hot Embossing of polymers is one of the most attractive manufacturing methods of high-quality and complex microparts needed for biological and chemical processes. A little simulation work has been done to study the deformation mechanism and the required load in the Ultrasonic Hot Embossing of polymethyl methacrylate (PMMA). This paper developed a 2D coupled thermo-mechanical finite element model to simulate the forming behavior of the ultrasonic embossing process of PMMA, optimize the mold microfeature corner, and predict the embossing load as well. VDISP ABAQUS subroutine has been used to describe the downward motion of the mold assisted with ultrasonic vibration. The Arbitrary Eulerian-Lagrangian re-meshing technique has been implemented to refine the deformation zone during simulation to avoid divergence due to localized excessive deformation. Embossing load, temperature, stresses, strains, and energy dissipation have been recorded and analyzed. Simulation results revealed that the coupled thermo-mechanical FE Model efficiently captures the deformation behavior and Embossing load. It also proved that a Mold microfeature corner of 20 μm filet radius is recommended to adequately fill out the area around the mold and maintain uniform temperature and strain distributions.

Utilization of cross‐correlation function for assessment of replication quality in ultrasonic embossing of microchannels on polymethyl methacrylate

AbstractUltrasonic embossing—a process where a horn vibrating at 20–30 kHz compresses on a thermoplastic substrate sitting on a mold to replicate the features on the mold to the substrate—is a promising method for fabricating microchannels on thermoplastics due to reduced cycle time and relatively low equipment cost. Replication quality in ultrasonic embossing has been investigated in the literature by primarily referring to the replication depth. However, this approach does not fully reflect the fidelity between the mold and the replicated feature, especially at the side walls, which are typically designed to be vertical in microchannels. We propose using cross‐correlation—a method that quantifies the similarity between two signals by measuring the overlap of their patterns—between the derivative of the mold profile and the embossed profile as a figure of merit that accurately reflects the fidelity of the side wall. For testing purposes, we embossed straight microchannels on polymethyl methacrylate (PMMA) using micron‐scaled protrusions on a brass mold fabricated by CNC milling. The mold comprised 100, 300, and 1000‐μm‐wide protrusions of same designed height of 300 μm, resulting in aspect ratios (AR) of 3, 1, and 1/3, respectively. Cross‐correlations between the derivatives of the profiles ranged between 0.50 and 1.00, while cross‐correlations between the profiles were greater than 0.97 in all cases, showing the sensitivity imposed by utilizing the derivatives. Setting average of all cross‐correlation values (0.8) as the quality threshold, we observed that high AR (3) features were replicated at low quality, while low AR (1/3) features were replicated at high quality, regardless of the process parameters. In replicating unit AR features, the process parameters were observed to affect the quality, where the combination of vibration time and pressure was the most significant compared to individual effects of the parameters.Highlights Parameters' effect on replication of varied aspect ratio features was assessed. Assessment was carried out by cross‐correlating mold and channel profiles. Cross‐correlating derivatives of profiles provide a more sensitive means. General rules for replication quality in ultrasonic embossing were driven.

Effect of ultrasonic embossing and welding time on the joint performance of ultrasonically welded short carbon fiber reinforced PEEK

Ultrasonic plastic welding (UPW) is a highly efficient and environmental friendly method that has gained gradually increased attention in joining carbon fiber reinforced thermoplastic (CFRTP). A crucial aspect in UPW of CFRTP is the design of the energy director (ED). This paper employs ultrasonic embossing, a cost-effective way to manufacture ED on the surface of CFRTP sheets. The effect of ultrasonic embossing time and welding time on the joint performance is investigated in terms of microstructure, tensile-shear property, and fracture surface morphology. The results show that the structured surface made by ultrasonic embossing can be used as ED to concentrate welding energy. This process reduces the randomness and dispersion of weld distribution, improves the failure load of welded joints by 30 % compared with the joints made without using ED. The ultrasonic embossing time has a limited influence on the joint failure load. Sound welded joints can be obtained when welding with one structured surface and welding time of 1.5 s.

Enhancing the ultrasonic plastic welding strength of Al/CFRTP joint via coated metal surface and structured composite surface

Ultrasonic plastic welding (UPW) is a promising technology for joining metal to carbon fiber reinforced thermoplastic composite (CFRTP) but shows poor joint strength in the existing studies. This work conducts UPW of AA6061 aluminum alloy to carbon fiber reinforced PA66 (CF/PA66) by employing a polymer coating as an interlayer. Simple metal surface grinding and silane coupling agent (SCA) treatment are used to strengthen the bonding of the metal/coating interface. Structured CF/PA66 surface fabricated by ultrasonic embossing acts as energy directors to improve the bonding strength of the coating/plastic interface. The results show that relatively high tensile-shear strength (about 31.0 MPa) can be obtained. Micro-mechanical interlocking and chemical bonding (Al-O-C and Al-O-Si bonds) are considered as the bonding mechanism of the metal/coating interface.

Investigation of process-affected zone in ultrasonic embossing of microchannels on thermoplastic substrates

In this paper, the process-affected zone in ultrasonically embossed thermoplastic substrates is investigated both numerically and experimentally. Commercialization of microfluidic devices challenges the need for high-speed manufacturing of plastic chips. Ultrasonic embossing is considered as an alternative method since the cycle time can be as low as a few seconds per chip while keeping the cost relatively low. To examine the ultrasonic embossing process, experiments were carried out to replicate 200 μm wide and 150 μm high straight channels on 3 mm thick polymethylmethacrylate (PMMA) substrates. The mold was fabricated by milling on aluminum. The features could be embossed by applying an 85 N static force at 28 kHz ultrasonic vibration and 10 μm amplitude for 5 s at room temperature with replication rates of 99.5 % and 100 % for the width and the depth, respectively. During the experiments, a clearly visible process-affected zone typically bounded by a half-circle with the center at the channel axis was observed. It was proven that the process-affected zone was bounded by the isothermal surface at the glass transition temperature of the substrate material (107 °C), both numerically and experimentally. It was also shown that the composition of the substrate material remains unaffected within the process-affected zone.

Low-cost and fast fabrication of the ultrasonic embossing on polyethylene terephthalate (PET) films using laser processed molds

This paper presented ultrasonic embossing using metal molds to replicate microstructures on polyethylene terephthalate (PET) films. The metal molds used in this study were fabricated by laser ablation processing technology. Aluminum 6061 was adopted to be mold material because of its better machinability and the optimized laser processing parameters were laser power of 10 W, scanning numbers of 20 times and scanning speed of 500 mm/s, respectively. Effects of the ultrasonic embossing parameters on replication quality, especially for replication depth were investigated. The results showed that the ultrasonic pressure F, welding time T2, and holding time T3 were significant factors of replication depth. Then optimized ultrasonic parameters obtained by orthogonal experiments were determined to be ultrasonic pressure of 400 kPa, welding time of 1 s and holding time of 4 s. The corresponding maximal depth and replication rate on PET films can reach 271.7 µm and 99.74%, respectively. By using laser processed molds, the micro mixers and hydrophobic surface can be obtained successfully through ultrasonic embossing process. No leakage of blue ink in the micro mixers was observed, which meant high quality and high sealing property of the micro mixers. The instant contact angle of embossed PET films increased from 70.7° to 100.4°, which can be concluded that it was possible to change the wettability of surface and obtain the hydrophobic surface from hydrophilic surface by using laser processed molds and replicating microstructures after ultrasonic embossing. Laser ablation processing technology provides a novel way to fabricate molds and the result of this experiment offered a possibility of mass manufacture of polymer microstructure or micro device.

Analysis of the Influence of High-Frequency Excitation Into Quality of the Replicated Microstructure

In the present research, surface relief diffraction gratings were fabricated and investigated. The purpose of this research was to determine the collection of parameters, which influence the diffraction efficiency most positively. For replication process ultrasonic thermal embossing was selected with different manufacturing regimes (time, pressure, and temperature). Diffraction efficiencies of periodical microstructures were measured experimentally. The results have shown increase of periodical microstructure quality with the help of high-frequency oscillations during manufacturing. Combination of pressing time, pressure, temperature, and vibrations improved the efficiency of replication process.

聚合物超声压印非成形面熔融缺陷形成机理及抑制

This paper analyzes the reason why the polymer is melted on a non-forming surface during ultrasonic embossing and proposes a method to inhibit the polymer melting.On the basis of the heating mechanism of ultrasonic,it points out that the polymer melting phenomenon on non-forming surface is resulted by the friction in a horn-substrate interface.Then,it proposed the methodtwo interfaces of different friction coefficientsto inhibit the polymer melting and implemented the method by coatings surface protection films on the non-forming surface.To optimize the protection films,and the influences of the four coating film conditions on the softening time are examined through Taguchi method.The results show that the Sekisui#622E-50 film shortens the softening time by 3.4sandthe Sekisui#622WB film reduces the softening time error by 0.64 s.It demonstrates that surface protection films coated can avoid polymer melting on the non-forming surface,and improve the process replication ability and the process stability in ultrasonic embossing.

Local thermal-assisted ultrasonic embossing for the fabrication of polymer microstructures

A new technique was developed for embossing microstructures on thermoplastic substrates, which can achieve high accuracy replication with little loss of the production efficiency. The technique is no need of the preheating process and cooling device. In the new technique, just the surface layer of the polymer substrate was heated through heat transmission and ultrasonic viscoelastic heating was the major heat source. For our new technology, the temperature of the mould just provided the initial temperature of the mould-substrate interface and a higher boundary temperature for embossing. The replication accuracies of three embossing technologies were contrasted, including ultrasonic embossing at room temperature (HER), thermal assisted ultrasonic embossing (TUE) and local thermal assisted ultrasonic embossing (L-TUE). The results indicated that, the replication accuracy of L-TUE was approximate with TUE. Moreover, the effects of the processing parameters on the replication quality, including average replication depth and uniformity over the entire chip, were investigated. Different with our prediction, the replication accuracy did not monotonously improved with the ultrasonic force and the temperature of the mold. Finally, the temperature test was carried out to study the temperature characteristic of our new technology.

Fabrication of Micropattern of Plastic Film Using Ultrasonic Micro Embossing

This study indicates the micropattern of molded plastic film from a mold insert using ultrasonic micro embossing. A mold insert and plastic film are heated above the glass transition temperature of plastic, and the softened plastic is flowed into the micropattern of a mold insert by applying pressure via a conventional technique. A longitudinal ultrasonic wave is added to the ultrasonic micro embossing process. The longitudinal ultrasonic wave generated by an ultrasonic system at a frequency of 35 KHz, has amplitude of 20 μm and output power of 900 W. The micropatterns of the Ni mold insert are groove-shaped and they are 2-μm wide and 200-nm deep. The Polypropylene (PP) is chosen as the replication materials. This study identifies the replication properties of the plastic film using different process parameters (working pressure, ultrasonic pressure, packing pressure, working time, ultrasonic time and packing time). Results of this study demonstrate that ultrasonic time is the most important process parameter for ultrasonic micro embossing.

聚合物微结构热辅助超声波压印成形

A thermal-assisted ultrasonic embossing method was proposed based on silicon molds to replicate thermoplastic substrates in a low cost and high efficiency.The ultrasonic vibration was applied to the mold-polymer interface to heat the polymer rapidly to the embossing temperature.To reduce the risk of damaging the mold,the die was preheated to a temperature which is 35-50℃ below the glass transition temperature(Tg)of the polymer.Then,the influences of the ultrasonic amplitude, ultrasonic force,ultrasonic time,and the thermal-assisted temperature were studied by orthogonal array experiments to reveal the mechanism of ultrasonic embossing.The influence of the substrate thickness was also investigated.The experimental results show that the most important parameter for replication is the thermal-assisted temperature,follows by the ultrasonic amplitude.Moreover,the ultrasonic force is the most important parameter for replication uniformity,while the thinner polymersheets are more conducive to be replicated under the same circumstances.With the optimized parameters,the replication accuracy has reached 99%on a Polymethyl Methacrylate(PMMA)substrate,and the cycle time is less than 50s.All theses studied show that thermal assisted ultrasonic embossing has high replication efficiency and is a potential way to mass formation of polymer microstructures.

Development and Application of Molded Interconnect Devices

With the improvements of electromechanical systems' automation and intelligence, contradiction between the high integration, high performance and miniaturization, low cost has become the principal reason restricting the development of electromechanical system. The emergence of molded interconnection device (MID) technology provides a new way to resolve this contradiction. Integration of the mechanical and electrical functions in electromechanical system onto the same polymer molded base structure, replacement of the tradition printed circuit board (PCB), design and processing of 3D circuit system on polymer molded base structure surface distinguishes MID technology from others. MID technology can not only save space occupied by the electromechanical system and improve the system integration, but also can simplify the assembly process and lower the cost. In this study, present research and future development of MID technology were introduced first. Then the main technical problems involved in MID processing including the design method of MID, materials technology, equipment technology, surface mounted devices (SMD) assembly technique, and so on were analyzed systematically. Finally, using the ultrasonic micro embossing technology, a manufacturing method of polymer circuit board, radio frequency identification (RFID) antenna, microelectrode arrays, and some other polymer foil MID was proposed. Based on the in-depth analysis of polymer foil MID's characteristics, polymer foil MID are expected to have a broad application in the field of microfluidic chip.

Fabrication of polymer electronic boards by ultrasonic embossing and welding

A method has been developed allowing fabrication of electronic boards from flexible polymer film by ultrasonic embossing and welding within seconds. A commercially available ultrasonic welding machine and micro patterned tools from aluminum are employed first to generate conductor paths on a flexible polymer film, in a further step, surface mounted devices are assembled and fixed on the flexible polymer film by a lid, and meanwhile electrical connected via a z axis conductive tape, both the molding of the lid and the bonding between the lid and electronic boards are implemented on an ultrasonic welding machine. Finally, the effectiveness of electrical interconnection is investigated at elevated temperature, humidity and bending load, exemplified by three simple circuit boards assembled with light-emitting diodes and resistors and capacitor separately, and the experimental results show that the electrical interconnection is effective, stable, and durable.

Study of Double-Side Ultrasonic Embossing for Fabrication of Microstructures on Thermoplastic Polymer Substrates

Double-side replication of polymer substrates is beneficial to the design and the fabrication of 3-demensional devices. The ultrasonic embossing method is a promising, high efficiency and low cost replication method for thermoplastic substrates. It is convenient to apply silicon molds in ultrasonic embossing, because microstructures can be easily fabricated on silicon wafers with etching techniques. To reduce the risk of damaging to silicon molds and to improve the replication uniformity on both sides of the polymer substrates, thermal assisted ultrasonic embossing method was proposed and tested. The processing parameters for the replication of polymethyl methacrylate (PMMA), including ultrasonic amplitude, ultrasonic force, ultrasonic time, and thermal assisted temperature were studied using orthogonal array experiments. The influences of the substrate thickness, pattern style and density were also investigated. The experiment results show that the principal parameters for the upper and lower surface replication are ultrasonic amplitude and thermal assisted temperature, respectively. As to the replication uniformity on both sides, the ultrasonic force has the maximal influence. Using the optimized parameters, the replication rate reached 97.5% on both sides of the PMMA substrate, and the cycle time was less than 50 s.

Using silicon molds for ultrasonic embossing on Polymethyl Methacrylate (PMMA) substrates

This paper presents ultrasonic embossing using silicon molds to replicate microstructures on Polymethyl Methacrylate (PMMA) substrates. The pattern of the silicon mold consists of micro grooves with different sizes. The molds were fabricated by wet etching, and both concave and convex types were fabricated. The effects of the processing parameters on replication quality, including average microstructure depth, uniformity and the location-related replication depth were investigated via orthogonal experiments. The results show that the ultrasonic amplitude is the most important parameter for replication depth. The ultrasonic time benefits the accumulation of the heat, so it also influences replication depth. As for ultrasonic force, it has less influence on replication depth but significant influence on replication uniformity. The width of the grooves of the high density patterning molds ranged from 10 to 30 μm, and the center distance between the two microstructures from 20 to 50 μm in our experiments. The concave molds were intended to reach higher replication depth than that of convex molds with the same micro grooves. The average replication depth reached 98 %, and the uniformity on one chip reached 99 % with an area of 11 × 11 mm. All experiments were finished in 60 s, which is more efficient than the hot embossing technique, thus this paper provides a potential method for medium-sized bulk production and rapid fabrication for polymer microcomponents.

Microstructuring of multiwell plates for three-dimensional cell culture applications by ultrasonic embossing

Since three-dimensional (3D) cell culture models better reflect tissues in vivo in terms of cell shape and microenvironment compared to conventional monolayer cultures, 3D tissue culture substrates gain more importance for a wide range of biological applications like drug discovery, toxicological studies, cancer and stem cell research. In this study we developed a method for the fabrication of 3D cell culture substrates in a multiwell plate format by microstructuring the bottom of 96-well cell culture plates using an ultrasonic embossing process. The resulting microstructured area consists of cubic microcavities in which adherent multicellular aggregates can be formed. We performed the biological evaluation of the system with the liver-derived human cell-line HepG2 and compared the novel substrate with a commercially available 3D culture system comprising porous alginate sponges. Metabolic activity (alamarBlue® reduction) and induction of four biotransformation enzymes (EROD, ECOD, UGT, SULT) were determined by fluorimetry or HPLC. Our results revealed that HepG2 cells in microstructured plates showed a higher mitochondrial activity, as well as enzyme activity of ECOD and UGT after treatment with an inducer when compared to cells cultured in alginate sponges at otherwise comparable conditions. Since we have modified standard cell culture plates, the obtained system is adaptable to automated screening and might be useful for all kinds of cultures including adult, progenitor and stem cells which need a 3D culture configuration to restore or maintain the differentiated status.

Rapid fabrication of surface-relief plastic diffusers by ultrasonic embossing

This paper discusses an innovative and effective ultrasonic embossing process, which enables the rapid fabrication of surface-relief plastic diffusers. The metallic mold bearing the microstructures is fabricated using a tungsten carbide turning machine. A 1500-W ultrasonic vibrator with an output frequency of 20 kHz was used to replicate the microstructure onto 1-mm-thick PMMA plates in the experiments. During ultrasonic embossing, the ultrasonic energy is converted into heat through intermolecular friction at the master mold/plastic plate interface due to asperities to melt the thermoplastic at the interface and thereby to replicate the microstructure. Under the proper processing conditions, high-performance plastic diffusers have been successfully fabricated. The cycle time required to successfully fabricate a diffuser is less than 2 s. The experimental results suggest that ultrasonic embossing could provide an effective way of fabricating high-performance plastic diffusers with a high throughput.

Manufacture of dual-side surface-relief diffusers with various cross angles using ultrasonic embossing technique

This paper reports a simple and effective ultrasonic embossing method which enables the rapid fabrication of dual-side surface-relief plastic diffusers with various cross angles. Metallic master molds bearing microstructures are fabricated using a tungsten carbide turning machine. A 1500-Watt ultrasonic vibrator with an output frequency of 20 kHz was used to replicate the microstructure onto 1 mm thick PMMA and PET films in the experiments. During ultrasonic embossing, the ultrasonic energy is converted into heat through intermolecular friction at the master mold/plastic plate interface due to asperities to melt the thermoplastic at the interface and thereby to replicate the microstructure. Under the proper processing conditions, high-performance dual-sided plastic diffusers of various cross-angles can be successfully fabricated. The proposed method shows great potential for fast fabrication of micro-optical components due to its simplicity and versatility.

Zero flash ultrasonic micro embossing on foamed polymer substrates: A proof of concept

AbstractThis article reviews a novel method to produce microembossed features with an aspect ratio of three and negligible flash on polymer surfaces. An embossing technique that utilizes localized heating (ultrasonic energy) was used with polystyrene and polypropylene substrates. It was demonstrated that when foamed substrates were used, the amount of flash produced was negligible compared to nonfoamed substrates, which has been a significant unresolved problem with embossing using localized heating. The depth of microembossed features as a function of heating times and amplitudes of ultrasonic embossing is detailed in this article, along with a characterization of complex embossed geometries. It was seen that embossing depth was generally proportional to heating time and amplitude until the maximum feature depth was achieved. Although this article deals with embossing of microfeatures for lab‐on‐a‐CD applications, it is envisioned that it is also suitable for lab‐on‐a‐chip applications. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers