Ultrasonic Moulding Research Articles

Ультразвуковое формообразование изделий из мелкодисперсных порошков

The article deals with the current state of the physics and technology of the process of ultrasonic molding (USM) of products from finely dispersed metal and non-metal powders. The relevance of a comprehensive consideration of the process is substantiated, structural and technological schemes for its implementation are presented, types of ultrasound sources – ultrasonic transducers and ultrasonic generators, as well as designs and methods for calculating concentrators (transformers) of ultrasonic vibrations are given. The results of experimental studies of the USM process as applied to fine powders of various physical and chemical nature are analyzed. Physical models of the USM process are presented and discussed.

Polypropylene-Based Polymer Locking Ligation System Manufacturing by the Ultrasonic Micromolding Process.

In recent years, there has been a growing demand for biocompatible medical devices on the microscale. However, the manufacturing of certain microfeatures has posed a significant challenge. To address this limitation, a new process called ultrasonic injection molding or ultrasonic molding (USM) has emerged as a potential solution. In this study, we focused on the production of a specific microdevice known as Hem-O-Lok, which is designed for ligation and tissue repair during laparoscopic surgery. Utilizing USM technology, we successfully manufactured the microdevice using a nonabsorbable biopolymer that offers the necessary flexibility for easy handling and use. To ensure high-quality microdevices, we extensively investigated various processing parameters such as vibration amplitude, temperature, and injection velocity. Through careful experimentation, we determined that the microdevice achieved optimal quality when manufactured under conditions of maximum vibrational amplitude and temperatures of 50 and 60 °C. This conclusion was supported by measurements of critical microfeatures. Additionally, our materials characterization efforts revealed the presence of a carbonyl (C=O) group resulting from the thermo-oxidation of air in the plasticizing chamber. This finding contributes to the enhanced thermal stability of the microdevices within a temperature range of 429-437 °C.

Manufacturing PLA/PCL Blends by Ultrasonic Molding Technology.

Ultrasonic molding (USM) is a good candidate for studying the plasticization of polymer mixtures or other composite materials due to either the little amount of material needed for processing, low waste or the needed low pressure and residence time of the mold. Thus, the novelty of this research is the capability of USM technology to process PLA/PCL blends and their corresponding neat materials, encompassing all the production stages, from raw material to the final specimen. The major findings of the work revealed that the thermal properties of the blends were not affected by the USM process, although the crystallinity degree experienced variations, decreasing for PLA and increasing for PCL, which was attributed to the crystallization rate of each polymer, the high process speed, the short cooling time and the small particle size. The employed ultrasonic energy increased the molecular weight with low variations through the specimen. However, the degradation results aligned with the expected trend of these material blends. Moreover, this study also showed the effect pellet shape and dimensions have over the process parameters, as well as the effect of the blend composition. It can be concluded that USM is a technology suitable to successfully process PLA/PCL blends with the correct determination of process parameter windows.

Ultrasonic nodal point, a new configuration for ultrasonic moulding technology

Ultrasonic moulding is a new technology that uses high power ultrasound to melt and mould thermoplastic polymers to produce samples with mini and micro features. The main feature of this technology is the use of ultrasonic energy as the heating source instead of a conventional injection screw. Even if ultrasonic moulding overcomes some of the drawbacks of conventional mini and micro-injection moulding, it still presents two main limitations that are hindering its widespread applicability: the lack of stability of the process and the difficulty to obtain samples with good mechanical properties for some materials. This article presents a new configuration, called nodal point ultrasonic moulding (NPUSM), to surmount such limitations. This configuration improves the stability of ultrasonic moulding technology and it is capable of processing materials with good mechanical properties. To prove its efficacy, the nodal point ultrasonic moulding configuration is used to obtain the processing window of a polyoxymethylene material and these results are compared with standard ultrasonic injection and conventional injection moulding. The results obtained show that NPSUM configuration improves the capabilities of ultrasonic moulding technologies.

Fabrication of Micro Ultrasonic Powder Molding Polypropylene Part with Hydrophobic Patterned Surface.

Constructing regular micro-structures with certain geometric characteristics on the surface of the polymer part can obtain some specific functions. Micro ultrasonic powder molding (micro-UPM) is an efficient processing technique for the fabrication of well-filled micro-structured Polypropylene (PP) parts. The micro-structure array on the surface of the core insert was obtained by low speed wire electrical discharge machining (WEDM-LS). PP polymer surfaces with micro-structured patterns were successfully replicated from the core insert surface after micro-UPM. By studying the detailed topography characterizations of micro-structured PP parts, the effects of processing parameters (ultrasonic energy, welding pressure and holding time) on the micro-structured filling show that when PP polymer was formed under the conditions of 1000 J, 115 kPa and 8 s during micro-UPM, well-filled micro-structured parts can be obtained. Besides, without low surface energy coating modification, the water contact angles (WCAs) of micro-structured PP parts increased from 85.3° to 146.8°, indicating that the wettability of the surface can be changed by replicating the micro-structure on PP parts after micro-UPM.

Ultrasonic Molding Technology: Recent Advances and Potential Applications in the Medical Industry.

Recently, ultrasonic molding (USM) has emerged as a promising replication technique for low and medium volume production of miniature and micro-scale parts. In a relatively short time cycle, ultrasonic molding can process a wide variety of polymeric materials without any noticeable thermal degradation into cost-effective molded parts. This research work reviews recent breakthroughs of the ultrasonic injection molding and ultrasonic compression molding process regarding the equipment and tooling development, materials processing and potential applications in the medical industry. The discussion is centered on the challenges of industrializing this technology, pointing out the need for improvement of the current process’s robustness and repeatability. Among the most important research areas that were identified are the processing of novel engineered and nanomaterials, the understanding and control of the ultrasonic plasticization process and the tooling and equipment development.

Replicability of Ultrasonic Molding for Processing Thin-Wall Polystyrene Plates with a Microchannel.

Ultrasonic molding is a new technology for processing small and micro polymeric components with reasonable cost and energy savings when small and medium batch sizes are required. However, when microcomponents are manufactured, the replicability of different micro features has to be guaranteed. The aim is to investigate the capability of ultrasonic molding technology for processing thin-wall plates of polystyrene with a microchannel, analyzing the filling behavior, the optical transparency, and the dimensional accuracy of the thin plate. The replicability of the manufactured microchannel is studied according to dimension and shape. The results reveal that plunger velocity influences transparency and filling cavity, whereas the vibration amplitude has less effect in both cases. The thickness deviation achieved on the final part is below 7% and the replication of the microchannel is better in depth than width, obtaining an average deviation of 4% and 11%, respectively. This replication also depends on the orientation of the microchannels and the distance from the injection gate. The replicability and repeatability for processing thin-wall plates with microchannel in polystyrene polymer are proved in this paper.

Processing of ultra-high molecular weight polyethylene/graphite composites by ultrasonic injection moulding: Taguchi optimization

Ultrasonic injection moulding was confirmed as an efficient processing technique for manufacturing ultra-high molecular weight polyethylene (UHMWPE)/graphite composites. Graphite contents of 1 wt%, 5 wt%, and 7 wt% were mechanically pre-mixed with UHMWPE powder, and each mixture was pressed at 135 °C. A precise quantity of the pre-composites mixtures cut into irregularly shaped small pieces were subjected to ultrasonic injection moulding to fabricate small tensile specimens. The Taguchi method was applied to achieve the optimal level of ultrasonic moulding parameters and to maximize the tensile strength of the composites; the results showed that mould temperature was the most significant parameter, followed by the graphite content and the plunger profile. The observed improvement in tensile strength in the specimen with 1 wt% graphite was of 8.8% and all composites showed an increase in the tensile modulus. Even though the presence of graphite produced a decrease in the crystallinity of all the samples, their thermal stability was considerably higher than that of pure UHMWPE. X-ray diffraction and scanning electron microscopy confirmed the exfoliation and dispersion of the graphite as a function of the ultrasonic processing. Fourier transform infrared spectra showed that the addition of graphite did not influence the molecular structure of the polymer matrix. Further, the ultrasonic energy led oxidative degradation and chain scission in the polymer.

Feasibility of manufacturing low aspect ratio parts of PLA by ultrasonic moulding technology

Ultrasonic moulding is a promising technology capable of producing complex mini and micro components highly demanded both electronical and medical sectors. This research work presents a preliminary study to evaluate the feasibility of producing low aspect ratio parts of polylactide acid (PLA) by ultrasonic moulding process. Additionally, mould design considerations are presented to increase literature regarding USM tooling. Finally, some moulding trials were performed to demonstrate the process feasibility to obtain parts fulfilling dimensional requirements.

Study of the Ultrasonic Molding Process Parameters for Manufacturing Polypropylene Parts

Applications of polymeric materials are becoming a huge opportunity to innovate in new manufacturing technologies. In this sense Ultrasonic Molding (USM) process is an innovative technology to produce polymeric micro parts. Here, ultrasonic energy is used for melting polymeric pellets and fill a mold cavity. This paper presents a preliminary study to analyse the influence of three process parameters of USM on filling cavity, porosity, part weight and dimension. The process parameters studied are: humidity of the pellets, sonotrode velocity and mold temperature. The results show that dried pellets, velocities lower than 7mm/s or using increasing ramps velocities provide better parts. Although in future works the effect of the ultrasonic time on filling cavity and part dimensions should be studied and more material tested to extend the knowledge to this new technology.

Process planning considerations for micromilling of mould cavities used in ultrasonic moulding technology

The current trend in miniaturization of products and components requires appropriate technologies for the manufacture of miniature dies and moulds. The work presented here deals with the process planning of micromilling for the production of miniature mould cavities, required in ultrasonic moulding in order to reach high precision. Several aspects of process planning are addressed, including cutting tool geometry selection, segmentation of cavity geometry, minimum chip thickness, chordal tolerance, and type of interpolation. The case study involves the successful micromilling of a complex aluminium mould cavity for ultrasonic moulding. The proposed process plan is demonstrated through the micromilling of the mould cavity and silicone replicas of the miniature geometrical model. In general terms, good precision is obtained following the proposed methodology. In a randomly located set of geometric features, the dimensional error was below 5% for most features (32 out of a total of 40).

Ultrasonic moulding of plastic powders

Polypropylene powder has been moulded by the application of ultrasonic vibrations and attempts have been made to optimize the strength of the mouldings. The most important variables are the duration of the ultrasonic vibrations and the subsequent dwell time during which the pressure is maintained. It was also found that the smaller the particle size of the powder the greater was the tensile strength of the mouldings. The compaction pressure did not have any significant effect on strength. Under the best conditions a tensile strength of 20 MPa was recorded, which is about 85% of the value achieved by injection moulding. However, the ductility of the mouldings was always considerable less than that which would normally be expected from polypropylene.