Microinjection molding (µIM) appears to be one of the most efficient processes for the large-scale production of thermoplastic polymer microparts. The microinjection molding process is not just a scaling down of the conventional injection process; it requires a rethinking of each part of the process. This review proposes a comparative description of each step of the microinjection molding process (µIM) with conventional injection molding (IM). Micromolding machines have been developed since the 1990s and a comparison between the existing ones is made. The techniques used for the realization of mold inserts are presented, such as lithography process (LIGA), laser micromachining and micro electrical discharge machining (µEDM). Regarding the molding step, the variotherm equipment used for the temperature variation is presented and the problems to solve for each molding phase are listed. Throughout this review, the differences existing between µIM and conventional molding are highlighted.

https://iopscience.iop.org/article/10.1088/0960-1317/17/6/R02/pdf

Microinjection molding of thermoplastic polymers: a review

Recent progress in flexible and stretchable piezoelectric devices for mechanical energy harvesting, sensing and actuation

A BP-neural network predictor model for plastic injection molding process

Piezoelectric sensing is of increasing interest for high-temperature applications in aerospace, automotive, power plants and material processing due to its low cost, compact sensor size and simple signal conditioning, in comparison with other high-temperature sensing techniques. This paper presented an overview of high-temperature piezoelectric sensing techniques. Firstly, different types of high-temperature piezoelectric single crystals, electrode materials, and their pros and cons are discussed. Secondly, recent work on high-temperature piezoelectric sensors including accelerometer, surface acoustic wave sensor, ultrasound transducer, acoustic emission sensor, gas sensor, and pressure sensor for temperatures up to 1,250 °C were reviewed. Finally, discussions of existing challenges and future work for high-temperature piezoelectric sensing are presented.

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High-Temperature Piezoelectric Sensing

Ultrasonic Generation by Pulsed Lasers

A software package that provides an interactive and graphical environment for surface acoustic wave (SAW) and plate-mode propagation studies in arbitrarily oriented anisotropic and piezoelectric multilayers is described. The software, which runs on an IBM PC with math coprocessor, is based on a transfer-matrix formulation for calculating the characteristics of SAW propagation in multilayers that was originally written for a mainframe computer. The menu-driven software will calculate wave velocities and field variable variations with depth for any desired propagation direction: the graphics capability provides a simultaneous display of slowness or velocity and of SAW Delta v/v coupling constant curves, and their corresponding field profiles in either polar or Cartesian coordinates, for propagation in a selected plane or as a function of one of the Euler angles. The program generates a numerical data file containing the calculated velocities and field profile data. Examples illustrating the usefulness of the software in the study of various SAW and plate structures are presented. >

PC software for SAW propagation in anisotropic multilayers

Flexible ultrasonic transducers (UTs) consisting of a metal foil, a piezoelectric ceramic film, and a top electrode have been developed. The flexibility is realized owing to the porosity of piezoelectric film and the thinness of metal foil. In this paper, the stainless steel (SS), lead-zirconate-titanate (PZT)/PZT composite and silver paste were chosen as metal foil, piezoelectric film, and top electrode materials, respectively. The SS foil serves as both substrate and bottom electrode. The PZT/PZT piezoelectric composite film is made by the sol-gel spray technique. PZT/PZT films of thicknesses from 40 to 70 mum were fabricated onto SS foils. The capability of these flexible sensors operated in the pulse-echo mode for nondestructive testing on flat and curved surfaces of different materials at room temperature and 160degC has been demonstrated. Numerical simulations of the effects of the metal foil thickness on the ultrasonic performance of flexible UTs also were carried out, and the results are in reasonable agreement with experimental data. In addition, a PZT/PZT flexible transducer showed a signal strength comparable with that obtained by a commercial room temperature broad bandwidth transducer

/pdf/flexible-ultrasonic-transducers-2a6vb96eb4.pdf

Flexible ultrasonic transducers

On-line ultrasonic monitoring of injection molding of a simple polymer box is studied using pulse-echo techniques. The flow front of molten polymers inside the mold has been probed by a multiple-channel probing system with a time resolution of 2 ms. This information can be used to control the plunger movements. The gap development, because of the shrinkage of the part in the mold, is also monitored. This information, which is important for the understanding of the part's cooling process, has been found to be superior than that measured by a conventional pressure probe. The relation between the gap formation time and the packing pressure has been investigated at various part locations characterized by different thicknesses. The velocity and the amplitude variations of ultrasonic waves, in a reflection as well as in a transmission configuration, have also been measured in the part's material during its solidification. The behavior of these ultrasonic parameters contributes to the interpretation of the solidification process.

On-line ultrasonic monitoring of the injection molding process

In-line ultrasonic monitoring of polymer co-extrusion and twin-screw extrusion are presented. Co-extrusion of high density polyethylene (HDPE) and a thermoplastic elastomer based on polypropylene-EPDM (ethylene-propylene-diene monomer) has been investigated by ultrasonic sensors consisting of piezoelectric transducers and clad buffer rods. One extremity of the rod (probing end) was installed flush with the die surface so as not to disturb the material flow. The other end was air cooled in order to protect the transducer from excessive heating. This approach has been demonstrated to be quite convenient for monitoring and controlling industrial material processes: first, it can work at temperatures up to 1000°C; second, the clad buffer rod probing end can be machined to the same shape as those of commercial temperature and pressure sensors commonly used in the extrusion process. Therefore, no modifications are required for the installation in the original equipment. The information obtained includes the position of the interface between polymers and the stability of the process. The same ultrasonic probe has also been installed on a barrel of a twin-screw extruder. This study was performed using polyethylene and polystyrene. It has been verified that the ultrasonic sensor can be successfully operated along the extruder screw and that the ultrasound can give access to the material properties while the polymer is being processed. This means that the technique can be exploited to monitor and control in situ the characteristics of the polymer being transformed in operations typically performed on twin-screw extruders, such as compounding, visbreaking or reactive extrusion.

Ultrasonic in-line monitoring of polymer extrusion

Ultrasonic sensors and associated methods for on-line monitoring of material properties for die casting, molding and extrusion processes at elevated temperatures are disclosed. The sensors include the use of ultrasonic waveguides embedded in the processing machines and piezoelectric ultrasonic transducers. The sensors are operated in the reflection geometry in which one side access of the processing machines is required. The monitoring parameters are the flow front, gap development and temperature of the materials being processed and filled in the cavities of the die in casting processes and the mold in injection molding, and the temperature and viscosity of the molten polymers in the polymer extrusion machines. Piezoelectric ultrasonic transducers made of high Curie temperature materials, fabricated by sol-gel techniques and directly deposited on top of the ultrasonic waveguides or the external walls of the shot sleeve of the die caster, die of the die caster, mold of the injection molding machine or barrel of the extruder are also used.

Cheng-Kuei Jen

Papers

PC software for SAW propagation in anisotropic multilayers

Flexible ultrasonic transducers

On-line ultrasonic monitoring of the injection molding process

Ultrasonic in-line monitoring of polymer extrusion

Ultrasonic sensors for on-line monitoring of castings and molding processes at elevated temperatures