Transient viscoelastic heating characteristics of polyethene under high frequency hammering during ultrasonic plasticizing.

As a polymer molding technology developed in recent years, ultrasonic plasticizing micro-injection molding has great advantages in the manufacture of micro-nano parts by virtue of low energy consumption, less material waste and reduced filling resistance. However, the process and mechanism of transient viscoelastic heating for polymers under ultrasonic high-frequency hammering are unclear. The innovation of this research is that a combination of experiment and MD (molecular dynamics) simulation was adopted to study the transient viscoelastic thermal effect and microscopic behavior of polymers with different process parameters.

Molecular Insights into the Wall Slip Behavior of Pseudoplastic Polymer Melt in Nanochannels during Micro Injection Molding.

Wall slip directly affects the molding quality of plastic parts by influencing the stability of the filling flow field during micro injection molding. The accurate modeling of wall slip in nanochannels has been a great challenge for pseudoplastic polymer melts. Here, an effective modeling method for polymer melt flow in nanochannels based on united-atom molecular dynamics simulations is presented.

An Effective Shrinkage Control Method for Tooth Profile Accuracy Improvement of Micro-Injection-Molded Small-Module Plastic Gears.

An effective method to control the non-linear shrinkage of micro-injection molded small-module plastic gears by combining multi-objective optimization with Moldflow simulation is proposed. The accuracy of the simulation model was verified in a micro-injection molding experiment using reference process parameters. The maximum shrinkage (Y1), volume shrinkage (Y2), addendum diameter shrinkage (Y3), and root circle diameter shrinkage (Y4) were utilized as optimization objectives to characterize the non-linear shrinkage of the studied gear.

A new fuzzy rule based multi-objective optimization method for cross-scale injection molding of protein electrophoresis microfluidic chips.

Injection molding is one of the most promising technologies for the large-scale production and application of polymeric microfluidic chips. The multi-objective optimization of injection molding process for substrate and cover plate on protein electrophoresis microfluidic chip is performed to solve the problem that the forming precision is difficult to coordinate because of the cross-scale structure characteristics for chip in this paper. The innovation for this research is that an optimization approach and a detailed fuzzy rule determination method are proposed in multi-objective optimization for protein electrophoresis microfluidic chip.

Numerical Simulation on the Acoustic Streaming Driven Mixing in Ultrasonic Plasticizing of Thermoplastic Polymers.

The acoustic melt stream velocity field, total force, and trajectory of fluorescent particles in the plasticizing chamber were analyzed using finite element simulation to investigate the acoustic streaming and mixing characteristics in ultrasonic plasticization micro-injection molding (UPMIM). The fluorescence intensity of ultrasonic plasticized samples containing thermoplastic polymer powders and fluorescent particles was used to determine the correlation between UPMIM process parameters and melt mixing characteristics. The results confirm that the acoustic streaming driven mixing occurs in ultrasonic plasticization and could provide similar shear stirring performance as the screw in traditional extrusion/injection molding.

Polymer-Metal Interfacial Friction Characteristics under Ultrasonic Plasticizing Conditions: A United-Atom Molecular Dynamics Study.

Understanding the properties of polymer-metal interfacial friction is critical for accurate prototype design and process control in polymer-based advanced manufacturing. The transient polymer-metal interfacial friction characteristics are investigated using united-atom molecular dynamics in this study, which is under the boundary conditions of single sliding friction (SSF) and reciprocating sliding friction (RSF). It reflects the polymer-metal interaction under the conditions of initial compaction and ultrasonic vibration, so that the heat generation mechanism of ultrasonic plasticization microinjection molding (UPMIM) is explored.

New Considerations on the Determination of the Apparent Shear Viscosity of Polymer Melt with Micro Capillary Dies.

Capillary rheometers have been widely used for the rheological measurement of polymer melts. However, when micro capillary dies are used, the results are usually neither accurate nor consistent, even under the same measurement conditions. In this work, theoretical modeling and experimental studies were conducted for a more profound understanding of the mechanism by which the initial and boundary conditions influence the inaccuracy in the apparent shear viscosity determination with micro capillary dies (diameters: 500 μm, 200 μm, 100 μm).

Tuning Power Ultrasound for Enhanced Performance of Thermoplastic Micro-Injection Molding: Principles, Methods, and Performances.

With the wide application of Micro-Electro-Mechanical Systems (MEMSs), especially the rapid development of wearable flexible electronics technology, the efficient production of micro-parts with thermoplastic polymers will be the core technology of the harvesting market. However, it is significantly restrained by the limitations of the traditional micro-injection-molding (MIM) process, such as replication fidelity, material utilization, and energy consumption. Currently, the increasing investigation has been focused on the ultrasonic-assisted micro-injection molding (UAMIM) and ultrasonic plasticization micro-injection molding (UPMIM), which has the advantages of new plasticization principle, high replication fidelity, and cost-effectiveness.

A General and Efficient Approach for the Dual-Scale Infiltration Flow Balancing in In Situ Injection Molding of Continuous Fiber Reinforced Thermoplastic Composites.

In situ injection molding of continuous fiber reinforced thermoplastic composites is challenged by unbalanced dual-scale infiltration flow due to the pronounced capillary effect. In this paper, a general and efficient approach was proposed for dual-scale infiltration flow balancing based on numerical simulation. Specifically, Stokes and Brinkman equations were used to describe the infiltration flow in inter- and intra-fiber bundles.

A Practical Numerical Approach to Characterizing Non-Linear Shrinkage and Optimizing Dimensional Deviation of Injection-Molded Small Module Plastic Gears.

This paper was aimed at finding out the solution to the problem of insufficient dimensional accuracy caused by non-linear shrinkage deformation during injection molding of small module plastic gears. A practical numerical approach was proposed to characterize the non-linear shrinkage and optimize the dimensional deviation of the small module plastic gears. Specifically, Moldflow analysis was applied to visually simulate the shrinkage process of small module plastic gears during injection molding.

Progressive Molecular Rearrangement and Heat Generation of Amorphous Polyethene Under Sliding Friction: Insight from the United-Atom Molecular Dynamics Simulations.

Frictional heat has been widely used in various polymer-based advanced manufacturing. The fundamental understanding of the thermodynamics of the interfacial friction of polymer bulk materials can help to avoid compromising the process controllability. In this work, we have performed united-atom molecular dynamics (MD) simulations to reveal the interfacial friction heating mechanism of amorphous polyethene (PE) in both the single sliding friction (SSF) and reciprocating sliding friction (RSF) modes.

Effects of the Processing Parameters on the Shear Viscosity of Cyclic Olefin Copolymer Plasticized by Ultrasonic Vibration Energy.

Shear viscosity of the cyclic olefin copolymer (COC) plasticized by ultrasonic vibration energy is characterized by high pressure capillary rheometer. Two different plasticization modes were adopted to prepare the samples with an in-house developed prototype machine. Single-factor experiments were conducted to investigate the effects of ultrasonic energy on the shear viscosity.

Evolution of Interfacial Friction Angle and Contact Area of Polymer Pellets during the Initial Stage of Ultrasonic Plasticization.

Interfacial friction heating is one of the leading heat generation mechanisms during the initial stage of ultrasonic plasticization of polymer pellets, which has a significant influence on the subsequent viscoelastic heating according to our previous study. The interfacial friction angle and contact area of polymer pellets are critical boundary conditions for the analysis of interfacial frictional heating of polymer pellets. However, the duration of the interfacial friction heating is extremely short in ultrasonic plasticization, and the polymer pellets are randomly distributed in the cylindrical barrel, resulting in the characterization of the distribution of the interfacial friction angle and contact area to be a challenge.

Characterization of the Fluidity of the Ultrasonic Plasticized Polymer Melt by Spiral Flow Testing under Micro-Scale.

The fluidity of a molten polymer plasticized by ultrasonic vibration was characterized by spiral flow testing based on an Archimedes spiral mold with microchannels. Mold inserts with various channel depths from 250 to 750 µm were designed and fabricated to represent the size effect under micro-scale. The effect of ultrasonic plasticizing parameters and the mold temperature on the flow length was studied to determine the rheological nature of polymers and control parameters.

Numerical Simulation and Experimental Investigation of the Viscoelastic Heating Mechanism in Ultrasonic Plasticizing of Amorphous Polymers for Micro Injection Molding.

Ultrasonic plasticizing of polymers for micro-injection molding has been proposed and studied for its unique potential in materials and energy-saving. In our previous work, we have demonstrated the characteristics of the interfacial friction heating mechanism in ultrasonic plasticizing of polymer granulates. In this paper, the other important heating mechanism in ultrasonic plasticizing, , viscoelastic heating for amorphous polymer, was studied by both theoretical modeling and experimentation.