Quantified Surface Improvement Using Temperature Cycle Injection Moulding
Production of Glossy Weldline-free Parts Including in Foamed and Filled Resins
(323-330) International Polymer Processing #3 (2011)
Wlodarski et al ofSwansea University and of Gas Injection Worldwide, Great Britain, studied the temperature cycle injection moulding (TCIM) of thermoplastics in which the mould cavity surface is heated rapidly to a temperature close to the glass transition or crystalline melting point of the resin before melt injection, and then cooled after injection is complete.  A range of important benefits of the process are listed, among which is surface improvement, and results are presented that quantify in detail the improvements achhieved. Weldline dimensions and surface roughness are determined using white light inteferometry, with a scale of inspection below 5 nm. For a qualitative comparison of the surface finish, photography and stereomicroscopy are used. Weld lines on conventional ABS/PMMA parts are up to 17 μm deep and 70 μm wide, hence clearly visible, whereas they are not detectable on TCIM parts. Surface roughness, Ra, on these parts is found to be 37 nm for conventional parts, reducing to 20 nm using TCIM. Surface roughness is compared for conventional and TCIM mouldings in chemically foamed ABS, foamed PP with and without talc, and long-fibre-glass filled PP. For the conventionally produced foamed parts, Ra is approximately 1 500 nm. Using TCIM, Ra reduces to 30 nm for ABS, 70 nm for unfilled PP and 130 nm for PP with talc. Visually, this corresponds to a change from a heavily patterned, striated appearance to a uniform glossy surface. The parts in long-fibre (11 mm) filled PP show a reduction in Ra from 1 600 nm to 150 nm using TCIM. The conventionally moulded parts have a rough, pitted surface; the TCIM parts are smooth and glossy.   (RDC 7/5/2011)

The Effects of Various Variotherm Processes and Their Mechanisms on Injection Molding
(265-274) International Polymer Processing #3 (2011)
Huang et al ofCoreTech System and Dragonjet, Taiwan, found that increasing mold temperature is one way to eliminate surface defects and improve the quality of molded parts.  Using high mold temperature can eliminate weld lines, reduce molding pressure, residual stress and clamping force and improve part surface quality. However, with the increasing of mold temperature, the cycle time will also be increased. Hence, people have paid the attention to mold temperature control technologies. Among them, the variotherm molding technologies, including Rapid Heat Cycle Molding (RHCM), Induction Heating Molding (IHM), and Electricity Heating Mold (Emold), are some effective methods. Although those variotherm technologies have been proposed, how does the external or internal heating source affect the injection molding process and the final product? The true function and the efficiency study of each technology still remain vague. Hence, in this paper, we have systematically conducted various technologies, including Conventional Injection Molding (CIM), RHCM, IHM, and Emold, by using true 3D transient cool technology. Through the inside mechanism investigation at various moments in time, the functions and the heating-cooling efficiency for each technology can be visualized. Besides, experimental study and verification of IHM are also performed.  (RDC 7/5/2011)

Research and application of a new rapid heat cycle molding with electric heating and coolant cooling to improve the surface quality of large LCD TV panels
(476–487)Polymers for Advanced Technologies 22 #5 (2011)
Zhao et al of Shandong University, China, studied rapid heat cycle molding (RHCM) for improving the surface quality and mechanical properties of molded plastic products.  In RHCM, the vario-thermal mold temperature control system is the key technique because it directly affects the molding cycle time and the final part quality.  The results showed that the electric-heating mold with a separate cooling plate can efficiently enhance the heating efficiency.  The thermal expansion of the cavity surface can be reduced by increasing the alleviating-gap between the cavity and the cavity-retainer plate.  Then, the service lifetime of the electric-heating mold can be improved. A RHCM production line with electric heating for the large LCD TV panel was constructed.  Both the simulation and test production results indicate that the proposed electric heating RHCM technique can realize high-temperature injection molding without increasing the molding cycle time.  The surface appearance of the LCD TV panels was dramatically improved and the surface marks that usually occur in CIM process were eliminated completely.  (RDC 6/9/2011)

Fully Coupled Transient Heat Transfer and Melt Filling Simulations in Rapid Heat Cycle Molding with Steam Heating
(423 – 437) Polymer - Plastics Technology and Engineering 50 #4 (2011)
Liu et al of Shandong University, China, developed a three-dimensional numerical model coupled with heat transfer analysis and melt-filling processes for rapid heat cycle molding with steam heating.  The thermal response analysis for the heating stage was performed by solving heat conduction equations.  The heat transfer analysis results right after the mold cavity surface is heated up to the required temperature are taken as initial temperature conditions of the mold cavity for the following melt filling simulation. The pressure implicit splitting of operations solution algorithm was used to solve the pressure-velocity coupled Navier-Stokes equation for melt filling process.  The moving interface between melt and air was captured by using the volume of fluid method. The energy equations for melt filling process were solved in a coupled manner for the cavity and mold domain at the matrix level. The proposed fully-coupled numerical model was applied in simulation of the molding processes, including a two-dimensional rectangular cavity with different heating times and a three-dimensional large scale LCD panel with a stem-heated stationary mold. The results show that the fully coupled numerical method provides reliable temperature and flow field predictions with the thermal response analysis and melt flow estimation.  (RDC 3/25/2011)