Experimental investigation of infrared rapid surface heating for injection molding

Abstract

A low cost and practical infrared rapid surface heating system for injection molding is designed and investigated. The system was designed to assemble on the mold and a control system was used to operate the motion of the lamp holder. Four infrared halogen lamps (1 kW each) were used as the radiative source to heat the surface of mold insert. The temperature increase is verified on the mold plate with a thermal video system. Two types of specular reflectors combined with different bulb configurations were applied to study the heating ability of radiation heating. A modified spiral flow mold was used to test the enhancing filling ability of the rapid surface heating system. Three resins, PP, PMMA and PC were molded in the spiral flow injection molding experiments. If spherical reflector and centralized lamp configuration are used, the temperature at the center of the mold surface is the highest. The temperature of mold center surface is raised from 838C to 1888C with 15 s of infrared heating. Because the surface temperature of the mold insert is higher than the glass transition temperature of resins before filling, the flow distance of resins in the modified spiral flow mold will be increased. The location effect of the infrared surface heating system on a thin-long cavity was studied to demonstrate the possibility of using smaller infrared heating area on a large mold surface. A microprobe cavity also demonstrated that with the assistance of infrared heating technology the formability of a microprobe can be greatly improved.

Microinjection Molding of Enhanced Thermoplastics

“…When mould temperature is close to processing temperature, even microstructures of the high aspect ratios may be eventually filled. Moreover, isothermal filling induces less residual stresses and surface defects in the micro parts (Chang & Hwang, 2006). How it can be easily noticed from Fig.…”

“…The main limitation to use water as a heating media is that the maximum heating temperature does not exceed 95°C, which is less than the glass transition/melt temperature of the majority of polymers. As a result, water is generally used for cooling in the variotherm process (Su et al, 2004;Chang & Hwang, 2006;Xie & Ziegmann, 2008). Heat retention properties of oil and its ability to be heated up to 140°C makes it a more adequate candidate as heating medium.…”

“…In a number of studies infrared heating has been applied for precise localized heating of the microcavity surface Although the local temperature rise with an aid of halogen lamps requires considerably less time in comparison to the resistive heaters, it may lead to uneven distribution of the mould surface temperature and therefore, special attention should be given to more uniform distribution of the heating sources (Gornik, 2004;Chang & Hwang, 2006). During processing, residual oil or resin particles may burn and contaminate the microcavity surface causing surface defects in the micromolded parts.…”

“…During processing, residual oil or resin particles may burn and contaminate the microcavity surface causing surface defects in the micromolded parts. This problem could be eventually solved with periodical cleaning of the mould cavity (Chang & Hwang, 2006). Direct infrared radiation heating of polymer inside the cavity has been proposed by Saito et al (2002).…”

Compression moulding of LFT components with increased quality by variothermal mould technology

“…Variothermal temperature control is well known for different applications in injection moulding in order to increase surface quality, flowability and to reduce flow lines [11,12,13]. To dynamically control the temperature of the compression mould additively manufactured cavity inserts with a three-dimensional network (Figure 1 (a)) of heating and cooling channels arranged directly behind the cavity surface are used.…”