High light is a typical outstanding embodiment of seamless injection molding, but it is not all of seamless injection molding. We have been making high-gloss molds for several years, mainly for exterior decorative parts of home appliances, such as front panels, decorative sheets, etc., but every time we have encountered same problem, that is, we cannot solve molding of weld lines, shrinkage marks, etc. problem, which greatly affects structural strength and appreciation taste of product.

 

We compare traditional injection molding process to illustrate characteristics of high-gloss seamless injection molding process. In traditional ordinary injection molding process, when mold temperature is set low, although warpage and sink marks can be reduced and molding cycle can be shortened, it is easy to produce poor appearance quality such as welding marks and material lines, dark luster, rough surface, etc. On the contrary, when mold temperature is set high, appearance quality of product surface can be improved, but warping, sink marks, and dimensional defects are prone to occur, and at the same time, molding cycle is prolonged and cost is increased.
High-gloss traceless injection molding technology adopts special rapid cooling and rapid heating temperature control equipment, which can solve above two problems at the same time. It uses steam generated by steam oven or high-temperature water and cooling water to control temperature of mold in a molding cycle through rapid exchange, so that advantages of above two methods can be exerted.
First, feed high temperature water or steam into mold before injection (for example, temperature is 150℃), so that temperature of mold reaches viscous flow temperature exceeding thermal deformation of resin, and then inject molten resin, so that temperature of material at the front end of feed can be maintained in a viscous flow state, a molded product with no sink line (weld line) and good surface quality will be formed. After molten resin is injected, cooling process begins. Use cooling water to quickly drop mold temperature to below thermal deformation temperature of resin (such as 40℃). In this way, molding cycle can be shortened by accelerating curing speed of resin, problems such as warping and sinking can be solved.
High-gloss traceless injection molding can eliminate weld lines, weld marks, ripples and silver lines on the surface of product, completely solve surface shrinkage of plastic products, and make surface finish of product reach mirror level, which can almost completely reproduce surface state of mold and achieve effect of no trace.
Product does not require subsequent processing of spraying, which effectively reduces costs and shortens delivery time. In addition, high-gloss injection molding can also solve phenomenon of floating fibers produced by fiber-added products, so as to make product quality more perfect. In thin-wall molding, injecting molten resin at high temperature helps to improve injection fluidity, reduce injection pressure, avoid problems such as insufficient pouring and trapped air, improve product quality and strength. Moreover, rapid cooling after molding can also reduce shrinkage stress and make demoulding easier. At the same time, it can also reduce injection molding cycle of thick wall molding by about 60-70%.

 

High-gloss non-marking injection molding can be widely used in exterior panels of audio-visual players such as DVD/DMR/BD/BR/PDD, LCD TVs, computer LCD monitors, automotive LCD monitors, air conditioners, automotive interior parts, lights, optical instruments and other home appliances, automobiles, communications, medical and other industries.

Full closed-loop system controls detection of input and output temperature. A temperature sensor is designed inside mold, and actual temperature of mold is fed back to PLC. Digital color map changes and displays to ensure accurate and stable output.

High-gloss traceless injection molding, technical key points lie in mold, material, and mold temperature control machine.
Response sensitivity of injection molding machine should be high, stability should be good, it should be able to feedback signals in real time and quickly.

In terms of mold design, high temperature resistance design, applicable waterway design, installation matching and other factors should be considered. High-gloss injection molding uses high-temperature hot water or steam to make a balanced heating channel on mold. When injection molding machine is ejected, high-temperature circulating water is introduced. Firstly, mold temperature is raised to a set value, then start to inject plastic into cavity. After injection molding machine completes pressure holding and turns to cooling, start to recycle hot water and inject cold water, mold temperature quickly drops to a set value, then mold is opened to recycle cold water to complete the entire injection molding process. Because it is a sudden cooling and hot forming process, mold has to withstand rapid thermal shock, so material selection of mold is very important, and mold steel with good thermal fatigue strength must be selected.

It can quickly generate a sufficient amount of high-temperature water (steam), and can interlock with injection molding machine signal to realize closed-loop control.

Due to use of matching waterway design and high temperature resistant components, cost of small and simple molds will increase slightly by about 15-30%, and cost of large molds should be calculated according to actual conditions.

It consists of a high-speed heating (steam or high-temperature water) device, a rapid cooling device, a control device, and an injection molding machine.