High gloss is a typical highlight 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 and 3C digital products, such as front panels, shells, decorative sheets, etc., but every time we have encountered the same problem, that is, we cannot solve the welding problem. Molding problems such as marks and shrinkage marks greatly affect the structural strength and appreciation taste of the product.
1. Technical principles
We compare the traditional injection molding process to illustrate the characteristics of the high-gloss, traceless injection molding process. In traditional ordinary injection molding processing, when the mold temperature is set low, although warpage and sink marks can be reduced and the molding cycle can be shortened, it is easy to produce Poor appearance quality such as weld marks and material lines, dark gloss, and rough surface. On the contrary, when the mold temperature is set high, the appearance quality of the product surface can be improved, but it is prone to warping, sink marks, dimensional defects, etc., and at the same time, the molding cycle is prolonged and the cost is increased.
High-gloss, traceless injection molding technology uses special rapid cooling and rapid heating temperature control equipment to solve the above two problems at the same time. It uses steam generated by a steam furnace or high-temperature water and cooling water to control the temperature of the mold within a molding cycle through rapid exchange, so that the advantages of the above two methods can be brought into play.
First, before injection, pass high-temperature water or steam (for example, the temperature is 150°C) into the mold to make the temperature of the mold reach the viscous flow temperature that exceeds the thermal deformation of the resin. Then, the molten resin is injected, so that the material temperature at the front end of the confluence can be maintained at In the viscous flow state, a molded product with no convergence lines (welding lines) and good surface quality will be formed. After the molten resin injection is completed, the cooling process begins. Use cooling water to quickly drop the mold temperature below the thermal deformation temperature of the resin (such as 40°C). In this way, the molding cycle can be shortened and problems such as warping and sagging can be solved by accelerating the curing speed of the resin.
High-gloss, traceless injection molding can eliminate weld lines, weld marks, ripples and silver lines on the product surface, completely solve the surface shrinkage phenomenon of plastic products, and make the surface finish of the product reach mirror level, and can almost completely reproduce the surface condition of the mold, achieving trace-free Effect.
The product does not require subsequent processing by spraying, effectively reducing costs and shortening delivery time. In addition, high-gloss injection molding can also solve the problem of floating fibers caused by fiber-added products, thereby making the product quality more perfect. In thin-wall molding, injecting molten resin at high temperatures can help improve injection fluidity, reduce injection pressure, avoid problems such as insufficient pouring and trapped air, and 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 the injection cycle of thick-wall molding by about 60-70%.
2. Technology application
High-gloss, traceless injection molding can be widely used in exterior panels of current DVD/DMR/BD/BR/PDVD audio-visual players, LCD TVs, computer LCD monitors, automotive LCD monitors, air conditioners, automotive interior parts, and car lights. , optical instruments and other home appliances, automobiles, communications, medical and other industries.
3. Control principle
The fully closed-loop system controls the detection of input and output temperatures. A temperature sensor is designed inside the mold to feed back to the PLC the actual temperature of the mold. The digital color chart changes are displayed to ensure that the output is accurate and stable. Steam (high temperature water, cold water, and mold temperature display, interlocked with injection molding machine signals using time and action.
4. Technical points
The key technical points of high-gloss, traceless injection molding lie in the mold, materials, and mold temperature control machine.
The injection molding machine should have high response sensitivity, good stability, and be able to quickly feedback signals in real time.
4.1 Mold matching
In terms of mold design, factors such as high temperature resistance design, applicable waterway design, and installation matching should be considered. High-gloss injection molding uses high-temperature hot water or steam to create a balanced heating channel on the mold. When the injection molding machine is ejected, high-temperature circulating water is introduced. First, the mold temperature is raised to a set value, and then plastic injection into the mold cavity begins. , after the injection molding machine completes the pressure maintenance and switches to cooling, it begins to recycle hot water and inject cold water. The mold temperature quickly drops to a set value and then the mold is opened to recycle the cold water to complete the entire injection molding process. Because it is a molding process of sudden cooling and sudden heating, the mold must withstand rapid hot and cold shocks, so the material selection of the mold is very important, and mold steel with good thermal fatigue strength must be selected.
4.2 Mold temperature machine (control machine) matching
It can quickly generate a sufficient amount of high-temperature water (steam), and can interlock with the injection molding machine signal to achieve closed-loop control.
5. Investment analysis
5.1 Mold cost
Due to the matching waterway design and the use of high-temperature resistant components, the cost of small and simple molds increases slightly by about 15-30%, and large molds must be calculated based on actual conditions.
5.2 Equipment plan
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.