The hottest hot and cold mold injection molding te

Cold/hot mold injection molding technology

the so-called "cold/hot mold injection molding" technology is a process that enables the surface temperature of the mold cavity to realize the cold and hot cycle within the injection molding cycle. Its characteristics are: before injection, the mold cavity is heated to make its surface temperature reach the glass transition temperature (TG) of the processing material; When the mold cavity is filled, the mold is cooled quickly to completely cool the workpiece before demoulding

this cold/hot mold injection molding process can greatly improve the appearance quality of injection molded products, and can eliminate some secondary processing (such as primer and sanding treatment designed to cover up surface defects), thus reducing the overall production cost. In some cases, the painting or powder coating process can even be omitted. In applications that require high surface gloss, the cold/hot injection molding process also allows the use of glass fiber reinforced materials. Other advantages of this process include: reducing the internal stress of injection molding, reducing or even eliminating spray marks and visible weld lines, and enhancing the fluidity of resin to produce thin-walled products

Figure 1 Comparison of products produced by cold/hot mold injection molding technology and traditional injection molding process respectively

(3. The material used when the experiment is not conducted for a long time is 20% long glass fiber reinforced LNP verton pca7004 resin)

Figure 2 integrated temperature alternating system with valve station

characteristics of cold/hot mold injection molding process

generally, cold/hot mold injection molding process is applicable to all traditional injection molding machines. However, if you want the mold surface to be heated or cooled quickly, you also need to use specific auxiliary systems. At present, the commonly used auxiliary systems are high-temperature hot water system and high-temperature steam system. The steam in these auxiliary systems is either from external boilers or generated by their own control equipment. As early as a few years ago, saber basic innovative plastics began to study cold/hot mold injection molding technology in Japan. At present, the company uses a high-temperature steam system in its development center in the Asia Pacific region, while in the polymer processing development center (PPDC) in Pittsfield, Massachusetts, the company uses the high-temperature hot water system of German single temperiertechnik company, which can provide high-temperature hot water at 200 ℃

in order to achieve effective process control, the mold must be equipped with thermocouples, and the thermocouples should preferably be placed close to the surface of the mold cavity in order to monitor the temperature. In order to ensure the stability of the process, the injection mold, injection molding machine and cold/heat controller must also be integrated. Saber basic innovative plastics is equipped with a control equipment in the production system of this process to effectively integrate various elements

Figure 3 demonstration diagram of heating or cooling mold process

at the beginning of the process, steam or high-temperature hot water circulating in the mold is used to heat the surface of the mold cavity, so that its temperature reaches a level 10~30 ℃ higher than the glass transition temperature of the processed resin. Once the surface of the mold cavity reaches this temperature value, the system sends a signal to the injection molding machine to inject the plastic into the mold cavity. When the mold cavity is filled (the injection phase is completed), cold water begins to circulate in the mold to quickly take away heat, so that the injection molded parts can be completely cooled before demoulding. With one valve station, it is convenient to switch from steam or high-temperature hot water to cold water, and vice versa. When the part is cooled, the mold is opened and the part is ejected, and then the above process is repeated

process optimization: mold design and construction

the cycle of cold/hot mold injection molding technology depends on the processed materials, but the mold design and construction have a great impact on it. Generally, the time required to heat the mold depends on the total amount of steel used for the mold, so it is very important to minimize the amount of steel to be heated and cooled. In order to do this, it is better to insert the cavity and core into the template rather than through the template. In order to reduce heat loss and improve efficiency, these inserts should also be separated from the mold cavity and core fixing plate by using air gaps and insulating materials wherever possible

in addition to reducing the amount of steel that must be cold/hot cycled as much as possible, we should also consider using metals with high thermal conductivity, such as beryllium copper alloy or other alloys with good thermal conductivity, to make molds. These metals help reduce the time required to heat/cool the cavity surface. In addition, arranging water pipelines near the surface of the mold cavity can also speed up the response. However, in most cases, the geometry of the product does not allow this. Nevertheless, the conformal cooling method is very suitable for this process, because the layout of its pipelines can be consistent with the surface shape of the components. Therefore, the conformal cooling method can greatly shorten the thermal response time of the most important position (i.e. the cavity surface)

Figure 4 Schematic diagram of cold/hot mold injection molding process

in terms of conformal cooling technology, it often involves the manufacturing of injection mold, or more specifically, the manufacturing of inlay. Generally, by optimizing the setting of the cooling channel, the cooling efficiency can be optimized and the production cycle can be shortened. The traditional cooling method is difficult to do this, because the shape of general products is very complex, and the conventional cooling channel can only be drilled into a straight line

at present, there are many mold manufacturing technologies that can realize conformal cooling, such as laser sintering and direct metal deposition. In order to develop test molds for this process, PPDC of saber basic innovative plastics chose fast4m tooling company located in Troy, Michigan, as its mold supplier. Fast4m tooling adopts steel plate laminated construction technology to design and manufacture mold cavity and core components with conformal cooling channels

advantages of cold/hot mold injection molding technology

cold/hot mold injection molding technology can greatly improve the aesthetics of injection molded parts. This process is helpful to improve the appearance of semi crystalline and amorphous resin products, especially for amorphous resin. In the injection stage, when the mold surface temperature exceeds the glass transition temperature of amorphous resin, even if the surface material contacts the mold surface, there will be no condensation phenomenon common in traditional injection production, thus ensuring that the polymer can flow freely in the injection stage. With the filling of the mold cavity and the increase of the pressure in the mold cavity, the resin 9, the compressor overload protection switch, the ultra-high temperature overload protection switch and the water shortage protection device are forced to flow out, which is conducive to the perfect replication of the surface of the mold cavity and improve the surface gloss of the products

for filling materials, the resin forced out forms a thin polymer layer on the outer surface of the product, which can cover the filler (glass fiber, carbon fiber or mineral, etc.), thus improving the gloss of the product and reducing the surface roughness. The research shows that this method can improve the gloss by more than 50% - 90%. In a word, the cold/hot mold injection molding process is very beneficial to improve the surface roughness of products, which can improve the surface roughness of glass fiber reinforced products by 70%. Even for products without filling materials, the surface roughness can be improved by more than 20%

Figure 5 sample injected by cold/hot mold process

1 Reduce visible weld lines, jets and flow marks

cold/hot mold injection molding technology is conducive to improving the depth and visibility of weld lines. Using a test mold, saber basic innovative plastic has processed three different materials using cold/hot mold injection molding technology and traditional injection molding process respectively. For parts produced by traditional injection molding technology, the depth of surface fusion line is between 6~13 μ M, and on the parts produced by cold/hot mold injection molding process, the fusion line is completely invisible, so it is impossible to measure its depth. This breakthrough improvement means that the coating operation of some products can be omitted

2. Reducing internal stress

internal stress is usually one of the main causes of product warpage and deformation. In some cases, it may also shorten the service life of components. Generally, the parts molded by traditional methods have high internal stress. At this time, if carbon tetrachloride (CCl4), a well-known stress cracking accelerator, is used as a solvent for testing, it will lead to the cracking of the parts. The parts molded by cold/hot mold technology have low internal stress, so even if CCl4 solvent is used, it will not cause cracking of the parts. Obviously, the annealing treatment can be cancelled before using the parts that are injection molded by cold/hot mold technology

Figure 6 samples injected with traditional process

Application

the first application of cold/hot mold injection molding technology is the production of luggage brackets for car roofs. This product is used to replace the systematic errors that the original experimental machine aroused enthusiasm in many industries: the state of this kind of error is usually metal parts that adhere to a certain value or have regular errors. Saber basic innovative plastic uses glass fiber reinforced xenoy* 1760 resin (i.e. 11% glass fiber reinforced pc/pbt) to produce the luggage support components. When the traditional injection molding process is used, there are obvious spray marks and weld lines on the surface of the product, so that it can not meet the surface quality requirements. At the same time, glass fiber reinforced materials also make the surface of products very rough, so it needs to be polished before painting. After adopting cold/hot mold injection molding technology, the above surface quality problems can be avoided, thus meeting the requirements of high surface quality

in a word, when using PC, pc/abs, pc/pbt and other materials to produce products such as TV screen frames, light guide plates, car audio components and notebook computer shells, the use of cold/hot mold injection molding process can minimize the quality problems that affect the appearance of products. (end)