Timing valve control technology

Timing valve control technology (SVG technology) is gradually replacing the traditional valve control, as the most difficult to manufacture parts of the manufacturing method. SVG technology will replace the traditional valve control technology Currently in the automotive and other industries, the complex structure of large parts is difficult to produce, because in the production, it is easy to produce accumulation, warping and splashing and other issues, difficult to meet the surface More stringent quality requirements. For these problems, the use of traditional valve control hot runner system is difficult to solve. In traditional valve control hot runner systems, opening and closing all of the valves at the same time will inevitably affect the control of such issues as welding or tight lines, gas valves, local packing and unstable flow. Fortunately, at the moment, a technique known as Time-Varying Valve Control (SVG) has been able to control these issues at any time. Although the introduction of programmable timing valve opening or closing process is not new technology, but this method has helped people to solve these problems. For example, when one cavity is a complex geometry and the other one is simpler, or a multi-runner component is irregularly shaped or has some areas of varying thickness and with ribs, When the molding process is very difficult. Under such circumstances, if the traditional valve control system molding process is used, some parts of the part need to be tightly packed so that other parts can be fully filled. These over-packed parts not only waste raw materials but also Easily lead to sticky, warping and stress freezing and other issues. During continuous lacquering operations, local stresses can cause chamfering or paint sticking. Further, in the event of tight packing, a more robust press is used to obtain a larger injection unit and achieve a high level of fixing. Injecting raw materials simultaneously from multiple channels can also cause problems with other decorating steps, including delamination (or post-forming) in the cavity. If the injection process flow is not balanced, the fiber or film embedded in the tool may fold or fold. For multi-runner single-cavity parts, the location and appearance of the weld line is very important. If the weld line appears in the critical stress area, the integrity of parts and performance will be damaged. At the same time, the welds produced by the runner can still be seen even after painting. According to Kurt Weiss, manager of GE Plastics' component properties and new material introduction, the bonding wires on colored parts lead to significant visual defects, while for glass filled products the bonding wires have a negative impact on aesthetics and performance. He said many methods have been tried, including adding a slide to the mold to control the high cost of injection. Harald Schmidt, head of Mold Hot Runner Solutions, MHS, added: "Many molders are trying to control injection by limiting nozzle holes and jets to reduce over-packing, stress and weld line problems. However, smaller Can cause excessive melt shear. "He added that one can not change the viscosity, pressure and temperature of the material. However, with the SVG method, molders can achieve high-quality parts by controlling the injection of mold cavities, even if materials or the environment change. Murali Annareddy, Production Line Manager for Molding Simulation Software Provider Moldflow, believes that it might be a good idea to move the wire position by adjusting the size of the runner instead of the size of the valve. "This artificially balanced flow technique is well suited for multi-cavity casting," Moldflow said, providing an automated flow balancing program that regulates flow path size, however, this practice may still lead to melting in the melt Different shearing forces affect the quality of the part. "Annareddy also cautioned that another risk is sluggishness in smaller runners, and artificially regulated flow rates are more sensitive to changes in process equipment. In the past, when producing high-precision parts, problems such as these forced some molders to abandon the use of multi-pass or multi-cavity molding because it was difficult for these methods to produce uniform and accurate parts. Advantages of the SVG Method After 10 years of practical application, as an alternative to traditional valve control and thermal control, SVG technology is gaining acceptance. SVG technology has obvious advantages in controlling the bonding wire, which can transfer the bonding wire to the non-critical area and can even be moved to the exit. The valve timing also enables multi-cavity molds to be evenly filled, eliminating over-packing and splashing. At the same time, the damaged cavity in the multi-cavity model can be separated without removing the entire casting. Mr. Neil Dewar, Production Engineer at Mold-Masters, said molders can adjust and balance the injection process by using valves without the need to adjust the runner and many more sizes. Manufacturers also cited other benefits such as: Sequential injection from multiple runners can reduce the tonnage of fixtures by 20% to 30% compared to simultaneous injection from multiple runners. In addition, the finished parts maintain high accuracy during packaging and storage and withstand long-term, high-intensity extrusion when transported to their destination. Currently, at least eight hot runner technology suppliers are able to provide SVG technology. These suppliers include DME, Incoe, Husky, MHS, Mold-Masters, Osco Systems, PETS and Synventive. Allegedly, these eight companies have set up tens to hundreds of sets of SVG system. SVG technology is used to make automotive parts SVG technology is mainly used to make automotive parts, especially some of the major components such as: bumpers, baffles, tire liners, rocker bars, grilles, exhaust fans, Radiators, suction system and instrument panel. In addition, optical components such as lenses are also areas of application. SVG opens the way for valve control to be used in leading-edge automation applications such as in-mold laminations, inline film modifications, co-injection, soft-hard multi-material molding, gas-assisted and long glass fiber composites . Mark Moss, Head of Sales, Marketing and R & D at Synventive, said: "Co-injection molded parts for the TPO bumper have not yet formed a large market yet, but the market is undergoing successful development." With a pollution-free housing The continuous molding of the TPO buffer with the recirculation core helps automotive manufacturers meet the growing demand for "green" vehicles, with traditional valve control systems that are impossible to shape for such parts. Often, mold-making workers in automobile parts are mostly disgusted with the process of painting. In response, suppliers have suggested that molded-on-insert molded products should be used instead of exterior-painted parts such as door panels, and SVG technology has played an important role in the development of this product. For the first time, Osco Systems, which claims to have invented SVG technology, uses SVG to solve the problem of coverage of automotive parts. Peter Rebholz, the company's sales director, said: "At least 10 years ago, we had produced a lot of molds for trucks and car grills for GM, and we ran into the problem of splice lines at the time. We applied SVG technology to splice splice lines From smooth to edge. "He added:" At the same time, we started to study the interior trim, using SVG technology to get the plastic into the mold, neither degrading nor blowing it out of the mold, The SVG technology is used in multi-cavity molds to make containers and their caps in a single mold cavity. "Mr. Dewar of Mold-Masters said:" After 10 to 15 years of development, SVG technology has been applied Such as the production of television back cover and other products.This technology allows molders to produce large parts do not need to paint.At the same time, this technology has also been applied to 30% glass-filled nylon car hood.SVG technology Application, solves the problem of damage to the surface of the part by the bonding wire, and the influence on the structure of the part. "According to Collins & Aikman of Troy, Mich.'s interior decoration development project Mr. Li Mark Nietzke said they were SVG technology will be used to mold the inner layer of the project. "With the SVG system, it is possible to control the injection process inside the mold cavity and help reduce the pressure on the foam-embedded vinyl inserts during injection." Previously, molders at Owasso, Mich. Engineering Plastics Products Division PETS SVG systems were used to produce 16x20 inch polypropylene parts that were injection molded and then foamed vinyl coated. Mark Nietzke said Collins & Aikman will soon launch another SVG project to make vinyl-clad door panels for GM's Epsilon cars. Three of the four models required for the project have been built and confirmed ready for production, while fiber-coated instrument panels made with SVG are being considered as models for the 2006-2007 model year. In addition, Collins & Aikman uses SVG technology to make seat backs for Visteon. One of the most distinctive parts in SVG technology is the two-component weather strip on the Ford F150 open-top pick-up truck. Innatech, an injection molding specialist specializing in multi-step injection operations at Rochester, Mich., Predicts that 14 million such parts will be formed each year. According to reports, the molding of the parts, the first injection is 20% talc filled polypropylene, the second injection is generated in a rotating mold containing silicone lubricant soft Santoprene TPV, Among them, only TPV edge seals used SVG technology. In molding, the material is gradually injected from the center of the five runners to eliminate defects such as runner defects, weld lines and gas pockets. All flow channels are set within the temperature range of 30 ° to 45 ° to avoid runner flaws. In addition, Innatech designed his own PLC process control system that discretely controls each valve multiple times during the injection cycle with pressure-setting set screws. The 38-inch thin weather strip, which swings between the front and rear side doors, combines the features of noise reduction, weather protection and bonnet coverage. Allegedly, this part qualifies for the final in this year's SPE Automotive Plastics Innovation Awards. Improving the appearance is the main reason for applying SVG technology, but not the only one. According to Kevin Golden, production manager at Husky, Husky has produced a 1500mm long automotive dash impact damper that uses SVG technology to reduce the fixture's tonnage by nearly 30%. He said: "Our components are mainly used to create a large number of car grille, of which most of the large spout system is based on SVG technology." In fact, as early as 1995, the leader in the automotive components industry We have adopted SVG technology. Among them, NASCAR Nashville, Illinois, uses GE's Xenoy polycarbonate / polyester resins to make buffers that reduce the production cycle from 110 s to under 75 s. In fact, the time savings are largely due to the SVG technology Application reduces the pressure on the fixture, the company believes that the use of SVG technology not only speeds up the production cycle, but also without additional pressure can increase the production capacity, to some extent overcome the open fixture and paint adhesion And other issues. In addition, SVG technology can also be used in conjunction with other leading-edge forming technologies. For example, Synventive's dynamic injection system is used for coinjection molding to make a bumper, which is a non-contaminating material housing with a recycled material inside. Mr. Schmidt of MHS believes that the SVG technology opens the way to making thin-walled, large parts using multi-cavity molds. "In the future, we will see that the thickness of the TPO bumper dash will be only or less than 2mm." "The thin wall helps to shorten the cooling time but will increase the flow resistance of the melt. The formation and higher pressure drop results in deeper bond wires, which are prevented by the use of SVG technology in the manufacture of thin-walled large parts. "SVG technology also has a significant presence in the non-automotive industry. GE Plastics used SVG technology to develop a notebook box with a thickness of only 1mm, which was poured sequentially over eleven runners. Greg Tremblay, GE's senior machining engineer, said: "We're also going to use SVG technology to make the cover." GE used its Lexan polycarbonate product to develop a carbon-filled conductive compound that resembles dry Shrink the same flow of mud. In the traditional valve control system, it can not be normal injection, but the use of SVG technology, the compound can fill the cavity within 1.5s. Some aspects of SVG Most SVG systems have 4 to 12 drops, of course, some SVG systems can have as few as 2 drops, or some SVGs can have as many as 24. Mr. Casey at PETS said SVG systems cost about 15% to 20% more than conventional valve control systems, primarily because of their extra control. The SVG technology is mainly used in two aspects: it is used in multi-cavity molds, such as family components, in order to obtain a balanced injection without causing over-packing; in addition, it is used for so-called cascade molding, Or large parts, to improve the quality of parts forming. Cascading molding is used to mimic a single melt flow leading edge and eliminate the bonding wire when using a single flow path. In a cascade concept, the position of the sprue is set so that the melt flows right through the valve of the other spout when it flows to one spout end. As the melt passes through a spout, the spout is opened and a new melt is added after the previous melt. In this way, in the newly opened spout, the hot melt heats up the front fluid and thus does not form a bond wire. In SVG technology, it is important that the leading edge of the melt flow from one valve to the other, as well as the time it takes to open and close the valve. Mr. Elder of Innatech cautioned: "If the second valve opens too early, there will be backflow and other serious consequences; if it is pushed too late, the material flowing in from the first valve will solidify on the surface. In either case, the benefits of timing valve control can not be demonstrated, as the material is cooling and depressurizing as it reaches the second valve, and the fluid flowing from the new valve is warmer and more stressed, resulting in a backflow . "Normally, the opening of the valve can be triggered by time, screw orientation or pressure sensor, and the trigger switch of the feedback valve probe orientation can be used as a safety check. In SVG technology, proper ventilation is also crucial. Casey from PETS said: "If the cavity is not properly vented, the air between the two melts will stay in the module." Due to the complexities involved in SVG technology, many hot runners Suppliers advocate the use of computers in the design of mold simulation of mobile. For SVG flow simulation users, the weld line should pay particular attention. Moldflow has been involved in SVG simulation several years ago, according to the company's Annareddy. "There is currently no simulation to predict the actual strength of the joint, so the best way to do this is to align the bond wire The predicted temperature and pressure are generally higher for hot and high pressure lines and we can set the valve on and off timing to minimize or eliminate these bonding wires. "It is important to note that SVG techniques and It is impossible to precisely and locally control the pressure of injection and accumulation of large and complex parts. According to Synventive, dynamic injection of SVG technology can make up for the lack of standard SVG technology in this regard. In the traditional valve control technology, either completely open the valve, or completely shut the valve. In contrast, the degree of opening and closing of the orifice of the DF system is adjustable to change the effective size of the flow outlet. Therefore, DF can inject and stack each individual valve for real-time control. Mr. Moss of Synventive said: "The DF system is equivalent to a light switch." As early as 1998, a closed loop DF system utilized a hydraulic cylinder to move the flow control probe in the nozzle. The pressure sensor in the hot runner sends a signal to the controller, which compares the actual pressure with the set pressure and controls the operation of the hydraulic cylinder by manipulating the slave valve. However, conventional injection molding is speed-controlled during the injection phase and pressure-controlled during the final injection and packing phases. The DF system only pressure control, due to the pressure at the valve can be accurately sensed, so people think DF system in the packing stage of the most accurate control. Moldflow's Annareddy said: "This control ensures that all cavities can be filled at the same time." Moldflow and Synventive are currently working together on DF modeling simulations. Tier-one's auto parts suppliers Corp., Southfield and Mich., Have used DF technology to make many A-, B-, C-pillar and HVAC doors, buffers, wheel rims and three-component supermodels Plastic poly spotlight. In addition, other suppliers use DF technology to make interlocked arm supports, precision inkjet cartridges and column sensor assemblies. In the four-valve model, thin-walled, multi-cavity solutions can be used to produce front and rear mobile phone shells. PC / ABS parts manufactured by Mikron Mold Technology, Faareveje, Denmark, have wall thicknesses ranging from 0.7mm to 1.5mm, injection times of only 0.4s, complete parts production cycles of only 13s, 8.85g. Allegedly, PETS company may produce in the first quarter of 2004 a new valve probe SVG, when the valve is started, its role is not just open or turn off all the channels.

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