Today I will share an example of gas-assisted molding of a monitor shell. Through two different sets of solutions, we will explore optimal molding solution and analyze molding problems from data results. This will reduce trial mold cost and molding cycle before opening mold, thereby increasing profits. Mold flow analysis plays a vital role, and everyone can learn from it.
Tag: melt temperature
In filling and holding pressure drop section, cavity pressure increases with time. After filling cavity, pressure will remain in a relatively static state to supplement insufficient amount of glue due to shrinkage. In addition, this pressure can prevent phenomenon of colloid backflow caused by reduction of injection. This is pressure holding stage. After pressure holding is completed, cavity pressure gradually decreases, and can theoretically drop to zero over time, but it is not actually zero. Therefore, after demolding, internal stress of product is stored, so some products need to be post-processed to remove residual stress.
POM (also known as Saigang, Trane). It is obtained by polymerization of formaldehyde as raw materials. POM-H (polyoxymethylene homopolymer) and POM-K (polyoxymethylene copolymer) are thermoplastic engineering plastics with high density and high crystallinity. Has good physical, mechanical and chemical properties, especially excellent friction resistance. POM is a crystalline plastic with obvious melting point. Once it reaches melting point, melt viscosity drops rapidly. When temperature exceeds a certain limit or melt is heated for too long, it will cause decomposition. Copper is a catalyst for POM degradation, copper or copper materials should be avoided in parts in contact with POM melt.
Plastic temperature control in injection molding usually uses rotation of screw and heating plate on barrel to heat low-temperature solid plastic particles into high-temperature liquid melt. Melt temperature will affect quality of product. If it is too high, there will be problems such as material cracking and yellowing; if it is too low, it will reduce fluidity of material and increase flow resistance. Temperature of melt cannot be directly controlled by injection machine, but is indirectly affected by plasticizing process. There are three main conditions in plasticizing process that will affect melt temperature, including heating plate temperature, screw speed and back pressure. How plasticizing process affects material temperature will be explained below.
Consistent melt temperature is necessary for consistent part quality, but achieving this requires balancing multiple factors including barrel usage, barrel temperature, screw speed, back pressure, dwell time, and more. During injection molding process, plastic injected into mold must be molten, homogeneous, and have desired melt density. Under action of heating belt and screw, melt is prepared in barrel. Temperature setting of heating belt, screw speed and back pressure all have a direct effect on melt quality
Injection pressure refers to pressure exerted on plastic melt by top of plunger or screw. Its function is to overcome flow resistance of plastic melt flowing from barrel to mold cavity, giving melt a certain filling rate, compacting and feeding melt. During injection process, pressure at nozzle of injection machine is the highest to overcome flow resistance in the whole process of melt. After that, pressure gradually decreases along flow length to front wave front of melt. If inside of cavity is well vented, final pressure at the front of melt is atmospheric pressure. On injection machine, gauge pressure is commonly used to indicate injection pressure, which is generally between 40 and 130MPa.
【Abstract】Finite element analysis method was used to simulate and analyze injection molding of ART18Z stent with biodegradable polymer polylactic acid (PLA) as molding material, to explore influence of melt temperature, mold temperature and injection pressure on stent molding process. Numerical results show that increase of melt temperature in plasticizing stage will increase filling rate of scaffold; filling rate of scaffold in filling stage increases with increase of mold temperature and injection pressure. Under premise of ensuring quality of injection molding, injection temperature of 280℃, mold temperature of 90℃ and injection pressure of 150MPa are suitable process parameters. Research results reveal influence of different process parameters on injection molding quality of polymer vascular stents, which can provide guidance for improving optimization of vascular stent injection molding process.
"Just make the product." I'm sure everyone has heard this saying? But things are not so simple. Designing and developing a quality product, mold, injection molding process requires a deep understanding of plastics and injection molding machine variables. While there are many plastic molding strategies, following three methods developed by RJG can be effectively adapted to different scenarios - DECOUPLED MOLDING® I, II, III. It is very important to review and evaluate each of above methods to ensure that you are choosing right one for your product. Here we will use a product as an example to evaluate part design, material selection, mold design, and actual process data for each molding method to determine impact of using DECOUPLED MOLDING® I, II, III on product results, and to determine , which method is most effective for this product.
Main reason is that water vapor and other gases in resin cannot be discharged or because of insufficient mold filling, condensing surface condenses too quickly to form a "vacuum bubble". According to causes of bubbles, it can be divided into following types:
Melt usually flows from nozzle into gate, but for some molds, nozzle is part of mold because it extends to bottom of mold. There are two main types of nozzles: open-ended and closed-ended. In injection molding production, open-ended nozzles should be used because they are cheaper and less likely to stay. If injection moulding machine is equipped with a pressure relief device, then even lower viscosity melts can use this nozzle. Sometimes it is necessary to use a closed-end nozzle, which acts as a check valve, blocking plastic in injection cylinder. Make sure that nozzle is properly inserted into nozzle sleeve, top hole is slightly smaller than nozzle sleeve, which makes it easier for nozzle to withdraw from mold. Nozzle sleeve hole is 1mm larger than shooting nozzle, that is, nozzle radius is 0.5mm thinner than nozzle sleeve radius.
Gud Mould 