Lifter is a common term for mold industry in Pearl River Delta region, which is dominated by Hong Kong-funded mold factories. It is a mechanism used to form internal barb of product in mold design. .
It refers to a phenomenon in which gate connecting molded product, main runner, and branch runner is not easily cut off when molding with a point gate. If you use point gates or latent gates, when mold is opened and product is connected, gates of main runner and runner will automatically break. However, if shape or size of gate is not appropriate, gate will not be cut properly and will remain inside mold.
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.
All movements in injection molding process, whether hydraulic or electric, generate pressure. Appropriate control of required pressure produces a finished product of reasonable quality. Pressure regulation and metering system is on hydraulic injection molding machine, and all movements are performed by oil circuit responsible for following operations:
Injection molding is to inject molten plastic into a closed mold with a lower temperature through a nozzle under high pressure. Both thermoplastics and thermosetting plastics can be injection molded. In production of packaging containers, it can mainly produce various box-type packaging containers, such as various turnover boxes, small boxes, etc. For box-type packaging containers, following aspects should be considered in structural design.
Property of friction between macromolecules when molten plastic flows is called plastic viscosity. Coefficient of this viscosity is called viscosity, so viscosity is a reflection of fluidity of molten plastic. The greater viscosity, the stronger viscosity of melt, the worse fluidity and the more difficult processing. In industrial applications, comparing fluidity of a plastic is not based on its viscosity value, but on its melt flow index (called MFI): so-called MFI means that at a certain melting temperature, melt is subjected to a rated pressure, weight of melt passing through standard die per unit time (usually 10 minutes). It is expressed in g/10min, such as injection molding grade PP material, grade is different, MFI value can vary from 2.5 to 30. Viscosity of plastic is not static. Change of characteristics of plastic itself, influence of external temperature, pressure and other conditions can all contribute to change of viscosity.
Figure 1 shows a sliding part in an electronic product, which is composed of an iron part and a plastic part. TIron part is made of stainless steel W304 to support and connect other parts; plastic part is made of polyoxymethylene POM 500P. It is main part of inner chute, which acts as a sliding guide rail, allowing parts to slide along guide rail to realize reciprocating movement of parts. The overall size of part is about 23 mm*5 mm*2 mm, and inner chute is high polished SPI A3. Effect of high polishing makes surface of contact surface smooth and reduces frictional resistance, so that part slides smoothly.
Gas-Assisted Injection Molding (GRIM) is a new type of injection molding process, which has been widely used abroad in recent years, is also used more and more domestically. Principle is to use inert gas with relatively low pressure (nitrogen is commonly used because it is cheap and safe, has function of coolant, pressure is 0.5-300 MPa) to replace part of resin in cavity in traditional molding process to maintain pressure, , so as to achieve purpose of better molding performance of product.
Precision injection molding will be affected by many related factors and environmental conditions, and the most basic are four basic factors of plastic materials, injection molds, injection molding process and injection molding equipment. In the early stage of designing plastic products, engineering plastics with corresponding performance requirements should be selected according to application environment.
Skeleton of printer is shown in Figure 1. There are undercuts, inclined holes, threads and multiple deep ribs, which require stable dimensions and high strength, cannot change with ambient temperature. Material selection is PA6+GF30%, and shrinkage rate is 0.7%. It has characteristics of high heat distortion temperature and strength, good fluidity, good filling and molding. Maximum external dimension of plastic part is 348 mm*73 mm*41 mm, main wall thickness is about 1.7 mm, and wall thickness is relatively thin. During actual injection, 2-point feeding is required to prevent insufficient filling of cavity.
Gud Mould 