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The injection molding process of plastic parts mainly includes 4 stages:
Filling, holding, pressure, cooling, demolding
These 4 stages directly determine the molding quality of the product, and these 4 stages are a complete continuous injection process.
Filling stage
The filling is the first step in the entire process injection molding cycle, from the time the mold closes to the start of injection molding until the mold cavity is filled to about 95%.
In theory, the shorter the filling time, the higher the molding efficiency, but in practice, the molding time or injection speed is restricted by many conditions.
High-speed filling
When filling at high speed, the shear rate is high, and the viscosity of the molten plastic decreases due to the effect of shear thinning, which reduces the overall flow resistance; the local viscous heating effect will also make the thickness of the solidified layer thinner.
Therefore, during the flow control phase, the filling behavior often depends on the volume to be filled. That is to say, in the flow control stage, due to the high-speed filling, the shear thinning effect of the melt is often great, but the cooling effect of the thin wall is not obvious, so the effect of the rate prevails.
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State 2 reasons why it is important to monitor food safety procedures at key stages in the process?
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How the production process is carried out through 3 stages of production in plastic chair manufacturing?
•Plastics -3 Stages of production •Manufacturing the resin -Most dangerous due to vapours involved •Molding, extruding, casting the resin •Bending, machining, polishing and decorating
What is plastic injection molding process?
Moulten plastic is injected at high pressure into an injection mould tool. The plastic cools inside the tool and takes the inverse form of the cavity machined into the tool. The process takes several stages: 1/ Closing - The tool is closed (the 2 halves are brought together) and clamped under high force. This force is maintained until the end of step 4 2/ Injection - Plastic is injected into the tool at pressure (up to about 2000 bar thus high clamping force required in step 1) 3/ Hold Pressure - Plastic shrinks as it solidifies. The pressure of moulten plastic is maintained for a period of a few seconds (depends on part) to keep filling the tool as this happens. 4/ Cooling - The tool remains closed whilst the plastic cools and becomes solid enough to be ejected. 5/ Opening - The tool is opened. 6/ Ejection - The part is ejected from the tool. The process continues at step 1. The total time for these 6 steps is usually between about 8 seconds and 3 minutes depending on the thickness of the part being moulded. (Steps 3 & 4 take much longer with thick parts.) Times of 20 to 40 seconds are typical.Plastic injection molding is a complex and intricate process. Simply put, the injection molding uses a plunger to force hot, liquid plastic into a mold cavity.
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describe the key stages in the moitering process
Why is injection speed important?
Injection speed is a critical factor when creating a plastic product. It can affect the adhesion, orientation, and shrinkage of a finished product. This article will cover the factors that influence speed. We’ll also discuss the advantages and disadvantages of different injection speeds. Depending on the type of product, injection speed can make a big difference. Influence of injection speed on adhesion Injection speed affects the degree of orientation and adhesion between two materials. It also determines the degree of shrinkage and composite strength. Higher injection speeds lead to higher shear heating and shorter pressure delay times. In addition, higher injection speeds lead to higher molecular orientation, which hinders bonding. Adhesion in the first stages of the injection molding process can be explained by the theory of adsorption and diffusion, as well as by van der Waals forces on the roll surface. However, to observe these processes properly, a thorough study of the physical properties of the material is necessary. Moreover, a complete understanding of the adhesion properties of a substance is necessary to optimize the process. Injection speed and barrel temperature have a strong impact on interfacial adhesion. The original film was tested with 13 N of load and 120-150 mm of elongation. The resulting load-displacement curves are shown in Fig. 9. Each curve represents different failure modes. In Type 1, the film will fail to adhere to the substrate, resulting in peeling. Influence of injection speed on orientation Injection speed plays a critical role in the molecular orientation of composite materials. Moreover, it influences the strength of the composite, adhesion, and shrinkage of the component. Higher injection speeds result in higher temperatures, shorter pressure delay times, and stronger composites. In addition, high injection speeds decrease the likelihood of stress peaks and notch formation. During the injection molding process, the material undergoes a pseudoplastic laminar profile. This results in chains that are stretched out during the mold filling phase while remaining in a coil configuration at the core. This orientation continues throughout the process. The injection speed can be increased or decreased to achieve the desired orientation. High-molecular-weight polymers and fiber-reinforced polymers are especially vulnerable to orientation problems. Injection speed also affects the thickness of the core region. A higher injection speed results in a thicker core layer (37%) than that of a low-speed injection. On the other hand, low-speed injection speeds result in a thinner core layer (21%) and a lower shear rate. Numerous researchers have examined the fiber orientation distribution of injection-molded SFRP parts. Some have developed numerical methods to predict the orientation distribution of SFRP parts based on reliable experimental results. This can be useful in the part design phase. Influence of injection speed on shrinkage If shrinkage is a concern in your injection molding process, you should understand the relationship between injection speed and shrinkage. The lower the injection speed, the lower the melt temperature, and the slower the injection time, the more likely your part will shrink. If shrinkage is an issue, you may need to increase the injection pressure or lengthen the injection time. The SN ratios between post-molding shrinkage and warping are a measure of how these two factors interact. The SN ratios between the two factors are calculated using Eq. 1. The response table of average SN ratios is used to determine the optimal process parameter combination. The optimal combination is the one that exhibits the highest SN ratio. Moreover, injection speed also affects the core region thickness. At high injection speed, the relative core thickness is greater than in low-speed injections. This is because a thinner core region experiences higher shear rates. As a result, it has a flatter velocity profile and a greater pseudoelasticity. In short, a smaller cavity has a thinner core region. The shrinkage changes are logarithmic in both PP20 and PP80 samples. These trend lines are represented by the trend line equations in Figure 2. The highest primary shrinkage occurs when polymeric parts are processed at higher mold temperatures. This is not desirable in industrial practice, but it is possible to reduce it by adjusting injection molding process parameters. For instance, extending the holding phase can reduce the primary shrinkage.
Problems And Solutions In Injection Molding Process Of PC/ABS Alloy?
PC/ABS is a thermoplastic plastic made of PC and ABS, which combines the excellent characteristics of the two materials. Can be widely used in automotive trim, lampshade, handle, and other parts; Home and commercial appliances such as computers and peripherals, such as mobile phones, can be used instead of PCS for thin-walled, long-flow products. Camera parts, instrument panel, FAN cover, hard hat housing, screw cap, radiator grille, computer and optical equipment housing, hair dryer, coffee pot, etc. Injection grade ABS/PC alloy refers to a class of ABS/PC alloy with a high melt flow rate suitable for the actual injection molding process. This kind of material has good melting fluidity, easy processing molding, heat flow resistance, and good rigidity. Mainly used in automotive interior and exterior decoration materials, mobile phone shells, and laptop shells. The common problems and solutions in the injection molding process of PC/ABS alloy are as follows: Pitting problem The solution: For poor dispersion, add dispersant or oil, increase injection molding temperature, and add back pressure. Keep an eye out for mold problems. Try something else. Whether the baking material temperature time is sufficient. Mold temperature adjustment. Warping and deformation problem The warping deformation of injection molding parts is due to the unreasonable design of parts, improper gate position, and injection processing conditions are not reasonable. So the internal stress, uneven or excessive shrinkage caused by the mold temperature is too high or the mold temperature is not uniform, causing the mucous membrane of the parts and demold difficult, or cooling is not uniform, the same will produce warping deformation. The solution: Processing technology: lengthen the injection molding cycle, reduce the injection temperature, adjust the injection pressure and injection speed properly, slow down the ejection speed, increase the ejection area, and maintain the balance of the ejection force; product design: increase the wall thickness, increase the reinforcement and the reinforcement at the rounded corner can reduce the warping deformation; Flow mark problem Flow marks are produced when the material is injected. The reason is that the material has poor fluidity. Unlike silver marks, flow marks are not caused by moisture or material decomposition, and their appearance is also different. The solution: It can be avoided by increasing the material temperature to improve fluidity. It can also be solved by increasing the mold problem to increase the material fluidity in the injection mold and reduce the injection speed. Shrinkage and indentation Shrinkage cavity is caused by the insufficient high-speed filling of material in the mold cavity The solution: Appropriately raising the mold temperature and material temperature to improve the material fluidity, extend the injection pressure holding time, increase the injection pressure, and increase the injection speed to improve the mold filling, can also increase the size of the gate, heating the gate runner to reduce and eliminate the shrinkage of products. Speckle problems It is usually caused by “melt rupture” caused by the expansion of molten material into the mold cavity during the high-speed injection. The solution: Injection molding process: to increase the temperature of the material, increase the nozzle temperature, slow down the injection speed to reduce the appearance of markings; Mold: increase mold temperature, add overflow groove, increase gate size, and modify gate shape. Silver wire problem Bad silver wire is the most common problem of PC/ABS materials, silver wire is also known as silver grain, spray, material flower, etc., is in the product surface along the flow direction of silver hair white filamentous-stripe phenomenon. The main reason is the interference of gas, which is mainly divided into three components: Air: air involved in the glue melting and injection stages; The moisture contained in the material itself; Pyrolysis gas: gas produced by high-temperature hydrolysis/thermal decomposition. The solution: Firstly, check whether the material is sufficiently dry. After confirming that the material is sufficiently dry, adjust the injection molding process to improve the silver wire defects. At the same time, bad injection silver wire is also related to mold exhaust.
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The answer is C
