Silicone Injection Molding
Silicone injection molded products have excellent processing performance, wear resistance, flame retardancy, and environmental friendliness, and are widely used in insulation sealing, moisture-proof, waterproof, shockproof, and mold proof shells of heating elements.
Injection Molding Services|Technical Issues and Solutions
Injection molding companies can provide exclusive custom injection molding services according to customer needs, whether it is design or manufacturing, they have corresponding professional teams to provide precise design and new technology. Injection molding is a cutting-edge manufacturing process with a high level of automation, which can ensure high accuracy. Silicone injection molding can also manufacture products with complex and strict tolerances.
Analysis of Shrinkage Problem During Injection Molding Process
In the process of providing injection molding services, shrinkage problems are prone to occur, mainly due to the mold temperature being too low and the injection speed being too fast. The specific reasons are:
- The Melt Temperature is too Low
If the melt temperature is too high, there is a high possibility of shrinkage in the injection molded parts. To improve this problem and provide better injection molding services, manufacturers usually lower the temperature appropriately by 10-20 ℃. But if the shrinkage of the injection molded part occurs in the thicker part of the wall, the low melt temperature at this time is not conducive to solving the shrinkage problem, and even more serious. The thicker the injection molded part, the more likely it is to experience shrinkage. The main reason for the shrinkage problem is that the condensation speed of the melt is too fast, which prevents the formation of a large temperature difference between the shrinkage position and the gate, which is not conducive to shrinkage. It will prematurely seal the shrinkage channel at the shrinkage position, making solving the problem more difficult. It can also be seen that the faster the condensation speed of the melt, the more unfavorable it is to solve the shrinkage problem. PC material is a raw material with a relatively fast condensation speed, so its shrinkage problem is one of the more difficult to solve among all materials. In addition, too low a melt temperature can lead to an increase in concentrated shrinkage, which is not conducive to increasing the overall shrinkage, thus exacerbating the problem of shrinkage. Therefore, if manufacturers want to solve the shrinkage problem by adjusting the machine, they need to check whether the melt temperature is set too low. In addition to looking at the temperature gauge, using air injection or idling to check the temperature and viscosity of the melt is also a more intuitive method.
- The Mold Temperature is too Low
The main reason for surface shrinkage and internal shrinkage of the product is that during cooling shrinkage, the voids left by concentrated shrinkage cannot be fully replenished by the melt in the direction of the gate, resulting in this defect. This is very unfavorable for providing injection molding services. So, any factors that are not conducive to shrinkage will affect the solution of shrinkage problems. In general, injection molding designers and operators prefer to solve the shrinkage problem caused by excessive temperature by reducing the mold temperature. However, it is worth noting that if the mold temperature decreases too much, it is also not conducive to solving the shrinkage problem. Because if the temperature of the mold is too low, it will accelerate the cooling rate of the melt. For plastic parts with slightly thicker walls that are far from the gate, the cooling rate in the middle part is too fast, resulting in the blockage of the feeding channel and the inability to fully replenish the melt in the farther parts, making the shrinkage problem more serious, especially for injection molded parts with thicker walls. In addition, if the mold temperature is too low, it will also lead to an increase in concentrated shrinkage, which is not conducive to increasing the overall shrinkage of the injection molded parts, resulting in more serious shrinkage problems. Therefore, when solving difficult shrinkage problems, technicians check the temperature of the mold and usually touch the surface of the mold cavity with their hands to see if the temperature is too high or too low. The suitable mold temperature for each type of raw material varies. For example, when PC materials encounter such problems, using hot oil injection molding can effectively improve the shrinkage problem. However, if the mold temperature is too high, the injection molded parts may experience shrinkage problems.
- Injection Speed too Fast
The preferred method for manufacturers and technicians to solve shrinkage problems is to increase injection pressure and extend injection time. However, when adjusting the injection speed, it should be noted that too fast is not conducive to solving the shrinkage problem. Therefore, when the shrinkage problem occurs and is difficult to eliminate, it can be solved by cooperating with reducing the injection speed. Reducing the injection speed can result in a significant temperature difference between the molten material at the front end and the gate, which is beneficial for supplementing higher pressure at locations far away from the gate. At the same time, the molten material can also undergo solidification and shrinkage in order from far to near, greatly helping to solve shrinkage problems. Due to the decrease in injection speed, the temperature of the molten material at the front end is lower, and the possibility of edge overflow in the injection molded part is lower. Therefore, it is advisable to increase and extend the injection pressure and time appropriately, which is more advantageous when the shrinkage problem is severe. In addition, if the end filling is carried out using a slower speed, higher pressure, and longer time method, combined with a stepwise slowing and pressurization pressure holding method, the improvement effect will be more significant. Therefore, if the initial injection speed is slow, the best remedy is to use this method from the later stage of injection. However, it should be noted that slow filling is also detrimental to solving the shrinkage problem, as, by the time the mold cavity is filled, the melt has completely cooled down, just like if the melt temperature is too low, the system has lost the ability to compensate for the shrinkage in the distance.
Analysis of Long Injection Molding Cycle
In the process of providing injection molding services, both manufacturers and customers hope to accelerate the production cycle of products, thereby increasing production efficiency. When there is a problem with a long molding cycle, the cause should be analyzed promptly and solutions should be proposed.
- In the process of providing injection molding services, the machine’s injection system is unstable, resulting in nozzle drooling. At this point, improvement can be achieved by controlling the temperature of the material barrel and nozzle or switching to a self-locking nozzle.
- The high temperature of plastic causes the cooling and shaping time of the product to be too long. At this point, the temperature of the material barrel can be appropriately reduced, and the temperature of each section can be adjusted to reduce the screw speed or back pressure.
- To shorten the molding cycle, hot runner molds can also be used. Firstly, CAE was used to analyze the mold flow, and a regular flow channel was used. The original molding cycle of the mold was 51.28 seconds; But after changing to a hot runner mold, its forming cycle was only 25.63 seconds, which was shortened by half of the original.
- The mold temperature is high and the melt solidification time is long, but a high mold temperature is often beneficial for forming and achieving a good product appearance. Therefore, targeted measures should be taken to strengthen the cooling of the water channel.
- The thermal conductivity of the material is poor and the crystallization rate is low. In this case, reducing the mineral filling ratio in the material can be considered a solution.
- If the wall thickness of the formed plastic part is too thick, resulting in a long curing time, the structure of the mold can be redesigned to minimize the wall thickness of the plastic part.
- Insufficient heating of the material barrel can easily lead to prolonged plasticization time. At this point, it is possible to preheat the raw materials in advance or use equipment with high plasticizing capacity.
Problems that are Prone to Occur during Injection Molding of Transparent Parts
In some special circumstances, injection molding manufacturers often need to provide transparent injection molding services. The difficulty level of transparent parts injection molding is much greater than that of colored injection molding, and it is more prone to problems such as shrinkage and bubbles.
Surface Shrinkage
The main reason for the surface shrinkage of transparent parts is that the wall thickness of plastic parts is too thick, which can easily increase the shrinkage of the product. In this shrinkage process, to prevent the shrinkage of the melt, more melt is needed to enter, and a higher mold temperature is needed to make the product shrink as a whole, to reduce concentrated shrinkage.
The solution to surface shrinkage is as follows:
Manufacturers can increase the number of gates on the mold and increase the volume of cold material cavities.
Slow down the injection speed, increase the temperature of the material, increase the back pressure, increase the holding pressure, extend the holding and cooling time, and raise the mold temperature.
Bubbles Appear Inside the Product
The main reason for the appearance of bubbles is the presence of gas in the melt or the vacuum bubbles generated by contraction. The gas inside the melt mostly comes from the decomposition of air and a small amount of plastic, which can be solved by fully drying the raw materials; The solution to vacuum bubbles is quite difficult, requiring the coordination of molds and forming processes, and the solution is the same as shrinkage.
The ultimate goal of manufacturers providing injection molding services is to receive good feedback from customers and manufacture more precise components.
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