As a Plastic Injection Molding factory Molder, My pleasure to share CAE which help you to detect the injection molding products or parts appearance problems.
Preface
Since I have been engaged in the China plastic injection molding industry, among the cases I have handled using CAE and the technical commissions I have accepted, the most difficult to judge is appearance defects. For conventional CAE results, only sutures and encapsulation are directly linked to cosmetic defects. Others such as flow marks, impressions, etc. do not have corresponding results, so this article will use CAE analysis and field experimental results to share with readers how to judge such appearance defects.
Why do finished plastic injection molding products have cosmetic defects?
Before that, we have to figure out how these defects occur? What are the factors related to it? In the client projects I have participated in, I sometimes encounter some interesting phenomena. If you are a plastic injection molding product designer, when you are told that your product has appearance defects, you may wonder whether the mold design is not done well or the molding parameters are not adjusted properly. If you are a mold designer, you may think that the product is defective. The design is unreasonable and the mold test parameters are incorrect. If you are a mold tester and you fail to adjust it for a long time, you may think it is a problem with the mold design or product design. Engineers in each position have their own technical theories, and the final result is to lead to T1, T2, T3…
In fact, from the perspective of product design, mold design, and on-site mold testing, the factors that affect product appearance are basically not single. We can refer to the contents of Table 1.
Table 1: Factors affecting product appearance in Chinese.
From Table 1 we can see that many common appearance problems are not necessarily caused by a single factor. And our focus is not to shift the blame to others, but to find the real problem and solve it. The quality of finished products is interrelated with design, materials, and molding parameters. If the design is more reasonable, then the plastic injection molding window during mold trial will be wider; if there are complete and scientific mold trial standards and equipment with better performance on site, then even if the design structure is more complex and the molding window is narrower, we can still find Correct molding parameters. CAE is a very important tool in scientific and digital design. If you are a CAE engineer, your problem may be how to judge the risk of appearance through the results and avoid repeated mold modifications and test trials. This is what this article will focus on.
Determining defects through plastic injection molding CAE results
Determining Defects Through Flow Results The advantage of computerized mold testing is that it can easily simulate the plastic flow process no matter how large the plastic injection molding product is. By looking at the flow results alone, we can determine many problems such as: suture lines, flow stagnation, trapped air, flow imbalance, etc. As shown in Figure 1, the flow results can directly determine the suture line formed due to the thicker flesh on both sides, resulting in melt flow competition. As can be seen from the actual sample on the right side of Figure 1, the suture lines are in the same position.
Figure 1: Flow results of suture lines caused by structure and actual sample picture
As shown in Figure 2, this product has 3 points of pouring. From the flow results, we can judge that due to the design of the number of pours, there will eventually be multiple melt junctions, and the customer will also need to increase the cost of later spraying.Figure 2: The flow results of the suture line caused by the amount of pouring and the actual sample picture
Through the flow results, you can also directly judge whether the thickness distribution of the product is reasonable. As shown in Figure 3, due to the thin thickness of the circular area, when the melt passes through this area, the flow resistance will increase, so it is more likely to Flows from both sides of the circle, forming a back-packing phenomenon. This type of flow behavior can easily lead to color differences in the appearance of the product.
Figure 3: Flow stagnation and encapsulation caused by uneven meat thickness
Determining defects by shearing results Shearing results may be a result that CAE users often ignore. I believe readers who have done CAE have seen the viscosity curve of the material (Figure 4). This is a viscosity curve for a common thermoplastic material. Molten plastics are basically non-Newtonian fluids, which means that the viscosity of the liquid changes with the shear rate.
Figure 4: Viscosity curve of thermoplastic materials
Shear force and shear rate can be explained by Figure 5. Figure 5 can be seen as two parallel boards, and the middle is filled with molten plastic. At this time, when a force to the right is applied to the upper board, the speed and force will In the form of a “relay race”, one layer is passed from one layer to the next, and each pass will produce a speed difference. In addition, the melt has different heat dissipation effects in the mold cavity and is divided into a skin layer, a shear layer and a flow center layer. Therefore, there will be a “Fountain Flow” phenomenon in which the plastic injection molding melt is fast in the middle and slow on both sides.
Figure 5: Shear force transfer & fountain flow diagram
After understanding these principles, we can know that based on the “fountain flow” behavior of the melt, when the shear is more severe, the speed difference of the melt will be greater. The differences in the speed and temperature of different laminar flows will be amplified and eventually become defects in appearance. The variable mold temperature technology (RHCM), also known as rapid cooling and rapid heating technology, can improve most appearance defects such as suture lines, flow marks, gloss, color difference, etc., mainly because it changes the original properties of the melt under high temperature. The “fountain flow” behavior enables the melt to flow more smoothly in the mold cavity, and the temperature of the melt welding is more uniform. So after understanding the way the melt plastic injection molding flows, let’s take a look at an example.
For example, the cause of stress marks is mainly due to the increase in the temperature of the shear layer, which may soften and melt the previously solidified skin layer again, or even burst the aligned skin layer to form chromatic stress marks. In CAE, although the phenomenon of softening and melting of the skin layer cannot be shown, it can be manifested as high shear stress and high flow front temperature. Use these results to determine whether there is a risk of stress marks on the product’s appearance.Figure 6: Shear stress results and actual sample
In addition to stress marks, there are also flow marks, color differences, and injection marks that cannot be judged by direct results on CAE. We can judge whether there are severe speed differences through shear rate, velocity vector, and wavefront temperature results. Temperature difference to determine whether there is a problem with the plastic injection molding design or process. As shown in Figure 7, there is a problem with a circle of traces that look like flow marks. Looking at the velocity vector results through CAE, you can see that the green area is where the velocity is high, and the blue area is where the velocity is low. Here Drastic changes in speed risk creating cosmetic defects.
Figure 7: Actual sample and velocity vector results
Another example is the problem of white marks and color difference on the exterior surface. As shown in Figure 8, the product always produces a white mark on the exterior surface above the gate. Through on-site experiments, it was verified that this defect is related to the mold temperature and shooting speed. When only adjusting the plastic injection molding mold temperature, there is a chance to improve the defects, but there are still slight white marks (bottom left in Figure 8). If the speed is reduced at the gate and the shear rate is reduced, the defects can be perfectly eliminated (bottom right in Figure 8) ). Figure 8: Experimental results of multi-stage setting of mold temperature and shooting speed
Through the shear rate results in CAE (Figure 9), the settings of the firing rate and gate speed reduction were simulated, and the results were similar to the actual results. That is, the more drastic the speed change of the appearance surface, the greater the risk of producing such appearance color difference.
Figure 9: Mold flow analysis results of one-stage shooting speed and gate speed reduction
JBR focuses on “precision molds” and “intelligent plastic molding technology and equipment integration” . “Precision molds” are the most competitive in multi material (multi component), multi cavity, and liquid silicone rubber (LSR) technology; plastic injection molding molding processes include injection, extrusion, injection drawing and blowing, and other processes. Equipment integration refers to the integrated application of patented molds, customized molding machines, turntables, self-developed supporting equipment, detection systems, control and management software to form efficient molding solutions. We provide high-quality products and services to globally renowned brand customers in the fields of “Maternal and Child Health Products” , “Medical Machinery Components” , “Industrial and Automotive Components” , and “3C and Intelligent Technology” .
What are the appearance criteria for plastic injection molding CAE results?
Many customers will ask a question: Are there fixed judgment standards for these CAE results? For example, the shear rate value should be within a certain range before there will be no appearance problems, and the wavefront temperature should be within a certain range before there will be any problems. There are rumors on the Internet about the maximum shear rate values of different plastics. Is it true that as long as the CAE results are lower than that value, there will be no appearance problems? The answer is obviously no. The CAE results mentioned above such as shear rate, velocity vector, and wavefront temperature are all judged through indirect means and comprehensively, unlike the suture results, which can be judged directly. Take stress marks as an example: the thickness of the molded product, the speed of the injection speed, as well as the temperature of the plastic injection molding mold and material will all affect the shear layer. If your shear rate is high, but the mold temperature and material temperature are also controlled at a high and uniform level, or if the thickness of the product is not very different, and the design transition is reasonable, the actual sample may not be There are cosmetic issues.
Therefore, in addition to using software, CAE users should also have certain product design, mold design and molding process capabilities. This will help each CAE engineer establish his or her own result judgment standards. For example, the standards for 3C products and home appliances are definitely different. As a tool, CAE software has different values for different users. I hope this article can give some inspiration to engineers. If there is anything wrong, please feel free to discuss it.
CAE a tool to find appearance problems
As a Plastic Injection Molding factory Molder, My pleasure to share CAE which help you to detect the injection molding products or parts appearance problems.
Preface
Since I have been engaged in the China plastic injection molding industry, among the cases I have handled using CAE and the technical commissions I have accepted, the most difficult to judge is appearance defects. For conventional CAE results, only sutures and encapsulation are directly linked to cosmetic defects. Others such as flow marks, impressions, etc. do not have corresponding results, so this article will use CAE analysis and field experimental results to share with readers how to judge such appearance defects.
Why do finished plastic injection molding products have cosmetic defects?
Before that, we have to figure out how these defects occur? What are the factors related to it? In the client projects I have participated in, I sometimes encounter some interesting phenomena. If you are a plastic injection molding product designer, when you are told that your product has appearance defects, you may wonder whether the mold design is not done well or the molding parameters are not adjusted properly. If you are a mold designer, you may think that the product is defective. The design is unreasonable and the mold test parameters are incorrect. If you are a mold tester and you fail to adjust it for a long time, you may think it is a problem with the mold design or product design. Engineers in each position have their own technical theories, and the final result is to lead to T1, T2, T3…
In fact, from the perspective of product design, mold design, and on-site mold testing, the factors that affect product appearance are basically not single. We can refer to the contents of Table 1.
Table 1: Factors affecting product appearance in Chinese.
From Table 1 we can see that many common appearance problems are not necessarily caused by a single factor. And our focus is not to shift the blame to others, but to find the real problem and solve it. The quality of finished products is interrelated with design, materials, and molding parameters. If the design is more reasonable, then the plastic injection molding window during mold trial will be wider; if there are complete and scientific mold trial standards and equipment with better performance on site, then even if the design structure is more complex and the molding window is narrower, we can still find Correct molding parameters. CAE is a very important tool in scientific and digital design. If you are a CAE engineer, your problem may be how to judge the risk of appearance through the results and avoid repeated mold modifications and test trials. This is what this article will focus on.
Determining defects through plastic injection molding CAE results
Determining Defects Through Flow Results
The advantage of computerized mold testing is that it can easily simulate the plastic flow process no matter how large the plastic injection molding product is. By looking at the flow results alone, we can determine many problems such as: suture lines, flow stagnation, trapped air, flow imbalance, etc. As shown in Figure 1, the flow results can directly determine the suture line formed due to the thicker flesh on both sides, resulting in melt flow competition. As can be seen from the actual sample on the right side of Figure 1, the suture lines are in the same position.
Figure 1: Flow results of suture lines caused by structure and actual sample picture
As shown in Figure 2, this product has 3 points of pouring. From the flow results, we can judge that due to the design of the number of pours, there will eventually be multiple melt junctions, and the customer will also need to increase the cost of later spraying.Figure 2: The flow results of the suture line caused by the amount of pouring and the actual sample picture
Through the flow results, you can also directly judge whether the thickness distribution of the product is reasonable. As shown in Figure 3, due to the thin thickness of the circular area, when the melt passes through this area, the flow resistance will increase, so it is more likely to Flows from both sides of the circle, forming a back-packing phenomenon. This type of flow behavior can easily lead to color differences in the appearance of the product.
Determining defects by shearing results
Shearing results may be a result that CAE users often ignore. I believe readers who have done CAE have seen the viscosity curve of the material (Figure 4). This is a viscosity curve for a common thermoplastic material. Molten plastics are basically non-Newtonian fluids, which means that the viscosity of the liquid changes with the shear rate.
Shear force and shear rate can be explained by Figure 5. Figure 5 can be seen as two parallel boards, and the middle is filled with molten plastic. At this time, when a force to the right is applied to the upper board, the speed and force will In the form of a “relay race”, one layer is passed from one layer to the next, and each pass will produce a speed difference. In addition, the melt has different heat dissipation effects in the mold cavity and is divided into a skin layer, a shear layer and a flow center layer. Therefore, there will be a “Fountain Flow” phenomenon in which the plastic injection molding melt is fast in the middle and slow on both sides.
After understanding these principles, we can know that based on the “fountain flow” behavior of the melt, when the shear is more severe, the speed difference of the melt will be greater. The differences in the speed and temperature of different laminar flows will be amplified and eventually become defects in appearance. The variable mold temperature technology (RHCM), also known as rapid cooling and rapid heating technology, can improve most appearance defects such as suture lines, flow marks, gloss, color difference, etc., mainly because it changes the original properties of the melt under high temperature. The “fountain flow” behavior enables the melt to flow more smoothly in the mold cavity, and the temperature of the melt welding is more uniform. So after understanding the way the melt plastic injection molding flows, let’s take a look at an example.
For example, the cause of stress marks is mainly due to the increase in the temperature of the shear layer, which may soften and melt the previously solidified skin layer again, or even burst the aligned skin layer to form chromatic stress marks. In CAE, although the phenomenon of softening and melting of the skin layer cannot be shown, it can be manifested as high shear stress and high flow front temperature. Use these results to determine whether there is a risk of stress marks on the product’s appearance.Figure 6: Shear stress results and actual sample
In addition to stress marks, there are also flow marks, color differences, and injection marks that cannot be judged by direct results on CAE. We can judge whether there are severe speed differences through shear rate, velocity vector, and wavefront temperature results. Temperature difference to determine whether there is a problem with the plastic injection molding design or process. As shown in Figure 7, there is a problem with a circle of traces that look like flow marks. Looking at the velocity vector results through CAE, you can see that the green area is where the velocity is high, and the blue area is where the velocity is low. Here Drastic changes in speed risk creating cosmetic defects.
Figure 7: Actual sample and velocity vector results
Another example is the problem of white marks and color difference on the exterior surface. As shown in Figure 8, the product always produces a white mark on the exterior surface above the gate. Through on-site experiments, it was verified that this defect is related to the mold temperature and shooting speed. When only adjusting the plastic injection molding mold temperature, there is a chance to improve the defects, but there are still slight white marks (bottom left in Figure 8). If the speed is reduced at the gate and the shear rate is reduced, the defects can be perfectly eliminated (bottom right in Figure 8) ).
Figure 8: Experimental results of multi-stage setting of mold temperature and shooting speed
Through the shear rate results in CAE (Figure 9), the settings of the firing rate and gate speed reduction were simulated, and the results were similar to the actual results. That is, the more drastic the speed change of the appearance surface, the greater the risk of producing such appearance color difference.
JBR focuses on “precision molds” and “intelligent plastic molding technology and equipment integration” . “Precision molds” are the most competitive in multi material (multi component), multi cavity, and liquid silicone rubber (LSR) technology; plastic injection molding molding processes include injection, extrusion, injection drawing and blowing, and other processes. Equipment integration refers to the integrated application of patented molds, customized molding machines, turntables, self-developed supporting equipment, detection systems, control and management software to form efficient molding solutions. We provide high-quality products and services to globally renowned brand customers in the fields of “Maternal and Child Health Products” , “Medical Machinery Components” , “Industrial and Automotive Components” , and “3C and Intelligent Technology” .
What are the appearance criteria for plastic injection molding CAE results?
Many customers will ask a question: Are there fixed judgment standards for these CAE results? For example, the shear rate value should be within a certain range before there will be no appearance problems, and the wavefront temperature should be within a certain range before there will be any problems. There are rumors on the Internet about the maximum shear rate values of different plastics. Is it true that as long as the CAE results are lower than that value, there will be no appearance problems? The answer is obviously no. The CAE results mentioned above such as shear rate, velocity vector, and wavefront temperature are all judged through indirect means and comprehensively, unlike the suture results, which can be judged directly. Take stress marks as an example: the thickness of the molded product, the speed of the injection speed, as well as the temperature of the plastic injection molding mold and material will all affect the shear layer. If your shear rate is high, but the mold temperature and material temperature are also controlled at a high and uniform level, or if the thickness of the product is not very different, and the design transition is reasonable, the actual sample may not be There are cosmetic issues.
Therefore, in addition to using software, CAE users should also have certain product design, mold design and molding process capabilities. This will help each CAE engineer establish his or her own result judgment standards. For example, the standards for 3C products and home appliances are definitely different. As a tool, CAE software has different values for different users. I hope this article can give some inspiration to engineers. If there is anything wrong, please feel free to discuss it.
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