Multi physical field simulation of the hottest inj

2022-08-12
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Injection molding multi physical field simulation

structural analysis software has been used very well in predicting the performance of injection molded products (or workpieces). But the result can never give all the facts, because the mechanical properties of these products depend heavily on the molding process. This is the main reason why engineers with plastic knowledge often supplement their structural analysis work with mold filling simulation that gives the influence of forming conditions of "organic and inorganic composite materials", which has long been abolished by the Ministry of public security in the current market

"in the past, engineers had to complete quite a lot of lattice and model import, export and processing to integrate the results of these two different simulations, and processing these results was quite time-consuming and laborious," Paul vanhuffe, a senior engineer and simulation expert of cascade engineering, pointed out, "some theoretically meaningful analyses are not practical in practical work."

now, Moldflow has redefined what is practical and what is not. The company adopted the multiphysics method in its version 5.0 software, and fully combined its mold filling simulation program with its self-developed 3D structure analysis software. Although it can not replace the special structural analysis products, the multi physical field simulation technology has helped the power users of Moldflow company understand a lot of new things for the power users of the new company, including the performance of its products and the economy of the molding process. "Multi physical field simulation technology has opened up a new field of analysis for us." Vanhuffe said

cascade engineering uses the multi physical field simulation technology of Moldflow software to select the best size molding machine for large plastic products (like these garbage cans)

if these products are not formed under the best pressure, they may be heavier than their design indicators, and the production cost is higher

moving metal

the most important aspects of these new fields include the structural analysis of molds and molding machine components during the filling and compression phase of the injection molding cycle. The simulation program (which may also include a few engineers) has always assumed that the mold and molding machine components will remain rigid during high pressure on the injected plastic, but this is not the case. "Any engineer who has spent some time in a mold store knows that metal will move." Vanhuffe said

according to vanhuffel, understanding how the mold and machine are offset can not only provide valuable analysis of product performance (including weight and shape), but also provide some useful information for mold design. In addition, it also helps to select a molding machine with the best size for products. This is a decision that will affect the unit cost of the product

in the "core shift" simulation module recently released by Moldflow, it provides the ability of structural analysis. As its name indicates, this module pioneers a method for simulating the displacement of mold cores due to plastic melt flow pressure. The software uses the pressure distribution results from the filling analysis and imports them into the structural analysis to calculate the mold offset. "The pressure distribution of molten material on the mold core becomes the boundary condition of structural analysis," murali annareddy, product manager of Moldflow company, explained

then, the software uses this offset to adjust the lattice elements representing the melt flow around the mold core, and the lattice elements representing the melt flow around the mold core, so that the subsequent filling analysis can reflect any changes in the position of the mold core. This process is repeated at user-defined times during the filling and pressing operation cycle, thus providing a quasi dynamic view of how the core offset changes the shape of the mold cavity with its position

mold filling simulation has traditionally assumed that tools and molding machines will remain rigid during the molding process, while the new multi physical field simulation technology can simulate the offset between the mold and machine components. This kind of deviation (such as the elongation of the machine pull rod, etc.) will have an adverse impact on the product quality and molding cost

the function of this module is not only the core offset, but also the deformation of each part of the mold system can be simulated by the same multi physical field simulation method, such as sliding plate, injection molding system and even template. It can also be used to analyze the movement of the workpiece in the mold. Last year, Moldflow users conducted a lot of analysis on the core deviation in a wide range of applications. Including some fine molds, such as electrical connector molds. In addition, it also includes the application of molds with longer sizes and unsupported cores, such as injection machines, industrial dustbins, etc

the development of core shift

vanhuffel took core shift another step forward, and he proposed a method that can predict the elongation of forming machine fixture pull rod and the tendency of injection mold burr

although the stretching of the draw bar is a normal phenomenon in the clamping operation of the molding machine, it may become excessive when the operator tries to use the mold on the minimum possible molding machine in order to control the hourly production cost. Service standards and tool specifications in this "over tonnage" case, the pull rod can be stretched long enough to make the mold slightly open. In the worst case, the mold will have burrs as the molten plastic flows through the open parting line, which will increase the rate of unqualified products and require expensive burrs removal process

even if there is no burr, vanhuffel found that the weight of the product increases because the slightly open mold contains more molten material, which will increase the material consumption of large products. "Less pressure seems to save costs, but if the final weight of the product exceeds the standard, the result will be counterproductive." He said. "In terms of cost, it may not be a big problem to slightly increase the material consumption of small products," he continued, "but you will also take a greater risk of mold damage because rough edges will erode the parting line."

in the past, vanhuffel tried to "manually" simulate this "over tonnage" phenomenon by combining Moldflow simulation and calculation results into an excel table. But in addition to consuming a lot of time, the accuracy of this method is also limited, because it assumes that the mold is always rigid and ignores the deformation of the metal mold and the hardness enhancement caused by the mold support. These factors can partially offset the influence of the bar elongation, vanhuffel pointed out

with core shift, vanhuffel can now mesh the entire inner core edge of the mold with most parts on the pull bar and the fixture end of the molding machine. In addition, he also added a series of imperceptible thin (1.0e-6) flow elements along the mold parting line. These "burr" elements are some elements whose thickness is close to zero and which the Moldflow program cannot support at present

in the multi physical field simulation analysis, vanhuffel uses the displacement load corresponding to the clamping force required for a given molding operation to "lengthen" the pull rod. If this load lengthens the draw bar to open the mold, it will show in the corresponding mold filling analysis that the thin "burr" element will become thicker and melt will flow in, indicating that the mold will produce burr. On the contrary, if the clamping force of the die can resist the tension of the draw bar, the burr element will effectively remain zero. In addition, vanhuffel also uses its burr element analysis to predict whether the mold vent will be blocked

with the development of multi physical field simulation technology, vanhuffel believes that he can use the software to do more things in the future. His next project may be the most valuable one. Vanhuffel pointed out that when Moldflow increases its ability to display not only offset but also pressure distribution (a feature under development), it can even predict the fatigue life of mold components. That will be a great progress

senior Joe Ogando can be contacted through the following email address: jogando@

fiber arrangement

another progress intended to combine mold filling simulation with structural analysis was made by BASF. The company's plastic experts proposed a special method to predict the direction of the fiber passing through the thermoplastic reinforcement, and then import this detailed direction information into the commercial structure analysis software (currently ABAQUS or LS-DYNA)

the subsequent structural analysis can take full advantage of this detailed directional information in predicting the bending shape and mechanical behavior of these anisotropic reinforcements. The method also includes a data transmission tool, which makes it easy to simulate the nonlinearity of the reinforcement (such as large deflection and high strain rate)

the core of this method is a special software called fiber. Jim McGuire, senior CAE Engineer of BASF company, explained that the software is built on the standard Moldflow simulation results and has its own long-term fiber directivity prediction function. Fiber software uses BASF's own anisotropic material model to process Moldflow results

the model takes into account the non-uniform material properties caused by the local direction difference of the fiber passing through the reinforcement. According to Stefan glas, manager of structural application engineering of BASF company, and comparator of bromine flame retardant polypropylene, this local direction difference can be caused by various reasons, including jet flow at the gate or melt extension at the front of the flow, etc

in sharp contrast, in the past, the structural analysis of plastic reinforcements was calculated based on the following assumption, that is, the reinforcements have isotropic properties. In fact, the reinforcement is anisotropic, and CAE analysts generally reduce its hardness value to 75% of the expected hardness value of isotropic reinforcement. Glaser said that this method obtained irrelevant hardness predictions, which were either 25% higher or 25% lower depending on the geometric size of the fiber and reinforcement. This precision in turn forces engineers to adopt a greater factor of safety for the reinforcement they design. Glaser has even seen this situation, that is, the analysis results lead to the weight of reinforced structural members exceeding the standard by about 30%

the flow effect in the injection molding process can make the fibers arranged in different directions,

thus producing anisotropic materials that are difficult to simulate. Source: BASF

once fiber software can calculate the directional action of reinforcement at different levels with the number of layers specified by the user, it can generate input values for structural analysis software. Glaser pointed out that data transmission is "purely geometric", so data can be used in various practical lattices. Although fiber does not combine filling and structural analysis into one analysis environment, it maps lattice from filling software to lattice used by structural analysis software, and vice versa. "This is a very clever design, although it is the elasticity of polymers," McGuire said

perhaps the biggest problem with fiber now is that it can't be bought in the market. BASF currently only uses it as an internal application simulation tool. BASF engineers can comfortably use it to analyze the structural plastic applications of their customers or potential customers, but the company is not ready to list it in the near future. For details, please visit: (end)

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