Ji-Horng Plastic Co., Ltd. Plastic Injection Molding-Moldflow Simulation
What is Moldflow Simulation? The Purpose of Moldflow Simulation
" Moldflow Simulation" , also known as " Mold Analysis " is a new technology in modern times, which uses software to simulate the forming process of plastic products in molds to diagnose, verify, and then optimize the product design. The application of moldflow simulation help saving a lot of time as traditional ways to build models for injection simulation takes a lot of time, it can predict possible product defects in advance, avoiding repeated modifications to product design after the mold is completed.
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Advantage of Moldflow Simulation
To assure evenly filling to mold cavities
Optimize gate location
Predict possible defects to reduce defective rate
Shorten cycle time
Reduce the times of mold trial and mold repair cost
Economize material consumption
Provide estimated injection molding parameters such as appropriate injection temperature, pressure, and clampling force
Combining the advantages of moldflow simulation above, the biggest benefit that mold flow analysis brings to users is the improvement of efficiency. Through optimized product design, delivery time can be greatly shortened, prevent the occurrence of defective products, improve the competitiveness, and achieve maximum economic benefits of the enterprises.
Application of Moldflow Simulation
At present, mold flow analysis has been widely used in various industries. Well-known moldflow simulation software on the market include Moldflow, Moldex3D, 3D TIMON, etc. Before using the software, it is recommended to take the courses launched by various brands to acquire basic knowledge. Only after understanding the background knowledge, we can then correctly interpret moldflow analysis result and use it effectively.
How to Read a Moldflow Analysis Result?
How to interpret moldflow analysis? Mold flow analysis uses color graphics to display the flow of molten plastic materials in the mold, mold surface temperature, shrinkage coefficient, etc. Through correct interpretation, the mold design can be optimized. We briefly list a few key points of mold flow analysis interpretation below:
Filling Analysis
Melt Front Time: By observing the melt front time, we can understand the current status of raw material filling and predict possible defects in the molded product. When the molten raw material fills all the mold cavities at the same time, the most ideal state is achieved. Mold flow analysis will show "short shots" or "hesitation" in gray in the color map. When the melt flow rate is uneven and some cavities are filled with molten material first, overpacking is likely to occur, resulting in uneven weight of the molded product, overfilling of some mold cavities, and even warping or deformation.
Weld Lines: It is easy to occur when there is a significant difference in melt flow rate, mainly located at the confluence of two melts, or at the junction of thick and thin due to uneven flow rate caused by differences in thickness. Reducing the number of gates, adding vents, and enlarging the gates can reduce the occurrence of weld lines, or improve it by changing the location of the gates and adjusting the thickness. It should be noted that the darker the color of the weld line, the weaker the structure.
- Flow Marks: Usually in the shape of ripple, it is a surface defect that appears near the gate. The main reason is that the temperature of moltien material is too low, resulting in partially solidification, which lead in ripples on the surface. By narrowing the runner to generate frictional heat, or increase the temperature directly to improve it.
Entrapped-air (Air-traps): The higher probability of occurrence is at the intersection of molten plastic from all directions. When air-trap occurs at the weld line, the gas can be discharged easily, wheras it occurs elsewhere, it is recommended to add vent, adjust the thickness, the position of the gate, or cycle time to eliminate entrapped-air.
- Gate Contribution: It indicates the efficiency of the volume of the injected material, expressed as a percentage. The contribution of the gates should be as equal as possible.
Flowfront Temperature: The flow front temperature represents the temperature at the center point of the melt cross section. The change of temperature should not be too large. Excessive temperature change can easily lead to residual stress inside the molded product and even cause warpage. The temperature tends to drop in the area where hestitation occurs, which can easily lead to flow marks or weld lines. However, if the temperature is too high, it can also easily cause the raw materials to deteriorate and degrade.
- Pressure at End of Filling: Observe pressure at end of filling to check if the pressure is balance at each part, unbalance pressure distribution will make the shrinkage uneven, residual stresses in the finished product may cause areas of under- or over-packing.
Frozen Layer Ratio: Moldflow simulation software simulates the process of molten plastic from cooling to complete solidification. Generally, the thinnest part solidifies first and the thickest part solidifies last. In the color map, red indicates the area that solidifies first. If the result is 1 (or 100%), indicating that the cross section has been fully cured. Achieving a high proportion of curing too early will cause the cross section of the flow path to become smaller, resulting in increased flow resistance and a higher chance of generating internal porosity.
Volumetric Shrinkage Rate: The change in shrinkage rate of a part during the period of packing until cool down to room temperature. A positive value indicates volume expansion, while a negative value indicates volume contraction. Pay attention to whether the shrinkage changes in an average value, by adjusting packing pressure to prevent uneven shrinkage and avoid warpage of molded part.
Packing Pressue Analysis
Sink Mark Index: Used to determine the probability of sink marks. A larger positive value indicates a more serious sink mark, while a negative value indicates that there migh be protrusion. The sink mark index takes volumetric shrinkage rate and product thickness into account and is an important tool in moldflow simulation.
XY Plot
Clamping Force, XY Plot: To detect occurance of burr by showing changes of clamping force during filling process.
Sprue Pressure, XY Plot: Check the pressure changes near the gates, if there's dramatically increase of pressure, it may lead in uneven filling.
Warpage Analysis
Temperature〔Top/Bottom〕, part: " Top " represents female die, and " Bottom " represents male die, the temperature should be uniform, there should not be large temperature difference.
Temperature Difference, part: it shows the temperature difference between male and female die, the value is calculated by temperature Top minus temperature Bottom, it the difference of temperature is huge, then it is easily to cause bending.
Basic Elements for Moldflow Simulation
In addition to the basic knowledge of moldflow simulation, several conditions must be met to achieve high-precision moldflow simulation results:
Correct material data:
It is the most important foundation of mold flow analysis, and the basis for all simulation analysis. If this most basic data is wrong, the subsequent simulation results will be full of uncertainty. Different plastic materials have different physical properties, mechanical properties, and viscosity curves. Important data such as temperature, humidity, and humidity are recorded in the database based on actual measurements by the laboratory.
Verify the result in factory injection machine:
The simulated parameters can be tested in the user's machine, or the actual parameters of the production can be recorded and then re-simulated in the moldflow simulation software to achieve the consistency of the simulated molding parameters with the actual injection molding machine.
Accuracy of mold processing:
The actual data of the mold must be consistent with the moldflow simulation model. Technicians need to have a certain level of mold processing ability and must be equipped with advanced processing machines and programs to achieve the corresponding details. Only then will the mold flow analysis result have reference value.
The Necessity of Moldflow Simulation
Do all plastic injection molding factories need to use mold flow analysis? In fact, this is not always the case. There are still many factories that judge the quality of product design based on their accumulated industry experience when tooling molds. However, by using mold flow analysis software, the causes of defects can be eliminated in advance to avoid repeated mold adjustments. The steps have indeed greatly improved the accuracy of the mold and have been very helpful in improving efficiency.
From the initial design of product development to mass production, and even subsequent maintenance and repair of mold, the application of moldflow simulation at different stages is a great help that cannot be underestimated:
Product Design
Find out appropriate thickness
Recommend suitable material
Optimize / Lightweight product structure
Predict possible defect on surface
Verify the structure design
Mold Design
Recommend position of gate
Optimize runner/cooling system
Predict shrinkage rate
Simulate filling of melt plastic to analyze molding result
Mold Trial & Mass Prodution
Optimize injection parameter
Lower defective rate
Maintenance & Repair
Find out the reason of defects
Price of Moldflow Simulation Software
Different brands of mold flow analysis software have different pricing. It is recommended to contact individual distributors to obtain pricing details. This article is for academic research reference only and does not provide sales and services for mold flow analysis software.
Injection Molding Tooling Service
Ji-Horng Plastic Co., Ltd. has our own mold department. We have experienced professional technicians and advanced mold processing equipment, combined with Moldex 3D mold flow analysis software, to provide efficient and high-quality plastic injection molding OEM & ODM services. If you have any injection molding mold development needs, please contact us to discuss more details!
TEL: +886-4-8355057 / FAX: +886-4-8355059
E-mail: service@ji-horng.com.tw
References
https://www.rapiddirect.com/zh-TW/blog/mold-flow-analysis/
https://www.smartmolding.com/21-04a02/