In recent years, as the production volume of automobiles centered on engines has decreased, 3D printer technology (additive manufacturing; AM) has played an important role in prototyping, small-to-medium volume production, and repair functions. Plays. In addition, metal AM not only reduces lead time but also improves performance. For example, in terms of design flexibility, finding better thermal compatibility can lead to improved fatigue resistance and consistent quality. For that purpose, it is necessary to understand the typical design process in metal AM.
1.First of all
In recent years, as the production volume of automobiles centered on engines has decreased, AM plays an important role in prototyping, small- and medium-volume production, and repair functions. Using AM not only reduces lead times, but also improves performance. For example, in terms of design flexibility, finding better thermal compatibility can lead to improved fatigue resistance and consistent quality.
This paper describes the improvement of the cooling performance of die-cast molds used for automobile parts by design, and the design and manufacturing processes when metal AM is used in actual production. Specifically, assuming a die-cast mold for a certain automobile part, we design mold data with two types of channels: a linear channel and a shape-adaptive channel. After that, after numerically analyzing the cooling performance of two types of molds with CAE software, we conducted a comparative evaluation and explained the design process and utilization value assuming AM production of molds with shape-adaptive channels. I'm here. It does not refer to practices in the automotive industry.
*Note: This report is a report created by 3D Printing Corporation, Inc., assuming the use of AM and CAE (Computer Aided Engineering) in the "die-cast" manufacturing method used in the "automotive industry". To the last, it is a hypothetical test based on hypothetical applications, and no actual die-cast experiments have been conducted.
2. [Design process] About mold cooling
As a premise, the cooling performance of the mold in the casting process has a great impact on the product quality, productivity, and mold life. Therefore, designing and manufacturing molds with optimum cooling performance is essential. The same goes for molds, mainly for die casting.
StraightDrilled Cooling Channel is the mainstream for mold cooling channel. StraightDrilled Cooling is a tool that uses cutting technology to create a ruler-like straight channel around the cavity. Since it is a cutting process with a simple shape, it is easy for mold producers to process and cools smoothly. However, Straight Drilled Cooling molds can result in non-uniform cooling as the cooling performance is limited by the cavity geometry. Therefore, it becomes necessary to design and develop a channel that has uniform cooling performance regardless of the cavity shape.
In order to solve these problems, research on conformal[1] cooling channels (shape-adaptive cooling channels) is actively progressing. Conformal Cooling, which designs cooling channels along the shape of the cavity, differs from Straight Drilled Cooling in that cooling channels can be designed at equal intervals along the shape of the cavity, enabling uniform cooling of the entire cavity. . However, due to the complicated shape of the inside of the mold to which conformal cooling is applied, it is impossible to manufacture it by general machining (hereafter referred to as CNC) and it cannot be put to practical use. I'm here.
Therefore, in order to overcome the difficulty of manufacturing, instead of the "subtraction" cutting method, attention is focused on the "addition" AM technology that has less restrictions on the shape to be manufactured and has a high degree of design freedom.
[1] Conformal means "shape adaptation".
3. [Design process] Design process
Based on the contents explained in 2, create mold data for Straight Drilled Cooling and Conformal Cooling respectively. First, we create the design of the die-cast mold (unevenness) for the automobile parts. Next, create two designs with Straight Drilled Cooling and Conformal Cooling channels under the conditions in Table 1. Now we have data like Fig1. Conformal Cooling molds are based on the premise that they are manufactured using a metal 3D printer (hereafter, metal 3DP) of the general AM method, Powder Bed Fusion (hereafter, PBF). AM has few restrictions on the shape to be manufactured, so there is no need to stick to straight channel design assuming cutting, and it is possible to design a shape with a high degree of design freedom (channel in this case) on the premise of manufacturing. .
In addition, the channel design of the ConformalCooling mold has been changed to a teardrop shape instead of a perfect circle as shown in Fig 2. If the channel cross-section of the design is perfectly round, the cross-section collapses in the direction of gravity, forming very steep overhangs and bridges as the laminations reach the top. This can lead to manufacturing failures, so the teardrop type, which is suitable for AM, is the optimal solution to improve feasibility [2] and molding success rate. This kind of (re)design suitable for AM is called DfAM (Design for Additive Manufacturing).
[2] Feasibility means feasibility.
4. [Simulation] AM and simulation
The reasons why CAE is a useful tool in AM include "1. AM process optimization" and "2. Rapid prototyping ([rapid] = rapid, [prototyping] = development of prototype models)". .
The PBF method metal 3DP for manufacturing Conformal Cooling molds has disadvantages. One of them is the high running cost. Specifically, it is necessary to equip and handle metal powder materials, large amounts of inert gas, large-scale incidental equipment, and PPE considering the possibility of dust exposure and explosion. These factors put pressure on the cost of each molding. By using CAE, it is possible to digitally repeat the analysis and evaluation iterations[3] of the model to be printed, minimizing the required number of expensive printing steps. As a result, 1 can be achieved, enabling economical utilization of PBF. With the digitization of design, this will reduce the workload through front loading (workload: planning>product design>process design>manufacturing).
[3] IIteration is a development cycle that repeats a series of processes in a short period of time.
In addition, companies spend an enormous amount of time in the prototyping and evaluation stages of product development. By utilizing CAE, most of the prototyping (1) planning, (2) design, (3) manufacturing, (4) analysis, (5) evaluation, (6) field verification, (7) redesign, and (8) production can be completed by setting hypotheses on simulation software (numerical values). Agile development makes it possible to reduce the time-to-market of products. For example, except ④ and ⑥, it is possible to complete on CAE. By using CAE, companies can save significant time in product development and use the time saved to iterate through rapid prototyping of more prototype candidates.
5. [Simulation] Simulation using CAE
CAE software (Ansys Fluent[4]) can be used to digitally analyze changes in the average temperature value of the cavity surface when aluminum is pressed into the designed mold data. The result of this time can be seen visually as shown in Fig 5-8.
[4] Ansys Fluent is a registered trademark of Ansys Corporation.
6. [Simulation] Results and discussion
The simulation results are summarized in Table 2. Analysis results showed that Conformal Cooling molds improved cooling performance by about 3% compared to Straight Drilled Cooling, and the average cooling temperature improved. Also, as can be seen in the contour diagrams of Fig. 6 and Fig. 8, it was found that the mold using Conformal Cooling was cooled more uniformly toward the inside than the mold using Straight Drilled Cooling.
7. AM molding process
In AM, data is the starting point in any method. When creating the mold data created this time, first slice it. Slicing is dividing the data into as many layers as necessary along the z-axis. In most cases, this slice data can be created with the software attached to the metal printer. After entering the slice data, you can run the print when you are ready. Depending on the shape to be molded, it is necessary to set and develop optimal parameters, and to mold a shape that is as close as possible to the finished product (this is called a near net shape). The build is complete when all layers have been deposited.
In order to be able to use the completed near-net-shape molded product as a mold, it is essential to adjust the dimensional tolerance by hybrid machining with CNC. If the cutting process is completed successfully, the product is completed.
8. Conclusion
In this paper, we compared the cooling performance of two types of mold data, Straight Drilled Cooling and Conformal Cooling, by CAE simulation, and explained that it can be obtained quantitatively. He also explained the process of producing the mold data with a metal 3D printer.
In this paper, by alternately using AM and CAE to improve the cooling efficiency of the mold, it is possible to apply complex shapes that could not be manufactured by conventional cutting methods such as conformal cooling with a high degree of freedom in design, which is the premise of AM manufacturing. , it can be implemented by developing the optimal design by simultaneously performing numerical analysis and comparative evaluation (rapid prototyping) of multiple design candidates digitally.
In the future, we plan to print the actually designed Conformal Cooling mold data with a metal printer and actually manufacture it. In addition, although we explained the manufacturing process up to processing between cuttings this time, there are cases where processing to remove residual stress is required in addition to cutting processing. In that case, it is necessary to carefully consider adding processes such as HIP processing.
[References]
Manufacturing Industries Bureau, Ministry of Economy, Trade and Industry, (September 8, 2022).
8th Industrial Structure Council Manufacturing Industry Subcommittee.
Reference Date: December 2022
Reference: Ministry of Economy, Trade and Industry: https://www.meti.go.jp/shingikai/sankoshin/seizo_sangyo/pdf/008_02_00.pdf
