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2023.7.27
Even in the die casting process, complex 3D conformal temperature control systems have drawn people’s attention. These systems can greatly improve the controllability, stability, sustainability, and cost-effectiveness of the casting process. To ensure the die casting process is truly reliable, the design of the conformal temperature control device must be considered throughout the entire system, including the die casting unit, mold, and production parameters. This article describes the complex 3D conformal temperature control system and the process of determining the optimal process settings.
The objective of each optimization measure in the die casting process is to have a positive impact on availability, efficiency, and product quality. The topic of die casting mold temperature control is as old as the process itself. Cycle time, mold lifespan, microstructure, warpage of parts, and other technical and economic aspects largely depend on the mold temperature. Therefore, the optimization of mold temperature control related to layout and process should be a focal point of mold and process design. This article introduces the Frontloading method, in which the development and validation of the mold temperature control device structure design are parallel to the structural design of the part. This method is based on virtual molding supported by automated Design of Experiments (DOE) and optimization algorithms. In this case, the evaluation for determining process variables is based on the actual production-related characteristics of Overall Equipment Effectiveness (OEE).
In most cases, the structural design of casting or die casting molds is based on the following (in order of importance): machine adjustments, including determining the number of mold cavities, mold release properties, and minimum mold separation forces. Only after this consideration will casting or process-related issues be taken into account, such as flow process or overall thermal balance design. Thermal balance control includes temperature cooling and heating, corresponding heating/cooling equipment with necessary power, and the definition of parameters such as cycle time.
On the other hand, the reality is that the thermal balance design of die casting molds must ultimately support the best results in the die casting process, such as casting quality, process stability, cycle time, or mold lifespan. However, if these variables are to be influenced, all devices and measures related to mold temperature control must have good repeatability, adjustability, and controllability while being related to casting results. This leads to two necessary boundary conditions related to mold temperature control:
1. Execution in the Subdivision Field of Mold: In the subdivision field related to thermal balance, temperature control must not only be unique and effectively controllable but also variable over time. Therefore, the relevant subdivision field must first have high thermal sensitivity. This can be achieved through high-performance heating/cooling equipment (with variable temperature control options) and the establishment of near-form and conformal temperature control areas.
2. Development Method: In the design of mold structures, the impact of temperature control measures and parameters on casting quality, process stability, cycle time, or mold lifespan must be known and recorded. This can be achieved through timely virtual evaluations and optimization of the casting process (including full consideration of the tested temperature control measures).
In the field of injection molding, the topic of thermal-sensitive mold areas equipped with temperature-stable control devices has been discussed for about 20 years. However, they are still a symbol of “high-end” mold technology. Experts estimate that conformal temperature control molds can significantly reduce the unit cost of castings. The advantages reported in the injection molding field almost always manifest in shortened cycle time and improved product quality. This allows for the calculable return on investment (RoI) of additional costs in mold manufacturing and operation processes.
Similarly, in the die casting field, conformal temperature control devices have long been used as core cooling devices. The fact that they have hardly gone beyond such a narrow application range may be due to several reasons. Firstly, in the traditional die casting mold manufacturing field, the heat dissipation channel on the die casting mold should not exceed about 10 to 15 millimeters from the mold cavity surface. It is traceable and problem-free when die casting is subjected to two severe thermal shocks during injection (high pressure stress) and demolding agent spraying process (high tensile stress). In addition, the significantly increased cost in mold subdivision fields, including near-form and conformal 3D temperature control fields, also plays an important role. Generally, when choosing a mold temperature control device, there is no detailed information about the actual heating and cooling requirements during the operation process. However, these pieces of information are exactly needed to identify and evaluate the risks and potential hidden in mold thermal balance and to prove that additional costs will be generated during the mold manufacturing process.
From this perspective, virtual design in the die casting process becomes the focus. Ensuring that temperature control work complies with the requirements of safe and economic production processes is not only necessary but also feasible, just like the structural design of castings. Once the 3D CAD data of the casting is obtained, the first batch of simulation calculations for the casting process can provide clear information about the necessary temperature control measures around the mold cavity. Then, in the design of casting runners and venting areas, other more detailed simulation calculations about the casting process can provide optimized design of casting runners and cross-sectional flow rate technology, as well as optimized design of thermal balance technology in the injection chamber, splitting cone, and flow area. The method described here is neither uncommon nor difficult to implement. What it provides is the Collaborative Engineering (CE) method, which has been proven to be economically effective in the development process, at least 40 years ago or even earlier. From a technical point of view, this method is supported by “state-of-the-art” CAE tools, from 3D CAD to FE simulation to virtual evaluation and automated process optimization. Today, CE is supported by the entire development process chain and even interdisciplinary platforms, which represent a common information platform between departments and companies formed by interrelated tasks.
According to the “Design of Temperature Control Methods and Tools for Die Casting Molds,” the position and size of temperature control channels are determined. The potential of Frontloading, which has been used in mechanical engineering for 140 years, the potential of computer-aided casting process optimization for the past 30 years, and the modern part-generation production technology potential for near-form and conformal temperature-controlled mold subdivisions have been known and quantified. In specific cases, decisions must be made for different methods.
Besides determining specific production technical solutions for molds and casting processes, the method proposed in this article can also identify the optimal balance solution that casting workers pursue in terms of quality and economy. Almost no economic or production risk exists to study the contribution of any situation to improving Overall Equipment Efficiency (OEE) in die casting units.
Regardless of the complexity of the problem, this systematic approach can generate the interrelationship between casting production parameters and quality characteristics early and systematically in the development process chain. Ensuring decision-making safety on the basis of the CAE development process, designers and casting workers can simultaneously optimize components and processes, providing guarantees and support for product developers, mold manufacturers, and professional casting workers in stable, low-cost, and resource-efficient product and process design processes.