In recent years, the die-casting sector has experienced robust growth and technological innovation, particularly with the development of integrated die-casting. The design and manufacturing of die-casting molds have become a core technological barrier of significant attention. Metal 3D printing technology, leveraging its advantages in conformal cooling channel and oil channel manufacturing, can more effectively control and balance the temperature of large molds, attracting widespread interest from industry clients and achieving mass production applications with leading customers, creating impressive economic value.

As mold sizes increase, product designs become more complex, and emerging technologies like 3D printing continue to penetrate the market, there will inevitably be new changes in material selection for die-casting molds. This is necessary to better adapt to the application characteristics of large die-casting molds and to align with new processes.

To understand how to select materials for die-casting molds, it is crucial to first identify the failure modes of die-casting molds and the specific performance requirements for mold materials.

For aluminum alloy die-casting, the most common failure mode is thermal fatigue failure. During the die-casting process, molds experience repeated thermal shocks from molten metal impacts, mold cooling, and the spraying of release agents, leading to surface cracking. When these cracks penetrate deeply, they can result in dimensional deviations during repairs. Furthermore, the presence of cracks can facilitate further crack propagation, eventually accelerating mold failure and resulting in direct scrap. Therefore, the thermal fatigue performance of the material is critical.

Surface cracks on die-casting molds, if left unaddressed, will worsen over time and eventually cause the mold to fail

Another concern is erosion and corrosion of the mold. This is influenced by the alloy composition of the molten aluminum, the mold material composition, mold structure, and surface condition. High-temperature, high-pressure molten aluminum interacts with the mold surface, causing physical abrasion and chemical reactions, which can lead to the formation of brittle iron-aluminum intermetallics that result in pitting corrosion. Over time, this can lead to significant erosion or corrosion of the mold surface. Thus, it is essential to focus on the aluminum erosion resistance of the mold material.

Mold sticking occurs on the surface of die-casting molds

Common failure modes also include brittle cracking. When the load on the mold is too high or concentrated, the insufficient toughness of the mold material can lead to brittle fractures due to localized stress concentrations.

Moreover, given that die-casting molds primarily operate under high temperatures, inadequate temper resistance can result in excessive high-temperature strength loss, potentially leading to the collapse of the mold parting line.

It is clear that the working conditions for die-casting molds are particularly harsh. Components that directly contact molten metal, such as cavities and gates, must meet the "four highs and one low" characteristics: high heat resistance (temper resistance), high wear resistance (hardness), high toughness, high thermal conductivity, and low affinity for aluminum. For large die-casting molds, toughness is prioritized over hardness. When toughness and hardness cannot both be achieved, higher toughness is often required to prevent cracking, which may necessitate a slight reduction in hardness requirements. The challenge is to ensure toughness without sacrificing hardness, a key consideration for materials used in large die-casting molds. Additionally, with the advantages of conformal cooling channels provided by 3D printing, the cooling efficiency of molds has significantly improved, allowing for more relaxed thermal conductivity requirements. Therefore, the most suitable materials for 3D printed die-casting molds should have high temper resistance, excellent high-temperature performance, high material toughness, low affinity for aluminum, good wear resistance, and adequate thermal conductivity.

Currently, commonly used materials for die-casting molds in China include 3Cr2W8V, 4Cr5MoSiV (H11), 4Cr5MoSiV1 (H13), and maraging steels, each with its own advantages regarding the aforementioned properties, with H13 being the most widely used. However, the 3D printing process, as a non-equilibrium solidification method, is fundamentally different from traditional alloy smelting. Therefore, when selecting mold materials, the suitability for the printing process must be considered. Traditional materials like H13 and H11 are challenging to adapt to the printing process, often resulting in micro-cracks or macro-cracks during printing, limiting the size and large-scale application of printed molds. Conversely, common 3D printing materials are not fully applicable to die-casting. For instance, mold material 1.2709 (18Ni300), which has seen some application in die-casting, exhibits poor thermal erosion resistance and wear resistance, resulting in a service life of only about 0.3-2W cycles on high-pressure die-casting molds, which does not fully meet the requirements of large die-casting. Therefore, specially designed 3D printing materials tailored for die-casting mold characteristics will be a better choice for industry clients and will play an important role in promoting the application of 3D printing technology in die-casting.