Mold Surface Treatment Technology
In mold operation, it is crucial that not only the base material has an optimal combination of high strength and toughness, but also that the surface properties significantly impact mold performance and longevity. These surface properties include wear resistance, corrosion resistance, friction coefficient, and fatigue performance.
Improving these properties solely by enhancing the base material is limited and often uneconomical. However, surface treatment technologies can achieve impressive results with less effort, which explains their rapid development.
Mold surface treatment technology is a systematic process that involves altering the mold surface’s morphology, chemical composition, microstructure, and stress state to achieve desired surface properties. This can be achieved through surface coating, surface modification, or composite treatment techniques.
In terms of treatment methods, they are generally categorized into chemical, physical, physicochemical, and mechanical methods. Although new technologies aimed at enhancing mold surface properties continue to emerge, the most commonly applied techniques in mold manufacturing are nitriding, carburizing, and hard film deposition.
- Nitriding
Nitriding processes include gas nitriding, ion nitriding, and liquid nitriding, each of which comprises multiple techniques to suit different types of steel and workpiece requirements.
Nitriding enhances surface properties effectively, and it aligns well with the quenching processes of mold steels. Moreover, its low processing temperature and mild cooling requirements lead to minimal mold deformation. For these reasons, nitriding is one of the earliest and most widely used surface-hardening techniques for molds.
- Carburizing
The primary goal of carburizing molds is to improve their overall strength and toughness, giving the working surface high strength and wear resistance. This approach allows the use of lower-grade materials by carburizing and quenching, substituting for higher-grade ones, thus reducing manufacturing costs.
- Hard Film Deposition
Currently, Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) are well-developed hard film deposition technologies. Various enhanced CVD and PVD methods have emerged to increase the bond strength between the coating and the workpiece surface.
Pre-Hardening Technology for Mold Materials
In mold manufacturing, heat treatment has long been a standard process for most molds. Since the 1970s, the concept of pre-hardening was introduced internationally. However, due to the limitations of machine rigidity and cutting tool durability, pre-hardened materials could not initially achieve the required mold hardness. As a result, investment in pre-hardening technology remained minimal.
With advancements in machine tools and cutting tool performance, pre-hardening technology for mold materials accelerated. By the 1980s, industrialized countries had adopted pre-hardened blocks for approximately 30% of plastic molds (now exceeding 60%). In China, pre-hardened blocks, mainly imported, began to see use in the late 1990s.
The development and implementation of pre-hardening technology are primarily carried out by mold material manufacturers. By adjusting the chemical composition of steel and equipping suitable heat treatment facilities, manufacturers can produce high-quality pre-hardened blocks in large quantities. However, China’s pre-hardening technology for mold materials is still in its early stages, with limited scale and insufficient capacity to meet domestic demand.
Using pre-hardened mold materials can simplify manufacturing processes, shorten production cycles, and improve manufacturing precision. With continued advancements in processing technology, pre-hardened mold materials are likely to be applied to an expanding range of mold types.