The service life of thermal spraying is 3-6 times longer than that of chrome-plated parts, which belongs to environmental protection coating technology. Low coefficient of friction, low energy consumption, reduced frictional energy consumption; less abrasion of sealing packing or mating parts, reducing maintenance; ceramic coating and steel matrix form a composite structure, effectively using the advantages of thermal spraying, high strength and wear resistance eclipse. Thermal spraying can increase the service life of the mold, and the traditional mold making method depicts a long production cycle and high cost. For example in the automotive industry. In the entire cycle from model description to mold description to production of mold debugging to product production, mold description and production account for about 2/3 of the time. The fiercely competitive shopping mall has put forward high-efficiency, high-quality and low-cost requirements for mold development. The rapid prototype RP (RapidPrototyping) concept was proposed in 1979. Professor Nakagawa Yoshio from the University of Tokyo invented the clear layered model appearance method. In 1988, 3DSystems in the United States launched the rapid prototype useful equipment SLA (StereoLightgraphy Apparatus). The rapid prototyping skills inductively use computer-aided drawing and production skills, laser skills, and data science skills. In the absence of traditional molds and fixtures, solid models are made based on rapid prototyping. Use imitation methods to quickly produce three-dimensional solid models. The rapid prototyping skills brought a leap to the description and production of the mold. It makes the description and production of molds gradually tend to be digitalized and rapid, which greatly shortens the mold production cycle and reduces production costs. Rapid prototype skills are now becoming more sophisticated. And in 1994 formally entered the implementation period. In the meantime. Based on rapid prototype thermal spraying direct metal mold making skills, which have short processing cycle, low processing cost, and high-level imitation accuracy, more and more attention has been paid by everyone.
The typical thermal spraying rapid mold making process includes:
Carry out CAD modeling according to requirements;
Coating metal on the RP prototype to form the mold surface shell shape;
Laying cooling pipelines. Then pour the back village material with low shortening rate on the shell;
Demould, polish the appearance of the mold, and obtain a metal mold with a bright and fine appearance. In the process of rapid thermal spraying and molding, there are no remaining shortening errors, so higher accuracy can be guaranteed. Early thermal spraying rapid mold making skills mostly used low-melting metal materials such as galvanic spraying zinc-based alloys. Zinc-based alloy materials have low hardness and poor wear resistance. The application plan of the mold has been greatly restricted. In recent years. Foreign countries have begun to study the rapid production of steel-based molds by arc spraying, and have achieved greater development. At present, it is believed that the effect is better to use high temperature resistant solid materials such as ceramics to imitate resin-based or paper-based parts models. After the imitations are dried and sintered, steel-based coatings can be thermally sprayed on them to make molds. Because the mold is made of high-strength steel and other high-strength metal materials sprayed. Therefore, a mold cavity with high strength and high surface wear resistance can be obtained. The British company Novac and Oxford University have developed a process for rapid production of molds by arc spraying steel-based materials. This process breaks through the constraints that thermal spraying skills are not easy to produce large-scale molds. Ford of the United States has used this technology to produce nearly 1 square meters. Drawing dies for large cars.
Nowadays, some domestic production units have begun to use arc spraying low melting point zinc-based alloys for molding skills. Some scientific research institutes have conducted research and development in the use of thermal spraying methods to quickly produce high melting point and high hardness molds. And made some development. Tsinghua University’s plasma spray rapid molding process is to spray metal thermal spray powder on the surface of the rapid prototype to form a metal shell. After some post-processing procedures, rapid molds can be quickly produced, which can be widely used in the production of molds such as injection molds and automobile cover drawing dies. Selected by Xi'an Adaptation University. Arc spraying and brush-plating integrated mold making skills for rapid production of medium and large stamping molds for the development of new car models. This skill uses the arc spraying process to make a low melting point metal cavity; after filling the appropriate backing material and demolding. The use of electric brush plating technology to brush plating on the surface of the mold to improve the surface hardness and wear resistance of the mold, and to make the mold surface conflicting characteristics closer to the steel mold, thereby completing the rapid production of the mold. The project has begun to constitute an industrialization plan and has been used in many domestic automobile factories.
There are also some limitations in the skills of rapid thermal spraying to make molds. Firstly, because the viewpoint of thermal spraying accumulation should be greater than 45, it is not suitable for making large rugged or messy-shaped molds; in the process of imitation of thermal spraying rapid molds Partial distortion of the mold may occur. The quality of the mold that affects the end requires unique attention.
According to the mold appearance enhancement and correction skills of thermal spraying, the unique feature is that the hot work mold not only works in a higher temperature environment. And suffer the effects of abrasion, kneading, impact and hot and cold fatigue. Therefore, there are usually strict requirements for its appearance function. If the appearance hardness, red hardness, oxidation resistance, and corrosion resistance are lacking, it will be simply damaged in the process of use. Shorten the service life, so the mold surface usually needs to be strengthened. When the surface of the mold is scratched, only the degree is not severe. It can also be modified. Extend the service life of the mold. Thermal spraying technology has the advantages of flexible and diverse process methods, wide data selection and planning, convenient and agile construction, strong adaptability, significant correction and strengthening effects, and high economic benefits in terms of appearance enhancement and part modification processes. It is suitable for large-scale molds and operations under severe wear conditions. Mold. Flame spraying, plasma spraying, and supersonic spraying are frequently used to strengthen and modify the appearance of molds. Among them, thermal spraying is one of wear-resistant spraying.
The flame spraying equipment is simple, convenient to operate, and low cost, but its spray coating strength is not high. The heat-affected zone and deformation are large, so it is often used for the surface shape correction of low-strength molds. After correction, the service life of the mold is low. Wuling Automobile Co., Ltd. uses flame spraying NiCr60A to modify the automobile beam forming die. A good effect has been achieved.
Plasma spraying heat source has high energy density, which can be used to modify the surface of molds, or to modify the surface of micro-wear molds. However, the spray coating and the substrate are mechanically connected, so they are mostly used for mold surface modification and shape modification under non-impact load conditions. For example, plasma spraying of cobalt-based alloys on the surface of hot work molds. Compared with the traditional method, the life span can be extended twice. Plasma spraying 0.5～1.0mm alumina coating on the high melting point metal kneading mold made of tool steel can increase the operating temperature from 1320℃ to 1650℃ and spraying with zirconia coating. The kneading temperature can reach 2370℃, and the service life of the mold can be extended by 5-10 times.
The supersonic spraying has a high strength of the same bond between the sprayed layer and the substrate, so it can be used for mold surface modification and correction under the effect of moderate impact load, and the mold after correction can be used without requiring or a small amount of machining. This technology has been successfully used by FAW to modify the appearance of important working surfaces of drawing dies. The service life of the mold has improved significantly. Guangzhou Nonferrous Metals Research Institute selects supersonic spraying hard Taiwan gold technology. Increase the frequency of Crl2 stainless actinium-controlled extended mold repairing from 500 pieces/time to 7000 pieces, and the life span is increased by 3 to 8 times.
The article is reproduced from: Shandong Changtai Metal Surface Treatment Co., Ltd.
