Technical analysis: ultra-high speed laser cladding decays into magic

Laser cladding 3D printing (ie, laser cladding molding) technology uses CAD software to make a part model without using a mold. After computer programming, a beam of laser is scanned onto the workpiece to melt the metal powder on the workpiece and fuse it layer by layer. Together and stacked, the result is a dense metal part. This technology can form metal parts in one step, and the dense metal parts formed by the intelligent process control are nearly net shape, almost no subsequent processing, realizing fast, cladding 3D printing metal parts.

It provides prototype parts that can be used as both product development, design concepts, performance test samples, and direct use as functional parts. Laser cladding technology can greatly reduce the time from product development to market, and greatly reduce product development costs, especially enabling faster, flexible, personalized, and diverse product manufacturing, in new product development and It has unparalleled advantages in single-piece and small-volume production, and is convenient for network manufacturing. It is also suitable for the trend of economic globalization. It can manufacture high-precision parts more efficiently in the civil fields of new automobile manufacturing, medical treatment, instrumentation, etc., in aerospace, The military industry can better manufacture high-performance special parts, especially the gradient functional materials and super-hard materials that were extremely difficult to process in the past, and can quickly manufacture intermetallic compound materials. Therefore, this technology has broad application prospects.

At present, laser cladding 3D printed parts have some shortcomings, such as poor quality stability, the accuracy and roughness required by the user, and further processing of the parts. Therefore, the limitations of this technology have caused it to fail. Better applied to production. The reason for the poor quality stability of the parts is that some process parameters will fluctuate during the process of manufacturing the parts. As a result, the shape and size of the cladding strip formed in some parts of the parts are not as expected; they will also expand when the cladding is carried out. The defects that have been formed make the protrusions more prominent, the depressions are more trapped, the thicker places are thicker, and the thinner places are thinner. In this way, the roughness and accuracy of the parts are not as expected, and the most serious is that the parts cannot be formed.

Laser cladding means that the selected coating material is placed on the surface of the substrate to be coated by different irradiation methods, and is irradiated with a thin layer of the substrate surface at the same time, and rapidly solidified to form a very low dilution. A surface coating that is metallurgically bonded to the substrate to significantly improve the wear, corrosion, heat, oxidation and electrical properties of the surface of the substrate to achieve surface modification or repair, which not only meets the surface specificity of the material. The performance requirements save a lot of valuable elements.

Compared with surfacing, spraying, electroplating and vapor deposition, laser cladding has the characteristics of small dilution, compact structure, good coating and matrix bonding, suitable for cladding materials, large changes in particle size and content, etc. The application prospects are very broad.

From the current application of laser cladding , it is mainly used in three aspects:

First, surface modification of materials, such as gas turbine blades, rolls, gears, etc.;

Second, the surface repair of the product, such as rotors, molds, etc. Relevant information shows that the strength of the repaired parts can reach more than 90% of the original strength, and the repair cost is less than 1/5 of the replacement price. More importantly, the repair time is shortened, and the continuous and reliable operation of the major complete sets of equipment of large enterprises is solved. The problem of rapid repair of rotating parts that must be solved. In addition, by laser cladding the super wear-resistant resist alloy on the surface of the key components, the service life of the components can be greatly improved without deforming the surface of the components; laser cladding treatment on the surface of the mold not only improves the strength of the mold, but also improves the strength of the mold. It can reduce manufacturing costs by 2/3 and shorten the manufacturing cycle of 4/5.

Third, rapid prototyping. The model is quickly fabricated using a layer-by-layer sintering stack of metal powder. The technology for rapidly manufacturing parts using laser cladding technology is also known as LENS (Laser Engineered Net Shaping), DLF (Direct Laser Fabrication), DMD (Direct Metal Deposition), LC (Laser Consolidation), and the like.

Cladding materials: Currently widely used laser cladding materials are: nickel-based, cobalt-based, iron-based alloys, tungsten carbide composites, ceramics and other materials. Among them, nickel-based materials are the most widely used, and they are cheaper than cobalt-based materials.

Laser cladding has the following advantages over surfacing, thermal spraying, and plasma spray welding, which are commonly used in the industry:

The bonding strength between the substrate and the cladding layer is high, the heat-affected zone is small, the cladding layer and the matrix grain are fine, the efficiency is high, the expensive material is saved, the gradient functional material can be prepared, the laser cladding technology is controllable, and the automatic control is easy to implement. The layer quality is stable.

The ultra-high-rate cladding technology uses a high-energy-density beam to simultaneously melt the surface of the additive material and the high-speed moving substrate, and rapidly solidifies to form a very low dilution rate, which is metallurgically bonded to the substrate. The cladding layer greatly improves the cladding rate and significantly improves the process characteristics of the surface of the substrate material such as wear resistance, corrosion resistance, heat resistance and oxidation resistance.

Suitable for parts requiring improvement in power, aerospace, aerospace, weapons, nuclear industry, and automotive manufacturing. According to the working conditions of the workpiece, the metal or non-metal of various design components is cladding to prepare a surface coating with heat resistance, wear resistance, corrosion resistance, oxidation resistance, fatigue resistance or light, electricity and magnetic properties.

Ultra-high speed laser cladding technology is a new economical technology that can produce high-performance alloy surfaces on metal substrates without affecting the properties of the substrate, reducing costs and saving precious and rare metal materials. The advanced industrial countries have attached great importance to the research and application of laser cladding technology.

Cladding process: Laser cladding can be divided into two major categories according to the supply method of cladding materials, namely preset laser cladding and synchronous laser cladding.

The preset laser cladding is to place the cladding material on the cladding portion of the surface of the substrate in advance, and then scan and melt by laser beam irradiation. The cladding material is added in the form of powder, silk and plate, and the powder is the most Commonly used.

Synchronous laser cladding is the direct feeding of the cladding material into the laser beam, so that the feeding and cladding are completed simultaneously. The cladding material is also mainly fed in the form of powder, and some are also fed by wire or plate.

The main process flow of the preset laser cladding is: pretreatment of the substrate cladding surface---pre-cladding material---preheating---laser melting---post-heat treatment.

The main process flow of synchronous laser cladding is: pretreatment of substrate cladding surface---feeding laser melting---post-heat treatment.

According to the process flow, the processes related to laser cladding are mainly the substrate surface pretreatment method, the cladding material feeding method, the preheating and the post heat treatment.