First, the definition and characteristics of laser cladding
1. Definition of laser cladding: Laser cladding technology refers to the placement of selected coating materials on the surface of the coated substrate by different filling methods, which are simultaneously irradiated with a thin layer of the substrate surface by laser irradiation, and quickly After solidification, a surface coating having a very low dilution and metallurgical bonding with the base material is formed, thereby significantly improving the wear resistance, corrosion resistance, heat resistance and oxidation resistance of the surface of the base material.
2. Features of laser cladding:
(1) Due to rapid heating and cooling, the laser cladding layer is uniform and compact, with few micro defects and better performance than other processes;
(2) The coating dilution rate is low (generally less than 5%);
(3) heat input and distortion are small;
(4) There is almost no limit to the selection of the powder, especially the deposition of the high melting point alloy on the surface of the low melting point metal;
(5) The power, position and shape of the laser beam can be precisely controlled, and it is easy to achieve selection and even micro-region cladding;
(6) The thickness of the cladding layer is large, and the thickness of the single-pass powder feeding is 0.2-2.0 mm;
(7) It can carry out zone welding, with less material consumption and excellent performance and price ratio;
(8) The process is easy to automate.
Second, the laser welding process and welding materials
1. Classification of laser cladding: 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: substrate cladding surface pretreatment - feed laser melting - post heat treatment.
2. Laser cladding material: According to the initial supply state of the deposited material, the deposited material can be divided into powder, paste, filament, rod and thin plate, and the most widely used powder is used. Powdered deposition materials widely used at present are: nickel-based, cobalt-based, iron-based alloys, tungsten carbide composite materials, and the like.
(1) Nickel-based (Ni) alloy powder has good wettability and corrosion resistance, high-temperature self-lubricating effect and appropriate price, and is mainly suitable for components requiring local wear resistance, heat corrosion resistance and thermal fatigue resistance;
(2) Cobalt-based (Co) alloy powder has good high temperature performance and corrosion resistance, suitable for parts requiring wear resistance, corrosion resistance and thermal fatigue resistance, such as petrochemical, electric power, metallurgy and other industrial fields;
(3) Iron-based (Fe) alloy powder has low cost and good anti-wear performance, and is suitable for parts requiring local wear resistance and easy deformation. The base body is mostly cast iron and low carbon steel.
Third, suitable for laser welding industry
With the continuous development of the machinery industry, the performance requirements of the workpiece are getting higher and higher, and some of the workpieces are expensive, such as direct scrapping after failure, causing a large amount of loss and waste, and re-manufacturing is time-consuming and labor-intensive, affecting production.
Since the 1980s, laser cladding technology has developed rapidly and has become a hot spot in laser surface modification research at home and abroad. Laser cladding technology has great technical and economic benefits, and is widely used in machinery manufacturing and maintenance, automobile manufacturing, textile machinery, marine and aerospace, and petrochemical industries.
The following is a brief introduction to the industry that is suitable for laser cladding.
(1) Mold industry
Common failure modes of molds are: wear, deformation and fracture. There are many types of mold industry, the work conditions are complex and diverse, and the mold materials are not the same, especially large-scale complex high-precision molds, once re-manufactured after failure, it is not only time-consuming and labor-intensive, but also costly. Therefore, it is very economical to surface-treat the mold, improve the service life and efficiently repair the failed mold.
At present, in the mold repair, the commonly used surface technology is laser cladding, and the surface of the mold is strengthened by laser cladding technology. The performance of the mold is different depending on the material to be welded, but the mold after repair is better than the original. The mold has superior surface hardness, wear resistance, red hardness and fatigue resistance. For example, after Cr12 die steel is repaired by laser welding technology, the hardness is high and the wear resistance is good, which improves the service life of Cr12 die steel.
(2) Aerospace industry
The main causes of aircraft structural failure are corrosion, wear and fatigue damage. In order to prevent parts working in high temperature, high pressure, high speed, heavy load, corrosive medium and other environments, it is scrapped due to partial damage of the surface, improving the reliability of parts and prolonging. Service life. At present, laser cladding is a highly economical technology that changes surface properties.
Modern aircraft and engines use aluminum alloy and titanium alloy in large quantities, but the strength of aluminum alloy is not high, plastic deformation is easy to occur when used, and wear resistance is poor; titanium alloy has low hardness and poor wear resistance. The surface of aluminum alloy and titanium alloy is strengthened by laser cladding technology, which solves the problem of easy plastic deformation of aluminum alloy and poor wear resistance of titanium alloy. For example, the turbine blade is repaired by laser welding technology, and the tip of the blade is restored to the original height. And the process is simple and saves time.
(3) There are also automotive industry, petroleum industry: automotive industry such as the engine's exhaust valve sealing cone surface, gear shaft and other parts; oil industry such as impeller, large rotor shaft, wheel, bushing and other parts, With laser cladding repair, the size of the part can be restored without preheating the workpiece, and the subsequent processing amount is small, metallurgical crack is not generated, the hardness is also very strong, and the repair effect is very good.
Fourth, how to process the workpiece after repair using laser cladding technology
The workpiece after repair by laser welding obtains higher hardness and better wear resistance, but at the same time, problems arise, how to process the required dimensions of the drawings, and how to ensure the surface precision. The surface of the workpiece after laser welding is irregular, and the ceramic tool is easy to collapse because the cemented carbide tool is not wearable. Therefore, laser cladding has always been the object of mechanical processing. Until Hualing Superhard (formerly Henan Superhard Research Institute) developed the BN-S20 grade of CBN tool, it is no longer a problem to process laser cladding workpiece.
Valin Superhard is the most well-known tool company in the industry with CBN tool (CBN blade) solution. Its tooling solution can complete all kinds of machining such as turning and milling of various parts in the hard material processing industry in an all-round way. . It is widely used in high-hardness materials, high-hardness workpieces after heat treatment, and other difficult-to-cut materials. It has many tool grades that customers trust.
Hualing super-hard CBN tool BN-S20 grade processing laser welding workpiece advantages: high hardness, good wear resistance, high impact resistance, high-speed cutting; not only improve processing efficiency, but also reduce processing costs.
The following is a brief introduction to the case of Hualing superhard CBN tool BN-S20 brand processing laser welding workpiece.
Five, Valin super hard CBN tool BN-S20 brand processing laser welding workpiece hydraulic prop case
Valin super hard CBN tool BN-S20 grade processing laser cladding workpiece hydraulic support case
Machined parts: hydraulic props
Processing material: 27SiMn (surface hardness HRC55 after laser welding)
Processing steps: semi-finishing and finishing
Tool number: BN-S20 CNMN120712
Cutting parameters: ap = 1 mm, Fr = 0, 15 mm / r, Vc = 145 mm.
Processing method: dry cutting.
Machining effect: Compared with cemented carbide tools, Hualing CBN tool BN-S20 grade not only improves processing, reduces production time, saves processing cost, but also achieves surface roughness of Ra0.4 and long tool life.
Summary
With the rapid development of the machinery manufacturing industry and the rising cost of workpieces, the mechanical manufacturing industry uses laser cladding technology or other technologies to achieve better surface properties and improve the service life of the workpiece. However, the hardness of the workpiece after repair by laser cladding technology is difficult to process, which once affected the processing efficiency, but this is a good opportunity for the tool industry, as long as the tool material with high hardness, wear resistance and impact resistance is developed. Or the tool number can not only obtain better economic benefits for the company, but also further promote the development of China's machinery manufacturing industry.
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