Based on the need to strengthen the cutting edge of agricultural machinery tools, the laser cladding equipment and material process of industrial robots for cutting edge agricultural machinery tools were studied and developed, realizing batch strengthening processing of the cutting edge of agricultural machinery tools, effectively improving the wear resistance and corrosion resistance of the core parts of agricultural machinery, and promoting agricultural development. In addition, for the laser cladding equipment and process in the agricultural machinery industry, reasonable suggestions and application development directions are proposed.
Laser cladding technology uses high-energy laser beams as heat sources to melt metal powder materials on the surface of parts to prepare high-performance protective coatings, improve the surface hardness of parts and components, and improve wear resistance, corrosion resistance, oxidation resistance, high temperature resistance and other properties, thereby extending the service life of parts. As the core parts of agricultural machinery, agricultural machinery tools play a key role in conventional farming links such as harvesting and farming. In order to ensure agricultural production efficiency, the development of agricultural machinery with higher operating efficiency, shorter downtime and longer service life has become a technical problem that needs to be solved urgently.
1 Development status of strengthening core parts of agricultural machinery
Agricultural machinery tools are important parts of agricultural machinery and are also one of the vulnerable parts. The cutting edge of a high-speed rotating tool is very easy to wear, affecting the efficiency of farming or harvesting. When the cutting edge of the tool is severely worn, it may even be impossible to continue working. The tools on the equipment must be replaced in batches before farming and harvesting tasks can be continued. At present, the surfacing technology and high-frequency quenching technology used at the cutting edge of the tool are two commonly used technologies to improve the wear resistance of the cutting edge of agricultural machinery tools. Surfacing technology is prone to thermal effects on the tool, causing the tool to deform or crack. Although high-frequency quenching technology can increase the surface hardness of the cutting edge, the actual wear resistance is poor.
As a green and environmentally friendly material surface strengthening technology, laser cladding has many advantages such as low surface dilution rate, strong bonding force, small heat input, and expandable powder materials. It is effective in metal material additive strengthening and repair. In view of the failure characteristics of agricultural machinery tools, the cost and added value of the tools are fully considered. The laser cladding technology is used to strengthen the surface of the cutting edge of agricultural machinery tools, which improves the wear resistance and corrosion resistance of the cutting edge of the tool and extends the service life of the tool.
2 Core equipment for laser cladding of agricultural machinery tools
The core equipment for laser cladding of agricultural machinery tools consists of laser, water cooler, laser cladding head (wide spot), powder feeder, six-axis industrial robot and customized tooling, as shown in Figure 1.
2.1 Six-axis industrial robot
The system uses FANUC six-axis industrial robot M-20iD/25, with an arm span of 1831 mm and a repeat positioning accuracy of ±0.02 mm. It can realize logical operations such as loop, offset, condition judgment, and complete the teaching programming of complex actions. The action range of M-20iD/25 is shown in Figure 2.
2.2 Wide spot laser cladding head
According to the shape and processing characteristics of the cutting edge of agricultural machinery tools, a wide spot laser cladding head was developed to realize pneumatic coaxial laser cladding of rectangular spot. The size of the cladding belt is 20 mmx2 mm. With pneumatic powder feeding, coaxial center powder feeding can be completed, the powder utilization rate is above 85%, and the replacement rate of protective lenses is less than 5%. The wide spot pneumatic coaxial powder feeding laser cladding head is shown in Figure 3.
2.3 Tool workbench
In order to effectively improve production efficiency and facilitate batch processing of agricultural machinery customers, combined with the characteristics of low added value of agricultural machinery tool bodies and large processing quantity, an agricultural machinery tool workbench is designed and developed to achieve standardized batch placement, uninterrupted production, powder collection and other convenient functions. The tool workbench structure is shown in Figure 4.
3 Laser cladding strengthening process for agricultural machinery tools
According to the working environment and working conditions of agricultural machinery tools, the appropriate wear-resistant components are matched to greatly improve the tool operation efficiency, reduce the frequency of tool replacement, and achieve the purpose of reducing costs and increasing efficiency. The process parameters of laser cladding: laser power is 2100 W, the spot is a 12 mmx2 mm rectangular spot, the spot focal length is 400 mm, the powder distance of the rectangular coaxial pneumatic powder feeding is 17 mm, the robot running speed is 40 cm·min‘-1, the protective gas is Ar, the gas flow rate is 6L·min‘-1, the laser head and the tool blade are 90°, and the powder feeding amount is 2.5r·min’-1. Among them, the spot length is 12 mm, the actual cladding width is slightly narrow, about 11 mm, and the side points should pay attention to the actual cladding of the edge of the blade to avoid edge ablation or incomplete edge cladding.
Under the above laser cladding process parameters, a certain thickness of cladding coating (about 50 threads) can be applied to the front or back of the cutting edge, and there is no edge ablation or no cladding layer on the edge of the cutting edge. The cladding layer under this process parameter can ensure the hardness and wear resistance of the coating without reducing the sharpness of the cutting edge of the cutting tool. The appearance of the cutting edge after cladding strengthening is shown in Figure 5.
The wear-resistant layer material is iron-based alloy powder, and the mass percentage of each component is shown in Table 1. The particle size of the iron-based alloy powder is 270~400 mesh, and the average hardness is 58~62 HRC. Considering the low added value of agricultural machinery tools, the laser cladding powder selects high-strength iron-based alloy materials with low cost and stable hardness performance, combined with a high proportion of wear-resistant components close to 60%, to improve the wear resistance of the cutting edge of agricultural machinery tools.
4 Conclusion
The research and development of laser cladding equipment and technology for agricultural machinery tools is carried out. First, the equipment uses a coaxial pneumatic powder feeding cladding head with a rectangular wide spot, and realizes flexible processing actions of different tool forms through robot program logic editing, and realizes batch non-stop processing with the standard tooling placement of the tool. Secondly, the coaxial rectangular wide spot pneumatic cladding head has higher efficiency and easier nozzle maintenance, which is particularly suitable for tool processing with flat cutting edges, simplifying the laser cladding operation process. Thirdly, according to the shape of the easily worn area of the cutting edge agricultural machinery tool, the cladding layer in the strengthening area is designed with a strip-shaped first wear-resistant layer and a second wear-resistant layer. The length of the first wear-resistant layer is greater than that of the second wear-resistant layer, forming a “long and short” wear-resistant layer shape, which not only ensures the strengthening effect, but also saves powder materials, improves the efficiency of cladding production, and reduces processing costs. Finally, to promote laser cladding equipment and technology to the agricultural machinery industry, it is necessary not only to consider processing efficiency, equipment durability and stability, but also to meet production reality, and develop alloy powder composition ratios with lower cost and higher wear resistance.
