Hard and brittle materials or refractory materials with high melting points are widely used in industrial fields due to their excellent material properties. The functional structures of fuel injectors and water jet nozzles in industrial products such as engines and waterjets need to process large depth-to-diameter ratio small holes (referred to as "deep small holes") on hard and brittle or high melting point difficult-to-machine materials. Conventional It is difficult to control the taper of the small hole by the mechanical processing method and the electric processing method, and it is difficult to process small holes with a diameter of less than 0.1 mm on hard and brittle, insulating materials.
The laser processing method has significant advantages in achieving the effects of forward taper, reverse taper, and zero taper.
The laser and intelligent energy field team of the Advanced Manufacturing Institute of the Ningbo Institute of Materials Science, Chinese Academy of Sciences uses a picosecond laser combined with a five-axis motion system to solve the problem of deep and small hole machining with controllable taper of difficult-to-machine materials. The picosecond laser outputs a light spot of Φ0.03 ～ Φ0.05mm, with a power density of 1012W / cm2. It can process deep and small holes with a controllable taper of Φ0.05mm ～ Φ0.5mm in ceramics and high-temperature alloy materials.
The 5 + 2 axis laser processing system (see Figure 1) is used to solve the problems of spatial positioning, focus correction and real-time angle compensation of deep and small holes on the workpiece. The five-axis linkage motion control system realizes the accurate positioning of the workpiece in space (accuracy is less than 3μm), and the real-time focus of the focus ensures accurate focus positioning. The depth of the machining of small holes increases with the depth, and the incident angle of the laser increases accordingly. Gaussian distribution characteristics and coupling effects, the energy absorption rate of the inner wall of the small hole material is reduced, and the laser removal efficiency is weakened. The five-axis coordinated motion system controls the incident angle θ of the laser focus and the workpiece surface through angle compensation transformation, and reduces the incident angle θ of the laser. Increase the energy absorption rate per unit area of the material and increase the material removal rate (see Figure 2). After theoretical analysis and process strategy optimization, 45 ° positive taper countersinks, zero taper holes and -11 ° reverse taper small holes have been controllably processed.
The team used this system and method to carry out deep and small hole machining tests on zirconia ceramics and a certain superalloy material. The picosecond laser processing system processes deep and small holes. Using real-time focus correction and angle transformation compensation can obtain Φ0.05mm ～ Φ0.5mm deep small holes. Through process experiments, deep and small holes can be processed in ceramics, certain high temperature alloys and other materials, and the achieved depth-diameter ratio can be greater than 15: 1. Part of the measured data is shown in Table 1. Figure 3 shows the measured data of a zirconia ceramic material through a Keyence confocal microscope. The entrance diameter is Φ0.302mm, the exit diameter is 0.301mm, the material thickness is 4mm, and the taper is close to zero. Such controlled taper deep and small holes can be automatically processed on curved workpieces. This technology lays the foundation for the processing of difficult-to-machine materials with controllable taper, large depth-to-diameter ratio, and small-diameter holes. It is of great significance for the application of micro-holes such as nozzle processing and wire drawing processing of multiple types of power systems.