Objective   The uniformity of oil injection flow of the aerospace engine oil supply device is a key technical index to determine its performance quality, in which the shape and size of the injection hole and the state of the internal surface are important influencing factors of the oil injection flow. The traditional oil injection hole processing method is based on EDM, there is a thick recast layer, and the processing efficiency is low. The laser hole is made with a typical non-contact hole making method, which has significant advantages of high processing efficiency, good quality and less recast layer. In order to meet the high-efficiency and high-quality manufacturing requirements of a certain type of aerospace engine fuel supply device, the ultra-short pulse femtosecond laser screw hole making process with a pulse width of 200 fs was adopted, and the flow numerical simulation and process test study with 0.39 mm hole diameter as the processing benchmark were carried out for the 1.5 mm thick GH3044 nickel-based alloy material.

  Methods  By means of numerical simulation, the effect of hole diameter (Fig.6), taper (Fig.8), roundness (Fig.9), internal wall roughness (Tab.2) and hole depth (Fig.10) on the flow rate of oil supply hole is studied. The effect of single pulse energy (Fig.13), single layer scan time (Fig.14) and single layer feed (Fig.15) on the hole diameter is analyzed, and the hole diameter deviation is controlled by process optimization to ensure the flow stability.

  Results and Discussions  Numerical simulations were used to investigate the factors influencing the hole flow rate. The results show that the hole diameter is the main factor affecting the hole flow rate, and the flow rate is linearly related to the square of the hole diameter (Fig.6). The internal wall roughness has an inhibitory effect on the flow rate of holes. For a 0.39 mm diameter micro-hole, the flow rate is reduced by 3.3% when the roughness is 0.01 mm and by 5.96% when the roughness is 0.05 mm (Tab.2). The roundness (Fig.9) and height (Fig.10) of the micro-hole had no significant effect on the flow rate. Since the hole internal wall roughness of the femtosecond laser hole making was low and did not change significantly for different process parameters, only the effects of single pulse energy, single layer scan time and single layer feed on the micro-hole diameter were investigated. The process optimization was carried out according to the effect law of different process parameters on the micro-hole diameter. Using the optimized process for drilling, the maximum deviation of micro-hole water flow rate is finally less than 1.8% to meet the usage requirements.

  Conclusions   In this paper, the influence law of micro-hole quality on water flow is studied by numerical simulation. The micro-hole flow rate is mainly determined by the diameter of the hole entrance and exit. Under the premise of the same entrance and exit hole diameter, the depth and roundness of the hole have basically no effect on the hole flow rate. The larger the roughness of the internal wall of the micro-hole is, the smaller the flow rate is. The smaller the hole diameter is, the more significant the effect of roughness is. When the roughness height is 0.01 mm, the flow rate of 1 mm diameter is reduced by 0.32%, and the flow rate of 0.39 mm diameter is reduced by 3.30%. The effect of process parameters on the micro-hole diameter was analyzed. With the increase of single pulse energy, the entrance and exit hole diameter increased simultaneously and the taper decreased. The effects of single layer scan time and single layer feed on hole diameter were not significant. Finally, the deviation of the hole diameter was controlled within ±5 μm and the taper was 0.01° by process optimization. The water flow rate test was conducted, and the maximum flow rate was 3.28 g/s, the minimum flow rate was 3.17 g/s, and the average flow rate was 3.23 g/s with a maximum deviation of 1.8%, which satisfied the usage requirements.