1. Introduction
With the rapid development of China’s aviation industry, the overall performance requirements of aircraft engines have also increased. As a key component of aircraft engines, integral blisks can effectively reduce their overall weight and improve aerodynamic performance. However, due to the complex structure, narrow channel, and poor openness of the overall blisk, it is difficult to manufacture and process it, which has become a major technical problem in the aviation field. In recent years, a series of manufacturing techniques have been explored, such as milling [
1], electrical discharge machining [
2], electrolytic machining [
3], laser cladding [
4], and other techniques to manufacture blisks. Among them, milling has the advantages of having high reliability and a small production cycle and has been widely used in the field of blisk manufacturing [
5]. Disc-milling is the first process of grooving the whole blisk. The blank material of the blisk is cut with a large margin, and the whole blisk is processed in cooperation with other technologies.
Titanium alloys have been widely used in the aviation field due to their high specific strength, low thermal conductivity, and good high-temperature performance, such as aircraft engine integral blisks. At present, scholars at home and abroad have carried out active research on residual stress in titanium alloy milling and proposed many theories and methods. Residual stress can affect the surface integrity of the workpiece. Zhang et al. [
6] proposed an ultrasonic longitudinal–torsional composite milling method to obtain large residual compressive stress on the surface of the workpiece and improve the surface integrity and fatigue life of the workpiece. The influence of different process parameters on the surface residual stress of titanium alloy thin-walled parts was studied. Finally, the experimental results show that the method is effective. In order to study the effect of residual stress on the hardness value of weld metal, Terentyev et al. [
7] studied and analyzed titanium alloy welded joints obtained by electron beam welding and argon arc welding. The results showed that the nature of residual stress distribution depends on welding parameters and can affect the hardness value of titanium alloys in welds. When machining titanium alloy blades, abrasive belt grinding can prolong the fatigue life of the blade, but it will also affect its performance. Xiao et al. [
8] used ABAQUS to establish a simulation model of titanium alloy grinding and analyzed the effect of grinding process parameters on the action law of surface residual stress; the final simulation results are consistent with the actual experiment results. Kaifa et al. [
9] established 3D finite element models associated with two original surface roughnesses as well as without original surface roughness based on Gaussian distribution combined with exponential autocorrelation function and performed integrated coupled DEM–FEM simulations of the shot peening process for these three target models to study shot peening residual stresses. The results showed that the shot peening surface residual stresses with the presence of original surface roughness were more uniformly distributed. In titanium alloy additive manufacturing, high residual stresses can exist in the sample due to layer-by-layer fabrication, which can affect the fatigue strength of the product. Karpenko et al. [
10] proposed a numerical method to predict the effect of residual stresses on the fatigue crack expansion rate (FCGR) and verified the validity of the method experimentally. Kyaramyan et al. [
11] proposed several parameters for the combined surface heat treatment and air shot peening machining process of VT41 titanium alloy compressor impeller blades for advanced engines and analyzed the residual stresses in the initial state of the blades and after finishing treatment to derive the effects of each parameter on the microstructure and life of the blades. During titanium milling, the effect of thermal–mechanical coupling on the surface integrity of titanium alloy was studied [
12].
During the machining process of blisk disc-milling grooving, the milling force is large, and the milling temperature is high. Due to the thermal–mechanical coupling effect, the machined surface and the subsurface will inevitably undergo mechanical, physical, and chemical changes; thus, a deep plastic deformation surface layer is formed on the machined surface. The working environment of the blisk is extremely harsh, and its surface quality requirements are very high. The size and direction of the surface residual stress and the depth of the residual stress layer affect the fatigue life of the blisk and, thus, affect the safety performance of the engine [
13,
14]. At present, scholars at home and abroad have carried out relevant research on the residual stress of the blisk. In order to study the influence of alumina ACW (abrasive cloth wheel) polishing parameters on the surface residual stress of a GH4169 superalloy blisk blade, Lin [
15] obtained the residual stress prediction model of the polishing surface based on Minitab software and obtained the optimal range of process parameters, which can be used to obtain large and stable surface residual compressive stress. Alcaraz et al. [
16] used a new horizontal vibration shot peening method to understand the combined shot peening and polishing mechanism during the vibration shot peening a process of the three-stage blisk of a gas turbine engine. They achieved a simultaneous reduction in overall production cost and time of vibratory peening for all three stages of blisks. In order to better study the residual stress of aircraft engine blades, Xian Chao et al. [
17] established a simple mathematical model of residual stress based on the force effect, thermal effect, and the coupled effect of force and heat and verified the accuracy of the model by experiments. Wu et al. [
18] established an empirical model of the surface residual stress based on the polishing process parameters and quantitatively analyzed the effect of the polishing process on deformation through finite element analysis and experimental testing. The results showed that this surface polishing process can effectively improve surface integrity.
It can be seen from the above that, although there have been some achievements in the related experimental research on the residual stress of titanium alloy materials and the residual stress of the overall blisk machining process at home and abroad, the above research concerns the residual stress under the processing technology of shot peening, polishing, and grinding; however, none of the studies involved the analysis of residual stress in the milling and grooving of the blisk. Therefore, the research on the residual stress of the high-efficiency grooving machining of the blisk disc-milling is carried out here, and the theoretical and practical basis for the elimination of the residual stress in the grooving machining of the disc-milling is provided, and it is of great significance to finally make the disc-milling and grooving of the blisk meet the technological requirements. In this paper, the titanium alloy TC17 blisk blank is used as the processing object, a single-factor experiment and an orthogonal experiment of blisk disc-milling and grooving are designed, the residual stress prediction model is established, and the residual stress on the surface of blisk disc-milling and grooving is carried out, analyzing the influence of process parameters on residual stress and providing theoretical support for improving the fatigue life of blisk parts.