In the CNC machining of cold-pressed terminals, the distribution of residual stress is closely and complexly related to the machining sequence. This relationship not only affects the machining quality of the terminals but also has a profound impact on their long-term stability and reliability.
The machining sequence directly affects the internal stress state of the material during CNC machining of cold-pressed terminals. When rough machining is performed first, a large amount of material is removed, leading to significant residual tensile stress within the terminal. This tensile stress may further accumulate during subsequent finishing processes. If not eliminated in time through process methods, it will form stress concentration areas on the terminal surface, increasing the risk of cracking. For example, if finishing of critical parts is performed directly after rough machining, the residual tensile stress may be exacerbated by the superposition of cutting forces, leading to microcracks on the machined surface.
The influence of the machining sequence on the distribution of residual stress is also reflected in the coupling effect of thermal and mechanical stress. In CNC machining, cutting heat causes local temperature increases in the terminal, resulting in thermal expansion and contraction. If the machining sequence is unreasonable, such as repeatedly cutting the same area, the area will repeatedly experience thermal cycling, leading to uneven distribution of residual stress. Specifically, this manifests as a layered distribution of surface tensile stress and internal compressive stress. This stress gradient reduces the fatigue strength of the cold-pressed terminal, making it particularly susceptible to fatigue fracture under alternating loads.
A proper machining sequence can effectively optimize the distribution of residual stress. For example, employing a symmetrical machining strategy—machining one side of the cold-pressed terminal first, then the symmetrical other side—can cancel out the residual stresses generated on both sides, reducing overall deformation. Furthermore, scheduling high-precision machining operations after heat treatment can avoid the superposition of phase transformation stress and cutting stress caused by heat treatment. Heat treatment can eliminate some residual stress, providing a more stable stress state for subsequent finishing, thereby improving the dimensional accuracy and surface quality of the cold-pressed terminal.
The machining sequence also affects the release path of residual stress. In CNC machining, if weak parts of the terminal, such as slender structures or thin-walled sections, are machined first, these parts may deform due to stress release during subsequent machining, affecting overall assembly accuracy. Conversely, if the more rigid parts are machined first, followed by the weaker parts, the rigid parts can constrain deformation in the weaker areas, allowing residual stress to be released more evenly and reducing springback and torsion after machining.
The impact of different machining sequences on residual stress is also reflected in the choice of toolpath. In CNC programming, toolpath planning directly affects the distribution of cutting forces. Using a single path such as climb milling or conventional milling may lead to localized stress concentration in the terminal. Optimizing the toolpath, such as using helical interpolation or contour milling, can distribute the cutting force more evenly on the machined surface, reducing peak residual stress and improving the fatigue resistance of the cold-pressed terminal.
Adjusting the machining sequence can also be combined with optimizing process parameters to further control residual stress. For example, using a larger depth of cut and feed rate in the roughing stage to quickly remove most of the material, and then reducing cutting parameters in the finishing stage to reduce cutting heat generation. This staged machining sequence, combined with dynamic parameter adjustment, can effectively reduce the accumulation of residual stress and improve the machining quality of the terminal. The residual stress distribution in CNC-machined cold-pressed terminals is closely related to the machining sequence. By rationally planning the machining sequence, combined with heat treatment, toolpath optimization, and process parameter adjustment, the generation and distribution of residual stress can be effectively controlled, improving the terminal's machining accuracy, fatigue strength, and long-term stability. In actual production, a scientific machining sequence should be formulated based on the terminal's material properties, structural characteristics, and machining requirements to minimize residual stress and maximize machining quality.
