The stress in a machine tool bed can influence machining quality in several ways:
Machining Accuracy
Deformation and Displacement: Stress in the bed can cause structural deformation, which in turn affects the positional accuracy of various machine components. For example, insufficient rigidity at the tailstock support of the bed may lead to positional deviations of the tailstock center, with maximum displacement deformation reaching up to 0.13465 mm. Such deformation directly impacts the relative positioning between the tool and the workpiece, resulting in machining errors.
Stress Concentration: High stress values in concentrated areas, such as the connection between the guideways and the bed or the transition area between the column and the bed, can lead to localized deformation, affecting machining accuracy.
Surface Quality
Surface Roughness: Vibrations and deformations caused by bed stress can affect the surface roughness of the machined part. Mechanical structural vibrations are inevitable during machining and can reduce machining efficiency and affect surface roughness.
Cracks and Fatigue Strength: Stress concentration can lead to cracks on the part surface, reducing its fatigue strength.
Tool Durability
Tool Wear: Vibrations and deformations caused by bed stress can accelerate tool wear, reducing tool life.
Machine and Fixture Service Life
Structural Fatigue Failure: High stress values in concentrated areas can lead to structural fatigue failure, affecting the service life of the machine and fixtures.
Noise Pollution
Noise Generation: Vibrations from the mechanical structure not only affect machining quality but also generate noise pollution.
Control and Optimization of Bed Stress
To mitigate the impact of bed stress on machining quality, the following measures can be taken:
Optimize Bed Structure Design:
Stiffener Design: Properly designed stiffeners can enhance the rigidity and torsional resistance of the bed. For example, using a grid or cross-shaped stiffener structure.
Material Selection: Choose materials with high rigidity and low thermal expansion coefficients, such as granite.
Stress Relief Techniques:
Vibration Aged: Vibration aging technology releases internal stress in workpieces by applying cyclic loads, reducing residual stress.
Thermal Aged: Thermal aging processes can effectively eliminate residual stress in the bed, improving dimensional stability.
Finite Element Analysis and Optimization:
Finite Element Modeling and Analysis: By creating finite element models, analyze the static and dynamic characteristics of the bed under different operating conditions to obtain information on deformation and stress distribution.
Structural Optimization: Based on the analysis results, optimize the bed structure, such as adding stiffeners and adjusting the layout of the guideways.
Process Optimization:
Reduce Load: Optimize cutting parameters to reduce cutting forces and inertial forces.
Increase Process System Rigidity: Replace components with lower rigidity with high-strength materials to enhance the overall rigidity of the process system.
By implementing these measures, the impact of bed stress on machining quality can be effectively reduced, improving the machining accuracy and stability of CNC machines.
