The core of optimizing shaft structural design lies in improving its strength, stiffness, fatigue life, and assembly performance, while also considering manufacturing costs and manufacturability. The following are systematic optimization strategies based on engineering practice:
1. Reduce Stress Concentration and Improve Fatigue Strength
Stress concentration is a major cause of shaft fatigue fracture. Optimization measures include:
Smooth Transitions: Use large fillet radius transitions (R value as large as possible) at shaft diameter changes to avoid sharp or right angles.
Avoid Transverse Grooving: Avoid horizontal holes, cuts, or grooves on the shaft as much as possible; if grooving is necessary, widen the transition area.
Optimize Keyway Design: Use end mills to machine keyways (smoother than disc mills), and prioritize involute splines over rectangular splines to reduce stress concentration.
2. Optimize Component Placement and Improve Stress Condition
Reduce bending moment and torque peaks by adjusting the layout of components on the shaft:
Place gears, pulleys, and other transmission components closer to bearing supports, shorten cantilever length, and reduce maximum bending stress. When power needs to be output from two wheels, placing the input wheel in the middle position halves the maximum torque on the shaft.
3. Improving Shaft Stiffness and Strength
Increasing Shaft Diameter: According to the formulas of mechanics of materials, torsional strength is proportional to the cube of the diameter; a small increase in shaft diameter can significantly improve strength.
Using Hollow Shafts: In applications where weight is limited or where wiring/conduit is required, hollow shafts offer higher torsional stiffness for the same mass.
Optimizing Support Structure: Increasing the number of bearing support points or selecting high-rigidity bearings (such as cylindrical roller bearings) reduces shaft deflection.
