I. Key technologies for lead screw design and selection
1. Screw types and applicable scenarios
Ball screw: mainstream high-precision transmission solution, which reduces friction through ball circulation, has an efficiency of more than 90%, and supports high-speed and high-acceleration motion. Suitable for precision grinding and multi-axis linkage processing.
Trapezoidal lead screw: traditional sliding contact structure, low cost but high friction loss, mostly used in light load, low speed scenarios or economical equipment.
2. Accuracy grade and preload design
ISO accuracy classification: C0-C10 grade accuracy selection needs to match the machine tool repeat positioning accuracy requirements (such as C3 grade lead screw can reach ±5μm/300mm).
Double nut preload technology: eliminate axial clearance, and the preload force needs to be controlled at 5%-10% of the rated dynamic load to avoid temperature rise deformation due to overload.
3. Thermal deformation compensation measures
Hollow screw cooling: Constant temperature oil or coolant is introduced inside to suppress the pitch error caused by temperature rise.
Closed-loop temperature sensor: Real-time monitoring of screw temperature, compensation of thermal elongation through the CNC system (compensation coefficient is usually 12μm/℃·m).
4. Materials and surface treatment
Base material: SCM420 alloy steel (hardness HRC58-62 after carburizing and quenching) or ceramic-coated screw (wear resistance increased by 3 times).
Thread raceway: Super-finished polishing after precision grinding, surface roughness Ra≤0.2μm.
II. Key points of guide rail system design
1. Comparison of guide rail types
Type Advantages Limitations Applicable scenarios
Sliding guide rail High rigidity, strong vibration resistance Large friction resistance, easy to crawl Heavy load and low speed grinding
Linear guide rail Low friction, fast dynamic response Limited load capacity High-speed precision grinder
Hydrostatic guide rail Zero contact wear, long precision life Requires complex hydraulic system Ultra-precision nano-level grinding
2. Plastic-coated guide rail technology upgrade
Composite guide rail design: Bonding polytetrafluoroethylene (PTFE) soft tape (thickness 0.5-1.5mm) on the cast iron substrate, the friction coefficient is reduced to 0.04, and creep-free motion is achieved with minimal lubrication.
Process control: Bonding surface roughness Ra1.6-3.2, curing pressure 0.1-0.2MPa, to avoid blistering or peeling of the soft tape.
3. Optimization of guide rail layout
Wide span design: The ratio of guide rail span to moving part length is ≥1:1.5, which improves the anti-overturning moment capacity (for example, when the span is 400mm, it can bear 3000N·m moment).
V-flat combined guide rail: The V-shaped guide rail provides guiding accuracy, the flat guide rail carries the main load, and the preload spring is used to eliminate the gap.
4. Sealing and protection
Multi-stage scraping device: A combination of metal scraper + flexible sealing strip prevents grinding dust from invading the guide pair (protection level reaches IP54).
Centralized automatic lubrication: The quantitative distributor supplies 0.1-0.3ml of oil per stroke cycle to ensure an oil film thickness of 3-5μm.
III. Screw-guide rail collaborative design strategy
1. Stiffness matching principle
The axial stiffness of the screw (typical value 500-800N/μm) needs to be higher than the stiffness of the guide rail system (300-500N/μm) to avoid system resonance.
Optimize the span of the screw support bearing and the thickness of the guide rail mounting surface through finite element simulation (for example, shortening the bearing span by 20% can increase the stiffness by 35%).
2. Dynamic error coupling control
Reverse clearance compensation: The screw preload and guide rail preload need to be adjusted synchronously to ensure that the reverse clearance is ≤2μm.
Servo parameter setting: Based on the mass-stiffness distribution of the linkage components, optimize the servo gain and acceleration feedforward parameters.
3. Life prediction model
Formula for lead screw life:
(P_e is equivalent load, including vertical/horizontal load components)
IV. Application cases of advanced technologies
Linear motor + magnetic suspension guide rail: Eliminate mechanical transmission chain and achieve nanometer-level positioning (resolution 0.1μm), used for optical lens grinders.
Dual-drive lead screw synchronous control: The lead screws on both sides use full closed-loop grating feedback, and the synchronization error is <1μm, which solves the problem of overloading of large gantry grinders.
Intelligent health monitoring system: Integrated vibration sensor and oil particle counter, early warning of lead screw wear or guide rail scratch failure.
