The accuracy of the linear guide directly determines the transmission stability of the equipment and processing quality, the source of the error involves manufacturing, installation, use and other full life cycle, the specific factors affecting can be divided into four categories.
First, the manufacturing process: the accuracy of the "innate gene"
guide rail substrate processing error
guide rail slide straightness error (such as a single rail in 1000mm length of the amount of curvature) is the core indicator, determined by the grinding process: high-precision guide rail using precision cylindrical High-precision guideway using precision cylindrical grinding machine (positioning accuracy ≤ 0.001mm), with laser interferometer real-time calibration, straightness can be controlled at ≤ 0.002mm / m; while the ordinary grinding machine processing guideway Straightness may reach 0.01mm/m, which directly leads to the trajectory offset when the slider is running.
Guideway cross-section size tolerance (such as the width of the square guideway, height deviation) will affect the clearance with the slider: if the tolerance is too poor (such as the provisions of the f7 actual up to f8), it will lead to uneven contact between the slider and the guideway, the local stress is too large to trigger the micro-deformation, the long-term operation of the accuracy of the attenuation of the accelerated 30%.
Rolling body and slider precision matching
Ball / roller diameter consistency (tolerance ≤ 0.0005mm) directly affects the distribution of contact stress: diameter deviation of more than 0.001mm, part of the rolling body to withstand more than 80% of the load, resulting in increased localized wear, so that the slider running resistance fluctuations increase (± 15%), positioning accuracy decline.
Slider raceway radius of curvature error (design value is usually 52% -53% of the diameter of the rolling body): if the curvature is large, the contact area decreases, easy to produce elastic deformation; small will increase frictional resistance, both will lead to repeat positioning error expansion (from ±0.001mm to ±0.003mm).
Material and heat treatment stability
Uniformity of the guide material: 42CrMo steel if there is compositional segregation (such as carbon content fluctuations of ± 0.05%), the hardness difference after quenching may be up to HRC5, the soft spot area of the decline in abrasion resistance, the formation of localized depressions, the cumulative error in the 100km run up to 0.01mm.
Insufficient aging treatment: not eliminate the internal stress of the guide in use will be due to temperature changes (± 10 ℃) to produce a small amount of deformation (0.005mm / m), especially in the precision machine tools outside the constant temperature workshop, the ambient temperature fluctuations will amplify this error.
Second, the installation process: accuracy of the "acquired shaping"
Installation of the base surface of the flatness and parallelism
equipment installation of the base surface of the flatness error (such as 1000mm × 1000mm base surface of the height difference) will force the guide rail to produce bending: When the flatness error of up to When the flatness error reaches 0.05mm/m, the guideway will be deformed with the base surface, resulting in an increase in the additional torque when the slider is running and a 40% decrease in positioning accuracy.
Parallelism error of multiple guide rails (e.g. parallelism deviation of double guide rails when the distance between them is 100mm): when the deviation exceeds 0.02mm/m, the slider will be subjected to uneven force at both ends, resulting in the phenomenon of "hysteresis", and the dynamic response speed will be reduced by 20%, as well as accelerating the wear of guide rails on the side.
Stress impact of the fixing method
Bolt fastening torque improper: too loose will lead to poor fit of the guide and the base surface, resulting in vibration errors; too tight will cause the guide to produce micro-deformation (such as 1000mm rail bending 0.005mm after fastening), especially in the aluminum alloy base rail, too tight bolt is easy to trigger the base of the plastic deformation, irreversibly reduce the accuracy. Incorrect installation sequence: If the rail is not fastened step by step "from the center to the ends", the rail will be distorted due to the local uneven force, and the straightness error may increase from 0.003mm/m to 0.008mm/m before installation.
Third, the use of the environment: the accuracy of the "continuous erosion"
Compound effect of temperature and humidity
Temperature gradient impact: guide and equipment base material linear expansion coefficient differences (such as steel guide α = 11.5 × 10-⁶ / ℃), cast iron base α = 9 × 10-⁶ / ℃), will produce 0.03mm/m relative displacement, resulting in positioning reference offset. and cast iron base α=9×10-⁶/℃) will produce a relative displacement of 0.03mm/m when the ambient temperature varies by 30℃, resulting in a shift in the positioning reference. High humidity environment (≥85% RH): unprotected guideway surface is prone to corrosion (even with chrome plating layer, corrosion is still possible at pinholes), and the corrosion particles will aggravate the wear and tear of the rolling body, increasing the running resistance and decreasing the accuracy by 10% in a short period of time (100 hours).
Dust and pollutant intrusion
Industrial dust (e.g. flour, metal shavings) enters the inside of the slider: particles with a particle size ≥5μm will be embedded between the rolling body and the raceway, forming an "abrasive agent", which can result in a wear amount of 0.001mm per 100 hours of operation, and in dusty environments such as woodworking machinery. In dusty environments such as woodworking machinery, this rate can increase by a factor of 10. Cutting fluid / lubricant contamination: oil containing impurities will destroy the lubrication film, resulting in direct metal contact, resulting in adhesive wear, so that the slider running "jump", positioning accuracy fluctuations up to ± 0.005mm.
Fourth, the supporting system: the accuracy of the "synergistic error"
Parallelism of the ballscrew and the guideway
Axis parallelism error of the screw and the guideway (e.g., deviation of 0.1mm within a length of 1000mm): it will cause the slider to bear additional axial force, resulting in the rolling body and the raceway The contact angle between the rolling element and the raceway changes (from 45° to 50°). ° to 50°), reducing the positioning accuracy and accelerating the wear of the screw nut.
Dynamic response of the drive system
Mismatch between the pulse equivalent of the servomotor and the accuracy of the guideway: If the minimum resolution of the motor is 0.001mm and the actual positioning accuracy of the guideway is only 0.005mm, it will lead to the phenomenon of "over-positioning", and the system will not be able to stabilize at the target position after repeated adjustments, resulting in an oscillation of ± 0.003mm. 0.003mm of oscillation error. Eccentricity error of the coupling: If there is 0.1mm radial runout in the elastic coupling, it will convert the rotational error into a periodic error in the linear direction (the frequency is the same as the rotational speed), and the amplitude can be up to 0.002mm in the case of high-speed operation (3000r/min).
Five. Long-term use: the "law of decay" of accuracy
Wear accumulation effect
Fatigue wear of the contact between the rolling body and raceway: after 5000 hours of operation under rated load, micropitting will occur on the contact surface, which will increase the rolling resistance by 10%-15%. Repeatable positioning error from class C5 ( ±0.001mm) to nearly C7 level (±0.005mm). Slider seal deterioration: dust lip wear (usually 8000 hours), the amount of dust ingress increased by 5 times, accelerating the internal wear, so that the speed of precision degradation increased by 2 times.
Accelerated degradation by improper maintenance
Insufficient lubrication: 100 hours of operation without grease increases the local temperature of the rolling element and raceway by 10°C, leading to softening of the material and permanent wear. Incomplete cleaning: maintenance without removing the metal debris on the surface of the guideway will cause "indentation" when the slider is running, and each indentation can make the local accuracy drop by 0.001mm, and when more than 10 places are accumulated, the overall positioning accuracy will be exceedingly poor.
Summarize: the core logic of precision control
The precision of linear guide rail is the comprehensive result of "manufacturing precision - installation precision - use and maintenance", in which manufacturing precision determines the upper limit, installation precision determines the actual performance, and use and maintenance determines the precision life. In precision equipment, the need for "laser interferometer calibration installation + regular vibration monitoring wear + constant temperature and humidity environment control" combination of programs, in order to make the guide rail long-term to maintain the design accuracy (such as C5 level guide rail in 5 years after the use of precision attenuation ≤ 10%).
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