How To Install Ball Screw?

First, the installation of the core objectives: so that the screw "go straight", precision to "hairline level"

Ball screws installation key is to ensure that the screw axis and the parallelism of the equipment guide (error needs to be ≤ 0.02mm / m, similar to a straightedge and the fit of the desktop ), and the perpendicularity of the nut holder and the screw (error ≤ 0.01mm). If the installation deviation is too large, it will lead to equipment operation jam, noise surge, and even shorten the life of the screw by more than 50%.

Stepper Motor Bracket

Second, the installation of the "three checks" before the preparation: parts, tools, the environment is indispensable

Parts status check

visual inspection of the silk rod surface whether there are scratches, bumps (especially the threaded raceway, finger slide should be no burrs);

turn the nut, should be able to slide smoothly along the silk rod, no obvious jamming (if the jamming may be the balls are worn or embedded in foreign objects);

check the end of the axle Check the fit between the inner hole of the support seat (bearing seat) and the shaft diameter of the screw, the interference fit needs to be "just embedded" by gently pushing with the hand, and the clearance fit needs to be detected with a plug ruler with a clearance of ≤ 0.01mm.

List of necessary tools

Measuring tools: micrometer (accuracy 0.001mm), marble platform (calibration reference), laser interferometer (high-precision parallelism detection);

Installation tools: hydraulic press (to avoid deformation from hammering), torque wrench (to control the bolt torque, such as M8 bolts usually need 20-25N・m), dust-free cloth (to wipe off the grease);

Auxiliary materials: high-temperature lubricating grease (coated with the raceway of the screw), anti-loosening glue (bolt locking); auxiliary materials: high temperature lubricating grease (coating), anti-loosening glue (bolt locking). Auxiliary materials: high-temperature grease (for coating the screw raceway), anti-loosening adhesive (for bolt locking), and aluminum alloy shims (for height adjustment).

Environment and benchmark calibration

Installation table needs to be level (detected with a level meter, bubble offset ≤ 0.05mm/m), avoid vibration sources;

Take the equipment rail as the benchmark, calibrate the flatness of the marble platform with a micrometer, to ensure that the installation benchmark is stable.

Third, the standardized installation of six-step process: from positioning to locking the details of the control

Pre-positioning of the support seat and the guide rail

The motor end support seat (fixed end) and the tail end support seat (floating end) will be temporarily fixed on the base of the equipment to the guide rail as a reference, use a micrometer to adjust the height of the support seat:

Fixed end of the support seat axis is required to be parallel to the top of the guide rail, the deviation is ≤ 0.01mm/100mm (can be compared to the analogy) The axis of the fixed end support seat should be parallel to the top surface of the guide rail, with a deviation of ≤0.01mm/100mm (analogous to "use a straightedge to stick to the guide rail, and the gap between the axis of the screw and the straightedge is less than a hair's breadth");

The floating end support seat needs to be left with an axial travel clearance of 0.02-0.05mm to prevent it from jamming by thermal expansion.

Combined installation of screw and nut

Firstly, install the nut into the nut holder (grease should be applied to the nut raceway in advance, similar to greasing the gears), and then thread the screw from the fixed-end support seat:

If it is installed vertically, it is necessary to support the middle of the screw with a sling to avoid sagging and deformation;

When the nut engages with the screw, it is necessary to rotate it slowly to push it forward, and if it feels that there is a sudden increase in resistance, it should be stopped immediately to check whether there is any misalignment of balls (there have been cases of forceful installation resulting in the breakage of balls, which can lead to the breakage of balls. (There was a case where the ball was broken due to forced installation, and the equipment made a "clicking" noise when running).

Axial and radial accuracy calibration

Axial runout calibration: put the micrometer head against the end of the screw shaft, manually rotate the screw, the needle swing amount should be ≤ 0.005mm (equivalent to the thickness of a piece of A4 paper), otherwise the bearing preload needs to be adjusted;

Radial runout calibration: fix the micrometer in the middle of the screw, rotate the screw for one week, the runout amount should be ≤ 0.01mm (can be compared to the analogy of "turning a bicycle wheel, the rim of the wheel and the brake leather"). Bicycle wheel, the rim and the brake skin clearance uniform"), if exceeded need to check the support seat coaxiality.

Adjustment of perpendicularity of the nut seat and guide rail

Use a right-angle ruler to fit the side of the guide rail, the micrometer is fixed on the nut seat, move the nut seat along the guide rail, the needle deviation needs to be ≤0.01mm/100mm (analogous to "use a triangle ruler to stick to the wall, and the gap between the nut seat and the wall remains unchanged when the nut seat is moved");

If it is overdifficult, you can pad the copper foil between the nut seat and base If the gap is exceeded, put copper foil gasket (thickness 0.01-0.1mm) between the nut holder and the base, or slightly grind the mounting surface of the base.

Bolt locking and anti-loosening treatment

Tighten the bolts of support seat and nut seat in diagonal order in 2-3 times (e.g., tighten 1/3 of the force first, and then tighten them to the standard torque after checking the accuracy);

Apply anti-loosening adhesive to the head of the bolts after locking and mark the position to avoid loosening in operation (an automation line was scrapped due to the loosening of the bolt of the nut seat, which resulted in the deviation of the silk rod and the processing of the work piece with abnormal dimensions).

Trial run and accuracy review

Slowly rotate the screw manually, make sure the nut moves smoothly without stagnation, and the noise is ≤ 45dB (similar to a soft conversation);

Turn on the machine and run at a low speed (30% of the rated speed) for 10 minutes, and use the laser interferometer to check the positioning accuracy of the screw:

Repeat positioning accuracy should be ≤ ± 0.003mm;

Full positioning accuracy should be ≤ ± 0.01mm/1000mm.

Typical Misoperation and Consequence Warning

Insufficient rigidity of support seat

A machine tool was installed with cast iron support seat instead of the standard steel seat, and the vibration caused the radial runout of the screw to be exceedingly poor, and the surface of the workpiece appeared wavy, so the support seat had to be replaced eventually.

Failure to pre-stretch

The long stroke screw (more than 1.5 meters) was not pre-stretched according to the requirements, and it elongated by 0.05mm due to temperature rise during operation, resulting in jamming of the nut and overloading of the motor and burnt-out of the motor.

Grease application error

Misuse of ordinary grease instead of high-temperature grease, 3 months after the operation of the ball due to poor lubrication and wear, the screw drive efficiency decreased by 30%, the speed of the equipment slows down significantly.

five. Intelligent installation tools to improve the efficiency of the program

laser alignment meter + digital micrometer: real-time display of parallelism of the screw and guide rail data, adjust the efficiency of 50% (an automotive mold factory with this program will be a single piece of equipment to shorten the installation time from 8 hours to 4 hours);

electric servo press: accurate control of the screw bearing pressure (error ± 10N), to avoid deformation of the inner ring of the bearing caused by artificial hammering, bearing life Extend the life of bearings more than 2 times.

Summarize: Installation remembering the principle of "three quasi"

Benchmark quasi: calibrate the support seat and nut seat with the guide rail as the benchmark;

Force quasi: use torque wrenches to control the bolt torque, to avoid over-tightening and deformation or over-loosening loosening;

Measurement quasi: use high-precision instruments to monitor the deviation in real time, to eliminate the "installation by experience". ".

Ball Screw Rod Assembly