What are the straightness requirements for ball screws?

What are the straightness requirements for ball screws?

Hi! Hello everyone, as a supplier specializing in the production of ball screws, customers often ask: "How much 'straightness' of this screw must be achieved to qualify ah?" Ball screws are like "long-distance runners" in the equipment, and straightness is its "gait standard" - the straighter it runs, the higher the precision of the equipment. If the "run off", light is to affect the quality of processing, heavy is to let the equipment "broken foot". Today we will talk about, the "athlete" of the straightness in the end what to say.

First, the first to understand the "straight vigor": what is straightness?
Straightness is said to be the axis of the ball screw is straight, like a measure of the runway is not straight enough. It reflects the degree of curvature of the screw over its entire length, and is usually expressed in terms of the maximum deviation per meter of length (unit: mm/m). For example, a 3-meter-long screw, if the straightness requirement is 0.1mm/m, it means that each meter can not be bent more than 0.1mm, the total length of the bending must be controlled within 0.3mm.

This "straightness" of the equipment is too important: like athletes will affect the performance, the screw is not straight will lead to run "left and right", so that the positioning of the equipment is not allowed, vibration becomes bigger, and even wear faster. In precision machine tools, screw straightness difference of 0.01mm, the accuracy of the processed parts may be out of 0.1mm, which can be called "a tiny difference, a thousand miles".

Second, different "track" of the "rules": straightness requirements are divided into levels
Just like different races on the runway straightness requirements are different, different equipment on the straightness requirements of the ball screws are not the same. It can be roughly divided into three levels, namely, "general track", "precision track" and "ultra-precision track".

1.Ordinary track (general transmission scenarios): like ordinary conveyor belts, lifting platforms, these "not the pursuit of extreme precision" of the equipment, screw straightness requirements are more relaxed, usually in 0.1-0.3mm / m. Like a park walking path, a little bit of a bend does not affect walking. A warehouse lifting platform with a screw, straightness control in 0.2mm / m, running smoothly, fully able to meet the needs of goods lifting.

2. Precision track (processing and automation equipment): machine tools, automated assembly lines, these "precision" equipment, the screw straightness requirements are strict, generally in the 0.02-0.1mm/m. This is like a track and field track, must be straight enough to ensure that the athletes do not run off. The straightness of the screw of a precision lathe is controlled at 0.05mm/m, and the dimensional error of the processed parts can be stabilized within 0.01mm.

3. super-precision track (high-end precision equipment): semiconductor manufacturing equipment, laser measuring instruments, these "precision ceiling" level of equipment, screw straightness requirements are harsh to 0.005-0.02mm / m. Like the orbit of the space launch, the slightest deviation may affect the overall situation. A chip photolithography machine screw, straightness control in 0.008mm / m, in order to ensure that the precision of laser etching to the nanometer level.

Third, the "bias" of the consequences: what happens if the straightness is not enough?
If the screw "is not straight enough", like athletes running always run off the mark, the trouble can not be small:
accuracy "hit the water": poor straightness will lead to the positioning of the equipment is not allowed, like archery always off target. A CNC milling machine due to the straightness of the screw to 0.2mm / m, machining parts verticality error from 0.03mm up to 0.1mm, directly into the scrap.

1. "Extra burden" to find the door: bending the screw rotation will produce additional radial force, like a person limping walking will wear out shoes. This will make the bearing seat, nut "follow the suffering", wear and tear accelerated, life may be shortened by more than half.

2. Vibration and noise "nuisance": the screw is not straight will lead to running "wobble", resulting in vibration and noise. An automated production line screw straightness is too poor, running noise from 70 decibels rose to 90 decibels, the workers can not stand, replace the qualified screw before restoring quiet.

Fourth, let the screw "stand straight": how to ensure straightness?
Want to keep the screw "straight stature", have to be from the production to the installation of the whole process of gatekeeping, like training athletes to be in place from training to equipment.

1. "Shape" in production: rolling or grinding should be precisely controlled, just like giving the screw "orthopedic". Large screws also have to go through aging treatment "shaping" to eliminate internal stresses, to avoid late "bending". A manufacturer of 6-meter-long screw, through three aging treatment, straightness stabilized at 0.05mm/m within.

2. Transportation "waist protection": long screws should be transported "lying flat" or fixed with a special bracket, like giving it a "good lumbar pillow" to avoid bumps lead to bending. There have been customers due to the transportation of random stacking, screws are bent, straightness super poor to 0.5mm / m, can only be scrapped.

3. Installation "calibration": check the straightness before installation, just like checking the runway before the race. You can calibrate with a level, a percentage meter, and if necessary, fine-tune it through shims to make the screw "straighten up". A machine tool factory installation found that the screw has 0.1mm/m bending, by adjusting the support base, and ultimately let the straightness of the standard, the equipment operation accuracy enhancement is obvious.

Fifth, the selection of "straight" screw: how to see the straightness of the selection?
Pick the screw, you have to choose the right straightness level according to the needs of the equipment, do not "big material" or "small material":

1. Look at the equipment "temperament": ordinary equipment do not force high precision, or "spend money"; precision equipment do not use low precision, or "delay". For example, the carving machine choose 0.05mm/m screw is just right, choose 0.008mm/m is a waste.

2. Check the test report: reliable suppliers will provide straightness test report, like the athlete's physical examination report. To see the deviation per meter, full-length deviation and other data, to avoid "verbal commitment".

3. Ask the application case: Ask the supplier what the straightness of the screws used for similar equipment is, like a reference to "the results of the same track players". An automotive parts factory reference peer case, selected 0.08mm/m screw, both to meet the accuracy and control the cost.

Summarize
The straightness of ballscrews is not a "one-size-fits-all" standard, but like "dress size", it is graded according to the demand for equipment precision: 0.1-0.3mm/m for normal scenarios, 0.02-0.1mm/m for precision scenarios, and 0.005-0.02mm/m for ultra-precision scenarios. 0.005-0.02mm/m. This "straight slip strength" seems to be subtle, but it directly affects the accuracy, life and stability of the equipment.

Selection of screws, like the equipment "choose running shoes" - fit (matching accuracy) is the most important. At the same time, from production, transportation to installation are well controlled, in order to let the screw always maintain a "straight posture", in the equipment "run" out of good results.

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