assembly errorIt refers to the difference between the installation position of the part and the ideal position required by the design of the assembly specification and the process.

   Cause of 1. assembly error

1. Part error: the manufacturing error of the part and the additional error formed by the deformation and wear after the operation.

2. Tools and measuring tools error: Tools and measuring tools have manufacturing errors, and systematic errors will occur if they are used for measurement and positioning.

3. Operation error: due to hand feeling (such as tightness, flush, sharpness, smoothness, beating, shaking, vibration, spacing, pulling force, hand knocking, hand pulling gap and hand feeling relaxation, etc.), visual inspection (size, level, straight, vertical, parallel, alignment and tangent, etc.), ear hearing (various abnormal noises), nose smell (air leakage, etc.), errors generated by human sensory identification.

4. Environmental error: errors caused by temperature, relative humidity, light direction, air flow direction, ground movement, etc.

5. Consciousness error: error caused by lack of concentration or sense of responsibility.

Rigorous work style, the spirit of technical excellence, and an extremely responsible attitude towards work are the ideological basis for reducing assembly errors. In specific operations, there are several methods that directly reduce assembly errors that need attention.

     2. selection of reasonable assembly datum

In order to make the assembly position of the parts accurate, select a certain part (point, line, surface) of the positioned parts as the positioning basis for the parts to be installed. This part is called the assembly benchmark. The correct selection of assembly datum is an important factor to improve assembly accuracy and reduce assembly errors, which must be taken seriously. Correct selection of assembly datum, generally should consider the following factors.

1. Try to select parts with high machining accuracy, that is, parts with small dimensional tolerance, high shape accuracy, small position deviation and low roughness as the reference. For example, the diameter tolerance and radial runout of the groove part when the roller is manufactured are lower than that of the smooth surface part, so when checking the bending of the roller and correcting the roller spacing, the groove part is used as the reference.

2. The reference part should be as close to the assembly adjustment point as possible. For example, when the car surface is flat, the height of the car surface should be adjusted by the frame lifting screw. Therefore, the flat ruler iron should be placed as close to the frame as possible. If the flat iron is placed far away from the frame, the reference point is far away from the frame. When the height of the adjacent frame is adjusted, the iron will be lifted and lowered, causing the reference to drift. The farther the flat ruler iron is from the frame, the greater the change in the height of the datum plane, which affects the assembly accuracy.

3. Try to reuse the same datum to eliminate the deviation of the surface shape of the part. For example, because the top surface has a certain degree of long-direction bending and wide-direction distortion, it is necessary to place the flat ruler with a long-direction horizontal view of the vehicle surface, the level gauge with a wide-direction horizontal view of the vehicle surface, and the circular roller with a high-low line of the front roller in the same position to avoid additional errors caused by uneven top surface of the vehicle surface.

4. The convenience of paperback operation should also be considered when selecting the benchmark. If the spindle shaft helical gear is positioned left and right, there are generally two methods: one is to insert the spindle, take the spindle as the reference, and use the clamping plate to position; The other is not to insert the spindle, and the following dragon rib oil cup is taken as the reference. Although the spindle diameter tolerance is smaller than the oil cup hole tolerance, it is more difficult to locate after the spindle is inserted. The oil cup hole as a benchmark, can meet the spindle shaft gear left and right positioning requirements, can not insert spindle, so that the operation is convenient.

5. as far as possible and machinery manufacturing plant parts processing and pre-assembly of the reference position.

3. avoid multiple transfer of assembly reference (reduce accumulated error)

There are two ways to divide a 1m long straight line into ten equal parts: one is to use a 150mm steel ruler and move the steel ruler once every 100mm, measuring ten times in total; The other is to use a 1m long steel ruler without moving, but to take ten points in turn according to the corresponding scale line. Obviously, the error of the latter method is relatively small. Because of the former method, two or more assembly errors (tool, operation errors) are superimposed due to a plurality of movements of the measurement reference, and a cumulative error is generated. By the same token, when measuring the gap with a specified feeler gauge, a single-page feeler gauge should be used as far as possible to measure more accurately, and avoid using two or more thin feelers stacked to measure.

     4. master the change law of error (eliminate system error)

If the change law of the error is found and the value is identified, such as trying to eliminate the error value in the assembly, this regular error is called the system error. For example, when the inner diameter measuring claw of a vernier caliper is obliterated by 0.02mm, making the reading of each measurement 0.02mm larger, the reading can be actively subtracted by 0.02mm to obtain the required real reading. Another example is when the bubble of the level meter is not allowed, after the positioning and turning inspection, it is found that the bubble is not allowed, and after the positioning is biased to one end, it is the horizontal state. Therefore, when looking at the level, the main bubble should be deliberately biased to one end to make the part reach the horizontal state.

5. reasonable allocation or adjustment error value (reduce assembly error)

1. Loan Law

When large castings such as drawing machine face, bottom plate, roving machine head and tail wall plate, frame, car face and so on are distorted and deformed, due to inconvenience in orthopedic, only multiple points of verticality or levelness can be checked to make the maximum values of positive and negative readings equal after flat assembly, or to make the difference after subtracting the maximum values of positive and negative directions not greater than the allowable difference. This method is called mutual borrowing method.

2. Regulation Law

When the accumulated error exceeds the tolerance in the assembly, the size and shape of one of the links can be changed, or an unimportant size can be abandoned without control, so that the total size is within the allowable range. This changeable link is called "adjusting ring". For example, when the roller seat of the drawing machine is turned on, the left and right positions of the wall plate on the car are determined from the outer line of the front of the car, the position of the first roller seat is determined based on the wall plate on the front of the car, and the positions of the second, third and fourth roller seats are determined in turn. However, the size between the fourth roller seat and the wall plate on the rear of the wall can only be abandoned and the rear of the rear of the car, the change of the size, shape or position of the adjusting ring is often achieved by filing, pad, welding, or adjusted with adjustable parts, such as adjusting screws, adjusting washers, foot pads, etc., using these parts to adjust It can improve the accuracy of assembly and save manual filing and repair.

3. Select assembly method In order to reduce assembly errors and improve the accuracy of parts assembly, parts with certain errors can also be selected, matched or grouped, so that the upper and lower errors between parts can be matched to improve the accuracy, which is called selection assembly. Selection, matching or grouping, so that the upper and lower error between parts with appropriate to improve the accuracy, called selection assembly.