Assembly error is the difference between the installation position of the parts
and assembly specifications design provisions and the ideal position required by the process.
Assembly error causes.
1, parts error: the manufacturing error of the parts and the deformation and wear formed after the operation of the additional error.
2, tools, gauges error: tools, gauges have manufacturing errors, with its measurement, positioning, the system error will occur.
3, operation error: due to hand feeling (such as loose, flush, sharp, smooth, beating, shaking, vibration, distance, trigger force, hand knocking real, hand pulling gap, hand slack, etc.), visual inspection (size, level, straight, vertical, parallel, alignment, tangent, etc.), ear hearing (a variety of strange sound), nose smell (air leakage, etc.), by the human senses to identify the error.
4, environmental errors: errors arising from temperature, relative humidity, light shooting, air flow, foundation walking, etc.
5, consciousness error: errors arising from lack of concentration or lack of responsibility in the mind.
Rigorous work style, the spirit of technical excellence, extreme responsibility for the work is the ideological basis for reducing the assembly error, in specific operations, there are several direct ways to reduce the following assembly errors need to pay attention to.
First, choose a reasonable assembly benchmark
In order to make the parts assembly
position accurate, select a part of the parts have been positioned (point, line, surface), as the basis for the positioning of the parts to be installed, the part is called the assembly benchmark. The correct choice of assembly benchmark, is to improve assembly accuracy, reduce the assembly error is an important factor, must be taken seriously. The correct choice of assembly benchmark, generally should consider the following factors.
1, try to choose the parts of high precision parts processing
, that is, small size tolerance, high shape accuracy, small position deviation, low roughness as a benchmark. Such as roller manufacturing groove part diameter tolerance and radial runout than the light surface part is low, so in the check roller bending, correction roller spacing, are groove part as a benchmark.
2, benchmark parts as close as possible to the assembly adjustment point, such as flat surface, rely on the frame lift screw to adjust the height of the surface, so the flat ruler iron should be placed as far as possible against the frame parts. Such as the flat ruler set aside iron placed far from the frame, so that the benchmark point away from the frame, when adjusting the height of the neighboring frame, will drive this set aside iron lift, so that the benchmark drift. The farther away from the frame, the greater the change in the height of the datum surface, affecting the accuracy of the assembly.
3, try to re-use the same benchmark, excluding the surface shape deviation of the parts. For example: because the top surface has a certain degree of long to bend and wide to distort, therefore, to see the surface of the long to level the level of the flat iron, to see the surface of the wide to level the level of the level of the meter and to the front roller height line of the bracket line round roller, placed in the same part, to avoid additional errors due to the top surface of the car surface uneven.
4, the choice of benchmark should also consider the factors of convenient operation of flat assembly. Such as spindle axis helical gear left and right positioning, there are generally two methods: one is to insert the spindle, the spindle as the benchmark, with the card plate positioning; the other is not to insert the spindle, the following dragon tendon oil cup as the benchmark. Although the tolerance of the diameter of the spindle is smaller than the tolerance of the oil cup hole, but the difficulty of positioning increases after inserting the spindle. The oil cup hole as the benchmark can meet the positioning requirements of the spindle gear left and right, without inserting the spindle, so that the operation is convenient.
5, as far as possible and machine manufacturing plant parts processing
and pre-assembly of the benchmark parts up in line.
Second, to avoid multiple passes of the assembly benchmark (to reduce the cumulative error)
To divide the 1m-long straight line into ten equal parts there are two methods: one is to use 150mm steel ruler, every 100mm move a steel ruler, a total of ten times; the other is to use 1m-long steel ruler, do not move, but according to the corresponding scale line in turn to take ten points. Obviously the error of the latter method is relatively small. Because the former method, due to the measurement of the benchmark for many times to move, so that two and more assembly errors (tools, operating errors) superimposed on each other, it produces a cumulative error. The same reason, when measuring the gap with the specified degree of the ruler, should be as accurate as possible to use a single page of the ruler measurement, and avoid the use of two pages or more thin ruler stacked measurement.
Third, master the law of change of the error (eliminate systematic error)
If you find the law of change of the error, identify the value, as in the assembly to try to eliminate this error value, this regularity of the error, called the system error. Such as when a vernier caliper inside diameter measuring claw wear out 0.02mm, so that each measurement of the reading false 0.02mm, you can take the initiative to subtract 0.02mm from the reading, to get the true reading needed. Another example is when the level meter bubble is not allowed, after the positioning of the head check, found that the bubble is not allowed, after positioning to a certain end off a frame, only then is the level state, therefore, when looking at the level, should deliberately let the main bubble to a certain end off a frame, so that the parts to reach the level state.
Fourth, reasonable allocation or adjustment of error values (to reduce assembly errors)
1、Mutual borrowing method
The parallel machine car surface, bottom plate, roving machine head and tail wall plate, frame, car surface and other large castings distortion deformation, due to the inconvenience of straightening, can only check the multi-point straightness or level, so that the reading after flat assembly is equal to the maximum value of the positive and negative direction, or so that the difference after subtracting the maximum value of the positive and negative direction is not greater than the tolerance, this method is called the inter-borrowing method.
When the accumulated error in the assembly exceeds the tolerance, you can change the size, shape or one of the links, or give up an unimportant size, not to control, so that the total size within the allowable range. This link can be changed is called "adjusting ring", for example, school and strip machine roller seat open file, first from the head of the outer line to decide the wall plate on the left and right position, and then the head of the wall plate as the benchmark for the first roller seat position, and then the second, third, fourth roller seat position, and the fourth roller seat to the end of the wall plate between the dimensions can only be abandoned In practice, the adjustment ring size, shape or position change, often through the file, pad, welding methods to achieve, or adjustable parts to adjust, such as adjusting screws, adjusting washers, foot pads, etc., the use of these parts to adjust can improve the accuracy of the assembly, save manual filing and repair work.
3、Select assembly method
In order to reduce assembly errors and improve the accuracy of parts assembly, you can also have a certain error parts, through the selection, matching or grouping, so that the error between the upper and lower parts with appropriate to improve accuracy, called selection of assembly. Titanium Hao machinery is to machine tool spindle, rotary thimble, screw screw, shaft processing, CNC lathe processing
, toolholder tool bar, collet joint rod as the main products of the company, for example, the rubber roller core and iron shell grouping matching, so that the gap is consistent; the diameter of the rubber roller is divided into several grades, so that the diameter of the rubber roller of the same table or the same area of the machine is consistent.