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The application of three coordinates in the slow deviation detection of engine cylinder block

the cylinder block is the installation matrix of each mechanism and system of the engine, and its inner and outer, front and rear, left and right, up and down are full of spatial holes. The internal movement of the engine can be attributed to the linkage of the crankshaft, piston, connecting rod and camshaft. In fact, the connection dimensions of various components of the engine can be confirmed by the above aspects. Because the crankshaft and piston are installed in the cylinder body of the engine, the processing quality of the cylinder block is particularly important, especially the position dimension and shape and position tolerance of its hole system are the basis to ensure the assembly and operation life of the engine

1 establishment of the benchmark coordinate system for measuring the position and size of the cylinder block space hole system

the position, size, shape and position tolerance of the cylinder block space hole system can be measured very conveniently and quickly on the coordinate measuring machine

for the position dimension, shape and position tolerance of the three coordinate measurement hole system, the key is how to establish the measurement reference coordinate system. The establishment principle of the measurement reference coordinate system is that it must be consistent with the processing reference coordinate system. Only by making the inspection datum consistent with the machining datum coordinate system of the part, can the conformity of the inspection be guaranteed and the machining quality of the part be effectively monitored. Therefore, in the CMM program, the measuring elements of the positioned machining datum should be measured first, and then constructed and calculated Establish the reference coordinate system of the part to be measured, and then according to the detection requirements of the space size of the part to be measured, carry out the reference conversion of the reference coordinate system, such as translation or rotation, then take points to measure the measured elements, calculate and evaluate the position of each measured element (such as holes) in the reference coordinate system, and finally output the coordinate values (x, y, z) of the measured element (such as holes) in the reference coordinate system. If other shape and position tolerances are required, only evaluate the various relationships between the measured element and the reference element, and then output the measurement results. Therefore, the key of measurement is to establish a measurement reference coordinate system

1.1 establishment and embodiment of the three base plane system

as shown in Figure 1, the ideal position of the hole is to use three mutually perpendicular datum planes a, B and C for positioning. These three mutually perpendicular datum planes a, B and C form a three plane system, which is often called the three base plane system. It is the starting point to determine the geometric relationship of the elements on the part. In the three base level system, the datum planes are divided in order according to the functional requirements. The most important is the first datum plane (a), followed by the second (b) and third (c) datum planes

The three base plane system is an ideal spatial system, and the actual datum elements on the parts have form and position errors, and at the same time, there are orientation and positioning errors between the actual datum elements Therefore, when the actual parts are positioned according to the sequence specified in the drawing in the three base plane system, the actual datum elements cannot completely contact the ideal datum plane. Therefore, it is necessary to stipulate the principle and simulation embodiment method of establishing the three base level system(1) establish a three datum system from the actual datum surface

the first datum of the three datum system is the main datum, and the positional relationship between the first datum actual surface a and the first datum plane should meet the "minimum condition"; On this basis, the relationship between the actual surface B of the second datum and the second datum plane should meet the requirement that the maximum deviation is the minimum; The third benchmark only needs a touch. In production, the following simulation embodiment method can be adopted, that is, the actual surface of the first datum should meet 3-point contact with the first datum plane; The actual surface of the second datum should meet 2-point contact with the second datum plane, that is, the actual surface of the third datum should meet 1-point contact with the third datum plane. Accordingly, the orientation of the measured elements in the three base plane system is completely determined, so that the only determined result can be obtained when evaluating the "orientation and positioning errors". However, because the datum sequence of the same part is determined differently, the position of the tolerance zone of the measured element in the three base plane system is also different

(2) establish a three datum system from the actual datum cylindrical surface

in the datum system of different parts, there are often both actual datum surfaces and actual datum cylindrical surfaces. At this time, the relationship between the actual datum cylindrical surface and the three datum system is formed by the intersection of two datum planes to form the datum axis

when the datum axis is the first datum, the intersection line composed of the first and second datum planes in the three datum system is the datum axis, which can be regarded as two datums. At this time, the ideal minimum circumscribed cylinder is in contact with the actual cylindrical surface a, and the second datum actual surface B is in contact with the third datum plane at 1 point

when the datum axis is the second datum, the actual surface of the first datum and the first datum plane should meet the "minimum condition", that is, 3-point contact should be met; The actual cylindrical surface of the second datum is closely contained by the minimum circumscribed cylindrical surface with the intersection line composed of the second and third datum planes as the axis. Under the condition that the first datum meets the minimum condition, due to the error of the actual datum elements, the minimum circumscribed cylindrical surface containing the actual cylindrical surface of the second datum only needs 2 points of contact with the actual cylindrical surface of the second datum

the machining process of Fukang car engine block adopts a typical three base plane system to construct the machining coordinate system

1.2 adopt the typical machining coordinate system,

use the three coordinate measurement program to realize the detection of batch products. Before entering the program, first establish the control coordinate system of the current position of the parts, that is, manually establish the initial measurement coordinate system before establishing the part measurement reference coordinate system. The three coordinate system is to find the position of the measured hole or other elements according to the control coordinate system to realize the automatic measurement of the part measurement reference coordinate system, According to the elements of automatic measurement, the part measurement reference coordinate system is established, and then the automatic measurement or evaluation of the measured hole or surface is realized. The establishment principle of the control coordinate system is to make the position of the tested parts and the control coordinate system relatively unchanged, or the displacement is very small, so we should find those machined smooth surfaces or holes. If it is a blank, we should use the measurement support, and build the control coordinate system on the measurement support as the control coordinate system for batch inspection. The following mainly describes the establishment of part measurement datum coordinate system

(1) the reference coordinate system used for opl0 positioning datum processing

a. positioning and clamping

the processing of cylinder block positioning datum is based on the cylinder block blank as the positioning datum. Due to the characteristics of blank positioning, in order to ensure the processing accuracy, special tooling fixtures must be used, and the reference coordinate system must be established on the special tooling fixtures. Positioning and clamping are shown in Figure 2

it can be seen from Figure 2 that P4, P5 and P6 constitute the three datum planes for positioning hole processing. P4 plane: symmetrical point of the 3rd and 4th clamping points; P5 side; The plane symmetrical to two probes 2 and perpendicular to P4; P6 surface: the surface of support 1 is perpendicular to the surface of P4 and P5

b. establishment of the part measurement reference coordinate system. The cylinder block is placed on the three coordinate marble plate in the way that the left measurement surface of the opl0 support is parallel to the X axis and placed on the marble plate. The cylinder block is freely placed on the four support points of ① in the support and clamped by the four support points of ④ and ③. The establishment method and steps of the datum coordinate system used for cylinder block opl0 positioning datum processing are as follows

· measure a plane on the left measuring surface of opl0 bracket

· measure a plane on the three coordinate marble platform

· take 1 point on both sides of the third sand cleaning hole on the right side of the cylinder block, and calculate the midpoint

based on the normal of the plane measured on the marble platform, the first axis is the Z axis, and the coordinate offset of the Z axis is set to z=301.968, which is the P6 surface; Take the normal of the plane measured by the left measuring surface of the opl0 support to build the second axis, which is the Y axis, and set the coordinate offset of the Y axis, y=-179.797, which is the P4 surface; The CMM automatically generates the x-axis, and clears the 0 point of the x-axis at the midpoint of the third sand cleaning hole, which is P5 surface

in this way, the cylinder block opl0 positioning reference processing measurement reference coordinate system is established, which is completely consistent with the processing reference coordinate system. The position measurement of other processed holes and surfaces can be accurately measured only through element collection and evaluation

(2) the coordinate system used in the rough machining process of op20op40op50op60 op90opl20

a. positioning and clamping

the coordinate system used in the rough machining process of the cylinder block adopts one side and two pins, that is, one space ideal plane p1 on the side + one cylindrical pin 52 ① + one diamond pin 52 ②. Positioning and clamping are shown in Figure 3

it can be seen from Figure 3 that P1, P2 and P3 constitute the rough machining three base datum. P1 plane: a plane passing through datum points ① and ②, 22mm away from datum point ④ and 88mm away from datum point ③; P2 surface: the surface passing through two locating pin holes (52) and perpendicular to P1; P3 surface: the surface passing through two locating pin holes (52) and perpendicular to P1 and P2

b. establishment of part measurement reference coordinate system

the cylinder block is placed vertically on the three coordinate platform, with the oil pan facing the positive direction of the X axis, the timing facing down parallel to the marble plate, and the flywheel facing up

the method and steps of establishing the coordinate system used in the rough machining process of the cylinder block are as follows

· take 1 point on each of the four small planes ①, ②, ③ and ④

· measure a circular section of the cylindrical pin locating hole and a circular section of the diamond pin locating hole

· offset the X coordinate of point ③ by 88 along the positive direction of the Y axis, and offset the X coordinate of point ④ by -22 along the positive direction of the Y axis

· construct a plane with point ② and offset points ③ and ④. This plane is P1 plane, and the first axis is Y axis based on the normal of this plane, and clear y=o on this plane; The second axis is the Z axis by connecting the two locating pin holes. The plane where the Z axis is located is the P2 surface. Clear x=o on the centroid point of the line, and the coordinate measuring machine automatically generates the X axis.

this is the P3 surface. Clear z=o on the center of the cylindrical pin locating hole

in this way, the benchmark coordinate system used for the measurement of the rough machining process of the cylinder block is established, which is completely consistent with the machining benchmark coordinate system. The position measurement of other machined holes and surfaces can be accurately measured only through element collection and evaluation

(3) op130p140p1 the earliest experimental machine is the static experimental machine 50 op170p190p230. The coordinate system used in the finishing process of positioning and clamping

a. the coordinate system used in the finishing process of the cylinder block is also one side with two pins, but the surface and pin hole of this coordinate system are completely different from the rough machining coordinate system, that is, the bottom plane P10 + 1 cylindrical pin 39 ① + 1 rhombic pin 39 ②. Positioning and clamping are shown in Figure 4

it can be seen from Figure 4 that P10, P11 and p12 planes constitute the three datum planes for finish machining. P10 plane: the plane passing through the bottom plane 200 and the four supporting points; P11 surface: the surface passing through the axis of the cylindrical locating pin hole (39), 28 mm away from the diamond locating pin hole (39) and perpendicular to P10; P12 surface: the surface passing through the axis of the cylindrical dowel hole (39) and perpendicular to P10 and P11

b. establishment of part measurement reference coordinate system

the cylinder block is placed vertically on the three coordinate platform, with the top plane facing the positive direction of Y axis, and the timing face down parallel to the marble plate The flywheel faces up

the establishment method and steps of the reference coordinate system used for the measurement of the cylinder block finishing process are as follows

· measure a plane on the oil pan surface, that is, P10 surface

· measure the two circular sections of the cylindrical pin locating hole cylinder and the diamond pin locating hole cylinder

· offset the center points of the two circular sections measured in the diamond pin locating hole by -28 along the positive direction of the X axis

· offset the center points of the two circular sections measured in the cylindrical pin positioning hole and the center points of the two circular sections measured in the diamond pin positioning hole

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