RU2277038C1 - Part producing process state judging method - Google Patents

Abstract

FIELD: all types of large- and small-lot production processes, namely of processes providing preset dimensions of mutual arrangement of part constructional members.

SUBSTANCE: method for controlling part forming process at providing preset dimensions of mutual arrangement of constructional members of parts comprises steps of measuring coordinates of arrangement of constructional members for each part by check sampling; registering coordinate values in data table; comparing measured table data with ranges of admissible factors of controlled process; evaluating process state according to number of out-of-range values among measured data. In order to realize it in CAD system provided with parametric simulation procedure, absolute coordinate system is plotted. In said system points corresponding to nominal value of constructional member arrangement are applied according to drawing and also limit boundaries of zone of admissible fluctuations of said point positions relative to nominal ones. Contour of said boundaries depends upon allowance value according to drawing and upon part number of check sampling. According to part quantity in check sampling, local coordinate systems are built whose order number depends upon order number of part in sampling. Arrangement of said local coordinate systems is determined according to variable distance values of their center from axes of absolute coordinate system and to rotation angle relative to said absolute coordinate system. In each local coordinate system points corresponding to measured coordinates of arrangement of all constructional members of respective part of check sampling are applied. For each local coordinate system with the aid of computer program optimal value of variable distance relative to absolute coordinate system is fetched in such a way that to provide the least distance value for each point of local coordinate systems from respective limit boundary to become the most value. For points placed outside limit boundary range said values are negative ones. Diagrams of scattering fields are built according to coordinates of absolute coordinate system for points in local coordinate systems after changing their positions in accordance with optimal values of variables.

EFFECT: improved reliability of part checking.

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Description

The invention relates to a method for assessing the state of the manufacturing process of a part, ensuring the relative sizes of its structural elements, which is intended to make a decision on controlling the production process of parts when controlling production quality by statistical control methods, and can be used in all sectors of large- and small-scale production, where products at the output of the process or at its individual stages is produced in batches or continuously, in particular, this method can be used Used during the control tests of technological equipment intended for the manufacture of these parts.

In the improvement of modern production management, methods prevail that use statistical methods of process quality management, designed to ensure and maintain product quality indicators at an acceptable and stable level.

The above methods are widely used in practice, described in the technical literature, their application is regulated by a number of state and industry standards for quality systems. Similar to the claimed methods are implemented in computing devices for controlling the manufacturing process of products according to patents of the Russian Federation: No. 2145731, cl. IPC G 06 G 1/06 2000 and No. 2133980, cl. IPC G 06 F 17/18 1999, as well as GOST 51814.3-2001 and GOST R 50779.40-96 (ISO 7870-93).

The essence of these methods is described in more detail in GOST R 50779.4D-96 (ISO 7870-93), which we take as a prototype.

Known methods of production management using statistical methods of process quality control include measuring the actual sizes on each part of a certain control sample, entering the values of these measurements into the data table, comparing the data of the measurement table with the boundaries of the allowed indicators of the capabilities of the controlled process, evaluating the processes according to cases of output of the measurement values beyond these boundaries and making decisions on the acceptance of equipment or on the possibility of continuing the process or, in the case of negative th assessment on the implementation of corrective adjustment actions.

A disadvantage of the known methods is the biased understatement of the capabilities of the controlled process for the production of parts, ensuring the relative sizes of their structural elements, which is due to errors in the installation of parts during measurements. This is especially evident when the dimensions in the drawing are tied to unprocessed or insufficiently accurate bases. The named errors are random and do not relate to the actual accuracy of the relative positioning of the elements of the part, so the results of measurements with such errors do not allow an objective assessment of the capabilities of the controlled process.

The technical solution is aimed at achieving a more objective assessment of indicators of the capabilities of the controlled process for the production of parts, ensuring the sizes of the mutual arrangement of their structural elements by eliminating the influence of errors in the installation of parts during measurements on the results of measurements of the sizes of the mutual arrangement of structural elements.

The goal is achieved by the fact that in any known computer-aided design system containing parametric modeling technology, an absolute coordinate system is built in which points corresponding to the nominal value of the arrangement of structural elements in the drawing are plotted, as well as control boundaries of the areas of permissible deviations of the position of these points from nominal, the shape of which depends on the type of tolerances established by the drawing for these elements, and the dimensions of these areas depend on the tolerance The design and number of parts in the control set, based on the number of parts in the control set, build local coordinate systems numbered in accordance with the part number in the sample, the location of which is determined by the variable values of their distances from the coordinate axes of the absolute system and the rotation angles relative to it corresponding to each local coordinate system , in each of the local coordinate systems, points are applied that correspond to the actually measured coordinates of the arrangement of all structural elements of the corresponding part from the control sample, for each local coordinate system using a computer program, search for the optimal values of the variable values of its position relative to the absolute coordinate system at which the smallest value from the distances of all points plotted in the local coordinate systems from the control boundary corresponding to each point , considering these values negative for points located outside the control boundaries, takes the greatest value, and the scatter field diagrams I build on the coordinate values in the absolute system of points plotted in local coordinate systems in the modified positions of the latter, corresponding to the found optimal values of the variables.

Figure 1 shows an example of a drawing view of the part.

Figure 2 and 3 is a diagram showing the dependence of the results of measurements of coordinates on the errors of installation of parts during measurements.

Figure 4 - arrangement of the absolute coordinate system with points of the nominal position of the holes and the areas of their permissible positions, and local coordinate systems with points corresponding to the actually measured coordinates of the holes.

Figure 5 is an example of the display of control boundaries and areas of dispersion of the results of measurements to the exclusion of errors in the installation of parts during measurements.

Figure 6 - diagrams of the scattering fields of the measurement results to the exclusion of errors in the installation of parts during measurements.

Figure 7 is an example of the display of control boundaries and scattering regions of the measurement results after eliminating the errors in the installation of parts during measurements.

On Fig - diagrams of the scattering fields of the measurement results after eliminating the errors in the installation of parts during measurements.

The method is described by the example of controlling the processing process on an aggregate machine with multi-spindle heads of part 1 (Fig. 1) containing a central hole 2 and four holes 3 located at the corners of part 1, as well as two sides 4 and 5 perpendicular to each other. 2 and 3 and the sides 4 and 5 are regulated by the dimensions in the rectangular coordinate system XY0 in the working drawing of the part. The working drawing is used to control the manufacturing process of parts (not shown in the application materials). The distance of the sides 4 and 5 from the center of the hole 2 is set by free dimensions L1 and L2 without tolerances along the X and Y axes by the coordinate of the system. The location of the center of the hole 2 relative to the center of the upper right (in Fig. 1) hole 3 is defined by two sizes of the form A ± Δa and B ± Δb, where

A and B are the nominal sizes of the distances of the center of the hole 2 from the hole 3 along the axes X and Y, (see figure 1);

Δa and Δb are symmetrical tolerances for sizes A and B.

With this setting of dimensions and tolerances, the region 6 of permissible deviations of the center of the hole 2 from the nominal position has the shape of a rectangle with sides equal to 2Δa and 2Δb.

(рамочками обозначают размеры, общий позиционный допуск которых назначается на размере диаметра отверстий), при этом рабочим чертежом установлен позиционный диаметральный допуск ⌀δb. При таком задании размеров и допусков области 7 допускаемых отклонений от номинального положения центров отверстий 3 имеют форму окружностей диаметром, равным δb.The mutual arrangement of the centers of the holes 3 is set in the drawing (Fig. 1) with nominal dimensions of the type

(frames indicate the dimensions, the general positional tolerance of which is assigned to the size of the diameter of the holes), while the positional diametrical tolerance ⌀δb is set by the working drawing. With this setting of dimensions and tolerances, the area 7 of permissible deviations from the nominal position of the centers of the holes 3 have the shape of circles with a diameter equal to δb.

The processing process is controlled by a statistical method using the T-FLEX CAD computer-aided design system of the Russian company "Top Systems" (www.topsystems.ru), the official T-FLEX Paramitric CAD trademark. At the same time, some control batch of parts (sample) is processed (or selected processed) on the machine; measure the dimensions actually obtained during processing on the machine on all parts of the sample; enter the measurement values into the data table, then compare the table data with the boundaries of the allowed indicators of the capabilities of the monitored process and evaluate the process for cases when the measurement values exceed the specified boundaries.

The standards of the company AVTOVAZ JSC regulated the requirement to provide indicators of the capabilities of the processes With _p ≥1.33 and With _pk ≥1.33, where:

With _p is the reproducibility index of the process, reflecting its variability with respect to the tolerance field;

C _pk is the reproducibility index of the process, reflecting its variability and attunement to the center of the tolerance field.

For equipment suppliers, more stringent acceptance standards have been established With _p ≥ 1.67. Based on these requirements, the number of parts in the sample and the control boundaries as part of the tolerance field are determined. To accept new equipment, the control limits are regulated to be set equal to half the tolerances defined in the drawing. The test results of new equipment are considered positive when the controlled dimensions do not go beyond the control limits.

From the condition of acceptance standards at AvtoVAZ for new equipment, the control borders 6 are set for the center of the hole 2 in the form of a rectangle with the sides Δa and Δb, and the control borders 7 for the centers of the holes 3 are set as circles with a diameter of δb / 2.

During the measurement process, parts 1 are installed in measuring instruments based on sides 4 and 5, and installation errors occur, depending on the quality of surfaces and the relative positions of sides 4 and 5 of parts 1, dx, dy and da in the measuring instruments, where:

dx and dy - offset point 0 'of the intersection of sides 4 and 5 relative to the origin 0 of the measuring system, (figure 3),

da is the angular displacement of the part (skew) relative to the measuring system, (Fig.3).

These errors are random in nature, the actual accuracy of the mutual arrangement of holes 2 and 3 does not depend on them, but they affect the results of measurements of deviations of the centers of the holes from the nominal positions.

Figure 2 shows a diagram of measuring the dimensions of the mutual arrangement of holes 2 and 3 on one part at zero values of the installation errors dx, dy and da, i.e. in the case when the sides 4 and 5 of part 1 are strictly mutually perpendicular and their surfaces perfectly flat, and Fig. 3 shows this measurement scheme in the non-ideal case when the roughnesses of the sides 4 and 5 and their deviations from the mutual perpendicularity are due to errors dx, dy and da settings during measurements (control limits and errors are conditionally increased).

Points x ₂ , y ₂ , x ₃ and y ₃ are the projections of the centers of the control boundaries 6 and 7 on the coordinate axis of the measuring system, Ra;

points x ₂ ', y ₂ ', x ₃ 'and y ₃ ' are the projections of the centers of the measured holes 2 and 3 on the coordinate axis of the measuring system;

и

- соответствуют номинальным размерам А и В на фиг.1;distances

and

- correspond to the nominal sizes A and B in figure 1;

и

- замеренные значения размеров А±Δа и В±Δb на фиг.1.distances

and

- measured values of dimensions A ± Δa and B ± Δb in figure 1.

From the diagrams in FIGS. 2 and 3, it is obvious that the measured values differ for the same actual size of the center-to-center distance between these holes.

Thus, we note that the errors in the installation of parts during measurements affect the results of evaluating the actual values of the deviations of the centers of the holes from their nominal positions, and even with relatively small values of the errors of the installation, their influence can be significant and lead to an incorrect assessment of the process capability indicators.

A complete operational description of the proposed method in order to perform actions in time can be described as follows.

- on the equipment make a batch of parts 1 (hereinafter referred to as the "control sample") or make its selection in the production process;

- details 1 in the control sample are numbered and marked;

- measure the coordinates of the centers of the holes 2 and 3, using for installation when measuring the sides 4 and 5 of part 1;

- the measurement results are entered into a table, each row of which contains the part number, hole number and the coordinates of the center of this hole along the X and Y axes;

- in the computer-aided design system containing parametric modeling technology, the absolute coordinate system 8 is built (Fig. 4);

- in the absolute system 8 put the points X ₀₀ , Y ₀₀ and X _0i , Y _0i corresponding to the nominal position of the centers of the holes 2 and 3, where

X ₀₀ , Y ₀₀ - coordinates of the nominal position of the center of the hole 2;

X _0i , Y _0i - coordinates of the nominal position of the center of the i-th hole 3;

- according to existing rules, depending on the number of parts in the sample and the type of tolerance, define the control boundaries of the rectangular 6 and round 7 areas of permissible deviations of the coordinates of the centers of the holes 2 and 3 from their nominal positions, allowing to evaluate the capabilities of the controlled process;

- in the absolute coordinate system 8, the control borders 6 with the center at the point X ₀₀ , Y ₀₀ and the control borders 7 with the centers at the points X _0i , Y _{0i are plotted} in real scale (exaggerated);

- build a local coordinate system 9, the start offset and rotation angle of which relative to the absolute coordinate system 8 is determined by special variables dx, dy, and da, which are introduced into the system;

- additionally introduce into the system the variable j corresponding to the part number in the sample;

- in the local coordinate system 9, points X _j0 , Y _j0 and X _ji , Y _{ji are plotted} in real scale, the coordinates of each of which are set using special expressions that allow the computer system to read from the table in the line corresponding to the part number j and the hole number in this part corresponding to the point number in the local coordinate system (Fig. 4 shows for j = 1),

Where

X _j0 , Y _j0 - coordinates of the measured position of the hole 2 of the j-th part in the sample;

X _ji , Y _ji - coordinates of the measured position of the center of the i-th hole 3 of the j-th part in the sample,

- using the function of the computer system "specification", create a new table of calculated values of the coordinates of the centers of the holes, into which the coordinates of the points X _j0 , Y _j0 and X _ji , Y _ji are automatically entered in the absolute system 8;

- alternately for each part in the control sample, changing the value of the variable j in the system, for the points X _j0 , Y _j0 and X _ji , Y _ji set the values of the measured coordinates in the local coordinate system 9, and then using the special function of the computer system "optimization" organize, by entering into the system of special expressions and necessary boundary conditions, the search for the optimal values of the variables dx, dy and da, at which the smallest value of all the distances of each point X _j0 , Y _j0 and X _ji , Y _ji applied in the local coordinate system 9, from the control boundaries 6 or 7 corresponding to this point, considering the distance values for points X _j0 , Y _j0 and X _ji , Y _ji negative, located outside the control borders 6 or 7, while the position of the local coordinate system 9 changes to in accordance with changes in the variables dx, dy and da;

- using a computer system, the data of the table of calculated values of the coordinates of the centers of the holes 2 and 3 are automatically recalculated, thus, for each specific part 1, the measurement results are corrected with the exception of the installation errors dx, dy and da introduced during the measurement;

- the state of the system is stored as a fragment under the name corresponding to the number of the measured part;

- starting with a change in the system variable j, this operation is performed with the remaining measurements;

- after processing all the measurements, a composite measurement model is created, for this, on the previously constructed absolute coordinate system 8 with the drawn control boundaries 6 and 7, in which the remaining structures are previously deleted, all the fragments obtained above with the correct positions of the points X _j0 , Y _j0 and X _ji , Y _ji , using the "specification" function, the data of the tables of all fragments are automatically combined into one pivot table, in which the installation errors introduced during measurements are excluded. Points X _j0 , Y _j0 and X _ji , Y _ji , of all the fragments of the measurements form the scattering field 10 (Fig.5 and 7);

- to visualize boundaries 6 and 7 with scattering fields 10 in the composite model, a large-scale viewing is organized using a computer system in special viewing windows or on separately displayed remote windows. In Fig. 5, for the described example, a mapping of the scattering fields 10 before optimization is shown; for comparison, Fig. 7 shows what it looks like after excluding installation errors during measurements;

- according to the summary table, graphs 11 of the scattering fields 10 are constructed (Fig.6 and 8);

- carry out an assessment of the process for cases when the values of the measurements recalculated in the manner described above are exceeded for the control boundaries 6 and 7 on the scattering fields 10 displayed on the display screen, as well as analyzing the summary table and graphs 11.

The proposed method allows to provide a more objective assessment of indicators of the capabilities of the controlled process for the production of parts, at which the relative positions of their structural elements are fulfilled by eliminating the influence of installation errors on the measurements on the results of measurements of the relative sizes of the structural elements of the parts.

Claims (1)

A method for assessing the state of the production process of parts, ensuring the relative sizes of the structural elements of the parts, comprising measuring the coordinates of the location of these elements on each part of a certain control sample, entering the values of these coordinates in the data table, comparing the data of the measurement table with the boundaries of the allowed indicators of the capabilities of the controlled process, process evaluation in cases of measurement values exceeding the specified boundaries, characterized in that in any known system the computer design, containing the technology of parametric modeling, build an absolute coordinate system in which the points corresponding to the nominal value of the location of the structural elements in the drawing are plotted, as well as the control boundaries of the areas of permissible deviations of the position of these points from the nominal ones, the shape of which depends on the type of tolerances established by the drawing for of these elements, and the dimensions of these areas depend on the tolerance according to the drawing and the number of parts in the control sample, according to the number of parts in for the control sample, local coordinate systems are numbered in accordance with the part number in the sample, the location of which is determined by the variables corresponding to each local coordinate system of the distance of their centers from the coordinate axes of the absolute system and the rotation angles relative to it, points corresponding to the actual measured coordinates of the location of all structural elements of the corresponding part from the control sample, for each local system Coordinates using a computer program search for the optimal values of the variables of its position relative to the absolute coordinate system at which the smallest of the distances of all points plotted in the local coordinate systems from the control border corresponding to each point, considering these values to be negative for the points located outside the control boundaries, takes on the greatest value, and the scattering field diagrams are built according to the coordinate values in the absolute system of points plotted in l local coordinates systems in a change of the last positions corresponding to the found optimal values of variables.

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