KR102464657B1 - Method of evaluating the geometric tolerance process capability for the condition of the product to be processed - Google Patents

Abstract

The present invention relates to a method for evaluating geometric tolerance (GD&T) for the quality of mechanically processed parts, and more particularly, to more efficiently managing the statistics of mechanical parts, and static for complex geometric tolerances. It relates to an evaluation method for evaluating accurate statistics considering the assemblyability between actual products through dynamic calculation of the limitations of statistical calculations.

Description

Method of evaluating the geometric tolerance process capability for the condition of the product to be processed}

The present invention relates to a method for evaluating geometric tolerance (GD&T) for the quality of mechanically processed parts, and more particularly, to more efficiently managing the statistics of mechanical parts, and static for complex geometric tolerances. It relates to a geometric tolerance process capability evaluation method that can evaluate accurate statistics considering the assemblyability between actual products through dynamic calculation of the limitations of statistical calculations.

In general, as the mass production system is generalized, the importance of precision, performance, and quality required for various machines is required. This is because it is difficult to secure the function or compatibility of parts if the efficiency and unity of organic work are not maintained among designers, manufacturers, inspectors, and assemblers.

To this end, geometric dimensional tolerances (hereinafter referred to as “geometric tolerances”) are applied in addition to the normal dimensional tolerances at the stage of designing parts for various mechanical devices, and geometric Tolerance can be measured only by using a special machine such as a 3D measuring machine or a dedicated inspection).

The geometric tolerance measuring device (or device) is a utility model registered in Republic of Korea No. 20-0301327-00-00, Utility Model No. 20-0336668-00-00 (a device for measuring shape tolerance of products), and Utility Model No. 20-0336500 (a device for measuring shape tolerance of products), and the like, and as a technology related to a geometric tolerance evaluation method, there is Korean Patent Laid-Open No. 10-2015-0093433 (a method for inspecting geometric tolerance of a polymer cell using a gono jig).

The geometric tolerance measuring machine is equipped with a sensor called a probe that can measure the shape tolerance of the product (hereinafter referred to as the “sensing unit”), stores the measured values of the sensing unit, and analyzes the stored data for product function or compatibility through statistical analysis. can determine whether

In other words, prior to manufacturing the actual product, it is decided to what extent the processed product does not interfere with the function or performance, and by judging whether it falls within that range, it regulates the state of assembly with the counterparty, and It is to evaluate (judgment) the geometric tolerance of the product in order to increase the compatibility and precision during processing.

Among the important statistical values used for product quality control, the most commonly used in the field is the process capability index (Cp, Cpk) evaluation method.

However, since the above-described process capability index evaluation method of quality control is calculated based on a fixed tolerance, there is a distinct problem in that it does not reflect the assembly allowance of the actual product.

The main cause of this problem is the difference in collaboration (designer, manufacturer, inspector, assembler) between fields and fields as the currently used statistical field and geometric tolerance area are developed and established.

In other words, in actual statistics, the standard has already been established to some extent for a long time, whereas the field of geometric tolerance has undergone rapid change and development since 2000.

Geometric tolerance includes shape tolerance, posture tolerance, position tolerance, and runout tolerance (refer to KS A ISO1101 for more details). The process capability index of the conventional geometric tolerance is unilateral tolerance calculation method , and is calculated through the following formula.

USL: Upper Specification Limit

: 데이터 평균값

: Data average value

δ: standard deviation of the measured values

However, the above calculation method has a problem in that only static calculations are possible as the material condition area considering the assemblyability of the product is added in the geometric tolerance field, and evaluation of the tolerance for assemblyability is impossible.

In other words, as shown in the above calculation method, since the value of the upper tolerance (USL) is fixed, there is a clear problem that the actual applicable allowable value is not reflected.

This means that any one value cannot be fixed and used because the product condition of the geometric tolerance always changes the relative allowable value by reflecting the actual product size.

))은 허용범위가 항상 변경되게 되므로 정량적 데이터 수집 자체가 불가능하다는 것이다.In addition, in order to calculate the process capability index, statistical analysis is possible only when the same conditions are given, but the material conditions (maximum actual condition (ⓜ) and minimum actual condition (ⓜ) of geometric tolerances)

)) means that quantitative data collection itself is impossible because the allowable range is always changed.

, LMC: Least Material Condition), 형체치수무관계(기호 없음 또는 ⓢ) 등 3가지로 분류되고 있으나 위 수식을 통한 공정능력지수의 평가방법은 모두 형체치수무관계(ⓢ)의 경우를 가정하여 계산되고 있다.The material conditions for geometric tolerance are the maximum material condition (ⓜ, MMC: Maximum Material Condition) and the minimum material condition (

, LMC: Least Material Condition), and shape dimension-independent relationship (no symbol or ⓢ) are classified into three categories, but the evaluation method of the process capability index through the above formula is calculated assuming the shape-size relationship (ⓢ). .

That is, when calculating the process capability index, the upper limit tolerance (USL) is fixed and used in the calculation.

However, ASME (American Association of Mechanical Engineers) Y14.5 standard and ISO (International Organization for Standardization) 1101 standard both allow material conditions of geometric tolerance, so it is necessary to find out how the tolerance of the actual product changes.

For example, assuming that the geometrical tolerance position diagram is regulated at Ø 0.1 for a product with a hole size of Ø 12±0.05, the allowable tolerance value for this hole according to the content of the regulated auxiliary symbol after the tolerance is As in 3, the position also causes a difference in tolerance.

hole size Allowable position diagram tolerance regulatory sign Ø11.950 Ø0.100

Ø11.975 Ø0.100 Ø12.000 Ø0.100 Ø12.025 Ø0.100 Ø12.050 Ø0.100

Table 1: Changes in tolerances when regulated by shape dimension-independent relationship

hole size Allowable position diagram tolerance regulatory sign Ø11.950 Ø0.100

Ø11.975 Ø0.125 Ø12.000 Ø0.150 Ø12.025 Ø0.175 Ø12.050 Ø0.200

Table 2: Tolerance change when regulated by the maximum actual condition ( ⓜ )

hole size Allowable position diagram tolerance regulatory sign Ø11.950 Ø0.200

Ø11.975 Ø0.175 Ø12.000 Ø0.150 Ø12.025 Ø0.125 Ø12.050 Ø0.10

)으로 규제된 경우의 공차 변화Table 3: Minimum entity conditions (

), tolerance change when regulated by

As can be seen from the above tables, the upper tolerance value to be applied in the actual product should dynamically reflect the actual size of the product. If not, even though there is a very large allowable tolerance when assembling the product, it is statistically very unfavorable.

Therefore, the manufacturer faces a situation in which the manufacturing cost is inevitably increased due to unfavorable statistical values despite the fact that the processed product can be assembled.

The present invention has led to the invention of the present invention in order to solve the problems as described above, and there are remarkable achievements, so it is to be proposed through the present invention.

The present invention was created to solve the above-mentioned problems, and the main object of the present invention is to more efficiently manage product statistics and to dynamically calculate the limitations of static statistical calculations for complex geometric tolerances. It is intended to provide an evaluation method to evaluate accurate statistics in consideration of the assemblability between actual products.

The conceptual principle for solving the object of the present invention is to use the allowance tolerance (bonus tolerance) that can be assembled within the allowable range of the product without considering only the drawing tolerance for the product in the field of geometric tolerance. It is characterized by a method of increasing the amount of actual permissible tolerance through an assembly allowance equal to the part with different dimensions.

The geometric tolerance process capability evaluation method according to the present invention,

As a method for evaluating the geometric tolerance processing capability of a product through a geometric tolerance measuring device,

inputting drawing tolerances;

inputting product dimensions;

measuring the geometrical tolerance of the product through a geometrical tolerance measuring device;

calculating whether the product is assembled according to the size of the product by the arithmetic processor;

calculating, by the computational processor, a ratio of the measured value and the maximum allowable amount;

collecting statistics by the computational processor;

It is characterized in that it consists of a step of calculating and outputting the process capability index in consideration of the maximum allowable capacity by the operation processor.

It is characterized in that the value measured by the above method evaluates the process capability for the product condition through the following formula.

USL: upper tolerance

X: the actual value of the geometrical tolerance of the product

Tx: Maximum allowable tolerance by material condition

n: product quantity

δ: standard deviation of the measured values

According to the present invention, individual maximum permissible for individual measured values Possible tolerances can be derived, and the ratio of the actual value of the product to the maximum tolerance for the actual product can be derived by dividing it into the measured value/maximum tolerance form.

Therefore, product statistics can be managed more efficiently, and accurate statistics can be calculated and evaluated by reflecting the assemblability between actual products through dynamic calculation of the limitations of static statistical calculations for complex geometric tolerances.

As a result, it will provide the effect of reducing the manufacturing cost of the product.

1 is a flowchart of an apparatus for measuring geometric tolerances according to a method for evaluating geometric tolerance processing capability for conditions of a product to be processed according to the present invention.
2 is a plan view and a front perspective view of a specific product illustrating the shape dimension relationship;
3 is a diagram of a specific product according to the maximum actual condition.
4 is a diagram of a specific product according to the minimum entity condition.

Hereinafter, a preferred embodiment of the method for evaluating the geometric tolerance processing capability for the conditions of the product to be processed according to the present invention will be described in detail.

In this specification, the terms includes, includes, has, etc. are intended to designate the existence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features It is to be understood that this does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

When a component is described as being connected or combined with another component and being created, it may be directly connected or coupled to the other component, but other components may exist in between. can be understood

In this specification, terms according to the components according to the embodiment are used only to describe the illustrated embodiment, and are not limited thereto. Also, the singular expression is to be understood as including the plural expression unless the context clearly dictates otherwise.

In addition, it should be understood that all conditional terms and examples listed in this specification are, in principle, only used to more easily explain and understand the concept of the present invention, and do not limit the exemplary embodiments.

The geometrical tolerance measurement value defined below means the geometrical tolerance measurement value of the product through the geometrical tolerance measurement device regardless of the measuring device.

The geometric tolerance measuring device includes an interface (not shown in the drawing) comprising a sensing unit (probe) for measuring a part (surface) of a product, a data input display window for inputting drawing tolerances and product dimension values, and the sensing It includes a memory unit for storing the negative measurement value, an operation processor (not shown in the drawing) for calculating the measurement value and the input product setting value of the sensing unit and outputting the result, and a display unit for displaying the above-described interface and evaluation result do.

The above-described interface includes an input window for inputting or modifying drawing tolerances and product dimension values while being displayed on a touch pad (referred to as a display unit), and each information input through the input window is stored in the memory unit.

The above-described operation processor calculates through an evaluation equation to be described later and outputs the result to the display unit.

The geometric tolerance measuring device performs the following process.

(a) The drawing tolerance and product dimension values are saved through the input window for the interface of the geometric tolerance measuring device (10).

(b) Measure the geometric tolerance of the product to be measured through the sensing unit and store the measured value in the memory unit (20). In this case, the measurement part of the product to be measured may measure a plurality of desired parts, and the value is stored in the memory unit.

(c) Through the calculation process, the assembly according to the product size, that is, the bonus tolerance is calculated (30).

Bonus tolerance (additional tolerance according to assembly allowance) is calculated differently depending on the requirements of the drawing, but in this example, it is explained based on the maximum actual condition (ⓜ).

The bonus tolerance is calculated according to how large and small the actual product size is from the maximum material size (MMS) of the product.

For a hole, the largest actual dimension is the dimension when the hole is heaviest, and the smallest dimension.

The bonus tolerance is the difference between the actual product size and the maximum actual size,

For holes, Actual Dimensions - Maximum Actual Dimensions = Bonus Tolerance (Assembly Allowance)

For shafts, the maximum actual dimension - actual dimension = bonus tolerance (assembly allowance).

(d) The computational processor calculates the ratio of the measured value to the maximum allowable amount (40).

(e) The computational processor derives statistics (mean value, standard deviation) from the measured values (50).

(f) The process capability index is calculated in consideration of the maximum allowable capacity (60), and the result is output to the display unit (70).

In the following, the process capability index results according to the conventional geometric tolerance process capability evaluation method compared to the present invention are recorded in Tables 4 and 5, respectively, that the geometric tolerance position diagram is regulated by ø0.1 in the product to be processed with Ø12±0.05. .

No. Geometric Tolerance Measurements Drawing tolerance Product dimensions (Ø) maximum tolerance #One 0.055 0.100 12.023 0.173 #2 0.011 0.100 12.001 0.151 #3 0.074 0.100 12.002 0.152 #4 0.092 0.100 12.039 0.189 #5 0.041 0.100 12.000 0.150 #6 0.048 0.100 12.000 0.150 #7 0.081 0.100 12.031 0.181 #8 0.097 0.100 12.002 0.152 #9 0.006 0.100 12.038 0.188 #10 0.094 0.100 12.026 0.176 #11 0.017 0.100 11.997 0.147 #12 0.095 0.100 12.040 0.190 Average 0.059 Standard Deviation 0.034 cpk 0.392

Table 4: Conventional process capability index without considering the maximum allowable capacity

No. Geometric Tolerance Measurements Drawing tolerance Product dimensions (Ø) maximum tolerance #One 0.055 0.100 12.023 0.173 #2 0.011 0.100 12.001 0.151 #3 0.074 0.100 12.002 0.152 #4 0.092 0.100 12.039 0.189 #5 0.041 0.100 12.000 0.150 #6 0.048 0.100 12.000 0.150 #7 0.081 0.100 12.031 0.181 #8 0.097 0.100 12.002 0.152 #9 0.006 0.100 12.038 0.188 #10 0.094 0.100 12.026 0.176 #11 0.017 0.100 11.997 0.147 #12 0.095 0.100 12.040 0.190 Average 0.353 Standard Deviation 0.197 cpk 1.097

Table 5: Process capability index considering the maximum allowable capacity

"인이 경우, 종래의 방식으로, 항상 정적인 계산을 시행해야 하고, 도 3에 도시된 바와 같이 "

"인 경우, 정적인 계산이 아닌 동적인 계산을 시행해야 한다.2 to 4, the drawings in each figure are intended to explain the difference in the geometric tolerance regulation method for the same product, and even for the same product, the requirements of the drawings are as shown in FIG.

"In this case, in the conventional manner, one must always perform a static calculation, as shown in Fig. 3"

", then a dynamic calculation, not a static calculation, should be performed.

"인 경우도 정적인 계산이 아닌 동적인 계산을 시행해야 한다.As shown in Figure 4, "

"Even in the case of , dynamic calculations should be performed rather than static calculations.

보조기호가 있는 것은 서로 반대의 개념으로, ⓜ 기호의 경우, 구멍의 크기가 커질수록 보너스 공차가 추가적으로 발생되며,

기호의 경우, 구멍의 크기가 작아질수록 보너스 공차가 추가적으로 발생된다.However, if there is an auxiliary symbol ⓜ,

The presence of an auxiliary symbol is the opposite concept, and in the case of the ⓜ symbol, the larger the hole size, the more bonus tolerance is generated.

In the case of symbols, the smaller the hole size, the more bonus tolerances are generated.

Table 4 and Table 5 above show quantitative data under the same conditions in calculating the process capability index. Table 4 is the calculation of the conventional process capability index, and Table 5 shows the relative allowable amount and actual value of the product. The correlation between the allowable amount and the actual value is calculated by converting it into a ratio. The process capability index calculation of the present invention was calculated by the following formula.

USL: upper tolerance

X: the actual value of the geometrical tolerance of the product

Tx: Maximum allowable tolerance by material condition

n: product quantity

That is, for each measured value, the individual maximum allowable tolerance is calculated and divided by the measured value/maximum allowable tolerance, the ratio of the actual value to the maximum allowable tolerance for the current product is derived.

In the conventional method, the part of applying the upper limit tolerance (USL) as the tolerance in the drawing is the original method of the process capability index by designating a fixed value of 1 as the upper limit tolerance (USL) because the present invention uses the total ratio in the above formula. It is possible to achieve the same result as the purpose of

As can be seen from the results of Table 4 above, it can be seen that the conventional process capability index (Cpk) is 0.392, which can be said to be a statistically very unstable statistic. However, the statistics generated in the process of assembling the actual products inevitably show a very different trend from the statistics calculated by the conventional method.

On the other hand, in Table 5, it can be seen that the process capability index calculated by reflecting the maximum allowable tolerance for each product is shown as 1.097, which shows a significant difference compared to the conventional process capability index (Cpk). , which suggests that the safety of the assembly is better in the present invention.

As shown in Tables 4 and 5 above, in the present invention, it can be seen that the statistical value as a result of calculating the process capability index in consideration of the maximum allowable tolerance is improved by more than two times, which lowers the manufacturing cost of mechanical parts by two and makes production easier. It suggests that it is possible, and also suggests that the defect rate according to the conventional statistical values can be lowered to 50% or less.

It is also possible that the geometric tolerance measuring device of the present invention can automatically detect whether a product is defective in response to the process capability index (Cpk) calculated through the calculation processor.

However, there may be differences in the defect rate or cost reduction depending on the tolerance of the product and the condition of manufacturing dimensions. In addition, in the case of items that do not require assembly, such as mechanical parts, the results are reliable enough even with the conventional process capability index evaluation method. You will have to put in a lot of production costs.

As described above, the present invention is a process capability index evaluation method that can satisfy both the statistical requirements and the geometric tolerance requirements of mechanical drawings by substituting the geometric tolerance domain of mechanics into the typical calculation formula of the conventional process capability index. It can be done, and it will be very usefully used in calculating the statistical values of many machine parts.

Although the present invention has been described through the above-mentioned preferred embodiments, this is merely an exemplary description, and a person skilled in the art to which the present invention pertains may change and apply various modifications and application examples. However, it is to be noted in advance that such modifications and application examples are included in the technical spirit of the true meaning intended by the present inventors and the claims defined below.

Claims (2)

As a method for evaluating the geometric tolerance processing capability of a product through a geometric tolerance measuring device,
inputting drawing tolerances;
inputting product dimensions;
measuring the geometrical tolerance of the product through a geometrical tolerance measuring device;
calculating whether the product is assembled according to the size of the product by the arithmetic processor;
calculating, by the computational processor, a ratio of the measured value and the maximum allowable amount;
collecting statistics by the computational processor;
The process capability index is calculated and output in consideration of the maximum allowable capacity by the operation processor,
The calculation of the process capability index is,

USL: upper tolerance
X: the actual value of the geometrical tolerance of the product
Tx: Maximum allowable tolerance by material condition
n: product quantity
δ: standard deviation of the measured values
Geometric tolerance processing capability evaluation method for the condition of the processed product, characterized in that calculated as
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