CN116460664A - Tolerance control method and product detection method in machining process design - Google Patents

Abstract

The invention discloses a tolerance control method and a product detection method in machining process design. Among them, a tolerance control method in machining process design, in the design product and mechanical drawing, the marked tolerance requirements a ₁ , a ₃ , δ _N ; when the first and second positioning datum each control the position of the processed element in a non-constant direction; when the second positioning datum is processed, the machine tool table does not rotate and directly processes the processed element; δ _N is calculated according to the following formula. The beneficial effect of the present invention is: the present invention converts "the tolerance of the geometric relationship between the measured element and the positioning line on the second positioning datum" to "the geometrical requirement tolerance of the measured element on the entire second positioning datum", and uses the "geometric requirement tolerance of the measured element to the entire second positioning datum" to carry out mechanical design and process design, the second positioning datum can be realized, and the product qualification rate is improved.

Description

Tolerance Control Method and Product Inspection Method in Machining Process Design

technical field

The invention relates to a tolerance control method and a product detection method in machining process design.

Background technique

At present, my country issued the "Shape and Position Tolerance" standard in 1974, which standardized the labeling of shape and position tolerances in mechanical drawings.

However, due to the emergence of machining centers and boring and milling machines, multiple elements in multiple directions can be added to one process. Among the multiple processed elements, if there is a geometric requirement among them, the reference of this geometric requirement is the element that has just been processed. Because the procedure remains unchanged, the original second positioning reference cannot be realized.

The current tolerance control method is: as shown in Figure 2, plane E needs to use plane A and plane B to control its position in the two rotational degrees of freedom around the y and z axes. At present, two geometric tolerances are often marked on the plane E on the drawings with plane A and plane B as the first positioning reference. But plane E has only one chance to process. Only one primary positioning datum can be used. Another first positioning reference can no longer be used, and the requirement cannot be guaranteed.

In practice, two situations may occur: as shown in Figure 2, the two reference planes A, B and E all have only one same non-constant degree direction. Among the two reference planes A and C in FIG. 3 , the second positioning reference plane C is parallel to the plane E, and both have the same two non-constant degree directions.

In the labeling of Figures 2, 4, and 6 in this specification, the first and second positioning references have only one same non-constant degree direction as the processed element. For the labels in Figures 3, 5, and 7, the second positioning datum has the same non-constant degree directions as the processed elements.

Today, with the investment of machining centers and boring and milling machines, one process can process multiple elements in multiple directions. When there is a geometric tolerance requirement among these processed elements, the customary second positioning datum cannot be realized.

Contents of the invention

The technical problem to be solved by the present invention is: how to realize the second positioning reference in the tolerance control method and product detection method in the process design, and improve the qualified rate of products.

Technical scheme of the present invention is specifically:

A tolerance control method in machining process design, characterized in that: in the design product and mechanical drawing, the marked tolerance requirements a ₁ , a ₃ , δ _N ;

When the first and second positioning datums each control the position of the processed element in a non-constant direction;

When the second positioning datum is processed, the machine tool table does not rotate and directly processes the elements to be processed;

δ _N is calculated according to the following formula;

δ _N = a ₂ ;

When the second positioning datum and the element to be processed have two same non-constant directions, the second datum can only supplement the deficiency of the first datum, and cannot reposition in the direction where the first datum has been positioned. _δN is calculated according to the following formula:

in:

a ₁ ——the geometric requirement between the measured element and the first positioning datum;

a ₂ ——Tolerance of the geometric relationship between the measured element and the positioning straight line on the second positioning datum;

a ₃ ——The geometrical tolerance between the second positioning datum and the first positioning datum;

δ _N ——The geometric requirement tolerance of the measured element to the whole second positioning datum.

A product inspection method, measuring the real data of a ₁ , a ₃ , δ _N of the product above, and comparing it with the theoretical value a ₁ , a ₃ , δ _N , if the former is smaller than the latter, the product is qualified, otherwise the product is unqualified.

The beneficial effect of the present invention is: the present invention converts "the tolerance of the geometric relationship between the measured element and the positioning line on the second positioning datum" into "the geometrical requirement tolerance of the measured element on the entire second positioning datum", and uses the "geometric requirement tolerance of the measured element to the entire second positioning datum" to carry out mechanical design and process design, the second positioning datum can be realized, and the qualified rate of products is improved.

Description of drawings

Figure 1 is a summary table of the functions of the positioning reference system.

Fig. 2 is a schematic diagram of a three-basal plane system processing plane element--two datum system combinations in which the positioning directions of two datums complement each other.

Fig. 3 is a schematic diagram of the combination of the three-basal plane system processing plane element--two datums with repeated positioning directions.

Fig. 4 is a schematic diagram of the machining axis of the three-basal plane system-the datum system combination in which the two datums complement each other and locate each other.

Fig. 5 is a schematic diagram of the machining axis of the three-basal plane system-the datum system combination with possible repeated positioning.

Fig. 6 is a schematic diagram of the machining plane of the hole-surface datum system--the datum system combination in which the two datums complement each other.

Fig. 7 is a schematic diagram of the machining plane of the hole-surface datum system-the datum system combination with possible repeated positioning.

FIG. 8 is a schematic diagram of accuracy calculation of the reference system corresponding to FIG. 2 .

Fig. 9 is a schematic diagram of the perpendicularity relationship.

Fig. 10 is a schematic diagram of the accuracy calculation of the reference system in Fig. 3 .

Fig. 11 is a schematic diagram showing that the closed ring is flat.

Among them, in Figure 1,

① The direction of the rotational degree of freedom of the actual positioning of the first positioning datum;

② The geometric relationship and tolerance requirements of the measured elements to the first positioning datum;

③ The direction in which the second positioning datum has positioning capability in the rotational degree of freedom;

④ The direction of the rotational degree of freedom that the second positioning datum actually plays a role in positioning;

⑤ Geometric relationship and tolerance requirements between the measured elements and the second positioning datum

⑥The direction of the rotational degree of freedom to be positioned for the measured element;

⑦ The tolerance value of the measured element to the positioning line on the second positioning datum within the range of 2r;

a ₁ ——the geometric requirement between the measured element and the first positioning datum;

a ₂ ——Tolerance of the geometric relationship between the measured element and the positioning straight line on the second positioning datum;

a ₃ ——The geometrical tolerance between the second positioning datum and the first positioning datum;

δ _N ——The geometric requirement tolerance of the measured element to the whole second positioning datum.

Detailed ways

The "variable second positioning reference" used in this patent application can meet the above requirements. The present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

This patent application proposes: use the two first positioning datums of these two shape and position tolerances to form a datum system according to the first and second positioning datums (plane A, B) respectively, and jointly control the position of the processed elements.

During mechanical design and process design, two or more geometric tolerance requirements should not be marked on one element. Because, an element has only one opportunity to be processed and formed. Only one primary positioning datum can be used. No geometric tolerance requirements are used without guarantee. If necessary, two positioning datums of shape and position tolerances can be used to form a datum system to control the position of the processed elements. The benchmarking system can be implemented as follows.

As shown in Figure 1, a tolerance control method in machining process design, in the design product and mechanical drawing, only mark a ₁ , a ₃ , δ _N (same as a ₂ );

When the first positioning reference and the second positioning reference respectively control the position of the processed element in a non-constant direction, δ _N is calculated according to the following formula;

δ _N = a ₂ ;

When the second positioning datum and the element to be processed have two same non-constant directions, the second datum can only supplement the deficiency of the first datum, and cannot reposition in the direction where the first datum has been positioned. _δN is calculated according to the following formula:

in:

a ₁ ——the geometric requirement between the measured element and the first positioning datum;

a ₂ ——Tolerance of the geometric relationship between the measured element and the positioning straight line on the second positioning datum;

a ₃ ——The geometrical tolerance between the second positioning datum and the first positioning datum;

δ _N ——The geometric requirement tolerance of the measured element to the whole second positioning datum.

The proof process of the above formula is as follows:

S1. When the first positioning reference and the second positioning reference respectively control the position of the processed element in a non-constant direction, refer to the tolerance requirements in Figure 2, Figure 4, and Figure 6, because the proof process of the formula is similar, and only take the tolerance requirements in Figure 2 as an example:

As shown in Figure 8, the first datum plane A is the xoy coordinate plane, the second datum plane B is approximately the yoz coordinate plane, and the processed element plane E is a plane parallel to the coordinate plane xoz. Referring to Figure 8, there must be a verticality tolerance a ₃ /2r between the first and second positioning references, that is, the plane B is rotated around the y-axis by an angle of γ. The maximum tolerance can reach the position of DFGO; after the first datum of the part and the fixture are fully fitted, due to the existence of the angle γ, the second datum of the part can no longer be completely fitted with the second datum of the fixture, and the part will rotate around the z-axis until a straight line OD on the second datum fits with the y-axis of the coordinate system. The ideal processed elements may reach the HOKM position. The perpendicularity tolerance a ₂ /2r of the processed element to the positioning line (y-axis) can be guaranteed. That is, it is rotated by an angle β around the z-axis. After processing, the perpendicularity tolerance a ₁ /2r of the processed element to the first datum. That is, it is rotated by an angle α around the x-axis. Because, the processed element of the part has been rotated around the z axis to the HOKM position. Therefore, it can be considered approximately that the processed element rotates around the OH line by an angle of α (a ₁ /2r). Arrive at the ONPH location. Because it cannot be adjusted during processing to ensure that all elements of the second datum participate in the positioning. It is proved that the perpendicularity tolerance δ _N /2r of the processed element to the second datum can be guaranteed.

Because there is a verticality tolerance between the first and second positioning datums, this tolerance makes the second positioning datum rotate a ₃ /2r around the y-axis.

According to the formula of analytic geometry: the three-point formula of the plane is

2rx+a ₃ z=0

The coordinates of three points on the second datum plane are:

O(0,0,0)

G(-a ₃ , 0, 2r)

D(0, -2r, 0)

Then, the equation of the second positioning datum is:

Right now

2rx+a ₃ z=0

Processed element equation calculation:

The perpendicularity a ₂ /2r of the processed element to a positioning line on the second datum indicates that the measured element may rotate around the z-axis at an angle of β(a ₂ /2r) to reach the OH position. The perpendicularity of the processed element to the first datum is a ₁ /2r, and the processed element will be rotated around the x-axis by α angle (namely a ₁ /2r), because the β angle is very small, it is approximately considered that the processed element rotates around the straight line OH to reach the ONPH position. The coordinates of the three points on it are:

Point O: (0, 0, 0)

Point H: (2r, -a ₂ , 0)

N points: (0, a ₁ , 2r)

Then, the processed element equation is:

That is, - a ₂ x - 2ry + a ₁ z = 0

Let the angle between the processed element and the actual second positioning datum be θ.

Referring to the accompanying drawing 9, the included angle when the processed element is perpendicular to the second positioning datum is:

δ _N ——perpendicularity tolerance of the processed element to the second datum.

After the above equations are calculated and sorted

δ _N =a ₂ (2)

It can be seen that the plane E of the processed element shown in Figure 2 adopts plane A as the first positioning reference, and plane B as the second positioning reference, and the perpendicularity δ _N of plane E to plane B can be guaranteed after processing. It seems that a positioning line on the second positioning datum can represent the positioning of the entire plane B, which can meet the direction/position/runout requirements on the drawing. However, the actual plane on the part is not an absolutely ideal mathematical plane, and its flatness tolerance will have a certain influence (not too much), and it needs careful operation to use a straight line to represent the entire plane during processing. At the same time, it is suggested that in product design and process design, among the two pre-selected positioning datums, the element with lower direction requirements should be the second positioning datum.

S2. When the second positioning datum and the processed element have two same non-constant directions, refer to the tolerance requirements in Figure 3, Figure 5, and Figure 7, because the proof process of the formula is similar, and only take the tolerance requirement in Figure 3 as an example:

Referring to Figure 10, the first positioning reference plane A is the xoy coordinate plane, the theoretical position of the second positioning reference plane C is the xoz coordinate plane, and the processed element plane E is a plane parallel to the coordinate plane xoz. As shown in Figure 10, because there is a verticality tolerance a ₃ /2r between the first and second positioning datums, that is, the actual second positioning datum will rotate around the x-axis by an angle of γ to reach the maximum OGFD position. After the first datum of the part and the fixture are fully fitted, they can only be rotated around the z-axis until a straight line on the second datum fits with the x-axis of the coordinate system. Due to the possible adjustment and machining errors during processing, the part is rotated by β angle around the z axis, that is, the tolerance a ₂ /2r is rotated to reach the OHLK position. Then, process the plane E of the processed element to ensure its perpendicularity tolerance a ₁ /2r to the first positioning datum. That is, the maximum rotation α angle around the x-axis. Because the part has reached the OHLK position, it can be approximated that the processed element has rotated α angle (ie a ₁ /2r) around OH to reach the OHPN position. It can be seen that the direct relationship between the processed element OHPN and the second positioning datum (plane OGFD) is: the straight line (OH) on the processed element is rotated by an angle β around the z-axis relative to the positioning line (x-axis), that is, the tolerance a ₂ /2r. This requirement can be guaranteed by tuning. However, the parallelism tolerance δ _N /2r between the processed elements and the second positioning datum cannot be guaranteed!

Because there is a verticality tolerance a ₃ /2r between the first and second positioning datums, the amount of rotation of the second datum around the x-axis is limited. As shown in Figure 10.

The coordinates of three points on the second datum plane are:

O(0,0,0)

G(0, a3, 2r)

D(2r,0,0)

The equation for the second benchmark is:

2ry-a ₃ z=0

Calculate the processed element equation:

Coordinates of three points on the processed element:

O point (0, 0, 0)

N points (0, -a1, 2r)

point H(2r, -a2, 0)

The processed element equation is:

a2x+2ry+a1z=0

Angle θ between the processed element and the actual second datum.

After tidying up and ignoring higher-order infinitesimals

As shown in Figure 8, the included angle when the two elements are parallel is:

but,

After tidying up and ignoring higher-order infinitesimals

It can be seen from the above formula that after the processing plane E is positioned using the reference system in Figure 3, the parallelism of the plane E to the second reference plane C consists of errors in two different directions.

Rotation error around the x-axis: a ₁ , a ₃ ;

Rotational error around the z axis: a ₂ .

Due to the different directions, the vector sum should be taken, which is exactly the same as formula (4).

It can be seen from the calculation results:

The accuracy (a ₂ ) of the processed element in the positioning direction of the second datum can be guaranteed; the geometric relationship (δ _N ) of the processed element to the second datum cannot be guaranteed. This is because please refer to Fig. 3 : the second positioning datum can perform positioning on the processed elements in two rotational degrees of freedom. The design only needs to limit the rotation of the processed elements around the z-axis. Rotation around the x-axis is already controlled by the first positioning datum. However, the rotation error around the x-axis will still be transmitted to the processed elements. Can the selection of such a benchmark system guarantee the product requirements? Product designers should think carefully. If, the product requires this requirement. You need to find a way when designing the process.

As mentioned above, when the first and second positioning references respectively control the position of the processed element in a non-constant direction (as shown in Figure 2). After processing, it can be guaranteed that the processed element requires the position between the first and second positioning datums. The geometric relationship between the processed element and the second datum is calculated by formula (2). This marking method can be used in product design, and the process can be arranged according to this requirement in process design. However, it is best to measure the geometric relationship between the processed elements and the second positioning datum after the processing is completed, and evaluate whether it is qualified or not.

When the second positioning datum and the processed element have two same non-constant directions (as shown in Figure 3), the second datum cannot be repositioned in the direction where the first datum has been positioned. However, the second positioning reference still has an error in this unlocatable direction, which must be transmitted between the two. Only formula (4) can be used for design and calculation in process design.

In this method, the above a ₁ and a ₃ are the positional relationship between the processed element and the second positioning reference relative to the first positioning reference in the same direction. The positional relationship in another direction between the processed element and the second positioning datum is a ₂ . δ _N is the positional relationship between the processed element and the second positioning reference in two directions. That is, the directions of a ₁ , a ₃ and a ₂ are different, and δ _N should take the vector sum of the two directions (the proof will be given later).

A product testing method, which measures the real data of a ₁ , a ₃ , and _δN of the product above, and calculates them if necessary. Compare it with the theoretical values a ₁ , a ₃ , and _δN , if the former is not greater than the latter, the product is qualified, otherwise the product is unqualified.

Features of this application:

1. One element of a part should not be marked with two or more geometric tolerance requirements. If it is necessary to control the position in two directions, it is better to form a datum system to control the position of the processed elements. A variable second positioning reference is then generated.

2. When forming a reference system to control the position of the processed elements, if the first and second positioning references have only one non-constant direction with the processed elements, the calculation according to the formula δ _N = a ₂ can meet the design requirements. The product must be qualified.

3. When forming a datum system to control the position of the processed element, if the second positioning datum and the processed element have two same non-constant directions, the formula should be used calculations and cannot guarantee design requirements. If the design needs to use this situation, be careful. Or reduce the value of a ₂ to reserve a certain amount for a ₁ and a ₃ .

4. In order to improve the machining accuracy, the formula In the case of calculation, in addition to controlling a ₂ , it can also control the direction of the parts placed on the machine tool table.

For other content, refer to the prior art.

The above are only preferred implementations of the present invention. It should be pointed out that for those skilled in the art, some changes and improvements can be made without departing from the overall concept of the present invention, and these should also be regarded as the protection scope of the present invention.

Claims (2)

1. A tolerance control method in machining process design, characterized in that: in the design product and mechanical drawing, the marked tolerance requirements a ₁ , a ₃ , δ _N ; When the first and second positioning datums each control the position of the processed element in a non-constant direction; When the second positioning datum is processed, the machine tool table does not rotate and directly processes the elements to be processed; δ _N is calculated according to the following formula; δ _N = a ₂ ; When the second positioning datum and the element to be processed have two same non-constant directions, the second datum can only supplement the deficiency of the first datum, and cannot reposition in the direction where the first datum has been positioned. _δN is calculated according to the following formula: in: a ₁ ——the geometric requirement between the measured element and the first positioning datum; a ₂ ——Tolerance of the geometric relationship between the measured element and the positioning straight line on the second positioning datum; a ₃ ——The geometrical tolerance between the second positioning datum and the first positioning datum; δ _N ——The geometric requirement tolerance of the measured element to the whole second positioning datum. 2. A product detection method, characterized in that: measure the real data of a ₁ , a ₃ , δ _N of the product as claimed in claim 1, and compare it with the theoretical values a ₁ , a ₃ , δ _N , if the former is smaller than the latter, the product is qualified, otherwise the product is unqualified.