Tolerance control methods and product testing methods in machining process design

Abstract

The present 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 of products and mechanical drawing, the marked tolerance requirements are a1, a3, δ N ; when the first and second positioning references each control the position of the machined feature in a non-constant direction; when the second positioning reference is machined and the machine tool table does not rotate and directly machines the machined feature; δ N It is calculated according to the following formula. The beneficial effects of the present invention are: the present invention converts the "geometric relationship tolerance of the measured feature to the positioning straight line on the second positioning reference" into the "geometric requirement tolerance of the measured feature to the entire second positioning reference", and uses the "geometric requirement tolerance of the measured feature to the entire second positioning reference" for mechanical design and process design. The second positioning reference can already be realized, improving the product qualification rate.

Description

Technical Field

[0001] The invention relates to a tolerance control method in machining process design and a product detection method. Background Art

[0002] At present, my country issued the "Form and Position Tolerance" standard in 1974, which standardized the marking of form and position tolerances in mechanical drawing.

[0003] However, due to the emergence of machining centers and boring and milling machines, a process can add multiple elements in multiple directions. Among these multiple processed elements, if there is a geometric tolerance between them, the reference of this geometric tolerance is the element that has just been processed. Because the process remains unchanged, the original second positioning reference cannot be realized.

[0004] The current tolerance control method is: Figure 2 , plane E needs plane A and plane B to control its position in the two rotational degrees of freedom directions around the y and z axes. Currently, two geometric tolerances are often marked on plane E on drawings with plane A and plane B as the first positioning reference. However, plane E has only one chance to be processed. Only one first positioning reference can be used. The other first positioning reference cannot be used anymore, and the requirements cannot be guaranteed.

[0005] In practice, two situations may occur: Figure 2 The two reference planes A, B and plane E each have only one common non-constant degree direction. Figure 3 Of the two reference planes A and C, the second positioning reference plane C is parallel to plane E, and both have two identical non-constant degree directions.

[0006] In this manual Figure 2 , 4 , 6, the first and second positioning datums have only one common non-constant degree direction with the processed element. Figure 3 , 5 , 7, the second positioning reference has two identical non-constant degree directions with the processed element.

[0007] Nowadays, with the introduction of machining centers and boring and milling machines, multiple elements in multiple directions can be processed in one process. When there are geometric tolerance requirements between these processed elements, the second positioning reference used in the past can no longer be realized. Summary of the invention

[0008] 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 processing design and improve the product qualification rate.

[0009] The technical solution of the present invention is specifically as follows:

[0010] A tolerance control method in machining process design. In product design and mechanical drawing, the tolerance requirements are marked. 1 、a 3 , δ N ;

[0011] When the first and second positioning datums each control the position of a non-constant degree direction of the processed element;

[0012] When the second positioning reference is processed, the machine tool table does not rotate and directly processes the processed element;

[0013] δ N Calculate according to the following formula;

[0014] δ N =a 2 ;

[0015] When the second positioning reference and the processed element have two identical non-constant degrees of direction, the second positioning reference can only supplement the deficiency of the first positioning reference and cannot be re-positioned in the direction where the first positioning reference has already positioned. N Calculate according to the following formula:

[0016]

[0017] in:

[0018] a 1 - geometric tolerance of the measured element to the first positioning reference;

[0019] a 2 ——Geometric tolerance of the measured element to the positioning straight line on the second positioning reference;

[0020] a 3 ——Geometric tolerance between the second positioning datum and the first positioning datum;

[0021] δ N ——The geometric tolerance of the measured element to the entire second positioning reference.

[0022] A product testing method, measuring the above-mentioned a of the product 1 、a 3 , δ N The actual data and compare it with the theoretical value a 1 、a 3 , δ N Compare and if the former is less than the latter, the product is qualified, otherwise the product is unqualified.

[0023] The beneficial effects of the present invention are as follows: the present invention converts "the geometric tolerance of the measured element to the positioning straight line on the second positioning datum" into "the geometric tolerance of the measured element to the entire second positioning datum", and uses "the geometric tolerance of the measured element to the entire second positioning datum" to perform mechanical design and process design, so that the second positioning datum can be realized, thereby improving the product qualification rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a summary table of the functions of the positioning benchmark system.

[0025] Figure 2 Schematic diagram of the combination of a three-base surface system for machining planar elements - two base positioning directions complement each other.

[0026] Figure 3 It is a schematic diagram of the combination of a three-base surface system for machining planar elements - two base surfaces with repeated positioning directions.

[0027] Figure 4 It is a schematic diagram of the machining axis of the three-base system - a combination of datum systems in which two datums complement each other in positioning.

[0028] Figure 5 Schematic diagram of the machining axis of the three-plane system - a combination of reference systems with possible repeated positioning.

[0029] Figure 6 Schematic diagram of the machining plane for the hole-surface datum system - a combination of datum systems in which the two datums complement each other in positioning.

[0030] Figure 7 Machining a plane for a hole-face datum system - Schematic diagram of a datum system combination with possible duplicate positioning.

[0031] Figure 8 for Figure 2 Schematic diagram of the corresponding benchmark system accuracy calculation.

[0032] Fig. 9 Schematic diagram of verticality relationship.

[0033] Fig.10 for Figure 3 Schematic diagram of the accuracy calculation of the benchmark system.

[0034] Fig.11 Schematic diagram of the closed loop for parallelism.

[0035] in Figure 1 middle,

[0036] ① The direction of rotational freedom of the actual positioning of the first positioning reference;

[0037] ② The geometric relationship of the measured element to the first positioning datum and its tolerance requirements;

[0038] ③ The direction in which the second positioning reference has positioning capability in the rotational degree of freedom;

[0039] ④ The direction of the rotational freedom of the second positioning reference that actually plays a positioning role;

[0040] ⑤ The geometric relationship and tolerance requirements between the measured element and the second positioning reference

[0041] ⑥ The direction of rotational freedom in which the measured element needs to be positioned;

[0042] ⑦ The tolerance value of the measured element to the positioning straight line on the second positioning reference within the range of 2r;

[0043] a 1 - geometric tolerance of the measured element to the first positioning reference;

[0044] a 2 ——Geometric tolerance of the measured element to the positioning straight line on the second positioning reference;

[0045] a 3 ——Geometric tolerance between the second positioning datum and the first positioning datum;

[0046] δ N ——The geometric tolerance of the measured element to the entire second positioning reference. DETAILED DESCRIPTION

[0047] This patent application uses a "variable second positioning reference" to meet the above requirements. The present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0048] This patent application proposes: using the two first positioning datums of the two geometric tolerances to form a datum system according to the first and second positioning datums (planes A and B) respectively, to jointly control the position of the processed element.

[0049] In mechanical design and process design, two or more geometric tolerance requirements should not be marked on one element. Because one element has only one chance to be processed and formed. Only one first positioning datum can be used. The geometric tolerance requirements that are not used cannot be guaranteed. If necessary, two geometric tolerance positioning datums can be combined into a datum system to control the position of the processed element. The datum system can be implemented as follows.

[0050] like Figure 1 , a tolerance control method in machining process design. In product design and mechanical drawing, only a 1 、a 3 , δ N (with a 2same);

[0051] 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 Calculate according to the following formula;

[0052] δ N =a 2 ;

[0053] When the second positioning reference and the processed element have two identical non-constant degrees of direction, the second positioning reference can only supplement the deficiency of the first positioning reference and cannot be re-positioned in the direction where the first positioning reference has already positioned. N Calculate according to the following formula:

[0054]

[0055] in:

[0056] a 1 - geometric tolerance of the measured element to the first positioning reference;

[0057] a 2 ——Geometric tolerance of the measured element to the positioning straight line on the second positioning reference;

[0058] a 3 ——Geometric tolerance between the second positioning datum and the first positioning datum;

[0059] δ N ——The geometric tolerance of the measured element to the entire second positioning reference.

[0060] The proof process of the above formula is as follows:

[0061] S1. When the first positioning reference and the second positioning reference respectively control the position of the processed element in a non-constant direction, see Figure 2 , Figure 4 , Figure 6 The tolerance requirement of the formula is similar, only Figure 2 Examples of tolerance requirements in:

[0062] like Figure 8 , the first positioning reference plane A is the xoy coordinate plane, the second positioning reference plane B is approximately the yoz coordinate plane, and the processed element plane E is a plane parallel to the coordinate plane xoz. Figure 8 There must be a verticality tolerance a between the first and second positioning datums. 3 / 2r, that is, plane B rotates around the y-axis by an angle of γ. The maximum tolerance can reach the DFGO position; after the first positioning datum of the part and the fixture is fully fitted, due to the existence of angle γ, the second positioning datum of the part can no longer be fully fitted with the second positioning datum of the fixture, and the part will rotate around the z-axis until a straight line OD on the second positioning datum fits the y-axis of the coordinate system. The ideal processed element may reach the HOKM position. The perpendicularity tolerance a of the processed element to the positioning straight line (y-axis) can be guaranteed 2 / 2r. That is, it rotates around the z axis by an angle of β. After processing, the perpendicularity tolerance a of the processed element to the first positioning reference 1 / 2r. That is, it rotates by an angle α around the x-axis. Because the processed element of the part has rotated to the HOKM position around the z-axis. Therefore, it can be approximately considered that the processed element rotates by an angle α (a 1 / 2r). Arrive at the ONPH position. Because the second positioning datum cannot be adjusted during the machining process to ensure that all elements participate in the positioning. It is proved that the verticality tolerance δ of the processed element to the second positioning datum can be guaranteed N / 2r.

[0063] Because there is a verticality tolerance between the first and second positioning datums, this tolerance causes the second positioning datum to rotate around the y axis by a 3 / 2r.

[0064] According to the analytic geometry formula: the three-point form of the plane is

[0065] 2rx+a 3 z=0

[0066] The coordinates of the three points on the second positioning reference plane are:

[0067] O(0, 0, 0)

[0068] G(-a 3 , 0, 2r)

[0069] D(0, -2r, 0)

[0070] Then, the equation for the second positioning reference is:

[0071]

[0072] Right now

[0073] 2rx+a 3 z=0

[0074] Calculation of the processed element equation:

[0075] The verticality a of the processed element to a positioning straight line on the second positioning reference 2 / 2r, indicating that the angle of rotation of the measured element around the z-axis is β(a2 / 2r), reaching the OH position. The verticality of the processed element to the first positioning reference is a 1 / 2r, the processed element will rotate around the x-axis by an angle α (i.e. a 1 / 2r), because the angle β 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 are:

[0076] Point O: (0, 0, 0)

[0077] Point H: (2r, -a 2 ,0)

[0078] Point N: (0, a 1 , 2r)

[0079] Then, the equation of the processed element is:

[0080]

[0081] That is, -a 2 x-2ry+a 1 z=0

[0082] Let the angle between the processed element and the actual second positioning reference be θ.

[0083]

[0084] See attached Fig. 9 As shown in the figure, the angle between the processed element and the second positioning reference when it is perpendicular is:

[0085]

[0086] δ N ——Perpendicularity tolerance of the processed element to the second positioning reference.

[0087] but:

[0088] After calculating and rearranging the above equation

[0089] δ N =a 2 (2)

[0090] It can be seen from this that Figure 2 The processed element plane E of the part shown in the figure uses plane A as the first positioning reference and plane B as the second positioning reference. After processing, the perpendicularity of plane E to plane B can be guaranteed. NIt 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 / jump 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 impact (not too large). It is necessary to carefully operate when using a straight line to represent the entire plane during processing. At the same time, it is recommended that in product design and process design, the element with lower direction requirements should be the second positioning datum among the two pre-selected positioning datums.

[0091] S2. When the second positioning reference and the processed element have two identical non-constant degrees of orientation, refer to Figure 3 , Figure 5 , Figure 7 The tolerance requirement of the formula is similar, only Figure 3 Examples of tolerance requirements in:

[0092] See attached Fig.10 As shown in FIG. 1 , 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. Fig.10 As shown, there is a verticality tolerance a between the first and second positioning datums. 3 / 2r, that is, the actual second positioning reference will rotate around the x-axis by an angle of γ, reaching the maximum OGFD position. After the first positioning reference of the part and the fixture are completely aligned, they can only be rotated around the z-axis until a straight line on the second positioning reference is aligned with the x-axis of the coordinate system. Due to possible adjustments and processing errors during processing, the part is rotated around the z-axis by an angle of β, that is, it is rotated by a tolerance of a. 2 / 2r, reaching the OHLK position. Then, the plane E of the element to be processed is processed to ensure its perpendicularity tolerance a to the first positioning reference 1 / 2r. That is, the maximum rotation angle α around the x-axis. Because the part has reached the OHLK position, it can be approximately considered that the processed element rotates around OH by an angle α (i.e., a 1 / 2r) to reach the OHPN position. It can be seen that the direct relationship between the processed element OHPN and the second positioning reference (plane OGFD) is: the straight line (OH) on the processed element is rotated about the z axis by an angle of β relative to the positioning straight line (x axis), that is, the tolerance a 2 / 2r. This requirement can be met through adjustment. However, the parallelism tolerance δ between the processed element and the second positioning reference cannot be guaranteed. N / 2r!

[0093] Because there is a verticality tolerance a between the first and second positioning references 3 / 2r, which limits the amount of rotation of the second positioning reference around the x-axis. Fig.10 .

[0094] The coordinates of the three points on the second positioning reference plane are:

[0095] O(0, 0, 0)

[0096] G(0, a3, 2r)

[0097] D(2r, 0, 0)

[0098] The equation for the second positioning reference is:

[0099] 2ry-a 3 z=0

[0100] Calculate the equation for the processed element:

[0101] Coordinates of three points on the processed element:

[0102] Point O (0, 0, 0)

[0103] Point N (0, -a1, 2r)

[0104] Point H (2r, -a2, 0)

[0105] The equation of the processed element is:

[0106] a2x+2ry+a1z=0

[0107] The angle θ between the processed element and the actual second positioning reference.

[0108] After sorting and ignoring higher-order infinitesimals

[0109]

[0110] As attached Figure 8 As shown, the angle between the two elements when they are parallel is:

[0111]

[0112] but,

[0113] After sorting and ignoring higher-order infinitesimals

[0114]

[0115] From the above formula, we can see that: Figure 3 After the reference system locates the processing plane E, the parallelism of plane E to the second positioning reference plane C is composed of errors in two different directions.

[0116] Rotation error around the x-axis: a 1 、a 3 ;

[0117] Rotation error around the z axis: a2 .

[0118] Due to the different directions, the vector sum should be taken, which is exactly the same as formula (4).

[0119] From the calculation results we can see that:

[0120] The accuracy of the processed element in the second positioning reference positioning direction (a 2 ) can ensure that the geometric relationship of the processed element to the second positioning reference (δ N ) cannot be guaranteed. This is because please see the attached Figure 3 :The second positioning datum can position the processed element in two rotational degrees of freedom. The design only needs to limit the rotation of the processed element around the z-axis. The 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 element. Can the selection of such a datum system guarantee the product requirements? Product designers should think carefully. If the product requires this requirement, a solution needs to be found during process design.

[0121] As mentioned above, when the first and second positioning references respectively control the position of the processed element in a non-constant direction (such as Figure 2 ). After processing, the position requirements of the processed element to the first and second positioning datums can be guaranteed. The geometric relationship between the processed element and the second positioning datum is calculated using formula (2). This marking method can be used in product design, and the process can be arranged according to this requirement during process design. However, it is best to measure the geometric relationship between the processed element and the second positioning datum after processing is completed, and evaluate whether it is qualified.

[0122] When the second positioning reference and the processed element have two identical non-constant degrees (such as Figure 3 ), the second positioning reference cannot be positioned again in the direction where the first positioning reference has been positioned. However, the second positioning reference still has an error in this direction that cannot be positioned, and this error must be transmitted between the two. During process design, only formula (4) can be used for design and calculation.

[0123] In this method, the above a 1 、a 3 , is the positional relationship between the processed element and the second positioning reference in the same direction to the first positioning reference. The positional relationship between the processed element and the second positioning reference in another direction is a 2 δ N It is the positional relationship between the processed element and the second positioning reference in two directions. 1 、a 3 with a 2 Different directions, δ N The vector sum of the two directions should be taken (proven later).

[0124] A product testing method, measuring the above-mentioned a 1 、a 3 , δ N The actual data, after calculation if necessary. 1 、a 3 , δ N Compare and if the former is not greater than the latter, the product is qualified, otherwise the product is unqualified.

[0125] Features of this application:

[0126] 1. Two or more geometric tolerance requirements should not be marked on one element of a part. If the position in two directions needs to be controlled, it is best to form a reference system to control the position of the processed element. Thus, a variable second positioning reference is generated.

[0127] 2. When the datum system is composed to control the position of the processed element, if the first and second positioning datums have only one non-constant direction in common with the processed element, according to the formula δ N =a 2 Calculation can meet the design requirements. The product must be qualified.

[0128] 3. When the datum system is composed to control the position of the processed element, if the second positioning datum and the processed element have two identical non-constant directions, the formula should be used. Calculation cannot guarantee the design requirements. If the design requires this situation, be cautious. Or reduce a 2 The value of a 1 、a 3 Set aside a certain amount.

[0129] 4. In order to improve the processing accuracy, use the formula Calculation, except for control a 2 In addition, it can also control the direction of the parts placed on the machine tool workbench.

[0130] For other contents, please refer to the prior art.

[0131] The above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several changes and improvements can be made without departing from the overall concept of the present invention, which should also be regarded as the scope of protection of the present invention.

Claims

1. A tolerance control method in machining process design, characterized in that: In product design and mechanical drawing, the tolerance requirements for marking are a1, a3, δ N ; When the first and second positioning datums each control the position of a non-constant degree direction of the processed element; When the second positioning reference is processed, the machine tool table does not rotate and directly processes the processed element; δ N Calculate according to the following formula; δ N =a2; When the second positioning reference and the processed element have two identical non-constant degrees of direction, the second positioning reference can only supplement the deficiency of the first positioning reference and cannot be re-positioned in the direction where the first positioning reference has already positioned. N Calculate according to the following formula: in: a1——Geometric tolerance between the measured element and the first positioning reference; a2——Geometric tolerance of the measured element to the positioning straight line on the second positioning reference; a3——Geometric tolerance between the second positioning datum and the first positioning datum; δ N ——The geometric tolerance of the measured element to the entire second positioning reference.

2. A product detection method, characterized in that: Measuring the product a1, a3, δ as described in claim 1 N The real data is compared with the theoretical values ​​a1, a3, δ N Compare and if the former is less than the latter, the product is qualified, otherwise the product is unqualified.

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