Method and device for judging vacuum adsorption clamping state of thin-wall part

Abstract

The invention provides a thin-wall part vacuum adsorption clamping state judgment method and device, and the method comprises the steps: 1, calculating a gap phi between the lower surface of a part and the surface of a vacuum clamp according to the actual position of the upper surface of a part web in a vacuum adsorption region and the thickness of the web after vacuum adsorption is started; and 2, a judgment threshold value tau is set according to the machining stage, and the vacuum adsorption clamping state of the thin-wall part is judged by comparing the gap phi with the judgment threshold value tau.

Description

Technical Field

[0001] This invention relates to the field of machining clamping and inspection technology, and in particular to a method and apparatus for determining the vacuum adsorption clamping state of thin-walled parts. Background Technology

[0002] With the advancement of industrial technology, aerospace structural components are gradually moving towards lightweight design, leading to the widespread application of thin-walled parts. Thin-walled is a relative characteristic, related to the span of the part. Large panels and skins, which are weakly rigid parts, also fall into the category of thin-walled parts. Thin-walled parts have poor structural rigidity, making them prone to deformation and difficult to process. To address this core issue of insufficient rigidity, ensuring the rigidity of thin-walled parts during processing is crucial. Enhancing the rigidity of thin-walled parts during processing generally starts with process design and clamping scheme planning, with the clamping support method being paramount. The clamping principle for thin-walled parts is to ensure uniform, sufficient, and stable support while minimizing clamping force. Currently, suitable clamping devices for thin-walled parts include vacuum chucks, specialized contour jigs, low-melting-point alloy fillers, and hydraulic clamps. Among these, vacuum adsorption clamping is widely used due to its advantages such as large support area, uniform clamping stress, strong adaptability, high clamping efficiency, simple operation, and no damage to the part surface, making it an ideal choice for thin-walled, weakly rigid, large-sized, or complex-shaped parts. Vacuum adsorption also has certain limitations. For example, insufficient vacuum level, sudden failure of the vacuum system, and clamping interference can lead to incomplete vacuum adsorption, resulting in excessive wall thickness and affecting part quality. Currently, the inspection of vacuum adsorption clamping status relies heavily on rough judgments of vacuum level, such as manual observation and tapping to listen to sounds. This makes it difficult to accurately and quantitatively determine the degree of adsorption failure and the overall failure state, resulting in low detection accuracy and poor reliability.

[0003] In the field of CNC machining, aerospace structural components are gradually developing towards high added value and high precision. The traditional inspection method that relies on manual experience to check the clamping status is labor-intensive, inefficient, and the skill level of operators varies greatly, resulting in a high degree of randomness. Especially for large parts, in order to fully check the vacuum adsorption clamping status, the operator needs to stand on the part. The added weight of the personnel will inevitably interfere with the detection and judgment of the vacuum status, posing a significant quality risk.

[0004] To address the aforementioned issues, the continuous development of in-machine measurement technology has gradually enabled continuous automated production processes such as automatic alignment, automatic measurement, and automatic compensation machining. This provides a solution for the automatic inspection of vacuum adsorption clamping status. Specifically, in-machine measurement technology automatically measures the actual position of the upper surface of the part being adsorbed. By analyzing the deviation between the actual and theoretical positions, the effectiveness of adsorption is determined, and an automatic warning is issued for ineffective adsorption positions, thus achieving automated inspection of the vacuum adsorption clamping status. The web thickness of the adsorbed part determines the theoretical position of the upper surface. However, existing online measurement devices cannot directly obtain the web thickness of the part. Even using the cumbersome two-sided measurement method assumes no deformation of the web before and after flipping, which is clearly unsuitable for thin-walled parts. Therefore, relying solely on existing online measurement devices is not feasible.

[0005] With the development of online ultrasonic thickness measurement technology, online ultrasonic thickness measurement devices have begun to be applied in the field of CNC online measurement. By mounting an online ultrasonic thickness measurement device on the machine tool spindle, the thickness of CNC parts can be measured and stored on-machine, making up for the shortcomings of existing online measurement devices that cannot directly measure the thickness of the web plate of parts. The combined use of online measurement devices and online ultrasonic thickness measurement devices provides a convenient and feasible solution for the automated inspection of vacuum adsorption clamping status, which is of great significance for realizing the development of CNC machining towards automation and intelligence. Summary of the Invention

[0006] This invention provides a method for determining the vacuum adsorption clamping state of thin-walled parts, which can realize the automatic determination of the vacuum adsorption clamping state.

[0007] Technical solution: In a first aspect, this application provides a method for determining the vacuum adsorption clamping state of thin-walled parts, including: Step 1: After vacuum adsorption is started, calculate the gap φ between the lower surface of the part and the surface of the vacuum fixture based on the actual position of the upper surface of the web of the part in the vacuum adsorption area and the thickness of the web. Step 2: Set the judgment threshold τ according to the processing stage, and judge the vacuum adsorption clamping status of the thin-walled part by comparing the gap φ and the judgment threshold τ.

[0008] Specifically, step 1 includes: Step 11: Measure the thickness δ of the web of the part in the vacuum adsorption region; Step 12: Measure the distance h between the Z0 reference plane and the surface of the vacuum fixture; Step 13: Calculate C based on the positional relationship between the Z0 datum plane and the surface of the vacuum fixture; Step 14: Measure the actual position Pz of the upper surface of the web of the part in the vacuum adsorption area; Step 15: Calculate the gap φ between the lower surface of the part and the surface of the vacuum fixture based on the web thickness δ, distance h, C, and actual position Pz.

[0009] Specifically, step 12 includes: Step 121: Measure the Z-value of the upper surface of the vacuum fixture before clamping the part; Step 122: After clamping the part and starting the vacuum system for adsorption, measure the Z value of the reference plane for setting the machining coordinate system Z0; Step 123: Calculate the distance h based on the absolute value of the difference between the Z value of the upper surface of the vacuum fixture and the Z value of the Z0 reference surface.

[0010] Specifically, step 13 includes: Determine the positional relationship between the Z0 reference edge and the surface of the vacuum fixture; If the Z0 datum plane coincides with the surface of the vacuum fixture, then C=0; if the Z0 datum plane is lower than the surface of the vacuum fixture, then C=-1; if the Z0 datum plane is higher than the surface of the vacuum fixture, then C=1.

[0011] Specifically, step 15 includes: The gap φ between the lower surface of the part and the surface of the vacuum fixture is calculated using the gap calculation formula φ=Pz+C*h-δ.

[0012] Specifically, step 2 includes: Step 21: Determine the judgment threshold τ based on the processing stage; Step 22: Compare the gaps φ and τ. If φ ≤ τ, the vacuum adsorption clamping state of the thin-walled part is valid; otherwise, the vacuum adsorption clamping state of the thin-walled part is invalid. Specifically, step 21 includes: If the processing stage is the roughing stage, the judgment threshold τ is less than the machining allowance after processing; if the processing stage is the finishing stage, the judgment threshold τ is half of the one-sided tolerance based on the median wall thickness. Secondly, this application provides a device for determining the vacuum adsorption clamping state of thin-walled parts, the device being used to implement the above-mentioned method for determining the vacuum adsorption clamping state of thin-walled parts.

[0013] Compared with existing technologies, the advantages of this invention are as follows: The method for determining the vacuum adsorption state of thin-walled parts by combining an online measuring device and an online ultrasonic thickness measuring device provided by this invention can efficiently and accurately determine the adsorption state of each part after vacuum adsorption clamping, improving the accuracy and reliability of inspection. Simultaneously, it achieves automatic inspection of the vacuum adsorption clamping state, and can provide judgment and warnings, reducing manual intervention, improving the efficiency and quality of vacuum adsorption clamping, effectively avoiding wall thickness deviations caused by incomplete local adsorption, eliminating reliance on worker experience, and ensuring the processing quality of thin-walled parts. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the vacuum adsorption clamping state of thin-walled parts; Figure 2 This is a schematic diagram showing the relative position of the machining coordinate system Z0 datum plane and the surface of the vacuum fixture; Figure 3 This is a schematic diagram of the layout rules for the detection points in the vacuum adsorption clamping state; Figure 4 This is an application diagram of the automatic inspection of the vacuum adsorption clamping status of a thin-walled part. Figure 5 This is the result of an automatic check and calculation of the vacuum adsorption clamping status of a thin-walled part. The numbers in the figure are explained as follows: 1. Vacuum adsorption area of ​​the part web; 2. Vacuum fixture surface; 3. Upper surface of the web; 4. Vacuum adsorption fixture; 5. Machining coordinate system; 6. Z0 datum plane; 7. Vacuum adsorption area of ​​thin-walled part; 8. Boundary of vacuum adsorption area of ​​thin-walled part; 9. Detection point. Detailed Implementation

[0015] Example 1 This application provides a method for determining the vacuum adsorption clamping state of thin-walled parts, including: Step 1: Calculate the gap φ between the lower surface of the part and the surface of the vacuum fixture based on the actual position of the upper surface of the web of the part in the vacuum adsorption area and the web thickness δ. like Figure 1 As shown, after vacuum adsorption is initiated, the web 1 of the part in the vacuum adsorption area is adsorbed by the vacuum adsorption fixture 4. If the adsorption is effective, the lower surface of the web is tightly fitted to the surface 2 of the vacuum fixture, and the distance H from the upper surface 3 of the web to the surface 2 of the vacuum fixture is equal to the web thickness δ at the corresponding location. If the adsorption is ineffective, there is a gap φ between the lower surface of the web and the surface 2 of the vacuum fixture, where φ = H - δ. The gap φ is the direct basis for determining the vacuum adsorption state. H cannot be directly measured, but can be determined by online measurement of the actual position P of the upper surface 3 of the web. Z Obtained indirectly. (P) Z It is the Z coordinate value of the upper surface 3 of the web plate, which is measured based on the current machining coordinate system of the workstation.

[0016] Reference Figure 2 There are three scenarios for setting the machining coordinate system 5. Scenario 1: The machining coordinate system Z0 datum plane 6 coincides with the vacuum fixture surface 2, φ=P Z -δ; Case 2: The machining coordinate system Z0 datum plane 6 is lower than the vacuum fixture surface 2, φ=Pz-h-δ; Case 3: The machining coordinate system Z0 datum plane 6 is higher than the vacuum fixture surface 2, φ=Pz+h-δ, where h is the Z-direction distance between the machining coordinate system Z0 datum plane 6 and the vacuum fixture surface 2, which can be obtained by measuring with an online measuring device.

[0017] comprehensive Figure 2 The three cases yield the gap calculation formula φ=Pz+C*h-δ; where, if the Z0 datum plane coincides with the surface of the vacuum fixture, then C=0; if the Z0 datum plane is lower than the surface of the vacuum fixture, then C=-1; if the Z0 datum plane is higher than the surface of the vacuum fixture, then C=1.

[0018] Specifically, step 1 includes: Step 11: Measure the web thickness δ of the web 1 of the part in the vacuum adsorption region.

[0019] Step 12: Measure the distance h between the machining coordinate system Z0 datum plane 6 and the vacuum fixture surface 2; Where h is the Z value of the vacuum fixture surface 2 measured before clamping the part, with the machine tool coordinate system as the reference. After clamping the part and starting the vacuum system for adsorption, the Z value of the machining coordinate system Z0 reference surface 6 is measured again, and the difference between the two is taken as the absolute value.

[0020] Step 13: Measure the actual position Pz of the upper surface 3 of the web of the part in the vacuum adsorption area; Step 14: Determine the positional relationship between the machining coordinate system Z0 reference plane 6 and the vacuum fixture surface 2; if the Z0 reference plane 6 coincides with the vacuum fixture surface 2, then C=0; if the Z0 reference plane 6 is lower than the vacuum fixture surface 2, then C=-1; if the Z0 reference plane 6 is higher than the vacuum fixture surface 2, then C=1. Step 15: Calculate the gap φ between the lower surface of the part and the surface of the vacuum fixture according to the gap calculation formula φ=Pz+C*h-δ.

[0021] Step 2: Set the judgment threshold τ according to the processing stage, and judge the vacuum adsorption clamping status of the thin-walled part by comparing the gap φ and the judgment threshold τ. Step 2 specifically includes: Step 21: If the machining stage is roughing stage, the threshold τ is less than the machining allowance after machining; if the machining stage is finishing stage, the threshold τ is half of the one-sided tolerance based on the median wall thickness. It should be noted that the judgment threshold τ is set according to the roughing and finishing stages of the machining process. The vacuum adsorption state judgment threshold before the final finishing process is defined by the roughing threshold. The roughing threshold can be appropriately increased. For example, for the vacuum adsorption state check before roughing and semi-finishing, the threshold should be less than the machining allowance after machining, which ensures both accuracy and economic benefits. In the finishing stage, the primary goal is to ensure machining accuracy. Based on the wall thickness tolerance of the part, the finishing threshold is set to half of the one-sided tolerance based on the median wall thickness, to prevent the part wall thickness from exceeding the tolerance or approaching the tolerance limit.

[0022] Step 22: Compare the gaps φ and τ. If φ ≤ τ, the vacuum adsorption clamping state of the thin-walled part is valid; otherwise, the vacuum adsorption clamping state of the thin-walled part is invalid.

[0023] Example 2 Step 1: Based on the shape of the vacuum adsorption clamping area of ​​the thin-walled part and the specific structural characteristics of the part, plan and lay out the inspection points and mark them with serial numbers; like Figure 3 As shown, step 1 includes: based on the vacuum adsorption area 7 and the boundary 8 of the vacuum adsorption area of ​​the thin-walled part, and combined with the specific structural characteristics of the part, planning and laying out the detection points 9 and marking them with serial numbers. It should be noted that when planning the layout of detection point 9, the number of detection points should be minimized while covering the adsorption area 7, and the adsorption state of detection point 9 can effectively radiate to the surrounding area. For large-area thin-walled web areas, the step distance is planned to be within 300mm, and the measurement points are arranged at a distance of about 50mm from the boundary of the vacuum adsorption area to avoid incomplete boundary adsorption caused by interference between the process bosses or material frames and tooling around the parts.

[0024] Step 2: Based on the planned detection points, develop an automatic judgment program for the vacuum adsorption clamping status of thin-walled parts; Specifically, step 2 includes: Step 21: Online ultrasonic thickness measurement program for web thickness δ; Step 22: Position P on the upper surface of the web Z Online measurement program; Step 23: Comparison and judgment calculation procedure; It should be noted that the online ultrasonic thickness measurement program and online measurement program are compiled in sequence according to the detection point number to ensure that the detection positions correspond one-to-one, which facilitates subsequent comparison and calculation.

[0025] Step 3: Execute the automatic determination program for the vacuum adsorption clamping status of thin-walled parts, and sequentially execute the online ultrasonic thickness measurement program, the online measurement program, and the comparison and determination calculation program; Step 4: Output the judgment result. If there are invalid adsorption points, the invalid point number will be automatically alerted to remind the operator to handle it.

[0026] After the operator has investigated the cause and handled the fault, they must continue to execute the online ultrasonic thickness measurement program, the online measurement program, and the comparison and judgment calculation program until all point judgment results are valid and the vacuum adsorption clamping status check is completed before subsequent processing can proceed.

[0027] Example 3 like Figure 4 As shown, this embodiment takes the automatic inspection process of vacuum adsorption clamping status of a thin-walled double-sided slotted frame part as an example to further illustrate the solution of the present invention. The web of the thin-walled double-sided slotted frame part consists of two parallel planes, but this method is applicable to double-sided structures composed of parallel curved surfaces, non-parallel planes, and non-parallel curved surfaces. One side of the part is a large web surface, and the other side has multiple slots. In this embodiment, the large web surface is first finished when the slot side has a large allowance, sufficient rigidity, and no support is required. Then, the slot surface is machined. This machining station has insufficient rigidity and is the final process to ensure the part's accuracy, so vacuum adsorption clamping is required. The CNC system is a Sinumerik 840D, but other CNC systems are also applicable.

[0028] The first step is to establish a comparison and judgment model. 1) For example... Figure 4 As shown, the machining coordinate system Z0 reference plane 6 is lower than the vacuum fixture surface 2, so C=-1, and the gap calculation formula φ=Pz-h-δ is established; 2) According to the machining stage, the judgment threshold τ is reasonably set. Taking finishing as an example, the finishing stage should first ensure the machining accuracy. According to the wall thickness tolerance of the part ±0.2, the threshold is set to half of the single-sided limit tolerance based on the median wall thickness, i.e., τ=0.1. The final comparison judgment model is: Pz-h-δ≤0.1.

[0029] The second step is to plan and lay out the testing points. For example... Figure 4 As shown. 1) Based on the shape of the vacuum adsorption clamping area of ​​the thin-walled part and the distribution characteristics of the part's cavity, the area of ​​each cavity is approximately 230mm × 230mm. The detection points are set in the middle of the cavity, and the detection points are arranged at a distance of about 50mm from the boundary of the vacuum adsorption area, for a total of 35 detection points; 2) The detection points are numbered from left to right and from top to bottom, from 1 to 35.

[0030] The third step is to develop an automatic inspection program for the vacuum adsorption clamping status of thin-walled parts. Following the numbering sequence of inspection points 1-35, an online measurement program, an online ultrasonic thickness measurement program, and a comparison and judgment calculation program are developed sequentially.

[0031] The fourth step is to execute the automatic inspection program for the vacuum adsorption clamping status of thin-walled parts, and to collect and judge measurement data. 1) Before and after clamping, using an online measuring device with the machine tool coordinate system as the reference, measure the Z value of the upper surface of the vacuum fixture and the Z value of the reference surface of the machining coordinate Z0 after adsorption clamping. The absolute value of the difference between the two is taken to obtain h=35.01; 2) Execute the online measurement program (measure and store Pz of 35 detection points), the online ultrasonic thickness measurement program (measure and store δ of 35 detection points), and the comparison and judgment calculation program in sequence, and finally give the judgment results of each detection point and output a report; 4) The online measurement values ​​and online ultrasonic thickness measurement values ​​of 1-35 detection points are as follows: Figure 5 The comparison report shows that all judgment results are T (T represents effective vacuum adsorption, F represents ineffective vacuum adsorption), indicating that the overall adsorption state of the part meets the requirements of the current processing stage and can proceed with subsequent processing. However, the gap values ​​at detection points 1-7 and 29-36 are too large, close to the judgment threshold of 0.1, and are concentrated near the two side edges of the part in the Y direction. After investigation, detection points 1-7 and 29-36 are the connection area of ​​the process boss. Checking the dimensions of the process boss, it was found that the Z-direction dimension of the boss is too large, causing over-positioning interference. After revising the dimensions of the process boss, the phenomenon disappeared. Therefore, the Z-direction dimension of the process boss should be strictly controlled during subsequent processing of this part to avoid affecting the vacuum adsorption effect.

Claims

1. A method for determining the vacuum adsorption clamping state of a thin-walled part, characterized in that, include: Step 1: After vacuum adsorption is started, calculate the gap φ between the lower surface of the part and the surface of the vacuum fixture based on the actual position of the upper surface of the web of the part in the vacuum adsorption area and the thickness of the web. Step 2: Set the judgment threshold τ according to the processing stage, and judge the vacuum adsorption clamping status of the thin-walled part by comparing the gap φ and the judgment threshold τ.

2. The determination method according to claim 1, characterized in that, Step 1 includes: Step 11: Measure the thickness δ of the web of the part in the vacuum adsorption region; Step 12: Measure the distance h between the Z0 reference plane and the surface of the vacuum fixture; Step 13: Calculate C based on the positional relationship between the Z0 datum plane and the surface of the vacuum fixture; Step 14: Measure the actual position Pz of the upper surface of the web of the part in the vacuum adsorption area; Step 15: Calculate the gap φ between the lower surface of the part and the surface of the vacuum fixture based on the web thickness δ, distance h, C, and actual position Pz.

3. The determination method according to claim 2, characterized in that, Step 12 includes: Step 121: Measure the Z-value of the upper surface of the vacuum fixture before clamping the part; Step 122: After clamping the part and starting the vacuum system for adsorption, measure the Z value of the reference plane for setting the machining coordinate system Z0; Step 123: Calculate the distance h based on the absolute value of the difference between the Z value of the upper surface of the vacuum fixture and the Z value of the Z0 reference surface.

4. The determination method according to claim 2, characterized in that, Step 13 includes: Determine the positional relationship between the Z0 datum plane and the surface of the vacuum fixture; If the Z0 datum plane coincides with the surface of the vacuum fixture, then C=0; if the Z0 datum plane is lower than the surface of the vacuum fixture, then C=-1; if the Z0 datum plane is higher than the surface of the vacuum fixture, then C=1.

5. The determination method according to claim 2, characterized in that, Step 15 includes: The gap φ between the lower surface of the part and the surface of the vacuum fixture is calculated using the gap calculation formula φ=Pz+C*h-δ.

6. The determination method according to claim 1, characterized in that, Step 2 includes: Step 21: Determine the judgment threshold τ based on the processing stage; Step 22: Compare the gaps φ and τ. If φ ≤ τ, the vacuum adsorption clamping state of the thin-walled part is valid; otherwise, the vacuum adsorption clamping state of the thin-walled part is invalid.

7. The determination method according to claim 6, characterized in that, Step 21 includes: If the processing stage is the roughing stage, the judgment threshold τ is less than the machining allowance after processing; if the processing stage is the finishing stage, the judgment threshold τ is half of the one-sided tolerance based on the median wall thickness.

8. A device for determining the vacuum adsorption clamping state of thin-walled parts, characterized in that, The determination device is used to implement the method for determining the vacuum adsorption clamping state of thin-walled parts according to any one of claims 1 to 7.

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