Method for controlling precision of end part of prepreg tow

Abstract

The invention relates to the technical field of automatic forming of composite materials, in particular to a prepreg tow end precision control method which comprises the steps that a prepreg tow end precision control model is established according to cutting edge parameters of a cutter, the laying speed of a prepreg tow and the speed of the cutter in the downward cutting movement process; according to a preset cutting precision range value and the laying speed V1 of the prepreg tow, cutting edge parameters of a cutter are calculated; or according to the preset cutting precision range value and the cutting edge parameters of the cutter, the laying speed V1 of the prepreg tow is calculated. By means of the control method, different laying speeds are matched with cutters with appropriate cutting edge shapes, so that the requirement for cutting precision can be met, and difficulty cannot be brought to cutter machining.

Description

Technical Field

[0001] The invention relates to the technical field of automated composite material forming, and in particular to a method for controlling the precision of a prepreg tow end. Background Art

[0002] With the widespread application of automatic placement technology in large aerospace components, in order to meet the high-efficiency manufacturing of large composite structural parts, increasing the placement speed is the most direct and effective way. However, as the placement speed increases, how to ensure the accuracy of the cut end of the prepreg tow becomes a problem.

[0003] During the cutting process of the automatic placement machine, the factors that affect the end precision of the prepreg tow are mainly the shape of the cutter blade, including the size of the blade inclination angle, the number of blades, etc. At present, the common cutter blades mainly include horizontal straight blades, inclined blades, V-shaped blades and serrated blades. The cutting process of the prepreg tow can be roughly divided into three stages, including the cutter empty blade operation stage, the cutting stage and the cutting stage. For the straight-blade edge, the shearing surface with the prepreg filament bundle during the cutting process is the entire cross-section, and the required cutting force is very large, which makes it difficult to cut, and it is easy to wear and has a short service life. For the inclined blade, its initial shearing surface is a point, and the required cutting force is small, and the cutting efficiency is high. However, during the cutting process, a horizontal force will be generated, causing the filament bundle to deviate to one side, affecting the subsequent wire feeding process. For the V-shaped blade and the serrated blade, the initial contact surface is multiple points, and the shearing surface is a process of gradually cutting two adjacent contact points toward the center. The required cutting force is small and easy to cut, and the wire will not deviate to one side. However, as the number of blades increases, it brings difficulties to tool processing and the economic benefits gradually decrease. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method for controlling the end precision of prepreg tows, matching different laying speeds with cutters with suitable blade shapes, so as to meet the cutting precision requirements without causing difficulties in tool processing.

[0005] The present invention is achieved by adopting the following technical solutions:

[0006] A method for controlling the end precision of a prepreg tow comprises the following steps:

[0007] Step S1. According to the cutting edge parameters of the cutter, the laying speed of the prepreg tow, and the speed of the cutter when cutting downward, a control model for the end precision of the prepreg tow is established:

[0008]

[0009] Where, ε is the cutting accuracy error at the end, V1 is the laying speed of the prepreg tow, V2 is the speed of the cutter when it moves downward, h is the height of the cutter from the prepreg tow, n is the number of cutter edges, θ is the inclination angle of the cutter edge, and d is the width of the cutter;

[0010] Step S2. Calculate the cutting edge parameters of the cutter according to the preset cutting accuracy range value and the laying speed V1 of the prepreg tow; or calculate the laying speed V1 of the prepreg tow according to the preset cutting accuracy range value and the cutting edge parameters of the cutter.

[0011] It also includes introducing the influencing factor α of the placement speed to optimize the control model of the end precision of the prepreg tow in step S1. The optimized control model is:

[0012]

[0013] The influencing factor α of the laying speed is calculated by a reverse verification method.

[0014] The specific calculation method of the influencing factor α of the laying speed is: setting multiple groups of experiments, each group of experiments sets the same cutting knife edge parameters and the speed of the cutting knife when cutting downward, and sets different laying speeds of the prepreg bundles; after the laying is completed, the cutting accuracy error of the corresponding end is measured, and based on the optimized control model, the influencing factor of the laying speed of each group of experiments is obtained, and the average value is taken as the final influencing factor α of the laying speed.

[0015] The method also includes calculating the cutting force F, and comparing the calculated cutting force F with a preset cutting force range value, and controlling the calculated cutting force F to be within the preset cutting force range value through parameter adjustment.

[0016] The calculation method of the cutting force F is:

[0017] F=KdtV2ncosθ

[0018] Where K is the cutting force correction coefficient, d is the cutter width, t is the cutting depth, V2 is the speed of the cutter when it moves downward, n is the number of cutter edges, and θ is the inclination angle of the cutter edge.

[0019] The cutting force correction coefficient K is calculated by a reverse verification method.

[0020] By adjusting the parameters, the calculated cutting force F is controlled within the preset cutting force range value, specifically: if the calculated cutting force is less than the preset cutting force range value, the speed V2 of the cutter's downward cutting movement is increased; if the calculated cutting force is greater than the preset cutting force range value, the speed V2 of the cutter's downward cutting movement and the height h of the cutter from the prepreg tow are reduced.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. The present invention establishes a control method for the precision of the end of the prepreg tow based on the matching relationship between the cutting edge parameters of the cutter, the laying speed of the prepreg tow, and the speed of the cutter when the cutter moves downward. The three are coordinated to control the precision of the rear end of the prepreg tow after cutting. And the control method can easily calculate the cutting precision error of the end of the prepreg tow at different laying speeds, so that the cutter with a suitable cutting edge shape can be selected according to different laying speeds, and the suitable laying speed can also be selected according to the cutting edge shape of the cutter, so that the cutting precision of the end of the prepreg tow meets the requirements, and it will not cause difficulties in tool processing, thereby improving economic benefits.

[0023] 2. During the laying process of the prepreg tow, there is a certain deviation in the laying speed of the prepreg tow on surfaces of different shapes. The influencing factor α of the laying speed is introduced in the present invention to reduce the influence of the laying speed fluctuation on the end precision error.

[0024] 3. The influencing factor α of the laying speed is obtained through reverse verification calculation through multiple groups of experiments. The obtained influencing factor α of the laying speed is more precise.

[0025] 4. The present invention also includes calculating the cutting force F and further adjusting the parameters so that the cutting force F and the cutting accuracy requirements can be met simultaneously during cutting. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, wherein:

[0027] Figure 1 It is a schematic diagram of the process of the present invention;

[0028] Figure 2 The figure is a schematic diagram of the cutters with different edge shapes and the fracture morphology of the cutting ends in the present invention. DETAILED DESCRIPTION

[0029] Example 1

[0030] As a basic embodiment of the present invention, the present invention includes a method for controlling the precision of the end of a prepreg tow, comprising the following steps:

[0031] Step S1. According to the cutting edge parameters of the cutter, the laying speed of the prepreg tow, and the speed of the cutter when cutting downward, a control model for the end precision of the prepreg tow is established:

[0032]

[0033] Where ε is the cutting accuracy error at the end, V1 is the placement speed of the prepreg tow, V2 is the speed of the cutter when it moves downward, h is the height of the cutter from the prepreg tow, n is the number of cutter edges, θ is the inclination angle of the cutter edge, and d is the width of the cutter.

[0034] Step S2: Calculate the cutting edge parameters of the cutter according to the preset cutting accuracy range and the laying speed V1 of the prepreg tow. Alternatively, calculate the laying speed V1 of the prepreg tow according to the preset cutting accuracy range and the cutting edge parameters of the cutter.

[0035] Example 2

[0036] As a preferred embodiment of the present invention, refer to the attached specification Figure 1 The present invention includes a method for controlling the end precision of a prepreg tow, comprising the following steps:

[0037] Step S1. According to the cutting edge parameters of the cutter, the laying speed of the prepreg tow, and the speed of the cutter when cutting downward, a control model for the end precision of the prepreg tow is established:

[0038]

[0039] Where ε is the cutting accuracy error at the end, V1 is the placement speed of the prepreg tow, V2 is the speed of the cutter when it moves downward, h is the height of the cutter from the prepreg tow, n is the number of cutter edges, θ is the inclination angle of the cutter edge, d is the cutter width; α is the influencing factor introduced into the placement speed.

[0040] The influencing factor α of the laying speed is calculated by a reverse verification method.

[0041] Step S2. Calculate the cutting edge parameters of the cutter according to the preset cutting accuracy range value and the laying speed V1 of the prepreg tow; or calculate the laying speed V1 of the prepreg tow according to the preset cutting accuracy range value and the cutting edge parameters of the cutter.

[0042] Example 3

[0043] As another preferred embodiment of the present invention, the present invention includes a method for controlling the precision of the end of a prepreg tow, comprising the following steps:

[0044] Step S1. According to the cutting edge parameters of the cutter, the laying speed of the prepreg tow, and the speed of the cutter when cutting downward, a control model for the end precision of the prepreg tow is established:

[0045]

[0046] Where ε is the cutting accuracy error at the end, V1 is the placement speed of the prepreg tow, V2 is the speed of the cutter when it moves downward, h is the height of the cutter from the prepreg tow, n is the number of cutter edges, θ is the inclination angle of the cutter edge, and d is the width of the cutter.

[0047] Step S2. Calculate the cutting edge parameters of the cutter according to the preset cutting accuracy range value and the laying speed V1 of the prepreg tow; or calculate the laying speed V1 of the prepreg tow according to the preset cutting accuracy range value and the cutting edge parameters of the cutter.

[0048] Step S3. Calculate the cutting force F, and compare the calculated cutting force F with a preset cutting force range value, and control the calculated cutting force F to be within the preset cutting force range value by adjusting parameters.

[0049] The calculation method of the cutting force F is:

[0050] F=KdtV2ncosθ

[0051] Where K is the cutting force correction coefficient, d is the cutter width, t is the cutting depth, V2 is the speed of the cutter when it moves downward, n is the number of cutter edges, and θ is the inclination angle of the cutter edge.

[0052] Furthermore, the cutting force correction coefficient K is calculated by a reverse verification method.

[0053] Example 4

[0054] As the best embodiment of the present invention, the present invention includes a method for controlling the precision of the end of a prepreg tow, comprising the following steps:

[0055] Step S1. During the cutting process of the automatic placement machine, the factors that affect the accuracy of the end of the prepreg tow mainly include the blade shape of the cutter blade, i.e., the cutting edge parameters of the cutter blade, including the size of the cutter blade inclination angle, the number of cutter blades, the width of the cutter, etc.; the placement speed of the prepreg tow; the time of one cutting movement of the cylinder, including the speed of the cutter when cutting downward, the height of the cutter from the prepreg tow, etc. Based on the matching relationship between the three, a control model for the accuracy of the end of the prepreg tow by the cutter blade is established, so that the cutting accuracy error of the end of the prepreg tow under different placement speeds can be easily calculated, so that the cutter with a suitable blade shape can be selected according to different placement speeds, so that the cutting accuracy of the end of the prepreg tow meets the requirements.

[0056] Specifically, according to the cutting edge parameters of the cutter, the laying speed of the prepreg tow, and the speed of the cutter when cutting downward, a control model for the end precision of the prepreg tow is established:

[0057]

[0058] Where ε is the cutting accuracy error at the end, V1 is the placement speed of the prepreg tow, V2 is the speed of the cutter when it moves downward, h is the height of the cutter from the prepreg tow, n is the number of cutter edges, θ is the inclination angle of the cutter edge, and d is the width of the cutter.

[0059] Refer to the instruction manual Figure 2 When the cutter blade is straight, the cutter contacts the entire cross section of the prepreg bundle at the same time during the cutting process. First, when the cutter is not in contact with the prepreg bundle, the time t of the cutter moving downward is h / V2, and the movement distance of the prepreg bundle is V1h / V2. Since the inclination angle θ of the straight blade edge is 0 degrees, tanθ=0, so when cutting the prepreg bundle, the precision error of the cutting end is:

[0060]

[0061] When the cutter blade is single-bevel, after receiving the cutting command, the cutter moves downward at a speed of V2 under the action of the cylinder until the lowest point of the cutter just touches the prepreg tow. At this time, the time used is t=h / V2. The prepreg tow starts to move forward a distance of V1h / V2 within the time t after the automatic fiber laying machine sends the cutting command. Since the cutter blade has a certain inclination angle θ, in order to completely cut off the prepreg tow, the cutter needs to continue to move downward for a certain time t2=(dtanθ) / V2. During the time t2, the prepreg tow moves forward again by (V1dtanθ) / V2. Therefore, for the bevel-shaped blade, the precision error of the end when cutting the prepreg tow is:

[0062]

[0063] When the cutter blade is V-shaped, the motion state is the same as that of the oblique blade. The lowest point of the cutter contacts the prepreg tow first, and the time taken is t=h / V2. The prepreg tow advances a distance of V1h / V2. The difference is that the time t2 taken by the cutter to contact the tow and finally cut off is different, t2=(d tanθ) / 2V2. Therefore, the precision error of the end when cutting the prepreg tow is:

[0064]

[0065] When the number of cutting edges is 4, the operation process of the cutter is similar to that of the V-shaped cutter. The lowest point of the cutter first contacts the prepreg tow, and the time taken is t=h / V2. The prepreg tow advances a distance of V1h / V2. During the cutting process, the time taken for the cutter to contact the tow and finally cut off is t2=(d tanθ) / 4V2. Therefore, the precision error of the end when cutting the prepreg tow is:

[0066]

[0067] Furthermore, during the prepreg tow placement process, there is a certain deviation in the placement speed of the prepreg tow on surfaces of different shapes, so the placement speed influence factor α is introduced to reduce the influence of the placement speed fluctuation on the end precision error. The optimized control model is:

[0068]

[0069] The influencing factor α of the laying speed is calculated by the reverse verification method. Specifically, the specific calculation method of the influencing factor α of the laying speed is as follows: set multiple groups of experiments, each group of experiments sets the same cutting edge parameters and the speed of the cutting knife when the cutting knife moves downward. Set different laying speeds of the prepreg tow, respectively V 1a , V 1b , V 1c After laying, measure the cutting accuracy error of the corresponding end: ε a , ε b , ε c :

[0070]

[0071] The influence factors α1, α2, and α3 of the laying speed of each group of tests are obtained, and the average value is taken as the final influence factor α of the laying speed. The influence factor α of the laying speed can be calculated through more verification tests, and the influence factor α obtained is also more accurate.

[0072] Step S2. Calculate the cutting edge parameters of the cutter according to the preset cutting accuracy range value and the laying speed V1 of the prepreg tow; or calculate the laying speed V1 of the prepreg tow according to the preset cutting accuracy range value and the cutting edge parameters of the cutter.

[0073] Preferably, the method further includes calculating the cutting force F. For different types of prepreg tows, their mechanical properties such as strength and hardness are different, and the cutting force F required to cut the prepreg tows is also different. The calculation method of the cutting force F is:

[0074] F=KdtV2ncosθ

[0075] Wherein, K is the cutting force correction coefficient, d is the cutter width, t is the cutting depth, V2 is the speed of the cutter when it is cutting downward, n is the number of cutter edges, and θ is the inclination angle of the cutter edge. The cutting force correction coefficient K is calculated by the reverse verification method.

[0076] Since the cutter is driven by a cylinder to cut the yarn bundle, increasing the cutting force requires increasing the cylinder pressure, and the speed V2 of the cutter's downward cutting movement also increases accordingly; correspondingly, when the cutting force required to cut the prepreg yarn bundle is small, the cylinder pressure needs to be reduced, and the speed V2 of the cutter's downward cutting movement also decreases accordingly.

[0077] The calculated cutting force F is compared with the preset cutting force range value. If it is within the range, it means that the calculated cutting edge parameters of the cutter meet the requirements. Conversely, the cutting force value can be adjusted by adjusting the cylinder pressure driving the cutter to adjust the speed V2 of the cutter's downward cutting movement so that the cutting force meets the requirements.

[0078] Specifically, if the calculated cutting force is less than the preset cutting force range, the speed V2 of the cutter when it is cutting downward is increased, and the end precision of the prepreg tow is improved to meet the use requirements. If the calculated cutting force is greater than the preset cutting force range, the cylinder pressure should be reduced, the speed V2 of the cutter when it is cutting downward and the height h of the cutter from the prepreg tow should be reduced to maintain the end face precision of the prepreg tow to meet the use requirements.

[0079] In summary, after reading the present invention document, ordinary technicians in this field can make various other corresponding transformation schemes based on the technical scheme and technical concept of the present invention without creative mental labor, which all fall within the scope of protection of the present invention.

Claims

1. A method for controlling the end precision of a prepreg tow, characterized in that: The following steps are involved: Step S1. According to the cutting edge parameters of the cutter, the laying speed of the prepreg tow, and the speed of the cutter when cutting downward, a control model for the end precision of the prepreg tow is established: Where, ε is the cutting accuracy error at the end, V1 is the laying speed of the prepreg tow, V2 is the speed of the cutter when it moves downward, h is the height of the cutter from the prepreg tow, n is the number of cutter edges, θ is the inclination angle of the cutter edge, and d is the width of the cutter; Step S2. Calculate the cutting edge parameters of the cutter according to the preset cutting accuracy range value and the laying speed V1 of the prepreg tow; or calculate the laying speed V1 of the prepreg tow according to the preset cutting accuracy range value and the cutting edge parameters of the cutter.

2. A method for controlling the end precision of a prepreg tow according to claim 1, characterized in that: It also includes introducing the influencing factor α of the placement speed to optimize the control model of the end precision of the prepreg tow in step S1. The optimized control model is:

3. A method for controlling the end precision of a prepreg tow according to claim 2, characterized in that: The influencing factor α of the laying speed is calculated by a reverse verification method.

4. A method for controlling the end precision of a prepreg tow according to claim 3, characterized in that: The specific calculation method of the influencing factor α of the laying speed is: setting multiple groups of experiments, each group of experiments sets the same cutting knife edge parameters and the speed of the cutting knife when cutting downward, and sets different laying speeds of the prepreg bundles; after the laying is completed, the cutting accuracy error of the corresponding end is measured, and based on the optimized control model, the influencing factor of the laying speed of each group of experiments is obtained, and the average value is taken as the final influencing factor α of the laying speed.

5. A method for controlling the end precision of a prepreg tow according to any one of claims 1 to 4, characterized in that: The method also includes calculating the cutting force F, and comparing the calculated cutting force F with a preset cutting force range value, and controlling the calculated cutting force F to be within the preset cutting force range value through parameter adjustment.

6. A method for controlling the end precision of a prepreg tow according to claim 5, characterized in that: The calculation method of the cutting force F is: F=KdtV2ncosθ Where K is the cutting force correction coefficient, d is the cutter width, t is the cutting depth, V2 is the speed of the cutter when it moves downward, n is the number of cutter edges, and θ is the inclination angle of the cutter edge.

7. A method for controlling the end precision of a prepreg tow according to claim 6, characterized in that: The cutting force correction coefficient K is calculated by a reverse verification method.

8. The method for controlling the end precision of a prepreg tow according to claim 6, characterized in that: By adjusting the parameters, the calculated cutting force F is controlled within the preset cutting force range value, specifically: if the calculated cutting force is less than the preset cutting force range value, the speed V2 of the cutter's downward cutting movement is increased; if the calculated cutting force is greater than the preset cutting force range value, the speed V2 of the cutter's downward cutting movement and the height h of the cutter from the prepreg tow are reduced.

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