CN110580363B - Topological optimization design method for base structure of friction stir welding robot - Google Patents
Topological optimization design method for base structure of friction stir welding robot Download PDFInfo
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Abstract
The invention relates to the field of structural analysis of friction stir welding robots, in particular to a topological optimization design method of a friction stir welding robot base structure, which comprises the following steps of 1: determining an analysis factor; step 2: dynamically optimizing and designing the base to obtain a base topology optimized structure; and step 3: the relation between the sand outlet holes of the rib grid units and the inherent frequency of the rib grid units is further optimized; and 4, step 4: further optimizing the relation between the wall thickness and the side length of the rib plate of the rib grid unit and the inherent frequency of the rib grid unit; and 5: further optimizing the unit density of the rib grids in the base, and determining the number of the rib grid unit layers and the size of a base frame; step 6: and verifying the optimal scheme of the base structure. The invention finds the design variables sensitive to the optimization target of the base structure through finite element analysis, and obtains a group of optimal solutions of the design variables in a multi-target weighted optimization algorithm based on designation, finally, a reasonable scheme of structural design is provided for improving the comprehensive dynamic performance of the base structure.
Description
Technical Field
The invention relates to the field of structural analysis of friction stir welding robots, in particular to a topological optimization design method of a friction stir welding robot base structure.
Background
Friction Stir Welding (FSW) is a novel, energy-saving, environment-friendly and efficient solid phase connection technology invented by British welding research institute in 1991. The technology is mainly applied to the connection of low-melting-point light metal materials such as aluminum alloy, magnesium alloy and the like at the beginning of the development, so as to solve the problems of air holes, weakened joint strength, unstable joint quality and the like which are often caused by welding the materials by the conventional fusion welding method. With the development of research and the maturity of the technology, the friction stir welding technology has been popularized and applied to the connection of some dissimilar materials with high melting points, such as titanium alloy, aluminum alloy, stainless steel and the like. Meanwhile, the friction stir welding has the advantages of small deformation, small stress, unobvious strength weakening and the like, and is widely applied to the industrial manufacturing fields of aerospace, rail transit, ship manufacturing, automobile manufacturing, nuclear power energy, digital products and the like. Over 20 years only, research into friction stir welding technology has been directed to welding processes, joint performance, process simulation, equipment development, and the like. Research on such welding equipment has been focused on the optimization design of the stirring head, and in recent years, attention has been focused on the development of numerical control systems for structural design of friction stir welding equipment.
As shown in fig. 1, the friction stir welding robot in the prior art mainly includes three parts, namely a welding body, an a-B shaft and a stirring head, wherein the welding body includes a base, an upright post, a ram, and the like, the a-B shaft and the stirring head are mounted at the front end of the ram, in addition, a workpiece is placed on a turntable and rotates along with the turntable when the device works, the whole robot therefore includes 7 degrees of freedom altogether, which are X, Y, Z three degrees of freedom realized by the welding body, 2 rotational degrees of freedom realized by the a-B shaft, a telescopic degree of freedom of the stirring head, and a rotational degree of freedom of the turntable, wherein X, Y, Z three degrees of freedom are mainly realized by driving and moving through a guide rail slider pair and a ball screw pair. The base, the upright post, the saddle and other large structures of the existing robot are mainly cast by gray cast iron, the ram and the like are main bearing structural members, the existing robot is of a cantilever structure and is welded and manufactured by alloy steel to ensure the rigidity of the whole robot, a rotary table is removed, the mass of the whole robot is about 71 tons, the outer envelope size of the whole robot is about 1.8m multiplied by 1.6m, the reduction is needed, and the welding speed, the rotation speed, the pressing amount, the axial pressure, the torque and the like in the friction stir welding process all influence the welding process to further influence the welding quality, for example, the stirring head is stressed greatly in the friction stir welding process, the welding equipment structure is easy to deform to cause deviation of the welding position, so the structure optimization is needed while the equipment weight is reduced to ensure the whole rigidity of the equipment. In the entire weight of the robot, the base occupies a large specific gravity as a support body, and therefore, optimization of the base is one of the keys to reduction and structural optimization of the robot.
Disclosure of Invention
The invention aims to provide a topological optimization design method of a base structure of a friction stir welding robot, which finds design variables sensitive to the optimization target of the base structure through finite element analysis, and obtains a group of optimal solutions of the design variables in a multi-target weighting optimization algorithm based on designation, and finally provides a reasonable scheme of the structural design for improving the comprehensive dynamic performance of the base structure.
The purpose of the invention is realized by the following technical scheme:
a topological optimization design method for a base structure of a friction stir welding robot comprises the following steps:
step 1: determining analysis factors, wherein the factors influencing the dynamic characteristics of the base structure comprise rib grid units consisting of rib plates and sand outlets in the base and a frame of the base;
step 2: dynamically optimizing and designing the base to obtain a base topology optimized structure;
and step 3: on the basis of the base structure after topological optimization in the step 2, the inherent frequency relation between the sand outlet holes of the rib grid units and the rib grid units is further optimized, and the shape, the aperture and the number of the sand outlet holes are determined;
and 4, step 4: on the basis of the step 3, further optimizing the relation between the rib plate wall thickness and the side length of the rib grid unit and the inherent frequency of the rib grid unit, and determining the proportional relation between the rib plate wall thickness of the rib grid unit and the side length of the rib grid unit;
and 5: on the basis of the step 4, further optimizing the rib cell density in the base, and determining the number of rib cell layers and the size of the base frame;
and 6: and 5, verifying the optimal scheme of the base structure obtained in the step 5.
In the step 2, grid division is carried out on the base by adopting a full hexahedral grid in software, the fixing positions of the guide rail, the sliding block, the screw rod mounting seat and the bolt are defined as non-design domains, other parts are design domains, a variable density method is adopted, a material part with unit density larger than 0.3 is reserved, and finally the topology optimized structure of the base is obtained.
In step 3, selecting the sand outlet 105 to be a round hole or a square hole, performing modal analysis in software to compare the two hole types, determining that the sand outlet is round, performing modal analysis in software to determine that the aperture of the sand outlet accounts for 40% -50% of the total length of the side length of the rib grid unit, and opening 4 or 6 sand outlets on the rib grid unit, wherein each sand outlet is respectively opened on different planes of the rib grid unit.
In the step 3, 6 sand outlets are preferably formed in the rib grid unit.
In step 4, modal analysis is carried out in software to determine that the integral first-order natural frequency of the rib grid unit is reduced along with the increase of the side length of the rib grid unit, and the thickness of the rib plate needs to be increased reasonably in the rib grid unit designing process.
In the step 4, the ratio of the rib plate wall thickness of the rib grid unit to the side length of the rib grid unit is preferably 5-10%.
And step 5, determining that the rib grid cells of the base are distributed with an optimal density interval by performing modal analysis in software, and determining the number of layers and the interval of the rib grid cells according to the optimal density interval during design.
In step 5, when designing the base, the base frequency needs to avoid the first-order natural frequency of the whole machine.
The above steps all adopt the software as hypermesh software.
The invention has the advantages and positive effects that:
1. according to the invention, through finite element analysis, design variables sensitive to the optimization target of the base structure are found, a group of optimal solutions of the design variables in a designated multi-objective weighted optimization algorithm are obtained, and finally, a reasonable scheme of the structural design is given for improving the comprehensive dynamic performance of the base structure.
2. The invention firstly carries out topology optimization analysis on the base structure, adopts the full hexahedral mesh to carry out mesh division, adopts a variable density method to obtain the topology optimized structure of the base, and then further optimizes other structures on the structure basis to ensure that the dynamic performance of the base structure is improved to the maximum extent.
3. In order to quantify the influence of the proportion percentage of the length, the width and the height of the rib grid units on the integral natural frequency of the rib grid, the three-dimensional size of the rib grid units is taken as a design variable to carry out various optimization analyses, and the highest fundamental frequency of the rib grid units is realized while the lightest integral quality of the rib grid structure is ensured.
4. The invention verifies the optimized X-axis base structure of the robot, improves the static and dynamic stiffness of the base simultaneously, and shows that the dynamic optimization design process adopting the base structure frame and the rib plate structure unit is feasible.
Drawings
FIG. 1 is an overall composition diagram of a friction stir welding robot,
figure 2 is a schematic view of the base of figure 1 taken as the X-axis,
figure 3-1 is a schematic view of the topology optimization of the base structure one,
figure 3-2 is a schematic view of the topology optimization of the base structure two,
figure 4-1 is a schematic view of a rib grid inside the base,
figure 4-2 is a schematic view of another rib grid inside the base,
FIG. 5 is a schematic diagram showing the relationship between rib size and rib thickness and frequency,
figure 6 is a schematic view of a rib grid in a cross-sectional view of a base structure,
figure 7 is a schematic diagram of the variation of the X-axis fundamental frequency with the base height,
figure 8-1 is a 3D model of a base of a ribbed structure,
figure 8-2 is another 3D model of the base in a rib grid configuration,
figure 9 is a first graph of a static analysis of the base of a circular sand hole,
figure 10 is a second graph of the static analysis of the base of a circular sand hole,
FIG. 11-1 is a modal analysis diagram of a circular sand outlet,
figure 11-2 is a modal analysis of a square sand outlet,
figure 12 is a schematic comparison of round and square sand outlets,
figure 13 is a bar grid cell layer number modal analysis plot,
FIG. 14 is a schematic diagram of the penalty effect of different penalty factors on density when the variable density method is used for analysis.
The device comprises a base 1, a guide rail 101, a lead screw mounting base 102, a grating ruler 103, a rib plate 104, a sand outlet 105, a hoisting hole 106, a foundation bolt mounting frame 107, a travel switch 108, a stand column 2, a ram 3, a turntable 4, a saddle 5 and a guide rail slider pair 6.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1, the welding body part of the friction stir welding robot includes a base 1, a column 2, a ram 3, a turn table 4, and the like, wherein the column 2 as the Y axis is located between the base 1 of the X axis and the ram 3 of the Z axis. The connection position of the upright post 2 and other large-scale component structures is more, so the loading condition is relatively complex, wherein the lower bottom surface of the upright post 2 is connected with the base 1 through a guide rail slider pair and a ball screw pair, the front end surface and the rear end surface of the upright post 2 and the two inner end surfaces are also connected with the saddle 5 on the ram 3 through a guide rail slider pair 6 and a ball screw pair, and the connection structures are all known in the art.
As shown in fig. 2, the base 1 mainly includes an internal rib plate 104, a sand outlet 105, an external guide rail 101, an anchor bolt mounting frame 107, a hoisting hole 106, a lead screw mounting base 102, a grating scale 103, a travel switch 108, and the like. In order to research various dynamic performances of the structure of the X-axis base 1, different external frame sizes and internal structure unit styles are required to be combined, design variables and target responses for optimizing analysis problems are specified, design variables sensitive to the structure optimization target of the base 1 are found through finite element analysis, a group of optimal solutions of the design variables in a multi-target weighting optimization algorithm based on the specification are obtained, and a reasonable scheme of the structural design is finally given for improving the comprehensive dynamic performance of the structure of the base 1.
The specific process is as follows:
step 1: determining analysis factors, wherein the factors influencing the structural dynamic characteristics of the X-axis base 1 comprise rib grid units formed by rib plates 104 and sand outlets 105 in the base 1 and an external frame of the whole base 1.
As shown in fig. 2, the rib plate 104, the sand outlet 105, the guide rail 101, and the anchor bolt mounting frame 107 in the structure of the base 1 can be analyzed as separate structural units, and the hoisting hole 106, the lead screw mounting seat 102, the grating scale 103, and the travel switch 108 have little influence on the dynamic characteristics of the structure of the X-axis base 1, and can be ignored. Three guide rails 101 are installed on the upper top surface of the X-axis base 1, and due to the material and layout of the guide rails 101, the rigidity of the structure of the base 1 is significantly enhanced, but in order to simplify the scale of the problem, the structures may be temporarily disregarded in the preliminary optimization analysis process. Similarly, the geometrical dimensions of the anchor bolt mounting frame 107 vary within a relatively small range, with little effect on the rigidity of the foundation 1, and can be temporarily disregarded.
The analysis can determine that the factors influencing the dynamic characteristics of the X-axis base 1 structure only include the rib cell pattern and the rib cell basic size formed by the rib plates 104 and the sand outlet holes 105 in the base 1 and the frame size of the whole base 1.
And 2, step: and (4) dynamically optimizing the design of the base 1 to obtain the topology optimized structure of the base 1.
In order to reduce the weight as much as possible, the base 1 structure is firstly subjected to topology optimization analysis.
In hypermesh software, as shown in fig. 3-1, a full hexahedral mesh is adopted to perform mesh division on a base 1, the guide rail 101, the sliding block, the lead screw mounting seat 102 and the bolt fixing position are defined as non-design domains, other parts are design domains, a variable density method is adopted, a material part with unit density larger than 0.3 is reserved, and finally a topology optimized structure of the base 1 is obtained as shown in fig. 3-2. The density-variable method is a known technology in the field, and the basic principle is to adopt a hypothetical material with adjustable density, and determine the removal of the material through the pseudo density of a unit, specifically: during optimization, the density of the unit is taken as a design variable, the objective function of the unit can be the rigidity, the flexibility, the fundamental frequency and the like of the structure, wherein the material characteristic of topological optimization is an exponential function of the density of the unit, and the expression is as follows:
E(x)＝E 0 ρ(x) P (1-1)
in the above formula 1-1: e (x) is the elastic modulus of the structure; e 0 Initial modulus of elasticity for the structure; ρ is the relative density of the material; p is a penalty factor. The penalty factor P can promote the relative density of the units to be close to 0 or 1 to clearly show the distribution position of the material after topology, and the variation curve of the elastic modulus of the structure with the relative density is shown in fig. 14 under the condition of different penalty factors.
And step 3: and (3) further optimizing the relation between the rib grid unit sand outlet 105 and the inherent frequency of the rib grid unit on the basis of the topology optimized base 1 structure obtained in the step (2), and determining the shape, the aperture and the number of the sand outlet 105.
The interior of the X-axis base 1 of the friction stir welding robot is filled with structural units of different styles instead of a complete entity, so that the weight of the structure is greatly reduced while the robot base 1 is ensured to have good rigidity, and the cost is saved. The structural units forming the interior of the X-axis base 1 of the robot are rib grid units, and the upper top surface of the base 1 structure including the guide rail 101 mounting surface is supported by the rib grid units. The cavities of the rib lattice units are not closed, which mainly takes the factors in the aspect of casting processing technology into consideration, generally, a certain number of holes, namely, sand outlets 105, need to be opened on the cavities, and from the viewpoint of production and the like, generally, the sand outlets 105 are selected from round holes or square holes, the rib lattice units when the sand outlets 105 are round holes are shown in fig. 4-1, and the rib lattice units when the sand outlets 105 are square holes are shown in fig. 4-2.
According to the finite element analysis result, the rib plates 104 of the rib grid units are weak links of the whole frame structure, the first two-stage vibration modes of the rib plates 104 are mainly expressed as 'breathing' vibration of the rib plates 104 and torsional vibration of the whole rib grid units, and the torsional vibration has a serious influence on the deformation of the guide rail surface on the base 1, so that the influence factor needs to be reduced to the minimum. In addition, since the length, width, height, and size of the rib lattice unit and the shape and size of the sand outlet 105 have a great influence on the modal frequency and the mode shape of the whole rib lattice structure, it is also necessary to study the dynamic performance of the rib lattice based on these several influencing factors, and by simplifying the dynamic performance into a hexahedron composed of three-dimensional solid units as shown in fig. 4-1 and 4-2, the three-dimensional size l of the framework of the rib lattice and the size d of the sand outlet 105 are set as design variables, and the first four-order modal frequency of the structure is taken as a target function.
The method comprises the following specific steps:
the rib lattice unit is assumed to be a cubic structure with a side length of l =300mm, an elastic modulus of 1.73 × 1011Pa, a density of 7600kg/m3, and a poisson's ratio of 0.3. The sand outlet holes 105 are formed in four faces, the shapes of the holes are respectively circular and square, the hole opening position is located in the center of every two opposite faces, the specific style of the structural unit is changed by changing the size of the sand outlet holes 105 and the number of the sand outlet holes 105, and finally, frequency data curves and modal vibration of each step of the rib grid unit are obtained in hypermesh software through modal analysis.
As shown in FIGS. 11-1 and 11-2, it can be found by analysis that:
(1) The larger the aperture of the sand outlet 105 of the rib grid unit is, the smaller the first-order natural frequency of the rib grid unit is.
(2) As for the circular sand outlet 105, as shown in fig. 11-1, it can be found from the mode analysis of hypermesh software that when the aperture d of the circular sand outlet 105 occupies about 40% -50% of the total length of the side length l of the rib grid unit, the fundamental frequency of the rib grid unit starts to significantly decrease, when the number of the circular sand outlets 105 of the rib grid unit is 2 or 4, the fundamental frequencies of the rib grid unit in the two cases are relatively close, and when the number of the circular sand outlets 105 is increased to 6, that is, each face is opened, the overall mass of the rib grid unit is significantly reduced and the vibration form of the rib grid unit is changed, so that the first-order natural frequency of the obtained rib grid unit is relatively high.
(3) For the square sand outlet 105, as shown in fig. 11-2, it can be found from the mode analysis of hypermesh software that, as the side length of the square sand outlet 105 increases, the natural frequency of the rib lattice unit gradually decreases, and when the side length d of the square sand outlet 105 accounts for more than 40% of the side length l of the rib lattice unit, the fundamental frequency of the rib lattice unit starts to significantly decrease, and when 2, 4, or 6 square sand outlets are opened on the rib lattice unit, the fundamental frequency of the rib lattice unit has a small difference.
The basic principle of rib grid unit selection of the base 1 structure can be determined through the analysis: on the premise of ensuring the rigidity of the robot X-axis base 1, the aperture of the sand outlet 105 should be moderate (i.e. the aperture d accounts for 40% -50% of the total length of the side length l of the rib grid unit) and the number of the sand outlet is large, so as to reduce the weight of the structure as much as possible, and as shown in fig. 12, as can be known from modal analysis, the rib grid unit adopting the circular sand outlet 105 is more advantageous than the rib grid adopting the square sand outlet 105, the first 4 th order natural frequency of the whole circular sand outlet 105 is higher, and as a result of comparing the base frequencies of the 6 circular hole rib grid units and the 6 square hole rib grid units, the modal frequency of each order of the rib grid units does not change significantly with the number of the sand outlets under the condition that the aperture or the ratio of the aperture d of the sand outlet 105 to the side length l of the rib grid units is not too large. Therefore, 4 or 6 sand outlets can be formed in the rib grid unit of the X-axis base 1 of the robot, and a better rib grid unit structure with 6 round holes can be relatively selected to reduce the weight of the base to the maximum extent.
And 4, step 4: on the basis of the step 3, the relation between the wall thickness and the side length of the rib cell unit rib plate 104 and the natural frequency of the rib cell unit is further optimized, and the proportional relation between the wall thickness and the side length of the rib cell unit rib plate 104 is determined.
In designing the rib plate 104 arrangement of the robot base 1, it is sometimes difficult to make the rib cells exactly square, which is subject to other size limitations and restrictions on the overall structure. However, when the length-width-height ratio of the rib lattice units is greatly different, the torsional vibration mode is easy to occur, which will result in lower fundamental frequency of the whole rib lattice unit, so that in order to quantify the influence of the percentage of the length, the width and the height of the rib lattice units on the integral natural frequency of the rib lattice, the three-dimensional size of the rib lattice unit needs to be regarded as a design variable.
The size of the X-axis base 1 of the robot is optimized, the integral layout of the rib grid unit structure in the robot is still kept, the natural frequency of the rib grid can be changed to a certain extent, and the rib grid unit structure can be influenced by the size of the rib grid. The rib lattice unit structure in fig. 4-1 is taken as a research object, as shown in fig. 5, a change relation curve of a first-order natural frequency of a rib lattice unit under the conditions of different side lengths and different rib plate 104 thickness ratios is obtained through modal analysis in hypermesh software, wherein the diameter d of a specified circular sand outlet 105 accounts for 40% -50% of the total length of the side length l of the rib lattice unit, the number of the sand outlet is six, each surface of the rib lattice unit is provided with a hole, meanwhile, the ratio of the rib plate 104 wall thickness of the rib lattice unit to the side length of the rib lattice unit is set to be 5% -10%, as shown in fig. 5, the integral first-order natural frequency of the rib lattice unit is reduced along with the increase of the side length of the rib lattice unit, and is reduced along with the reduction of the wall thickness of the rib plate 104, so that the thickness of a rib plate is reasonably increased in the rib lattice unit design process, and the integral quality of the rib lattice unit structure is guaranteed to be the lightest.
And 5: and (4) further optimizing the rib cell density in the base 1 on the basis of the step 4, and determining the number of rib cell layers and the frame size of the base 1.
As shown in fig. 6, a cross-sectional structure of the X-axis base 1 of the friction stir welding robot along a plane parallel to the ground is shown, wherein the fundamental frequency of the X-axis base 1 and the vibration mode of each order vibration mode can cause the robot to have a large influence on the welding precision of the workpieces to be welded, and the modal analysis result of the structure of the X-axis base 1 is limited by the external frame size and the internal rib cell density configuration of the whole base. We elaborate by way of example by studying the relationship of these two factors to the natural frequency of the rib grid as a whole.
In one design example, given the three-dimensional dimensions of the robot X-axis base 1 structure, length, width and height of 3000mm, 1600mm and 500mm, respectively, the rib grid cell arrangement strategy of the base 1 still follows the design of a cube. The number of layers of the rib grid unit along the height direction of the base 1 is a design variable to be solved, the maximum number of the layers is not more than 6, the thickness of the rib plate 104 of the rib grid unit is 15mm, other parameters are the same as those of the rib grid unit in the step 4, the ratio of the wall thickness of the rib plate 104 of the rib grid unit to the side length of the rib grid unit is set to be 5% -10%, the diameter d of the circular sand outlet 105 accounts for 40% -50% of the total length of the side length of the rib grid unit, the number of the sand outlet is six, and each surface of the rib grid unit is provided with one hole, then the natural frequency of the X-axis base 1 formed by the rib grid units with different numbers of layers is calculated, so that a change curve of the fundamental frequency of the structure of the X-axis base 1 along with the number of the rib grid layers can be obtained, as shown in fig. 13, through the mode analysis in hypermem software, the rib grid unit of the robot base 1 has an optimal density interval, and the density of the rib grid units is too large arranged, so that the base can be rapidly reduced, as can be seen from fig. 13, when the base frequency is given that the height of the base 1 is 500mm, the base frequency of the rib grid unit is not more than 6 layers, and the base is distributed under the base with the fundamental frequency of the base frequency is higher than 2 layers. Therefore, in the design example setting, when the rib grid units of the base 1 are designed and arranged, the distance between any two rib grid units should be kept between 250mm and 500mm (that is, the number of the rib grid units is ensured to be 1-2), so that the optimal dynamic performance of the whole base can be ensured while the light weight of the base is ensured.
In the actual welding process, the length and width of the robot base are determined by the size range of the parts to be welded, and the height of the robot base is allowed to be continuously changed in a certain specific interval. In another design example, we specify that the length of the robot base is 3500mm, the width is 1600mm, the height is changed from 500mm to 2000mm, and 3 layers of rib grid units are arranged in the height direction, then the space between the rib grid unit and the rib grid unit is set to be 200mm, 250mm, 300mm and 350mm respectively, the wall thickness of the rib grid is 20mm, the ratio of the wall thickness of the rib plate 104 of the rib grid unit to the side length of the rib grid unit is set to be 5% -10%, the diameter d of the circular sand outlet 105 accounts for 40% -50% of the total length of the side length of the rib grid unit, the number of the sand outlet is six, and each surface of the rib grid unit is provided with one hole. Through finite element modal analysis in hypermesh software, as shown in fig. 7, a variation curve of the natural frequency of the structure of the X-axis base 1 along with the height of the base 1 is obtained when the rib grid units are at different intervals, and it is found from the figure that the natural frequency of the base 1 increases along with the increase of the height, when the height and the width of the base 1 are approximately equal, the whole base 1 has the optimal natural frequency, and when the width of the base 1 is smaller than the height of the base 1, the first-order natural frequency of the base 1 is gradually reduced, which is mainly caused by the change of the vibration mode of the base 1. It can also be seen that the first order natural frequency of the base 1 is not significantly changed with the spacing dimension of the rib grid, and the first order natural frequency of the base 1 structure is the highest when the height of the base 1 is between 1400mm and 1800 mm. However, when a friction stir welding machine is actually developed, due to the limitation requirement of the overall dimension of a workpiece to be welded, the X-axis base is required to be large, and the dimension of the base 1 in the height direction is difficult to be consistent with the width of the base, so that the fundamental frequency of the base 1 can effectively avoid the first-order natural frequency of the whole machine in the actual design process.
And 6: and (5) verifying the optimal structure scheme of the base 1 obtained in the step (5).
Through the parameterized finite element analysis based on the base 1 frame and the rib grid unit cells, the selection standard and the design principle of the modularized optimization design of the robot X-axis base 1 structure are summarized. In order to further prove the correctness and effectiveness of the design concept. We have compared two robot X-axis base 1 configurations designed as shown in fig. 8-1 and 8-2. Fig. 8-1 shows the base 1 of the square sand outlet 105, fig. 8-2 shows the base 1 of the round sand outlet 105, the length, width and height of the two models are 7100mm × 1900mm × 480mm, and the thickness of the rib plates 104 of the rib grid units is 30mm. When the rib grid unit sand outlet 105 is a round hole, the proportion of the aperture d to the side length l of the rib grid unit changes, the front four-order natural frequency of the X-axis base 1 gradually increases along with the diameter of the sand outlet 105, the natural frequency of the X-axis base 1 also drops, and the drop amplitude is obvious when the proportion of the aperture d to the side length l reaches about 50%, which is consistent with the result of the previous analysis. When the sand outlet 105 is a square hole, along with the change of the ratio of the side length d of the sand outlet 105 to the side length l of the rib grid unit, the inherent frequency of the first four-order gradually increases along with the side length d of the sand outlet 105, the inherent frequency of the X-axis base 1 is in a descending trend, and the inherent frequency is reduced fastest when the ratio of the side length of the sand outlet to the side length of the rib grid unit reaches more than 50%. In addition, the frequency values of the orders of the base 1 of the square sand outlet 105 are generally lower than the frequency values analyzed by the base 1 of the round sand outlet 105, and the descending trend of the curve is faster, which also indicates that the dynamic characteristics of the base 1 of the round sand outlet 105 are better than that of the base 1 of the square sand outlet 105.
The natural frequency f of the large parts (such as the base 1, the upright post 2 and the like) of the friction stir welding robot is a function of rigidity and quality, and is a comprehensive evaluation index with the expression of
Therefore, the criteria for evaluating the dynamic performance of the designed structure are often expressed by the natural frequency of the structure. The rigidity of the large structures forming the whole robot is the basis of the rigidity of the whole robot, and the feasibility of the structural design of the whole robot can be finally guaranteed only if the large structures have excellent dynamic performance. Generally, only good dynamic stiffness of the large-piece structures needs to be ensured, so that the static stiffness of the large-piece structures can be effectively ensured, and the conclusion is not established.
In order to calculate the influence of the aperture d of the circular sand outlet 105 on the static stiffness of the X-axis base 1, 10000N of vertical downward static load is applied to the corresponding position on the upper surface of the model guide rail 101 in hypermesh software, so as to obtain a diagram of fig. 9, namely a deformation cloud diagram of the base 1 with the circular sand outlet 105. The proportion of the aperture d of the sand outlet 105 to the side length l of the rib grid unit is taken as a design variable, a parameterized finite element model is established in hypermesh software, and finite element analysis shows that the maximum deformation of the guide surface in the vertical direction along with the aperture d of the sand outlet 105 is shown in a graph 10, and the graph shows that when the proportion of the aperture d of the sand outlet 105 of the rib grid unit to the side length l of the rib grid unit is close to 0.5, the deformation of the whole X-axis base 1 of the robot in the vertical direction rapidly rises, the static rigidity in the corresponding direction is obviously reduced, after the structure of the X-axis base 1 of the robot is dynamically optimized, the static rigidity and the dynamic rigidity are improved and enhanced simultaneously, and the design process of the dynamic optimization of the large part of the friction stir welding robot adopting the structural frame and the structural unit is correct and feasible.
Claims (5)
1. A topological optimization design method for a base structure of a friction stir welding robot is characterized by comprising the following steps:
step 1: determining analysis factors, wherein the factors influencing the dynamic characteristics of the base structure comprise rib grid units consisting of rib plates and sand outlet holes in the base and a frame of the base;
step 2: the base dynamic optimization design is designed to obtain a base topology optimized structure, and the method specifically comprises the following steps: adopting a full hexahedral grid to grid the base in software, defining the fixing positions of the guide rail, the sliding block, the screw rod mounting seat and the bolt as non-design domains, and other parts as design domains, adopting a variable density method, reserving a material part with the unit density being greater than 0.3, and finally obtaining a topology optimized structure of the base;
and step 3: on the basis of the base structure after topological optimization in the step 2, the relationship between the sand outlet holes of the rib grid units and the inherent frequency of the rib grid units is further optimized, and the shape, the aperture and the number of the sand outlet holes are determined, specifically: selecting a sand outlet with a round hole or a square hole, performing modal analysis in software to compare the two hole types, determining that the sand outlet is circular, performing modal analysis in the software to determine that the aperture of the sand outlet accounts for 40% -50% of the total length of the side length of the rib grid unit, forming 4 or 6 sand outlets on the rib grid unit, and respectively forming the sand outlets on different planes of the rib grid unit
And 4, step 4: on the basis of the step 3, further optimizing the relation between the rib plate wall thickness and the side length of the rib grid unit and the inherent frequency of the rib grid unit, and determining the proportional relation between the rib plate wall thickness of the rib grid unit and the side length of the rib grid unit, specifically: modal analysis is carried out in software to determine that the integral first-order natural frequency of the rib grid unit is reduced along with the increase of the side length of the rib grid unit, and the thickness of the rib plate is reasonably increased in the process of designing the rib grid unit;
and 5: on the basis of step 4, the rib lattice unit density in the base is further optimized, and the number of rib lattice unit layers and the size of the base frame are determined, specifically: determining that the rib grid cells of the base are distributed with an optimal density interval by performing modal analysis in software, and determining the number of layers and the interval of the rib grid cells according to the optimal density interval during design;
and 6: and 5, verifying the optimal scheme of the base structure obtained in the step 5.
2. The method for topologically optimally designing a friction stir welding robot base structure according to claim 1, wherein the method comprises the following steps: in the step 3, 6 sand outlets are preferably formed in the rib grid unit.
3. The method for topologically optimally designing a friction stir welding robot base structure according to claim 1, wherein the method comprises the following steps: in the step 4, the ratio of the rib plate wall thickness of the rib grid unit to the side length of the rib grid unit is preferably 5-10%.
4. The method for topologically optimally designing a friction stir welding robot base structure according to claim 1, wherein the method comprises the following steps: in step 5, when designing the base, the base frequency needs to avoid the first-order natural frequency of the whole machine.
5. The method for topologically optimally designing a base structure of a friction stir welding robot according to any one of claims 1 to 4, wherein: the software is hypermesh software.
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