Method for establishing general lumped parameter thermal network model of machine tool structural member

Abstract

The invention discloses a method for establishing a general lumped parameter thermal network model of a machine tool structural member. The machine tool structural member takes a frame-type cuboid as a basic unit; the method comprises the steps that geometric parameters and material parameters of a frame type cuboid unit of the machine tool structural part are obtained; the node dimension and the node number of the frame type cuboid units of the machine tool structural part are determined, meanwhile, the node alignment rule at the unit splicing position is determined, and it is ensured that adjacent unit nodes can be directly connected; calculating lumped thermal resistance and lumped thermal capacity parameters of the frame-type cuboid units in different directions, and establishing a lumped thermal resistance matrix, a lumped thermal admittance matrix and a lumped thermal capacity matrix of the machine tool structural member in combination with the arrangement relation of the frame-type cuboid units; determining a connection mode of the frame type cuboid unit thermal network model; according to the connecting mode of the frame type cuboid units, the unit thermal models are assembled to form a machine tool structural part total thermal model; the device is coupled with a machine tool body structural mechanical model, structural-thermal coupling design is achieved, and machining precision and operation stability are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of numerical control machine tool bed positive design, and particularly relates to a machine tool bed general lumped parameter thermal network model establishment method. BACKGROUND

[0002] In the positive design process of high-end numerical control machine tools (such as five-axis blade machining centers), the bed body, as the core load-bearing and precision reference component of the whole machine, its thermal performance (such as temperature rise distribution and thermal deformation) directly determines the final machining precision and long-term operation stability of the machine tool. In order to achieve the comprehensive design goal of lightweight, high rigidity and low thermal deformation, the designer needs to iteratively optimize the bed body structure multiple times, and the iteration content covers multiple levels from local parameters (such as the thickness of a single rib plate) to overall layout (such as the transverse / longitudinal arrangement number of frame units).

[0003] However, the traditional bed body thermal performance evaluation methods, such as finite element method (FEA) and computational fluid dynamics method (CFD), are difficult to adapt to the needs of high-frequency iteration in positive design; the finite element method needs to reconstruct the geometric model and perform fine meshing based on each version of the design draft, and the single simulation process takes several days, which seriously slows down the design cycle; the computational fluid dynamics method can accurately capture the fluid-structure coupling effect, but the calculation resource consumption is huge, and the hardware computing power requirement is high, which cannot realize fast response; more importantly, the traditional method lacks special adaptation to the 'frame cuboid modular structure', and cannot realize the efficient process of'modifying local parameters and quickly updating the overall model', resulting in a large amount of repetitive work.

[0004] Therefore, in the high-frequency iteration scenario of numerical control machine tool bed positive design, there is an urgent need for a thermal performance analysis method that adapts to the frame cuboid modular structure, supports parameterized rapid modification, and has both precision and efficiency: it can update the thermal network without rebuilding the overall model when modifying the thickness of the rib plate, the arrangement of the frame unit and other local parameters; it can also ensure the accuracy of temperature rise prediction and meet the design verification requirements, thereby solving the pain points of traditional methods such as 'long process, low efficiency and poor adaptability', and shortening the bed body positive design cycle. SUMMARY

[0005] The purpose of the present application is to provide a machine tool structure general lumped parameter thermal network model establishment method that adapts to the frame cuboid modular structure, supports parameterized rapid modification, and has both precision and efficiency, solves the pain points of traditional thermal performance evaluation methods such as long process, low efficiency and poor adaptability, and supports high-frequency iteration and thermal-structure coupling optimization in machine tool structure positive design.

[0006] In order to solve the problems in the background art, the present application adopts the following technical scheme:

[0007] The method for establishing a general lumped parameter thermal network model of a machine tool structure comprises the following steps:

[0008] The method comprises the following steps:

[0009] Obtaining the geometric parameters and material parameters of the frame cuboid unit of the machine tool structure;

[0010] Determining the node dimensions and node number of the frame cuboid unit of the machine tool structure, and specifying the node alignment rules at the unit splicing positions to ensure that the nodes of adjacent units can be directly connected;

[0011] Calculating the lumped thermal resistance and lumped thermal capacity parameters of the frame cuboid unit in different directions, and establishing the lumped thermal resistance matrix, lumped thermal admittance matrix and lumped thermal capacity matrix of the machine tool structure in combination with the arrangement relationship of the frame cuboid unit;

[0012] Determining the connection mode of the frame cuboid unit thermal network model, considering the contact thermal resistance between different units, specifying the unit thermal connection rules of horizontal arrangement and vertical stacking, and the thermal connection relationship between the guide rail slider reserved nodes and the units;

[0013] According to the connection mode of the frame cuboid unit, the unit thermal models are assembled to form the machine tool structure general thermal model.

[0014] Further, the method further comprises confirming the heat exchange conditions of the machine tool structure and the external environment or cooling medium under different heat dissipation conditions.

[0015] Further, the method for confirming the heat exchange conditions of the machine tool structure and the external environment or cooling medium under different heat dissipation conditions is to add external heat exchange thermal admittance to the nodes of the frame cuboid unit and the external environment / cooling medium.

[0016] Further, when determining the connection mode of the frame cuboid unit thermal model, the connection mode comprises:

[0017] Full connection of the frame cuboid unit edge nodes;

[0018] Partial full connection of the frame cuboid unit edge nodes;

[0019] One-to-one connection of the frame cuboid unit edge nodes.

[0020] Further, the method is applicable to the establishment of a frame cuboid modular machine tool bed thermal network model in one-dimensional, two-dimensional and three-dimensional arrangement of frame cuboid units.

[0021] Further, the machine tool structure comprises a machine tool bed, a slide plate, a column or a beam.

[0022] Further, the frame cuboid unit can be a machine tool rib plate.

[0023] Further, for the most basic heat network unit cuboid unit constituting the frame type cuboid unit, the lumped thermal resistance is represented as,

[0024]

[0025] wherein, L m , A m are the heat transfer path length and heat transfer cross-sectional area of a single frame type cuboid unit in a certain direction respectively; k m represents the heat transfer coefficient of a single frame type cuboid unit in a certain direction; R m1 , R m2 are the lumped thermal resistances of a single frame type cuboid unit in two opposite directions on the x, y or z axis respectively;

[0026] For the most basic heat network unit cuboid unit constituting the frame type cuboid unit, the lumped thermal capacity is represented as:

[0027] C=Mc p

[0028] wherein, M represents the mass of the frame type cuboid unit, and c p represents the specific heat capacity of the frame type cuboid unit.

[0029] Further, for the frame type cuboid unit, if the heat exchange form is convective heat exchange, then the convective heat exchange thermal resistance thereof is:

[0030]

[0031] wherein, k cov is the convective heat exchange coefficient, and A cov is the convective heat exchange cross-sectional area;

[0032] For the frame type cuboid unit, the convective heat exchange admittance is the inverse of the convective heat exchange thermal resistance.

[0033] The beneficial technical effects of the present application are:

[0034] 1. The method provided by the present application is based on the modular design of the frame type cuboid unit and can efficiently establish a machine tool bed thermal network model in different arrangement modes; when modifying local parameters (such as the thickness of the rib plate and the number of unit arrangements), the model updating efficiency is significantly improved, and compared with the traditional finite element method, the single simulation time is shortened from several hours to several minutes, and the generality and efficiency are outstanding;

[0035] 2. The method provided by the present application does not need to pay attention to the complex node definition and parameter assignment process of the thermal network matrix of the machine tool bed components and between components during the machine tool bed design process, but only needs to pay attention to the setting of the top layer of the bed thermal model, such as the geometric parameters and the component contact mode, and has the characteristics of being intuitive and easy to implement.

[0036] 3. The method provided by the application can conveniently couple the thermal model with the mechanical model of the machine tool bed structure to realize structure-thermal coupling design, accurately predict the thermal deformation of the bed in the forward design stage, and ensure the machining precision and operation stability. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a flow chart of the method for establishing the general lumped parameter thermal network model of the machine tool structural member provided by the embodiment of the application;

[0038] Fig. 2(a) is a schematic diagram of the appearance structure of the machine tool bed in the embodiment of the application;

[0039] Fig. 2(b) is the frame cuboid unit arrangement topology of the cross section A of the machine tool bed in Fig. 2(a) in the embodiment of the application;

[0040] Fig. 2(c) is the frame cuboid unit arrangement topology of the cross section B of the machine tool bed in Fig. 2(a) in the embodiment of the application;

[0041] Figure 3 The right side is a general frame cuboid structure similar to the frame cuboid structure topology inside the bed, and the left side is a frame cuboid unit thermal network connection diagram composed of 21 thermal network nodes;

[0042] Figure 4 is a general assembly diagram of the bed thermal network model according to the structural characteristics of the bed;

[0043] Figure 5 is a comparison and verification diagram of the temperature of the guide rail mounting surface of the bed extracted from the finite element software and the temperature of the guide rail mounting surface position extracted from the thermal network. DETAILED DESCRIPTION

[0044] The method for establishing the general lumped parameter thermal network model of the machine tool structural member provided by the application will be further clearly and completely described below in combination with the drawings, and the following specific examples and comparative examples will be described in detail:

[0045] This example analyzes the method for establishing the general lumped parameter thermal network model of the machine tool structural member, which includes the following steps:

[0046] S1, obtaining the geometric parameters (the geometric parameters include the length L, width W, height H, rib thickness t, transverse arrangement number N, and longitudinal arrangement number M of the frame cuboid unit) of the frame cuboid unit of the machine tool structural member, the geometric parameters are described by using the Cartesian coordinate system x, y, and z axis parameters; obtaining the material parameters (the material parameters include the heat transfer coefficient k, specific heat capacity c p , and density p) of the frame cuboid unit; calculating the mass M of the frame cuboid unit according to the volume V and density p of the frame cuboid unit i= pV, the geometric parameters and material parameters are matched according to the node subdivision of S2, and the structure of the corresponding position of the corresponding frame cuboid unit is distributed to the corresponding 21 nodes. As shown in Figure 3 Fig. 2(b), the left side is a thermal network diagram of the frame cuboid unit, which is composed of 21 cuboid thermal network nodes, wherein the purple part is the second half of the purple part of the right frame cuboid unit, the white part is the middle part, the blue part corresponds to the first half, the green part is the reserved node for the guide rail connection, and the yellow part is the reserved node for the connection of the two frame cuboid units in the longitudinal direction. These parameters are determined by the actual geometric dimensions of the frame cuboid unit on the right of the figure. The parameters of each frame cuboid are variable, for example, the lengths of the five frame cuboid units in Fig. 2(b) are different, so the parameters in the length direction of the frame cuboid unit are set as L m The bed size corresponding to the actual position is consistent.

[0047] S2, determine the node dimension and node number of the frame cuboid unit of the machine tool structure, and clearly define the node alignment rules at the unit joint to ensure that the nodes of adjacent units can be directly connected; specifically, according to the accuracy requirement of temperature calculation, the machine tool bed is divided into a series of nodes, and the division fineness in different spatial dimensions should be able to be given to ensure the accuracy in different spatial dimensions;

[0048] In this embodiment, as shown in Fig. 2(a), the machine tool bed is symmetrical, the A cross section is a schematic diagram of the cross section of half of the bed as shown in Fig. 2(c), and the actual structure is arranged in two units in the transverse direction, and the geometric dimensions of the two units are different. The B cross section is a schematic diagram of the longitudinal cross section of half of the bed as shown in Fig. 2(b), and the actual structure is arranged in five units in the longitudinal direction, and obviously the lengths of the five frame cuboids are different. According to the accuracy requirement of temperature calculation, the nodes of a single frame cuboid unit are divided: l=3 nodes are arranged along the x axis (transverse direction), m=3 nodes are arranged along the y axis (longitudinal direction), and n=3 nodes are arranged along the z axis (height), and a single unit has 21 nodes; therefore, half of the bed is composed of 2x5=10 frame cuboid units, and the parameters of the overlapping nodes of adjacent units are set as shown in Fig. 2(b), and the half of the wall thickness d is taken as L m (including the x axis direction L x of the transversely jointed unit), and the total number of unit nodes is 210, which ensures the alignment of the x, y and z axis nodes of adjacent units.

[0049] S3, calculate the lumped thermal resistance and lumped thermal capacity parameters of the frame cuboid unit in different directions, establish the lumped thermal resistance matrix, the lumped thermal admittance matrix and the lumped thermal capacity matrix of the machine tool structure according to the arrangement relationship of the frame cuboid unit;

[0050] For lumped thermal resistance, it is expressed as:

[0051]

[0052] Among them, L m A m These represent the heat transfer path length and heat transfer cross-sectional area (units: m², m³) of a single frame-type cuboid unit in a certain direction. 2 );k m R represents the heat transfer coefficient of a single frame-type cuboid element in the m direction (unit: W / (m·K)); m1 R m2 These are the lumped thermal resistances of a single frame-type cuboid unit in two opposite directions along the m-axis;

[0053] For a frame-type cuboid element, the lumped heat capacity is expressed as:

[0054] C = Mc p

[0055] Where M represents the mass of the frame-type cuboid unit (unit: kg), c p The specific heat capacity of the rectangular block unit is expressed in J / (kg·K).

[0056] Based on the node precision of a single unit, the lumped thermal resistance and lumped heat capacity in the x, y, and z directions are calculated as described above, and the thermal resistance and heat capacity parameters are entered into the thermal network unit model. Then, combined with the arrangement relationship of the frame cuboid units, the lumped thermal resistance matrix, lumped thermal admittance matrix, and lumped heat capacity matrix of the machine tool structural components are established.

[0057] S4. Determine the connection method of the frame-type cuboid unit thermal model, considering the contact thermal resistance between different units (such as the gap between unit splicing surfaces and the sealing layer of the stiffener mating surface), clarify the thermal connection rules of units arranged laterally and stacked longitudinally, and the thermal connection relationship between the reserved nodes of the guide rail slider and the units; there are three connection methods: ① full connection of the edge nodes of the frame-type cuboid unit (suitable for longitudinally close arrangement); ② full connection of some edge nodes of the frame-type cuboid unit (suitable for laterally staggered arrangement); ③ one-to-one connection of the edge nodes of the frame-type cuboid unit (suitable for reserved nodes on the mounting surface of the guide rail slider); specifically including the thermal connection between the frame-type cuboid units in lateral splicing and longitudinal stacking, as well as the gap heat transfer between the reserved thermal network nodes of the guide rail slider and the units.

[0058] In this embodiment, as Figure 4 As shown, the element connection method is defined as follows: two horizontally arranged rectangular box elements use "full edge node connection" (nodes in the x-axis direction correspond one-to-one), and five vertically stacked elements use "partial edge node connection" (only the mating surface nodes are connected in the y-axis direction); as shown... Figure 3As shown, Figure 3 It is a general frame-shaped cuboid structure with a topological similarity to the internal frame-shaped cuboid structure of the bed; Figure 3 The left side is a single frame-type cuboid unit, which is composed of 21 basic cuboid thermal network nodes. The right side is a general frame-type cuboid structure with a topology similar to the frame-type cuboid structure inside the bed. Blue, white and purple represent the one-to-one correspondence between the positions of the basic cuboid units and the frame-type cuboid units. The green part represents the interface for the reserved guide rail, and the yellow part represents the interface for connection when the frame-type cuboid units are arranged and combined in the longitudinal direction. The reserved nodes of the units at the guide rail slider installation point adopt a "one-to-one connection" (the second node in the z-axis direction is connected to the slider node).

[0059] S5. Based on the connection method of the frame-type cuboid units, assemble the thermal models of each unit to form the overall thermal model of the machine tool structure. That is, assemble all the unit thermal models according to the arrangement of the frame-type cuboid units (N horizontal units + M vertical units), integrate the connection relationships between the units, and form the overall thermal model of the machine tool structure. At the same time, based on the cooling method of the machine tool bed (natural cooling, air cooling, water cooling, or oil cooling), add external heat exchange thermal admittance to the heat exchange nodes such as the outer surface of the unit, the mounting base of the guide rail slider, and the heat dissipation surface of the rib plate. Also, consider the convective heat transfer coefficient at the unit gaps and the air gaps of the guide rail slider to supplement the air gap convective heat transfer admittance and improve the overall thermal model.

[0060] In this embodiment, as Figure 4 As shown, Figure 4 This is an assembly drawing of the bed thermal network model based on the structural characteristics of the bed. It forms a 2×5=10 frame-type cuboid unit array based on the arrangement of 2 horizontal and 5 vertical frame-type cuboid units. The connection relationships between units and the thermal resistance / heat capacity matrix are integrated to form the overall thermal network model, and the unit connection nodes and heat exchange surface positions are marked. The overall bed thermal model is further refined based on the arrangement of 2 horizontal and 5 vertical units, the thermal resistance / heat capacity matrix established in step S3, and the connection relationships between units defined in step S4. In this embodiment, the machine tool bed uses convective heat transfer coefficients set on the outer surface of the units and the guide rail slider mounting surface to update the lumped admittance matrix.

[0061] For the frame-type cuboid unit, whose heat transfer mode is convection heat transfer, its convection heat transfer thermal resistance is:

[0062]

[0063] Where, k cov Convection heat transfer coefficient (unit: W / (m²)) 2 ·K)), A cov Convection heat transfer cross-sectional area (unit: m²) 2 );

[0064] For a frame-type cuboid element, its convective heat transfer admittance is the reciprocal of the convective heat transfer thermal resistance.

[0065] Of course, in practical applications, when the actual operating conditions of the machine tool are input into the model (such as the heat generation power of guide rail friction, heat dissipation coefficient of stiffeners, ambient temperature, etc.), there is no need to rebuild the geometry and mesh. Key data such as the temperature distribution of each frame element node and the temperature rise of the guide rail mounting surface can be output within minutes, which greatly improves efficiency compared to the several days cycle of the traditional finite element method. When designers modify local structural parameters (such as stiffener thickness, length, width, height, etc.) or increase the number of stiffeners, they only need to update the geometric / material parameters of the corresponding elements. The model can automatically and synchronously update the thermal resistance / heat capacity matrix and the total thermal network, quickly reflecting parameter modifications. The impact on thermal performance (such as whether the temperature rise of the guide rail base surface decreases after the stiffener is thickened) supports high-frequency iteration in forward design; for different modular layouts of the bed (such as horizontal and vertical arrangements of other quantities, increasing to two or more layers of frame-type cuboid arrangement), multiple sets of thermal network models can be quickly established to compare the thermal deformation risk and heat dissipation efficiency of each scheme, providing data support for the optimal structural layout; without relying on high-end computing equipment, a regular computer with only 16GB of MATLAB memory can complete the simulation, while reducing repetitive work of geometric modeling and mesh generation, reducing the time and manpower costs of the design team.

[0066] Based on the established thermal network model, the machine tool operating conditions (heat generated by the guide rail Q, ambient temperature T0, and natural convection heat transfer coefficient) are input to calculate the temperature relationship between each node of the frame unit and the temperature of the guide rail mounting surface.

[0067] A total of 15 thermal network nodes (corresponding to 15 key measuring points on the guide rail mounting surface) are established longitudinally. Temperature data from these nodes are extracted to characterize the temperature distribution of the surface. Figure 5 The red triangles and black curves represent the temperature distribution of the guide rail base surface extracted from the finite element method. The temperature decreases from left to right, as shown in Figure 2(b) where the cross-section corresponds to the geometric position from left to right. The temperature on the left is higher than that on the right, possibly because the spacing between the stiffeners on the left is larger than that on the right, and the air cooling effect on the left is less effective than the more concentrated solid medium heat conduction effect on the right.

[0068] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for establishing a general lumped parameter thermal network model of a machine tool structure, characterized in that, The machine tool structure is a basic unit of a frame type cuboid; The method comprises the following steps: Obtaining the geometric parameters and material parameters of the frame type cuboid unit of the machine tool structure; Determining the node dimension and node number of the frame type cuboid unit of the machine tool structure, and specifying the node alignment rule at the unit splicing position to ensure that the nodes of adjacent units can be directly connected; Calculating the lumped thermal resistance and lumped thermal capacity parameters of the frame type cuboid unit in different directions, combining the arrangement relationship of the frame type cuboid unit, and establishing the lumped thermal resistance matrix, lumped thermal admittance matrix and lumped thermal capacity matrix of the machine tool structure; Determining the connection mode of the frame type cuboid unit thermal network model, considering the contact thermal resistance between different units, specifying the unit thermal connection rules of horizontal arrangement and vertical stacking, and the thermal connection relationship between the guide rail slider reserved node and the unit; According to the connection mode of the frame type cuboid unit, the total thermal model of the machine tool structure is formed by assembling the thermal models of each unit.

2. The method according to claim 1, characterized in that, The method further comprises confirming the heat exchange between the machine tool structure and the external environment or the cooling medium under different heat dissipation conditions.

3. The method according to claim 2, characterized in that, The method for confirming the heat exchange between the machine tool structure and the external environment or the cooling medium under different heat dissipation conditions is to add external heat exchange thermal admittance to the nodes of the frame type cuboid unit and the external environment / cooling medium.

4. The method according to claim 1, characterized in that, When determining the connection mode of the frame type cuboid unit thermal model, the connection mode comprises: Full connection of the edge nodes of the frame type cuboid unit; Partial full connection of the edge nodes of the frame type cuboid unit; One-to-one connection of the edge nodes of the frame type cuboid unit.

5. The method according to claim 1, characterized in that, The method is suitable for establishing the thermal network model of the frame type cuboid modular machine tool bed arranged in one dimension, two dimensions or three dimensions.

6. The method according to claim 1, characterized in that, The machine tool structure comprises a bed, a slide plate, a column or a beam.

7. The method according to claim 1, characterized in that, The frame type cuboid unit can be a machine tool rib plate.

8. The method according to claim 1, characterized in that, For the most basic thermal network unit cuboid unit constituting the frame type cuboid unit, the lumped thermal resistance is represented as, wherein, L m , A m are the heat transfer path length and heat transfer cross-sectional area of a single framed cuboid unit in a certain direction, respectively; k m represents the heat transfer coefficient of a single framed cuboid unit in a certain direction; R m1 , R m2 are the lumped thermal resistances of a single framed cuboid unit in two opposite directions on the x, y or z axis, respectively; For the most basic thermal network unit cuboid unit constituting the frame type cuboid unit, the lumped thermal capacity is represented as: C = Mc p where M represents the mass of the frame-like cuboid unit, c p represents the specific heat capacity of the frame-like cuboid unit.

9. The method according to claim 1, characterized in that, For the frame type cuboid unit, the convective heat transfer resistance is: where k cov is the convective heat transfer coefficient, A cov is the convective heat transfer cross-sectional area; For the frame type cuboid unit, the convective heat transfer admittance is the inverse of the convective heat transfer resistance.

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