A machine case lightweight design method and a machine case

Abstract

Provided is a casing lightweight design method, which divides the casing into smooth regions and non-smooth regions, and models the smooth regions and the non-smooth regions respectively to form a smooth region model and a non-smooth region model; obtains wall thickness data at each circumference of the smooth region model at which the membrane strain energy of the smooth region model is at a minimum, and selects the maximum value of the wall thickness data as the smooth region thickness; and adopts a topology optimization method to determine a thinning region for the non-smooth region model. The casing lightweight design method can effectively reduce the weight of the casing while ensuring the strength and stiffness. Also provided is a casing designed using the method.

Description

Technical Field

[0001] This invention belongs to the field of aero-engine design, specifically relating to the weight reduction design of aero-engine casings. Background Technology

[0002] The thrust-to-weight ratio of an aero-engine is one of the comprehensive indicators for measuring the engine's technological level and operational capability. Reducing weight can significantly improve the engine's thrust-to-weight ratio. Controlling and reducing engine weight to ensure better flight maneuverability, reduce fuel consumption, and lower emissions is an inevitable trend in aero-engine design. Researching lightweight design technologies for the engine casing, and minimizing engine weight while meeting safety requirements, is one of the effective ways to improve the engine's thrust-to-weight ratio.

[0003] For example, the combustion chamber casing is a major load-bearing component of an aero-engine. During the design and development of the casing structure, it is necessary to minimize the weight of the casing while meeting the requirements for rigidity and strength. The casing is a thin-walled cylindrical structure, but fuel nozzles and ignition nozzles are installed on the combustion chamber. Therefore, multiple mounting bosses and holes are also provided on the casing, making the structure complex.

[0004] Traditional weight reduction methods often involve thinning material in low-stress areas of the casing. However, this method can easily alter the structural stiffness and force transmission path of the casing, causing stress levels in other areas to exceed material strength. Therefore, an automated, geometrically modified optimization method is needed for weight reduction design, allowing for iterative stiffness and stress adjustments. Topology optimization is one such automated optimization method. However, when using topology optimization for overall casing weight reduction, the optimized structure exhibits geometric discontinuities due to multiple material removals, significantly complicating manufacturing. Furthermore, multiple material removals necessitate milling and turning operations at multiple locations, significantly increasing manufacturing difficulty and costs.

[0005] Therefore, it is necessary to propose a lightweight design method for the combustion chamber casing structure to solve the above problems. Summary of the Invention

[0006] One objective of this invention is to provide a lightweight design method for a casing that can effectively reduce weight while ensuring the structural rigidity and strength of the casing, and can control the manufacturing cost of the casing.

[0007] The lightweight casing design method for achieving the above objectives includes the following steps: dividing the casing into smooth and non-smooth regions, and modeling them separately to form smooth region models and non-smooth region models; obtaining circumferential wall thickness data at various points that minimize the membrane strain energy of the smooth region model, and selecting the maximum value of the wall thickness data as the smooth region thickness; and using a topology optimization method to determine the thinning area for the non-smooth region model. The above lightweight casing design method can effectively reduce the weight of the casing while ensuring strength and stiffness. A casing designed using the above method is also provided.

[0008] In one or more embodiments, the non-smooth area includes areas with protrusions and / or grooves and / or holes.

[0009] In one or more embodiments, smooth regions are modeled using shell elements to form design domain shell elements; and non-smooth regions are modeled using solid elements to form three-dimensional solid elements.

[0010] In one or more embodiments, a virtual shell unit is provided between the three-dimensional solid unit and the design domain shell unit, the virtual shell unit being attached below the three-dimensional solid unit and connected to the design domain shell unit at common nodes.

[0011] In one or more embodiments, upper and lower limits for wall thickness are defined, and wall thickness data that minimizes membrane strain energy is determined within the range of the upper and lower limits.

[0012] In one or more embodiments, the method further includes a volume constraint requirement that the volume reduction of the smooth region model during variable wall thickness calculation is no more than 30%.

[0013] In one or more embodiments, the volume is calculated using the following formula: h i Let A be the thickness of the i-th element, N be the total number of design variables, and A be the thickness of the i-th element. i Let be the area of ​​the i-th unit.

[0014] In one or more embodiments, the formula for calculating the membrane strain energy is: U is the membrane strain energy, E is the elastic modulus, q is the wall pressure, r is the casing radius, θ and z are the circumferential and axial axes of the cylindrical coordinate system, respectively, and h is the design variable vector.

[0015] In one or more embodiments, a variable density optimization design method is used for the non-smooth region model. The variable density optimization design method includes the following steps: determining a range of density values; calculating compliance within the range of density values, while assigning volume constraints and / or mass constraints; and obtaining optimized weight reduction results when the compliance is minimized and the volume constraints and / or mass constraints are met.

[0016] In one or more embodiments, in the optimized weight loss results, regions with a density less than or equal to 0.4 are selected as weight loss regions.

[0017] In one or more embodiments, the mass constraint is that the weight reduction ratio of the non-smooth region model is greater than or equal to 50% of the model mass before optimization, and the volume constraint is that the volume reduction of the non-smooth region model after optimization is not higher than 50%.

[0018] Another object of the present invention is to provide a casing obtained using the above-described method.

[0019] The aforementioned lightweight casing design method can be used for partitioned design of casings with different structures. For thin-walled structures with special and complex structures such as bosses and perforated thin walls, the local topology optimization method is used to obtain the thinning area. For ordinary smooth thin-walled casing areas, the variable wall thickness optimization method is adopted to achieve the maximum weight reduction target while ensuring the overall structural rigidity and manufacturing cost. Attached Figure Description

[0020] The above and other features, properties and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, wherein:

[0021] Figure 1 This is a schematic diagram of the combustion chamber.

[0022] Figure 2 This is a schematic diagram of one embodiment of the combustion chamber.

[0023] Figure 3A This is a schematic diagram of one embodiment of a smooth region model.

[0024] Figure 3B This is a schematic diagram of an embodiment of a non-smooth region model.

[0025] Figure 4A This is a schematic diagram of an embodiment of the thickness distribution at various points in a smooth region model.

[0026] Figure 4B This is a schematic diagram of an embodiment of a smooth region model after taking the maximum wall thickness.

[0027] Figure 5 This is a schematic diagram of an embodiment of finite element modeling.

[0028] Figure 6 This is a partial schematic diagram of an embodiment of a non-smooth region model.

[0029] Figure 7A This is a schematic diagram of one embodiment of the weight reduction area of ​​the mounting base.

[0030] Figure 7B This is a schematic diagram of one embodiment of the weight reduction area of ​​the boss.

[0031] Figure 8 This is a flowchart illustrating the steps involved in lightweight chassis design.

[0032] Symbol marking explanation

[0033] 1. Fuel injector

[0034] 2. Outer ring of the flame tube

[0035] 3. Combustion outdoor unit casing

[0036] 4. Inner ring of the flame tube

[0037] 5. Combustion chamber casing

[0038] 6. Head Adapter Section

[0039] 7. Diffuser

[0040] 62. Remove region

[0041] 300. Upstream wall of the outer casing

[0042] 301. Downstream wall of the outer casing

[0043] 302. Nozzle seat mounting wall surface

[0044] 303. Downstream mounting edge of the outer casing

[0045] 304. Upstream mounting edge of the outer casing

[0046] 401. Nozzle mounting seat spacer groove

[0047] 402. Nozzle seat mounting hole

[0048] 411. Design Domain Shell Unit

[0049] 412. Three-dimensional solid element

[0050] 413. Virtual Shell Unit

[0051] 501. Smooth Region Model

[0052] 502. Non-smooth region model Detailed Implementation

[0053] The present invention will be further described below with reference to specific embodiments and accompanying drawings. More details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention can obviously be implemented in many other ways different from those described herein. Those skilled in the art can make similar extensions and derivations based on actual application situations without departing from the spirit of the present invention. Therefore, the scope of protection of the present invention should not be limited by the content of this specific embodiment.

[0054] It should be noted that these and other accompanying drawings are merely examples and are not drawn to scale, and should not be construed as limiting the scope of protection of the present invention.

[0055] The engine casing is a typical thin-walled load-bearing and force-transmitting stator component in aero-engines. Aero-engine casing components mainly include fan casings, low-pressure compressor casings, intermediate casings, high-pressure compressor casings, combustion chamber casings, turbine casings, turbine rear casings, and accessory casings. The quality of the casing structural design directly affects the engine's aerodynamic performance, safety, reliability, durability, and thrust-to-weight ratio. Therefore, lightweight casing design technology is one of the effective ways to improve the engine's thrust-to-weight ratio.

[0056] Figure 1 A schematic diagram of the combustion chamber is shown. The outer ring 2 and inner ring 4 of the flame tube form the flame tube, and the head transition section 6 connects the flame tube inlet to the outer casing of the combustion chamber. The compressed airflow from the compressor is decelerated and diffused by the diffuser 7 before entering the flame tube, where it mixes with the fuel injected by the fuel nozzle 1. The fuel-air mixture is then ignited by a high-energy electric spark generated by an ignition electrode (not shown) that passes through the outer casing of the combustion chamber 3 and the outer ring 2 of the flame tube, thus achieving combustion within the flame tube cavity.

[0057] The outer combustion chamber casing 3 and the inner combustion chamber casing 5 form the area that houses the flame tube. The combustion chamber casing, a thin-walled cylindrical structure, is the main load-bearing component, requiring a certain level of rigidity and strength. The combustion chamber casing also houses multiple structures such as fuel nozzles and ignition nozzles; therefore, it is designed with multiple mounting bosses and holes for mounting these components. These bosses, holes, and slots make the surface structure of the thin-walled cylindrical combustion chamber casing relatively complex. The weight reduction design for this complex casing needs to balance the requirements of load-bearing strength and rigidity.

[0058] The lightweight casing design method described in this disclosure can reduce the weight of the casing to the maximum extent while ensuring the rigidity and strength of the casing, thus avoiding problems such as changes in structural rigidity and force transmission path.

[0059] It should be noted that the lightweight design method of the casing described in this disclosure is not only applicable to the combustion chamber casing mentioned above, but also to casings with complex structures such as bosses, grooves, holes, steps, and flanges in other components.

[0060] Combination Figure 8 Understanding that the first step 601 of this design method is to divide the casing into smooth and non-smooth regions based on the structural distribution characteristics of the casing, and to model them separately to form smooth region models and non-smooth region models. Then, an automatic optimization design technique that processes the regions separately is used to achieve weight reduction.

[0061] Smooth regions refer to portions that only have annular thin-walled structures, such as... Figure 3A As shown; non-smooth areas refer to regions including those with protrusions and / or grooves and / or holes, that is, parts that do not have a single, uniform annular thin-walled structure, such as... Figure 3B The area shown.

[0062] Such as combination Figure 2 As understood from Figure 3, the outer casing 3 of the combustion chamber includes an upstream wall 300, a downstream wall 301, a downstream mounting edge 303, and an upstream mounting edge 304. The outer surface, which is a thin annular wall, has hole structures, boss structures, or groove structures such as a nozzle seat mounting wall 302, a nozzle seat spacer groove 401, and a nozzle seat mounting hole 402. This creates a non-uniform, non-smooth annular thin-walled structure.

[0063] Continue to refer to Figure 3A and Figure 3B Understand the specific divisions of the combustion chamber casing. Figure 3A The smooth region model 501 is shown, which is a ring-shaped thin-walled structure with a smooth surface; Figure 3B Model 502 of a non-smooth region with bosses and slots is shown.

[0064] After dividing the casing into regions, different thinning methods are applied to different regions. For the smooth region model 501, as shown in steps 602 and 603, the wall thickness data of each part of the model where the membrane strain energy is at its minimum is obtained, and the maximum value of the wall thickness data is selected as the thickness of the smooth region. Weight reduction is achieved through a maximum wall thickness adjustment scheme. For the non-smooth region model 502, as shown in step 604, a topology optimization method is used for automatic optimization to determine the thinning region.

[0065] Due to the internal pressure acting on the casing, the overall casing wall is primarily subjected to circumferential membrane stress. The magnitude of this membrane stress is directly related to the thickness of the casing wall. Therefore, for the smooth region model 501, a weight reduction design is implemented using variable wall thickness. In the variable wall thickness design, it is essential to ensure that the circumferential membrane stress is less than the yield strength. Therefore, membrane strain energy is used as an optimization variable, and the wall thickness at which the membrane strain energy is minimized effectively guarantees strength and avoids problems such as excessive material removal leading to geometric discontinuities and disruption of the force transmission path.

[0066] Topology optimization is a mathematical method that optimizes material distribution within a given region under given load conditions, constraints, and performance indicators. The non-smooth region model 502 employs topology optimization alone, with the goal of minimizing structural flexibility and material relative density as the design variable, to optimize a weight-reduced structure that meets stiffness and strength requirements.

[0067] It is worth noting that when optimizing the design of smooth regions, non-smooth regions are defined as non-design domains, and a variable wall thickness optimization program is initiated to complete the weight reduction design of smooth regions. Conversely, when optimizing the design of non-smooth regions, smooth regions are defined as non-design domains, and a topology optimization program is initiated to complete the weight reduction design of non-smooth regions. The optimized non-smooth region model 502, together with the smooth region model 501, forms the optimized casing as a whole, guiding subsequent processing.

[0068] The following is combined with Figures 3A to 5 The overall weight reduction design process of the casing will be further explained.

[0069] After determining the ranges of the smooth and non-smooth regions, a model of the smooth region is constructed, such as using ANSYS simulation software. In one embodiment, shell elements are used to model the smooth region, forming a design domain shell element 411. Based on the design domain shell element 411, the element thickness can be easily adjusted by changing the cross-sectional properties. From the membrane strain energy calculation formula, it can be seen that the membrane stress in the radial direction of the annular casing is average, and the optimization variable is the element thickness. In ANSYS, to facilitate changing the element thickness, a shell element capable of changing cross-sectional properties is used to simulate the wall thickness optimization design domain.

[0070] Solid elements are used to model non-smooth areas, forming three-dimensional solid elements 412. The mesh modeling of the three-dimensional solid elements 412 can simulate the thickness of areas such as bosses and grooves, thereby accurately simulating the structural stiffness.

[0071] Because the degrees of freedom of the three-dimensional solid element 412 and the design domain shell element 411 are mismatched, if the three-dimensional solid element 412 and the design domain shell element 411 are directly connected at common nodes, the rotational degrees of freedom cannot be correctly transmitted. Therefore, in one embodiment, a virtual shell element 413 is provided between the three-dimensional solid element 412 and the design domain shell element 411. The virtual shell element 413 is attached below the three-dimensional solid element and is connected at common nodes with the design domain shell element 411.

[0072] Specifically, refer to Figure 5 As shown, a virtual shell element 413 with a thickness of 0 is added below the three-dimensional solid element 412. The virtual shell element 413 with a thickness of 0 does not affect the structural stiffness. The virtual shell element 413 shares nodes with the design domain shell element 411, and their degrees of freedom are matched, so they can correctly transmit forces. The three-dimensional solid element 412 is only used to simulate stiffness.

[0073] After connecting the three-dimensional solid element 412 and the design domain shell element 411, the wall thickness at which the membrane strain energy U is minimized is sought. Under high internal pressure, the casing stress is mainly circumferential membrane stress. The optimization design objective is to maximize casing stiffness, minimize deformation, and minimize stress, thereby meeting strength requirements. Therefore, the membrane strain energy U is used as the optimization objective. By changing the wall thickness parameter h, the stiffness performance of the structure is affected, thereby reducing the structural membrane strain energy. Through iterative analysis of the wall thickness as a design variable, the minimum strain energy is obtained, and the optimal wall thickness solution is found.

[0074] The formula for calculating membrane strain energy is: Where E is the elastic modulus, q is the wall pressure, r is the casing radius, θ and z are the circumferential and axial axes of the cylindrical coordinate system, respectively, and h is the design variable vector, i.e., the aforementioned wall thickness. Within the aforementioned upper and lower limits of wall thickness, the wall thickness is selected and iterated multiple times. For example, an APDL command flow is written to extract the element membrane strain energy, an optimization program is written using MATLAB to adjust the wall thickness variable, and the ANSYS program and data transfer program are called to achieve wall thickness optimization. The wall thickness that minimizes the membrane strain energy is the optimal solution.

[0075] In one embodiment, upper and lower limits of wall thickness are defined, such as defining wall thickness h = {h1, h2, ..., h}. N The wall thickness is searched within the above selection domain, looking for the data that minimizes the membrane strain energy within the upper and lower limits of the wall thickness. Setting upper and lower limits for the wall thickness is to consider practical processing feasibility. If the optimized wall thickness is too thin, large-sized thin-walled parts are prone to deformation during processing; therefore, upper and lower limits for the wall thickness need to be defined.

[0076] Figure 4A The diagram shows the final optimized circumferential wall thickness distribution in the wall thickness parameter optimization region under the optimization objective. When the membrane strain energy is minimized, the circumferential wall thickness dimensions of the smooth region model 501 vary, as indicated by points A and B. At this point, the wall thickness h at each circumferential position forms a data set, and each wall thickness satisfies the minimum membrane strain energy requirement at that location. Considering ensuring the overall strength of the casing, the optimization results are geometrically reconstructed, and the maximum value of the wall thickness data set is selected as the final actual processed thickness of the smooth region casing, as shown below. Figure 4B The finished smooth area model 501' is shown.

[0077] Figure 4BThis describes the geometrically reconstructed structure based on the optimized results. In one specific embodiment, along the axial direction, several nodes are defined according to the mesh size of the divided elements. For example, if the design domain uses a 5mm mesh size, a point is defined every 5mm from the small opening to the large opening. Then, a ring of elements is taken out according to the axial position of that point to obtain the maximum thickness of the element, such as the thickness at point A. This achieves maximum wall thickness regularization, balancing manufacturability and manufacturing cost. For example, the final dimensions could be such that the wall thickness of the upstream wall 300 of the outer casing can be designed to be 4mm, and the wall thickness of the downstream wall 301 of the outer casing can be designed to be 5mm.

[0078] Considering the maximum optimization limit, in one embodiment, volume constraints are also taken into account when calculating the membrane strain energy U, ensuring that the volume reduction of the smooth region model is no more than 30% during variable wall thickness calculations. The volume constraint calculation formula is as follows: h i Let A be the thickness of the i-th element, N be the total number of design variables, and A be the thickness of the i-th element. i Let be the area of ​​the i-th element. Volume is a constraint for weight reduction. Wall thickness optimization must be performed under volume constraints to minimize strain energy; without constraints, the optimization program will not converge. To avoid over-optimization, necessary stiffness and strength must be guaranteed. 30% is set as the initial value. If the final optimized strength is insufficient or the margin is too large, the volume constraint value can be adjusted appropriately.

[0079] for Figure 6 The weight reduction design of the non-smooth region model 502 shown independently employs a topology optimization method different from the method described above. In one embodiment, the stiffness properties of the material are affected by changing the density of the unit material; therefore, a variable density optimization design method is used to design and reduce the weight of the non-smooth region model.

[0080] The variable density optimization design method includes the following steps. First, determine the range of density values ​​to be selected and assign a relative density selection threshold, such as ρ = {ρ1, ρ2, ..., ρ...}. N}

[0081] Within the aforementioned density value range, compliance is calculated, while volumetric and / or mass constraints are applied to ensure geometric continuity and structural stiffness and strength. Pressure and temperature loads are applied to the model, along with true boundary constraints on the mounting edges. Topology optimization is then performed using the methods described above. The optimized weight reduction result is obtained when compliance is minimized and the volumetric and / or mass constraints are met.

[0082] The optimization results will contain a large number of intermediate density cells. The smaller the intermediate density value of a cell, the lower the load-bearing capacity, and the more material can be removed from that area. Larger intermediate density areas have higher load-bearing capacity and are not suitable for direct material removal. For example, in one embodiment, areas with a relative density greater than 0.4 are not suitable for direct material removal; instead, areas with a density less than or equal to 0.4 are selected as weight reduction areas. The actual mass of removable material is less than the mass reduced by the optimization result; therefore, when setting mass constraints, the weight reduction ratio must be higher than the design requirement value.

[0083] For example, in one or more embodiments, mass constraints may include a weight reduction ratio greater than or equal to 50% of the original mass, meaning the weight reduction must not exceed half of the original mass. Volume constraints may include a volume reduction of no more than 50% after optimization. Those skilled in the art will understand that the above values ​​can be determined by personnel based on the specific casing structure and design requirements.

[0084] The formula for calculating flexibility is C = X. T KX, where C is the member flexibility, K and X are the structural stiffness matrices (details omitted here), and T represents matrix inversion. Using flexibility as the calculation variable can better reflect the stiffness characteristics of the structure.

[0085] Figure 7A and Figure 7B An optimization result is shown at the nozzle mounting spacer slot 401 of the non-smooth region model 502. Based on the optimization result, the local structure of the nozzle mounting on the casing is geometrically reconstructed. The material between the nozzle mounting bosses on the casing can be removed, i.e., the removal area 62 is shown. The periphery of the removed material is rounded to avoid stress concentration caused by geometric abrupt changes.

[0086] The final weight-reduced overall casing is obtained by independently calculating the smooth region model 501 and the non-smooth region model 502. This method targets particularly complex thin-walled structures such as casings with bosses and openings. It employs a weight-reduction optimization method combining zoned control with variable wall thickness across the entire ring and local topology optimization. The casing is divided into different regions, each using variable wall thickness and local topology optimization weight-reduction design methods to achieve maximum weight reduction. Compared to topology optimization design of the entire casing, this method avoids excessive weight reduction and geometric discontinuities caused by multiple material removals in the structure. The separate treatment of smooth regions ensures structural stiffness and force transmission paths, and also makes smooth thin walls easier to process, effectively reducing manufacturing costs.

[0087] Based on the above introduction to the lightweight design method of the casing, we can also understand a casing designed using this method that can effectively reduce weight while ensuring rigidity and strength, thereby improving the thrust-to-weight ratio of the engine.

[0088] This application uses specific terms to describe embodiments of the application. Terms such as "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of the application. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.

[0089] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the invention, fall within the protection scope defined by the claims of the present invention.

Claims

1. A lightweight design method for a casing, characterized in that, Includes the following steps: The casing is divided into smooth and non-smooth areas, and modeled separately to form a smooth area model (501) and a non-smooth area model (502); Obtain the circumferential wall thickness data at various points that minimize the membrane strain energy of the smooth region model (501), and select the maximum value of the wall thickness data as the thickness of the smooth region. Use the topology optimization method to determine the thinning region for the non-smooth region model (502).

2. The lightweight casing design method as described in claim 1, characterized in that, The non-smooth area includes areas with protrusions and / or grooves and / or holes.

3. The lightweight casing design method as described in claim 1, characterized in that, For smooth regions, shell elements are used to model the design domain shell elements (411); for non-smooth regions, solid elements are used to model the three-dimensional solid elements (412).

4. The lightweight casing design method as described in claim 3, characterized in that, A virtual shell unit (413) is provided between the three-dimensional solid unit (412) and the design domain shell unit (411). The virtual shell unit (413) is attached below the three-dimensional solid unit (412) and is connected to the design domain shell unit (411) at the same node.

5. The lightweight casing design method as described in claim 1, characterized in that, Define upper and lower limits for wall thickness, and determine the wall thickness data that minimizes membrane strain energy within the range of the upper and lower limits.

6. The lightweight casing design method as described in claim 1, characterized in that, The method also includes a volume constraint requirement that the volume reduction of the smooth region model during variable wall thickness calculation should not exceed 30%.

7. The lightweight casing design method as described in claim 6, characterized in that, The formula for calculating the volume is: h i Let A be the thickness of the i-th element, N be the total number of design variables, and A be the thickness of the i-th element. i Let be the area of ​​the i-th unit.

8. The lightweight casing design method as described in claim 1, characterized in that, The formula for calculating membrane strain energy is: U is the membrane strain energy, E is the elastic modulus, q is the wall pressure, r is the casing radius, θ and z are the circumferential and axial axes of the cylindrical coordinate system, respectively, and h is the design variable vector.

9. The lightweight casing design method as described in claim 1, characterized in that, A variable density optimization design method is applied to the non-smooth region model. The variable density optimization design method includes the following steps: Determine the range of density values ​​to select; Calculate compliance within the range of density values ​​selected, while simultaneously imposing volume constraints and / or mass constraints; Optimized weight reduction results are obtained when the flexibility is minimized and the volume constraint and / or mass constraint are met.

10. The lightweight casing design method as described in claim 9, characterized in that, In the optimized weight loss results, regions with a density of less than or equal to 0.4 are selected as weight loss regions.

11. The lightweight casing design method as described in claim 9, characterized in that, The mass constraint is that the weight reduction ratio of the non-smooth region model is greater than or equal to 50% of the mass of the model before optimization, and the volume constraint is that the volume reduction of the non-smooth region model after optimization is not higher than 50%.

12. A casing, characterized in that, Obtained using the lightweight casing design method as described in any one of claims 1-11.

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