CAD modeling and assembly method of the hottest ra

CAD modeling and assembly method for railway freight powder cargo tank car

in manufacturing enterprises, effective software can not only shorten the design cycle of products, but also improve the design quality. According to the technical characteristics of large and small products led by the enterprise itself and then measured the output, the author uses SolidWorks software to explore the implementation methods and design skills from part design, component design to final product assembly design, for readers' reference

I. overview of SolidWorks functions

SolidWorks software is powerful and easy to learn and use, so it has been widely used in the mechanical design industry in recent years. Its functional characteristics mainly include the following points:

(1) parametric design, feature modeling technology and the full correlation of the design process make it have good design flexibility, that is, the design process is flexible and easy to modify

(2) the feature manager with full windows features makes the operation and management of the design process clear and simple. The complete dynamic interface and mouse dynamic control are very practical and particularly important technical means for designing complex parts

(3) the powerful CAD module includes sketch design, surface modeling, solid modeling and sheet metal part design, which can complete the establishment of feature-based CAD model and meet the requirements of mechanical design

(4) assembly oriented part design provides an important technical method for the modeling of large-scale assemblies. Its IPA animation can realize dynamic simulation assembly and motion analysis, so as to verify the correctness of part design in the computer

(5) SolidWorks is an integrated software with cad/cam/cae functions, which fully meets the integration requirements of design, analysis, manufacturing and product data management

to sum up, the basic design idea of SolidWorks software is "solid modeling → virtual assembly → two-dimensional drawings". Three-dimensional solid modeling makes the design process visual and intuitive. Virtual assembly can verify the design process at any time, so as to avoid possible direct economic losses. The automatic drawing of two-dimensional drawings also meets the needs of actual production, which fully meets the design and production requirements of mechanical design enterprises, so it has been widely used

II. Relevant technical basis

1 Parametric modeling

in parametric modeling (also known as dimension driven geometric modeling technology), the geometric shape of an object is defined by constrained mathematical relations, not just by simple and isolated dimensional parameters. Its main technical features are: feature-based, full-size constraints, size driven design modifications, and full data correlation

(1) based on features, some representative geometric shapes are defined as features, and all their dimensions are defined as variable parameters, so as to form entities, which are used as the basis for the construction of more complex geometric bodies

(2) full size constraint combines shape and size, and realizes the control of geometric shape through size constraint. The modeling must take the complete size parameters as the starting point (full constraint), and it is not allowed to omit the size (under constraint), nor to note too much size (over constraint)

(3) dimension driven design modification drives the change of geometry by modifying the dimension value

(4) the modification of full data related dimension parameters drives the update of related dimensions in other related models, thus driving the model update

the biggest advantage of using parametric modeling for design is that the CAD system will automatically record the whole process of geometric modeling. In other words, the system records not only the geometric model, but also the design intent, that is, the relationship between entities. When modifying the shape of a part, only the numerical value of the size is needed to change the shape

2. Associative design

in traditional CAD systems, assembly (component) design mostly adopts the bottom-up method, that is, first design the constituent parts of each part, and then assemble the designed parts together. There is no correlation between the parts. When the function or structure of a component needs to be adjusted, the structural form and size of relevant parts will not automatically change accordingly; On the contrary, when a part changes, the function of the part will not be adjusted automatically when it reaches the limit of 1 or the structure will not be adjusted automatically. The assembly relationship and size coordination between parts completely rely on designers to complete manually. In fact, this CAD system only plays the role of auxiliary drawing. To make the CAD system work effectively, we must adopt the design method based on Association, that is, taking all kinds of geometric information contained in parts as the data source, obtaining other required information through geometric inheritance, mathematical derivation, etc., and selecting appropriate constraint propagation and solution models to build a highly shared system of information resources with the ability of real-time response to changes

SolidWorks software can well realize the relevance of the design process. For parts with assembly relationship, the dimension association of their mating parts can be established, and the dimension values can drive and affect each other. For example, there is a dimension relationship b=a+0.1 between the a dimension of part a and the B dimension of Part B. If you change the dimension value a in part a model, you can drive the synchronous and coordinated change of Part B model. This can not only improve the design efficiency, but also avoid mistakes in the design process. Thus, the correlation design between parts is realized, which is of great practical significance for the three-dimensional uneven force design of large-scale assembly

III. implementation method

the main products of our factory are finished railway tank cars and related supporting parts, so the main work of the design department includes parts design and final product assembly design. Due to the increasingly fierce market competition, there are more and more types of products, and the replacement is faster and faster, which puts forward higher requirements for design, production and management. For the design department, the design efficiency and the accuracy of the design process are of great significance to shorten the product development cycle and reduce production costs. Therefore, our factory has invested heavily in the software and hardware of the design department, and has adopted SolidWorks, which is powerful and easy to master, as the software platform for product design

the specific instructions are as follows:

(1) parts can be divided into three categories: the first is commonly used standard parts for general parts (such as screws and springs, because the production capacity has not increased synchronously with the strong market demand), the second is sub parts for a large category of products (which can be regarded as semi standard parts), and the third is unique parts for a certain category of products. After analyzing the design requirements of products, the sub parts can be classified and managed, which is convenient for rational division of labor and coordination of the design process between designers and even different departments. At the same time, it can avoid repeated labor (because the design of standard parts and semi standard parts may have been completed), and grasp the key and difficult points of design tasks, so as to effectively improve work efficiency

(2) component design can also be divided into two categories. One is the general standard structure, which can be completed at ordinary times and can be applied to most assembly ligands. The second is the subassembly of special parts. This part of design is an innovative part of product design, so special attention should be paid to its design progress and quality, so as to ensure the overall design quality and efficiency

(3) IPA animation assembly design verification is an important technical means to ensure the design quality. Using virtual animation assembly of SolidWorks and mechanism motion analysis can not only check the parameters of part design (excluding the influence of human factors), but also analyze the rationality of the structure and function of the whole product, so as to effectively avoid possible errors in scheme design and manual design, Avoid greater direct economic losses

(4) design skills. Because the assembly of large tank car products contains hundreds or even thousands of parts, it is necessary to appropriately "simplify" the parts in the design process, otherwise the animation simulation of the final assembly of the product and even simple rotation are very slow. Therefore, on the premise of not affecting the overall effect, the following two methods are adopted to improve the design efficiency:

1) the parts in the assembly are displayed in solid, wireframe and other ways (even whether the parts are displayed in the assembly can be controlled by parameters). For some non key parts, the internal shape and detail description can be ignored, which can effectively reduce the requirements for computer hardware, Thus, the display operation of large assemblies becomes fast and realistic

2) use layer settings to classify and manage the parts and components in the large assembly (the design of a single part should also be layered to manage the entity, datum and sketch accordingly), which is of great significance for graphic display and animation simulation. The assembly information between parts and components can be obtained by using the property manager of SolidWorks software, so as to check whether the correct assembly operation is carried out according to its due assembly constraints (such as fitting, alignment, coaxial, etc.)

IV. application examples

based on the above design ideas and technical means, we have adopted the three-dimensional full parametric design method in the product design process. Compared with the traditional manual drawing design and two-dimensional software design, it not only improves the design efficiency, but also improves the accuracy of the design, which actually improves the market competitiveness of the product and injects new vitality into the development of the enterprise

the following takes the railway horizontal powdery cargo tank car designed by our factory as an example to illustrate the parametric design of its parts and the assembly design method of products

Figure 1 shows the parameterized 3D model of the can body. The main function of the tank is to transport and load and unload goods. The length L, radius R and wall thickness of the tank shall be designed according to the self weight, load, working pressure, etc δ， At the same time, the assembly relationship between it and several cover plates should be considered in the design, and it should be treated as the parent part of other parts. The datum axis and datum plane for assembly are established in the model at the same time, and these features are also parameter driven and placed in a special layer

Figure 1 parameterized 3D model of the tank

Figure 2 is the assembly drawing of the tank with the upper cover plate of the sleeper beam and the upper cover plate of the traction beam. The two cover parts take the tank body as their parent node in the assembly tree. When carrying out parametric modeling, in addition to the parameter drive of the model itself, the parameter association between it and the parent part (tank body) should also be established: the radius of the cover plate on the sleeper beam and the cover plate on the traction beam is equal to the half diameter of the tank body plus the wall thickness of the tank body. At the same time, the reference axis and reference plane for assembly are established. During assembly modeling, the parametric assembly model can be established through the axial coaxial constraint with the can body and the fitting constraint with the reference plane. At the same time, the change of the can body radius can transmit and drive the update of the two cover plate models

Figure 2 assembly drawing of the tank body and the upper cover plate of the sleeper beam and the upper cover plate of the traction beam

Figure 3 shows the final assembly effect of the tank body assembly and other parts of the vehicle body. Because layer management and good parameter control are used in part modeling, assembly verification becomes very simple and clear. The display of parts and components (special and general) is controlled by closing layers, suppressing and anti suppressing parts in the assembly tree, and the design results are checked by parameter association, transmission, model driving and IPA methods, so as to ensure the coordination between part design and assembly design, The possible interference between components is also avoided through IPA animation simulation

Figure 3 final assembly of tank body and other parts of vehicle body