Application of three-dimensional CAD software in the expansion of structural parts

0 Introduction

The riveting and welding structure in the fan manufacturing industry occupies a large proportion, and some structural parts need to be carried out before processing. The quality of lofting directly affects the quality and processing cost of the product.

Lofting is a highly professional skill, which requires the operator to have basic knowledge of descriptive geometry, space imagination and rich practical experience. The traditional expansion lofting is done on the plane as a method of graph. In this way, it is more difficult to complete the complicated deployment.

With the development of computer application technology, three-dimensional CAD software has been widely used in China in recent years. This paper introduces a method of using three-dimensional CAD software to expand the structure, which makes the development of complex structure parts simple, convenient and quick.

1 Expansion Method Overview

The three-dimensional CAD software is applied to the development of more complicated and non developable surfaces.

Three-dimensional CAD software for the expansion of the lofting is roughly divided into 4 steps.

1.1 Drawing sketches

Sketches are the basis for generating surfaces and entities. Sketch drawing should be based on design drawings, for the sake of technological considerations can be modified; more complex graphics can be inserted into sketches after drawing on two-dimensional design software, and constraints are added after sketching.

1.2 Building the Model

Modeling is on the basis of sketch contour, through the function of the software generation surface or entity.

As the unfolding lofting is carried out on a characteristic surface of an object (such as a neutral layer), the characteristics of the surface are generally carried out during the modeling operation. The modeling methods used to expand the lofting are: stretching surface, lofting surface, rotating surface, extension surface, etc.

1.3 Decomposition surface

Sketch drawing and modeling is the process of lofting, and obtaining data is the ultimate goal.

The three-dimensional CAD software provides only the expansion function of the general gold-plated parts, and does not provide the function of surface expansion. The decomposition surface is the decomposition of a surface into a number of interconnected, in different planes of the triangular region, these triangular planes to replace the surface, in order to achieve the approximate expansion of the purpose.

1.4 Drawing Expansion Diagram

Drawing an expansion chart is the formation of the decomposed surface, the triangles connected to each other drawn on the same plane. The expansion plan should be sorted according to the process requirement, and the dimension and relevant information should be marked to guide the production.

2 Expansion Method Features

Using three-dimensional CAD software to carry out lofting and traditional expansion lofting method comparison, has the following characteristics.

2.1 Simple

Based on the knowledge of descriptive geometry, the traditional expanded lofting method studies the projection relation of point, line and plane. A series of techniques, such as projection method, rotation method, radiation method, section method and surface change method, are used to obtain the real length of the space segment, so as to achieve the purpose of expansion. This method is highly professional and difficult to master. More lines and heavy workload.

The three-dimensional CAD software is used to carry out lofting, which is completely different from the traditional layout method in principle. It no longer needs descriptive geometry knowledge, does not need to study the projection relation, also does not need to unfold the principle, the method and the technique. Because in the three-dimensional CAD software generated to expand the surface, a variety of geometric relationships can be at a glance. The expanded data can be obtained by decomposing the surface. This method has a minimal amount of drawing and only needs to draw the relevant contour lines.

2.2 Accurate

The traditional expansion of lofting because of the complexity of the method, there are many lines, inevitable mistakes. Once an error occurs, all subsequent work will be affected. The inspection of the lofting process is also very difficult.

The three-dimensional CAD software is used to carry out lofting, by adding geometrical relation and dimensioning the relative dimensions in the car diagram, so as to restrain each geometrical element in the graph, and improve the accuracy of drawing and the speed of drawing. Each step of the operation can be modified. When modified, it will automatically adjust subsequent related procedures or prompts for information.

2.3 Practical

Using three-dimensional CAD software to carry out lofting process is simple, general engineering and technical personnel can quickly grasp. Suitable for the development of more complex structural parts in production.

3 Expand the instance

It is difficult to unfold the wing type vane and the oblique cone of the inlet air blower in the fan industry. Although some of the data introduced the airfoil blade expansion method, but because of the complexity of the steps, the real grasp and application of very few. It is easy to unfold with three-dimensional CAD software.

The following is an example of the 4-72nolo airfoil blade expansion, and the unfolding process is briefly described.