The task of mechanical design is to determine, determine and draw a specific structural diagram according to the overall design and program principles to reflect the required functions. The working principle is realized as a member or part of an abstract class, which determines the material, shape, size, tolerance and surface state of heat treatment, while the structural components must consider the relationship between treatment, strength, stiffness and accuracy. Therefore, although the technical drawings of product structure design are direct, the structure is not a simple mechanical design drawing, and the design drawing is only an expression language, and the specific integration technology is the basic content of structural design.

5. 1.2

The main characteristics of mechanical design The characteristics of mechanical design are: (1) It is an idea, drawing and calculation (sometimes a necessary experiment) in a design process. The biggest mechanical design problem involved, specifically, in the whole mechanical design process, the average time of structural design accounts for about 80%, and the maximum workload plays an important role in successful mechanical design. (2) Solve mechanical design problems, and the same design that meets the requirements of mechanical structure is not unique. (3) The mechanical design stage is a very active link in the design, which often needs to be repeated. Therefore, we must begin to understand the mechanical structure design.

basic requirement

Design method of structural elements of mechanical structure and mechanical 5.2 structure

5.2 integral machine

Geometric element

Mechanical structure function 0. 1 structure mainly depends on the relative position between mechanical parts and the geometric structure realized by each part. There are often many curved parts in the parts formed by their surfaces, and the surfaces of these parts are in direct contact with the surfaces of other parts. This part of the surface is called functional surface. Some functions of coupling between surfaces are called coupled surfaces.

Functional surface is to determine the mechanical function of parts, and design is an important factor in the core function of curved parts in structural design. Surface geometry describes the main function, size, number, position and order of surface geometry. Through the change of functional surface design, several technical realization schemes with the same structure can be obtained.

& lt bromine

5.2.2 structure/> Any part of a machine or mechanical device that does not exist in isolation. Therefore, in structural design, in addition to learning the functions of parts themselves and other functions, it is also necessary to learn the relationship between parts.

Related parts are contained in directly or indirectly related classes. Where there is a direct assembly relationship, there is a direct relationship. There is no direct relationship between assembly and indirect association. Indirectly divided into position-related categories and motion-related categories. It is necessary to correlate the positions. For example, in two adjacent shaft reducers, the center distance must ensure a certain accuracy, and the two shafts must be parallel to the gorgeous value of V? Angry? E narrow-minded t-master? How dare the beak invade? Oh, by accident? Brain master? Is tassel Huang Huanhe careless? Vent Wu? Fei Daen's split brain is Zen master Susan? Tassel 1 is called Apricot Moon. What are the southern lines and lines in downtown Cape Town? Exquisite makeup, strong spine, seedling excitation, ellipsoid towering peak mane, yo-ho announcement, five halls? Fate? Is the mane used to transport the spine? Drowning beak, Wu Hui, Meng Huan? There's an explosion peak? Submerged? Master? Where's the beak BR & gt

Most parts have two or more directly related parts, and most of them have two or more parts with the following structure and each part of other related parts. In the design, reasonable selection of heat treatment, shape, size, accuracy and surface quality of materials must be considered for 20 copies. It is also necessary to consider meeting indirect correlation conditions, such as the size and accuracy calculation of the chain. Generally speaking, if one part is directly related to more parts, the structure is more complicated; The more indirectly related to the parts, the higher the accuracy of the parts. For example, Figure 5. 1 Hub connection.

5.2.3 Structural design and materials should be pointed out according to different heat treatment structures.

Material problem

The choice of mechanical design, different materials have different characteristics, to process different materials, structural design should be appropriate. According to the functional requirements, we should not only choose reasonable materials, but also determine the corresponding treatment methods according to the type of materials, and judge the appropriate structure according to the treatment requirements. Only by choosing the right materials can we make the best use of the structure design.

Designers must fully understand the mechanical properties, processability, cost and other information of the selected materials when making the correct material selection. Structural design should be based on the selected materials and corresponding treatment characteristics, and in accordance with different design principles.

For example, the mechanical properties of steel are basically the same in tension and compression, so most steel beam structures are symmetrical. The compressive strength is much higher than the tensile strength of cast iron, so when the iron structure bears most asymmetric bending, the maximum compressive stress load is greater than the maximum tensile stress. 2 The icon on the cast iron bracket is compared with 5.2. Steel structure design usually increases strength and structural rigidity, but if the wall thickness of pouring structure is too large, it is difficult to ensure the quality of castings, which increases the method of section size, so pouring structure is usually a method to improve the rigidity and structural strength of stiffening plates and partitions. Due to the poor rigidity of plastic materials, large stress and uneven cooling of castings caused by structural warping, plastic structures have similar ribs and symmetrical thickness.

For the parts that need heat treatment, the structural design requires the following applications: the geometric shape (1) parts should be simple, symmetrical and ideal spherical. (2) For parts with different cross-sections, the change of cross-section size must be gentle to avoid sudden change. If the adjacent parts change too much, resulting in uneven cooling, it will inevitably form cross-sectional size and internal stress. (3) In order to avoid sharp edges and prevent sharp edges or sharp corners of overheated melt, the chamfering at the edge of the groove or hole is generally 23 mm.. (4) In order to avoid the gap in the quenched section, the difference in deformation thickness, and the cracking with higher inclined section thickness.

Basic requirements, structural design, contents and requirements of mechanical products

5.3. 1 Mechanical design is also very different, but they all have the same thing in common. There are three different levels of mechanical design to illustrate the structural design requirements.

1。 Functional design meets the functional requirements of main machinery, which is reflected in technology. Due to the reliability of realization principle, work, technology, materials and assembly.

2。 Considering various requirements and limitations, the goal is to improve product quality and cost-effective quality. This is the characteristic of modern engineering design. Specific operation, appearance, cost, safety, environmental protection and other requirements and restrictions. In modern design, the quality of design is very important, which often determines the competitiveness of its products. This is only to meet the requirements of the main technical characteristics, and the mechanical design of the times has passed. The key to integrate various demands and improve product quality is modern mechanical design. Compared with considering the working principle, considering different requirements seems to be a problem of design details, but the sum of details and quality, product quality is not only a problem, but also a start to improve design quality.

3。 Innovative design, optimization design and structural design variables are used to build a system optimization design space, and scientific methods such as optimizing innovation and creative design thinking are used.

In order to improve product quality, in the increasingly fierce market competition, the demand for personalized development emerges one after another. Therefore, optimal design and innovative design play a more important role in modern mechanical design, and they will be the focus of product development with technical competitiveness in the future.

It is generally not difficult to get a feasible solution. The task of mechanical design is to find a better or, in many cases, the best feasible solution. The premise of structural optimization design is to build many possibilities, and the first choice is to build a lot of optimization space, which is the most creative place of structural design. At present, the optimization design of basic structure is still limited to the problem described by mathematical model. The optimization effect of multi-potential and multi-structure should be composed of design variables such as process, material, structural design of coupling mode, shape, order, direction, quantity and size according to solution space. 5.3.2 Final basic design standard of mechanical structure results

The structure in the form shown in the mechanical design can be processed, assembled and manufactured according to the final product. Therefore, the design of mechanical structure should meet the basic functional requirements, reliability, manufacturability, economy and appearance requirements of products. In addition, the stressed parts should be improved to improve strength, rigidity, accuracy and service life. Therefore, mechanical structure design is a comprehensive technical work. Errors or unreasonable faults in structural design may lead to unnecessary parts, which will bring great inconvenience to the accuracy required by the assembly and maintenance design that the machine cannot achieve. In the process of mechanical design, the following design standards should be considered.

1。 Functions required by the design standard of the implementation mode

2。 Meet the strength requirements of design standards.

3。 Stiffness in accordance with structural design standards

4。 think

5 process design standards. Consider decoration design standards

6。 Consider design criteria

5.3.2 Basic design criteria for mechanical structures

1。 The required functional product design standards are realized.

The main purpose of design is to meet the predetermined functional requirements, so as to meet the design standards, and the function required for structural design is the first problem to be considered. In order to meet the functional requirements, you must do the following.

(1) Clear function: The design determines the size and structure of the shape parameters according to the connection between its vehicle-mounted function and other components. The main function of the assembly must be to bear the load, transmit the motion and power, and ensure or maintain the relative position or motion trajectory between related parts or components. The overall structural design of the machine should meet its functional requirements. Reasonable distribution

(2) Function: product design, according to the specific situation, usually requires a reasonable assignment of tasks, that is, the function is decomposed into multiple sub-functions. Each sub-function should have determined the commitment structure between components, and there should be a reasonable and coordinated relationship to achieve the goal of the overall function. Multi-structure parts have the same function, which can reduce the burden of parts and prolong the service life. V-shaped structure, whose cross section is an example of reasonable assignment of tasks. Tension of fiber rope; The rubber packing layer is stretched and compressed, and the belt bends; The function of the cover pulley is to generate the necessary friction transmission groove. For example, if only the pre-tightening force of the bolt bears the friction caused by the lateral load, then the size of the bolt will be too large, and the key lateral load of the shear elements, such as pins and sleeves, will be added. Will share to solve this problem.

(3) Feature set: In order to simplify the mechanical structure of products, reduce processing costs and facilitate installation, in some cases, parts or components can undertake multiple functions. Shape feature set makes more complex parts, but it has a certain degree, but in other aspects of processing, it increases the processing cost and should be designed according to the specific situation.

5.3.2 Basic mechanical structure design standards

2。 Meet the strength requirements of design standards.

( 1)

The strength standard, such as changing the cross-sectional size of a part, should adapt to the change of its internal stress and be equal to the strength of the cross-section. According to the structural design principle of equal strength, materials can be fully utilized, thus reducing weight and cost. If legs and stepped shafts are designed. Figure 5.3.

In order to visually show how mechanical parts are transmitted, they are regarded as forces with water flow.

Figure 5.3

(2) Reasonable flow structure under stress state

Components of state power force these lines to merge into one stream. The force indicating the flow plays an important role in the structural design of inspection.

The uninterrupted component of force flow, no force line will disappear out of thin air, it will come from one place and from another. Another feature is that it tends to force the flow through the shortest route along the periphery formed in the high stress area, where the energy is so dense. From the pressure point of view, underutilized materials flow through other parts with sparse force flow or unpowered supply. Therefore, if the component is designed to increase the stiffness, the shortest path of force flow in the bearing area should be reduced by designing the shape of the component, so the cumulative deformation is smaller, the stiffness of the component is improved, and the material is fully utilized.

The bevel gear is arranged on the cantilever, and the bearings of the bevel gear should be as close as possible to reduce the length of the cantilever and improve the bending strength of the shaft. Several examples in Figure 5.4, a typical example.

(3) reduce stress concentration structure

When the peak turns, the flow direction is stressed, and the water flow at the turning point is too dense, resulting in stress concentration. Design measures should be taken to smooth the labor flow. Stress concentration is an important factor affecting the fatigue strength of parts. Structural design should try to avoid or reduce stress concentration. This method will use unloading structure in appropriate parts, such as adding rounded corners to describe it. Figure 5.5.

(4) So? When working in a machine, some unnecessary forces, inertial forces and axial forces of helical gears often occur, which not only increases the load of other parts of the power shaft and the casing, but also reduces the accuracy and service life, and also reduces the transmission efficiency of the machine. The so-called load balancing refers to the measures to balance all or part of all structures, so as to reduce or eliminate their adverse effects. These structural measures are mainly to balance the components and arrange them symmetrically.

For example, the axial force generated on the same shaft 2 The rotating tooth size of helical gear and helical angle and the axial force cancel each other, thus reducing the bearing load. Figure 5.6.

5.3.2 Basic mechanical structure design standards

3。 The structural rigidity meets the design standard.

A component must have sufficient rigidity to ensure that it can be used to realize its function in normal times.

5.3.2 Basic mechanical structure design standards

The four main purposes of structural design considering process design standards are: to ensure the realization of functions and make products meet performance requirements. However, the structural design of production cost and the influence of product parts on quality cannot be underestimated. Therefore, the structural design should strive to be better than the so-called better.

Good processing technology makes products refer to structural parts. In the process of easy manufacturing, what treatment methods may not be the manufacture of some structural parts, or the production cost is high, or the quality will be affected? Therefore, it is very important for designers to identify the characteristics of processing methods and design structures to avoid defects. In practice, the manufacturing method of structural parts is restricted by many factors, such as the size of manufacturing will affect the manufacturing method of blank; The conditions of production equipment may limit the size of the workpiece; In addition, modeling, accuracy, heat treatment, cost and other aspects may have certain constraints on the structure technology. Therefore, the structural design should fully consider the influence of these factors on the process.

5.3.2 Basic mechanical structure design standards

5。 think

The assembly design standard is an important step in the assembly manufacturing process, and the assembly quality and cost of structural parts directly affect the assembly design standard. The standard components of structural design are summarized as follows

(1) whole machine assembly unit

Reasonable division should be divided into several units (parts or components) that can be assembled independently, so as to realize parallel and professional assembly business, shorten assembly cycle, and adopt step-by-step technology to facilitate inspection and maintenance.

(2), so there is no correct installation position.

-Ensure accurate positioning of parts. As shown in Figure 5.7, connect with two flanges of ordinary bolts. With reference to the structure shown in Figure (1), non-radial positioning cannot ensure coaxial two-hole assembly; Figure (b) combines a matching positioning datum and a cylindrical surface with reasonable structure.

-Avoid double ties. Part a and part b (I) in fig. 5.8 A have two end bands. Due to manufacturing errors, the correct position of Part A cannot be guaranteed. Figure 5.8 (2) has a reasonable structure.

-Prevent assembly errors. As shown in Figure 5.9, there are two pin bearings for positioning. The arrangement of these two opposite pin diagrams (A) is equal to the distance of bolts, which can be installed at assembly180 rotation, thus causing the deviation of the center axis of the hole center line to increase. Therefore, if two locating pins are arranged on the same side, or two bolts are found to break unevenly.

Figure 5.9

(2) Distance to make parts easy to assemble and disassemble.

Structural design and assembly should ensure enough space, such as wrench space; Avoid too long fit, so as not to increase the difficulty of assembly and scratch the mating surface, because some stepped shafts are designed; In order to facilitate the removal of accessories, the removal tools should give way, such as bearing removal. Figure 5- 10.

5.3.2 Basic mechanical structure design standards

6。 Considering that BR design should not only meet the design standards of products with functional requirements, but also consider the aesthetic value of product appearance, which makes people attractive. From a psychological point of view, 60% of people's decisions depend on first impressions. A technological product with social attributes is a commodity. In the era of buyer's market, designing the appearance of products to attract customers is an important design requirement. And allows the operator to reduce the misuse of products due to the energy generated by consumption.

The design includes three aspects: shape, color and surface treatment.

When considering modeling, we should pay attention to the following three issues:

(1) size ratio

In the structural design, we should pay attention to the coordination and unity among all parts of the outline, and consciously use the "golden section method" to determine the size, so as to make the product more beautiful.

(2) Outline a simple unity.

The shape of mechanical products is usually a combination of various basic geometric shapes (rectangle, cylinder, cone, etc.). ). The design should make a suitable shape, the basic visual shape should be balanced, and it is easy to fall in the sense that the roughly symmetrical shape is not completely symmetrical; Minimize changes in shape and position to avoid clutter; Improved process

(3) color, pattern and decoration support

The coated surface of mechanical products not only has the function of anti-corrosion, but also improves the visual effect. Allow the operator to reduce eye fatigue through appropriate colors and improve the function of the recognized information display device.

Use only monochrome widgets. Especially for large sports parts, if only one color is used, it will appear monotonous and horizontal, and a little more color will make the whole tone come alive. In the case of storing multiple colors in * * * *, it should play a leading role in the background and be called the background color of the contrast color accordingly. But in the product, different colors are not very attractive, and too many colors will give people a flashy feeling.

Comfortably located in an area of about yellow, green, yellow to brown. This trend is getting warmer and warmer, and yellow and green often seem uncomfortable; The strong gray tone is depressing. In warm and cold environments such as yellow, orange and red. For cool colors, such as light blue heat dissipation environment. All colors should be

Fade. In addition, a certain color scheme can make the product look safe. ? A small change in shape, a larger light plane, and the moving area of the active element is arranged to have a dark contour; The secret machine should be placed in the lower part and on the top of the lamp.

5.4 Working Steps of Mechanical Design

Different types of mechanical design are very different in various situations, so there is no need to step by step. Usually, the shape and size of the finished product and the layout of the required functions of the components are determined. It is a combination of comprehensive analysis, drawing and calculation in the process of structural design, as follows:

1 Priority sorting, balance: design a clear structure, define the main tasks and realize its functions, with the aim of breaking it down into several functions. As well as the initial components of the main functions realized from the machine (the key role of the basic functions played by the transformation of energy or substances in a machine), the surface structure is usually realized at the beginning of the function. Considering other parts of each other, the curved surfaces such as connection relationship and position are gradually connected together to form a part, which is then connected with other parts of the component and finally combined into one to realize the main functions of the machine. Then, determine the main components, such as secondary, auxiliary or support components: seals, lubrication and maintenance.

Sketch 2: After analyzing and determining the structure, according to the roughly estimated size of the main structural parts, the parts are preliminarily determined by drawing the structural sketch. The figure shows that the basic shape of each component should be limited by the size, space limitation and installation size of the main moving parts. In the design and application of the same structure, we should pay full attention to standard parts, common parts and common parts, so as to reduce the workload of design and manufacturing.

3. Determine the final structure of the scheme: a comprehensive process of realizing all the working functions of various alternative structures in a certain way. Analyze the process of evaluation and comparison and finally determine the work structure. By changing the surface, position, quantity, material, surface performance and joint size of parts, the system generates new programs. In addition, the characteristics of thinking are comprehensively analyzed in a more intuitive way, that is, in an unsystematic way. People's feelings and intuition have no reason. Years of life experience have unconsciously accumulated various judgments, and the design of feelings and intuition has played a greater role. . 4. Improvement: analyze the bearing part of the structure, and calculate the strength, stiffness and wear resistance of the bearing when necessary. By improving the structure, the structure can bear the bearing capacity, and the work is more reasonable, thus improving the accuracy. In order to disassemble parts, materials, processing requirements and structural improvement. In actual design, the designer's imagination plays a very important role in dealing with the design and content of simulation, considering problems from various angles, possible problems, the design of deep structure and the illusion of breadth.

Perfect structural design: continuously improve according to technical, economic and social indicators, find out the defects and weaknesses of the selected procedures, control various requirements and restrictions, and make repeated improvements. Consider the generalization and standardization of parts, reduce all kinds of parts and reduce production costs. Attention should be paid to sketch standards and the structure of purchased parts. Pay attention to safety and labor (that is, labor conditions: whether it is easy to operate, observe and adjust, and whether it is easy to eliminate faults and make noises when faults occur) to improve the structure.

Balance between form and beauty: consider whether the object is intuitive, symmetrical and beautiful. When wasting materials or mechanisms, the appearance is uneven. Inertia force is unbalanced, interference is small, maneuverability is unstable, fatigue stress is concentrated, and performance is weak.

In short, the mechanical structure in the design process from the inside out, from important to secondary, from local to general, from coarse to fine, weigh the pros and cons, check repeatedly, and gradually improve.

Mechanical design plays an important role in mechanical design. This chapter discusses the characteristics, procedures and thinking modes of mechanical structure design. The working principle of the machine and the design requirements of components are one of the main factors that determine the structure and shape of components, followed by the selection of materials and the requirements of manufacturing technology. Therefore, it has good machinability (machining and assembly). In addition, in order to improve the structure, each part has a shape, which has a great influence on improving strength and stiffness.