In the process of producing a new machine or component (hereinafter referred to as assembly), it is generally necessary to design and draw an assembly drawing first, then disassemble and draw a part drawing from the assembly drawing, then manufacture the part according to the part drawing, and finally assemble the part into a machine or component according to the assembly drawing.

In the installation and maintenance of existing machines and components, assembly drawings are also indispensable technical data. In technological innovation, technical cooperation and commodity markets, assembly drawings are often used to reflect design ideas, exchange technical experience and convey product information.

Figure 7-26 is the assembly drawing of the milling head. A complete assembly drawing shall include the following contents:

Figure 7-26 Assembly drawing of milling cutter head

1. A set of views

The assembly relationship, working principle and main structural shape of each part of the assembly are clearly displayed.

2. The necessary size

Including specifications, performance, some dimensions required for assembly, inspection and installation.

3. Technical requirements

Use words or symbols to indicate the performance, assembly, adjustment requirements, acceptance conditions, test and use rules of the assembly.

4. Title bar, part (or component) number and parts list

Parts (or components) shall be numbered in the assembly drawing, and the relevant contents shall be filled in the title bar and detail column.

Second, the expression method of assembly drawing

Machines (or parts), like parts, should express internal and external structures. All the expressions and selection principles of parts mentioned above are applicable when expressing assembly. These methods are called general expressions in assembly drawings. According to the characteristics of assembly drawing, in order to express the structure of assembly clearly and concisely, the national standard "Mechanical Drawing" has also formulated some special expression methods, prescribed drawing methods and simplified drawing methods for assembly drawing. Now described as follows:

1. Universal expression method

Basic views, other views, sectional views, sectional views and various specified drawings used in part drawings are also applicable to assembly drawings, and are the most basic expressions, which are called universal expressions. As shown in figure 7-26.

2. Special expression methods

Because the machine (or component) is assembled by several parts, some new problems will appear in the expression, such as some parts covering other parts, and some parts need to show their range of motion in the machine. In order to solve these problems, the national standard Mechanical Drawing provides some special expressions.

(1) Disassembly drawing

When a part (or parts) covers the structure to be expressed in one view of the assembly drawing and they are clearly expressed in other views, it is conceivable to remove the part (or parts) and draw the remaining views. If you need to explain, you can mark "Demolition ×××, etc." . As shown in the left view of Figure 7-26.

(2) the drawing method of cutting along the joint surface of parts

In the assembly drawing, when a part covers other parts that need to be expressed, it can be assumed that the section plane is used to cut along the joint surface of some parts, and then the part between the section plane and the observer is removed to draw a section view.

Figure 7-27 Imaginary Projection Method

(3) Drawing method of representing parts separately

In the assembly drawing, when the shape of a part is unclear, you can draw the view of the part separately, indicate the view name of the part above the drawn view, indicate the projection direction with arrows near the corresponding view, and note the same letters.

(4) Imaginary projection diagram

1) In a machine (or component), some components reciprocate, rotate or swing. In order to represent the extreme position or middle position of moving parts, it is often drawn on one extreme position, and then imaginary projections of other positions are drawn with double dotted lines to represent another extreme position of the parts, and the dimensions are marked. For example, the range of motion of the handle in Figure 7-27. A, the axial movement range of the milling machine center is shown in figure 7-27. B are all drawn with double dotted lines.

2) In order to show the installation or assembly relationship between an assembly and other parts, the contour lines of parts (components) adjacent to the assembly but not belonging to the assembly are often drawn with double dotted lines. As shown in Figure 7-27 (a), the junction box is installed on the base shown by the two-dot chain line.

(5) Exaggerated painting

Some thin gaskets, thin springs, small gaps between parts, taper pins, taper holes, etc. are often encountered in assembly. If they are not obvious according to their actual dimensions, they are allowed to be exaggerated in the assembly drawing. As shown in figure 7-28. A, the adjusting gasket between the bearing gland and the box is exaggerated; Figure 7-28 shows the clearance between the bearing cover with sealing groove and the shaft. B is also drawn after enlargement.

Figure 7-28 Exaggerated Drawing Method

(6) start painting

In order to show the assembly relationship between the transmission route and the shaft of the component transmission mechanism, it can be cut and drawn along the axis according to the transmission order. Please note the "×××× expansion" above the expansion section.

Third, the prescribed painting method

In order to clearly distinguish each part and accurately express the assembly relationship between them, the drawing method of assembly drawing is stipulated as follows.

Drawing method of (1) contact surface and mating surface

Only one contour line (thick solid line) is drawn on the contact surface or mating surface of two adjacent parts. When two parts are nested together with different basic sizes, even if the gap between them is small, two clearly spaced contour lines must be drawn.

Figure 7-29 Drawing Method of Section Symbol

(2) Drawing of section symbols (Figure 7-29)

1) The section symbols of the same metal part shall be kept in the same direction and at equal intervals in all section drawings and drawings.

2) The inclination directions of section symbols of two adjacent parts shall be opposite.

3) When three parts are adjacent to each other, the third part should be separated by different section symbols and staggered with the section symbols in the same direction, except that the section symbols of the two parts are inclined in opposite directions.

4) In the assembly drawing, the cross section of a narrow area with a width less than or equal to 2mm may be blacked out instead of the cross section symbol.

(3) Drawings of solid parts and fasteners

1) In the assembly drawing, for solid parts (such as shafts, handles, connecting rods, hooks, balls, keys, pins, etc. ) and fasteners such as bolts, nuts, washers, etc. ), if they are cut longitudinally and the cutting plane passes through their symmetry plane or axis, these parts are drawn without cutting. However, when the section plane is perpendicular to the axis of some solid parts and fasteners mentioned above, these parts should be drawn according to the section view, and section symbols should be drawn.

2) If it is necessary to show some structural shapes and assembly relationships on solid parts, a partial sectional view can be adopted.

Fourth, simplify and omit drawing.

(1) is used for several identical parts groups (such as bolt connection, etc.). ) In the assembly drawing, only one or several groups can be drawn in detail, and the rest only need to be represented by dotted lines. As shown in Figure 7-26, a set of bolt connection diagrams.

(2) In the assembly drawing, the rolling bearing is allowed to simplify the drawing.

(3) On the assembly drawing, the technological structure of parts, such as fillet, chamfer, unloading groove, etc. , drawing is not allowed.

(4) In the assembly drawing, when the part passing through the cutting plane is a standard product or the part has been clearly expressed by other figures, it can be drawn without cutting.

Five, the assembly drawing dimensioning method

The dimensions on the assembly drawing are different from those on the part drawing. You don't need to mark all dimensions of all parts, just mark the following five necessary dimensions:

1. Body size

Dimensions that represent the performance or specifications of components are called feature dimensions. This size is determined before assembly design, and it is the basis for designing and using the machine. For example, the center height of the milling head in Figure 7-26 is 1 15, etc.

2. Assembly dimensions

Assembly dimensions are dimensions related to the assembly quality of the assembly, including:

(1) Suitable size

It is a dimension that indicates the nature of fit between two parts, and is usually marked with a fit code. As shown in Figure 7-26, Ф Ф 28H8/K7 and Ф Ф 80K7/H6.

(2) the relative position size

It is an important relative position dimension between related parts or components. Such as the distance between parallel principal axes, the distance between principal axes and reference plane.