9.1 Contents of assembly drawings9.1 Contents of assembly drawings

9.2 Representation Methods of assembly drawings 9.2 Representation Methods of assembly drawings

9.3 Dimensioning and Specifications for assembly drawings9.3 Dimensioning and Specifications for assembly drawings

9.4 Numbering and Item block of parts and assemblies9.4 Numbering and Item block of parts and assemblies

9.5 Rationality of Fitting Structures9.5 Rationality of Fitting Structures

9.6 The method and steps to produce an assembly drawing9.6 The method and steps to produce an assembly drawing

9.7 Interpreting and Separating Assembly Drawing9.7 Interpreting and Separating Assembly Drawing

Chapter 9 Assembly Drawings

Assembly Drawings

In addition to show structures and forms of major parts, assembly drawing is also used to represent the operating principles and connections of individual parts of the assembly

The assembly drawing is an important technical document for the design, manufacturing, use, assembly, and repair of the machine.

An assembly drawing is a drawing used to repre-sent a machine, an assembly unit and other equipment.

9.1 Contents of assembly drawings1. A group of viewsRepresents 1)relative mounting position of each part; 2)transmitting motion and operating principle; 3) basic structure of each part.2. Necessary dimensionsInclude 1) external dimensions;2) assembly dimensions;3) characteristic dimensions; 4) location dimensions;5) mounting dimensions;6)as well as, other important dimensions.3. Technical requirementMainly include 1) performance, assembly and debugging; 2) operation, acceptance check; 3) decoration.4. Title block, NO. ,item block1) name, scale, number of pieces, drawing number, specification of the machine or assembly unit; 2) drawing number, name, material, quantity, standard of all parts; 3) signature of the designer, drawer, checker.

装配图的内容

9.2 Representation Methods of Assembly Drawings

9.2.1 Conventional representation 1. The contact surface or fitting surface of two parts is represented as a line, while the non- contact surface or non-fitting surface is represented as two lines even small clearance. 2. Section lines in two contiguous metal parts must be opposite direction or unequally space, while section lines of the same part must be consistent in different views. 3. If the Screwed fastening piece and solid piece ( shaft, key, pin, ball, connecting rod, etc. ) are longitudinally ( axially) sectioned and cut plane goes through the center of symmetry, these parts are represented as though they were sectioned

Example of Conventional Representation Methods (1)

Fitting surface of two parts is represented as a line.

the non- contact surface is represented as two lines.

Example of Conventional Representation Methods (2)

9.2.1 Special representation

1. Cutting away along fitting surface representationTo represent the internal details of a machine or assembly, we can represent some pares as a cut away drawing along the fitting surface. In this representation, the section lines of the fitting surface are not needed, but the section lines of parts that pass through the fitting surface are needed.

2. Dismounting representationIf the fitting relationship or other parts to be represented are behind some other parts, one may assume that the interfering parts are removed, and then clearly draw the parts to be represented. Make sure to represent the removed part in other views and mark it a “removed xx” .

3. Imagination representation

To represent the moving range or limit location of moving parts or other parts related to the assembly but not belonging to the assembly, draw the contour using a double line with one long and two short dashes.

4. Single piece representation

If the structure of a certain part is not clearly represented and will thus affect the understanding of its fitting relationship and function, the part must be drawn separately and marked with “x x direction” near the corresponding view indicating with arrows and capital letters the projection direction.

5. Enlargement representation

6. Simplified representation

(2)If there are several groups of threaded part joints, one only needs to draw one of them and represent the others in the assembly drawing with center lines.

(1) In assembly drawings, certain technical structures, such as round, chamfer, and escape can be omitted.

9.3 Dimensioning and Specifications for assembly drawings

1. Characteristic and specification dimensionsThe dimensions that represent machine specifications or service behaviors are the foundation on which users choose the right products, such as travel distances, calibers and thread.

2. Fitting dimensions That represent the tolerance between parts or subassem-blies that have the following characteristics.

(1) The fitting relationship that must be kept after mounting.

(2) The important distances between two parts that must be kept after mounting.

9.3.1 Dimensioning

3. Mounting dimensionsThat represent the dimensions required to mount the machine or subassembly to its base or to another units.

5. Other dimensionsThat include important dimensions of major parts and limited dimensions of moving parts

4. External dimensions The dimensions that represent the general length, width, and height and are useful for packing, distribution and transportation.

9.3.2 Technical requirements

Use text or symbols to indicate the requirements of the performance, fitting, mounting, inspection, debugging, use of the machine or subassembly and transportation.

Technical requirements are very briefly written at the bottom right hand corner.

9.4 Numbering and Item block of parts and assemblies

1. part numbers shall be marked on the horizontal line inside or near the circle of the leader. The font size shall be one or two grades larger than the dimension number on the drawing. 2. A leader shall be drawn from the visible contour of the part or subassembly with a thin solid line. The end of the leader shall have a small dot. If it is not easy to draw a dot, one can point to the contour with an arrow. 3. The leader cannot be intercrossed or parallel to section lines. When necessary, a leader line may be formed by at most two pieces of line segments. 4. A group of fasteners or parts with a clear fitting relationship can be labeled with a shared leader. 5. the same part shall use the same number and be marked only once. The number shall be arranged clockwise or counterclockwise in the view along the horizontal or vertical direction.

9.4.1 Numbering9.4.1 Numbering

Part numbering

9.4.2 Item block

9.5 Rationality of Fitting Structures

1. If two parts assembly in the same direction, there should be only one pair of contact surfaces, reliable contact of the parts can be ensured, the processing requirements lowered and the cost reduced.

9.5.1 Structure of part contact

2. There should be only one pair of fitting surfaces in the same direction.

3. Two tapered parts are permitted to have only one contact surface in two directions (axial or radial).

4. When two parts contact with a pair of surfaces having a right-angle crossing each other, it is a must to machine a chamfer, groove or round at the corner of the contact surface of the two parts.

5. The boss or recessed surface is added to keep good contact between the surface of two parts and to reduce the machining area and manufacturing cost.

9.5.2 Convenient structures for disassembly

1. Add the hole or use the bolt stud

2. There should be enough space when there is a thread fastener so that the bolt can be removed. (1)

There should be enough space when there is a thread fastener so that the bolt can be removed.(2)

3. One should consider disassembly when there is a bearing by lowering the shaft shoulder.

Illogicality

Reasonableness

9.5.3 Dowel structure

9.5.4 Structures of sealing devices

9.6 The method and steps to produce an assembly drawing

9.6.1 Determining the representation

1.Requirement of representation

(1) Integrity

(2) Correctness

(3) Clarity

2. Contents of a representation.

representation

Selecting the front view

Determining how many views are neededApply various representations to improve understanding

3. The method and steps to produce the representation.

(1) Understanding the subassembly

Working principle

Structuralfeatures

the fitting relationship

the methods of how to connect and fix them,

the relative position

the working principles of the ball valve

The square hole of wrench (part 13)holds the quadrangular prism of the valve rod (part 12). When the wrench is in the position as shown in fig, the valve is open.

Axonometric drawing of a ball valve

Sealing gasket 3Valve core 4 Spacer 5

Nut 7Stud 6 Valve handle 12

Wrench 13

Packing set 11

Valve body1Valve cover 2Stuffing spacer 8

Normally, the part is positioned in the working position for producing the front view. One should show as much as possible the structure and features, especially the main fitting relationships and function and working principles of the machine or assembly.

One may use different views to represent various other portions not clearly represented in the front view. At this moment, consider the fitting relationship and working principle before considering the structural shape of the major.

(2) Selecting the front view

(3) Selecting other views

Selecting the front view

Selecting other views

9.6.2 Steps to produce an assembly drawing

1.Determing its drawing size and scale

2. Specify the drawing’s position

Arrange and draw the datum line to specify the location of each view. When positioning views, a place for dimension and part number should be reserved.

3. Draw the main assembly line

(1) According to the three-alignment rule, draw the major part—valve body.

(2) According to the relative position between the valve body and valve cover. draw the valve cover.

According to assembly sequence, draw the other parts on the main assembly line

(3) Draw the valve core.

(4) Draw the Seal-ing gasket.

4. Draw the other assembly line

(1) Draw the valve handle.

(2) Draw the packing set.

(3) Draw the wrench.

5. Draw the detailed structure

Draw the nuts, washers etc.

6. Draw the section lines.

7. Mark the dimensions and technical requirements.

8. Set the numbering, fill in the title block, item block, signatures.9. Check the entire content of the drawing.

In the design, manufacturing, use, maintenance and technical exchange of the machine or subassembly, the assembly drawing is needed. Therefore, it is a basic skill for engineering personnel to understand assembly drawings and to be able to produce one.

9.7 Interpreting and Separating Assembly Drawing

3. Read the structure shape of each part.

9.7.1 Objectives and requirements 1. Understand the performance, function and working principles of reading assembly drawings.

2. Clarify the purpose the relative position, the fitting relationship of each part, the methods of how to connect and fix them, and sequence for disassembly.

Assembly drawing of a safe valve

9.7.2 Methods and steps

(2) in order to understand the composition of the machine or subassembly, look up the name, quantity, and position of the standard part or subassembly and the non-standard part or subassembly. Locate these parts or subassemblies on the assembly drawing by comparing the number of the part or subassembly.

1. Understanding briefly

(1) the name, purpose, and specification can be acquired by consulting the item block, specification and investigation.

Item block

2. Analyzing views

According to the representation of the assembly

drawing, find out the location and projection direction

of each view, sectional view and cut view, note

whether they use any special representation,

conventional representation or simplified

representation. Make sure that the contents of each

view is clear.

Front view

Left side view

3. Understand working principles and fitting relationship

(1) Start from the views representing the movement

relationship. Make sure that the relative movement

between the moving part and nonmoving part is clear.

Then analyze the working principles and transmission

routes.

(2) Start from the view most clarified representing the

main assembling line. Make sure the fitting relationship

of each part including joint, fixing, and sealing

positions as well as the relative positions of each part.

(1) The working principles of the safe valve

(2) The fitting relationship of the safe valve

(3) adjust of spring

4. Analyze the structure and dimension of each part or subassembly

Get general information by analyzing the projection and referring to the corresponding dimensions according to the relation of lines and surfaces. First, begin with the view that id easier to distinguish from the projection contour, and then proceed to other views.

By combining dimensioning and technical requirements, further analyze the structure, transmission relations and working principles, create an image of the assembly structure.

5. Imaging the structure shape

9.7.2 Detail drawings from assembly drawings

One needs to produce detail drawings based on an assembly drawing, which is called assembly drawing separation.

1. Separating the parts

(1) Locate the parts according to its name and item block. Separate the part from other, according to the consistence of the section line in each view.

(2) According to the three-alignment rule and analysis of lines and faces, determine the structural shape of the part. Refine the part drawings with what is omitted in the assembly drawing.

Assembly drawing of controller valve

Front view of controller valve

Separating the part

Refining the structure of the parts

2. Determining the representation

When choosing the views, one should choose the best representation according to its structural features instead of copying from the assembly drawing, due to different starting points and requirements.

(1) Dimensions mark-ed in the assembly drawing

3. Dimensioning and tolerance

(2) Dimensions not marked in the assembly drawing

5. Filling in the technical requirements

1. 图中未注圆角均为 R5

2. 铸件不得有砂眼、气孔、裂纹等缺陷

其余

4. Determining the surface roughness

(3) Dimensioning standard structure

Valve body

参考资料 [1]. Fundamentals of Engineering Drawing, Warren J.Luzadde

r, 1986.by prentice, inc. Englewood Cliffs, N.J. 07632

[2]. Mechanical Drawing, Gu Wenkui, TongJi University Press, 1988

[3]. 《工程制图基础 ( 双语教学版 ) 》， 张庆伟， 重庆大学出版社

[4]. 《 Engineering Graphics 》 , 钟家麟，东南大学出版社，2005

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