Mechanical design and taboos of mechanical design

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Mechanical design and Taboos of mechanical design
Written By Jasmine HL
Mechanical design, according to the requirements of use, conceive, analyze and calculate the
working principle, structure, movement mode, force and energy transmission mode, material and
shape of each part, lubrication method, etc. and translate it into specific descriptions. Working
process as a basis for manufacturing.
Mechanical design is an important part of mechanical engineering, the first step in mechanical
production, and the most important factor determining mechanical performance. The goal of the
mechanical design is to design the best machinery under a variety of limited conditions (such as
materials, processing capabilities, theoretical knowledge and calculation methods), that is, to
make an optimal design. Optimal design requires comprehensive consideration of many
requirements, generally including: best working performance, lowest manufacturing cost,
smallest size and weight, most reliable in use, lowest consumption and least environmental
pollution. These requirements are often contradictory, and the relative importance of them
varies according to the type and use of the machine. The task of the designer is to weigh the
weight according to the specific situation and make overall plans to ensure that the designed
machine has the best comprehensive technical and economic effect. In the past, the optimization
of design mainly relied on the designer's knowledge, experience and vision. With the
development of new disciplines such as basic theories of mechanical engineering, value

engineering, and system analysis, the accumulation of technical and economic data and materials
for manufacturing and use, and the popularization and application of computers, optimization
has gradually abandoned subjective judgments and relied on scientific computing.
The design of various industrial machinery, especially the mechanical design of the whole and the
entire system, must be dependent on the relevant industrial technology and it is difficult to form
an independent discipline. Therefore, specialized branches of mechanical design such as
agricultural machinery design, mining machinery design, pump design, compressor design, steam
turbine design, internal combustion engine design, and machine tool design have emerged.
Mechanical design can be divided into three types: new design, inherited design and variant
design.
1.New design
Apply mature science and technology or experimentally proven new technologies, and design
new types of machinery that have not been in the past.
2.Inheritance design
According to the use experience and technological development, the existing machinery is
designed and updated to improve its performance, reduce its manufacturing cost or reduce its
operating cost.
3. Variant design
In order to meet the new needs, the existing machinery has been modified or added to delete
parts and developed variant products different from the standard type.
Main process
1. Formulate design tasks based on user orders, market needs and new scientific research results.
2. Preliminary design. Including determining the working principle and basic structural form of
the machine, conducting motion design, structural design and drawing preliminary general
drawings and preliminary review.
3. Technical design. This includes revising the design (based on the initial review), drawing all
parts and new master drawings, and a second review.
4. Work drawing design. Including the final modification (based on the opinions of the second
review), drawing all working drawings (such as parts drawings, component assembly drawings
and general assembly drawings, etc.), and developing all technical documents (such as parts lists,
wearing parts lists, instructions for use, etc.).
5, stereotyped design. Machinery for batch or mass production. For some design tasks that are
relatively simple (such as the new design of simple machinery, inherited design or variant design
of general machinery, etc.), the preliminary design process can be omitted.
design phase
The quality of a machine basically depends on the design quality. The effect of the manufacturing
process on machine quality is essentially to achieve the quality specified in the design. Therefore,
the design phase of the machine is the key to determining the quality of the machine.
The design process in question refers only to a narrow technical design process. It is a creative

work process, and it is also a job to make the most of the existing successful experience. It is
necessary to combine inheritance and innovation well in order to design high-quality machines.
As a complete machine, it is a complex system. To improve the quality of design, there must be a
scientific design process.
Each phase is briefly described below.
(I) Plan
During the planning phase, a full investigation and analysis of the needs of the designed machine
should be performed. Through analysis, the functions that the machine should have are further
clarified, and the constraints determined by the environment, economy, processing, time limit
and other aspects are proposed for future decisions. On this basis, the comprehensive
requirements and details of the design task are clearly written, and a design task book is finally
formed as a summary of this stage. The design task statement should generally include: the
function of the machine, economic and environmental protection estimates, rough estimates of
manufacturing requirements, basic use requirements, and the estimated time to complete the
design tasks. At this time, these requirements and conditions can generally only give a reasonable
range, rather than accurate figures. For example, it can be determined by the requirements that
must be achieved, the minimum requirements, and the requirements that are expected to be
achieved.
(Two) scheme design
According to different working principles, a variety of specific programs for implementing
agencies can be formulated. For example, in the case of cutting threads only, either the
workpiece can only be rotated and the tool can be moved in a straight line to cut the thread
(such as cutting a thread on an ordinary lathe), or the workpiece can be left and the tool can be
rotated and moved to cut the thread ( (Such as using thread processing). This means that even
for the same working principle, there may be several different structural solutions.
Of course, there are many options for the prime mover scheme. Due to the universality of power
supply and the development of electric drag technology, it can be said that most fixed machines
now prefer electric motors as the prime mover part. Thermal prime movers are mainly used in
transport aircraft, construction machinery or agricultural machinery. Even if the motor is used as
the prime mover, there are still options for AC and DC, high speed and low speed.
The transmission scheme is more complicated and diverse. For the same transmission task, it can
be accomplished by multiple mechanisms and a combination of different mechanisms. Therefore,
if Ⅳ is used to represent the number of possible schemes of the prime mover part, and N2 and
N3 represent the possible schemes of the transmission part and the execution part, respectively,
then the total number of possible schemes of the machine is Ni × N2 × N3.
The above is just a discussion of the three main parts that make up a machine. Sometimes, it is
necessary to consider the configuration of auxiliary systems, which will not be discussed in this
book.
Among so many solutions, only a few are technically feasible. For these several feasible solutions,
comprehensive evaluation shall be carried out from the aspects of technology, economy and

environmental protection. There are many evaluation methods, and the economic evaluation is
taken as an example to explain briefly. When evaluating based on economics, we must consider
both the economics during design and manufacturing and the economics during use. If the
structure of the machine is more complicated, its design and manufacturing costs will be
relatively increased, but its functions will be more complete and its productivity will be higher, so
it will be more economical to use. Conversely, machines with simpler structures and incomplete
functions have less design and manufacturing costs, but their use costs will increase. When
evaluating the design and manufacturing economics of a structural solution, it can also be
expressed in terms of the cost per unit effect. For example, the cost of unit output power, the
cost of a single product, and so on.
When performing machine evaluation, it is also necessary to analyze the reliability of the
machine and use reliability as an evaluation index. From a reliability standpoint, it is often unwise
to blindly pursue complex structures. Generally speaking, the more complex the system, the
lower the reliability of the system. In order to improve the reliability of complex systems, parallel
standby systems must be added, which inevitably increases the cost of the machine.
Environmental protection is also an important aspect that must be carefully considered in design.
Technical solutions that cause adverse effects on the environment must be analyzed in detail and
technically mature solutions must be proposed.
Through the program evaluation, finally make a decision to determine a schematic diagram or a
schematic diagram of the mechanism movement for the next technical design.
In the scheme design stage, the relationship between reference and innovation must be properly
handled. The successful precedent of similar machines should be used for reference. The original
weak links and the parts that do not meet the requirements of the existing tasks should be
improved or fundamentally changed. We must actively innovate, oppose conservative and copy
the original design, and also oppose blind innovation and discard reasonable original experience
without using these two wrong tendencies.
(Three) technical design
The goal of the technical design phase is to produce general assembly sketches and component
assembly sketches. The outline and basic dimensions of each component and its parts are
determined through the design of the sketch, including the connections between the
components, the outline and basic dimensions of the components. Finally, draw the work
drawings, assembly drawings and assembly drawings of the parts.
To determine the basic dimensions of the main parts, the following must be done:
Kinematic design of the machine. According to the determined structural scheme, the
parameters (power, speed, line speed, etc.) of the prime mover are determined. Then do
kinematic calculations to determine the motion parameters (speed, speed, acceleration, etc.) of
each moving component.
Machine dynamics calculations. Combine the structure and motion parameters of each part to
calculate the magnitude and characteristics of the loads on the main parts. The load obtained at
this time is only the nominal (or nominal) load acting on the part because the part has not yet

been designed.
Design of workability of parts. Knowing the magnitude and characteristics of the nominal load on
the main parts, the preliminary design of the parts and components can be done. The working
capacity criteria on which the design is based must be reasonably formulated with reference to
the general failure conditions, working characteristics, and environmental conditions of the
components. Generally, there are criteria such as strength, stiffness, vibration stability, and life.
By calculation or analogy, you can determine the basic dimensions of zeros and parts.
Design of component assembly sketches and general assembly sketches. According to the basic
dimensions of the main parts and components that have been determined, the assembly
assembly sketch and the general assembly sketch are designed. The outline and dimensions of all
parts need to be structured on the sketch. In this step, the structure and size of each part need to
be well coordinated, and the structural manufacturability of the designed parts and components
is fully considered, so that all parts have the most reasonable configuration.
Check of main parts. There are some parts, because the specific structure is not determined in
step 3) above, it is difficult to carry out detailed work capacity calculations, so only preliminary
calculations and designs can be done. After the component assembly sketch and the general
assembly sketch are drawn, the structure and dimensions of all parts are known, and the
relationship between adjacent parts is also known. Only at this time can the load acting on the
part be determined more accurately, and each detail factor affecting the working ability of the
part can be determined. Only under this condition, it is possible and necessary to carry out
accurate check calculations for some important or complex shapes and forces. According to the
results of the check, repeatedly modify the structure and size of the part until it is satisfactory.
In each step of technical design, the optimization design technology developed in the past thirty
to forty years has shown more and more that it can make the selection of structural parameters
the best ability. Some new numerical calculation methods, such as the finite element method,
can make the previously difficult quantitative calculations obtain excellent approximate
quantitative calculation results. For a few very important, complicated and expensive parts,
model test methods must be used for design when necessary. That is, the model is manufactured
according to the preliminary design drawings, and the weak points or excess sections on the
structure are found through tests The size is strengthened or reduced accordingly to modify the
original design, and finally reaches the level of perfection. The theory of mechanical reliability is
used in the technical design stage. From the perspective of reliability, the designed parts and
components and their parameters can be evaluated to meet the reliability requirements, and
suggestions for improving the design can be made to further improve the quality of the machine .
These new design methods and concepts mentioned above should be applied and promoted in
the design, so that they will develop accordingly.
After the sketch design is completed, the working drawing of the part can be designed according
to the basic dimensions of the part that have been determined by the sketch. At this time, there
are still a lot of details of the part structure to be considered and determined. When designing
the work drawings, full consideration should be given to the processing and assembly technology

of the parts, the inspection requirements and implementation methods of the parts during and
after processing. Some detailed arrangements must be returned to re-check the working ability if
it has a worthwhile effect on the working ability of the part. Finally, work drawings of all parts
except standard parts are drawn.
According to the structure and size of the final finalized part drawing, redraw the assembly
drawing and general assembly drawing. With this work, you can check for possible hidden
dimensions and structural errors in the part drawing. This work is commonly referred to as
assembling on paper.
(IV) Preparation of technical documents
There are many types of technical documents, including design calculation instructions, operating
instructions, and standard parts lists of commonly used machines.
When compiling the design calculation specification, all conclusive contents of the choice of
scheme and technical design should be included.
When compiling the instruction manual of the machine for use by the user, the user should be
introduced to the machine's performance parameter range, operating methods, daily
maintenance and simple repair methods, and spare parts catalogs.
Other technical documents, such as inspection certificate, detailed list of purchased parts, and
acceptance conditions, will be prepared separately as needed.
(V) Application of computer in mechanical design
With the development of computer technology, computers have been used more and more
widely in mechanical design, and many efficient design and analysis software have appeared.
With these softwares, multiple schemes can be compared at the design stage, and the structural
strength, stiffness, and dynamic characteristics of different, large and complex schemes can be
accurately analyzed. At the same time, a virtual prototype can also be built on the computer, and
the design can be verified using virtual prototype simulation, so that the feasibility of the design
can be fully evaluated during the design phase. It can be said that the popularization and use of
computer technology in mechanical design has changed the process of mechanical design, and its
advantages in improving design quality and efficiency are difficult to predict.
The above briefly introduces the design procedure of the machine. Broadly speaking, in the
manufacturing process of the machine, it is possible to modify the design at any time due to
process reasons. When amendments are required, certain approval procedures should be
followed. After the machine leaves the factory, a follow-up survey should be carried out in a
planned manner; in addition, users will also report problems that occur to the manufacturing or
design department during use. Based on this information, the design department may also
modify or even modify the original design after analysis. These works, although they are also part
of the design process in a broad sense, belong to another level of issues, and this book will not
discuss their specific content. However, as a designer, you should have a strong sense of social
responsibility. You must extend your vision of work to the entire process of manufacturing, use,
and even scrap. The design must be continuously improved to make the quality of the machine
continue to improve. To meet the needs of production and life.

Phase description
(I) Planning stage
After proposing new machines to be designed according to production or living needs, the
planning phase is just a preliminary phase. At this time, there is only a vague concept of the
machine to be designed.
(II) Scheme design stage
This stage plays a key role in the success of the design. The characteristics of multiple solutions
(schemes) in the design work are also fully demonstrated at this stage.
The function analysis of the machine is to comprehensively analyze the requirements, minimum
requirements, and requirements that must be achieved in the machine functions proposed in the
design task book, that is, whether these functions can be implemented, whether there are
contradictions between multiple functions, and the ability No alternative, etc. Finally, the
functional parameters were determined as the basis for further design. In this step, it is
necessary to properly deal with the possible conflicts between needs and possibilities, ideals and
reality, development goals and current goals.
After the functional parameters are determined, a possible solution can be proposed, that is, a
possible solution is proposed. When seeking a solution, discussions can be made separately
according to the motive part, transmission part and executive part. A more common approach is
to start with the implementation.
When discussing the executive part of the machine, it is first about the choice of working
principle. For example, when designing a machine for manufacturing screws, the working
principle can be either a method of turning threads on a cylindrical blank with a turning tool, or a
method of rolling threads on a cylindrical blank with a rolling die. This suggests two different
working principles. The working principle is different, of course, the designed machine will be
fundamentally different. In particular, it must be emphasized that new working principles must
be continuously researched and developed. This is an important way for the development of
design technology.
step
Before the design begins, design tasks must be established. When the design task is more
complicated, three-phase design is generally used, that is, preliminary design, technical design,
and work drawing design. When the task is relatively simple, such as the new design of a simple
machine, the inherited design or variant design of a general machine, The design achieved
technical design depth, and after reviewing, modifying, and approving, it worked as a drawing
design, and became a two-stage design. In the preliminary design phase of the three-phase
design, the main steps of the design are: determining the working principle and basic structural
type, motion design, designing the main parts, components, drawing preliminary general
drawings, and preliminary design review. In the technical design phase, the main steps are:
modify the design according to the review opinions, design all parts and components, draw a
new master plan, and review the technical design. In the working drawing design stage, modify
the design according to the review opinions, draw all working drawings and formulate all

technical documents. For mass or mass-produced products, a stereotyped design is also required.
In each step of the design, you may find that some decisions in the previous steps are
unreasonable. You need to go back to the previous step, modify the unreasonable decisions, and
redo the subsequent design work.
1.Develop design tasks
This is the preliminary work of the design. The design task is based on user orders, market needs,
and new research results. The design department applies various technologies and market
intelligence, draws up possible solutions, compares their advantages and disadvantages,
discusses with business departments and users, and formulates reasonable design task goals.
This is especially important for new designs. Mistakes in mission objectives will cause severe
economic losses and even total failure.
2. Determine the working principle and basic structure type 型
If the design task is not clearly specified, the first step in the design is to determine the overall
plan, that is, to determine the working principle to be applied and the corresponding structural
type. For example, when designing a high-power marine diesel engine, we must first determine
whether to use a two-stroke, double-acting, crosshead, low-speed diesel engine or a four-stroke,
single-acting, medium-speed diesel engine. For another example, a crushing machine designed
for coarsely crushing rocks must first determine whether it is a jaw or rotary crusher with
crushing and bending as the main crushing action, or a single-rotor or double-rotor impact with
the main role of impact Crusher.
3.Sports Design
After the design of the overall plan is determined, it is then necessary to use the knowledge of
mechanism to select the appropriate mechanism to obtain the required motion plan. The jaw
crusher mentioned above relies on the swing of its movable jaw plate to crush the rock entering
the crushing cavity by crushing, bending and splitting, and the swing of the movable jaw plate
can adopt the simple swing of the double toggle mechanism , Or the complex swing of a single
toggle mechanism. In new designs, it may be necessary to synthesize a new mechanism to obtain
the required motion plan, which is often a difficult task. Therefore, designers generally try to
apply the motion schemes provided by existing and mature institutions.
4.Structural design and preliminary preliminary drawing
After the motion design, the designer began to design the structure, calculate the force, strength,
shape, size, and weight of the main parts of the machine, and draw sketches of the main parts
and components. At this time, if you find that the originally selected structure is not feasible, you
must adjust or modify the structure. At the same time, it is also necessary to consider whether
there may be areas where overheating, excessive wear or vibration may occur.
In this step, the designer will find contradictions in the shape, size, proportion, etc. of each part
by drawing a sketch. In order to strengthen or improve one aspect, it may weaken or worsen
another aspect. At this time, the balance must be weighed and coordinated to achieve the best
overall effect. After repeated revisions of the draft are considered to be preliminary satisfactory, a
preliminary master plan and estimated cost can be drawn. The preliminary general drawing is

drawn strictly to scale, and enough views and cutaways are selected.
5. Preliminary review
After the preliminary general plan is drawn, it is necessary to ask the design, manufacturing and
use personnel who have experience in this type of machinery and the user or the representative
of the design unit to conduct a preliminary review. If the result of the review considers that the
design is not applicable (such as weight, volume, cost is too high, there is doubt about the
reliability of the structure, etc.), it is necessary to re-design the motion, or even use other
working principles and basic structural types. In most cases, some improvement measures are
taken in the design.
6.Technical design
Based on the preliminary review opinion, the design is modified and all parts and components
are drawn. Perform accurate stress analysis on the main parts and components, correct the
details such as the shape and size of the parts according to the analysis results, and specify the
materials and heat treatment. Determine the accuracy of part processing and the assembly
conditions of components and assemblies. Complete lubrication design, electrical design (drive
and control). General drawings are redrawn, and some important and mass-produced machines
sometimes need to be modeled. Submit the completed technical design for a second review.
7.Draw a working diagram
After making final modifications based on the opinions of the second review, you can draw
formal parts drawings, component assembly drawings, and general assembly drawings, and write
technical documents such as parts lists, wearing parts lists, and usage guidelines. The person in
charge of design should pay attention to coordinating the dimensions of parts, check the
tolerance fit between coupling parts, and check the strength and stiffness of some parts. After
the part drawing is completed, it is very important to check the drawing. Carefully proofed
drawings ensure smooth assembly after processing. The most reliable proofing method is to
redraw a general assembly drawing based on the drawn part drawing, and all the contradictions
will appear. When drawing the part drawing, two tasks are needed: one is the technical review to
make the part easy to process and reduce the manufacturing cost; the second is the standard
review to make the structural elements, dimensions, tolerances, heat treatment technical
conditions, and standard and general Parts, etc. meet the requirements of the standard.
8. Trial production and final design
For single piece or small batch production machinery, the design drawings completed through
the above steps can be put into formal production. For batch or mass-produced machinery, a
prototype should be trial-tested, functional tested and evaluated before formal production. After
passing the test, mass trial production should be carried out according to the batch production
process. Problems encountered in batch trial production may also require corresponding
modifications to the design before it becomes a definitive design that can be used in formal
production.
Constraint editing
The design of mechanical parts has many constraints, and the design criteria are the constraints

that the design should meet.
Technical Performance Guidelines
Technical performance All performance including product functions, manufacturing and
operating conditions, both static performance and dynamic performance. For example, the power,
efficiency, service life, strength, stiffness, anti-friction, wear performance, vibration stability,
thermal characteristics, etc. that the product can transfer. Technical performance criteria refer to
the relevant technical performance must meet the specified requirements. For example,
vibration will generate additional dynamic loads and strains, especially when the frequency is
close to the natural frequency of the mechanical system or part, resonance phenomenon will
occur, and the amplitude will increase sharply, which may lead to the rapid part or even the
entire system damage. The vibration stability criterion is to limit the relevant vibration
parameters of the mechanical system or part, such as natural frequency, amplitude, noise, etc.,
within the allowed range. Another example is that the heat generated during machine operation
may cause thermal stress, thermal strain, and even thermal damage. The thermal characteristic
criterion is to limit various related thermal parameters (such as thermal stress, thermal strain,
temperature rise, etc.) within the specified range.
Standardization criteria
The main standards related to the design of mechanical products are roughly:
Conceptual standardization: the terms, symbols, units of measurement etc. involved in the design
process should meet the standards;
Physical form standardization: The structural forms, dimensions, and performance of components,
raw materials, equipment, and energy should be selected in accordance with unified regulations.
Method standardization: Operation methods, measurement methods, test methods, etc. shall be
implemented in accordance with corresponding regulations.
Standardization criteria are all actions in the entire design process, which must meet the
above-mentioned standardization requirements. The standards related to the design of
mechanical parts that have been released can be divided into three levels: national standards,
industry standards, and enterprise standards. In terms of compulsory use, it can be divided into
two types: mandatory and recommended.
Reliability criterion
Reliability: The probability that a product or component can perform a specified function within
the expected life under specified conditions of use. The reliability criterion means that the
product, component or part designed can meet the specified reliability requirements.
Security guidelines
Machine safety includes:
Part safety: It means that the part does not occur such as fracture, excessive deformation,
excessive wear, and loss of stability within a specified external load and time.
Machine safety: refers to the requirements of the machine to ensure that it does not fail under
the specified conditions and can normally achieve the overall function.
Work safety: refers to the protection of operators, ensuring personal safety and physical and

mental health, etc.
Environmental safety: refers to not causing pollution and harm to the environment and people
around the machine.
Design Methodology Editor
The purpose of design methodology is to promote design thinking into a rational process, so that
design can follow a certain logic, so that more designers can make good designs. It roughly
includes the following:
1. Divide the stages of design very carefully, so that each stage becomes a rule-based and rational
thinking activity.
2. Store successful or good designs and build a design database for reference or use in future
designs.
3. Introduce the concept and method of value engineering in the design work, and weigh the
function and cost of the contradictions in the design to obtain a good use effect.
4. Use knowledge of emerging disciplines such as tribology, vibration, fracture mechanics, finite
element method, reliability design, optimization design, systems engineering, ergonomics, etc. in
the design to improve the scientificity of the design and reduce blindness.
5. Extend the scope of design work, forward to market prediction, and backward to after-sales
service.
6. Use computer-aided design to reduce design labor, improve design speed and design quality.
Outlook Editor
In the future, mechanical design will surely penetrate into semiconductor manufacturing,
bioengineering, nanotechnology, and robotics industries. While contributing to social
development, we will continue to improve ourselves and further innovate the theory.
(1) Further systemicity. That is, starting from a system perspective, treating mechanical products
as a system or a whole, relying on computer technology to achieve human, machine,
environment and mutual coordination. Specifically, it is to decompose the total system into
several subsystems, adopt various modern design theories and methods, and pursue system
optimization as the goal to coordinate the design and matching of each subsystem.
(2) Deepen intelligent design. With the advancement and development of science and technology,
design must consider more and more intelligent factors. A large number of design contents can
be used to establish models to describe the various behaviors of mechanical products, and to
solve the model to predict the performance of the product, the rationality and optimality of the
design. For example, intelligent decision-making systems for various vehicle performance
evaluations, gearbox design expert systems, and fault diagnosis systems have been applied to the
development and design of new vehicles.
(3) Pay more attention to green thinking. Green design technology is a technology designed to
meet the requirements of environmental protection, highest resource utilization and lowest
energy consumption in the life cycle of the product. The designer is required to consider the
environmental and basic attributes of the product from the entire cycle, and always base on the
physical and mental health and environmental protection of the product when designing. At the

same time, the designed product must be recyclable with minimal damage to the environment.
Editing of modern design methods
Professional modern
Computer software developed by mechanical design and computer professionals can reflect and
describe the mechanisms of various damages, failures and damages of mechanical products
under actual working conditions. It can quantitatively analyze and calculate the dynamic behavior
of mechanical parts and machinery, and form Fixed design procedures, which are professional
modern design methods, such as: vibration analysis and design, tribological design,
thermodynamic heat transfer design, strength, stiffness design, temperature field analysis, and so
on. These softwares are developed on the basis of traditional design methods using computer
technology. For example: Pro / M software is used to analyze the dynamic characteristics of the
mechanical device, and ANSYS software is used to analyze the stress. These are good examples in
this respect, which lays a foundation for accurately judging the reliability of the device and
selecting design parameters.
General Hyundai
In order to meet the high requirements for the performance of mechanical products, computer
technology is widely used in auxiliary design and system analysis in mechanical design. This is a
common modern design method. Common methods include optimization, finite element,
reliability, simulation, expert system, CAD, etc. These methods are not only for the research of
mechanical products, but also for their own scientific theories and methods.
1) Optimized design
Mechanical optimization design is the transplantation and application of optimization technology
in the field of mechanical design. The basic idea is to establish a mathematical model that reflects
engineering design problems and meets the requirements of mathematical planning according to
the theory, methods, and standards of mechanical design. Then, mathematical planning is used.
Methods and computer computing techniques automatically find the optimal solution for a
design problem. It is a modern design method formed by the combination of mechanical design
theory, optimization mathematics, and electronic computer.
2) Simulation and virtual design
Computer simulation technology is a comprehensive technology that uses a computer as a tool to
"build an actual or associative system model" and performs dynamic operation experiments on
the model under different conditions. The essence of virtual technology is the premise of
computer-supported simulation technology. During the product design stage, the entire product
development process and its impact on product design are simulated in parallel in real time, and
product performance, product manufacturing costs, and product manufacturability are predicted.
Performance, product maintainability and disassembly, etc., thereby improving the first-time
success rate of product design. This method not only shortens the product development cycle,
but also shortens the distance between product development and users.
3) Finite element design
This method uses mathematical approximation to simulate real physical systems (geometry and

load conditions). It also uses simple and interacting elements, ie units, to approach a real system
of infinite unknowns with a limited number of unknowns. It can be used not only to solve
complex non-linear and non-steady-state problems in engineering, but also to perform static and
dynamic analysis of complex structures in engineering design, and to accurately calculate the
stress distribution and deformation of parts with complex shapes , Become a powerful analysis
tool for the calculation of strength and stiffness of complex parts.
4) Fuzzy design
It is a design method that applies fuzzy mathematical knowledge to mechanical design. There is a
lot of fuzzy information in mechanical design. For example, in the design of mechanical parts, the
safety factor of a part is often taken from a conservative point of view, and it is not economical to
take a larger value, but there is a large fuzzy interval within its allowable range. Various kinds of
fuzzy problems are often encountered in the development of mechanical products at various
stages. Although the characteristics, nature, and requirements of policies for these problems are
different, the fuzzy analysis methods adopted are similar. Its biggest feature is that it can analyze
the influence of various factors on the design results comprehensively and quantitatively, and
obtain a comprehensive quantitative index as a basis for selecting decisions.
First, Taboo of mechanical design
I. Structural design to improve strength and stiffness
1. Avoid too much distance between the stress point and the support point
2. Avoid cantilever structure or reduce cantilever length
3. Do not ignore the beneficial effects that the working load can produce
4. Avoid frictional transmission of parts subjected to vibration load
5. Avoid unbalanced forces in the organization
6. Avoid thinking about only a single power transmission path
7. The influence of part deformation on the force distribution during work should not be ignored
8. Avoid heavy tensile stress on cast iron parts
9. Avoid bending stress on thin rods
10. Avoid excessive stiffness of parts under impact load
11. Avoid stressed or rough surfaces due to strained parts
12.Residual tensile stress should be avoided on the surface of parts subject to variable stress
13. Parts under variable load should avoid or reduce stress concentration
14. Avoid local structures that affect strength too close
15. Avoid pre-deformation in the same direction as the deformation caused by the work load
16. The diameter of the pulley and drum of the rope must not be too small
17. Avoid too many times of wire rope bending, pay special attention to avoid repeated bending
18. Leave a margin at the joint between the wire rope and the drum when lifting
19. The intermediate parts that can not transmit force should try to avoid stress
20. Try to avoid the additional force caused by misalignment of the axis during installation
21. Minimize the force acting on the foundation

Second, Structural design to improve wear resistance
1. Avoid the same material as sliding friction pair
2. Avoid excessive thickness of white alloy wear layer
3. Avoid increasing the requirements for the entire part in order to improve the wear resistance
of the surface of the part
4. Avoid partial wear of large parts and cause the entire part to be scrapped
5. When using white alloy as the bearing lining, pay attention to the choice of bearing material
and bearing structure design
6. Sufficient lubricant supply, covering the working surface
7. Lube oil tank cannot be too small
8. Do not make the filter filter out the additives in the lubricant
9. The size, position and shape of the oil groove of the sliding bearing should be reasonable
10. Do not add too much grease to rolling bearings
11.Increase a certain amount of wear margin for the wearable surface of the part
12. Pay attention to the adjustment after parts wear
13. The speed and pressure difference between points on the same contact surface should be
small
14. Adopt dust-proof device to prevent abrasive wear
15. Avoid step wear
16. Sliding bearings cannot be sealed with contact oil
17. Protect vulnerable parts
18. For wear-resistant parts, a structure that automatically compensates for wear can be used
Third, the structural design to improve accuracy
1. Try not to use structural solutions that do not conform to the Abbe principle
2. Avoid overlapping errors caused by the amount of wear
3. Avoid superimposing machining errors and wear
4. The driving force acting point of the guide rail should act on the pressure center of the friction
between the two guide rails, so that the torque generated by the friction between the two guide
rails is balanced with each other
5. For guide rails requiring high accuracy, it should not be supported by a small number of balls
6. In the reduction transmission chain that requires motion accuracy, the final stage transmission
ratio should take the maximum value
7. The number of screw nut buckles for measurement should not be too small
8. The axial movement of the spiral bearing must be strictly restricted
9. Avoid unreasonable matching of bearing accuracy
10.Avoid the unreasonable configuration of bearing radial runout
11. Avoid set screws affecting the accuracy of the rolling guide
12. When the gap between the push rod and the guide is too large, a sine mechanism should be
used instead of a tangent mechanism.

13. The accuracy of the sine mechanism is higher than that of the tangent mechanism
Fourth, consider the ergonomics of structural design
1. Reasonably select the operation posture
2. The ratio between the height of the worktable of the equipment and the size of the human
body should adopt a reasonable value
3. Reasonably arrange adjustment links to strengthen the applicability of equipment
4. Mechanical operation, control and display devices should be arranged in the most reasonable
position in front of the operator
5. The display device adopts a reasonable form
6. The lettering on the dashboard should be clear and legible
7. The knob size and shape should be reasonable
8. The keys should be easy to operate
9. The force required to operate the handle and the range of motion of the hand should not be
too large
10.Handle shape is easy to operate and exert force
11. Reasonably design the size and shape of the chair
12. Reasonably design the material and elasticity of the chair
13. Do not make excessive noise in the working environment
14. The lighting of the operation site must not be too low
Fifth, Structural design considering heat, corrosion, noise and other issues
1. Avoid using inefficient mechanical structures
2. Lubricant tank size should be large enough
3. The return fluid of the shunt system must be cooled
4. Avoid high pressure vessels, pipes, etc. in the hot sun
5. The parts exposed to high temperature should not be made of rubber, polyethylene plastic,
etc.
6. It is not advisable to arrange oil tanks inside the box parts of precision machinery to avoid
thermal deformation.
7. For longer mechanical parts, it is necessary to consider that they can be deformed freely when
dimensional changes occur due to temperature changes
8. The working temperature of the hardened material should not be too high
9. Avoid moisture condensation caused by high-pressure valve deflation
10. The box with large thermal expansion can be supported in the center
11. The flanges connected by bolts are used as the connection of the pipeline. When one side is
exposed to sunlight, the two sides will be bent due to different temperatures and elongations
12. Structures in contact with corrosive media should avoid slits
13. The liquid in the container should be able to be drained clean
14. Pay attention to avoid mechanochemical wear (fretting wear) on the contact surface between

the shaft and the hub
15. Avoid corrosive screw structures
16. When steel pipe and copper pipe are connected, it is easy to produce electrochemical
corrosion, and a section of pipe can be arranged to be replaced regularly
17. Avoid structures that are easily corroded
18. Pay attention to avoid the impact of the heat exchanger pipe fretting wear
19. Reduce or avoid shocks and collisions of moving parts to reduce noise
20. High speed rotor must be balanced
21. The quality of the impacted part should not be too small
22. In order to absorb vibration, parts should have strong damping
Sixth, Design of Casting Structure
1. Parting surface strives for simplicity
2. Avoid indentation on the casting surface
3. The surface boss is as concentrated as possible
4. There should be no small protrusions on the outer surface of large castings
5.Improve the structure that hinders ejection
6. Avoid large and thin water levels
7. Avoid shapes that generate large internal stresses
8.Prevent the misalignment from adversely affecting the appearance
9.Using easy-to-core structure
10. Minimize the parting surface
11. Strive for uniform wall thickness
12. Use reinforcing ribs to make wall thickness uniform
13. Design casting wall thickness considering the solidification sequence
14.Inner wall thickness should be less than outer wall thickness
15. Casting wall thickness should be gradually transitioned
16. The angle between two walls should not be too small
17. The inner cavity of the casting should be convenient for core making
18. No or less core stays
19. Try not to use a core
20. There should be a boss on the edge of the casting
21. Casting structure should be good for removing core sand
22.Core design should help improve casting quality
23. The holes of the casting should pass through as much as possible
24. Reasonably arrange the ribs
25. Ensure that castings shrink freely to avoid defects
26. Pay attention to the ribs
27. The structure of ribs must take into account the structural stability
28. Remove unnecessary rounded corners

29. Make big and small, simplify complicated
30. Pay attention to the reasonable power transmission and support of the casting
Seventh, Structural design of forged and stamped parts
1. Free forged parts should avoid cones and wedges
2. Intersecting bodies strive to simplify
3. Avoid using ribs
4. Free forgings should not be designed with complex bosses
5. There should be no boss inside the free-forged fork-shaped part
6. The size of the parting surface of the forging should be the maximum size of the part, and the
parting surface should be flat
7. The shape of the forging should be symmetrical
8. Die forgings should have a proper fillet radius
9. Die forgings should be suitable for demolding
10. Die forgings should be as simple as possible
11. The shape of stamping parts should be as symmetrical as possible
12. The partial width of the part should not be too narrow
13. The depth and shape of the boss and hole should have certain requirements
14. The design of stamping parts should consider, which is a material-saving metal processing.
The content is good and worthy of attention.
15. The shape of stamping parts should avoid large planes
16.Wrinkles should be avoided at the bends
17. Pay attention to the design slope
18. Prevent hole deformation
19. Simplified Exploded View
20. Note that the support should not be too thin
21. Thin plate bending parts must have cutouts at the bends
22.Ribs can increase stiffness but have directionality
23. The shape of the drawn part strives for simplicity
24. The convex edges of the drawn parts should be uniform
25. The structure can be simplified by using the incision process
26. The dimensioning of stamping parts should consider the die wear
27. The dimensioning of stamping parts should consider the stamping process
Eighth, Structure of the blank of welded parts
1. Reasonably designed shape
2. Reduce scrap
3. Cut with nesting
4. Welding seam should not be arranged at the cross section
5. Welding parts can not ignore their own characteristics, simply imitating the casting

6. The cross-sectional shape should help reduce deformation and stress concentration
7. Correctly select the weld position
8. Don't let the welding affected areas be too close
9. Pay attention to the stress on the weld
10.Reinforcement ribs should be arranged reasonably
11. Reduce the stress on the weld
12. Reduce thermal deformation
13. Use profiles reasonably, simplify welding process
14. Welds should avoid machining surfaces
15. Consider gas diffusion
16. Can use stamping parts instead of machined parts
17.Using sheet bending parts to reduce welding seams
Ninth, structural design of machining parts
1. Pay attention to reducing the blank size
2. The machined and non-machined surfaces should not be flush
3. Reduce the length of the machined surface
4. Separate surfaces with different processing accuracy
5. Change complex shapes to assemblies for easy processing
6. Avoid unnecessary accuracy requirements
7. The tool can easily enter or exit the working surface
8. Avoid processing enclosed spaces
9. Avoid the tool from approaching the workpiece
10. Can't adopt the structural shape of the part that is not suitable for the shape of the tool
11. To consider the impact of casting errors
12. Avoid multiple parts combined processing
13. Complex machining surfaces should be designed on the outer surface rather than on the
inner surface
14. Avoid chamfering of complex shapes
15. Stop fittings for non-circular parts must be avoided
16. Avoid unnecessary supplementary processing
17.Avoid parts structure that cannot be clamped
18.Avoid parts structure without measurement base
19. Avoid shock and vibration during processing
20. Avoid drilling holes on inclined surfaces
21. Don't drill through the bottom of the hole
22. Reduce the number of tools used to process the same part
23. Avoid multiple fixation during processing
24. Pay attention to the possibility of processing multiple parts at one time

Tenth, Structural design of heat treatment and surface treatment parts
1. Avoid disparity in wall thickness of parts
2. The size of the parts requiring high hardness (overall quenching treatment) cannot be too large
3. Avoid sharp corners and sudden dimensional changes
4. Avoid asymmetric structures
5.Avoid quenching of open parts
6. Avoid too complicated parts structure
7. Avoid too low rigidity of parts, resulting in quenching deformation
8. Use local hardening to reduce deformation
9. Avoid holes too close to the edge of the part
10. There should be a certain distance between the two gears of the high frequency quenched
gear block
11. The surface of galvanized steel parts should not be too rough
12. The thickness of the plating layer should be considered when machining the electroplated
mutually matching parts.
13. Note that the reflection of plated parts is not suitable for certain working conditions
Eleven, mechanical structure design considering assembly and maintenance
1. Avoid dismantling other parts when removing one part
2. Avoid loading two mating surfaces at the same time
3. Leave necessary operating space for disassembly and assembly
4. Avoid malfunction due to incorrect installation
5. Adopt special structure to avoid wrong installation
6. Simplified assembly process using symmetrical structure
7. Guidance is required when the flexible sleeve is installed
8. It is difficult to see the matching parts, and there must be a guide part
9. In order to facilitate installation with a robot, a snap or internal locking structure is used
10. The fastener head should have smooth straight edges for easy picking
11. There must be necessary chamfers at the parts installation site
12. The parts fed by the automatic feeding mechanism should avoid winding and overlapping
13. Simplify assembly movement
14. Reasonable division of parts for a machine
15. Minimize on-site assembly workload
16. Try to use standard parts
17. Parts should be easy to remove recycled materials after damage
Twelve, threaded structure design
1. When the height of the top nut is different, do not install it in reverse
2. The method of preventing loosening must be reliable
3. The screw structure under bending moment should minimize the thread stress

4. Avoid bending stress on the screw
5. Positioning with threaded parts
6. The screws should be arranged at the position where the rigidity of the joint is the largest.
7. Avoid excessive deformation of the connected parts when tightening the nut (or screw)
8. Do not arrange flange bolts directly below
9. The bolt pitch of the side cover should consider the sealing performance
10. Do not penetrate the screw holes to prevent leakage
11.Threaded holes should not pass through two welded parts
12. For deep screw holes, corresponding bosses should be designed on the parts
13. Do not stick out the head of the fastening bolt of the high-speed rotating body
14. Avoid intersecting screw holes
15. Avoid bolts passing through chambers with temperature differences
16. Anchor bolts should not be arranged near the end of the foundation concrete
17. Shear bolts should have a large contact length
18.Consider having enough wrench space when tightening the nut
19.Flange structure bolt diameter, spacing and joint thickness should be selected appropriately
20.Ensure space for bolt installation and removal
21. Set screws can only be applied in the direction that does not bear the load
22. Aluminum gaskets should not be used in electrical equipment
23. For screws with a coating on the surface, the plating size should be reserved for the
processing size before plating.
24. The edge of the screw hole must be chamfered
25. When the thread on the top of the screw is in danger of injury, a cylindrical end should be
provided to protect the thread
26. When fixing with multiple countersunk screws, each countersunk head cannot be close
Thirteen, structural design of positioning pins and coupling pins
1. The distance between two positioning pins should be as far as possible
2. For symmetrical parts, positioning pins should not be arranged in symmetrical positions
3. Two positioning pins should not be arranged on two parts
4. The pin holes of matching parts must be processed at the same time
5. Pin holes of hardened parts should also be used as
6. The positioning pin should be perpendicular to the joint surface
7. Make sure the pins are easy to pull out
8. Do not install positioning pins on the interference fit surface
9. Appropriate measures should be taken for difficult to observe pin assembly
10. Installing dowels should not make parts removal difficult
11. Avoid unbalanced force when transmitting force with pins
Fourteen, Structural Design of Bonding Parts

1. When two cylinders are docked, a sleeve or an additional connecting column should be added
inside
2. Improve the structure of the bonding joint and reduce the stress on the bonding surface
3. Use enhanced measures for the larger part of the peeling force
4.The bonding structure has different characteristics from the casting and welding parts
5. When bonding is used for repair, it cannot be simply bonded, and the bonding area must be
increased.
6. In addition to bonding heavy parts, wave keys should be added in addition to bonding
7. Apart from adhesive, other measures should be taken to repair cracked parts
Fifteen, key and spline structure design
1. The bottom corner radius should be large enough
2. There should be a closer fit on both sides of the flat key
3. When two flat keys are used for parts on one axis, higher machining accuracy is required
4. When using two oblique keys, the distance should be 90 ° ～ 120 °
5. When using two semicircle keys, they should be on the same busbar in the axial direction.
6. When fixing two parts with flat keys on the shaft, the keyway should be on the same bus
7. Do not open the keyway on the weak part of the part
8. The length of the keyway should not be opened to the stepped part of the shaft
9. Hook-head oblique key is not suitable for high speed
10. The long axis of the keyway on one side is easy to bend
11. The flat key tightens the set screw causing the eccentricity of the part on the shaft
12. Use a flat key on the tapered shaft as parallel to the axis as possible
13. When there are several parts stringed on the shaft, it is not suitable to use key connections
separately.
14. Special attention should be paid to the strength of spline shaft ends
15. Pay attention to the rigidity distribution of Luyi, and don't make the torque transmitted only
by some splines
Sixteen, Design of interference fit structure
1. Matching parts must be easy to fit
2. The interference fit should have a clear positioning structure
3. Avoid pressing both mating surfaces at the same time
4. Convenient disassembly for interference fittings
5. Avoid installing multiple interference fits in the same fit size
6. Pay attention to the influence of working temperature on interference fit
7. Pay attention to the effect of centrifugal force on interference fit
8. To consider the changes in other dimensions after the two parts are assembled with an
interference fit
9. Taper surface fit cannot be positioned with shaft shoulder

10. The taper of the mating surface should not be too small
11. The small shaft embedded in the cast iron is easy to loosen
12. The stainless steel sleeve will loosen the interference fit due to temperature
13. The mating surface of the shaft and hub with an interference fit must have a certain length
14. When the interference fit and key are used in combination, the key slot should be installed
first.
15. Do not make two holes of the same diameter make an interference fit
16. Avoid asymmetrical cuts on interference fit sleeves
Seventeen, Design of Flexible Transmission Structure
1. Belt drive should pay attention to increase the angle of the wheel
2. The pulley with the two shafts in the up and down position should make the sag of the belt
conducive to increasing the wrapping angle.
3. The diameter of the small pulley should not be too small
4. Belt transmission speed should not be too low or too high
5. The center distance of the pulley cannot be too small
6. The center distance of the belt drive must be adjustable
7. Belt should be easy to change
8. The belt wheel should not be cantilevered when the belt is too wide
9. Drive by belt tensioned by self-weight, add auxiliary device when self-weight is not enough
10. Pay attention to the parallelism of the two axes and the center position of the pulley
11. The flat belt drive small pulley should be made slightly convex
12. The working surface of the pulley should be smooth and clean
13.Semi-crossover flat belt drive cannot be reversed
14. The surface of high speed pulley should be slotted
15. Synchronous belt drive installation requirements are higher than ordinary flat belt
16. Synchronous pulley should consider installing retaining ring
17.Increase the fillet radius of the top of the tooth and the top of the tooth
18. The positive diameter of the synchronous belt should adopt positive deviation
19. Chain drive should be tight on the top
20. When two sprockets are arranged up and down, the small sprocket should be on it
21.Can't use a chain to drive multiple sprockets on a horizontal line
22. Pay attention to the impact of the change in the tension of the flexible transmission on the
bearing load
23. It is better to lubricate the chain with a small amount of oil
24. The center distance of the chain drive should be adjustable
25. The direction of the chain spring should be adapted to the running direction of the chain
26. Belt and chain drive should be covered
27. The diameter of the sheave must not be reduced arbitrarily
28. Avoid repeated bending of the steel rope

29. The designer must strictly define the scrapping standards for steel ropes
30. Steel rope must be lubricated regularly
31. The surface of the drum should have rope grooves
Eighteen, Design of Gear Transmission Structure
1. Gear arrangement should be considered to facilitate the force of the shaft and bearings
2. The tooth joint point (A) of the two directions of the herringbone gear should first enter the
meshing
3. When the gear diameter is small, it should be made into a gear shaft
4. Gear root circle diameter can be smaller than shaft diameter
5. The width of the small gear is larger than the width of the large gear
6. Gear block should consider the cutting distance of the tool when processing gears
7. Gear and shaft coupling should reduce processing during assembly
8. Pay attention to ensure that the stiffness of the gear is consistent along the width of the tooth
9. Make use of the uneven deformation of the gear to compensate the deformation of the shaft
10. Split large gears should be separated where there are no spokes
11. The hardened surface of the gear teeth should not be interrupted
12. The bevel gear shaft must be fixed in both directions
13. Both large and small bevel gear shafts should be capable of axial adjustment
14. The bolts in the combined bevel gear structure are not subject to tension
Nineteen, worm drive structure design
1. Worm self-locking is not reliable
2. The cooling fan should be installed on the worm
3. The direction of the heat sink outside the worm reducer is related to the cooling method
4. Worms are more severely affected by heat than worm gears
5. Worm position is related to speed
6. The rigidity of the worm is not only determined by the force at work
7. Precision of worm gear is affected by the precision of precision machinery
8. The force of worm drive affects the flexibility of rotation
Twenty, structural design of reducer and transmission
1. The transmission device should strive to form a component
2. The transmission ratio of the first-stage transmission must not be too large or too small
3. Should use high-power transmission
4. Try to avoid using vertical reducer
5. Pay attention to the pressure balance between the inside and outside of the gearbox
6. It is not appropriate to use gaskets on the box surface
7. Vertical box should prevent oil leakage on the split surface
8. There should be enough oil in the box and replace it in time

9. Planetary gearboxes should have a load sharing device
10. The shifting gear of the transmission must have a neutral position
11. Gearbox gears must have round teeth
12. Friction wheels and friction continuously variable transmissions should avoid geometric
slippage
13. Soft materials for active friction wheels
14. Conical friction wheel drive, compression spring should be installed on small conical friction
wheel
15. The design should try to increase the force transmission path and turn the pressing force into
an internal force
16. The mechanical characteristics of CVT should match the working machine and prime mover
17. The busbar of the working cone with pulley is not straight
Twenty-one. Structure Design of Transmission System
1.Avoid the motion uncertainty of the hinged four-bar mechanism
2. Pay attention to the dead points of the organization
3. Avoid the guide rail from receiving side thrust
4. The limit switch should be set on the component with a larger stroke in the linkage mechanism
5. Note that the transmission angle must not be too small
6. The swing lever of the cylindrical cam of the swing follower should not be too short
7. Correctly arrange the position of the offset cam follower cam to move the guide rail
8. Balance of Planar Linkage Mechanism
9. The motion coefficient should be considered when designing intermittent motion mechanisms
10. Analysis of Reliability of Locking Device by Using Instantaneous Stop
11. Select the gear transmission type, first consider using cylindrical gears
12. When the machine requires reversing, generally the motor reversing can be considered
13. Must consider starting performance of prime mover
14. Friction transmission must not be used in the crane structure
15. For mechanisms requiring slow movement, the spiral is better than the rack
16. Use standard gearbox with large transmission ratio instead of bulk transmission
17. Replace the prime mover and transmission with a reduction motor
18.Using shaft mounted reducer
Twenty-two. Structural design of coupling clutch
1. Reasonable choice of coupling type
2.Coupling balance
3. Couplings with sliding friction should pay attention to maintaining good lubrication conditions
4. High-speed rotating couplings must not have protruding protrusions
5. When using a coupling with a shoulder and groove centering, consider disassembly of the shaft
6. When the transmission parts at both ends of the shaft require synchronous rotation, it is not

suitable to use flexible couplings with elastic components.
7. When the intermediate shaft is supported without bearings, do not use cross slide couplings at
both ends
8.Single universal joint cannot achieve synchronous rotation between two axes
9. Don't use the jacket of the gear coupling as the brake wheel
10. Pay attention to the lubrication of the gear coupling
11. Notes on nylon rope couplings
12. Notes on shear pin safety clutch
13. Do not use oil-lubricated friction disc clutches for fast separation
14. It is not suitable to use multi-disc friction clutch in the case of high temperature work
15. The clutch control ring should be installed on the half clutch connected to the driven shaft
Twenty-three, shaft structure design
1. Minimize the stress concentration at the abrupt section of the shaft
2. To reduce the stress concentration of the shaft at the interference fit
3. Pay attention to the effect of stress concentration caused by keyway on the shaft
4. To reduce the difficulty of assembly and disassembly of interference fit parts
5. The starting point of assembly should not be sharp, and the starting points of two mating
surfaces should not be assembled at the same time.
6. Shaft shoulders or collars should be used for positioning of parts on the shaft
7. When inserting interference fit shafts into blind holes, consider exhausting air
8. Reasonably arrange the parts on the shaft and improve the structure to reduce the stress on
the shaft
9. Use load splitting to improve the strength and stiffness of the shaft
10.Using central equal distance drive to prevent poor torsional deformation at both ends
11. Improve the surface quality of the shaft and increase the fatigue strength of the shaft
12. Reasonable setting of multiple keyway positions on the shaft
13. The wall thickness of the lower part of the keyway of the hollow shaft should not be too thin
14. The keyway on the shaft should be easy to process
15. It is difficult to drill an elongated hole in a shaft
16. Cut the thread on the rotating shaft to facilitate the loosening of the fastening nut
17. Make sure the washer is properly installed on the shaft
18. Make sure that the shaft and the mounting parts are compressed or the size of the gap is
reserved.
19. To avoid the elastic clamping ring bearing axial force
20.Hollow shaft saves material
21. Do not make the operating frequency of the shaft coincide or be close to its natural frequency
22. The flexible coupling of the high speed shaft should be as close as possible to the bearing
23. Avoid zero bearing reaction force
24. It is not suitable to directly connect the small shaft at the shaft end of the large shaft

25. The journal surface requires sufficient hardness
Twenty-four. Structural design of sliding bearings
1. To allow the lubricant to enter the friction surface smoothly
2. Lubricating oil should be introduced into the bearing from the non-load bearing area
3. Do not leave the full ring oil groove in the middle of the bearing
4. Oil grooves should be opened at the joints of the split bearing pads
5. Make the oil ring full and reliable
6. Do not block the fuel hole
7. Do not form a non-flowing area of the lubricant
8. Prevent sharp edges or edges that cut off the oil film
9. Ladder wear occurs
10. Don't make the thrust end face of the bearing pad be in line contact
11. The thrust bearing and journal should not be in full contact.
12. The starting of high-speed rotating shaft of heavy-duty large machinery requires bearings of
high-pressure top shaft system
13. Do not hollow out the bearing seat and the bearing contact surface of the bearing under
heavy load or high temperature rise
14. Don't disassemble the bearing bush or bush
15. To reduce the edge pressure generated by the supporting bearings of the intermediate wheel
and the cantilever shaft
16. Select the self-aligning sliding bearing under the condition that the bearing seat hole is not
concentric or the axis is deformed after loading.
17. Relative movement of bearing bush and bearing seat is not allowed
18. To make two metal stickers firmly in the bimetal bearing
19. Ensure reasonable running clearance
20. Clearance required to ensure thermal expansion during shaft operation
21. Gap adjustment after considering wear
22. Cylindrical bearing pads used under high-speed and light-load conditions to prevent
instability
23. Bearings under high-speed and light-load conditions should use bearings with good vibration
resistance
24. Oil bearing should not be used for high speed or continuous rotation
25. Sliding bearings should not be combined with seals
26. Do not let the bearing shell fall off during the lifting process of the bearing cover or the upper
case
Twenty-five. Structural design of rolling bearing shafting
1. Consider the design of bearing disassembly
2. Fillet radius of bearing inner ring and shoulder fillet radius

3. Combination of a pair of angular contact bearings
4.Angular contact bearings are combined in the same direction in series
5.Angular contact bearings should not be paired with non-adjusting gap bearings
6.Bearing combination should be good for even load sharing
7. The need to ensure that the shaft expands or contracts due to temperature changes
8. The combination of tapered roller bearings considering the temperature change of the inner
and outer rings and thermal expansion
9. Shafts with high axial positioning accuracy should use bearings with adjustable axial clearance
10. Cruise ship and intermediate wheel should not be supported by a rolling bearing
11. Select a bearing with self-aligning performance on the shaft used in the case where the holes
of the two machine frames are not concentric or the axis is deformed after loading.
12. It is necessary to consider the difficulty of installing intermediate bearings when designing
multi-fulcrum bearings of equal diameter shafts
13. Not suitable for high-speed rolling bearings
14. High rigid bearings should be used for shafts with high rigidity.
15. Rolling bearings should not be used in combination with sliding bearings
16. Grease-lubricated roller bearings and dust-proof and sealed bearings are prone to heat
17. Avoid filling with excessive grease, do not form the end of the grease flow
18. When grease-lubricated angular contact bearings are mounted on a vertical shaft, prevent
the grease from detaching from the bearing from below
19. Avoid mixing oil and grease when lubricating with grease
20. Problems to pay attention to when lubricating with oil
21.Effect of bearing box shape and rigidity
22. The bearing bearing force direction should point to the supporting bottom surface
23. Simplify the bore of each hole of the bearing on the machine base
24. The assembly and disassembly of the bearings with inseparable inner and outer rings in the
base hole should be convenient.
25. It is not appropriate to use axial tightening to prevent the creep of the bearing mating surface
Twenty-six, structural design of the sealing device
1. Do not install wires between static seals
2. The surface of the static connection should have a certain roughness
3. The width of the contact surface of the high pressure vessel seal should be small
4. Gasket should be added when sealing with cutting edge
5. When O-ring is used for high-pressure sealing, a protective ring is required.
6. Avoid the edge of the O-shaped seal ring protruding and being cut off
7. When the center position of the shaft in contact with the seal often changes, it is not suitable
to use a contact seal
8. Proper use of aprons
9. Should not rely on the screw to rotate the gland to tightly seal the packing

10. When there is a lot of packing, the depth of the packing hole is not tight enough.
11. To prevent fillers from developing
12. Different parts of the seal should be separately supplied with oil
13. When lubricating the sealing device with oil, keep the oil surface at a certain height
14. When the seal is notched, the notch of the multilayer seal should be staggered
Twenty-seven, hydraulic system and pipeline structure design
1.Pipe arrangement should be easy to disassemble and inspect
2. The strength of the Y-shaped joint of the large diameter pipe is very poor
3. Avoid mixing air into oil pressure pipes
4. Pay attention to drainage in the lower part of the pipeline
5.Discharge pipes should avoid mutual interference due to confluence
6. The pipeline should be unobstructed, avoid disturbance when confluence
7. Avoid stress caused by pipeline expansion
8. The parts of the pipeline system that require frequent operation and observation should be
easy to operate
9. It is not advisable to use left and right threads for pipe joints
10. Pay attention to pipe support design
11. Do not move equipment when disassembling or assembling pipes
12. Pay attention to hysteresis of oil pressure and pneumatic equipment
13. Protect the hose from additional stress
14. When the medium pressure in the hose changes in a pulse, the hose should be fixed.
15. Consider fueling during start and stop
16. The built-in relief valve of the oil pump should not be commonly used
17. Cooling water pollution will reduce cooling capacity
18. Prevent condensation on the surface of the cooling water pipe

Mechanical design and taboos of mechanical design

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Mechanical design and taboos of mechanical design