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MindMap Gallery Mechanical Design Basics Introduction Mind Map

Mechanical Design Basics Introduction Mind Map

This is a mind map about the basic introduction to mechanical design, including machines and their components, Overview of mechanical design, failure modes of parts, Design criteria for parts, etc.

Edited at 2023-11-14 23:12:51

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Mechanical Design Basics Introduction Mind Map

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Outline

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introduction

Machine and its components

A device that performs mechanical motion designed according to certain usage requirements and is used to transform or transmit energy, materials, and information.

Machine characteristics

①Man-made physical combination; ② Each part has a certain relative movement; ③Replace or reduce human labor, complete useful work or realize energy conversion

The difference between machines and institutions

Mechanism: only considers the transmission and conversion of motion and force. Machine: 1) Consider the transmission and conversion of motion and force. 2) Consider energy to replace or reduce human labor. 3) Often includes electrical, hydraulic and other control systems.

The connection between machines and institutions

Machines are composed of mechanisms, and a machine contains different mechanisms; Different machines may contain the same mechanism.

Machine composition

functional perspective

Processing and manufacturing angle

Parts: manufactured units

Universal parts: parts that can be used in various machines

Special parts: only found in certain machines

Component: A set of coordinated tasks that are structurally grouped together to accomplish the same task. assembly of parts

kinematic perspective

Machines are composed of mechanisms and components, that is, component-mechanism-machine

Component: moving unit

Three major mechanisms: connecting rod mechanism, cam mechanism, gear mechanism

The difference between components and parts

① A component is a moving unit, and a component is from a kinematic point of view; Parts are manufacturing units and are defined from the perspective of processing and manufacturing. ② Components are rigid bodies, and only movement is studied, deformation is not considered, and it is within the scope of mechanical principles; Parts are deformable bodies, and rigidity, stress and deformation are considered in the scope of mechanical design.

Mechanical Design Overview

General process of mechanical design

Basic requirements for mechanical design

a) Under the premise of meeting the expected functions of the machine: good performance, high efficiency, low cost, etc. b) Within the scheduled use period: safe and reliable, easy to operate, beautiful in appearance, etc.

Basic requirements for mechanical parts design

a) Work normally and reliably within the scheduled working period to ensure various functions of the machine b) Minimize the production and manufacturing costs of parts

Failure modes of parts

Invalid

Parts lose their normal working capabilities or fail to meet design requirements

Common failure modes

Overall break

Fracture caused by the stress at the dangerous section of the part exceeding the strength limit of the part

Fatigue fracture of dangerous sections under the action of variable stress

Excessive residual deformation

Stresses on the part exceed the yield limit of the material

surface failure of parts

Corrosion, wear and contact fatigue (pitting corrosion)

stiffness failure

The elastic deformation of the parts exceeds the allowable value, affecting the working accuracy of the machine.

Failure caused by disruption of normal working conditions

Some parts can only work normally under certain working conditions

The difference between failure and damage

1. Failure is the inability to complete normal functions, which may be caused by design defects or working conditions during use. Failure can occur even if the part itself is intact. 2. Damage is damage to parts, mainly reflected in changes in geometric dimensions and internal structure. The function of the part itself is also damaged, but does not necessarily fail

Part Design Guidelines

strength criterion

Ensuring that parts do not undergo fracture damage or excessive plastic deformation is the most basic design criterion.

stiffness criterion

Ensure that parts do not undergo excessive elastic deformation y≤[y]

Abrasion Resistance Guidelines

Parts have sufficient resistance to wear P≤[P], PV≤[PV]]

life criterion

Usually related to fatigue, wear and corrosion of parts

Vibration Stability Criteria

The design of high-speed running machinery should pay attention to this criterion

Strength of mechanical parts

Strength: The ability of a part to resist damage under load

Strength classification of mechanical parts

Classification by failure location

Surface strength: When the surface is subjected to external loads, it resists surface contact fatigue or surface The ability to plastically deform.

Overall strength: When the entire body is subjected to external loads, it resists damage to a certain dangerous section The stress exceeds the ultimate stress of the part and causes fracture or plastic deformation.

Classification according to failure characteristics

Static strength: resistance to failure when subjected to static stress or variable stress with a small number of changes. the ability to be effective;

Fatigue strength: The ability to resist failure when subjected to variable stress.

Classification of stress

Static stress: does not change with time or changes slowly, static load generation

Variable stress: generated by static load or variable load

stable variable stress

Symmetric cyclic variable stress

Asymmetric cyclic variable stress

pulsating cyclic stress

Unsteady variable stress

regular unsteady variable stress

Randomly variable stress,

Principles for selecting materials for mechanical parts

Performance requirements: heavy load, high temperature, corrosion, (load change, etc.

Dimensional requirements of the blank: structural complexity, size, batch requirements, etc.

Processing process performance requirements: casting, welding, forging, heat treatment, etc.

Economics of materials: price, processing costs, utilization, combined use, valuable materials

Standardization of mechanical parts

International Standard ISO

National Standard GB

mandatory standards

The code is GBXXXX (for the standard serial number)-XXX (for the year of approval)

Mandatory national standards must be strictly followed and implemented

Recommended standards

The code is GB/TXXXX-XXXX

Accounting for the vast majority of the entire national standard

Industry standards JB, YB

Enterprise Standard QB

Friction and wear

Friction classification

Dry friction: friction without lubricant on the surface of parts.

Boundary friction: Friction that forms a boundary oil film on the friction surface

Fluid friction: The friction surface is separated by a fluid film, and the friction properties depend on the internal intermolecular adhesion of the fluid. Friction of sexual resistance. The friction coefficient during fluid friction is the smallest and no wear occurs, which is an ideal friction state.

Mixed friction: refers to a mixed state of boundary friction and fluid friction between friction surfaces. Mixed friction can effectively reduce friction resistance, and its friction coefficient is much smaller than boundary friction.

sliding friction

wear and tear

Wear process

Breaking-in stage: New parts are generally in this stage when they start to be used, and the wear rate is relatively high.

Stable wear stage: It belongs to the normal working stage of the parts, and the wear rate is stable and low.

Severe wear stage: It is the stage when the parts are about to be scrapped, and the wear and tear curve rate increases sharply.

Basic types of wear

Abrasive wear, also referred to as wear

Fatigue wear is also called pitting corrosion

Adhesive wear is also called gluing

corrosive wear

Erosion wear

Fretting wear

For plastic materials, take the yield limit as the ultimate stress

Brittle materials: take the strength limit as the ultimate stress