Selected Graduation Thesis of Mechanical Engineering Major

The engineering education of mechanical specialty should strengthen students' engineering practice training and improve the engineering education level of mechanical specialty. The following is my recommended graduation thesis for mechanical major for your reference.

Graduation Thesis of Mechanical Specialty Part I: Mechanical Processing Quality Technology

The quality of machined products is closely related to the processing quality of parts and the assembly quality of products, and the processing quality of parts is the basis of ensuring product quality, which includes the processing accuracy and surface quality of parts.

Keywords: machining; Accuracy; Geometric shape; Process system; mistake

First, the machining accuracy

1, meaning and content of machining accuracy

Machining accuracy refers to the degree to which the actual values of the dimensions, geometric shapes and surface positions of parts after machining are consistent with the ideal values, and the degree of deviation between them is called machining error. Machining accuracy is expressed by the size of machining error. Geometric parameters of parts include geometric shape, size and mutual position, so machining accuracy includes: (1) dimensional accuracy. Dimensional accuracy is used to limit the dimensional error between the machined surface and its benchmark within a certain range. (2) Geometric shape accuracy. Geometric accuracy is used to limit the macro geometric errors of the machined surface, such as roundness, cylindricity, flatness and straightness. (3) mutual position accuracy. The mutual position accuracy is used to define the mutual position error between the machined surface and its benchmark, such as the requirements expressed by the differences of parallelism, verticality, coaxiality and position, and special symbols are allowed.

Due to the influence of processing factors, the size, shape and surface position of a batch of parts processed under the same production conditions are not completely consistent, and there is always a certain processing error. At the same time, reasonable economy should be adopted to improve the productivity and economy of processing under the premise of complete tolerance.

2. The original error that affects the machining accuracy

In machining, many factors affect the process system and produce all kinds of original errors. These original errors are partly related to the structural state of the process system itself and partly related to the cutting process. According to the nature of these errors, they can be summarized as: (1) geometric errors of the process system. Geometric errors of process system include principle errors of machining methods, geometric errors and adjustment errors of machine tools, manufacturing errors of fixtures, clamping errors of workpieces and errors caused by wear of process system. (2) Error caused by stress and deformation of process system. (3) Error caused by thermal deformation of process system. (4) Error caused by residual stress of workpiece.

3. Classification of machining errors

(1) systematic error and random error. Errors can be divided into systematic errors and random errors (also called accidental errors) according to whether they are mastered or not. If the magnitude and direction of the error have been mastered, this is the system error. System error is divided into constant system error and variable system error. The value of the constant system error is constant. For example, the manufacturing errors of machine tools, fixtures, tools and measuring tools are constant errors. The error of variable-value system is that the magnitude and direction of the error change according to a certain law, which can be linear or nonlinear. For example, when the tool wears normally, its wear value is linearly proportional to time, which is a linear variable value system error; However, when the tool is heated to elongation, its elongation and time are nonlinear variable system errors. Anything that does not grasp the law of error is a random error.

(2) Static error, cutting state error and dynamic error. According to whether the error is related to the cutting state, it can be divided into static error and cutting state error. Errors in non-cutting process systems are usually called static errors, such as geometric accuracy and transmission accuracy of machine tools. The error of process system in cutting state is usually called cutting state error, such as machine room; Mechanical deformation and thermal deformation during cutting. The error of process system in vibration state is called dynamic error.

Second, the geometric error of the process system

1, the processing principle is wrong.

The error of machining principle is the error produced by machining with approximate forming motion or approximate blade contour. Usually, in order to obtain the specified machining surface, it is necessary to realize the precise forming movement between the tool and the workpiece, which is the machining principle in mechanical machining. Theoretically, in order to obtain accurate surface of parts, ideal machining principle and completely accurate forming movement must be adopted. However, in practice, completely accurate machining principle is often difficult to realize, and sometimes the machining efficiency is very low; Sometimes, the structure of machine tools or tools is extremely complex and difficult to manufacture; Sometimes due to many structural links, the transmission error of the machine tool increases, or it is difficult to ensure the rigidity and manufacturing accuracy of the machine tool. Therefore, adopting approximate machining principle to obtain higher machining accuracy is an effective technical measure to ensure machining quality, improve productivity and economy.

For example, there are two kinds of principle errors in hobbing hob. One is the error of approximate modeling principle, that is, due to the difficulties in manufacturing, Archimedes basic worm or normal straight profile basic worm is used instead of involute basic worm; Secondly, due to the limited number of hob blades, the tooth profile cutting is actually a broken line rather than a smooth involute, but the resulting tooth profile error is much smaller than that caused by hob manufacturing and grinding errors, so it is ignored. Another example is modular milling cutter forming and milling gears. The tooth profile parameters of gears with the same modulus but different teeth numbers are different. Theoretically, gears with the same modulus and different numbers of teeth should be machined with corresponding tooth cutters. In fact, in order to simplify the number of tools, modular milling cutters and approximate blade profiles are often used to process gears with a certain number of teeth.

2. Geometric error of machine tool

(1) The concept of spindle rotation motion error. The rotary accuracy of machine tool spindle directly affects the machining accuracy of workpiece. The so-called spindle rotation accuracy refers to the drift of the actual rotation axis of the spindle relative to its average rotation axis.

Instantaneous velocity is zero. In fact, due to various errors in the processing and assembly of spindle components and factors such as stress and heat during rotation, the spatial position of spindle axis rotation at every moment is in a changing state, resulting in axis drift, that is, there is rotation error. Super secretary network

Spindle rotation error can be divided into three basic situations: axial movement? The axial movement of the instantaneous rotating shaft along the direction of the average rotating shaft is shown in figure 1(a). Radial jump? The instantaneous rotation axis is always parallel to the radial motion of the average rotation axis, as shown in figure 1(b). Angle swing? The instantaneous axis of rotation forms an inclination angle with the average axis of rotation, and the intersection position is fixed.

Axial movement; (b) radial runout; (c) Angle swing, as shown in figure 1(c). Angle swing mainly affects the shape accuracy of the workpiece, and the cone will be produced when turning the excircle; When drilling, the hole will be oval. In fact, when the spindle works, its rotary motion error is often caused by the synthetic motion of the above three basic forms.

(2) Influencing factors of spindle rotary motion error. The main factors affecting the spindle rotation accuracy are spindle journal error, bearing error, bearing clearance, error of parts matched with bearings, radial unequal stiffness of spindle system and thermal deformation. When the spindle adopts sliding bearings, the roundness error and waviness of the spindle journal and bearing hole have a direct impact on the spindle rotation accuracy, but the influencing factors are different for different types of machine tools.

References:

[1] JUNG WOO. Research on damage detection method of mechanical structure [D]; Taiyuan University of Technology; In 2004

[2] Yin. Discussion on the reasons and countermeasures of machining affecting mating surface [N]. China Architectural News; In 2005

[3] Plateau. Study on improving the wear resistance of stainless steel surface by compound treatment.

Graduation thesis of mechanical specialty Part II: Management of enterprise construction machinery and equipment.

Abstract: The modernization of construction machinery has brought new development opportunities and high efficiency to the development of modern enterprises. However, there are still many problems in the management of mechanical equipment in enterprises, which restrict the rapid development of enterprises. This paper briefly discusses the problems existing in the management of mechanical equipment in modern enterprises and the methods to improve management.

Keywords: engineering; Mechanical equipment; Management; Problems; Countermeasures

The progress of science and technology and the demand of production and construction provide a broad space for the application of construction machinery, and also put forward higher requirements for equipment management. Rational allocation, scientific use, timely maintenance and timely maintenance of machinery and equipment, reducing the occurrence of equipment failures and improving the effective utilization of machinery and equipment are the main requirements for construction equipment management. Below, I will talk about the problems existing in the management of construction machinery and equipment in mining enterprises and the methods to improve the management of construction machinery.

First, the current construction machinery and equipment management problems and reasons

1, the management organization is not perfect and the management system is not perfect.

A considerable number of construction enterprises still lack a complete and strict management system for construction machinery and equipment, and the establishment of construction machinery and equipment ledgers and technical data files is not perfect. Management work is chaotic, and some enterprises don't even record new equipment in time or at all, resulting in passive management and chaotic use of equipment, and it is impossible to define the responsible subject for managing and using construction machinery.

2. Unwilling to invest in intelligence

(1) Although most construction enterprises have set up maintenance management departments according to the actual situation of their own enterprises, due to frequent changes in institutions and personnel, the time for equipment management and maintenance personnel to receive professional education is short, the overall understanding of equipment management by managers is still vague, and the technical management level is uneven.

(2) However, some enterprises only pay one-sided attention to immediate interests, preferring to spend a lot of money on advanced equipment, but are stingy with spending money on intellectual investment such as management personnel training. In this way, even with advanced equipment, management can't keep up, and the quality of personnel is poor, which makes it difficult to meet the needs of equipment management with high degree of mechanical automation and mechatronics.

3. The use and maintenance of construction machinery and equipment are out of touch with each other.

(1) At present, although most construction enterprises have implemented the "one person, one machine" system, that is, each operator regularly uses one mechanical equipment, they have neglected the "one person maintenance" system and failed to clearly implement the rules and regulations for mechanical equipment maintenance to individuals. Because of this, operators often just? Does it include repairs? Maintenance personnel are also careless in handling things. Whenever mechanical equipment fails, operators and maintenance personnel often shirk their responsibilities. This will not only affect the output and quality, but also increase the maintenance and operation costs and reduce the service life of the equipment.

(2) In addition, many project leaders only consider immediate interests, regardless of long-term plans, and their short-term behavior is serious, and they only pay attention to linking output value with benefits, which is manifested in the management and use of equipment. Multiplex light tube? In order to catch up with the construction period and progress, we do not hesitate to fight for equipment, which often leads to overload of mechanical equipment, or take it? What's wrong with you? Operation, even illegal operation, the result is that after the completion of the project, the mechanical equipment is seriously worn and aging, and it takes a lot of energy and cost to carry out maintenance when it is transported to the new project, which leads to the delay of the construction period and the project department shirks its maintenance costs and intangible fixed assets losses.

4. Maintenance of construction machinery and equipment? Lagging? Serious waste.

(1) At present, most construction enterprises have not effectively implemented maintenance measures such as spot inspection system, so equipment maintenance management is often limited to? Maintenance afterwards? ,? Preventive maintenance? If the consciousness is not paid enough attention, the failure and deterioration of equipment can not be found, prevented and repaired early, resulting in unnecessary waste of manpower, material resources and financial resources.

(2) Mechanical equipment of the construction enterprise? Waste maintenance? The phenomenon is also very serious. For the convenience of individual maintenance personnel, some old parts that still have great maintenance value are not maintained or used, and they are allowed to discard them at will. What's more, they don't consider the overall performance of other equipment. Rob Peter to pay Paul? Muddle along, as long as the machinery can move, it is work, and the result will only get twice the result with half the effort.

Second, improve the management of machinery and equipment methods

1, in terms of use, the value of equipment is mainly reflected in use. Any equipment has its prescribed scope of use, conditions and operating procedures. Only the correct use of equipment can ensure safe production. The quality of equipment use depends largely on the level of operators.

Therefore, in use, one is to educate operators to correctly use and operate all kinds of construction machinery, not to work under the maximum load that the machinery can bear, and to ensure the uniform increase and decrease of the mechanical load as much as possible, so that the machinery is in a relatively gentle load change, specifically, to increase or decrease the throttle evenly to prevent the ups and downs of the engine and working device. The second is to strengthen technical training and improve the quality of operators, so that operators can understand the structure, principle and performance, use, maintain, check and troubleshoot, and reduce and prevent mechanical failures caused by human errors from the source. Third, we should adhere to the chartered flight responsibility system, and put the responsibility on people. We should combine personal economic interests with the maintenance and fuel costs of responsible machinery, and at the same time conduct assessment, reward and punishment, strengthen the sense of responsibility in managing equipment, and arouse the enthusiasm of caring for equipment. Super secretary network

2. In terms of maintenance, the regular maintenance of equipment is the basis for keeping the machinery in good technical condition. For construction machinery, the most important thing in maintenance work is to ensure the reasonable lubrication of the machinery. Working surface wear, surface corrosion and material aging are the three main failure forms of mechanical parts under normal use conditions, and working surface wear accounts for the largest proportion of failure. In other words, the wear and tear of machinery is one of the main reasons that make its parts go to the limit technical state. Then, in order to solve the wear problem of mechanical parts, besides using excellent materials, selecting advanced manufacturing technology and designing reasonable mechanical structure, an important work to be done in the process of use is to ensure the reasonable lubrication of machinery.

According to statistics, more than half of the failures of construction machinery are caused by poor lubrication. Due to the precision of construction machinery parts, good lubrication can maintain normal working clearance and suitable working temperature, thus reducing the wear degree of parts and mechanical failures. Normal and reasonable lubrication is one of the effective measures to reduce mechanical failures. Therefore, first of all, we should choose lubricants reasonably, choose normal lubricant categories according to different types and application structures of machinery, choose appropriate quality grades according to the requirements of machinery, and choose appropriate lubricant brands according to the working environment and different seasons of machinery. Second, always check the quantity and quality of lubricating oil. Those with insufficient quantity should be replenished in time, and those with poor quality should be replaced in time. Third, according to the maintenance cycle, equipment technical conditions, working environment and other factors, make a mandatory maintenance plan, and then stop the machine for maintenance and lubrication.

Step 3 maintain

It is inevitable that all kinds of faults will occur in the use of machinery. Among these faults, some faults may have little impact on mechanical equipment, while others are serious, even causing serious accidents. Experience shows that serious mechanical faults are often caused by some minor faults. The reason is that the timely disposal of minor faults is neglected. Therefore, in terms of maintenance, first, pay attention to the timely handling of minor faults, so as to nip in the bud. Never let a small fault not affect the use. In order to catch up with the task and let the equipment work with faults, small faults eventually become major faults, which not only delays the construction period, affects the normal use, but also may lead to sudden scrapping of the equipment. In a sense, dealing with faults in time is an effective measure to reduce and prevent faults. The second is to take it? Regular maintenance? With what? Preventive maintenance? The maintenance system that combines the two systems scientifically and reasonably arranges the maintenance of equipment. Insist on planned maintenance? Pay equal attention to maintenance and prevention? The guiding ideology of, in use, according to the law of mechanical damage and parts wear, according to the working hours, regularly implement mandatory warranty items for equipment; Preventive maintenance persistence? Regular inspection and maintenance as needed? It is a maintenance method controlled according to the actual planned state of the maintenance object rather than the actual use time, which avoids the waste caused by compulsory maintenance, and at the same time, through regular inspection, avoids the warranty loss and disrepair caused by missing disassembly and inspection.

In a word, any equipment will inevitably break down after it is put into use. However, in the work, as long as we strengthen the equipment management, use it reasonably and scientifically, maintain it in place in time, and maintain it accurately in time, we can grasp the occurrence law of various faults during the service life of the equipment, effectively reduce the occurrence of faults, improve the effective utilization rate, maintain the good technical state of the equipment, and maximize the use value of the equipment.

Graduation thesis of mechanical specialty Part III: Analysis of green manufacturing technology of textile machinery.

First, the necessity of developing green manufacturing

Textile industry has always been a highly polluting industry. Due to the backwardness of traditional technology, a large number of production pollutants, including waste gas and sewage, and waste of resources will be produced in the textile production process, which has caused a serious crisis to the environment for human survival. As the largest textile producer and exporter in the world, China's modern textile manufacturing industry has developed very rapidly, so the pollution problem in the textile industry has always been the focus of attention. In today's era of vigorously promoting ecological civilization, textile machinery urgently needs to develop green manufacturing technology.

Environmental consciousness manufacturing, that is, green manufacturing, is simply the green and sustainable development of manufactured products, and it is a modern manufacturing model that takes into account both environmental development and economic benefits. Regarding the implementation of green manufacturing, the specific strategies are to reduce waste, reduce pollution and maximize the use of resources. Nowadays, considering the protection of ecological environment, the international community has begun to demand the green technology of trade products. Although there are not many such green barriers, as a big exporter of textile products, in order to maintain the advantages of the textile industry, the green manufacturing of textile machinery needs to be put on the development agenda as soon as possible.

Second, the embodiment of green manufacturing technology

(1) green material. The selection of green materials should consider the environmental protection of materials on the basis of ensuring the manufacturing requirements of textile machinery. Taking chemical fiber production as an example, a lot of acid and alkali are used in the production process, which leads to the production of toxic substances such as sulfate, so the primary condition of green materials is non-toxic and pollution-free. In addition, the non-degradability of chemical fiber products makes it a burden to the soil environment after being abandoned. Therefore, green materials need to be degradable and recyclable. Finally, due to the difficulty in processing chemical fiber products, energy is wasted, which requires green materials to be easy to process.

(2) Green design. Green design is the core of green manufacturing, because it needs to run through the whole life cycle of products. In the product design stage, we should consider the environmental protection of products from production to packaging to final abandonment and recycling. The selection of production resources, the maximum utilization of energy and the recycling of products are all tasks to be carried out in green design, which not only meets the economic requirements of technology, but also ensures the environmental requirements of green environmental protection.

(3) Green technology. First, we should choose the correct and appropriate process method, then optimize the process operation and design the most efficient process scheme, so as to improve work efficiency, reduce resource consumption, reduce energy consumption, and minimize the harm of harmful substances and pollutants such as waste gas and sewage to the ecological environment.

(4) Green packaging. The design of green packaging should start from the following three aspects: first, the selection of packaging materials is environmentally friendly, harmless, degradable, easy to recycle and easy to process; Secondly, the optimization of packaging structure, packaging structure should be simplified as much as possible, not extravagant; Finally, the used packaging and process wastes are recycled. The discarded packaging materials in the past have caused great damage to the ecological environment due to non-degradable or toxic pollution, and the discarded packaging itself is also a great waste of resources. Therefore, the use of recyclable materials will not cause environmental burden, but also reduce the waste of resources, killing two birds with one stone.

Third, the application of green manufacturing technology.

(1) packaging materials. Green packaging design needs the green ring of packaging materials.

Guaranteed, recyclable and simple in packaging. Commonly used packaging materials for textile products include corrugated paper, wood and plastic. Corrugated board is easy to recycle, but it is not strong enough and needs pretreatment, which not only wastes resources but also is not environmentally friendly. Wood board is strong enough, but as a non-renewable resource, excessive use of wood will lead to unbalanced ecological development, which is not conducive to environmental protection; Plastic packaging has the irreplaceable characteristics of wood and cardboard, which is light, durable and easy to produce, but it also has the disadvantage of non-degradation and is not the best green packaging material. At present, the best green packaging materials are pulp molding and honeycomb paperboard, which are compounded into honeycomb paper core composite board. This kind of packaging material is pollution-free and easy to recycle, which is the best choice for green packaging.

(2) Computer aided design. The green design of textile machinery can make use of modern computer technology. Paperless design reduces the waste of wood resources and saves resources. At the same time, high-tech can also shorten the design cycle, strengthen the design blueprint, and greatly improve the work efficiency and the quality of textile products. Nowadays, the combination of three-dimensional software and computer technology can simulate the stress of various parts of textile machinery and check their related properties.

(3) Process planning. The target system of textile machinery manufacturing process planning is

The key of TQCSRE system is to analyze the relationship between resource consumption R and environmental impact E, for example, by analyzing the relationship between production resource consumption and waste production, and the role of textile machinery technology in it, an optimized green technology is developed.

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With environmental issues becoming a hot topic today, the tide of environmental protection has gradually affected the manufacturing industry. The traditional manufacturing mode is no longer suitable for the development trend of today's society, and the development of green manufacturing of textile machinery is imminent. The popularization of green resources and green technology is not only conducive to reducing the environmental burden, but also conducive to the maximum utilization of resources. Green manufacturing gives consideration to the two-way development of environmental protection and economy, revealing that the harmonious development between man and nature is the right way for social development.

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