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学生：Y同学
GPA：3.7
TOEFL：109
GRE：323
申请专业：美研计算机科学
录取学校：杜克大学
Y同学是北京某重点大学计算机学院的学生，在校成绩优异，GPA达到了3.7。在找到求真教育想要申请美研计算机科学专业的时候，他对出国留学其实没有太多的了解，托福、GRE的考试都没有参加过，刚开始和申请老师聊天时，还问到他的条件能不能申请哈佛。老师发现Y同学对美研计算机科学专业申请知之甚少后，耐心地和他从最基础的考试准备开始聊起。
https://cdn.indeededu.com/uploads/2020/02/CC-768x512.jpg 768w, https://cdn.indeededu.com/uploads/2020/02/CC-705x470.jpg 705w, https://cdn.indeededu.com/uploads/2020/02/CC-450x300.jpg 450w, https://cdn.indeededu.com/uploads/2020/02/CC.jpg 840w" sizes="(max-width: 300px) 100vw, 300px" /> 图源：Unsplash托福、GRE考试如今是绝大多数美国大学研究生院最基本的申请条件，作为国际学生，如果没有托福、GRE成绩的话等同于已经被很多大学拒之门外了。这两项成绩的高低，再加上一项大学的综合GPA，构成了研究生申请中最基础，也是最重要的硬实力。Y同学在听过申请老师的解读后，立刻明白了自己短期内最主要的任务就是完成这两项考试，并且取得高分。拥有学霸素养的Y同学果然不负众望，考出了托福109，GRE 323的优异成绩。
除了硬实力外，软实力也是申请当中必不可少的条件。所谓软实力，指的是申请当中的文书写作、课外活动、科研/实习/工作经历等等。相比硬实力而言，这一部分是很多学生较为薄弱的方面，很多学生在被问到这方面的经历时，都是三言两语就总结完了自己的大学生活。这就需要经验丰富的申请和文书老师，从学生身上挖掘出值得突出的地方，体现出学生个人的特点。
在和Y同学的沟通中，申请老师问到他想出国留学的原因。他说这个想法萌生于一次美国之旅，途中他正好有机会参观了杜克大学，并且在那里遇见了一位杜克大学的在校生，在两人的交流中，他感受到了双方学习和生活方式上的巨大差异，这些见闻给他带来了极大的震撼。这样亲身的体验在老师的眼里就是非常好的写作素材，加上一些实习和志愿者经历，Y同学的文书工作进展地非常顺利。
充足的准备换来的是慢慢的收获，在加入求真教育的100天后，Y同学拿到了杜克大学投来的橄榄枝。美研计算机科学是当下大热的专业，Y同学拿到录取后十分满意。求真教育在这里也预祝Y同学求学之旅一切顺利！文章来源：https://indeededu.com
出国留学GPA究竟有多重要？作为体现学生在校成绩和学习能力的主要指标，GPA无论是在本科还是研究生申请中，都是招生官重点关注的对象。出国留学GPA如果太低，往往会影响招生官对申请者的第一印象，但有没有补救方法？今天求真老师将为大家分享补救低GPA的一些方法。
GPA全称Grade Point Average，即成绩平均绩点，是大多数美国大学及高等教育院校所采用的一种评估学生成绩的制度。美国的GPA满分是4分，即A=4，B=3，C=2， D=1。GPA的精确度往往达到小数点后1到2位，如：3.0，3.25。GPA的计算一般是将每门课程的学分乘以学时，加起来以后除以总的学时，得出平均分。
https://cdn.indeededu.com/uploads/2020/02/desk-705x529.jpg 705w, https://cdn.indeededu.com/uploads/2020/02/desk-450x338.jpg 450w, https://cdn.indeededu.com/uploads/2020/02/desk.jpg 739w" sizes="(max-width: 300px) 100vw, 300px" /> 图源：Freepik下定了赴美求学的决心，奈何GPA没有竞争优势，那么还会有别的补救办法吗？答案是肯定的。
1.提高标准化成绩分数：出国留学GPA能直观体现学生的专业能力，但GMAT、GRE、托福、雅思等标准化成绩同样可以体现学生的学习能力。在GPA不足的情况下，出众的标准化考试成绩能弥补在校成绩方面的劣势。
2.突显课外活动/科研经历/实习经历中的闪光点：成绩并非美国大学招生的唯一标准。招生官青睐的往往是在课堂上、社交上、实践中都表现优秀的综合型人才。因此，求真老师建议同学们尽早确定自己感兴趣的专业方向，并在此基础上有针对性地参加深层次的课外活动。对于申请研究生的同学而言，与申请专业相关的实习经历以及个中收获尤显重要。
3.一份出众的文书材料：文书是招生官最能了解到申请者的材料。一份好的文书材料能让你最大程度展现你对所选领域的热情以及个人素质，帮助你在低GPA的情况下仍能以出色的综合能力打动各大招生官。求真教育拥有一支美籍文书专家顾问团队，能在与你头脑风暴中充分挖掘你以往经历中的闪光点，助你获得招生官青睐，为你插上通往梦校的翅膀。
4.对低GPA作出合理解释：求真老师建议同学们在申请美国大学时，充分利用网申系统所提供的“Additional Information（附加信息）”一栏，对低GPA作出解释。无论是出于主观原因，还是由于专注自己感兴趣的领域而耽误专业学习，又或是受身体原因影响，同学们都应该客观地解释清楚GPA低的原因。美国大学尊重客观事实，如果申请者低GPA的情况情有可原，并且在其他能力上体现出巨大潜力，这样被录取的机会依然很大。
出国留学GPA非常重要，但GPA没有竞争优势的同学们也不要气馁。寻求专业的留学机构帮助，合理规划留学方案，在课外活动和文书上展现自己的闪光点，你也一样可以得到招生官的赏识，斩获梦校录取。求真教育坐落于美国洛杉矶，自2007年成立以来，已经助力上千名学子收获美国名校录取。出国留学GPA太低不要怕，求真教育拥有一支专业、富有经验的专家顾问团队，会为你量身定制留学方案，助你飞跃名校！文章来源：https://indeededu.com
纽约大学转学近年来已经深受大家的欢迎。纽约大学作为全美前30顶尖名校，由于其位于美国东部金融、经济大都市纽约，每年毕业生都拥有非常好的就业方向和职业发展方向。另外，由于排名靠前、筛选严格，每年直接申请竞争激烈。很多同学会通过先申请社区大学或者排名稍低的学校，再通过纽约大学转学这一捷径成功圆梦。求真老师今天就和大家聊聊纽大转学过程中那些需要注意的细节，让同学们有更加清晰的了解。
纽约大学成立于1831年，主要的校区位于曼哈顿格林威治村，因其顶尖的研究水平以及优异的就业质量和校友网络。另外，由于纽约是美国经济中心，很多世界五百强、跨国公司以及全球知名集团都将办公室设立于此。另外，纽约也是世界文化的中心，著名的百老汇、大大小小的艺术展览室和博物馆，让人们能够亲身接触高雅艺术，近距离和顶尖艺术家对话。纽约大学还培养出了许多知名校友，例如著名导演李安、美国流行天后Lady Gaga、著名女演员安妮海瑟薇等。
纽约大学转学需要同学们提前做好准备。不论是在社区大学或者其他四年制大学中学习前两年的通识教育课程，同学们需要在数学、英语、社会科学、人文科学、自然科学等科目中选择足够的学分。我们建议学生可以提前和学校的指导老师和高年级的师兄师姐沟通，合理安排好自己的课程，避免踩雷。好的选课在转学纽大过程中十分重要，因为如果没有拿到各个专业要求的课程学分，同学们就只能与纽大失之交臂。求真教育老师们建议同学们提前做好功课，确定好各个专业所需要或者推荐的课程有哪些，并且对课程大纲、历年开设情况、学生对教授评价等多维度来安排自己的课程表。
选课是大一大二通识教育十分关键的一个环节。求真老师不建议新生选太多课程，毕竟我们需要把有限的时间放在紧张繁忙的学业当中。而且除了课程学习之外，同学们还需要多注重自己的背景提升。社团活动、志愿者经历、体育赛事、科研项目等等都会是不错的选择。纽约大学转学时还注重申请者的领导力和创造力等个人品质。在递交网申时，同学们需要先静下心来，思考下学校录取我的理由有哪些以及我为什么选择纽约大学作为申请学校。如果你对这两个问题有清晰、通顺的答案，并且能从自己的活动经历中提炼出自己对于领导力、创造力等品质的理解，你离纽约大学又将会更进一步。
众所周知，纽约大学许多专业如经济、工程、计算机科学、统计学等每年竞争都十分激烈，那如何选择专业成为让许多留学生头疼的一个难题。在做决定之前，我们应该综合考虑我们前两年对各门课程的学习感受、成绩、自身兴趣以及就业趋势。专业选择的过程中一定要有自己独立的思考和判断，切忌人云亦云，导致之后无法顺利完成自己美国大学学业。美国大学实行宽进严出的制度，且本科GPA不能低于2.0。因此，在纽约大学转学专业这个问题上，我们建议同学们找到你身边专业的求真团队老师，一起探讨最适合自身的专业方向，并且结合目前就业趋势规划好之后两年的学习计划，做到有的放矢。
纽约大学转学对于同学们而言是一次重要的转身机会。希望同学们能提前做好规划，并且和求真转学团队老师积极沟通，积极拔高自己的硬件和软件实力，争取在完成两年的学业后，凭借优异的成绩成功转学纽约大学。文章来源：https://indeededu.com
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Characteristics of tunnel engineering:
The whole project is buried underground, so engineering geology and hydrogeology conditions play an important and even decisive role in the success or failure of the tunnel construction.
Should not only be detailed geological survey and exploration in exploration stage, as accurately as possible to grasp the tunnel project within the scope of the rock properties, the strength of rock mass, complete degree, ground stress field, the stable ability, the condition of groundwater state, the harmful gas and geothermal data, and according to these raw materials, preliminary selected appropriate construction methods, determine the corresponding construction measures and form a complete set of construction machinery.
Moreover, due to the complexity of geological conditions and the limitations of exploration methods, it is still inevitable that unexpected conditions occur during construction.
Therefore, in the construction of the long tunnel, it is necessary to take some technical measures such as test guide pit (such as qinghan tunnel in Japan), horizontal advance drilling, acoustic detection and lead guide pit, so as to further investigate the geological conditions in front of the excavation and timely grasp the changes.
In order to modify the construction method and technical measures as soon as possible.
The highway tunnel is a building with a flat shape. Under normal circumstances, there are only two working faces, namely, the inlet and the outlet, compared with the bridge and line engineering.
The construction speed of the tunnel is slow and the construction period is long.
Therefore, best drill bit for granite rock is necessary to excavate additional auxiliary works such as vertical shaft, inclined shaft and horizontal hole to increase working face and speed up tunnel construction.
In addition, the tunnel section is small, the worksite is long and narrow, some construction procedures can only work in sequence, and some procedures can be along with the tunnel longitudinal development, parallel operation.
Therefore, the construction requirements to strengthen management, reasonable organization, avoid mutual interference.
The equipment inside the hole and the pipeline layout should be carefully considered and properly arranged.
Tunnel construction machinery shall be compact and durable.
The underground construction environment is poor, and may even worsen it during the construction, such as the harmful gas generated by blasting.
Effective measures must be taken to improve, such as artificial ventilation, lighting, dustproof, muffling sound, sound insulation, drainage, so that the construction site in accordance with health conditions, and have enough illumination, in order to ensure the health of construction personnel, improve labor productivity.
Most highway tunnels pass through mountains, so construction sites are generally located in remote mountains and narrow valleys, often far away from existing traffic lines, inconvenient transportation, and difficult supply. These are also one of the issues that should be considered when planning tunnel projects.
Highway tunnel is buried in the ground, once built, it is difficult to change, so in addition to careful planning and design in advance, the construction should be done without any future problems.
Of course, the tunnel project also has many advantages. For example, the construction can not be affected by the change of day and night, the change of seasons, the change of climate and other natural conditions.
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(1) Installation site. Depending on the size of the trolley, it is necessary to leave the stacking and installation site, generally 20m x 20m;
(2) Sleepers and rails.
(3) Lifting equipment. When installing the gantry for most trolleys, it can be installed directly by the existing excavator or loader on the construction site. However, when installing the upper gantry and formwork, it must be installed with a crane of 16 tons or more;
(4) There are a total of 6-8 installation assistants. Generally, the trolley service is installed by the after-sales service personnel of the manufacturer;
(5) The welding machine and the gas cutting device are the connecting parts for processing the reinforcing parts during the transportation of the trolley;
(6) The board generally requires more than 5cm thick and is used for the mounting and operating platform.
When underground jumbo is positioned, the center line of the trolley must be determined first. The way to determine the center line is simple, with a positioning cross at the top center. The intersection point is the midpoint of the trolley that the manufacturer has set up in the production of the trolley. By passing this point and drawing the vertical line of gravity, the center line of the trolley can be found.
When the jacking cylinder is designed below, it is not easy to measure the widest point of the trolley because the cylinders on both sides hinder the direct measurement of the measuring tool. A horizontal line can be drawn on the trolley template, and the height of the two sides can be consistently matched by a tool such as a level gauge, and a rod (such as a thin thread steel) can be welded, and then the width of the section can be obtained by measuring the lead rod.
Before the lining work of the underground jumbo, the trolley must be positioned so that the profile size of the trolley conforms to the required size. After the trolley walks to the section to be lined, it is positioned by the following actions:
(1) Adjust the center line of the trolley by operating the translation cylinder of the hydraulic system to align it with the centerline of the tunnel;
(2) Operate the hydraulic system jacking cylinder to raise the trolley to the standard lining height, and then tighten the foundation jack, then review the height dimension;
(3) Operate the hydraulic system so that the lateral cylinder piston rod extends and reaches the standard lining section, and then manually pulls the lateral support screw to make it reach the lateral cylinder support position and tighten;
(4) After completing the above actions, the section size should be reviewed to prevent error
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In 2019, ANBIT exploration rigs and water well rigs have blossomed in domestic and foreign countries. Due to the quality and cost-effectiveness of water well rigs, many domestic and foreign customers have favored them. Orders have also expanded from the main domestic market to Asia, Europe, In the world, such as Africa and the Americas, ANBIT has occupied an advantageous position in the domestic industry in terms of cost performance. Over the past few years, it has been renewed, and it is constantly working for the goals of lower prices, more stable performance, and higher efficiency.
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Difference and concept between shock absorber and vibration isolator
A shock absorber is the main means to prevent vibration hazards in engineering. The wire rope shock absorber can be divided into active shock absorber and passive shock absorber. The active vibration damper is designed to eliminate the vibration source or reduce the energy or frequency of the vibration source. It is widely used in precision instruments, aerospace equipment, large steam turbine generator units and high-speed rotating machinery, but it is expensive and less used in common construction machinery. Passive shock absorbers include vibration isolators and absorbers. The wire rope vibration isolators can be divided into active isolator and passive isolator.
In order to prevent or limit the harm and influence caused by vibration, various measures are adopted in modern engineering, which is summarized as follows:
This is a positive fundamental measure. If the vibration is caused by the eccentricity of the rotating parts, the unbalanced centrifugal inertia force can be reduced by improving the dynamic balance accuracy. For reciprocating machinery such as air compressor, attention should also be paid to the balance of inertia force.
This is a negative protective measure. For example, precision instruments or equipment should be as far away as possible from factories or workshops with large power machinery, pressure processing machinery and vibration machinery, as well as railways and highways with busy transportation.
The commonly used index to measure the anti-vibration ability of the machine structure is the dynamic stiffness, which is equal to the dynamic force required by the unit amplitude of the machine structure. The larger the dynamic stiffness, the smaller the vibration of the machine structure under the dynamic force.
Change the natural frequency of the system (active damper) or the working speed of the machine (passive damper) as much as possible according to the actual situation, so that the machine does not work in the resonance area.
Damping absorbs the vibration energy of the system and makes the amplitude of the free vibration attenuate rapidly. It can restrain the amplitude of the forced vibration, especially in the resonance region.
For measuring or monitoring instruments on some equipment, the method of installing dynamic vibration absorber under the instrument can stabilize the pointer of the instrument and improve the measurement accuracy.
Using elastic vibration isolator to isolate the vibrating machine (vibration source) from the foundation, so as to reduce the vibration source to affect the surrounding equipment through the foundation, which is the active vibration isolator or active vibration isolator; or isolating the precision equipment to be protected from the impact of the surrounding vibration source, which is the passive vibration isolator.
Alcohols, a large group of organic compounds, are compounds in which hydrogen atoms in side chains of aliphatic hydrocarbons, alicyclic hydrocarbons or aromatic hydrocarbons are replaced by hydroxyl groups. In general, alcohols and hydroxyl groups are linked to a saturated, SP3 hybrid carbon atom. If hydroxyl group is linked to benzene ring, it is phenol; if hydroxyl group is linked to SP2 hybrid olefin carbon, it is enol. The properties of phenols and enols are quite different from general alcohols.
In industrial production, most of the simple saturated monoalcohols, except methanol, are produced from olefins. However, before the rise of the petroleum industry, some alcohols were produced by fermentation.
The following are several important alcohols:
Methanol (lignol) is synthesized from syngas (CO and H ramming) in the presence of heating, pressure and catalyst.
Ethanol, commonly known as alcohol, is one of the most widely used alcohols.
Glycol, the simplest and most important binary alcohol, is a sweet, viscous, colorless liquid.
Glycerol, commonly known as glycerol, is a colorless and sweet viscous liquid, which can be mixed with water, is insoluble in organic solvents and has strong water absorption.
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Different types of bacterial culture media:
(1) Synthetic medium. The components of the synthetic medium are all known chemicals. The chemical composition of this medium is clear, the composition is accurate, the repeatability is strong, but the price is expensive, and the growth of microorganisms in this medium is slow. For example, Gao's No.1 synthetic medium and Czapek medium belongs to this type.
(2) Natural medium. It is made of natural substances, such as steamed potato and common beef soup. The former is used to cultivate mold and the latter is used to cultivate bacteria. The chemical composition of this kind of culture medium is very unsteady and difficult to determine, but it is easy to prepare, rich in nutrition and good in culture effect, so it is often used.
(3) Semisynthetic medium. On the basis of natural organic matter, some inorganic salts with known components are added properly, or some natural components are added on the basis of synthetic medium. This kind of medium can more effectively meet the needs of microorganisms for nutrients.
(1) Solid medium. Coagulant is added to the culture medium, including agar, gelatin, silica gel, etc. The solid medium is often used in the separation, identification, counting and preservation of microorganisms. It is used for microorganism separation, identification and counting. As shown in the figure, microorganisms are separated into colonies and lichens.
(2) Semi-solid medium. A small amount of coagulant is added to the liquid medium to form a semi-solid state. It can be used to observe the movement of bacteria, identify bacteria and determine the titer of phage. It is used to observe the movement characteristics of microorganisms.
(3) Liquid medium. No coagulant was added to the liquid medium. The composition of the medium is even, and the microorganism can fully contact and use the nutrients in the medium, which is suitable for physiological research. Because of the high fermentation rate and convenient operation, it is also commonly used in the fermentation industry. It is also sed to observe the growth of microorganisms.
(1) The commonly used bacterial culture media are nutrient broth and nutrient agar.
(2) The commonly used actinomycete culture media is gauze No.1 .
(3) The commonly used yeast culture medium includes potato sucrose culture medium and malt juice culture medium.
(4) The commonly used mold culture media are potato sucrose culture medium, bean sprout juice sucrose (or glucose, glucose is more expensive) agar culture medium and chasser culture medium.
(1) Basic medium. It is a medium containing the basic nutrients for the growth and reproduction of general microorganisms.
(2) Enrichment medium. It is a medium made by adding blood, serum, animal and plant tissue extracts. It is used to cultivate some microorganisms with strict requirements.
(3) Selective medium. It is to add special nutrients or chemicals into the ordinary culture medium to inhibit the growth of unnecessary microorganisms, which is conducive to the growth of required microorganisms. It is used to separate a certain or a certain kind of microorganism from a mixed microbial population.
(4) Identification medium. It is to add some reagents or chemicals into the culture medium, so that some changes will occur after culture, so as to distinguish different types of microorganisms.
The groundnut oil pressing machine(groundnut oil press) is generally divided into vertical oil top type oil press and screw oil press. Peanut is crushed, selected (to separate peanut from the shell), stir-fried to 6-8 maturity and then physical pressed by oil press. The pressed product of groundnut oil press is peanut oil and peanut residue. Peanut residue is edible. Groundnut oil press can ensure the oil yield of groundnut oil press in four steps. Let's share with you.
The groundnut oil expeller machine can be widely used in rural oil processing and on-site processing and production of urban grain and oil market and can complete a working cycle in an hour. Once squeezed, consumers can get the oil products quickly, without further processing and filtering, they can eat it and there is no adulteration in the processed oil products, with high reliability.
Ordinary culture medium: a kind of artificial preparation, suitable for the growth and reproduction of microorganisms or the production of metabolites, or for other mixed nutrients.
Characteristics: any culture medium should have the six nutrient elements needed by microorganisms and should be proportioned appropriately. Once prepared, it must be sterilized immediately.
Uses: promote the growth of microorganisms; accumulate metabolites; isolate microbial species; identify microbial species; count microbial cells; preserve microbial species; prepare microbial products.
General configuration steps of ordinary culture medium
Formula conversion → add a small amount of water (distilled water, natural water) into the container → weigh all kinds of drugs according to the formula (add in order) → add enough water (one medicine and one spoon, and immediately cover the bottle after taking the medicine).
Starch dissolving: a small amount of cold water is mixed into paste
Heat and dissolve, especially the medium with agar must be boiled. The melting temperature of agar is 95-97 ℃ and it needs to be stirred while heating to prevent burning.
Adjust the medium to the required value with 1n hydrochloric acid or 1n NaOH.
Filter paper or cotton. (sometimes it can be omitted)
Generally, the culture medium is placed in a triangular flask or test tube for sterilization.
After repacking, plug the cotton plug, and wrap the cotton plug with kraft paper to prevent water from entering and wetting the cotton plug during sterilization.
Carry out high-pressure steam sterilization according to the temperature and pressure required on the formula. If the sterilization temperature is too high, the nutrients will be destroyed and cultured
The sugar and amino acid in the medium will darken the color of the medium.
After sterilization, the tubes that need to be placed in an inclined plane should be placed in an inclined position while it is hot, so that they will solidify into an inclined plane, accounting for about one second of the tube length.
The medium can be used without pollution after being placed at 30 ℃ for one day. It is generally wrapped with kraft paper and stored in 2-8 ℃ refrigerator for standby.
Configuration principle
Generally speaking, all microbial growth and reproduction need nutrient culture medium containing carbon source, nitrogen source, inorganic salt, growth factor, water and energy. However, due to the complex types of microbial nutrition, different microorganisms have different needs for nutrients. Therefore, first of all, we need to prepare targeted culture medium according to the nutritional needs of different microorganisms.
When the concentration of nutrients in the medium is appropriate, the growth of microorganisms can be good. When the concentration of nutrients is too low, it can not meet the needs of normal growth of microorganisms. When the concentration is too high, it may inhibit the growth of microorganisms.
The pH of the medium must be controlled within a certain range to meet the growth and reproduction of different types of microorganisms or the production of metabolites.
Different types of microbial growth have different requirements on redox potential (f). Generally, aerobic microorganisms can grow normally when the F value is above + 0.1V, and it is suitable to grow normally when the F value is + 0.3V + 0.4V. Anaerobic microorganisms can only grow when the F value is below + 0.1V, facultative anaerobic microorganisms can breathe when the F value is above + 0.1V, and ferment when the F value is below + 0.1V.
In the preparation of culture medium, we should try to use cheap and easy material to obtain raw materials as the components of culture medium, especially in the fermentation industry, and the amount of culture medium is very large, and the use of low-cost raw materials reflects its economic value.
In order to obtain pure culture of microorganism, contamination of mixed bacteria must be avoided, so the equipment and workplace should be disinfected and sterilized.
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Punching is a forming process that uses a punch press to force a tool, called a punch, through the workpiece to create a hole via shearing. Punching is applicable to a wide variety of materials that come in sheet form, including sheet metal, paper, vulcanized fiber and some forms of a plastic sheet. The punch often passes through the work into a die. A scrap slug from the hole is deposited into the die in the process. Depending on the material being punched this slug may be recycled and reused or discarded. Punch tooling (punch and die) is often made of hardened steel or tungsten carbide.
Very often the finished product requires various types of holes, differing by position and shape. The possibility of making these holes inside the roll forming line makes it possible to obtain the product without the need for additional processing steps, with better quality and reduced cycle time and semi-processed products warehouse. The workpiece is often in the form of a sheet or roll. Materials for the workpiece can vary, commonly being metals and plastics. The punch and die themselves can have a variety of shapes to create an array of different shaped holes in the workpiece. Multiple punches may be used together to create a part in one step.
Punching machine china has many advantages:
The dimensional accuracy is guaranteed by the mold, so the processed parts have stable quality and good consistency, and have the characteristics of “ exactly the same”.
Stamping can obtain parts that are thin, light in weight, good in rigidity, high in surface quality, and complex in shape that cannot be manufactured by other processing methods;
High material utilization rate, which is less and no chip processing;
High efficiency, convenient operation, and the required technical level of workers is not high;
The mold has a long service life and low production cost.
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Online cutting process analysis
The cross-section of the plasma laser cutter is not only closed but also complicated. The plasma profile closed section is composed of a vertical surface, a horizontal surface and a curved surface, and the material is a galvanized steel sheet of 1.25 mm. It is required to ensure not only the quality of the section but also the galvanized layer and the speed of the production line. This brings a lot of trouble to the mold design. If the conventional cutting die is used for the overall cutting, it will not be cut off, and the product requirements cannot be met. According to the characteristics of the parts, a deep analysis is made, and it is decided to reserve a cutting amount of 6.8 mm before cold forming. Because the shape of the part is very special, the edge of the punch must be shaped, not only to cut the curved surface, the horizontal surface, and the vertical surface, but also to have no sag and scratches. According to the process requirements, in order to prevent the sag and ensure the convexity Intensity, it is decided that the process hole should be pre-punched in the middle of the part and at the corner, and the pre-punching hole must be punched out before forming, that is, before the cold bending, a process is added - pre-punching, so a pre-punch is designed. Hole mold. That is, two sets of molds are required to cut the workpiece: a set of pre-punching dies and a set of cutting dies.
Pre-punching the design
From pre-punching to cutting, there is a forming process in the middle, so that the position of the pre-punching is more complicated. Not only to ensure the quality of the cut surface, but also to choose the right position to improve the strength of the die of the cutting die, and also to ensure that the cold forming of the cutting die is not affected, and according to the requirements of the stamping process, the hole of the punching part The distance between the holes and between the holes and the edges should not be too small to correct the position of the holes and repeatedly simulate through the computer. The hole in the middle portion is to ensure that the intermediate portion of the punch is not too long and too sharp, and the formed chips are easily discharged when the top of the workpiece is punched. The hole at the corner is to ensure that there will be no sag at the time of cutting, and at the same time, it will not produce chips that are difficult to discharge.
Directly use the Pro/E expansion command to expand the part to get the expanded view. Expand the Expand Create Sheet Metal Unbend Regular by expanding the command, select a datum plane or edge (unmoved or edge) when unfolding, then select the Unbcnd All command, and then click OK.
①Pre-punching die structure design
According to the unfolding diagram and precision requirements, the diagonal guide column formwork is selected, and the formal form is adopted, the punch is on the upper side, and the concave mold is on the lower side. For economical processing and easy maintenance and replacement, the male and female molds are in a block-like structure, so that the insert can be replaced without removing the entire mold. After the two punches and the punch fixing plate are fixed, they are directly fixed on the upper mold base 7 by screws together with the punch pad, and the two concave molds are symmetrically set in the lower mold base.
In order to prevent the sticking of the scrap, the unloading rubber is specially designed on the punch, and after the scrap is punched off, the scrap is smoothly separated from the convex and concave molds under the elastic force of the rubber. In order to reduce the labor, the edge portion is made 1. S0 slope. In addition, because it is an online automatic production, the strip is automatically fed, so a fixed discharge plate is adopted, so that the discharge plate not only functions as a discharge plate but also functions as a guide plate, and the fixed discharge plate has a discharge force. Large, simple structure. Single features.
②Analysis of the working process of pre-punching die
In the working process, the plate guides the guide plate (the guide plate and the discharge plate 3 are the same plates), and the feeding process is automatic feeding, and the punching position is determined by the photoelectric switch. The plate is taken to the proper position. Under the action of the hydraulic machine, the upper mold base drives the punch downward, and the punch starts to work. Under the joint action of the convex and concave molds, the punching is completed. Under the elastic force of the rubber, the waste is smoothly leaked from the leakage hole, and the punch is lifted up, and one stroke is completed.
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Compared with today's society, the use of table mats is becoming larger and larger! Users are also very broad, from all kinds of office workers to primary school students, and housewives are more expressing their love for it. It does not need to say the use and effect. At present, the use of table mats can be divided into: student desk mats, game mats, medical table mats, office desk mats, mats bar, desk mats and so on! Its material is roughly divided into: natural rubber table mats, environmental EVA and paper and PVC (environmental EVA and PVC direct printing) table mats, natural rubber adn paper and PVC (rubber and PVC direct printing) table mats, PVC transparent table mats (false glass or crystal mattress) and so on.
When you use it in your home or office, the table mats can protect your desktop and countertop very well, and bring warm protection to your furniture and body. The desktop is light, soft, fluent in writing, fast, safe and convenient in accessing and accessing data, which can help to improve the efficiency of document processing in banks, schools, government agencies and companies, thus reducing costs.
The table mats of the soft glass has high heat resistance, cold resistance, strong acid resistance, alkali resistance, heavy pressure resistance, static electricity, impact resistance, tension resistance, aging resistance, good transmittance and long service life. For restaurants, cleaning costs can be reduced and elegant and beautiful appearance of the restaurants can be added. For personal office, it us warm in winter and cool in summer, flexible, and has flame retardant, insulation, moisture-proof, heat insulation, sound insulation, anti-corrosion, impact resistance, non-deformation, continuous cracking, light resistance, anti-fading, weather resistance.
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In order to improve the softness and handle of tissues, the use of softeners in pulp is a common method in the paper-making industry. Although softeners can improve the softness of paper towels, the range of improvement is very limited. It has been reported that a certain amount of paper softener was added to the pulp, and the softness of the paper decreased by about 20%, but it still belongs to the hard paper. Therefore, it is urgent to develop a method that does not depend on paper softener to produce some paper with better softness.
Through experiments, the application of alcohol compounds in tissues and their adding methods can greatly improve the softness of tissues, and it can improve the moisture content of tissues at the same time. When contacting with human skin, it will not plunder skin moisture, and frequent wiping will not easily produce peeling phenomenon. Because of its high softness, it is especially suitable for infants.
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