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[《英语六级微信的利与弊》1900字]关于微信的利与弊

时间:2019-11-30 09:18:24 来源:学生联盟网
作文一:《英语六级作文预测:微信的利与弊》1900字

英语六级作文预测:微信的利与弊

Directions: For this part, you are allowed 30 minutes to write a position on the topic: On the Popularity of Wechat. You should write at least 150 words and base your position on the outline (given in Chinese) below:

On the Popularity of Wechat

1. 目前微信很流行

2. 微信流行的原因

3. 可能存在的问题

六级英语作文范文一:

Weixin has many functions. Weixin has basic functions, such as send hold-to-talk voice messages, text messages, pictures and videos. Weixin supports Wi-Fi and 3G data network. And it supports China, Hong Kong, Macau, Taiwan, Japan and US Phone Number.

Weixin has speakerphone. Gently press the button to speak. The other party will be able to receive the voice after the button release. Weixin can enjoy group chat up to 20 people. What’s more, Weixin has many other attractive functions. The most attractive function is search people around you. Weixin can search people near you who has Weixin base on your own location. This function can make user to know people around you and then to built a new relationship. Weixin alsosupports to send video. Shoot a video and send it to the other party immediately.

The pressed video is also suitable for transmission in mobile network. So you can always share the wonderful pieces of life with other people at any time. Weixin also has drift bottle function.

This function can share your messages to the world anonymously and make new friends. Weixin also has voice notes function. This function not only can save your voice memo, but also keep your pictures and texts in a convenient way. Weixin also can help you to catch your messages and keep you always updated. Weixin has QQ mail notifications which can alert you when new mails e to your QQ mailbox and you can read the mails right away. It supports sending and receiving messages from Tencent micro blog.

Weixin has English language edition. It is convenience for foreign to use it. It can help the pany to dominate the market outside of China.

作文二:《英语作文--广告的利与弊》1600字

广告的利与弊

The advantage and disadvantage of the advertisement

Advertisement is omnipresent in our modern society. It seems wherever we go. such small ads will greet our eyes: the supermarket. the subways. the stop sighs. the walls of public buildings. the garbage cans. and whatsoever. The ads can be about everything from selling mobile phone. renting houses. treating difficult diseases to producing fake diplomats.

(from domestic s to machinery. from toys to aircrafts.)It`s no exaggeration that we live in the world of advertisement.  The advantage of the ads is self-evident. They provide us with a good collection of goods and service. from which we can make our best choices. For the manufacturer. they can take advantage of the ads to project the characters of their products so as to seize the vision of the consumers and gain them huge profits.

However. we cannot belittle the disadvantages of the ads. ①To many ads do spoil our daily life and waste our time. They interrupt the TV programs. filling our letterbox. and ruin our appreciation of nature in place of interests. People often feel burdened with the ads instead of satisfying with them. ②On the other hand. some of the ads are illegal. spreading false information and planning to treat people who are eager to solve their problems.

广告的利与弊

广告在当今社会中无处不在.看起来无论你走到哪里.她都会映入你的眼帘:超市.地铁.车站.公共建筑的墙体.垃圾桶甚至T恤衫.广告的内容可以关于任何东西:从卖电话到租房.从治疗疑难杂症到办假证./(从家用物品到大型机器.从玩具到航天器) 毫不夸张的说.我们生活在一个广告世界里.

广告的优点很明显.它给我们提供大批量的商品和服务.供我们做出最好的选择.对于商家而言.他们可以利用广告展示自己商品的特点.以便抓住消费者的视线来获取利润.

然而.我们也不能小视广告的缺点.①太多的广告会搞乱我们的生活并浪费我们宝贵的时间.它们打断电视节目.塞满我们的信箱.损毁了我们对自然的欣赏代替兴趣.人们通常对它们感到负担而不是满足.②另一方面.有些广告是非法的.传递错误信息并意在欺骗那些想急于解决问题的人.

作文三:《电视利与弊英语作文》6000字

Television as a Better Source of News

Among the three mass media television, newspaper and radio (短语作引言句)I regard television as a better source of news(自己的观点,即全文的中心思想)。

My statement that television is a better source of news (段首句用同位语从句与首段中心思想衔接) is based on the following two reasons (对全段内容加以限定). The first reason is that television can report news more quickly (层次1). We can get the news at the same time when something is happening or immediately after something happened(拓展句). While(转折,引出其它媒体的缺点不足)newspapers can only offer the news that happened a day or two days ago. The second reason is that television can report news more vividly and impressively(层次2). With sounds and pictures on TV, we can be deeply impressed by the news as if we were personally on the spot(拓展句举例说明). But (转折,指出不足)when we try to get news from the newspaper, we have to concentrate our mind on the lines and use our imaginations to form a concrete image, which is always tiresome and time-consuming.

According to the above mentioned reasons, we can easily draw a conclusion that television is really a better source of news(总结,重申首段观点).

利与弊英语作文范文评析:The Main Difference between Exam-oriented Education and Quality-oriented Education

Education in China used to be exam-oriented one. But with the development of education reform, quality-oriented education is stressed again and again. So there rises a question: What is the main difference (题目要点) between these two? (提问法开头)

According to my understanding, exam-oriented education focuses on students’ ability of passing examinations of different levels. This education is to test the student’s mand of knowledge they have obtained from the textbooks. So examination results are the only criterion which is used to evaluate the students whether they are “excellent” ones or “bad” ones(应试教育的主要特点). However(转折引出素质教育的特点), quality-oriented education focuses on students’ various qualities, including academic quality, moral quality, cultural quality, most important, their individual personality and potentialities. The main purpose of the education is to bring students’ practical potentialities into full play. Quality-oriented education can teach students now to face difficulties and solve problems independently.

From the above parison between exam-oriented education and quality-oriented education, we find that the latter one is superior(表明作者的倾向性). So it is time for our universities and colleges to bring quality-oriented education into students’ daily life(提出建议).

the Advantages and Disadvantages of TV

We have to admit that TV has brought great changes to our life.Almost everyday,we watch all kinds of programs on TV.We need them as well as enjoy them.TV can amuse people,give us news and information we want,and expand our horizons.We can also relax ourselves by watching TV after hard studies or work.Hower,there are two sides to everything,and TV is without exception.TV also has some disadvantages.First,spending too much time on it will affect our studies and work.Second,there are now too many mercials(广告)on TV,which would make us care more about money,and it's not good for teenagers' growth.Third,sitting in front of TV too long would do harm to our health.

Therefore,we students should watch TV in our spare time but not be addicted to it.

电视的优缺点

必须承认,电视确给我们的生活带来了巨大变化。几乎每天我们都在电视里看各种各样的节目。我们需要它们,也很爱看。电视能娱乐大众,开阔视野,提供给我们新闻和信息。繁重的学习和工作后,我们还可以通过看电视来放松自己。然而,事物都是一分为二的,电视也不例外。电视也有它的弊端。首先,看电视太多会影响我们的学习和工作。其次,如今电视上太多广告,这些广告会使我们青少年过于看重钱,而不利于我们的成长。再说,坐在电视机前太久也会损害我们的健康。

因此,我们学生应该闲暇时看一下电视,而不可沉迷其中。

高3年级水平左右,不要太长。希望有厉害的朋友提供,谢谢了。最佳参考答案:The Advantages of Watching TV

First of all, watching TV is a good relaxation. After a day of hard work, we look forward to

a good relaxation. Watching TV can meet our requirements by easing our minds and forting our

physical bodies because the pleasant music and pictures can keep'us away from tension and fatigue.

Besides, watching TV is entertaining. There are so many kinds of entertainment, such as sports activities, performances, plays and movies, etc. in the world. Of course, it is impossible for us to be on every spot, even with the best means of transportation of our time. However, TV can bring

them right in front of us and with them our life is full of joys.

Above all, watching TV is educational. Education TV service offers teaching programs on all subjects for people of different professions as well as for students, children and aged people. No doubt, it provides the widest education and has the largest audience. Everyone of us, more or less, is benefited from watching TV. Indeed, TV has great influence on people's life, work and study.

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其他参考回答:

提问人的追问 有没有中文翻译?

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其他参考回答:

回答人的补充 看电视的益处

首先,观看电视是一种很好的消遣方式。辛辛苦苦工作一天之后,大家都想好好放松一下。看电视使人心情放松,身体舒适,可以满足我们的需要,因为令人愉快的音乐和图像能使我们消除紧张,摆脱疲劳。

此外,看电视给人以娱乐。我们有多种多样的娱乐方式,如世界各地的体育运动,演出演奏,戏剧电影等等。 当然,即便借助现代最好的交通工具,我们也不能处处在场。然而,电视机把以上所有娱乐带到我们面前。有了丰富多彩的娱乐,我们的生活才充满欢乐。

最为重要的是,看电视可以接受教育。教育电视频道不仅为学生、小孩和老年人,而且为不同职业的人们提供各类学科的教学节目。毫无疑问,电视提供最广泛的教育,拥有为数最多的观众。咱们每个人或多或少都从看电视中获得益处。 的确,电视对人们的生活、工作和学习影响很大。

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其他参考回答:

提问人的追问 可是并没有写他的坏处,我两样都要。

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其他参考回答:

回答人的补充 Every coin has two sides. The disadvantages are also obvious. For example, watching too much TV can easily bee short-sighted, especially for children and students. To make matters worse, some young students are keen on watching TV so that they give up their studies gradually.

Through above analysis, I think watching TV is a way of studying, it is good for us to watch TV. But when we watch TV, we should make a plan otherwise watching TV will destroy our life.

每样事物都有两面性。看电视的坏处也是显而易见的。比如看多了会影响你的视力,尤其是小孩和学生。更糟的是,一些学生很喜欢看电视,以至于他们渐渐的放弃了学习。

通过以上分析,我认为,电视是我们的一种学习方式,看电视对于我们有好处。但是当我们看电视时,应该做个计划,否则看电视将使我们的生活一团糟。

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其他参考回答:

提问人的感言非常有耐心,谢谢你。

作文四:《英语作文手机的利与弊》1700字

英语作文手机的利与弊

Advantages and Disadvantages of the Mobile Phone

Wherever you are, you can see many people equipped with mobile phones. It seems that the world bees smaller nowadays. You could be found wherever you are so long as you take the mobile phone with you. Some people wonsider the mobile phone necessary and useful to them, while others may dislike it.

People who like the mobile phone are much more concerned about its advantages. It is convenient, for you can connect others easily and quickly. You don' t have to wait for an important call at home all day long. The youth of today send messages, surf on the net, listen to music and even take photos by using the mobile phone. People find it advanced for its attractive functions. In some countries, it even stands for a person' s status.

However, some people don' t like it. Imagine that you go to spend your holiday with your family after days of busy and tiresome work. When you lay on the beach fortably, your phone rings. Then you have to go back to your office only to find an unimportant customer waiting for you. At that moment, you may even want to throw your phone away, for you just want to relax and get rid of your work.

However, whether you like the mobile phone or not, it has alresdy affected our lives and played an important role in the history of human beings.

手机的利与弊

无论你在何地,你都会看见许多人使用手机。如今,世界似乎越来越小了,只要你带部手机出门,你都会被找到。有些人认为手机对他们来说是非常有用的必需品;而有些人则有不同看法。

喜欢使用手机的人比较注重手机的好处。它非常便利,因为它让你与别人的联系既简单又快捷,你再也不用为了等一个重要电话成天守在家里了。现在的年青人喜欢用手机发短信、上因特网、听音乐、甚至照像。手机拥有非常吸引人的各种功能,是非常先进的科技产物。在某些国家。它甚至象征着使用者的地位。   当然,有些人不喜欢它。想像一下,在接连几天的繁重工作后,你好不容易可以与家人去度假。当你舒舒服服地躺在沙滩上时,手机响了。你不得不赶回办公室,却发现只是一位无关紧要的客户在等你。那时你或许想把手机扔了,因为你只想远离工作、彻底放松。

然而,无论你喜不喜欢手机,它已经改变了我们的生活,并在人类历史上发挥着重要的作用。

作文五:《网络的利与弊(英语作文)》5700字

网络教育:

As we all know, the 21st century of the Internet. With the development of the Internet, more and more people begin to use it to enjoy themselves or do something special. However, every coin has two sides , the Internet also has its own advantages and disadvantages.

Our life has a great change since we use the Internet. We benefit a lot from the Internet. As for me, I am accustomed to going shopping on the Internet, which is a good way to save my time and money. Many people do the same as me. What’s more, the Internet makes it convenient for us to make friends and get people closed . We can also go through the news all over the world. The Internet not only broaden our view but also assist us to know more about the world . On the other hand , more and more teenagers are addicted to virtual world and they all play puter games everyday they want, leading to a terrible result.

In conclusion, we should have selective using the Internet and keep away from the virtual world. Don’t always use the Internet to chew the fat and do something meaningful.

网店: On Students Running an Online Shop

Recently, it is frequently reported that a student can earn 60 ’000 a month by running an online shop. His business idea has inspired many students to set up their own online shops.

Some people hold that doing that, students can gain not only some money to reduce financial burden for their family but also the

precious experience of setting up a business. Most important of all, the petition in the job market is very fierce currently. If students cannot find a satisfactory job after graduation, an online shop can help them earn their living. While others hold that the duty of a student is to study. Running an online shop will definitely distract students from their primary tasks. It equals to putting the cart before the horse.

From my perspective,I am in favor of the former opinion. I agree that in college acquiring knowledge is of critical importance. However, acquiring practical skills and the ability to survive is even more

important. In a word,as long as a student can balance the two sides

well, running a business in the school years should not be

discouraged.

校园暴力:

School is not only a place we can learn something,but also is a small society.

So,boycott school videncen is what everyone in school should do.Teachers should have a sense of responsibility and carefully found the things which happened in your students and then timely educate and protect them.As we should have a sense of justive and also have a heart of fighting against with evil.Don't be feared,it just like a spring,you weak it will strong,you strong it will weak. I think if we unite together to fight against with evil.The school will peace and harmonious again!

校园占座:

Reserving a Seat

Nowadays, it is mon to see a textbook, a notebook or even apiece of paperon the desk in the classroom or library, indicating that the seat has been taken. And strangely enough, most students seem to take this for granted.

Although for most students, reserving seats is for the sake of study, it still has brought some negative effects. On the one hand, reserving seats violates the rule of fairness. Some students can not find a seat, even if they e to the classroom early. As a result, they tend to feel disappointed at college study. On the other hand, reserving seats is a selfish behavior. With a reserved seat, no matter how late one esto class, the seat is still kept him.Therefore, students who are used to reserving seats may bee insensitive, never concerning about others feelings.

Considering what has been mentioned above, I think it is high time that we college students reconsidered our behavior. As long as all of us improve our consciousness, it will not be difficult to get rid of the habit of reserving seats.

逃课:

Some people may believe that going to classes should be optional, but I disagree. I don't understand how university students can expect to learn anything if they don't attend classes. Personal experience can help people learn about themselves and the world outside the classroom, but when it es to learning about academic subjects, students need to be in class.

In class they receive the benefit of the teacher's knowledge. The best teachers do more than just go over the material in than class textbook. They draw their students into discussion of the material. They present opposing points of view. They schedule guest speakers to e, give the students additional information, or show documentary films on the subject.

Also, attending classes on any subject teaches more than just facts. It teaches students how to learn, how to absorb information and then apply what they've learned to other situations. Their teacher is the best one to help them with these skills. They can't learn them just by reading the textbook.

Going to class also teaches students how to work with the other members of the class. Many times students will be given group assignments. This is different from what they did in secondary school. Here they're with people from different backgrounds and experiences. In this situation, they learn how to handle working with people different from themselves to achieve a mon goal.

Going to class also teaches students responsibility and discipline. Having to be at a particular place at a particular time prepares them for getting a job. Being at a place on time with an assignment pleted prepares them for a career.

In short, by going to class students learn more than just information from the teacher. They also learn how to learn, how to work with others, and how to work responsibly. These are not optional skills in life, so attending classes should not be optional in college

作文六:《利与弊的英语作文》800字

关于中学生用手机利与弊的英语作文

这种题型往往要求先说明一下现状,再对比事物本身的利弊,有时也会单从一个角度(利或弊)出发,最后往往要求考生表明自己的态度(或对事物前景提出预测)

1. 说明事物现状

2. 事物本身的优缺点(或一方面)

3. 你对现状(或前景)的看法   As we all know ,the world develops more quicker than before. ,Many students use the mobile phone in the school .Now ,let me tell you the advantage and the disadvantage .

Many parent thinks use the mobile phone is bad for

students .It will must affect students' study. Most students will play the games in class .And they will send the information to their friends .That's too bad to them to study .

But ,using the mobile phone also have good things to students ,They can call their friends when they are not in school .It will makes your friendship more close . And ,if your parents can't find you ,they can call you at once .

In a word ,using the mobile phone have the good things and the bad things .The important is if you can  control yourself .

作文七:《英语作文 英语利与弊 模版》3000字

英语作文 英语利与弊 模版

对比观点题型 (1) 要求论述两个对立的观点并给出自己的看法。

1. 有一些人认为。。。

2. 另一些人认为。。。

3. 我的看法。。。

The topic of ①-----------------(主题)is being more and more popular recently. There are two sides of opinions about it. Some people say A is their favorite. They hold their view for the reason of ②-----------------(支持A的理由一)What is more, ③-------------理由二). Moreover, ④---------------(理由三).

While others think that B is a better choice in the following three reasons.

Firstly,-----------------(支持B的理由一). Secondly (besides),⑥------------------(理由二). Thirdly (finally),⑦------------------(理由三).

From my point of view, I think ⑧----------------(我的观点). The reason is that

⑨--------------------(原因). As a matter of fact, there are some other reasons to explain my choice. For me, the former is surely a wise choice .

(2) 给出一个观点,要求考生反对这一观点

Some people believe that ①----------------(观点一). For example, they think ②-----------------(举例说明).And it will bring them ③-----------------(为他们带来的好处).   In my opinion, I never think this reason can be the point. For one thing,④-------------(我不同意该看法的理由一). For another thing, ⑤-----------------(反对的理由之二).

Form all what I have said, I agree to the thought that ⑥------------------(我对文章所讨论主题的看法).

net

阐述主题题型 要求从一句话或一个主题出发,按照提纲的要求进行论述.

1. 阐述名言或主题所蕴涵的意义.

2. 分析并举例使其更充实.

The good old proverb ----------------(名言或谚语)reminds us that ----------------(释义). Indeed, we can learn many things form it.

First of all,-----------------(理由一). For example, -------------------(举例说明).

Secondly,----------------(理由二). Another case is that ---------------(举例说明). Furthermore , ------------------(理由三).

In my opinion, ----------------(我的观点). In short, whatever you do, please remember the say------A. If you understand it and apply it to your study or work, you”ll necessarily benefit a lot from it.

解决方法题型 要求考生列举出解决问题的多种途径

1. 问题现状

2. 怎样解决(解决方案的优缺点)

In recent days, we have to face I problem-----A, which is being more and more serious. First, ------------(说明A的现状).Second, ---------------(举例进一步说明现状)

Confronted with A, we should take a series of effective measures to cope with the situation. For one thing, ---------------(解决方法一). For another -------------(解决方法二). Finally, --------------(解决方法三).

Personally, I believe that -------------(我的解决方法). Consequently, I’m confident that a bright future isawaiting us because --------------(带来的好处).

说明利弊题型 这种题型往往要求先说明一下现状,再对比事物本身的利弊,有时也会单从一个角度(利或弊)出发,最后往往要求考生表明自己的态度(或对事物前景提出预测)

1. 说明事物现状

In my opinion, ----------------(我的观点). In short, whatever you do, please remember the

say------A. If you understand it and apply it to your study or work, you”ll necessarily benefit a lot from it.

解决方法题型 要求考生列举出解决问题的多种途径

1. 问题现状

2. 怎样解决(解决方案的优缺点)

In recent days, we have to face I problem-----A, which is being more and more serious. First, ------------(说明A的现状).Second, ---------------(举例进一步说明现状)

Confronted with A, we should take a series of effective measures to cope with the situation. For one thing, ---------------(解决方法一). For another -------------(解决方法二). Finally, --------------(解决方法

作文八:《英语作文:网上购物的利与弊》5500字

一、SLA,LOM,SLS,FDM,3DP技术的主要特点和比较;

在快速成型领域里主要的技术包括:SLA、LOM、SLS 、LOM及3DP等工艺技术,而这几种工艺又各有千秋,接下来就看一下这几种工艺的优缺点及比较:

1、SLA

光敏树脂选择性固化是采用立体雕刻(Stereolithography)原理的一种工艺,简称SLA,是最早出现的一种快速成型技术。

在树脂槽中盛满液态光敏树脂,它在紫外激光束的照射下会快速固化。成型过程开始时,可升降的工作台处于液面下一个截面层厚的高度,聚焦后的激光束,在计算机的控制下,按照截面轮廓的要求,沿液面进行扫描,使被扫描区域的树脂固化,从而得到该截面轮廓的树脂薄片。然后,工作台下降一层薄片的高度,以固化的树脂薄片就被一层新的液态树脂所覆盖,以便进行第二层激光扫描固化,新固化的一层牢粘结在前一层上,如此重复不已,直到整个产品成型完毕。最后升降台升出液体树脂表面,取出工件,进行清洗、去处支撑、二次固化以及表面光洁处理等。光敏树脂选择性固化快速成型技术适合于制作中小形工件,能直接得到树脂或类似工程塑料的产品。主要用于概念模型的原型制作,或用来做简单装配检验和工艺规划。

光固化成型(SLA)优点如下:

(1)尺寸精度高。SLA原型的尺寸精度可以达到±0.1mm。

(2)表面质量好。虽然在每层固化时侧面及曲面可能出现台阶,但上表面仍可以得到玻璃状的效果。

(3)可以制作结构十分复杂的模型。

(4)可以直接制作面向熔模精密铸造的具有中空结构的消失型。

SLA的缺点:

(1)尺寸的稳定性差。成型过程中伴随着物理和化学变化,导致软薄部分

易产生翘曲变形,因而极大地影响成型件的整体尺寸精度。

(2)需要设计成型件的支撑结构,否则会引起成型件的变形。支撑结构需在成型件未完全固化时手工去除,容易破坏成形性。

(3)设备运转及维护成本高。由于液态树脂材料和激光器的价格较高,并且为了使光学元件处于理想的工作状态,需要进行定期的调整和维护,费用较高。

(4)可使用的材料种类较小。目前可使用材料主要为感光性液态树脂材料,并且在太多情况下,不能对成型件进行抗力和热量的测试。

(5)液态树脂具有气味和毒性,并且需要避光保护,以防止其提前发生聚合反应,选择时有局限性。

(6)需要二次固化。在很多情况下,经过快速成型系统光固化后的原型树脂并未完全被激光固化,所以通常需要二次固化。

(7)液态树脂固化后的性能不如常用的工业塑料,一般较脆,易断裂,不便进行机加工。

2、LOM

箔材叠层实体制作(Laminated Object Manufacturing)快速原型技术是薄片材料叠加工艺,简称LOM。

箔材叠层实体制作是根据三维CAD 模型每个截面的轮廓线,在计算机控制下,发出控制激光切割系统的指令,使切割头作X 和Y 方向的移动。供料机构将地面涂有热溶胶的箔材(如涂覆纸、涂覆陶瓷箔、金属箔、塑料箔材)一段段的送至工作台的上方。激光切割系统按照计算机提取的横截面轮廓用二氧化碳激光束对箔材沿轮廓线将工作台上的纸割出轮廓线,并将纸的无轮廓区切割成小碎片。然后,由热压机构将一层层纸压紧并粘合在一起。可升降工作台支撑正在成型的工件,并在每层成型之后,降低一个纸厚,以便送进、粘合和切割新的一层纸。最后形成由许多小废料块包围的三维原型零件。然后取出,将多余的废料小块剔除,最终获得三维产品。叠层实体制作快速原型工艺适合制作大中型原型件,翘曲变形较小,成型时间较短,激光器使用寿命长,制成件有良好的机械性能,适合于产品设计的概念建模和功能性测试零件。且由于制成的零件具有木质属性,特别适合于直接制作砂型铸造模。

分层实体制造(LOM)优点如下:

(1)成型速度较快。由于只需要使用激光束沿物体的轮廓进行切割,无须扫描整个断面,所以成型速度很快,因而常用语加工内部结构简单的大型零件。

(2)原型精度高,翘曲变形小。

(3)原型能承受高达200摄氏度的温度,有较高的硬度和较好的力学性能。

(4)无需设计和制作支撑结构。

(5)可进行切削加工。

(6)废料易剥离,无须后固化处理。

(7)可制作尺寸大的原型。

(8)原材料价格便宜,原型制作成本低。

LOM的缺点:

(1)不能直接制作塑料原型。

(2)原型的抗拉强度和弹性不够好。

(3)原原型易吸湿膨胀,因此,成型后应尽快进行表面防潮处理。

(4)原型表面有台阶纹理,难以构建形状精细、多曲面的零件,因此,成型后需进行表面打磨。

3、SLS

粉末材料选择性烧结(Selected Laser Sintering)是一种快速原型工艺,简称SLS。

粉末材料选择性烧结采用二氧化碳激光器对粉末材料(塑料粉等与粘结剂的混合粉)进行选择性烧结,是一种由离散点一层层堆集成三维实体的快速成型方法。粉末材料选择性烧结采用二氧化碳激光器对粉末材料(塑料粉、陶瓷与粘结剂的混合粉、金属与粘结剂的混合粉等)进行选择性烧结,是一种由离散点一层层对集成三维实体的工艺方法。在开始加工之前,先将充有氮气的工作室升温,并保持在粉末的熔点一下。成型时,送料筒上升,铺粉滚筒移动,先在工作平台上铺一层粉末材料,然后激光束在计算机控制下按照截面轮廓对实心部分所在的粉末进行烧结,使粉末溶化继而形成一层固体轮廓。第一层烧结完成后,工作台

下降一截面层的高度,在铺上一层粉末,进行下一层烧结,如此循环,形成三维的原型零件。最后经过5-10小时冷却,即可从粉末缸中取出零件。未经烧结的粉末能承托正在烧结的工件,当烧结工序完成后,取出零件。粉末材料选择性烧结工艺适合成型中小件,能直接的到塑料、陶瓷或金属零件,零件的翘曲变形比液态光敏树脂选择性固化工艺要小。但这种工艺仍需对整个截面进行扫描和烧结,加上工作室需要升温和冷却,成型时间较长。此外,由于受到粉末颗粒大小及激光点的限制,零件的表面一般呈多孔性。在烧结陶瓷、金属与粘结剂的混合粉并得到原型零件后,须将它置于加热炉中,烧掉其中的粘结剂,并在孔隙中渗入填充物,其后处理复杂。粉末材料选择性烧结快速原型工艺适合于产品设计的可视化表现和制作功能测试零件。由于它可采用各种不同成分的金属粉末进行烧结、进行渗铜等后处理,因而其制成的产品可具有与金属零件相近的机械性能,但由于成型表面较粗糙,渗铜等工艺复杂,所以有待进一步提高。

选择性激光烧结(SLS)优点:

(1)可以采用多种材料。从理论上说,任何加热后能够形成原子间粘结的粉末材料都可以作为SLS的成型材料。

(2)过程与零件复杂程度无关,制件的强度高。

(3)材料利用率高,为烧结的粉末可重复使用,材料无浪费。

(4)无须支撑结构。

(5)与其他成型方法相比,能生产较硬的模具。

SLS的缺点:

(1)原型结构疏松、多孔,且有内应力,制作易变性。

(2)生成陶瓷、金属制件的后处理较难。

(3)需要预热和冷却。

(4)成型表面粗糙多孔,并受粉末颗粒大小及激光光斑的限制。

(5)成型过程产生有毒气体及粉尘,污染环境。

4、FDM

丝状材料选择性熔覆(Fused Deposition Modeling)快速原型工艺是一种

不依靠激光作为成型能源、而将各种丝材(如工程塑料ABS、聚碳酸酯PC 等)加热熔化进而堆积成型方法,简称FDM。

丝状材料选择性熔覆的原理如下:加热喷头在计算机的控制下,根据产品零件的截面轮廓信息,作X-Y 平面运动,热塑性丝状材料由供丝机构送至热熔喷头,并在喷头中加热和熔化成半液态,然后被挤压出来,有选择性的涂覆在工作台上,快速冷却后形成一层大约0.127mm 厚的薄片轮廓。一层截面成型完成后工作台下降一定高度,再进行下一层的熔覆,好像一层层

这种工艺方法同样有多种材料可供选用,如工程塑料ABS、聚碳酸酯PC、工程塑料PPSF 以及ABS 与PC 的混合料等。这种工艺干净,易于操作,不产生垃圾,并可安全地用于办公环境,没有产生毒气和化学污染的危险。适合于产品设计的概念建模以及产品的形状及功能测试。专门开发的针对医用的材料ABS-i,因为其具有良好的化学稳定性,可采用伽码射线及其他医用方式消毒,特别适合于医用。

熔融沉积制造(FDM)的优点:

(1)成本低。熔融沉积造型技术用液化器代替了激光器,设备费用低;另外原材料的利用效率高且没有毒气或化学物质的污染,使得成型成本大大降低。

(2)采用水溶性支撑材料,使得去除支架结构简单易行,可快速构建复杂的内腔、中空零件以及一次成型的装配结构件。

(3)原材料以材料卷得的形式提供,易于搬运和快速更换。

(4)可选用多种材料,如各种色彩的工程塑料ABS、PC、PPS及医用ABS等。

(5)原材料在成型过程中无化学变化,制件的翘曲变形小。

(6)用蜡成型的原型零件,可以直接用于熔模铸造。

FDM的缺点:

(1)原型的表面有较明显的条纹,成型精度相对国外先进的SLA 工艺较低,最高精度0.127mm。

(2)沿着成型轴垂直方向的强度比较强。

(3)需要设计和制作支撑结构。

(4)需要对整个截面进行扫描涂覆,成型时间较长,成型速度相对SLA 慢7%左右。

(5)原材料价格昂贵。

5、3DP

三维印刷(3DP)工艺是美国麻省理工学院Emanual Sachs等人研制的。E.M.Sachs于1989年申请了3DP(Three-Dimensional Printing)专利,该专利是非成形材料微滴喷射成形范畴的核心专利之一。

3DP工艺与SLS工艺类似,采用粉末材料成形,如陶瓷粉末,金属粉末。所不同的是材料粉末不是通过烧结连接起来的,而是通过喷头用粘接剂(如硅胶)将零件的截面“印刷”在材料粉末上面。用粘接剂粘接的零件强度较低,还须后处理。具体工艺过程如下:上一层粘结完毕后,成型缸下降一个距离(等于层厚:0.013~0.1mm),供粉缸上升一高度,推出若干粉末,并被铺粉辊推到成型缸,铺平并被压实。喷头在计算机控制下,按下一建造截面的成形数据有选择地喷射粘结剂建造层面。铺粉辊铺粉时多余的粉末被集粉装置收集。如此周而复始地送粉、铺粉和喷射粘结剂,最终完成一个三维粉体的粘结。未被喷射粘结剂的地方为干粉,在成形过程中起支撑作用,且成形结束后,比较容易去除。

三维打印(3DP)优点:

(1)成型速度快,成型材料价格低,适合做桌面型的快速成型设备。

(2)在粘结剂中添加颜料,可以制作彩色原型,这是该工艺最具竞争力的特点之一。

(3)成型过程不需要支撑,多余粉末的去除比较方便,特别适合于做内腔复杂的原型。

3DP的缺点:强度较低,只能做概念型模型,而不能做功能性试验。

SLA,LOM,LSL,FDM相互之间的比较:

二、激光束,电子束,等离子束金属成形技术的主要特点和成本,效率成本三方面的比较?

激光束

激光是一种强度高、方向性好、单色性好的相干光。由于激光的发散角小和单色性好,理论上可以聚焦到尺寸与光的波长相近的(微米甚至亚微米)小斑点上,加上它本身强度高,故可以使其焦点处的功率密度达到107~1011  W/cm2,温度可达10 000℃以上。在这样的高温下,任何材料都将瞬时急剧熔化和汽化,并爆炸性地高速喷射出来,同时产生方向性很强的冲击。因此,激光加工是工件在光热效应下产生高温熔融和受冲击波抛出的综合过程。

激光加工的特点主要有以下几个方面:

(1) 几乎对所有的金属和非金属材料都可以进行激光加工。

(2) 激光能聚焦成极小的光斑,可进行微细和精密加工,如微细窄缝和微型孔的加工。

(3) 可用反射镜将激光束送往远离激光器的隔离室或其它地点进行加工。

(4) 加工时不需用刀具,属于非接触加工,无机械加工变形。

(5) 无需加工工具和特殊环境,便于自动控制连续加工,加工效率高,加工变形和热变形小。

(6)价格昂贵。

电子束

电子束加工的原理是利用高速电子的冲击动能来加工工件的,在真空条件下,将具有很高速度和能量的电子束聚焦到被加工材料上,电子的动能绝大部分转变为热能,使材料局部瞬时熔融、汽化蒸发而去除。

电子束加工的特点如下:

(1) 电子束能够极其微细地聚焦(可达l~0.1 μm),故可进行微细加工。

(2) 加工材料的范围广。由于电子束能量密度高,可使任何材料瞬时熔化、汽化且机械力的作用极小,不易产生变形和应力,故能加工各种力学性能的导体、半导体和非导体材料。

(3) 可通过磁场或电场对电子束的强度、位置、聚焦等进行控制,所以整个加工过程便于实现自动化。

(4)  电子束的能量密度高,加工效率很高。

(5) 加工在真空中进行,污染少,加工表面不易被氧化。

(6) 电子束加工需要整套的专用设备和真空系统,价格较贵,故在生产中受到一定程度的限制。

(7)电子束加工需要一套专用设备和真空系统,价格昂贵。

等离子束

离子束加工加工 它的加工原理与电子束加工原理基本类似,也是在真空条件下,将离子源产生的离子束经过加速、聚焦后投射到工件表面的加工部位以实现加工的。所不同的是离子带正电荷,其质量比电子大数千倍乃至数万倍,故在电场中加速较慢,但一旦加至较高速度,就比电子束具有更大的撞击动能。离子束加工是靠微观机械撞击能量转化为热能进行的。

离子束加工有如下特点:

(1) 离子束加工是目前特种加工中最精密、最微细的加工。离子刻蚀可达纳

米级精度,离子镀膜可控制在亚微米级精度,离子注入的深度和浓度亦可精确地控制。

(2) 离子束加工在高真空中进行,污染少,特别适宜于对易氧化的金属、合金和半导体材料进行加工

(3) 离子束加工是靠离子轰击材料表面的原子来实现的,是一种微观作用,所以加工应力和变形极小,适宜于对各种材料和低刚件零件进行加工。

(4)成本相对不是那么昂贵,应用范围广泛。

作文九:《英语作文有关出国留学的利与弊》1800字

出国留学

Nowadays, many people like to study abroad. Studying abroad is often considered as a great opportunity which will lead to bright future in one's ride of passage. Not only can we learn different cultures and knowledge from foreign countries, studying abroad can also enrich our lives. One coin has two sides. Likewise, different people have different minds. Conservative and negative concerns about studying abroad have been gradually emerging from our society. People start to wonder what goes wrong with studying abroad. There are a couple of issues worth of our discussions. Disadvantages of studying abroad may affect one's life culturally and economically. We Chinese will experience cultural shocks if we study abroad and live in another country. Some peers may not be able to adapt to a new environment of their studying and living, which may be very different from that of theirs. Life is beautiful, and it is hard. If one does not feel fortable with the new culture of another country, he will not be happy about studying in that country. In addition, studying abroad can cost students a great deal of living expenses. Some Chinese students are so academically successful that they receive scholarships in their studies. However, most peers who study abroad do not receive scholarships. Furthermore, they have to deal with many unexpected hardships by living away from their parents and homeland. For example, medical insurance, daily foods, clothes, rents and transportation can generate a large amount of living expenses. Often time, they need to heavily depend on their parents' overseas monthly payments. I have discussed some benefits and disadvantages of studying abroad. Life is not easy that we know. My belief is that for those students who study abroad should build strong characters in facing of unexpected difficulties in their life.

作文十:《网络的利与弊英语作文比较少的》1100字

网络的利与弊英语作文比较少的

举报|  分享| 2016-01-21 14:02 图骑007 | 浏览 18 次  来自:手机知道

学习英语

网络的利与弊英语作文比较少的

2016-01-21 14:11 网友采纳

Long-term addicted to online games, will not only curb the normal development of the left front of the brain, and particularly affect the early and mid intellectual development. Japanese scientists for hundreds of playing "Nintendo" game with the other only briefly, detection and analysis of students' brain activity levels found repetitive math, puter games stimulate only a visual and sports-related activities and that part of the brain , and the arithmetic is responsible for stimulating learning, frontal left hemisphere and the right hemisphere activity of memory and emotion. Brain of medical workers like Figure 7-18 years on the part of students analysis, also reached a similar conclusion. Long sitting in front of the puter can cause autonomic disorders, imbalance in hormone levels, immune function is reduced, causing a variety of diseases, such as cardiovascular disease, gastrointestinal neurotic disease, tension headaches, anxiety, depression, etc., and may even lead death.