英语作文：网上购物的利与弊
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"画出"截面轮廓，如此循环，最终形成三维产品零件。
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。
作文范文之网购的坏处英语作文
网购的坏处英语作文 【篇一：英语作文：网上购物的利与弊】 1 with the development of the internet and the popularization of computers, shopping on the internet has become a commonplace in our life. here consumers can buy almost everything they need. ?? shopping on the internet has a lot of advantages, of which the most important is perhaps its convenience. people dont have to waste a lot of their energy and precious time to go from one shop to another to choose the commodities they like. this is especially desirable to the old, the sick and the busy people who cannot go to the shops in person. the goods come in all shapes, sizes and colors on the internet. all they need to do is to sit in front of their computers and click the mouses. the commodities they order will be delivered to them promptly. ?? however, shopping on the internet also has its disadvantages. the first disadvantage is that the consumers cant see the goods or try them on personally. sometimes, the real goods may not be the same as what they have seen on the computer. the second disadvantage is that some shops on the internet are not registered. they will never deliver anything to you after they get the money from you. once cheated, you will find that you have nowhere to go to complain. ???? 2 in current society, shopping on the interent is becoming more and more popular. it has many advantages and disadvartages . advantages: shopping on the internet is convient and faster for customers. they can stay at home looking for the items, they need or like through the internet which supplies a variety of products.people neednt to go shopping in stores . then it can reduce cars amount on the road. so it also can reduce pollution of the gas. its unpollutionand reduce energy. disadavantages:customers can buy false production. people will be demaged and have many bussniss also demaged . so we shopping on the internet shouid notice the production. and we should avoid the false production on the internet . 3
关于网上购物利弊的英语作文
关于网上购物利弊的英语作文 With the development of the Internet and the popularization of computers, shopping on the Internet has become a commonplace in our life. Here consumers can buy almost everything they need. Shopping on the Internet has a lot of advantages, of which the most important is perhaps its convenience. People don't have to waste a lot of their energy and precious time to go from one shop to another to choose the commodities they like. This is especially desirable to the old, the sick and the busy people who cannot go to the shops in person. The goods come in all shapes, sizes and colors on the Internet. All they need to do is to sit in front of their computers and click the mouses. The commodities they order will be delivered to them promptly. 查字典英语作文 However, shopping on the Internet also has its disadvantages. The first disadvantage is that the consumers can't see the goods or try them on personally. Sometimes, the real goods may not be the same as what they have seen on the computer. The second disadvantage is that some shops on the Internet are not registered. They will never deliver anything to you after they get the money from you. Once cheated, you will find that you have nowhere to go to complain.
英语作文：网上购物的利与弊
1 With the development of the Internet and the popularization of computers, shopping on the Internet has become a commonplace in our life. Here consumers can buy almost everything they need. Shopping on the Internet has a lot of advantages, of which the most important is perhaps its convenience. People don't have to waste a lot of their energy and precious time to go from one shop to another to choose the commodities they like. This is especially desirable to the old, the sick and the busy people who cannot go to the shops in person. The goods come in all shapes, sizes and colors on the Internet. All they need to do is to sit in front of their computers and click the mouses. The commodities they order will be delivered to them promptly. However, shopping on the Internet also has its disadvantages. The first disadvantage is that the consumers can't see the goods or try them on personally. Sometimes, the real goods may not be the same as what they have seen on the computer. The second disadvantage is that some shops on the Internet are not registered. They will never deliver anything to you after they get the money from you. Once cheated, you will find that you have nowhere to go to complain. 2 In current society, shopping on the Interent is becoming more and more popular. It has many advantages and disadvartages . Advantages: shopping on the Internet is convient and faster for customers. They can stay at home looking for the items, they need or like through the Internet which supplies a variety of products.People needn't to go shopping in stores . Then it can reduce cars' amount on the road. So it also can reduce pollution of the gas. It's unpollution and reduce energy. Disadavantages:customers can buy false production. People will be demaged and have many bussniss also demaged . So we shopping on the Internet shouid notice the production. And we should avoid the false production on the Internet . 3 Recently,there is a heat debate about on-line shopping is good or not. Everyone has his own idea. For me, I would love to buying things from internet. There are lots of advantages of on-line shopping. Firstly,you can enjoy the convenience of on-line shopping:surf the internet and order your things easily.Secondly,you can search as much information as you can which normal couldn't do. What's more, lots of people love to pursue the fashion and then they choose on-line shopping. But there is another voice:"The virtual is dishonest,it is not safe to do business through the internet." From https://www.360docs.net/doc/563924938.html,. In my view, on-line shopping's advantage outweights its disadvantage.With the development of network technology and human moral,our trade through the internet will be more safe.
作文范文之网上购物利弊英语作文
网上购物利弊英语作文 【篇一：网购好处与坏处英语作文】 nowadays, internet has made much large change. more and more people don’t go out. if people need some things, they would shop online. there is no doubt that shopping online can save much time and energy. people only sit aside a computer and press mouse constantly. then, the wares will be sent to home. of course, the price may be lower than store’s. every coin has two sides. shopping online means that people can’t touch the goods after they pay for it. so good quality needs luck. people who like shopping online enjoy themselves when they run over the photos of goods. and other people are happy with going window-shopping well. in a word, shopping online is not only a way of shopping but also a style of life. it is imaginable that the beneficiaries are the man who don’t want to be company with woman. 【篇二：英语作文对网购的看法】 the view of online shopping with the popularity of internet, more and more people like to go shopping online. this is not only the representation of the change of peoples shopping idea, but also the sign of internet era has coming. in my opinion, online shopping is a double-edged sword. first , through online shopping, we can leisurely sitting at home to buy items they want. second, online goods is complete, it can save our search time. third , online shopping is much cheaper than entity shop. but ,i think it also has disadvantages. firstly , online shopping goods will be different from the photos, sometimes mixed with poor quality goods. secondly , sometimes the arrival of the goods will be slow. whats more, for girls, they will lose the fun of shopping. in conclusion, we should comprehensive own situation to choose their way of shopping. 【篇三：网购英语作文】 篇一：网上购物英语作文
网购好处与坏处英语作文
Nowadays, internet has made much large change. More and more people don’t go out. If people need some things, they would shop online. There is no doubt that shopping online can save much time and energy. People only sit aside a computer and press mouse constantly. Then, the wares will be sent to home. Of course, the price may be lower than store’s. Every coin has two sides. Shopping online means that people can’t touch the goods after they pay for it. So good quality needs luck. People who like shopping online enjoy themselves when they run over the photos of goods. And other people are happy with going window-shopping well. In a word, shopping online is not only a way of shopping but also a style of life. It is imaginable that the beneficiaries are the man who don’t want to be company with woman.
英语作文：网上购物的利与弊
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。
关于网上购物利弊的英语作文
精品资料欢迎下载 关于网上购物利弊的英语作文 With the development of the Internet and the popularization of computers, shopping on the Internet has become a commonplace in our life. Here consumers can buy almost everything they need. Shopping on the Internet has a lot of advantages, of which the most important is perhaps its convenience. People don't have to waste a lot of their energy and precious time to go from one shop to another to choose the commodities they like. This is especially desirable to the old, the sick and the busy people who cannot go to the shops in person. The goods come in all shapes, sizes and colors on the Internet. All they need to do is to sit in front of their computers and click the mouses. The commodities they order will be delivered to them promptly. 查字典英语作文 However, shopping on the Internet also has its disadvantages. The first disadvantage is that the consumers can't see the goods or try them on personally. Sometimes, the real goods may not be the same as what they have seen on the computer. The second disadvantage is that some shops on the Internet are not registered. They will never deliver anything to you after they get the money from you. Once cheated, you will find that you have nowhere to go to complain.
有关网上购物的利弊英语作文
有关网上购物的利弊英语作文 导语：现在越来越多的人在网上购物，网购已成为流行趋势，网购的利弊也成为人们讨论的焦点，下面是yuwenmi 小编为大家整理的优秀英语作文，欢迎阅读与借鉴，谢谢! 请参考下面的信息，并结合就的观点些一短文，谈谈你的看法。 1. 方便，可以在家买东西，不受时间限制。 2. 有很大的商品信息，可以买到当地没有的商品。价格较便宜。 3. 买货容易退货难;实物和图片有差距。 4.网络支付不安全。 提示词：实物：materiai object Now Internet shopping is more and more popular in the world. It’s a new way of shopping. It has lots of most important is convient. You can shop whenever you like because the online shop are open 24 hours a day. It is often to buy goods and it is also easy to find the things that youcan’t buy in the shop . Besides,it’s cheaper . But “ Every coin has two sides.” So is Internet
shopping. You can’t see the material objects or check their quality. Usually the pictures are more beautiful than the goods. So when we get the goods and don’t like them, they sometimes are not easy to give back. What’s more , It’s not safe to pay through the internet. 现在网上购物在世界上越来越流行。这是一种新的购物方式。它有很多的优点，最重要的是方便。你可以随时购物，因为网上商店每天24小时营业。它通常是买商品，也很容易找到的东西，你不能在商店购买。此外，它更便宜。 但是“每个硬币都有两面”，互联网购物也是如此。你不能看到实物或检查他们的质量。通常图片比商品更漂亮。因此，当我们得到的货物，不喜欢他们，他们有时不容易给回。更重要的是，它是不安全的，通过互联网支付。
网购观点英语作文
网购观点英语作文 网上购物，对我们的生活增加了很多便利和乐趣，但是网上购物有利有弊，你怎么看呢？下面是小编为你准备的网购观点英语作文，希望对你有帮助！ 篇一：网上购物利弊的英语作文 With the development of the Internet and the popularization of computers, shopping on the Internet has become a commonplace in our life. Here consumers can buy almost everything they need. Shopping on the Internet has a lot of advantages, of which the most important is perhaps its convenience. People don＇t have to waste a lot of their energy and precious time to go from one shop to another to choose the commodities they like. This is especially desirable to the old, the sick and the busy people who cannot go to the shops in person. The goods come in all shapes, sizes and colors on the Internet. All they need to do is to sit in front of their computers and click the mouses. The commodities they order will be delivered to them promptly. However, shopping on the Internet also has its disadvantages. The first disadvantage is that the consumers can＇t see the goods or try them on personally. Sometimes, the real goods may not be the
网上购物的利与弊的英语作文
▲ dir ▲ attrib ▲ cd ▲ copy ▲ xcopy ▲ del ▲ undelete ▲ deltree ▲ dos=high ▲ doskey ▲ emm386.exe ▲ fc ▲ format ▲ unformat ▲ interlnk ▲ intersvr ▲ memmaker ▲ memitem等▲ mscdex ▲ msd ▲ prompt
▲ ramdrive ▲ subst ▲ mem ▲ "> < >> <<"工具 ▲ move ▲ append ▲ call ▲ defrag ▲ device dir [D:][PATH][NAME][[/A][:attrib]][/o:[sorted][/s][/b][/l][/c[h] (1)dir /a:attrib 缺省包含所有文件(系统文件.隐含文件) attrib[:][h/-h]只显示隐含文件或非隐含文件. [r/-r]只显示只读文件或非只读文件 [s/-s]只显示系统文件或非系统文件 [a/-a]只显示要归档文件或非归档文件 (2)/o[:]sorted:缺省完全按字母顺序,子目录显示在文件之前 /o[n/-n]:按字母顺序或按文件名顺序/反向显示 [e/-e]:按扩展名字母顺序/反向显示 [d/-d]:按时间顺序/反向显示 [s/-s]:按大小从大到小或/反向显示
[g/-g]:按子目录先于文件或文件先于子目录 (3)/s 参数:对当前目录及其子目录中所有文件进行列表 列名:dir /s/a/o:n c:\>PRN 将c盘上的所有子目录和文件按隶属关系并根据子目录和文件字母顺序打印输出 (4)/B 参数:将只显示文件名与扩展名 (5)/L 参数:将全部用小写字母对文件或子目录进行列表 训练: dir /a 列当前目录所有文件(含隐含及系统文件) dir /ah 列隐含文件(包含子目录(隐含的) dir /a-h dir /as 列系统文件dir /a-s dir /ad 列子目录dir /a-d dir /o 按字母顺序 dir /B 只显示文件名与扩展名 二、attrib [+r|-r] [+a|-a] [+s|-s] [+h|-h] [d: ] [name] [/s] 缺省attrib name 显示文件的(文件)属性 attrib io.sys (或子目录) shr c:\ io.sys 指定为系统(s) 隐含(h) 只读(r)文件 也可以attrib *.sys 显示扩展名为sys的文件属性 参数[+r|-r] 将文件属性设置或解除只读属性 [+a|-a] 将文件属性设置或解除归档属性 [+h|-h] 将文件属性设置或解除隐含属性(尤其对子目录也起作用)
初中英语作文和网购利弊
初中英语作文：网购利弊 随着互联网的发展和普及，网络购物在中国也变得越来越普遍了，甚至已经成了我们日常生活的一部分了；相信同学们身边一定有不少同学已经通过网络进行购物了，比如淘宝网，京东商城等；但是网络购物究竟有何利弊呢? 请写一篇短文，谈谈网上购物的好处与坏处。 ___________________________________________________ ____ ___________________________________________________ ____ ___________________________________________________ ____ ___________________________________________________ ____ 参考范文：
We talked about the advantages and disadvantages of internet shopping these days. Some students think it's very convenient for us to go shopping on the internet. The shops on Internet, for example https://www.360docs.net/doc/563924938.html,, https://www.360docs.net/doc/563924938.html, are open for almost 24 hours a day, so we can buy something we want at any time if we like. What's more, we needn't to wait in a queue. However, some students disagreed with them. We can't see the things while we are shopping. So we are not sure whether they are good or not.. Besides, we can't enjoy the happiness of shopping with our friend.
英语作文：网上购物的利与弊
With the development of the Internet and the popularization of computers, shopping on the Internet has become a commonplace in our life. Here consumers can buy almost everything they need. Shopping on the Internet has a lot of advantages, of which the most important is perhaps its convenience. People don't have to waste a lot of their energy and precious time to go from one shop to another to choose the commodities they like. This is especially desirable to the old, the sick and the busy people who cannot go to the shops in person. The goods come in all shapes, sizes and colors on the Internet. All they need to do is to sit in front of their computers and click the mouses. The commodities they order will be delivered to them promptly. However, shopping on the Internet also has its disadvantages. The first disadvantage is that the consumers can't see the goods or try them on personally. Sometimes, the real goods may not be the same as what they have seen on the computer. The second disadvantage is that some shops on the Internet are not registered. They will never deliver anything to you after they get the money from you. Once cheated, you will find that you have nowhere to go to complain. 2 In current society, shopping on the Interent is becoming more and more popular. It has many advantages and disadvartages . Advantages: shopping on the Internet is convient and faster for customers. They can stay at home looking for the items, they need or like through the Internet which supplies a variety of needn't to go shopping in stores . Then it can reduce cars' amount on the road. So it also can reduce pollution of the gas. It's unpollution and reduce energy. Disadavantages:customers can buy false production. People will be demaged and have many bussniss also demaged .
上网购物英语作文阅读英语作文上网的利弊
上网购物英语作文阅读英语作文上网的利弊随着互联网的普及和中国经济的快速发展，人们的消费观念也 随之发生变化，网络购物受到越来越多的关注并成为一种时尚。精心收集了上网购物英语作文，供大家欣赏学习! Nowadays， with the ever rapid development and increasing popularity of the information technology ， shopping on the Inter has been a fashion， especially among the youngsters. Online shopping has made our daily life more convenient and fortable. For example ， shopping on the inter can save students a great deal of time on the way between home and store，so they would be able to concentrate more time and energy on their academic work. The inter has shorten the distance between manufacturers and consumers and thus we can even buy goods in other countries .On the other hand ， lack of the face to face deal makes online shopping less reliable and trustworthy. What’s more the delivery will increase the risk of items’ damage. In my opinion， shopping on the inter is an irreversible trend. More and more people will be austomed to it. It will be