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As you know, the structure of a presentation has 3 main parts: The first part is the introduction, then the development, and finally the conclusion. Before each presentation, you should prepare carefully, understand the audience, check the equipment, and finally turn off your phone before presenting. During each presentation, you should not hold reading materials, should not look at the floor or ceiling, instead you should make eye contact and use gestures to express. After the presentation, you should thank the audience and try to answer everyone's questions. To impress the audience, you should present confidently, happily, and handle questions skillfully.

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The couplings are used to connect shafts together to transmit power and disconnect shafts for maintenance. It includes two types: input shaft and output shaft. The input shaft is used for connecting to the power source while the output shaft is used to connect to the destination. Couplings are divided into rigid coupling and flexible coupling. Rigid coupling is used to hold shaft in perfect alignment. While flexible coupling transmits torque without perfect alignment. The rigid coupling consists of sleeve-style coupling and it is used for reducing vibration of the shaft. The flexible coupling includes beam coupling, it is cut in sprial shape to accommodate misalignment.

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Gear is a rotating circular component with teeth which mesh with another toothed parts. We use gear to transmit torque. There are 5 types of gear including: spur gear, helical gear, bevel gear, worm and worm gear, rack and pinion. Firstly, spur gear is type of gear with teeth projecting towards or away from the center. It’s used in low-speed applications. Secondly, helical gears have their teeth cut in a spiral shape. They are used for high speed applications, large power transmission. Thirdly, worm has just one continuous tooth and worm pairs with a worm gear, which helps reduce speed. Next, rack and pinion gears consist gear engaging a linear gear. The function of rack and pinion gears are convert rotational motion into linear motion. Finally, bevel gears have a conical form and can be used to transmit rotational power through shafts at an angle, typically 90 degrees to each other.

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AutoCAD stands for Automatic Computer Aided Design, which means "Automatic Computer Aided Design" in English. This is a software used to create technical drawings using 2D vectors or 3D solid surface drawings. The difference between CAD and manual drawing has many different characteristics. CAD is a software that runs on a computer, Tools to support drawing 2D vectors and 3D solid surface objects, Create design drawings according to the exact ratio in reality, Support size adjustment tools, Can calculate the amount of materials needed for construction, work more efficiently and quickly. Manual drawing takes a lot of time, requires precision, and takes more effort than drawing. However, manual drawing helps us increase creativity and share more easily.

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SIEMENS NX is a new CAD program, it was released for the first time in 1973 by PLM Software. NX has become popular as it’s a simple, useful and powerful software. Designer can use it aerospace or automative companies. With NX, user can create both 2-D and 3-D technical drawings. It also can edit data, link data from various sources.NX has many advantages. The first advantage is that it’s very fast and flexible. Another benefit is that it can reduce the companies mistakes and maximize productivity. And a huge pros is that designer can create a very high level of control. However, NX has some disadvantages. It requires a profestional training time before the designers can use it.

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Writing:The process of making a car wheel

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Writing:The process of making a car wheel

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This picture shows the procces of making a car wheel. The car wheel is made of aluminum. There are 5 steps in the manufacturing process.

The first step is Casting,this steps means that hot liqiud material is poyred into a container and cooled to make the correct shape. Next step is Turning , this steps materials are turend on a machine called a lathe. Steps 3 is Drilling, in this step holes are made using a drill. After the drilling process, the next steps is Polishing. In this stage, a suface is polished to make it smooth and shiny. The final steps is Inspection, in this stage product is checked carefully.

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Plastic is synthetic materials that use polymers as a main ingredient. Plastic is able to be moulded or shaped to any forms. There are tons advantages of plastic, the first is that it’s convenient. Fox example, we can use shopping plastic bag when going to the supermarket. Another pro is that it’s lightweight so people use it to manufacture airplain. Besides, plastic is a cost-efficient material because it can be formed into final useful form quickly and inexpensively. Moreover, it’s durable and resistant to all kind of adverse outside factors. For instance, it’s quite resistant to heavy rain and storms. Finally, it’s reuseable. On the other hand, plastic has some disadvantages. First of all, using plastic so much can hurt the enviroment. Secondly, plastic canot be biodegradable. Last but not least we can recyle plastic.

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There are 7 types of plastic with different uses and features. The first group is  polyethylene terephthalate (PET/PETE). It’s mostly used for food and dink packaging due to its oxygen prevention. It’s also the most recycled plastic in the world. The second one is high density Polyethylene (HDPE), its products are very safe and are not known to transmit any chemicals into foods or drinks. For example, we have grocery bags, milk jugs or playground equipments, lids and shampoo bottles from HDPE. The third group is Polyvinyl Chloride (PVC). It’s widely used in building and manufaturing such as doors, pipes, wires or replace traditional material. Next group is  Low Density Polyethylene (LDPE), it’s a flexible, odorless, transparent, recyclable thermoplastic polymer. We use it for the infamous bags that are used for few time then discarded such as plastic bags, six-pack rings, containers and plastic wraps. The fifth group is polypropylene (PP), which being hard, sturdy and can withstand high temperatures. People use PP in car parts, thermal vests, yogurt containers and licing hinges. Another group is Polystyrene (PS) – a very cheap and easyto create plastic. It can be found everywhere from beverage cups, egg cartons or dinnerware. Although it’s inflammable, PP still dangerous as it leak harmful chemicals when heating. The last group include the plastics that can’t be identified in the six types, most well-known is polycartbonate(PC). Because of toughness and strongness, PC is commonly used in eye protection, sunglasses, sport and safety goggles.

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In the plastic injection moulding, we have many problem, some commonly problems can happen is shot short and sink mark. The cause of shot short isn't enough plastic in the shot or the plastic pressure is loss in the mould is too hight. The way to solve shot short is check the shot continously and use plastic with high melting capability or increase the fill speed and plastic or mould temperature. The second problem is sink mark. Its cause is internal stress is too high or the suface has to low. The way to solve it is increasing holding pressure and holding time, reduce mould temperature, or reduce wall thickness for faster cooling.

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From my point of view, there are 3 typical problem of plastic injection moulding. They are short shot, sink mark and void. As I know, short shot is cause of 2 reasons. Firstly, there is  not enough plastic in the shot. Secondly, the plastic pressure loss in the mould is too high. We have 2 ways to avoid these causes. The first one is increasing fill speed, plastic and moud temperature. Next, we could increase gate size and runner. The void is created by shrinkage. It is volume change of plastic when plastic is heated or cooled. To attack this problem, we have 3 ways. The firt way is reducing wall thickness. Then, you should slow down cooling rate. Beside, we can increase gae size and locate it at the thick oart of the moulding. The final problem is sink mark. There are some reasons of this phenomena as the internal stress is too high and the part has low surface rigidity. The ways to solve  is pretty simple. We need to have enough shot size and increase holding pressure, holding time. Beside that, we should reduce mould temperature and wall thichness for faster. Those are some typical problems of plastic injection moulding and the ways to attack them.

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The milling machine is a common machine in machining workshops. There are 5 maintenance in the list of the miling. They are clean guideways, inspect oil level, renew oil, clean machine thoroughly and Inspect bearing slackness. The customers clean the guideways every day. The guideways need to be cleaned daily to avoid interruptions and control the of motion of fluids. You should Inspect oil level daily to ensure engine efficiency and prevent overheating. The next, you need Renew oil semi-annually to ensure smooth operation. You need clean machine thoroughly weekly remove dust and dirt. The last, you must Inspect bearing slackness annually to prevent slippage.