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To make an effective presentation, we need a clear structure. The basic structure of a presentation has three parts: introduction, body, and conclusion. Before the presentation, you should prepare your slides, practice speaking, and check the equipment. During the presentation, you should speak clearly, keep eye contact, and use simple language. You should not speak too fast or read all the text from the slides. After the presentation, you should answer questions politely and thank the audience. To impress the audience, you can use pictures, examples, and a confident voice. Good preparation and practice will help you feel more comfortable. A good presentation is not only about information but also about how you connect with the audience.

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I bought three kinds of bearings because our stock was empty. I bought them on 20 September 2025 at a local hardware in Hanoi. The first kind is ball bearings. It has balls, an inner ring, an outer ring, and a cage. It helps reduce friction and supports light loads. It is used in motors and fans.

The second kind is roller bearings. It has rollers, rings, and a cage. It can carry heavy loads. It is used in conveyors and gearboxes. The third kind is journal bearings . It has a shaft and a smooth surface. It works with lubrication. It is used in engines and turbines. These bearings will support our daily work.

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Dear Supervisor,

I bought three kinds of couplings: rigid coupling, flexible coupling, and beam coupling. I bought them yesterday at a machine shop near our company. The rigid coupling has two sleeves and bolts. Its function is to join two shafts with no movement. It is used in simple machines.

The flexible coupling has two hubs and a rubber part. Its function is to allow small misalignment. It is used in pumps and conveyors. The beam coupling has one piece of metal with spiral cuts. Its function is to allow angle and parallel misalignment. It is used in robots and CNC machines.

Sincerely, Quy

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A gear is a round part with teeth. Gears are used to move power from one shaft to another. They can also change speed and direction. There are some common gears. Spur gear has straight teeth. It is simple and cheap. It is used in clocks and small machines. Helical gear has slanted teeth. It works more quiet and smooth. It is used in cars and heavy machines. Bevel gear looks like a cone with teeth. It is used when two shafts meet at an angle. Worm gear looks like a screw with a wheel. It gives big speed reduction. It is used in lifts and conveyors. Gears are very important for many machines in daily life.

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They have some differences.

Firstly, the function of BD is to transmit power from one shaft to another by means of pulleys, while CD is used to transmit power between parallel shafts. Secondly

BD is made of rubber, plastic, but CD is made of metal. Thirdly, BD is different from CD because BD can reduce noise and vibration. Besides, it doesn’t need to lubricate. Moreover, it requires more tension. While CD is not affected by atmospheric condition, BD is affected by weather condition. CD has higher efficiency than BD. The applications of BD are flour mills, coolant pump, lubricant pump, AC, cam shaft, alternator, lathe machines and lots of other machines, belt conveyors. However, CD are used in bicycle, motorcycles, agricultural machinery and textile machinery, material handling equipment.

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CAD is a computer program used to draw models. Manual drafting is drawing by hand on paper. CAD is faster than manual drafting because it can change and save designs easily. With CAD, engineers don’t need to draw again when they edit the model. Manual drafting is slower and less accurate than CAD. CAD can also show 3D images and realistic views of the final product. Manual drafting only shows 2D drawings. However, CAD is more expensive than hand drawing and needs a computer. Manual drafting is cheaper and easier to start, but it is not as efficient as CAD in engineering work.

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AutoCAD is a popular CAD program used in engineering and design. It has many features such as drawing tools, 2D and 3D modelling, and the ability to store and edit files easily. AutoCAD is used to create accurate technical drawings and realistic models of products. With this software, engineers can zoom, rotate and view the object from different angles to check the design before production. One advantage of AutoCAD is that it saves time because users don’t need to redraw the whole model when making changes. It also helps reduce mistakes and material waste. However, AutoCAD is more expensive than manual drawing and requires a compatible computer. Some beginners find it difficult to learn at first, but it is very useful in professional work.

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This process is called aluminum casting and finishing. The product is made of aluminum. There are five main steps in this manufacturing process.

First, the aluminum is melted and poured into a mould to form the basic shape.

When the metal cools down and becomes hard, it is removed from the mould and milled to make the surface flat.

Then, a hole is drilled in the center so it fits the machine shaft.

After that, the edges are polished to remove rough parts and make the wheel smooth.

As the final step begins, the product is inspected carefully by the worker to make sure there are no defects.

Finally, the aluminum wheel is completed and ready to be used in production.

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Plastic is a versatile and lightweight material made from polymers. It can be moulded into many complex shapes and is used to produce bottles, containers, ropes, and even parts of airplanes. The main properties of plastic are its strength, stiffness, transparency, and resistance to heat and chemicals. Plastic can withstand high temperatures and does not easily react with other substances. Its advantages include durability, flexibility, and low production cost. However, plastic also has disadvantages because most types are not biodegradable and can cause serious environmental pollution. In the future, it will be possible to develop more recyclable and biodegradable plastics. Scientists will certainly create new bioplastics that bacteria can break down easily, reducing waste and protecting our planet.

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There are seven main types of plastic used in daily life and industry. They include PET (1), HDPE (2), PVC (3), LDPE (4), PP (5), PS (6), and ABS (7). PET is lightweight, transparent, and used for beverage bottles. HDPE is strong and recyclable, used for containers and pipes. PVC is durable but should not contact food; it is used for cables and pipes. LDPE is flexible and used for plastic bags. PP is tough and can withstand high temperatures, so it is used in food packaging and car parts. PS is used for disposable cups and boxes. ABS is sturdy and used in electronics and medical equipment. Each type of plastic has different properties and applications, helping engineers choose the right material for specific mechanical purposes.

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As you can see in the figure, this is the process of plastic injection moulding. There are seven steps in this process.

First, pellets of plastic are fed from the hopper into a cylinder.

Second, the pellets are pushed along the cylinder by a rotating screw and heated.

Third, the screw stops rotating and then a ram in front of the screw moves straight forward.

Next, the soft, warm plastic is pushed toward a nozzle by the ram.

After that, the soft plastic is injected through the nozzle into a shaped cavity between the two halves of a mould.

Besides, the plastic is cooled within the mould and becomes hard inside the cavity. While the molten material is shrinking inside the mould due to cooling, the screw continuously forces more molten material into the cylinder and mould for replenishment.

Finally, the mould opens and the cold, hard, solid plastic shape is ejected.

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There are several common problems in plastic injection moulding that affect product quality. Short shot occurs when the mould cavity is not completely filled. This problem is usually caused by low injection pressure or short injection time. To solve it, we should increase the fill speed, pack pressure, or injection time. Flash appears when excess plastic leaks out of the mould, often due to a damaged mould or high pressure. The solution is to check the exhaust port and adjust the clamping force. Sink marks and voids happen when cooling is uneven or pressure is too low. They can be reduced by increasing packing pressure and ensuring uniform wall thickness. Proper temperature control and regular mould maintenance are essential to avoid these defects.

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The milling machine needs regular maintenance to work properly and safely. There are five types of maintenance work you should do. First, clean the guideways every day to avoid interruptions and help control the motion of fluids. Second, check the oil level daily to make sure the engine works efficiently and does not overheat. Third, renew the oil twice a year to keep the machine operating smoothly. Fourth, clean the whole machine every week to remove dust and dirt that can cause problems. Finally, inspect the bearings once a year to prevent slippage and damage. If you follow this plan carefully, your milling machine will run well, stay in good condition, and have a longer life.