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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.

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The process shown in the figure is called plastic injection moulding. It is a common process used to make plastic parts with different shapes. There are six main steps in this process: feeding, plasticization, injection, pressure holding, cooling, and ejection.
First, plastic pellets are fed from the hopper into the heated cylinder. Second, the pellets are moved and melted by the rotating screw. Next, the soft plastic is pushed through the nozzle into the mould cavity. After that, pressure is held to fill the mould completely. Then, the plastic is cooled and becomes hard inside the mould. Finally, the mould opens and the solid plastic part is ejected.
This process is fast, accurate, and suitable for producing many plastic products.

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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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Dear Supervisor,

I have purchased four kinds of couplings because our stock was out. I bought them from ABC Mechanical Supplies in Hanoi on September 21, 2025.

The first type is rigid couplings, which consist of two sleeves and bolts. Their function is to connect two shafts firmly without flexibility. They are applied in alignment-accurate machines.

The second type is flexible couplings, made of hubs, a flexible element, and bolts. They allow slight misalignment and are used in pumps and compressors.

The third type is beam couplings, which are made from a single piece of metal with spiral cuts. Their function is to compensate for angular misalignment and provide torsional flexibility. They are commonly used in servo motors and precision equipment.

The fourth type is sleeve-style couplings, consisting of a hollow sleeve and two shaft ends. They are simple, low-cost, and used in light-duty applications such as small conveyors and agricultural machines.

Sincerely,
Huy Thien

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To make an effective presentation, you need to follow a clear structure, usually including an introduction, a main body, and a conclusion. Before the presentation, it’s important to know your audience and outline what you want to present when preparing your speech. During the presentation, you should make eye contact, look at the audience, speak clearly, and use body language to express your ideas. You shouldn’t read directly from the paper or speak too fast, as this may reduce the impact of your talk. After the presentation, you should thank the audience and summarize the presentation briefly.

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Dear Supervisor,

I bought four kinds of bearings from ABC Mechanical Store in Hanoi on September 20, 2025, because our stock was empty.

The first is ball bearings, which consist of steel balls, inner and outer rings, and a cage. They reduce friction and are used in motors and fans.

The second is roller bearings, including rollers, rings, and a cage. They can carry heavy radial loads and are applied in conveyors and gearboxes.

The third is tapered roller bearings, made of tapered rollers and rings. Their function is to handle both radial and axial loads, commonly used in car wheels and truck axles.

The fourth is needle bearings, consisting of thin rollers and rings. They are designed for compact spaces and are applied in small gearboxes and pumps.

These bearings will support smooth and reliable machine operation.

Sincerely,
Huy Thien

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A gear is a round part of a machine with teeth that fit into another gear to transmit torque and motion. The main functions of gears are to change speed, torque, or direction of power. There are several common types of gears with different features. Spur gears are the simplest, with straight teeth, often used in low-speed machines but they can be noisy at high speed. Helical gears have slanted teeth, which work more smoothly and quietly, suitable for high-speed and heavy load systems. Worm gears use a screw-shaped part to reduce speed and increase torque. Rack and pinion gears convert rotation into linear motion, for example in car steering. Bevel gears have a cone shape and can transfer power between shafts at an angle, usually 90 degrees.

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CAD (Computer-Aided Design) is a technology that uses computers and software to create, modify, and optimize drawings, while manual drafting is the traditional method of drawing by hand with pencils, rulers, and compasses. In the past, designers used to rely on manual drafting, which was slower and less accurate. CAD is used for producing precise and complex designs more quickly. It has the capability of creating both 2D and 3D models, something manual drafting cannot do. People who work with CAD are used to using digital tools and commands. Compared with manual drafting, CAD is more efficient, flexible, and easier to edit. Although CAD software is more expensive and requires computer skills, it saves time and improves accuracy, making it more suitable for modern design 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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Both belt drive and chain drive are systems used to transmit power between shafts in machines. A belt drive, like a flexible rubber or plastic loop, transfers motion through friction between belt and pulleys. A chain drive, unlike a belt drive, uses metal links with sprockets, so it runs without slippage. Belt drives are similar to chain drives in their ability to connect shafts over distances, but they are different from chain drives because they are quieter and need less lubrication. However, unlike belt drives, chain drives are more efficient, usually about 95%, and stronger for heavy-duty applications. Belt drives are commonly used in pumps, lathes, and conveyor belts, while chain drives, like those in bicycles, motorcycles, and agricultural machines, are preferred when high strength and durability are required.

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AutoCAD is one of the most popular CAD programs developed by Autodesk. It is a powerful software used for creating 2D and 3D designs in engineering, architecture, and construction. Its main features include precise drawing tools, layer management, and compatibility with many file formats. AutoCAD has the capability of producing detailed technical drawings and 3D models. It is used for designing buildings, mechanical parts, and electrical systems. One major advantage of AutoCAD is its accuracy and efficiency, which help save time and reduce errors. Moreover, it allows users to modify and share drawings easily. However, AutoCAD is quite expensive and requires strong computer skills to operate effectively. Despite these disadvantages, it remains one of the most reliable CAD tools in modern design and engineering.

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There are three common problems in plastic injection moulding: short shot, void, and sink mark. A short shot happens when the mould is not completely filled because of low injection pressure or blocked gates. To fix this problem, the injection pressure and speed should be increased, and the gates should be cleaned regularly. A void appears when air is trapped inside the product or when the cooling rate is too fast. This problem can be solved by improving venting, increasing packing pressure, and cooling the mould evenly. A sink mark occurs when the product surface becomes uneven due to poor cooling or low packing pressure. To reduce sink marks, the cooling system should be improved and the holding pressure should be adjusted properly. Regular maintenance helps prevent these problems.