Find out everything you need to know about machining, from defining this process to top tips for your factory.
In many industries, such as automotive, shipbuilding, aerospace, electronics, and home appliances, machining is an extremely versatile process that can be used on various types of materials. Even the vast majority of industrialized products go through this process in some of their production phases.
To get an idea of how important this process is for manufacturing, did you know that 80% of holes in the industry are made through machining? In addition, 100% of the surface quality improvement processes are carried out using the same method.
But is it the same in the plastics industry? We will talk about this next.
What is machining?
First of all, it is important to discuss the meaning of this term. Machining concerns the entire process where material is removed in the form of chips. Chips, in turn, are a portion of material from the workpiece, removed by a tool.
This means that machining is a process that allows parts to have a shape, dimensions, or even a surface finish (or a combination of all these results).
The material is removed due to interference between the tool and the workpiece, and the tool is composed of a harder and stronger material, compared to the workpiece to be shaped.
It is worth mentioning that nowadays this process has also come to be known as precision machining. This is because, while previously the processes were completely manual, today high-precision machines are used. The machines even have a precision equal to 1 micron, which corresponds to 0.001 millimeters.
How does machining work?
You already know that machining consists of using a tool on the workpiece to be produced. But these tools can offer different results. Next, let’s talk about the main ones:
- Planing: This method makes surfaces flat, whether horizontal, vertical or slanted.
- Turning: in this process, the workpiece moves around its own axis. For this reason, it is widely used in cylindrical parts, for example.
- Milling: This method is ideal for creating gears, grooves and sprockets. After all, the teeth, grooves, and threads are cut gradually, with a series of cuts made by a tool known as a Caracol.
- Drilling: As you may already have guessed, this type of machining consists in opening, enlarging or finishing parts with holes.
- Broaching: this method consists of the progressive removal of material from the surface of the workpiece.
- Electrical Discharge Machining: in this case, the grinding does not occur through mechanical contact between a tool and the workpiece, but through electrical capacitor discharges.
Machining types
As you can see, machining allows numerous changes to be made to the workpiece. But what you may not know is that these changes can be carried out by different machining processes. Next, you will learn about some alternatives to traditional methods, which can guarantee greater precision, less waste generation and lower energy consumption.
LASER MACHINING
Also known as laser micromachining, this is a thermal process, which uses high temperatures. In this way, it allows the elimination of chips through melting and evaporation.
ULTRASONIC MACHINING
Ultrasonic machining uses the tool’s vibration in combination with an abrasive liquid to eliminate excess metal from parts and components. This process is considered a support procedure to other traditional forms, such as drilling and turning.
ROLLER BURNISHING
Roller burnishing is a surface finishing technique. It uses hardened and highly polished steel rollers, which are pressed against a softer workpiece, ensuring the required finish.
WATER JET CUTTING
Widely used in sheet profile cutting, this method consists of the application of water jets with great pressure on the workpiece to be worked, leading to a high cutting resolution.
Machining in plastic materials
In plastics, machining is usually done when the cost of obtaining a particular design on the workpiece is not worth it compared to traditional shaping methods. This process is also widely used to correct small defects that the final product may present, due to design flaws in the shape, machine adjustment difficulties, among other factors.
But, despite being increasingly common, machining in polymers demands attention. After all, materials behave in different ways. Want an example? PP is a very flexible plastic. And because it is more elastic than metals, it can suffer a great deal of deflection during machining, and can even tear if it is subjected to a concentrated load, such as that of a drill.
To avoid this type of problem, it is important to be aware of the following factors:
- Physical properties of the material, mainly the flexural modulus and hardness;
- Thermal properties of the material, especially the coefficient of thermal expansion, thermal conductivity, and glass transition temperature;
- Stress effects on plastic, which include both internal effects from shaping and external effects caused by further processes.
Machining tips
- To avoid warping, make sure that the thermoplastic parts are very well secured and supported during machining;
- Remember that cutting forces should be kept to a minimum;
- The cutting tool needs to be polished and have clearance between it and the workpiece to avoid excessive friction and temperature increase;
- Remember that the coefficients of thermal expansion for plastics are relatively high. This means that they regain elasticity during and after machining. Therefore, threads and holes can end up with smaller diameters than the tools;
- Plastics may need to be quenched before finishing to prevent the internal stresses of the workpiece from causing surface cracking or warping;
- Use tools with high cutting power;
- Remember that thermal expansion can lead to dimensional instability;
- To reduce heat buildup, use coolants;
- In most cases, high tool speed and slow material feed is recommended;
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