What is grinding?
Grinding is a process that uses a grinding wheel to cut a workpiece. Let the high-speed rotating grinding wheel contact the workpiece and gradually cut the surface of the workpiece. abrasive cutting is also unique in that it is the final finishing process for cutting and other processes. This section will introduce the different types of grinding, their advantages and disadvantages, their differences from other processing methods, and problems that may easily arise during the processing.
The processing methods of workpieces can be divided into: “removal processing” of cutting materials, “forming processing” of melting materials and injecting them into molds, “plastic processing” of using molds to deform materials, and joining or cutting apart materials. “Joining and cutting processing”. The processing of removing part of the material from the workpiece is called removal processing.
abrasive cutting is one of them. It removes surface material from the workpiece through a high-speed rotating grinding wheel. In the grinding process, a piece of equipment called a grinder is used. Although it takes longer than cutting with a tool, it produces a more precise and beautiful workpiece.
Grinding is often used as a finishing process in addition to other machining methods. For example, after the rough shape is obtained by cutting, the surface of the workpiece can be improved by grinding. Grinding can also process hard materials that are difficult to cut (such as cemented carbide, etc.). In some cases, grinding can also be used to machine high-hardness parts after quenching.
Advantages and Disadvantages of abrasive cutting
abrasive cutting has the following advantages and disadvantages.
Advantages of abrasive cutting
- High processing dimensional accuracy：Because abrasive cutting requires only a small amount of material to be removed per operation, high-precision machining is possible. Using a grinder can produce micron-level surfaces and make the surface smoother.
- Can process hard materials：abrasive cutting refers to the use of countless abrasive grains protruding from the surface of the grinding wheel to cut the surface of the workpiece. During the abrasive cutting process, even if one abrasive grain breaks, the next abrasive grain will automatically be exposed (self-sharpening effect), so the grinding wheel can always remain sharp. Even if the abrasive grains are softer than the workpiece, machining can continue.
- Can improve surface roughness：During the cutting process, the surface material of the workpiece will be ground away little by little, making the surface very smooth.
Disadvantages of abrasive cutting
- Processing time is very long：The advantage of abrasive cutting is that it can achieve high dimensional accuracy, but the disadvantage is that it takes a long time to complete. Therefore, large workpieces are usually formed by cutting and then grinding.
- Heat is easily generated during processing：During the abrasive cutting process, due to the friction between the grinding wheel and the workpiece, the temperature at the grinding point exceeds 1,000 degrees. Therefore, cutting fluid must be used to continuously cool the workpiece to prevent burning and cracking of the workpiece.
- Accidents are prone to occur during processing：Since the grinding wheel rotates at high speed during the grinding process, various accidents may occur if the grinding wheel is used improperly. Be careful not to exceed the maximum rotation speed of the grinding wheel, and do not press the workpiece too hard on the grinding wheel.
Main types and uses of grinding
There are many types of grinding processes. The following are some typical grinding processes and their characteristics.
surface grinding
It is a processing method for grinding the plane of the workpiece, and it is also the most commonly used method in grinding. It is also called “flat grinding”. Surface grinding is generally used to grind the surface of the workpiece to be smoother after cutting. Surface grinding is to fix the workpiece on the workbench and let the high-speed rotating cylindrical grinding wheel grind the surface of the workpiece. During the machining process, the grinding wheel moves up and down, and the workbench moves back and forth, left and right. This ensures a constant thickness of the workpiece while improving parallelism.
Cylindrical grinding
This method is used for grinding the surface of cylindrical workpieces. The workpiece rotates at a high speed while the center is fixed, and the grinding wheel in the opposite direction of rotation of the workpiece acts on the outer surface of the workpiece to grind the workpiece. Cylindrical grinding is used to produce shaft parts that have a sliding relationship with other parts.
Internal grinding
Internal cylindrical grinding is a processing method that grinds the inside of a cylinder or hole. It is also called internal cylindrical grinding. For example, it is used to process holes with high dimensional accuracy. In internal grinding, both the grinding wheel and the workpiece basically rotate, but there is also a method called “planetary” in which only the grinding wheel rotates. This method is used to process parts such as cylinders where other parts slide inside the cylinder.
Centerless grinding
Centerless grinding is a processing method for grinding the outer diameter of a cylinder, which is the same as cylindrical grinding. However, the two methods differ in how the workpiece is secured. In cylindrical grinding, the center of the cylindrical workpiece is fixed and the workpiece is allowed to rotate. In centerless grinding, the workpiece is supported by a platform called a carriage and a cylindrical guide wheel. The rotating grinding wheel contacts the workpiece, causing it to rotate naturally. This is similar to rolling out dumpling wrappers with your hands. In centerless grinding, the workpiece is evenly supported at three points: the bracket (bracket), the adjusting wheel (guide wheel) and the grinding wheel, so that the surface of the workpiece is processed evenly. It is suitable for processing slender cylindrical parts such as cylinder push rods.
Gear grinding
Gear grinding is a method of processing gears by grinding. The gear is produced by cutting the workpiece using a flat disc-shaped grinding wheel. Sometimes it is also used for the finishing of gears after cutting.
Differences between cutting and grinding processes
Both cutting and grinding processes use tools to gradually remove material through mechanical contact. The following is an introduction to the difference between cutting and grinding.
The difference from cutting processing
Cutting processing, like grinding processing, is also a type of removal processing. It is a method of cutting workpieces using tools such as cutting tools. Depending on the cutting method and the tools used, it can be divided into milling, turning and drilling. Generally speaking, the amount of chips in a single operation is greater in cutting than in grinding. Cutting refers to the method of roughly cutting out the desired shape with a tool, while grinding is the method of gradually grinding the ideal surface shape using a rotating grinding wheel. Cutting operations can be completed in a shorter time than grinding operations. But the machining accuracy is not as good as grinding.
Precautions during grinding processing
A high-speed rotating grinding wheel is required for grinding. Here, we will introduce three problems that are prone to occur during the processing of grinding wheels.
clogged
Clogging refers to the phenomenon that chips and other particles are trapped between particles on the surface of the grinding wheel, causing the sharpness of the grinding wheel to deteriorate.
When machining soft metals such as aluminum and copper, the likelihood of clogging increases. If clogging occurs, the “self-sharpening” function of the grinding wheel cannot be exerted, and new abrasive grains will not appear on the surface of the grinding wheel, resulting in a significant reduction in processing efficiency. Because the contact between the grinding wheel and the workpiece easily generates heat, it can easily cause burning and cracks in the workpiece. To prevent grinding wheel clogging, a suitable grinding wheel must be selected based on the workpiece material.
passivation
Passivation refers to the phenomenon that the cutting edge of the abrasive grains wears away, the surface of the grinding wheel becomes smooth, and the sharpness of the grinding wheel is greatly reduced. This is caused by the “self-sharpening” function of the grinding wheel not functioning as it should. After passivation occurs, the friction area will increase, so it is as easy to cause burning and cracks in the workpiece as clogging.
When passivation occurs, the grinding load should be adjusted so that the “self-sharpening” effect of the grinding wheel can be better exerted.
fall off
Normally, the abrasive grains in the grinding wheel will fall off naturally after losing their grinding force. However, if the bond holding the grains together is too soft, the grinding grains may fall off one after another. This is the shedding phenomenon of abrasive grains. The occurrence of abrasive grain shedding will greatly reduce the sharpness of the grinding wheel and shorten the life of the grinding wheel. Therefore, in order to prevent the abrasive particles from falling off during grinding, the softness and processing load of the binder should be appropriately adjusted.
In addition, when using grinding processing, you also need to pay attention to the designed shape. If you grind the inside of a stepped or cylindrical hole, it will be very difficult to grind at the intersection of the surfaces. Therefore, setting the undercut groove for grinding must be considered during design.
Summarize
Grinding is a method in which a high-speed rotating grinding wheel is pressed against the workpiece to gradually cut away the surface material of the workpiece. Although the grinding process takes a long time, its main advantage is that it can process workpieces with high dimensional accuracy and can also process hard materials such as carbide. There are many grinding processes that can be used to process workpieces of various shapes such as planes and cylinders.
