1. What is grinding?
Grinding is a processing method that removes the excess layer on the surface of the workpiece by the cutting action of the abrasive tool, so that the surface quality of the workpiece meets the predetermined requirements. Common grinding forms usually include: cylindrical grinding, internal grinding, centerless grinding, thread grinding, grinding of flat surfaces of workpieces, and grinding of forming surfaces.
2. What is an abrasive tool? What is the composition of the grinding wheel? What factors determine its performance?
All tools used for grinding, grinding and polishing are collectively referred to as abrasive tools, most of which are made of abrasives and binders.
Grinding wheels are composed of abrasive grains, binders and pores (sometimes without), and their performance is mainly determined by factors such as abrasives, particle size, binders, hardness and organization.
3. What are the types of abrasives?
The abrasive is directly responsible for the cutting work, and should have high hardness, heat resistance and certain toughness, and should be able to form sharp edges and corners when broken. At present, there are three types of abrasives commonly used in production: oxide series, carbide series and high-hard abrasive series. Commonly used abrasives are white corundum, zirconium corundum, cubic boron carbide, synthetic diamond, cubic boron nitride, etc.
4. What are the forms of grinding motion in cylindrical and surface grinding?
In cylindrical and surface grinding, the grinding motion includes four forms: main motion, radial feed motion, axial feed motion and workpiece rotation or linear motion.
5. Briefly describe the grinding process of a single abrasive particle.
The grinding process of a single abrasive grain is roughly divided into three stages: sliding, scoring and cutting.
(1) Sliding stage: During the grinding process, the cutting thickness gradually increases from zero. In the sliding stage, due to the extremely small cutting thickness acg when the abrasive cutting edge and the workpiece begin to contact, when the blunt circle radius rn>acg at the top corner of the abrasive grains, the abrasive grains only slip on the surface of the workpiece, and only produce Elastic deformation, no chips.
(2) Scribing stage: with the increase of the intrusion depth of the abrasive particles, the pressure between the abrasive particles and the surface of the workpiece gradually increases, and the surface layer also transitions from elastic deformation to plastic deformation. At this time, the extrusion friction is severe, and a large amount of heat is generated. When the metal is heated to the critical point, the normal thermal stress exceeds the critical yield strength of the material, and the cutting edge begins to cut into the surface of the material. The slippage pushes the material surface to the front and sides of the abrasive grains, causing the abrasive grains to carve grooves on the surface of the workpiece, and bulges on both sides of the grooves. The characteristics of this stage are: plastic flow and bulge occurs on the surface of the material, and chips cannot be formed because the cutting thickness of the abrasive particles does not reach the critical value of chip formation.
(3) Cutting stage: When the intrusion depth increases to a critical value, the cut layer obviously slips along the shear surface under the extrusion of abrasive particles, forming chips to flow out along the rake face, which is called the cutting stage.
6. What is high-speed grinding? Compared with ordinary grinding, what are the characteristics of high-speed grinding?
High-speed grinding is a process method to improve the grinding efficiency and grinding quality by increasing the linear speed of the grinding wheel. The difference between it and ordinary grinding lies in the high grinding speed and feed rate, and the definition of high-speed grinding is advancing with time. Before the 1960s, when the grinding speed was 50m/s, it was called high-speed grinding. In the 1990s, the maximum grinding speed reached 500m/s. In practical applications, the grinding speed above 100m/s is called high-speed grinding.
Compared with ordinary grinding, high-speed grinding has the following characteristics:
(1) Under the condition that all other parameters are kept constant, only increasing the speed of the grinding wheel will lead to a reduction in the cutting thickness and correspondingly reduce the cutting force acting on each abrasive particle.
(2) If the workpiece speed is increased in proportion to the grinding wheel speed, the cutting thickness can remain unchanged. In this case, the cutting force acting on each abrasive grain and the resultant grinding force do not change. The biggest advantage of this is that the material removal rate increases proportionally with the same grinding force.
7. What is precision grinding?
Precision grinding refers to selecting a fine-grained grinding wheel on a precision grinding machine, and by finely dressing the grinding wheel, the abrasive grains have micro-edge and contour properties. After grinding, the grinding surface left by the ground is ground. The traces are extremely fine and the residual height is extremely small. In addition to the effect of the non-spark grinding stage, a surface grinding method with a machining accuracy of 1 to 0.1 mm and a surface roughness of Ra of 0.2 to 0.025 mm is obtained.
Selection principle of grinding wheel in precision grinding of ordinary grinding wheel:
(1) The abrasive of the grinding wheel used in precision grinding is based on the principle of being easy to generate and maintain the micro-edge and its contour.
(2) Grinding wheel particle size: From the geometrical factor alone, the finer the grinding wheel particle size, the smaller the surface roughness value of grinding. However, when the abrasive particles are too fine, not only will the grinding wheel be easily blocked by abrasive debris, but if the thermal conductivity is not good, it will cause burns and other phenomena on the machined surface, which will increase the surface roughness value. .
(3) Grinding wheel binders: Grinding wheel binders include resins, metals, ceramics, etc., and resins are widely used. For coarse-grained grinding wheels, a vitrified bond can be used. Metal and ceramic binders are an important aspect of research in the field of precision grinding.
8. What is ultra-precision grinding?
Ultra-precision grinding refers to a grinding wheel grinding method with a machining accuracy of less than 0.1mm and a surface roughness of less than Ra0.025mm. Processing of materials and hard and brittle materials such as ceramics and glass.
Ultra-precision grinding mechanism:
(1) Abrasive particles can be regarded as an elastic body with elastic support and a large negative rake angle cutting edge. The elastic support is a binding agent. Although the abrasive particles have considerable hardness and their own deformation is very small, they are actually still elastomers.
(2) The cutting depth of the abrasive grain cutting edge gradually increases from zero, and then gradually decreases to zero after reaching the maximum value.
(3) The whole contact process between abrasive grains and the workpiece is followed by elastic zone, plastic zone, cutting zone, plastic zone and elastic zone.
(4) In ultra-precision grinding, micro-cutting action, plastic flow, elastic destruction action and sliding action appear in sequence according to the change of cutting conditions. When the blade is sharp and has a certain grinding depth, the micro-cutting effect is strong; if the blade is not sharp enough, or the grinding depth is too shallow, plastic flow, elastic damage and sliding will occur.
Features of Ultra Precision Grinding:
(1) Ultra-precision grinding is a systematic project.
(2) Superabrasive grinding wheel is the main tool for ultra-precision grinding.
(3) Ultra-precision grinding is a kind of ultra-micro cutting process.
Applications of ultra-precision grinding:
(1) Grinding of metal materials such as steel and its alloys, especially hardened steel that has been treated by quenching.
(2) Hard and brittle materials that can be used for grinding non-metals? For example, ceramics, glass, quartz, semiconductor materials, stone materials, etc.
(3) At present, there are mainly cylindrical grinders, surface grinders, internal grinders, coordinate grinders and other ultra-precision grinders, which are used for ultra-precision grinding of outer circles, planes, holes and hole systems.
(4) Ultra-precision grinding and ultra-precision free abrasive processing complement each other.