Factors affecting the surface roughness of grinding machines

1、 Factors related to grinding wheels

The main focus is on the particle size and hardness of the grinding wheel, as well as the dressing of the grinding wheel. The finer the grain size of the grinding wheel, the more abrasive particles per unit area of the grinding wheel, the finer the scratches on the grinding surface, and the smaller the surface roughness value. However, if the particle size is too fine, the grinding wheel is prone to clogging, increasing the surface roughness value and also easily producing ripples, causing burns.

2. Grinding wheel hardness refers to the difficulty of abrasive particles falling off the grinding wheel after being subjected to grinding force. The grinding wheel is too hard, and the abrasive particles cannot fall off after wear, causing strong friction and compression on the surface of the workpiece, increasing plastic deformation and surface roughness values. At the same time, it can also easily cause burns. The weakening of grinding effect will increase the surface roughness value, so choose an appropriate grinding wheel hardness.

The quality of grinding wheel dressing is closely related to the dressing tool used and the longitudinal feed rate of the dressing wheel. Grinding wheel dressing is the use of diamond to remove passivated abrasive particles from the outer layer of the grinding wheel, making the cutting edge of the abrasive particles sharp and reducing the roughness value of the grinding surface. In addition, the smaller the longitudinal feed rate of the shaping wheel, the more cutting micro edges on the shaping wheel, and the better the contour, thus obtaining a smaller surface roughness value.

2、 Factors related to workpiece materials

1. Including material hardness, plasticity, thermal conductivity, etc.

The hardness, plasticity, and thermal conductivity of the workpiece material have a significant impact on surface roughness. Soft materials such as aluminum and copper alloys are prone to clogging the grinding wheel, making it difficult to grind. Heat resistant alloys with high plasticity and poor thermal conductivity are prone to premature detachment of sand particles, resulting in increased surface roughness during grinding.

3、 Factors related to processing conditions

1. Including grinding amount, cooling conditions, precision and vibration resistance of the machining system.

The grinding amount includes grinding wheel speed, workpiece speed, grinding depth, and longitudinal feed rate. Increasing the grinding wheel speed will make the propagation speed of surface metal plastic deformation unable to keep up with the grinding speed, and the material will not deform in a timely manner, resulting in a decrease in surface roughness value. The grinding surface will be reduced. As the workpiece speed increases, the plastic deformation increases, and the surface roughness value increases. The greater the grinding depth and longitudinal feed rate, the greater the plastic deformation and the higher the surface roughness value. During grinding, the temperature of the grinding wheel is relatively high, and the effect of heat is dominant, so the role of cutting fluid is very important.

The use of cutting fluid can lower the temperature of the grinding area, reduce burns, wash away sand debris, and avoid scratching the workpiece, thereby reducing the surface roughness value. But it is necessary to choose the appropriate cooling method and cutting fluid.

For external cylindrical grinders, internal cylindrical grinders, and surface grinders, the spindle accuracy of the machine tool grinding wheel, the accuracy and stability of the feed system, the stiffness and vibration resistance of the entire machine tool are closely related to the surface roughness.

4、 It's the dressing technique for grinding wheels

Sharpening is the process of sharpening the abrasive grains of a superhard grinding wheel. In this process, it is necessary to remove the bond between the abrasive particles and the blunt grinding wheel abrasive particles, so that the abrasive particles with strong grinding performance protrude from the bond and form sharp cutting edges. Sharpening can also remove tiny substances from the pores on the surface of the grinding wheel, preventing an increase in grinding force acting on the wheel. The increase in grinding force on the grinding wheel can cause vibration and result in surface burns.

Without proper sharpening, even a very good grinding wheel cannot achieve high-quality and size consistent machined parts. In fact, when investing in high-quality grinding wheels, it is very important to have the wheels repaired in order to achieve high grinding performance.

Forming can be said to be a part of grinding wheel preparation, which is carried out simultaneously with the grinding of ordinary grinding wheels. For superhard abrasive grinding wheels, these two processes are carried out separately. Firstly, shape the grinding wheel. When using superabrasive grinding wheels for grinding, use forming tools or rollers for forming. Plastic surgery usually uses a dressing rod with ceramic adhesive. After forming, the grinding wheel is sharpened.

It is very important to ensure that the spindle bearings are at a certain temperature (such as the usual grinding state of the grinding wheel) before wheel dressing, including shaping and sharpening. This can avoid damaging the geometric shape of the parts and prevent abnormal wear of the grinding wheel and dressing tools. Tools used for trimming should be handled with caution, as they are typically made of hard, wear-resistant but very fragile diamond materials that are highly sensitive to small cracks and damage caused by minor impacts or external forces.

Because the diamond shaper itself is a tool, it needs to be very sharp. Using blunt tools to polish the surface of the grinding wheel will make it dull. In order to maintain high-quality and sharp diamond dressing tools, it is necessary to regularly rotate single point or conical dressing tools by 1/8 turn. The number of rotations can be determined based on the trimming situation, and according to experience, rotate one less time per day. For chisels and shaping tools, it is generally necessary to rotate 180 ° once before blunting.

Using small trimming to reduce trimming time seems to always have an idea of choosing a larger trimming depth. This is a wrong idea. Choose the appropriate trimming depth to trim the grinding wheel. Choosing an excessively large dressing depth will result in higher cutting temperatures, reduce the service life of the dressing tool, and also remove useful grinding wheel layers. The result is that both the dresser and the grinding wheel are damaged, which can have the opposite effect.

After multiple adjustments, not only can the geometric shape of the grinding wheel be restored, but also good grinding edges can be produced. Use a single point shaping tool to make contact with the diameter direction of the grinding wheel, so that the inclination angle of the grinding wheel axis is 10-15 degrees, and the single point shaping tool produces a sharpening effect when rotating regularly. Trimming tools with multi-point contact do not need to be tilted at this angle. On the contrary, the entire end face of the dressing tool is in contact with the surface of the grinding wheel.

The lateral movement speed is the speed at which the dressing tool passes through the surface of the grinding wheel during the dressing process. It plays a crucial role in the surface roughness and metal removal rate required for machining parts. If the lateral movement speed is too slow, it will clog the grinding wheel, damage the surface roughness and metal removal rate of the parts. Slow lateral movement speed can also cause the grinding wheel to vibrate and burn out the surface of the parts. A uniform and fast lateral motion speed can create a good grinding wheel surface, improve the grinding performance of the wheel, increase grinding efficiency, and reduce the surface roughness of the parts.

Keeping cool and using coolant appropriately can accelerate dressing speed and improve dressing efficiency. Based on experience, choosing a coolant with a diameter of 3/8 inch can remove a large amount of heat from the dressing table and extend its service life. When the diamond dressing tool passes through the grinding wheel, install a coolant nozzle to cover the entire surface of the grinding wheel or continuously add coolant to the diamond dressing tool. When the dressing tool comes into contact with the grinding wheel to start dressing, do not agree to the dressing tool and remove it from the coolant. Otherwise, diamond dressing tools may crack or fracture under changes in temperature.

Using a filter for high-precision filtration of coolant can avoid repeated circulation of dirt or debris in the coolant. Contaminated coolant will quickly wear down the grinding wheel and increase the frequency of wheel dressing. Only during dry grinding (in which case the cooling of the diamond dressing tool can be interrupted), should the grinding wheel be used for dry grinding. Before leaving work every day, turn off the coolant and let the sand wheel idle for a few minutes. This can prevent the grinding wheel from breaking.

Vibration is the enemy of clothing. It is very important to effectively reduce the vibration of the grinding wheel surface during the grinding wheel dressing process, avoid leaving dressing marks, collisions, and damage to the dressing tools on the grinding wheel surface. This means maintaining the balance of the grinding wheel, which is determined by the structural characteristics of the grinding wheel itself. The uneven density and geometric shape of the entire grinding wheel can affect its inherent balance. Therefore, choosing high-quality grinding wheels is also very important. If it is a high-quality grinding wheel, only correct installation can maintain good balance of the grinding wheel. According to the factory manual of the grinding wheel manufacturer, the grinding wheel is marked with an upward arrow, indicating the light end position of the grinding wheel after rough balancing. Users can follow the arrow to adjust the grinding wheel and achieve dynamic balance. Uniform addition of coolant can sometimes help maintain the balance of the grinding wheel.

To further avoid vibration, it is necessary to ensure that the trimming tool is firmly clamped on the fixture base and maintains a small amount of suspension to ensure that the trimming tool has sufficient rigidity. If the diamond cutting tool is not firmly clamped, it will generate vibration, noise, and ripples on the surface of the part, causing deformation of the part surface and damaging the repair tool. A superhard abrasive grinding wheel is shaped and sharpened before grinding.