What is grinding?
grinding
external cylindrical grinding
The machining of the outer cylindrical surfaces of rotating parts such as guide pillars and guide sleeves is completed on an external cylindrical grinding machine using a grinding wheel. The machining method involves a high-speed rotating grinding wheel grinding a low-speed rotating workpiece, with the workpiece reciprocating longitudinally relative to the grinding wheel. After external cylindrical grinding, the dimensional accuracy can reach IT5–IT6, and the surface roughness Ra can reach 0.8–0.2 μm. If a high-gloss grinding process is used, the surface roughness Ra can reach 0.025 μm.
outer circle grinding
When high surface roughness and dimensional accuracy are required for the outer cylindrical surface, grinding is necessary. In mass production, grinding is typically performed on a dedicated grinding machine. For single-piece or small-batch production, manual grinding with grinding tools can be used, achieving a grinding accuracy of IT3 to IT5 and a surface roughness Ra of 0.1 to 0.008 μm.
Internal grinding
For high-precision inner surfaces in mold parts, internal grinding is generally used for finishing. Internal grinding can be performed on an internal grinding machine or a universal external grinding machine. On an internal grinding machine, the dimensional accuracy of the ground hole can reach IT6 to IT7, and the surface roughness Ra is 0.8 to 0.2 μm. If a high-precision grinding process is used, the dimensional accuracy can be controlled within 0.005 mm, and the surface roughness Ra is 0.1 to 0.025 μm.
Inner honing
To further improve the surface quality of holes, a honing process can be added. For single-piece and small-batch production, simple honing tools can be used, and honing can be performed on a conventional lathe. As shown in Figure 3-10, during honing, a guide sleeve is fitted onto the honing head, and the workpiece is held by hand, making a reciprocating motion along the axis. The lathe spindle drives the honing head to rotate, while the hand holds the guide sleeve and makes a reciprocating linear motion along the axis on the honing tool.
The structure of the honing head is shown in Figure 3-11. The honing head consists of several grinding stones mounted on a honing frame. The honing head, with its grinding stones, is inserted into the hole to be machined, and the grinding stones contact the hole wall with a certain pressure for honing. Adjusting the adjusting shaft on the honing head allows adjustment of the honing head diameter, thus controlling the amount of honing.
Generally, the honing allowance is 0.015~0.02mm.
After honing, the dimensional accuracy grade is IT4~IT5, the surface roughness Ra is 0.1~0.25μm, and the roundness and cylindricity are 0.003~0.005mm, but it cannot improve the positional accuracy of the hole.
