Intermediate Grinding Technology

Author: Chief Editor: Wang Tingjiang et al.
Publisher:
Publish Date: 2004-04-01
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The grinding training for workpieces requires understanding the characteristics, grinding strategies, and methods of various medium-complexity workpieces such as long shafts, deep holes, thin-walled, and thin plate parts, and mastering their operation steps and basic principles.
Grinding of Long Shafts
Long shafts typically refer to shafts with a length-to-diameter ratio (referred to as the length-diameter ratio) greater than 10.
I. Characteristics of Long Shafts
Long shafts have poor rigidity and are prone to deformation. The larger the length-diameter ratio, the poorer the rigidity and the greater the difficulty of grinding. Under the action of grinding force and clamping force, the workpiece will bend, resulting in shape errors (such as drum-shaped, bamboo-jointed, elliptical, conical, etc.), polygonal vibration marks, and radial runout errors. During grinding, phenomena such as uneven and irregular grinding sparks often occur, affecting surface finishing quality. Additionally, long shafts are very sensitive to grinding heat and the stress of the material itself, which is another reason for grinding deformation. Therefore, the key issues in grinding long shafts are: how to reduce grinding force and improve the support stiffness of the workpiece to minimize deformation.
II. Countermeasures for Grinding Long Shafts
1. Eliminate Residual Stress of the Workpiece
Before and during grinding, the workpiece should undergo straightening and stress-relief heat treatment to avoid bending due to internal stress during grinding.
2. Rationally Select and Dress the Grinding Wheel
Use a grinding wheel with coarse grain, soft hardness, loose structure, and thin thickness to enhance its self-sharpening ability, reduce grinding resistance, prevent wheel clogging, and improve cooling conditions. The rough grinding wheel should be dressed to be sharp, using sharp diamond points and a larger longitudinal feed rate for dressing. For precision grinding, the final dressing of the wheel should be performed from right to left to make the left edge of the wheel sharp. To reduce grinding force, the width of the wheel can also be narrowed, and the periphery can be dressed into a concave shape to reduce radial force. During grinding, the wheel should be kept sharp.
3. Ensure Good Contact Surface of the Center Hole
The center hole of the workpiece should be ground, and the 60° external conical surfaces at the front and rear should be accurately ground to ensure good contact. To reduce friction between the center hole and the conical surface, lubricating oil should be frequently added during grinding.
4. Reduce the Clamping Force of the Tailstock
The clamping force of the tailstock should be smaller than that in general grinding (but should not have axial play) to reduce bending deformation caused by clamping force and also reduce bending deformation caused by thermal expansion of the workpiece during grinding.
5. Use a Double-Pin Chuck
A double-pin chuck can ensure balanced force on the workpiece, reducing vibration and roundness errors.
6. Rationally Select Grinding Parameters
At the beginning of grinding, the workpiece is in a bent state, and the wheel performs intermittent grinding. Therefore, the initial feed rate should be slow and the feed amount small to reduce impact force. During rough grinding, the depth of cut should be small, the worktable speed should be slow, and the workpiece speed should be low. During precision grinding, the depth of cut should be even smaller, and the workpiece speed should be lower to prevent vibration. When grinding the entire length of the workpiece, a slightly larger feed rate can be used near both ends of the shaft, while a smaller feed rate should be used in the middle section, and the number of feedings can be appropriately increased.