Lapping
Lapping is a precision finishing process used to obtain very smooth and accurate surfaces. In this process, a soft tool called a lap is charged with fine abrasive particles and rubbed against the workpiece surface. Lapping removes very small amounts of material and produces a high-quality surface finish.
Applications of Lapping
- Finishing precision measuring instruments.
- Improving surface accuracy of machine components.
- Finishing gauges, valves, and sealing surfaces.
- Producing mirror-like surface finish.
- Achieving very close dimensional tolerances.
Material for Lapping Tools
Lapping tools are usually made from materials softer than the workpiece so that abrasive particles can embed into the tool surface.
- Cast iron
- Copper
- Brass
- Lead
- Soft steel
- Wood (for special applications)
Lapping Abrasives
Abrasives are fine particles used in lapping to remove material from the work surface.
Common Lapping Abrasives
- Aluminium oxide
- Silicon carbide
- Diamond powder
- Boron carbide
These abrasives are usually mixed with oil or water to form a lapping compound.
Charging of Lapping Tool
Charging is the process of embedding abrasive particles into the surface of the lap.
Procedure
- Apply abrasive compound on the lap surface.
- Rub the abrasive into the lap using a hard roller or workpiece.
- Ensure uniform distribution of abrasives.
- The lap is then ready for finishing operations.
Surface Finish
Surface finish refers to the smoothness or roughness of a machined surface. It is an important factor that affects the performance, durability, and appearance of machine components.
Importance of Surface Finish
- Reduces friction between moving parts.
- Improves wear resistance.
- Enhances corrosion resistance.
- Improves sealing capability.
- Provides better appearance of products.
Equipment for Testing Surface Finish
Various instruments are used to measure and evaluate surface finish.
- Surface roughness tester
- Profilometer
- Optical microscope
- Comparator
Terms Related to Surface Finish
- Roughness: Small irregularities on the surface.
- Waviness: Larger surface variations.
- Lay: Direction of surface pattern produced during machining.
- Flaws: Defects such as scratches or cracks.
Equipment for Testing Surface Quality
Surface quality can be checked using various inspection tools.
- Surface roughness measuring instruments.
- Surface comparators.
- Optical inspection equipment.
- Precision measuring gauges.
Dimensional Tolerances of Surface Finish
Dimensional tolerances specify the allowable variation in size of a component. Surface finish requirements are often related to these tolerances because smoother surfaces help maintain accurate dimensions and proper functioning of machine parts.
- Fine tolerances require better surface finish.
- Rough surfaces may affect accuracy and performance.
- Surface finish is specified in engineering drawings using standard symbols.
Conclusion
Lapping is an important finishing process used to achieve extremely smooth and accurate surfaces. Proper selection of lapping tools, abrasives, and surface testing equipment ensures high-quality machining results and precise dimensional control in engineering components.