What is lapping?
Lapping is a finishing process, which is carried out using loose abrasives.
Surface smoothing is achieved by the abrasive grains that are supported by the lap, which acts as the cutting tool shank.
An extremely high accuracy of form and dimensions and a good surface quality are obtained.
Lapping is done by charging a lap, which is made of soft material with abrasive particles, and rubbing it over the workpiece surface with a slight pressure as shown in Figure.
The process is classified into hand and machine lapping and mechanical and chemo-mechanical.
It can be performed with free or forced lap charging with abrasives. Rotary, plane, and profile lapping also tackle different workpiece forms.
Diagram of lapping
Advantages of lapping:
- Extreme accuracy of dimensions
- Correction of minor imperfections of shape
- Refinement of surface finish
- Producing close fit between mating surfaces
- It does not require the use of holding devices; therefore, no workpiece distortion occurs.
- Additionally, in normal lapping, less heat is generated than in most of other finishing operations. This minimizes the possibility of metallurgical changes to the machined parts.
- When both sides of a flat workpiece are lapped simultaneously, an extreme accuracy in flatness and parallelism and the relief of inherent stresses can be achieved.
Disadvantages or limitations of lapping:
- It is a slow process
- It is a expensive process
Applications of lapping process
- It is used in Ceramic machining
- It is used in Brittle material machining
- It is used in Glass machining
Types of Lapping
The Rubbing action in lapping can be done manually or by use of machine. According to it, lapping can be divided into two types.
In hand lapping process, the work piece is rubbed over the lapping plate manually.
In this process first the plate is coated with the abrasive material which in in the form of paste. Now the work piece is rubbed over plate by applying a small pressure manually.
It is used for finish large quantity of similar parts.
This machine involves a rotating lapping plate and conditional rings. Conditional rings provide sits for work piece. This rings rotate and rubbed the work piece against lapping plate.
Abrasive particles are provided with suitable medium like liquid or in powder form. This rubbing removes metal in form of microchips and provide super finishing.