Lapping in Engineering – Why it’s required and how it works
The huge demands needed today by manufacturing engineers for machine parts and tools necessitate extremely accurate machining. The finishing processes are a critical aspect to be considered today to meet the objectives like parallelism, tolerances, flatness, and smooth surface. These high-precision abrasive processes are used to generate surfaces of desired characteristics such as geometry, form, tolerances, surface integrity, and roughness. Abrasive finishing processes are utilised in a wide range of material applications and industries. Typical examples are the finishing of various components used in aerospace, automotive, mechanical seals, fluid handling, and many other precision engineering industries. The lapping process is a fine finishing process, which leads to a surface with low roughness and high precision. The surface structure resulting from lapping is very beneficial in sliding joints, because of the high ability of lubricant retention, as well as in non-sliding joints because of the high load-carrying ability. The range of lapped materials is very wide. This necessitates the use of natural and artificial abrasive materials and mainly materials such as micro grains of alumina, silicon carbide, boron carbide, and diamond. Both the solid and liquid carriers distribute these grains on the surface of the lapping tool and chemical action takes place.
The lapping process has its roots in the origin of the finishing process. It is considered one of the oldest processes recommended to meet the requirements of the dimensions and to obtain a relatively good surface finish that is aimed mainly to remove surface roughness and surface waviness, and obtaining closer tolerances. The process is suitable to machine hard materials, brittle materials, etc. Although hardness is one of the features of ceramic materials, it also sometimes becomes a hindrance, especially when machining to tight tolerances. To obtain closer tolerances, ceramic materials demand very highly sophisticated equipment and skilled labour, which will obviously lead to high manufacturing costs and this is not at all desired. Subsurface damage is one of the biggest problems that is affecting the performance of ceramic components. Hence to obtain all the necessary machining qualities without much investment, design engineers have strongly recommended the lapping process.
Lapping has a wide range of applications. The process is favourable for the finishing of optical glasses and is also used in producing the required finishing for silicon wafers, which is a major component in computer architecture and electronic fields.
Lapping processes have the following characteristics that vary in degree according to the particular system and equipment:
- The rate of stock removal is low due to the cutting speeds and shallow penetration of the fine abrasive grains into the work surface.
- Considered a cool process as it is carried out without generating significant heat and hence does not cause thermal damage.
- Relatively low force is applied to the workpiece that is usually held in a supported manner, which supports it to surface finish fragile and brittle parts
- The shape of the surfaces worked by lapping is limited to basic forms such as flat, cylindrical and spherical, but the accuracy achieved in lapping is excellent, especially for flat surfaces
- Lapped surfaces are very smooth with regard to both the measurable surface finish and visual reflectivity (when checked with an optical flat and monolight). Work material and its hardness usually affect the reflectivity of the lapped surfaces, so soft materials have low reflectivity and are of matte finish even when lapped to a high degree of physical smoothness.
- Due to the low and constant material removal rate, the particle size can be controlled as the lapping action is consistent and uniform.
