Lapping is a popular operation today used for various surface finishing operations, using loose abrasive powders as grinding agents. It is performed normally at low speeds. This mechanical process is carried out on products that demand very tight tolerances of flatness, parallelism, thickness or finish.
Applications of lapping processes include cutting tools, printing equipment, transmission equipment, stamping, forgings, etc. Today you’ll get to know the definition, application, function, diagram, operations, working principle, types, advantages, and disadvantages of the lapping process. You’ll also get to know about lapping machines and their processes.
What is lapping?
The term lapping is a process by which material is precisely removed from a workpiece (or specimen) so that a desired dimension or shape can be obtained. The lapping process has been done on many applications and different materials such as metals, glasses, semiconductors, optics, ceramics, geological samples, gems, minerals, etc.
Lapping can also be seen as a finishing process performed using loose abrasion. The process may be carried out after the grinding operation to create a highly accurate finish surface. Although the process is similar to grinding and honing only that loose abrasive particle is used to remove the material rather than bonded material such as a grinding wheel.
Lapping processes usually remove 0.03. – 0.003 mm from the workpiece. Lapping (and polishing) techniques offer great benefits due to the precision and control with which material can be removed.
Lapping machines are special types of precision finishing machine that uses slurry abrasive particles mixed with oil or water. The slurry is a liquid cutting tool, it forms an abrasive film between the underlying lapping plate and the part to be lapped.
Lapping machines have the capacity to create flat surfaces, normally up to 0.001mm, with surface finishes better than Ra. 01. In its process, the workpiece is gradually removed through the rolling and sliding action of the abrasive grains between the lapping wheel and the workpiece. The removed material and slurry then drain away from the table.
Single-side and double-side machines are the two types of flat lapping and polishing systems. The single side literally means that only one side of a workpiece can be processed at a time. Multiple sides of a workpiece can also be processed but one after the other, only one at a time.
The double side means two sides can be processed simultaneously. Multiple sides of the workpiece can also be processed but only two at a time.
Applications of lapping
The applications of lapping in industries include aerospace, automotive, electronics, etc. Below are the various applications of lapping.
- Used in hydraulics and pneumatics: castings, valve plates, seals, cylinder bodies, and slipper plates.
- Pump production: vanes, impellers, seal faces, rotating valves, etc.
- Clutch plates, gears, spacers, and shims in transmission equipment.
- In stampings and forgings, lapping is performed on bosses, spacers, plates, type hammers, etc.
- Cutting tools: tips, slitter blades.
- Printing equipment: used in printing plates making either new or reconditioned ones.
- Inspection equipment: test blocks, micrometer anvils, surface plates, optical flats.
- Finally, aerospace components: gyro components, seals, and lock plates.
The application of lapping processes is so vast because almost all kinds of material can be machined. These materials include ceramic, glass, wood, etc. even brittle material can be machined.
The function of this lapping process is to obtain an extremely high accuracy of form and dimensions and a good surface quality.
Diagram of lapping processes:
Operations performed with lapping machines
Below is the special operation carried out on lapping machines:
- Modification of surface finish usually improved in surface and sub-surface qualitative values (smoother).
- The flatness (geometry) of a surface can become flat or spherical in contour using a lapping machine.
- Material removal.
- A passive form of grinding (low pressure, low speed, low removal rate)
- Lapping is utilized on flat surfaces, not spherical shapes or contours.
- A specific amount of movement is required on the part of the tool (lap plate), the workpiece, or both.
- Lapping machines are specifically made for high-tolerance materials.
- Material polishing
The working of lapping is less complex and can be easily understood. A lapping machine consists of 5 main components that include a rotating table (known as a lapping plate), several conditioning rings, the top weight, the slurry (tool), and the machine itself.
The controls, engine, coolant, filter, and other subsidiary components for proper operation of the mechanism are housed in the machine. The lapping plate is powered (rotate) by a motor and the conditioning rings turn automatically as the plate turns. This plate is usually made of high-quality soft cast iron, though copper and other soft metals may be used.
The function of the conditioning rings is to hold the workpiece. The rings help to distribute the wear evenly across the lapping plate increasing its life. Special rings may be fitted for some specific operations such as cylindrical, especially long pieces.
A top plate is used to press the workpiece down so that the abrasion can take place. it may be simple lids or mechanically operated piston-like covers. The slurry is made from various abrasive materials like diamond or carbon with a liquid base oil or water. It is fed between the lapping plate and the top plate, which is distributed evenly across the surface by the plate’s rotation. The tiny abrasives suspended in the liquid drag and tumble across the surface of the headpieces. It grinds away at any micro-irregularities in the part’s surface.
Read more: The working principle of a shaping machine
Watch the video below to learn more about the lapping process:
Types of lapping
The different types of lapping can be determined by the rubbing action, which can be done manually or by the use of a machine. Below are the various types of lapping:
Hand lapping is when the operation is performed manually, that is, the workpiece is rubbed over the lapping plate using hand. In this process, the plate is first coated with an abrasive material which is a form of paste. After this, the workpiece is then rubbed over the plate by manually applying little pressure.
The machine lapping involves a rotating lapping plate and conditional rings just as explained in the section on the working principle. The rings are used to hold the workpiece and it rotates and rubbed the workpiece against the lapping plate. These types of lapping processes are used for finishing large quantities of similar parts.
Read more: Understanding Machine
Advantages and disadvantages of lapping
Below are the benefits of lapping in their various applications:
- High accuracy of dimensions.
- Refinement of surface finish.
- An imperfect shape can be corrected.
- Producing close fit between mating surfaces.
- Extreme accuracy in flatness and parallelism is obtained when both sides of a flat workpiece are lapped simultaneously.
- Relief of inherent stresses can be achieved.
- Less heat is generated compared to most other finishing processes.
- Holding devices are not required. That is, workpiece distortion does not occur.
Despite the good advantages of lapping, some limitations still occur. Below are the disadvantages of lapping in their various applications.
- The process is expensive.
- It is a slow process.
- Required semi-skilled operator.
- The initial machine cost is high.
- The process is performed on just a flat surface.
- Maintenance cost is also high.
- Due to the slow production rate, operation costs may be expensive.
The lapping process is a very important finishing process in the industrial world today. The process can remove 0.03. – 0.003 mm from the workpiece. Lapping (and polishing) techniques offer great benefits due to the precision and control with which material can be removed. That is all for this article where I explained the definition, applications, operations, working, and types of lapping process. The advantages and disadvantages are also explained.
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