Master Lapping Process Definition, Working Principle, 2 Types, Material, Advantages, Application [PDF]

Contents

In this article, we will be discussing the definition, working, principle, types, material, advantages, and applications of the Lapping process. We have provided a PDF for the same.

Lapping Process Definition, Working Principle, 7 Types, Material, Advantages, Application [PDF] — ^{Photo By Austopic}

What is a Lapping

Lapping Process is a low-pressure machining process used to increase the dimensional accuracy and surface finish of the workpiece. The lapping process uses fine abrasive particles to perform cutting action on the surface of the workpiece.

The workpiece is rubbed against the lapping plate with the help of a machine or by hand, with powdered abrasive particles or abrasive paste in between. The lapping process smoothens outs the surface of the workpiece, this increases the functionality and aesthetics of the workpiece. It is also used to ensure the correct fit between two workpieces and correct minor imperfections.

Principle of the Lapping

The simple working of a lapping process involves three elements. A workpiece, a lapping plate, and Abrasive particles. Abrasive particles are poured over the lapping plate and the workpiece is rubbed on it. The Abrasive particles remove microscopic material from the workpiece when a force is applied during the relative motion between the plate and the workpiece. The Abrasive particles tend to reduce or flatten the microscopic peaks and valleys present on the surface of the workpiece.

schematic diagram of lapping — ^{Photo from Researchgate}

Characteristics of the Lapping Process

The size of Abrasive grit used in the lapping process varies from 120 to 1200 mesh depending upon desired surface smoothness.
The abrasive used can be in powdered form or can be mixed with some suitable oils or greases called vehicles.
A very small amount of material is removed in the lapping process that is about 0.025mm.
The lapping process can be done manually or with the help of machines.
Materials commonly lapped are hard materials like steel.
The pressure applied during the lapping process is low when compared to other surface finish processes.

How does lapping work

Lapping process is where one or more parts are machined in batches using abrasive mixed with a liquid vehicle, either oil or water-based. The parts being worked on are captured in retaining rings and kept separated by work holders or carriers to prevent damage to their edges. The abrasive is fed onto a flat lap plate surface, and the parts are dragged across it. Lapping aims to create parts with a uniformly smooth and usually flat surface, which exhibits a dull, non-reflective, and multi-directional appearance known as a “matte” finish.

However, there may be slight reflectivity on materials lapped with very small micron size aluminum oxide abrasive, especially if the material is hard and the surface roughness measurement is below 5 micro-inch. Lapped surfaces may also have very light “micro-scratches,” which are usually less than 0.000001″ deep and cannot be measured with a profilometer. These micro-scratches should not be confused with deeper scratches caused by contamination or other factors.

Factors to consider during the Lapping Process

Several factors can affect the lapping process, including the type of abrasive used, the pressure applied, the speed of rotation, and the type of material being lapped. The type of abrasive material used in the lapping process can significantly impact the outcome. The hardness, size, and shape of the abrasive particles can affect the surface quality and material removal rate. Additionally, the pressure applied during the lapping process plays a critical role in achieving the desired finish. Too little pressure can result in inadequate material removal, while excessive pressure can cause deformation or damage to the workpiece.

The speed of rotation is another critical factor that can affect the lapping process. The rotational speed of the lapping plate and the workpiece can impact the material removal rate and surface quality. Higher speeds can lead to greater material removal, but they can also produce more heat, which can cause thermal damage to the workpiece. Lastly, the type of material being lapped is a significant factor in the lapping process. Different materials have varying hardness, brittleness, and ductility, which can affect the lapping process’s outcome. Materials with higher hardness require more force and pressure to remove, while softer materials can be easily damaged during the lapping process.

Types of Lapping Processes

2 types of lapping processes and they are further subdivided as follows

Hand Lapping
- Flat Surface Lapping
- Cylindrical Lapping
Machine Lapping
- Vertical Lapping
- Centerless Lapping
- Spherical Lapping
- Belt Lapping

Machine Lapping Process — ^{Photo By Dreamstime}

Hand Lapping Process

As the name suggests the process of lapping in all the forces are applied manually is called hand lapping. There are two types of hand lapping systems involved in improving the surface quality of the workpiece.

Flat surface lapping

The lapping plate here is made of gray cast iron. This contains some groves which are used to collect the metallic chips and waste Abrasive particles in them. Abrasive grits of the desired size are sprinkled over the lap. Then the workpiece is rubbed carefully on the lap. More amounts of Abrasive particles of the same mesh are added when required. Use of suitable fluid can be done if required.

The process must be carried out by a skilled operator. Once the lapping is done, the lap must be cleaned for the next usage. Using an excess of Abrasive particles may damage the lap. This may result in improper finishing of the job and lap failure.

Cylindrical Lapping

The laps used for the lapping of internal and external surfaces of cylindrical workpieces are made of mild cast iron, copper, or brass. For lapping of the internal surface of a cylinder, the laps are made to have a close fit with the internal diameter. The laps move in random axial motion with respect to the workpiece. This increases the surface finish of the workpiece as well as the laps.

The Abrasive particles are mixed with oil or grease in the process. The laps used for the lapping of the external surface of a cylinder are called ring laps. It is provided with a screw to adjust with different diameters. The workpiece to be lapped is held in a lathe to provide rotational motion. The ring lap is then reciprocated on the rotating workpiece. Abrasive particles mixed with certain oils and greases can be used.

Machine Lapping Process

When lapping operation is done using machinery it is called machine lapping. Listed below are various machine lapping processes used for different types of workpieces.

Vertical Lapping Machine

A vertical lapping setup consists of a lower lap, an upper lap, and a work-holding device. The workpiece is kept on the lower lap and is positioned in a job holder. The upper lap is used to load and unload the workpiece. Abrasive particles mixed with paste-type vehicles are applied on the laps before the operation begins. In the case of lapping a flat surface, the lower lap is held stationary, while in the case of cylindrical lapping, the lower lap is allowed to move.

Various jobs are lapped using vertical lapping machines, for example, precision gauge blocks, rolls of roller bearing, and ball bearing balls. Another type of vertical lapping setup consists of an Abrasive cloth fixed to the lower lap. Identical workpieces can be lapped by moving about the work holder randomly. This is called transposing. The Lower lap must be fixed while machining a flat surface as it may topple.

Centerless lapping machine

A centerless roll lapping consists of a regulating roller, a lapping roller, a workpiece, and a V-notched fiber stick. The regulating roller is powered by a motor to provide rotational motion to the setup. A lapping roller is used to lap the workpiece from the other direction. The diameter of the lapping roller is twice the diameter of regulating the roller. Both the rollers are made up of cast iron, due to their stability and low cost.

The rollers are bonded with Abrasive particles. V notched fiber stick is used to hold the workpiece to be fed between the rollers. The workpiece is fed into the roller at a very slow rate with a reciprocating motion. Material removal takes place due to the action of Abrasive particles of the workpiece. A very fine finish of 0.05 microns can be obtained with the help of centerless lapping. The material removal is very slow in the case of centerless lapping.

Spherical lapping machine

The lapping machine used to lap spherical objects has a different construction. Two spindles are used in the case of spherical lapping. The workpiece to be lapped is attached to the first spindle which gives a rotating motion to the workpiece.

The other spindle is used to hold the tool to a certain angle concerning the workpiece. Pressure is also applied to the workpiece by the tool spindle. As soon as the rotation motion is given to the workpiece the material removal takes place due to the contact between the Abrasive tool and the workpiece.

Belt lapping

Belt lapping uses a belt made of Abrasive clothes used for the lapping process. The belt is driven with the help of a motor. There are two wheels used to drive the belt. The workpiece is manually touched to the belt over the wheel. Material removal takes place after the contact of the workpiece and the moving belt. This is a convenient method of lapping for low-precision jobs. There are no requirements for clamping the workpiece.

Abrasive used for the lapping process

Different types of Abrasives are used for lapping different material hardness.
Abrasives used for lapping hard materials generally are silica carbide and fused alumina.
Abrasives used for lapping soft materials are chromium oxide, unfused alumina, and garnet.

Vehicles used for lapping processes are generally water-soluble oils, vegetable oils, mineral oils, petroleum jelly, or greases. Vehicles must have the following properties.

The particles must be uniformly distributed when mixed with the vehicle. It must not contain lumps.
The viscosity of the vehicles should not be affected by temperature changes.
A vehicle should not evaporate at high temperatures.
It should not promote Corrosion for metal surfaces.
It should be non-toxic in nature.
It should not stick to the workpiece and can be easily removed by simple cleaning.

Materials that can undergo the lapping process

There are various elements originally compounds that can undergo a lapping process. Some of those are Cast iron, Ceramics, Tungsten, Plastics, Carbon compounds, Stainless steel, Bronze, Rubber, and Silicon.

lapping Tool Material — ^{Photo By Catalogue Zodiac}

Lapping process Parameters

Lapping speed: The lapping speed for an ideal lapping operation must range from 1.5 to 4m/s
Lapping pressure: Lapping pressure depends upon the hardness of the material and the Abrasive particles used. Lapping pressure varies from 10 to 30kPa for soft materials and up to 70kPa for hard materials.
Lapping allowance: Lapping allowance is directly proportional to the lapping time. As the lapping allowance increases, lapping time also increases. The lapping allowance also depends on the material being lapped.
Cast iron – 0.2mm
Aluminum alloy – 0.1mm
Soft steel – 0.05 to 0.1mm
Hardened steel – 0.005 to 0.02mm

Here’s a video on lapping process

^{Video by SuburbanTool Inc}

Difference between Lapping and Honing Process

Parameters	Lapping	Honing
Purpose	Lapping is mainly done to achieve high-precision flatness, parallelism, and surface texture/finish.	Honing is done to improve the geometric form, size, and surface texture of cylindrical bores and tubes.
Abrasive used	In lapping, a free abrasive slurry containing abrasive particles is used.	In honing, a bonded abrasive stick or stone is used.
Tool	In lapping, a flat lap or polishing pad is used.	In honing, a honing tool consisting of a set of abrasive sticks or stones is used.
Machine	Lapping is typically done on a machine with a rotating plate and a conditioning ring to hold the abrasive slurry.	Honing is done on a machine with a rotating spindle and an expandable honing mandrel to hold the abrasive sticks or stones.
Material removal rate	Lapping has a lower material removal rate than honing.	Honing has a higher material removal rate than lapping.
Surface finish	Lapping can achieve a surface finish down to a few microinches Ra.	Honing can achieve a surface finish up to 16 microinches Ra.
Tolerance	Lapping can achieve tight tolerances in flatness and parallelism.	Honing can achieve tight tolerances in size, roundness, and straightness of cylindrical bores.
Applications	Lapping is commonly used in the manufacturing of precision parts such as types of gauges, optical lenses, and semiconductor wafers.	Honing is commonly used in the automotive, aerospace, and hydraulic industries for producing high-quality cylinder bores, fuel injectors, and hydraulic valves.

Advantages of the Lapping Process

It increases the surface finish of the workpiece by reducing peaks and valleys on the material surface. It also provides aesthetic touch to the workpiece.
Lapping process also increases the life of the mating parts by reducing the friction between the Mating parts.
It increases the geometry and the dimensions of the workpiece. It also ensures a perfect fit between the workpieces.
No thermal stresses are developed inside the surface of the workpiece due to the minimum heat involved in the process.
The process can be carried out by unskilled labor as well. This is due to the simplicity involved and the absence of computerized controls.
It increases the parallelism between two parts kept parallel to each for various joining operations.

Lapping Advantages and Disadvantages — ^{Photos By Dreamstime}

Disadvantages of the lapping process

Lapping is an expensive process as the Abrasives loss is more. This result is increased use of Abrasive particles for polishing operations, which in turn gives rise to the production cost.
Another disadvantage of the lapping process is that the process is very slow. The metal removal rate in the case of the lapping process is very less. This makes the processing time-consuming which results in decreased production rate.
Waste management becomes a problem in the case of a lapping process. A large amount of Abrasive waste is produced in case of a lapping process. This makes it difficult to dispose of the waste.
Some of the Abrasive compounds may get embedded in the surface of the workpiece which results in later damage of the workpiece.
The process is not generally automated; these results increase labor-intensive and increase the cost of production.

lapping surface polish process — ^{Photo by Wikipedia}

Applications of the Lapping Process

The lapping Process is used for polishing hard and brittle metals which are difficult to be polished using other methods.
It is also used for machining materials like glass due to its slow material removal rates.
The lapping process is widely used for making specimens for metallurgical testing.
The lapping process is used for valve manufacturing due to its accurate uniform material removal feature.
Automotive industries also use lapping processes for various polishing operations.

Lapping Process Applications — ^{Photo By Dreamstime}

Conclusion

In conclusion, lapping process is a precision finishing process that produces smooth and accurate surfaces in a variety of materials. The process involves using abrasive materials and a rotating tool to remove a thin layer of material from the surface being worked on. There are different types of lapping processes, including flat lapping, cylindrical lapping, and centerless lapping, each with unique advantages and applications.

Lapping Process is widely used in aerospace, automotive, medical, and electronics industries, where high precision and surface finish are critical. With its ability to achieve tight tolerances and smooth surface finishes, lapping is a valuable manufacturing process that helps to enhance the performance and durability of precision components.