What is lapping process

The method of lapping is carried out primarily to increase accuracy.

What is lapping?

Lapping is a finish machining process in which two surfaces are rubbed together with an abrasive between them by manually or using a machine that used to producing geometrically real surfaces, correcting minor surface imperfections, improving dimensional precision, or making two contact surfaces very close to each other.

Material removal in lapping usually range from 0.003 to 0.03 mm but in many cases it reaches up to 0.08 to 0.1 mm.

Other important advantages of this process have obtained the correction of minor surface imperfections and improvement of surface finish.

Abrasives that used in the lapping process

• Al₂O₃ & SiC
• Cr₂O₃
• B₄C₃
• Diamond 

Factors to consider in Lapping Process 

• Type of material being processed
• Speed of plate
• Pressure on work-piece
• Plate material
• Size and type of abrasive
• Vehicle used
• Flatness of plate
• Feed system
• Method of charging and conditioning the plate
• Plate temperature

It is the process that is performed either manually or by machine. Hand-lapping is done with abrasive powder as a lapping medium and in the machine, lapping is done with abrasive powder or bonded abrasive wheel.

Conclusion 

Lapping is simple yet a beneficial process that can produce highly polished parts end, tight end and thickness tolerance, and flatness unbelievable by other processes. 

Explore more information:

1. What is Honing

What is stress relieving process?

Stress Relieving is applied to both ferrous and non-ferrous alloys and is intended to remove internal residual stresses generated by the prior manufacturing process such as machining, cold rolling and welding. The treatment is not intended to produce important modifications in material structures or mechanical characteristics and is therefore usually limited to comparatively small temperatures.

Carbon steels and alloy steels can be given two forms of stress-relieving : 

• Treatment at typically 150-200°C, after hardening, relieves peak stress without substantially decreasing hardness.
• Treatment at typically 600-680°C provides almost complete stress relief.

The purpose of treatment is not to make significant changes in material structures or mechanical properties and therefore it is usually limited to relatively low temperatures.

Working principle of stress-relieving

The steel parts relief temperature normally ranges from 550 to 650 ° C. The soaking time is approximately one to two hours. After the soaking time, the components should be gently cooled in the furnace or air. In order to prevent stress owing to the difference in material temperature, slow cooling speed is essential, it is particularly essential when stress relieves large components.

Stress relief is to heat the steel below the critical limit at a temperature to eliminate the stress induced by freezing, hair cutting or cutting off the gas.

This process does not change the structure of the material and does not affect its rigidity significantly.

Benefits of stress-relieving  

• Components with close dimensional tolerances must be stress relieved. 
• Parts that are going to be further processed must be stress relieved. 
• By relieving tension, welded structures can be stress-free.
• The component can be relieved stress to minimise stress after machining and the possibility of dimensional changes.

Applications of stress-relieving 

• Stress relieving does not change the structure of the material and does not significantly affect its hardness. 
• Stress relieving should be achieved at temperatures > 600°C before nitrocarburization.
• Copper and brass components can also be stress relieved. 
• Heat treatment for a high-temperature solution is usually required for stainless steels.

What is carburizing?

What is carburizing process?

Carburizing is one of the most widely used surface hardening processes for a long time. 

Carburising is a method to harden low-carbon steel. Carbon atoms are diffused to steel surface after carburisation, quenching is done and steel gets hardened.

Carburizing heat treatment is the introduction of carbon into the surface of the steel and produces a surface which is resistant to wear while maintaining toughness and strength of the core. It occurs when the steel is heated above the critical temperature in a carburizing furnace which contains more carbon than steel contains.

The process involves diffusing carbon into low carbon steel to form a high carbon steel surface.

It is essentially the addition of carbon at the surface of low carbon steels at appropriate temperatures.

Hardening agents :

There are different types of elements or materials that can be used to perform this process as hardening agents. Mostly used hardening agents are following below :

• Carbon monoxide gas ( CO )
• Sodium cyanide and barium carbonate 
• Hardwood charcoal 

Effects of carburizing in material properties :

Mechanical :

• Increased surface hardness.
• Increased wear resistance.
• Increased fatigue or tensile strength.

Physical :

• Grain growth may occur.
• Change in volume may occur.

Chemical :

• Increased surface carbon content.

Now we can discuss about the various carburizing processes commonly used by the industry.

• Pack carburizing 

It is a process in which carbon monoxide derived from a solid compound decomposes at the metal surface into nascent carbon and carbon dioxide.

Nowadays led to reduced use of pack carburizing because of environmental concerns. In this process low carbon steel components are packed in an environment with high carbon content such as carbon powder. 

The components are heated with the production of carbon monoxide, which is called a reducing agent. The steel components are become hardened because of the carbon absorption inside the component. 

Control of this process is difficult because it is difficult to maintain uniform temperatures. It is an effective process in introducing carbon but this method is exceedingly slow. In this process carbon monoxide is given off by coke or hardwood charcoal.

• Gas carburizing 

Gas carburizing is a surface hardening process which is carried out at a very high temperature. 

The parts are surrounded by a carbon-bearing atmosphere that can be continuously replaced and because of that, a high carbon potential can be maintained. 

The gas carburizing process is mostly similar to pack carburizing process aside from the supply of carbon monoxide (CO) gas to the heated furnace and the carbon decomposition. CO gas needs to be contained safely. 

Gas carburizing is the most effective and widely used method for carburizing steel parts in large quantities in many industries.

• Liquid carburizing 

Liquid carburizing is a process used for case hardening of steel or iron made components. 

In this process, the components made from steel are submerged in a liquefied carbon-rich environment. The main component in such baths is cyanide. 

Cases produced by liquid carburizing are lower in nitrogen and higher in carbon than cases produced by cyaniding. However, safety issues have led to baths that are non-toxic that produced similar results. 

Liquid carburizing involves faster heat-up so that cycle times for liquid carburizing are shorter than those for gas carburizing. The components are held in a molten salt that converts carbon into the steel. 

Carbon is diffused inwards producing a hardened case by rapid quenching process. The case produced by carbon diffusion is similar to that produced by the gas carburizing process. Cases that formed by liquid carburizing have low nitrogen and high carbon content.

• Vacuum carburizing :

The vacuum carburizing process involves carburizing under an absolute pressure environment which is free from oxygen. Since the heating environment is oxygen-free, the carburizing temperatures can be improved significantly without border oxidation of the surface or grain. The atmosphere is significantly simplified although the furnace enclosure is more complex. A single component environment containing hydrocarbons like methane and that can be used. 

The higher temperatures increase the solubility of carbon and the diffusion rate that is why the time necessary for case depth is reduced. The carbon potential of the gas in deep recesses and blind holes is rapidly depleted as vacuum carburizing is carried out under very low pressures and the furnace flow rate of the carburizing gas is very low.

Unless this gas is replaced, a great non-uniformity in case of depth over the surface of the part is likely to occur. The gas pressure is increased significantly, another problem arises, that of free-carbon formation, or sooting is an effort to overcome this problem.

Therefore, in order to obtain uniform depth over complex shape, the gas pressure must be increased periodically to refill the down atmosphere in recesses and then reduced again to the operating pressure. 

• Plasma carburizing 

Plasma carburizing is environment-friendly. 

With the use of plasma carburizing improve characteristics such as wear and corrosion resistance, hardness and load-bearing capacity with an even treatment of components with complex geometry.

In plasma carburization method, plasma impinges positive carbon ions on the surface of a steel part that used as a cathode. 

The primary difference between standard and plasma carburization is that plasma techniques achieve reduced carburizing times. 

Insignificant industrial plants, plasma carburization used rises because it improved the surface features of different steels and particularly stainless steels.

What is honing

Introduction of the Honing Process 

The process of honing that produces a good surface on a metal workpiece by scrubbing against it an abrasive stone and specifying the surface finish in the micro finish ranges.

Honing can consistently produce finishes as fine as 4μ inches and ever finer finishes are possible too. It also can remove as little as 0.0001 inches of material or as much as 0.125 inches. However, usually, only 0.002 inches to 0.020 inches of material is left on the diameter of honing. So honing is mainly used to correct some out of roundness, taper, tool marks, and axial distortion. 

Honing consists of a tool with three or more abrasive stones that are rotated by controlling pressure and velocity while in contact with the workpiece to obtain precise configuration and finish.

The stones are made of silicon carbide, oxide of aluminium, cubic nitride or diamonds.

Why Honing?

Honing is the cost-effective machining process for removing stock, generating exacting, bore tolerance, bore polishing, finishing bore of almost any material such as-sprayed coating, CGI, ceramics etc. 

What is a Honing Operation?

The tool is rotated manually and the workpiece is passed back and over the tool. The tool is given a slow reciprocal motion as it rotates for precision honing. Honing stones can be loosely held in holders, cemented in holders directly, or cast into plastic tabs held in holders.
The honing tool can be made in such a way that a floating action prevails between the tool and the work and any pressure exerted on the tool can be transmitted to all sides equally. Coolants are essential to this process in order to flush away small chips and maintain uniform temperatures.

Honing tools 

Honing process performed by the tool, including the motion of lifting, turning and feeding. These kinematics give the typical honing angle to this process. The feed movement causes the tool to spread radially, making contact with the bore walls by the abrasive. This is created by an electromechanical feed system, which allows the feed force to be controlled in adjustable limits.

Honing is done as an expedient on general-purpose machines like lathe, drill press, and portable drills but it is possible to obtain more economic results by honing machines for production work.

There are two general types of honing machine one is horizontal and another one is vertical. 

The honing process in a wide variety of materials offers advantages of low capital equipment cost, high metal removal rates, and extreme precision of 0.001 mm.

Honing can correct parts that are not square within limits which are used to correct some out of roundness, taper, tool marks and axial distortion.

Advantages of the Honing Process 

• Material removal in all materials regardless of hardness. 
• Any degree of surface finish in a part. 
• The high stock removal rate is up to 12 times faster than internal grinding. 
• Low-cost simple fixture
• Due to the lower pressures used in honing and the resulting lower fixing pressures, thin-walled parts are less likely to have distortion.
• The precision produced by honing is independent of the length of the bore.
• Honing maintains the original bore centreline.
• Bores are corrected with the least possible amount of material removal.

Applications of Honing Process

Ideal for finishing the internal surfaces of I.C. engine cylinders, hydraulic cylinders and other cylinders where retention of lubricants film over the surface is important functionally. It is mostly used for finishing automobile crankshaft journals.

Explore more information:

1. What is Lapping
2. What is Burnishing
3. What is Deburring
4. What is Polishing

What is hardening?

Hardening is a metallurgical metalworking process used to increase the hardness and strength of a metal. The hardness is directly proportional to the uniaxial.

Hardening is a way to make the steel knife harder by first heating the steel knife to between 1050 and 1090 ° C (1922 and 1994 ° F) and then immediately cooling it will be called quenching it, making the steel knife much harder but also more brittle.

The hardening process has three steps :

• The specimen to heat depends upon the carbon content.
• Sock at that temperature for sufficient time.
• Quenching is called fast cooling. 

The hardness of metal at the location of the imposed strain is directly proportional to the uniaxial yield stress.

For hardening of steel required a change in structure from the body-centered cubic structure to the face-centered cubic structure while BCC structure found at room temperature and FCC structure found in the austenitic region.

• If suddenly quenched, the Martensite is formed. This is a very strong and brittle structure. 
• If slowly quenched, it would form Austenite and Pearlite which is a partly hard and partly soft structures. 
• It would mostly be extremely soft Pearlite if the cooling rate is extremely slow.

Purpose of hardening?

• The main purpose is to develop high hardness. 
• To improve wear resistance for steel tool. 
• To improve tensile strength for structural steel. 
• To improve yield strength for spring steel. 

Factors affecting the hardening process 

• Chemical composition 
• Hardening cycle
• Size and shape of steel part
• Homogeneity and grain size of austenite
• Quenching media 
• The surface condition of the metal

Applications of hardening 

• High-strength construction material 
• Machine cutting tools like drill bits, taps, lathe tools 
• Knife blades 
• Bearings
• Armor plating 

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1. Anodizing

What is tempering?

What is the tempering process?

Tempering is a heat treatment process in metallurgy used to increase the toughness of iron-based alloy is mostly performed after hardening. Tempering operation depends on the steel and the tempering temperature.

Purpose of tempering 

• Adjust the strength, hardness, plasticity and toughness of the workpiece. 
• Eliminate residual stress during quenching and prevent cracking. 
• Improve the processability. 

How the tempering process is performed?

• First of all preheating previously quenched or normalized steel to a temperature below the critical range.
• Holding it for some time.
• The cooling process is again performed to obtain the desired mechanical properties. 

The hardness and strength obtained by tempering are depended upon the temperature at which tempering is carried out. If temperatures are high ductility also high, but low strength and hardness. 

This operation is performed on all carbon steels that have been hardened, in order to reduce the brittleness of the metal, so that they can be used effectively in desired applications.

Benefits of tempering 

• Tempering reduces hardness in material and increases the toughness.
• Material properties such as hardness/toughness ratio can be adapted to a specific application.

What is annealing?

What is the annealing process?

Annealing is a heat treatment process in the field of metallurgy and materials science that alters a physical and sometimes chemical property of a material to increase its ductility and reduce its hardness and make it more workable and this process used to bring a metal closer to its equilibrium state.

Annealing is a process of heat treatment used to bring a metal closer to its state of equilibrium. Annealing is the heating process of metal at a particularly high temperature held there for a period of several hours to several days and then allowing it to cool down.

How annealing can be performed?

Heating the steel in a furnace to a point not exceeding 50⁰ above or upper critical point in the annealing process and then holding it at that temperature for a considerable time likely to convert the entire steel into the austenite form for about 30 to 50 minutes after that a medium of hot sand or hot ashes or hot time dust allows the steel to cool down slowly. The cooling level must be sustained at 150-2000 per hour. Once this process has been finished, the formed metals are called annealed metal which is relatively soft and can be cut and shaped more easily, so when pressure is applied they bend easily.

Purpose of the annealing process

• To increase ductility and relieve internal stresses that contribute to brittleness.
• To reduce hardness, improve plasticity.
• To increases the toughness and homogeneity of metals.
• For improve machinability.
• Annealing softens the metal but working on the cold condition, it becomes hard and again works on the metal without any cracks, it should be softened by an annealing process.
• Eliminate internal stresses and process hardening to prevent cracking. 

Classification of annealing 

According to heating temperature annealing methods is divided into two types. 

Phase change recrystallization annealing above the critical temperature. 

• Complete annealing 
• Diffusion annealing 
• Incomplete annealing 
• Spherification annealing 

Phase change recrystallization annealing below the critical temperature. 

• Recrystallization annealing 
• Stress annealing

Advantages of annealing 

• It softens the steel.
• It reduces thermal stresses which occur due to a temperature gradient.
• It enhances and improves the machinability of steel.
• It increases the ductility of steel.
• It enhances the toughness of steel.
• It improves the homogeneity in steel.
• The grain size of the steel is refined by annealing.
• It prepares the steel for further heat treatment.

Disadvantages of annealing 

• The electrical resistance of the metal is decreased. 

What is normalizing? | Applications

What is the normalizing process?

Normalizing is a heat-treatment process. It is applied to ferrous materials. The objective of this process is to enhance the mechanical properties of the material by refining the microstructure.

In the normalizing process first of all, metal is heating it to a specific temperature and then letting the material cool to room temperature and the material can be normalized.

In the normalizing of steel, it is heated to slightly above its upper critical temperature and held for sufficient time to allow new smaller metal grains to form and high energy grain shapes to coalesce. This is known as grain refinement and it forms a more uniform metal product. 

Normalization is a type of heat treatment used to relieve stress thereby improving ductility and toughness. 

Normalizing Process is determined by 

• The heating temperature of the metal (20° - 50° C above the critical upper point)
• Holding Time  (Minimum time that is required to achieve uniform heating)
• Cooling Rate (150°-250°C per hour)

Normalizing is performed on structures or the structural components that will be subjected to machining because it improves the machinability of carbon steels. This process is less expensive than annealing.

Applications of normalizing 

• It is used in some plate mills in the production of large forging such as railroad wheels and axles and some bar products.
• For sheet metal forming and also for brackets, normalization is used.
• Used in stress relieve of castings.
• For recovery, the original mechanical properties of forged or cold worked steel.

What is turning? | Advantages | Applications

Turning operation is performed on the lathe machine and is a form of machining, a material removal process, which is used to create rotational parts by cutting away unwanted material. 

Turning is a typical process of the machining at a small radial depth of cut and multiple passes are made until the end diameter is reached. A single-point turning tool moves axially along the side of the workpiece removing material to form various characteristics including step tapers, chamfers, and contours.

Turning can be done manually on the lathe machine, which often requires the operator's continuous supervision or the use of an automated lathe. Nowadays the most common type of such automation is computer numerical control better known as CNC. CNC Turning services

The workpiece which itself is attached to the turning machine and allowed to rotate at high speeds the cutter is typically a single-point cutting tool for some operations make use of multi-point tools the cutting tool gives feeds into the rotating workpiece and cuts away material in the form of small chips to create the desired shape. 

Turning is used to produce rotational, typically axisymmetric, parts with many characteristics, such as holes, grooves, threads, tapers, steps of different diameters, and also contoured surfaces. It is also commonly used as a secondary process to add or refine features on parts that were manufactured using a different process.

Turning process capabilities:

• Shapes - Thin-walled cylindrical and also solid cylindrical 
• Part size - Diameter range is 0.02 to 80 in 
• Materials - Metals such as Alloy Steel, Carbon Steel, Cast Iron, Stainless Steel, Aluminum, Copper, Magnesium, Zinc
• Materials - Ceramics such as composites, lead, nickel, Tin, Titanium, Elastomer, Thermoplastics, Thermosets
• Surface finish - 2 to 250 µin
• Tolerance - Typical +0.001 in and Feasible up to + or - 0.0002 in 

Advantages of the turning process:

• All materials are compatible. 
• Very good tolerance. 
• Short lead time. 
• No high skilled operator required. 
• The material removal rate is flexible. 

Disadvantages of the turning process:

• Limited to rotational parts. 
• Part may require several operations and machines. 
• High equipment cost. 
• Significant tool wear. 
• A large amount of scrap. 

Applications of the turning process:

• Turning process is used for machine components, shafts, and engine components. 
• It is used to produce rotational, axisymmetric parts such as holes, grooves, threads, tapers, different diameter steps, and even contoured surfaces. 

What is rolling process? | Working principle | Types

The rolling process is a very economical process for producing large volumes of material with a constant cross-section. It is one of the most important and widely used industrial metal forming operations providing the final product with high production and close control.

Working principle of rolling

Rolling is a process where the metal is compressed to reduce its cross-sectional area between two rotating rolls. This is one of the most widely used of all the metalworking process, because of its higher productivity and low cost. Rolling would be able to produce components having a constant cross-section throughout its length. Many shapes such as L, I, T are possible, but not very complex shapes. Special sections such as railway wagon wheels can also be produced by rolling individual pieces.

Working principle of rolling 

Roll passes 

The final rolled products such as plates, flats, sheets, rounds and sections are obtained in a number of passes starting from billets or slabs. The roll passes sequence can be broadly classified into three types. 

• Break down pass :

There are used for reducing the cross-sectional area nearer to what is desired. This is the first pass of the sequence. 

• Roughing pass :

In this pass also, the cross-section gets reduced, but along with it, the shape of the rolled material comes nearer to the final shape. 

• Finishing pass :

This is the final pass, which gives the required shape of the rolled section. Generally, the finishing pass follows a leader pass. 

Rolling arrangement 

The arrangement of rolls in the rolling operation is also called a rolling stand. It varies depending on the application. The different possible configuration is presented below. 

Rolling Arrangement

The first one is the two high non-reversing rolling stand arrangement, is the most common arrangement. In this, the rolls always move in only one direction. Another 2-high rolling stand arrangement is the same but the direction of roll rotation can be reversed. 

The three high rolling mill is used for rolling of two continuous passes in a rolling sequence without reversing the drives. 

A four-high rolling mill is essentially a two-high rolling mill, but with small-sized rolls. The other two rolls are backup rolls for providing the necessary rigidity to the small rolls. A better backup with a cluster arrangement of rolls can be provided to the small rolls. 

Generally, the rolls are made of chilled cast iron, carbon steel and alloy steel. The smaller rolls may be made of hard materials like tungsten carbide.

Types of the rolling process 

The rolling process mainly divided into two types 

• Hot Rolling 
• Cold Rolling 

Hot Rolling 

Hot rolling is a process of milling that involves rolling the steel at a high temperature (usually above 1700°F) above the recrystallization temperature of the steel. It can be easily shaped and formed when steel is above the recrystallization temperature, and the steel can be made in much larger sizes. 

At the time of scaling, the major problem occurred. During the hot rolling process, no dimensional precision is maintained for hot rolled steel. 

Hot rolling can improve the processing performance of metals and alloys because coarse grains during foundry are broken, the cracks are healed, casting defects are reduced and eliminated hence, cast microstructure is transformed into a deformed structure to improve processing properties is the main advantage. The hot-rolled steel of various sections has residual stress caused by uneven cooling that has some influence on the performance of steel member under external force. Such as stability, deformation, fatigue and other aspects may have adverse effects is the main disadvantage. 

Cold Rolling 

Cold rolling is a process that introduces the sheet metal or strip stock between rollers and then compresses and squeezes it. The cold-rolled sheet can be manufactured under different conditions such as skin-rolled, quarter hard, half-hard, full hard depending on how much cold work has been performed.

In a cold rolling metal passes through rollers at temperatures below its recrystallization temperature so that increases the yield strength and hardness of the metal.

Commonly cold-rolled products include strips, sheets, bars and rods that are usually smaller than their counterparts that are hot rolled.

This process actually increases strength by up to 20 per cent through strain hardening and good dimensional accuracy and surface finish are the main advantages of cold rolling. There will be residual stress on the cross-section, which will affect the buckling resistance of the steel is the main disadvantages.