Water-Jet Cutting

Introduction: In the battle to reduce costs, engineering and manufacturing departments are constantly on the lookout for an edge. The water jet process provides many unique capabilities and advantages that can prove very effective in the cost battle. Learning more about the water jet technology will give us an opportunity to put these cost-cutting capabilities to work. Beyond cost cutting, the water jet process is recognized as the most versatile and fastest growing process in the world. Water jets are used in high production applications across the globe. They compliment other technologies such as milling, laser, EDM, plasma and routers. No poisonous gases or liquids are used in water jet cutting, and water-jets do not create hazardous materials or vapors. No heat effected zones or mechanical stresses are left on a water-jet cut surface. It is truly a versatile, productive, cold cutting process. The water jet has shown that it can do things that other technologies simply cannot. From cutting whisper, thin details in stone, glass and metals; to rapid whole drilling of titanium; for cutting of food, to the killing of pathogens in beverages and dips, the water jet has proven itself unique.
Theory Of Water-jet Cutting: Most water-jet cutting theories explain water-jet cutting as a form of micro erosion as described here. Water-jet cutting works by forcing a large volume of water through a small orifice in the nozzle. The constant volume of water traveling through a reduced cross sectional area causes the particles to rapidly accelerate. This accelerated stream leaving the nozzle impacts the material to be cut. The extreme pressure of the accelerated water particles contacts a small area of the work piece. In this small area the work piece develops small cracks due to stream impact. The water-jet washes away the material that "erodes" from the surface of the work piece. The crack caused by the water-jet impact is now exposed to the water-jet  The extreme pressure and impact of particles in the following stream cause the small crack to propagate until the material is cut through.

Water-jet Cutting Process: Pure water-jet is the original water cutting method.  Water-jet cutting uses only a pressurized stream of water to cut through material. This type of cutting is limited to material with naturally occurring small cracks or softer materials like disposable diapers, tissue paper, and automotive interiors. In the cases of tissue paper and disposable diapers the water-jet process creates less moisture on the material than touching or breathing on it. The figure shows the water-jet cutting process.

   In this process water is increased in pressure by high-pressure pump to about 40000-60000 PSI and is forced through the orifice on to the target material. This high-pressure water on striking the surface performs the machining operation. The potential energy contained in the water is converted in the process to kinetic energy, i.e., into jet velocity, thus achieving its "cutting" effect.

pure water-jet

The basic water-jet process involves water flowing from a pump, through plumbing, and out a cutting head.

   In water-jet cutting, the material removal process can be described as a supersonic erosion process. It is not pressure, but stream velocity that tears away microscopic pieces or grains of material. Pressure and velocity are two distinct forms of energy. The pump’s water pressure is converted to the other form of energy, water velocity by a tiny jewel. A jewel is affixed to the end of the plumbing tubing. The jewel has a tiny hole in it. The pressurized water passes through this tiny opening changing the pressure to velocity. At approximately 40,000 psi the resulting stream that passes out of the orifice is traveling at Mach 2. And at 60,000 psi the speed is over Mach 3.

Applications Of Water-jet Cutting:
• Sheet metal: Stainless steel, carbon steel, high-alloy nickel steels, aluminum, titanium, copper
• Building: Decorative stone, marble, granite, tiles, plasterboard, glass and mineral wool
• Glass: Laminated glass, safety glass, and bulletproof glass
• Foodstuffs: Baked goods, deep-frozen products and fish
• Paper: Cardboard, corrugated cardboard, printing papers
• Miscellaneous: Plywood, leather, textiles, composites, rubber, plastics, sealing materials and foams .

Read More

Friction Welding

Friction welding (FRW) is a welding process that generates heat through mechanical friction between a moving work-piece and a stationary component, with the addition of a lateral force called "upset" to plastically displace and fuse the materials. Technically, because no melt occurs, friction welding is not actually a welding process in the traditional sense, but a forging technique. However, due to the similarities between these techniques and traditional welding, the term has become common. Friction welding is used with metals and thermoplastics in a wide variety of aviation and automotive applications.

Benefits and uses:

• Friction welding techniques are generally melt-free, which avoids grain growth in engineered materials, such as high-strength heat-treated steels.
• Another advantage is that the motion tends to "clean" the surface between the materials being welded, which means they can be joined with less preparation. During the welding process, depending on the method being used, small pieces of the plastic or metal will be forced out of the working mass (flash). It is believed that the flash carries away debris and dirt.
• Another advantage of friction welding is that it allows dissimilar materials to be joined. This is particularly useful in aerospace, where it is used to join lightweight aluminum stock to high-strength steels. Normally the wide difference in melting points of the two materials would make it impossible to weld using traditional techniques, and would require some sort of mechanical connection. Friction welding provides a "full strength" bond with no additional weight. Other common uses for these sorts of bi-metal joins is in the nuclear industry, where copper-steel joints are common in the reactor cooling systems; and in the transport of cryogenic fluids, where friction welding has been used to join aluminum alloys to stainless steels and high-nickel-alloy materials for cryogenic-fluid piping and containment vessels.

Techniques used for friction welding:

1. Spin Welding: Spin welding systems consist of two chucks for holding the materials to be welded, one of which is fixed and the other rotating. Before welding one of the work pieces is attached to the rotating chuck along with a flywheel of a given weight. The piece is then spun up to a high rate of rotation to store the required energy in the flywheel. Once spinning at the proper speed, the motor is removed and the pieces forced together under pressure.This technique is also known as inertia welding,rotational welding or inertial friction welding.
2. Linear Friction welding: Linear friction welding (LFW) is similar to spin welding except that the moving chuck oscillates laterally instead of spinning. The speeds are much lower in general, which requires the pieces to be kept under pressure at all times. This also requires the parts to have a high shear strength. Linear friction welding requires more complex machinery than spin welding, but has the advantage that parts of any shape can be joined, as opposed to parts with a circular meeting point.
3. Friction Surfacing: Friction surfacing is a process derived from friction welding where a coating material is applied to a substrate. A rod composed of the coating material (called a mechtrode) is rotated under pressure, generating a plasticized layer in the rod at the interface with the substrate.

Video Presentation of Inertia Friction Welding:

Read More

Bernoulli Principle (Best Understanding)

Here i am sharing the video of Bernoulli Principle for better understanding.

Read More

Anti-lock Braking System (ABS)

• What is an ABS ?

Anti-lock braking systems (ABS's) are electronic systems that monitor and control wheel slip during vehicle braking. ABS scan improve vehicle control during braking, and reduce stopping distances on slippery (split or low coefficient of friction) road surfaces by limiting wheel slip and minimizing lockup. Rolling wheels have much more traction than locked wheels. Reducing wheel slip improves vehicle stability and control during braking, since stability increases as wheel slip decreases.
 ABS's can be applied to nearly all types of vehicles and can be successfully integrated into hydraulic and air brake systems (including air over hydraulic). This document applies to the ABS's used with air brake systems on commercial vehicles.
 The equipment requirements of FMVSS 121 specify that ABS's on truck-tractors and full trailers must control the brake pressures to at least one front axle and one rear axle. The ABS's on semi-trailers and dollies must control at least one axle of the vehicle. Additionally, the ABS's on tractors must control one of the rear axles with two modulator valves so that the brake pressure on one end of the axle is independent of the brake pressure on the other end. The performance requirements of FMVSS 121 can require an ABS on additional axles.

• How do ABS's works ?

An ABS consists of several key components: electronic control unit (ECU), wheel speed sensors, modulator valves, and exciter rings. Here’s how these components work together:

•  Wheel speed sensors constantly monitor and send electrical pulses to the ECU at a rate proportional to the wheel speed. 
•  When the pulse rates indicate impending wheel lockup, the ECU signals the modulator valve(s) to reduce and/or hold the brake application pressure to the wheel(s) in question.
•  The ECU then adjusts pressure, seeking one which gives maximum braking without risking wheel lockup.
•  When the ECU acts to modulate the brake pressure, it will also (on most vehicles) turn off the retarder (if so equipped) until the risk of lockup is over.
•  The ECU continually checks itself for proper operation. If it detects malfunction/failure in the electrical/electronic system, it will shut down that partof the ABS affected by the problem—or the entire ABS—depending upon the system and the problem. 
•  When this happens, the ABS malfunction lamp lights. 
•  An ABS adjusts brake pressure much faster and more accurately than can drivers. It’s faster because:

  Electronic controls are very fast and ABS modulator valves are physically closer to the brakes than is the driver’s foot brake valve. It is more effective, too, because an ABS can tailor the brake pressure to each wheel or set of wheels to provide maximum braking/stability. Some vehicles also use a traction control system in conjunction with the ABS. Traction control helps the ABS improve vehicle traction by minimizing wheel slip on the drive axle during acceleration. If a wheel on the drive axle starts to slip, the traction control system automatically brakes the wheel slightly, transferring engine torque to the wheels with better traction. If all the drive wheels start to slip, the traction control system may also reduce engine power.Traction control systems are referred to by several different names, depending on the manufacturer. These include: a. Automatic Traction Control (ATC) b. Traction Control (TC) c. Automatic Slip Regulation/Anti-Spin Regulation (ASR)

Read More

Drilling

• Drilling is an operation of producing circular hole in a work-piece by using a rotating cutter called DRILL.
• The machine used for drilling process is called drill machine.
• The drilling operation can also be accomplished in lathe in which drill is held in tailstock and work piece is held by chuck.
• The most common drill tool used is called TWIST DRILL.

DRILL MACHINE: It is the simplest and accurate machine used in production shop. The work piece is held stationary i.e. Clamped in position and the drill rotates to make a hole.

TYPES Of Drilling Machines: 

Sensitive drilling machine: Drill holes from 1.5 mm to 15 mm . Operator senses the cutting action so sensitive drilling machine.

Sensitive drill.

Up-right drilling machine: This type of machine can drill holes up to 50 mm .Table can move vertically and radially.

up-right drill

Radial drilling machine: It the largest and most versatile used form of drilling medium for large and heavy work pieces.

radial drill

Tool Nomenclature:

Precautions for drill machine: 

• Lubrication is important to remove heat and friction.
• Machines should be cleaned after use
• Chips should be removed using brush.
• T-slots, grooves, spindles sleeves, belts, pulley should be cleaned.
• Machines should be lightly oiled to prevent from rusting.

1. 
   
2. 
   

Read More

Advantages and Disadvantages of Submerged Arc Welding

• Advantages and major uses:

1.  high quality of the weld metal.
2.  extremely high deposition rate and speed.
3.  smooth, uniform finished weld with no spatter.
4.  little or no smoke.
5.  no arc flash, thus minimal need for protective clothing.
6.  high utilization of electrode wire.
7.  easy automation for high-operator factor.
8.  normally, no involvement of manipulative skills. 

• Uses: The submerged arc process is widely used in heavy steel plate fabrication work. This includes the welding of structural shapes, the longitudinal seam of larger diameter pipe, the manufacture of machine components for all types of heavy industry, and the manufacture of vessels and tanks for pressure and storage use. It is widely used in the shipbuilding industry for splicing and fabricating subassemblies, and by many other industries where steels are used in medium to heavy thicknesses. It is also used for surfacing and buildup work, maintenance, and repair.
• Disadvantages:

1. A major limitation of submerged arc welding is its limitation of welding positions. The other limitation is that it is primarily used only to weld mild and low-alloy high-strength steels.
2. The high-heat input, slow-cooling cycle can be a problem when welding quenched and tempered steels. The heat input limitation of the steel in question must be strictly adhered to when using submerged arc welding. This may require the making of multipass welds where a single pass weld would be acceptable in mild steel. In some cases, the economic advantages may be reduced to the point where flux-cored arc welding or some other process should be considered.
3. In semiautomatic submerged arc welding, the inability to see the arc and puddle can be a disadvantage in reaching the root of a groove weld and properly filling or sizing.  

Read More

Submerged Arc Welding (SAW)

Submerged arc welding is a process in which the joining of metals is produced by heating with an arc or arcs between a bare metal electrode or electrodes and the work.

The arc is shielded by a blanket of granular fusible material on the work.

Pressure is not used.

Filler metal is obtained from the electrode or from a supplementary welding rod.

b. Equipment.

(1) The equipment components required for submerged arc welding are shown by figure 10-59.

Equipment consists of a welding machine or power source, the wire feeder and control system, the welding torch for automatic welding or the welding gun and cable assembly for semiautomatic welding, the flux hopper and feeding mechanism, usually a flux recovery system, and a travel mechanism for automatic welding.

(2) The power source for submerged arc welding must be rated for a 100 percent duty cycle, since the submerged arc welding operations are continuous and the length of time for making a weld may exceed 10 minutes.

If a 60 percent duty cycle power source is used, it must be derated according to the duty cycle curve for 100 percent operation.

(3) When constant current is used, either ac or dc, the voltage sensing electrode wire feeder system must be used.

When constant voltage is used, the simpler fixed speed wire feeder system is used. The CV system is only used with direct current.

(4) Both generator and transformer-rectifier power sources are used, but the rectifier machines are more popular.

Welding machines for submerged arc welding range in size from 300 amperes to 1500 amperes.

They may be connected in parallel to provide extra power for high-current applications.

Direct current power is used for semiautomatic applications, but alternating current power is used primarily with the machine or the automatic method.

Multiple electrode systems require specialized types of circuits, especially when ac is employed.

(5) For semiautomatic application, a welding gun and cable assembly are used to carry the electrode and current and to provide the flux at the arc.

A small flux hopper is attached to the end of the cable assembly.

The electrode wire is fed through the bottom of this flux hopper through a current pickup tip to the arc.

The flux is fed from the hopper to the welding area by means of gravity.

The amount of flux fed depends on how high the gun is held above the work.

The hopper gun may include a start switch to initiate the weld or it may utilize a "hot" electrode so that when the electrode is touched to the work, feeding will begin automatically.

(6) For automatic welding, the torch is attached to the wire feed motor and includes current pickup tips for transmitting the welding current to the electrode wire.

The flux hopper is normally attached to the torch, and may have magnetically operated valves which can be opened or closed by the control system.

(7) Other pieces of equipment sometimes used may include a travel carriage, which can be a simple tractor or a complex moving specialized fixture. A flux recovery unit is normally provided to collect the unused submerged arc flux and return it to the supply hopper.

(8) Submerged arc welding system can become quite complex by incorporating additional devices such as seam followers, weavers, and work rovers.

Read More