Laser beam welding

Laser beam welding (LBW) is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications, such as in the automotive industry.

Operation

Like electron beam welding (EBW), laser beam welding has high power density (on the order of 1 Megawatt/cm²(MW)) resulting in small heat-affected zones and high heating and cooling rates. The spot size of the laser can vary between 0.2 mm and 13 mm, though only smaller sizes are used for welding. The depth of penetration is proportional to the amount of power supplied, but is also dependent on the location of the focal point: penetration is maximized when the focal point is slightly below the surface of the workpiece.

A continuous or pulsed laser beam may be used depending upon the application. Milliseconds long pulses are used to weld thin materials such as razor blades while continuous laser systems are employed for deep welds.

LBW is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminum, and titanium. Due to high cooling rates, cracking is a concern when welding high-carbon steels. The weld quality is high, similar to that of electron beam welding. The speed of welding is proportional to the amount of power supplied but also depends on the type and thickness of the workpieces. The high power capability of gas lasers make them especially suitable for high volume applications. LBW is particularly dominant in the automotive industry.^[1][2]

Some of the advantages of LBW in comparison to EBW are as follows: the laser beam can be transmitted through air rather than requiring a vacuum, the process is easily automated with robotic machinery, x-rays are not generated, and LBW result in higher quality welds.

A derivative of LBW, laser-hybrid welding, combines the laser of LBW with an arc welding method such as gas metal arc welding. This combination allows for greater positioning flexibility, since GMAW supplies molten metal to fill the joint, and due to the use of a laser, increases the welding speed over what is normally possible with GMAW. Weld quality tends to be higher as well, since the potential for undercutting is reduced.^[3]

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Equipment

• The two types of lasers commonly used in are solid-state lasers and gas lasers (especially carbon dioxide lasers and Nd:YAG lasers).
• The first type uses one of several solid media, including synthetic ruby and chromium in aluminum oxide, neodymium in glass (Nd:glass), and the most common type, crystal composed of yttrium aluminum garnet doped with neodymium (Nd:YAG).
• Gas lasers use mixtures of gases like helium, nitrogen, and carbon dioxide (CO2 laser) as a medium.
• Regardless of type, however, when the medium is excited, it emits photons and forms the laser beam.

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Solid state laser

Solid-state lasers operate at wavelengths on the order of 1 micrometer, much shorter than gas lasers, and as a result require that operators wear special eyewear or use special screens to prevent retina damage. Nd:YAG lasers can operate in both pulsed and continuous mode, but the other types are limited to pulsed mode. The original and still popular solid-state design is a single crystal shaped as a rod approximately 20 mm in diameter and 200 mm long, and the ends are ground flat. This rod is surrounded by a flash tube containing xenon or krypton. When flashed, a pulse of light lasting about two milliseconds is emitted by the laser. Disk shaped crystals are growing in popularity in the industry, and flashlamps are giving way to diodes due to their high efficiency. Typical power output for ruby lasers is 10–20 W, while the Nd:YAG laser outputs between 0.04–6,000 W. To deliver the laser beam to the weld area, fiber optics are usually employed.

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Gas laser

Gas lasers use high-voltage, low-current power sources to supply the energy needed to excite the gas mixture used as a lasing medium. These lasers can operate in both continuous and pulsed mode, and the wavelength of the laser beam is 10.6 μm. Fiber optic cable absorbs and is destroyed by this wavelength, so a rigid lens and mirror delivery system is used. Power outputs for gas lasers can be much higher than solid-state lasers, reaching 25 kW.^[4]

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Fiber laser

In fiber lasers, the gain medium is the optical fiber itself. They are capable of power up to 50 kW and are increasingly being used for robotic industrial welding.

Plastic Sealing/Welding Technologies

The purpose of this article is to outline the most commonly used heat sealing technologies in the Industrial Fabrics market using Engineered Textiles with Polymer coatings. Advancements in industrial materials/fabrics, such as greater heat resistance and strength, stronger weaves and coatings, and consistency roll to roll have opened the market up to new applications. These new applications have created a greater demand for sealing technologies that deliver more consistency and speed.

For example, we now have flexible hurricane shields, inflatable aircraft slides, fire resistant clothing, and countless new military products. Applications also exist in the Automotive industry, Photography products, Media storage,and retail promotion.

Common Product examples

Loose leaf binders, Checkbooks, Passport holders, and Shower curtains.

Radio Frequency Welding (RF)

Radio frequency welding is a very mature technology that has been around since the 1940s. Two pieces of material are placed on a table press that applies pressure to both surface areas. Dies are used to direct the welding process. When the press comes together, high frequency waves (usually 27.12 MHz) are passed through the small area between the die and the table where the weld takes place. This high frequency (radio frequency) field causes the molecules in certain materials to move and get hot, and the combination of this heat under pressure causes the weld to take the shape of the die. RF welding is fast. This type of welding is used to connect polymer films used in a variety of industries where a strong consistent leak-proof seal is required. In the Industrial Fabrics Industry, RF is most often used to fuse/weld vinyl (PVC) and polyurethane(PU) coated fabrics. This is a very consistent method of welding.

Please note that Exposure conditions experienced by RF heater operators can cause elevated body temperature, eye irritation, RF burns, and some neurological problems. To reduce exposure conditions the use of Electromagnetic shielding should be used as much as possible without hindering the manufacturing process.

The most common materials used in Radio Frequency Welding are Thermoplastics such as PVC and Polyurethane. It is also possible to weld other polymers such as Nylon, PET, EVA and some ABS Resins.

Hot Air/wedge Welding

Hot air welding uses hot air or a wedge to heat the coating on the fabric where it is to be bonded together. A Nozzle or heated wedge is positioned between two rollers that pull the material through the machine. As the material is pulled through the machine, hot air is applied to the surfaces to be fused together. Pressure from the rollers and heat form the hot air cause the plastic to fuse as the plastic cools. Like Radio Frequency RF—thermal welding is fast.

Ultrasonic Welding

Ultrasonic welding like radio frequency welding creates heat through friction, however,the heat is created between two layers of material rather than within the material itself. It uses a vibrating tool (die) to create the heat. Ultrasonic can be used on almost all plastic material. It is the fastest heat sealing technology available. It is a rather new technology for Industrial Fabric applications, however it can be more costly to weld large surface areas.

Oxy-fuel Welding and Cutting

Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas welding in the U.S.) and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouche and Charles Picard became the first to develop an oxygen-acetylene welding machine in 1903.^[1]

Oxy-fuel is one of the oldest welding processes, though in recent years it has become less popular in industrial applications. However, it is still widely used for welding pipes and tubes, as well as repair work. It is also frequently well-suited, and favored, for fabricating some types of metal-based artwork. Oxyfuel equipment is versatile, lending itself not only to some sorts of iron or steel welding but also to brazing, braze-welding, metal heating (for bending and forming), and also oxyfuel cutting.

In oxy-fuel welding, a welding torch is used to weld metals. Welding metal results when two pieces are heated to a temperature that produces a shared pool of molten metal. The molten pool is generally supplied with additional metal called filler. Filler material depends upon the metals to be welded.

In oxy-fuel cutting, a cutting torch is used to heat metal to kindling temperature. A stream of oxygen then trained on the metal combines with the metal which then flows out of the cut (kerf) as an oxide slag ^[2].

Torches that do not mix fuel with oxygen (combining, instead, atmospheric air) are not considered oxy-fuel torches and can typically be identified by a single tank (Oxy-fuel welding/cutting generally requires two tanks, fuel and oxygen). Most metals cannot be melted with a single-tank torch. As such, single tank torches are typically used only for soldering and brazing, rather than welding.

Uses

Oxy-gas torches are used for or have been used for:

• Welding metal: see below.
• Cutting metal: see below.
• Also, oxy-hydrogen flames are used:
  • In Stone Work for "flaming" where the stone is heated and a top layer crackles and breaks. A steel circular brush is attached to an angle grinder and used to remove the first layer leaving behind a bumpy surface similar to hammered bronze.
  • In the glass industry for "fire polishing".
  • In jewelry production for "water welding" using a "water torch". [1].
  • Formerly, to heat lumps of quicklime to obtain a bright white light called limelight, in theatres or optical ("magic") lanterns.
  • Formerly, in platinum works, as platinum is only fusible in the oxy-hydrogen flame and in an electric furnace.

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Apparatus

The apparatus used in gas welding consists basically of an oxygen source and a fuel gas source (usually cylinders), two pressure regulatorsand two flexible hoses (one of each for each cylinder), and a torch. This sort of torch can also be used for soldering and brazing. The cylinders are often carried in a special wheeled trolley.

There have been examples of oxyhydrogen cutting sets with small (scuba-sized) gas cylinders worn on the user's back in a backpack harness, for rescue work and similar.

There are also examples of pressurized liquid fuel cutting torches, usually using gasoline. These are used for their increased portability.

Welding Procedure Specification

A Welding Procedure Specification (WPS) is a formal document describing welding procedures. According to the American Welding Society (AWS), a WPS provides in detail the required welding variables for specific application to assure repeatability by properly trainedwelders and welding operators.

The American Society For Mechanical Engineers (ASME) similarly defines Welding Procedure Specification (WPS) as a written document that provides direction to the welder or welding operator for making production welds in accordance with Code requirements.

The American Welding Society defines welding Procedure Qualification Record (PQR) as a record of welding variables used to produce an acceptable test weldment and the results of tests conducted on the weldment to qualify a Welding Procedure Specification. The American Society of Mechanical Engineers (ASME), similarly defines welding Procedure Qualification Record (PQR) as a record of variables recorded during the welding of the test coupon. The record also contains the test results of the tested specimens.

Covered Arc-Welding Electrode

A covered arc welding electrode includes a steel core wire and a flux which is applied to the outside periphery of said steel core wire. The welding electrode can form a superior crack-resisting weld zone even if fluctuating stresses are continually applied to a base metal while the base metal is welded. The flux includes 40 to 60% metal carbonate, 10 to 25% metal fluoride and 4 to 25 metal oxide by weight. The flux comprises 24 to 32% of the total weight of said electrode. The composition of the welding electrode includes 0.005 to 0.05% carbon, 0.1 to 1.1% silicon, 1.5 to 2.5% manganese, not more than 0.007% sulfur and not more than 0.25% nickel by weight and the manganese/sulfur ratio is more than or equal to 350 to 1. In addition, the welding electrode can include 0.01 to 0.10% rare earth metal by weight. In which case, the Mn content may be 1.0 to 2.5% by weight and the manganese/sulfur ratio may be more than or equal to 270 to 1. In addition, the composition of the welding electrode can include titanium and zirconium, the total content of which may be less than or equal to 1.2% the total weight of the electrode, and/or aluminum and magnesium, the total content of which may be less than or equal to 1.2% of the total weight of the electrode.

1. A covered arc welding electrode comprising:
a flux including 40 to 60% metal carbonate, 10 to 25% metal fluoride and 4 to 25% metal oxide by weight; and a steel core wire, onto the outer periphery of which said flux is applied so as to comprise 24 to 32% of the total weight of said electrode, said electrode as a whole being comprised of 0.005 to 0.05% carbon, 0.1 to 1.1% silicon, 1.5 to 2.5% manganese, not more than 0.007% sulfur and not more than 0.25% nickel by weight and in which the manganese/sulfur ratio is more than or equal to 350 to 1.

2. A covered arc-welding electrode as set forth in claim 1, further comprising titanium and zirconium, the total content of which is less than or equal to 1.2% of the total weight of the electrode.

3. A covered arc-welding electrode as set forth in claim 2, further comprising aluminum and magnesium, the total content of which is less than or equal to 1.2% of the total weight of the electrode.

4. A covered arc-welding electrode as set forth in claim 1, further comprising aluminum and magnesium, the total content of which is less than or equal to 1.2% of the total weight of the electrode.

5. A covered arc-welding electrode comprising:
a flux including by weight 40 to 60% metal carbonate, 10 to 25% metal fluoride and 4 to 25% metal oxide; and a steel core wire, onto the outer periphery of which said flux is applied so as to comprise 24 to 32% of the total weight of said electrode;
said electrode as a whole being comprised of 0.005 to 0.05% carbon, 0.1 to 1.1% silicon, 1.0 to 2.5% manganese, not more than 0.007% sulfur, not more than 0.25% nickel and 0.01 to 0.10% rare earth metal by weight and in which the manganese/sulfur ratio is more than or equal to 270 to 1.

6. A covered arc-welding electrode as set forth in claim 5, further comprising titanium and zirconium, the total content of which is less than or equal to 1.2% of the total weight of the electrode.

7. A covered arc-welding electrode as set forth in claim 6, further comprising aluminum and magnesium, the total content of which is less than or equal to 1.2% of the total weight of the electrode.

8. A covered arc-welding electrode as set forth in claim 5, further comprising aluminum and magnesium, the total content of which is less than or equal to 1.2% of the total weight of the electrode.

Safety Issues

Welding can be a dangerous and unhealthy practice without the proper precautions; however, with the use of new technology and proper protection the risks of injury or death associated with welding can be greatly reduced.

[edit] Heat and sparks
Because many common welding procedures involve an open electric arc or flame, the risk of burns is significant. To prevent them, welders wear protective clothing in the form of heavy leather gloves and protective long sleeve jackets to avoid exposure to extreme heat, flames, and sparks.

[edit] Eye damage
The brightness of the weld area leads to a condition called arc eye in which ultraviolet light causes inflammation of the cornea and can burn the retinas of the eyes. Goggles and helmets with dark face plates are worn to prevent this exposure and, in recent years, new helmet models have been produced featuring a face plate that self-darkens upon exposure to high amounts of UV light. To protect bystanders, transparent welding curtains often surround the welding area. These curtains, made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc, but should not be used to replace the filter glass used in helmets.[26]
Those dark face plates must be much darker than those in sunglasses or blowtorching goggles. Sunglasses and blowtorching goggles are not adequate for arc welding protection.
In 1970, a Swedish doctor, Åke Sandén, developed a new type of welding goggles that used a multilayer interference filter to block most of the light from the arc. He had observed that most welders could not see well enough, with the mask on, to strike the arc, so they would flip the mask up, then flip it down again once the arc was going: this exposed their naked eyes to the intense light for a while. By coincidence, the spectrum of an electric arc has a notch in it, which coincides with the yellow sodium line. Thus, a welding shop could be lit by sodium vapor lamps or daylight, and the welder could see well to strike the arc. The Swedish government required these masks to be used for arc welding, but they were not used in the United States. They may have disappeared.[27]

[edit] Inhaled matter
Welders are also often exposed to dangerous gases and particulate matter. Processes like flux-cored arc welding and shielded metal arc welding produce smoke containing particles of various types of oxides. The size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger. Additionally, many processes produce various gases (most commonly carbon dioxide and ozone, but others as well) that can prove dangerous if ventilation is inadequate. Furthermore, the use of compressed gases and flames in many welding processes pose an explosion and fire risk; some common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.[28]

[edit] Interference with pacemakers
Certain welding machines which use a high frequency AC current component have been found to affect pacemaker operation when within 2 meters of the power unit and 1 meter of the weld site[29].

Consumable Electrode Methods

One of the most common types of arc welding is shielded metal arc welding (SMAW), which is also known as manual metal arc welding (MMA) or stick welding. An electric current is used to strike an arc between the base material and a consumable electrode rod or 'stick'. The electrode rod is made of a material that is compatible with the base material being welded and is covered with a flux that protects the weld area from oxidation and contamination by producing CO2 gas during the welding process. The electrode core itself acts as filler material, making a separate filler unnecessary. The process is very versatile, requiring little operator training and inexpensive equipment. However, weld times are rather slow, since the consumable electrodes must be frequently replaced and because slag, the residue from the flux, must be chipped away after welding.[16] Furthermore, the process is generally limited to welding ferrous materials, though specialty electrodes have made possible the welding of cast iron, nickel, aluminium, copper and other metals. The versatility of the method makes it popular in a number of applications including repair work and construction.[17]
Gas metal arc welding (GMAW) is a semi-automatic or automatic welding process that uses a continuous wire feed as an electrode and an inert or semi-inert shielding gas to protect the weld from contamination. When using an inert gas as shield it is known as Metal Inert Gas (MIG) welding. A constant voltage, direct current power source is most commonly used with GMAW, but constant current systems as well as alternating current can be used. GMAW welding speeds are relatively high due to the automatically fed continuous electrode, but is less versatile because it requires more equipment than the simpler SMAW process. Originally developed for welding aluminium and other non-ferrous materials in the 1940s, GMAW was soon applied to steels because it allowed for lower welding time compared to other welding processes. Today, GMAW is commonly used in industries such as the automobile industry, where it is preferred for its versatility and speed. Because it employs a shielding gas, however, it is rarely used outdoors or in areas of air volatility.[18]
A related process, flux-cored arc welding (FCAW), uses similar equipment but uses wire consisting of a steel electrode tube surrounding a powder fill material. This cored wire is more expensive than the standard solid wire and generates extra shielding gas and/or slag, but it permits higher welding speed and greater metal penetration.[19]
Submerged arc welding (SAW) is a high-productivity automatic welding method in which the arc is struck beneath a covering layer of flux. This increases arc quality, since contaminants in the atmosphere are blocked by the flux. The slag that forms on the weld generally comes off by itself and, combined with the use of a continuous wire feed, the weld deposition rate is high. Working conditions are much improved over other arc welding processes since the flux hides the arc and no smoke is produced. The process is commonly used in industry, especially for large products.[20] As the arc is not visible, it requires full automatization. In-position welding is not possible with SAW.