Selecting Welding Services  Selecting fabrication 

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Welding and fabrication services are businesses based upon their capabilities to provide customized metal processing. 'Metal fabrication' is a broad term—encompassing welding as well as blacksmithing, boilermaking, millwrighting, and ironworking. Capabilities are not typically limited to one service and CAD/CAM support, field operations, machining, prototyping, surfacing, and structure construction are common with these service businesses, also called 'fab shops.' Due to the inherent danger of these procedures, tasks are outsourced to contractors who are able to complete jobs within their service scope. Many considerations must be accounted for, including the service's location (or mobile capabilities), production volume, and experience.

 

In many instances contractors, equipment manufacturers, and resellers will contract welding and fabrication shops in a bidding process. Government-funded jobs are often required to undergo competitive bidding.

 

Welding Services

Through coalescence metals and thermoplastics are adhered by high heat and/or pressure. Many methods of welding exist, though the science is always based upon the aforementioned principle.

Video credit: Hobart Welders via Youtube

 

Types of Arc Welding

  • Flux-cored arc welding (FCAW) requires a constant, consumable electrode with a flux and constant voltage. A shielding gas is typically unnecessary. This is a portable welding process and is common in construction. This type of welding produces smoke, and operator skill and slag (contamination) exclusion largely determines the weld quality.
  • Gas metal arc welding (GMAW) forms workpieces by the used of a metal electrode. A shielding gas is fed through the welding gun to prevent weld filler impurities. This type of welding does not transfer metal across the arc, and metal is only deposited when the wire touches the workpiece. Spray-transfer GMAW welding streams molten drops across the arc from the electrode to the weld puddle.
  • Orbital/tube arc welding is a particular type of arc welding for the adhesion of metal tubing, piping, or round bar.
  • Plasma arc welding uses a collimated plasma stream to fuse workpieces and filler alloys. A plasma stream is expelled through the tool, transferring the arc to the workpiece. This type of welding provides high heat to a small area producing a strong weld.
  • Shielded metal arc welding (SMAW), or stick electrode welding, relies on the flux covering the electrode to melt during welding, forming gas and slag that shield the arc and molten weld pool. Upon completion, the slag must undergo finishing and the flux serves to add scavengers, deoxidizers, and alloy elements.

  • Stud/nut welding utilizes a threaded fastener on the end of the welding gun

Types of Resistance Welding

Resistance welding is a type of welding where the heat to weld surfaces is formed by the electrical resistance of the material. Factors to a piece's resistance include: surface coating, electrode materials and geometry, electrode pressing force, and weld current and time. Pools are formed at points of electrical resistance as a current is passed through the metal. These methods produce little pollution and are best suited for thin materials.

  • Flash welding uses a series of flashes or arcs between two components of similar cross sections and shapes along with clamping pressure. Parts are attached to electrically insulated platens. One platen oscillates to create flashing or arcing action when the power source is connected. Flash welding is a combination of melting and forging processes that produces high quality welds. It is used widely in the aerospace industry.
  • Spot welding heats contact points or spots to fuse adjacent materials. This welding process is easily automated at high production rates, and is best suited for lightweight metals.
  • Related to spot welding, projection welding relies upon raised sections or projections on the workpieces for a connection. Current flow is directed at these projections, which can form quality welds on heavy, cumbersome substrates. This process is common when welding hardware to metal plates, as well as joining wires and bars. Dimples or embossed projections are helpful for sheet metal welding.
  • Seam welding produces an overlap or butt weld, typically by a wheel-like electrode. High frequency power supplies are used in welding tube or coil seams because a higher percentage of current flows through the edges of a material at high frequencies.
  • Flash welding does not use any filling metal. The workpieces are set apart based on thickness, material, and weld quality, and the void between the pieces produces the arc to melt the metal. Pressure is then applied to forge the bond.

  • Upset welding requires the substrates to be clamped and to have matching cross-sections. Pressure is applied along the seam, and flash welding begins. As the seam has been heated to a forging temperature, the current is interrupted. The heat and pressure bring forth coalescence.

Types of Frictional/Fusion Welding

Friction welding is a forging technique relying upon the heat created from friction between a moving workpiece and a stationary workpiece, along with a lateral force to displace and fuse the workpieces. No actual melting occurs. Fusion welding includes a heat source to raise the materials to melting point and uniting the workpieces, typically with a filling material to ensure a strong bond.

  • Electron beam welding uses a narrow, concentrated energy source to melt a narrow joint in the workpieces. This minimizes any heat stress on the materials, and the weld can be completed without the use of material fillers. This process requires a vacuum atmosphere to prevent the absorption of electrons by the air.
  • Hot plate/plastic welding is used to merge thermoplastic materials. The workpieces are pressed against the hot plate, removed, and then compressed together. Direct contact and conduction heating is most common, but infrared, convection, and dielectric heating are also suitable hot plate welding heat sources.
  • Laser welding uses a laser beam to melt the workpiece. Laser beams provide a very narrow, concentrated energy source that melts a narrow region, resulting in a minimal heat affected zone. The welds can be made without filler metals or consumable electrodes.
  • Oxyfuel welding procedures require a fuel gas and oxygen to meld substrates. Pure oxygen is used to increase flame temperature, and typical fuels include acetylene, propane, and hydrogen. This process is becoming less common in industrial applications, but is still used in welding pipes and tubes.
  • RF welding, or radio frequency welding, places two polymer workpieces on a table press with dies to direct the welding. High frequency waves are directed at the intended joint, and the molecules of the material vibrate rapidly and generate heat. The weld takes the shape of the die. This process is fast, and PVC, polyurethane, nylon, and PET are most commonly welded by this process.
  • Thermite/exothermite welding uses an exothermic chemical reaction process to weld components together. A metal powder, which releases a great deal of energy (highly exothermic) when reacting with oxygen, is combined with the metal oxide with a much lower heat of formation. For example, powdered mixtures of aluminum metal and iron oxide are loaded into the weld seam or joint and ignited. The aluminum strips the oxygen away from the iron oxide leaving behind a deposit of iron and aluminum oxide.

  • Ultrasonic/linear friction welding utilizes ultrasonic vibration or reciprocating linear motion between workpieces to form a weld. Pieces are clamped under force between the welding tip connected to an ultrasonic transducer and an anvil. The process can be used to conjoin dissimilar metals and plastics.

Types of Brazing and Soldering

Brazing is a process where a filler metal is brought to its melting temperature in the presence of a flux, and joins two close-fitting metal parts via capillary action. Soldering is a similar in nature to brazing, but it is conducted at a lower temperature. In both brazing and soldering, the workpieces do not experience any melting.

  • Gas torch brazing utilizes a combustible gas to heat the workpiece and melt the filler alloy. The alloy melts and flows across the heated workpieces joint, forming a metallurgical bond once cooled.
  • Hot rod/iron brazing heats the workpieces themselves to melt the filler alloy, though no endothermic processes occur to the workpieces.
  • Hot dip brazing/soldering immerses the workpieces in a molten bath of filler alloy. The molten filler alloy wets and flows across the heated work surface, or is pulled into the joint by capillary action. Excess filler alloy runs off as the part is pulled from the molten bath.
  • Induction brazing uses an induction heating source to heat the workpiece and melt the braze filler alloy. A high frequency power supply and induction coil induces current flow in the workpiece and causes internal resistance heating. The molten braze alloy wets and flows across the heated work surface.
  • Infrared soldering/brazinguses infrared or furnace heat to melt the braze or solder filler alloy. It is also called reflow brazing/soldering because the filler alloy is pre-applied, and then reflowed during assembly.
  • Laser brazing/soldering heats the workpiece by laser technology, which heats the filler alloy to form coalescence.
  • Wave solderinguses a molten solder bath with a traveling wave. Printed circuit boards (PCB) are positioned so that the terminations just touch the solder wave, preventing the deposition of excess solder on the PCB. Wave soldering machines consist of a fluxing unit, a pre-heater, and a solder wave. The pre-heater heats the board and component termination prior to soldering, activating the flux and removing any solvent or water from the PCB. The board is passed over a wave of solder which laps up against the bottom of the board to wet and solder the metal surfaces to be joined.

  • Resistance brazing/soldering uses resistance heating to heat the workpiece and melt the braze filler alloy. Contact tips or horns clamp onto the part and pass current through a point adjacent to braze joint, causing internal and contact resistance heating.

Fabrication Services

Fabrication services provide important metal deforming capabilities that resellers, contractors, and manufacturers may not be able to provide on a limited run or customized basis. They also may assemble completed fabrication jobs in-shop or on-site. Common fabrication services include:

  • Welding, as outlined above.
  • Boilermaking, which is the assembly of metal fabrications produced by the deformation of metal plates and their components. Boilermaking outlines more than just the construction storage vessels.
  • Blacksmithing, which forges thick metal components by the use of extreme heat to make the metal malleable to high intensity strikes and deformation
  • Millwrighting, which is the erection of metal components in regards to the structural-load and maintenance of heavy industrial applications.

  • Ironworking, or the structural completion of fabricated components that sustain structures such as homes, bridges, towers, and buildings.

Fabrication Processes

Fabrication facilities process raw materials, most commonly sheet metals, and process them through a series of deforming procedures including, but not limited to:

 

  • Bending
Bending is a forming process where force is applied to sheet metal causing it to angle. Deformation is along one or more axes, and a complex part can be created. This process is completed by a press brake with a series of dies.

Selecting fabrication services

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  • Drawing
Though technically a type of stamping technique, drawing is a popular metal forming procedure. Drawing is a metal forming process where a tool forces sheet metal into a cavity in the shape of the desired part. Deep drawing refers to any drawing technique where the die produces a shape with a measurement that is deeper than its width. This is most effective with ductile metals such as aluminum, brass, copper, and mild steel.

Selecting drawing fabrication

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  • Flanging
Flanging relies on a press brake that provides a short bend along the perimeter of the workpiece. This small overhang can serve as an assembly point and it is common in tubing and piping.  

 Selecting flanging services

Image credit: The Fabricator

  • Machining
Machining regards the processes that form the final geometric shapes of formed metal. This includes turning, boring, drilling, grinding, milling, planing, and tapping. It is often one of the last procedures invoked due to its precise material subtraction.

Machining services

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  • Punching

Punching uses a press with an extrusion and a corresponding die to provide a localized shear through the workpiece.

Punching processes

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  • Rolling
Rolling requires sheet metal to be fed through a roller with extreme pressure that reduces the thickness of the metal. This can create variances in metal thickness.

Rolling services

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  • Shearing
Shearing is the simple division of workpieces by a cutting force. It is often accomplished by the use of a shear die which provides the appropriate clearance and strength to meet the materials shear strength without deforming the workpiece.

Selecting shearing services

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  • Spinning
By spinning a sheet metal disc at high speed and applying force with a mandrel, a cylindrical component is formed. This process requires a lathe, blank, mandrel, and roller tool.

Metal fabrication spinning

Image credit: Custom Part Net

  • Stretching
Stretching is a forming process where sheet metal is stretched and simultaneously bent over a die to form contoured parts. A stretch press is required to accurately form these components.

Stretch fabrication

Image credit: Custom Part Net

   

Surfacing

Some fabrication shops may be proficient at surfacing materials. There are a number of reasons why a customer may request this process, such as aesthetics, improve corrosion resistance, modify the hardness and conductivity of the material, remove surface flaws, and alter the material's friction and adhesion abilities.

   

Videos credit: IPS, Inc.

 

Welding and Fabrication Service Considerations

 

Experience

Fabrication shops are usually contracted based upon their ability to complete jobs with which they've had success in the past. Many fabrication shops specialize in components for specific applications, such as ship building, highway construction, power plant operations, or amusement park construction. The nature of the undertaking being contracted and a fab shop's proficiency in completing such task need to be closely examined.

In particular, experienced welders complete jobs competently and safely, and often provide higher-quality production.

 

Brokerage

Some fab shops may lack the comprehensiveness to complete jobs in-house, and may need to subcontract other fab shops to finish an order. This may be beneficial when prototyping assemblies or when orders have low quantities; additional expertise can gained from consulting specialty firms. Yet this generally slows orders and can make communication arduous. It is advised against on a high quantity, time-sensitive, or long term contract basis.

 

Automation

For assignments that require complex and time consuming welding or fabrication, automated systems can be preferable. Yet dynamic automation is limited to high-volume, in-house fabrication shops. Some equipment may require the real-time input of a human welder, especially when fabricating for customized jobs.

 

Location

Market demand determines the proximity of fabrication shops, and dedicated fabrication work may need to be outsourced to international fab shops to ensure application expertise. Many of the most common needs for fabrications shops, such as general construction and product design, warrant the demand for local and regional fabrication shops. When considering remote fab shops, shipping and communication costs should be analyzed.

 

Many fabrication tasks may require that the contract is fulfilled on-site, such as the construction of an office building. Extreme environments may require require on-site fabrication or welding, not unlike underwater construction. 

 

Schedule

Production schedule is an important aspect. Busy or low-volume fab shops may not be able to handle the requirements of the fabrication, or be unwilling to commit to a timetable suitable to the employer's request. Experience, brokerage, automation, and location all factor into the shop's production rate.

 

Design Services

The business may offer consultation services that include technical drawings or CAD design to assist the customer with their order. Computer-aided manufacturing may be beneficial as well. Suppliers will also assist with manufacturing costs, techniques, and material considerations.

 

Testing/Quality Assurance

Some fab shops may offer the customer inspection services to ensure that fabrication work, whether its own or a competitor's, will uphold to design specifications for structural integrity. Inspection capabilities may include ultrasonic inspection, magnetic particle inspection, material hardness, and material properties testing.

 

Welding and Fabrication Services Standards

Some of the following standards are regarded as the preeminent requirements of welding/fab shops and the integrity of their work.

 

ISO 9000 Guidelines for the selection of well-managed, competent industrial services

ISO 10721-2 Fabrication and erection of steel structures

ISO 14000 Guidelines for the environmental management of industrial services

ASTM E1158 Selecting materials for metal fabrication and its susequent ultrasonic testing

ASTM E428 The fabrication and control on non-aluminum metals

BS 13480-4 The fabrication and installation of metal piping

ASME B31.3 The fabrication, erection, examination of piping

ISO 3834 The selection of appropriate welding standards 

EN 1090 The construction of steel and aluminum structures

 

Resources

 

Custom Part Net - Sheet Metal Forming

 

Hobart welders - Welding Glossary

 

Wikipedia - Surface finishing; Metal fabrication; BrazingBlacksmithWelding; Soldering;Ironworker; Electrical resistance welding; Gas metal arc welding; Spot welding; Upset welding; Flash welding; Friction welding; Fusion welding; Oxy-fuel welding and cutting; High frequency welding; Shearing; Millwright (The modern millwright); Ironwork

 

Viking Group Inc. - Viking Fabrication Services

 

Jason Marovich (Hub Pages) - Forming and Flanging Sheet Metal in Stamping Dies 

 

Matter - The University of Liverpool - Fusion welding

 

Welding Works - Manufacturing Capabilities

 

GEA Process Engineering Inc. - Custom Fabrication Services 

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