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Secondary manufacturing processes, or fabrication, work on products from primary processes to create a metal part or structure that is suitable for end-use. In these processes, semi-finished metal products are reshaped and joined. Moreover, the properties of these semi-finished metal products are further modified to suit customer requirements. Some examples of steel fabrication products are steel trusses, storage tanks, automotive chassis, and metal enclosures. Steel fabrication is done in machine shops or "fab shops", or on the project site.
Steel fabrication is the process of creating steel products through secondary metal manufacturing processes. Examples of these processes are cutting, bending, and joining. Additional processes such as finishing and heat treatment are made to impart additional characteristics to the metal product. Steel fabrication is an important trade that caters to almost all industrial sectors. Steel products are essential to construction, transportation, energy, mining, agriculture, and consumer goods manufacturing.
To understand steel fabricating better, it is important to determine the difference between primary and secondary metal manufacturing processes. Primary manufacturing processes create simple, semi-finished metal products such as plates, sheets, tubes, and bars. These metal products are created by casting, forging, rolling, extrusion, wire drawing, and sintering. All of these processes transform raw metal ingots or billets into metal products that will be used for secondary manufacturing processes. Primary manufacturing processes are done in foundries and steel mills.
Secondary manufacturing processes, or fabrication, work on products from primary processes to create a metal part or structure that is suitable for end-use. In these processes, semi-finished metal products are reshaped and joined. Moreover, the properties of these semi-finished metal products are further modified to suit customer requirements. Some examples of steel fabrication products are steel trusses, storage tanks, automotive chassis, and metal enclosures. Steel fabrication is done in machine shops or "fab shops", or on the project site.
Steel is a type of metal composed of an iron base metal alloyed by carbon. Other types of metals can also be used as fabrication workpiece items. Commonly used metals are aluminum, copper, and nickel alloys. Steel is the most widely used metal because of its availability and cheap price. Though aluminum is more abundant, the process of smelting iron is less energy-consuming and thus, less expensive.
One of the special steel alloys is stainless steel that has a variety of uses and can be fabricated in the same way as steel. Like steel, stainless steel has various grades each of which is ideal for use in different applications. Grades 300 and 400 are the most commonly used with grade 304 being the most popular and widely used. For high temperature exhaust applications, stainless steel grade 321 is ideal since part of its alloy is titanium, which ensures very little weld decay.
Stainless steel grade 316, with molybdenum, is used for water applications due to its resistance to corrosion. It is referred to as marine grade stainless and can be used in applications where chloride is present, which is something that grade 304 is unable to do. The resilience and strength of grade 316 makes ideal for use in building nuclear reprocessing plants.
These are metal products produced from melting and solidifying metal ingots. Castings are shaped according to the end product but have some dimensions that are usually out-of-tolerance. Secondary processes such as machining, finishing, and heat treatment are used to produce a final product.
Blooms are metal stocks with a nearly square cross-section that has a dimension equal to or greater than 6 x 6 inches. They are the product from the first breakdown of the metal ingot.
Slabs are produced from rolling metal ingots in a steel mill. They have a rectangular cross-section with thicknesses around 8 inches or greater.
Billets are similar to blooms but have a square cross-section with dimensions of about 2 x 2 inches to 5 x 5 inches. They are blooms that have been further formed by either rolling, forging, or extrusion.
These semi-finished products are produced by further rolling blooms and slabs. Plates have a thickness greater than a quarter of an inch. Sheets and strips are thinner than plates. Sheets differ from strips by their large width-to-thickness ratio.
These are long, solid metal products with square, round, or rectangular cross-sections. They are produced by further rolling billets into smaller cross-sections. Typical cross-sections of bars are around 0.5 to 2 inches.
Rods are similar to bars but with a smaller cross-section. Their cross-sections are typically 0.2 to 0.5 inches. Since they have smaller cross-sections, they are easily bent. Rods are typically supplied in rolls or coils.
These are metal products with irregular cross-sections formed from blooms by progressive rolling. Grooved rolls are mated together with a gap in between. The product takes form as it passes through the gap.
Tubes and pipes are hollow metal products typically with a square, rectangular, or round form. They generally fall into two types: welded and seamless. Welded tubes and pipes are made by rolling a slab or plate into a coil. The edge of the coil is welded together by electric resistance welding. Seamless tubes and pipes are manufactured by rolling a round bar while piercing using a rotating cone. Forming the seamless tube is done at elevated temperatures near the transition temperature of the metal.
These are metal products with cross-sections that are greatly reduced by forming. Wires are formed by a metalworking process called drawing. In this process, a metal piece, typically a rod, is pulled from a die. Drawing is a cold working process since it is done at room temperature.
Before proceeding with the actual fabrication processes, it is important to know the preliminary steps. This involves conceptualizing and planning the design and features of the final product. The workpiece must be prepared before working to prevent any errors and material wastage.
Design and drafting is the preliminary stage of a fabrication process which involves:
Before, design and drafting were done using manual methods. The outputs are hand-drafted engineering drawings and manual calculations. Today, most designs are carried using computer software. Software such as AutoCAD, SolidWorks, and Tekla Structures are popular examples that perform both designing and drafting. Advanced calculations and modeling can be done which can streamline the process through quick design iterations.
Sub-finished metal products are typically supplied with a protective coat to keep the surface free of corrosion. The level of protection is not always effective, and some rusting can still occur. Handling, transfer, and storage can also build debris on the surface that must be removed before performing work on the workpiece. Coatings, scales, oils, old paint, rust, dirt, or any other surface contaminant that can impede or affect the fabrication processes and quality of the product must be removed.
Common workpiece preparations are pneumatic blasting, waterjet cleaning, mild pickling, scraping, and brushing.
Marking is the process of laying off the measurements from the design and into the workpiece. This is sometimes included in the preparation process. Edges, fold lines, and hole centers are scribed on the surface of the workpiece. These scribes or marks must remain visible during the actual fabrication. Common marking tools are metal scribers, pencils, chalks, dividers, and punches. Aside from the measuring devices, marking is aided by tools such as rulers, center squares, and T-squares.
Cutting is one of the three main steps of metal fabrication. Cutting involves the removal or separation of unwanted material from the main workpiece or product. These unwanted materials are in the form of metal chips and scraps that are collected and recycled.
Cutting can also involve a scrap-less operation wherein no material is lost for recycling. This method is commonly seen in cutting sheet metal. To conserve material, pieces of metal from both sides of the cut are used. A new part is produced with each cut.
Cutting can be divided into several main categories. These are shear cutting, wedge-action cutting, abrasion, and non-traditional methods.
Shear cutting, or shearing, is the process of cutting using two moving cutting tools. A cut is done by moving the two tools past each other with the metal in between. As the cutting tools press against the workpiece, the stress at the contact overcomes the material‘s shear resistance. A crack or tear starts to form which propagates through the material. This crack becomes the cutting line that separates the two pieces.
Shearing is further divided into other cutting processes. These are enumerated below.
Blanking is a shearing process performed by a punch and die. Its cutting line is a closed-ended line forming a closed region. This line becomes the outside features of the workpiece. The workpiece is the inner portion of the metal stock while the outer is discarded as scrap. Blanking is typically done in a sheet or strip metal.
Piercing is the same as blanking where the cutting line completely bounds an area. However, in piercing, the cutting line forms the edges of the internal features of the workpiece. The scrap is the inner portion of the metal stock.
This is a special type of blanking where the metal stock is completely clamped down during punching. The result is a clean cut with minimal burrs.
This type involves shearing with a cutting line whose ends do not meet. Parting divides a metal stock into two.
This is a shearing process where the cutting line does not completely divide the metal stock. This allows one side or area to be bent or formed.
Another open-ended cutting method used to create features (notches) along the edges of the metal stock.
Trimming is a shearing operation where excess material is removed from the edge of the stock to establish the final dimensions of the workpiece.
This is a type of cutting that involves removing material from stock using a tool with a sharp tip or edge. The cutting tool partially penetrates the material and moves towards the direction of the cutting line. Material is removed gradually until the final dimensions of the workpiece are obtained. The metal stock worked by these processes is solid blocks such as bars, rods, and slabs.
Wedge-action cutting can be further divided into different types as summarized below.
This is a cutting process where the stock is rotated while a cutting tool is made to move laterally past its outside surfaces. This generates the external features of the workpiece. The cutting tool slightly penetrates the stock as the stock rotates. A turning process is typically done in a lathe machine.
This process is the same as turning but the cutting tool moves along the inside surfaces of metal stock. It is typically done after drilling. Boring is used for creating large holes with greater dimensional accuracy.
Drilling is a cutting process for creating holes in a solid material. Its cutting tool consists of multiple cutting edges rotated against the metal stock. Drilling is often done with other machining processes such as boring, trepanning, reaming, and countersinking.
Trepanning involves cutting the face of round stock to produce a circular groove. Either the stock rotates, or the cutting tool revolves to create a cut. Trepanning is used for producing large circular holes and round disks.
This is the same as boring, but the cut is done at a lesser depth. It is used to improve the dimensional accuracy of the bored hole.
This process is used to enlarge the openings of drilled holes to accommodate the heads of a fastener such as bolts and screws.
This process removes material using a rotating cutting tool with multiple cutting tips. There are two major classifications of milling processes. These are face milling and peripheral milling. Face milling has the cutting tips oriented on one side of the cutter. Peripheral milling, on the other hand, has the cutting tips oriented radially outward along the circular edge of the cutter. Milling can produce a variety of cuts and can perform operations similar to other machining processes.
Planing is a machining process that removes excess material by moving a cutting tool against a stationary stock in a reciprocating motion. This process is used for flattening or creating straight contours on the surface of a large workpiece.
Sawing is a cutting process where a solid material is partially or completely cut using reciprocating or rotating tools such as power band saws, hack saws, and circular saws.
This process uses materials with high hardness and rough surfaces for scratching, eroding, rubbing, or wearing the surface of a workpiece. In fabrication, abrasion is done in a controlled manner which gradually removes excess material from the workpiece. The types of abrasion processes are mentioned below.
Grinding involves pressing an abrasive material against the surface of the workpiece with a force perpendicular to the contact plane. A relative motion parallel (or tangential for circular grinding tools) to the contact plane is made between the two surfaces.
Honing is a low-speed abrading process. This is commonly done on cylindrical surfaces. It combines a simultaneous rotating and reciprocating motion creating a crosshatch lay pattern. The main purpose of honing is to create a part with high dimensional accuracy and a fine finish.
Lapping is the same as honing but generally uses lower speed and lower pressure abrasions. It also produces parts with excellent surface finish and precise dimensions. Lapping is usually done by mating a workpiece with a tool called a lap or with another workpiece. The rubbing surfaces are separated by a film of an abrasive mixture.
These are non-conventional methods of cutting. They do not use mechanical action to remove material. Rather, they use electrical, electromagnetic, chemical, thermal, acoustic, or special mechanical phenomena to cut metal. These are usually preferred over traditional methods because of their precision and burr-free cuts. Examples of these methods are mentioned below.
This method uses high-speed jets of water to cut through a material. A special type of waterjet cutting, known as abrasive jet cutting, uses water mixed with abrasive materials to cut harder materials such as metals. Waterjet cutting cuts the material by eroding the exposed surface of the material along the cutting line.
Laser cutting is a cutting method that uses an intensely focused, coherent stream of light called lasers to cut through the material.
This process removes material by electrolytically dissolving the unwanted part. ECM is typically used for machining hard metals such as titanium, Inconel, and other high-strength alloys.
Bending is a fabrication process where the metal is formed according to its final shape by supporting the stock on at least two points and applying pressure in between. The metal stock is deformed according to the profile of the press or punch and the configuration of the supports or dies. Bending is commonly used to form metal sheets, plates, strips, rods, and bars.
The output of the bending process is angle bars, channels, V-shape and U-shaped bars, profiled sheets, and rounded plates.
Bending processes can be further classified according to how the bending load is applied. These are summarized below.
Air bending, also called free bending, is the most common type of bending process in metal fabrication. In this process, the workpiece is supported on two points by a die. Pressure is applied by a punch on the upper side of the workpiece. The opposite side or the bottom of the workpiece is free to bend and does not contact the die. This results in only three contact points. The position and movement of the punch depend on the desired cross-section of the part.
In bottom bending, the workpiece is also supported at two-point similar to air bending. However, bottom bending involves fully pressing the workpiece until its bottom side contacts the die. The resulting radius of the bend depends on the radius of the punch tip and some amount of spring back. Bottom bending is typically used for producing V-shaped cross-sections.
Coining involves fully pressing the workpiece against the die with enough force to cause the metal to flow. Thus, this process requires higher forces than air and bottom bending since it completely deforms the material in contact. The resulting cross-section depends on the profile of the punch and die. Coining is a highly accurate and repeatable bending process since it eliminates spring back.
Roll bending is done by passing the metal stock into a set of three rolls. A common configuration is composed of two stationary lower rolls and one moving upper roll. The movement of the upper roller bends the metal at a radius that depends on the radii and distances between the rolls.
This stage of the metal fabrication process involves combining and integrating all the cut and shaped parts to form a single, larger structure. The parts are first assembled piece by piece to get a general view of the structure to be made. Initial assembly is done using non-permanent joints such as temporary tack welds or bolted connections. This process is important to ensure that every part mates with the other parts properly.
Once the metal parts are properly aligned and put in place, permanent joints are created. Examples of permanent joints are final or full welds and adhesive-bonded surfaces. In most metal fabrications, welding is the most commonly used joining method followed by bolting, screwing, and riveting. These joining processes are explained below.
Welding is a fabrication process commonly used to join metals. It involves heating and melting the metal joints and filler metal. The molten metals are mixed to form a weld pool. This molten metal pool is then cooled and fused forming a solid joint. There are many different types of welding which are classified according to the method of producing heat to melt the metal, type of shielding used to protect the weld, thickness of the material to weld, and so on. Common examples of welding processes are shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW/TIG), gas metal arc welding (GMAW/MIG), and electroslag welding (ESW).
Soldering and brazing are two joining processes that involve melting a filler metal and depositing it into the joint. Unlike welding, these two processes do not melt the workpiece or the base metal. In principle, soldering and brazing are the same. However, brazing uses filler metals that melt at a higher temperature. Brazing typically uses brass as filler while soldering uses tin-lead alloys and silver alloys.
Bolting and screwing create joints by using threaded machine elements. The result is a semi-permanent joint that can be dismantled without damaging the part. These joining processes require holes for inserting the fasteners while having access to one or both sides. Bolts and screws must be checked regularly since vibrations can cause these fasteners to loosen over time.
This is another semi-permanent joint that typically joins sheet metals. Like bolting and screwing, it does not cause permanent deformation or damage to the workpiece.
Secondary processes are performed to add features to the final product. These processes can refine and modify both external and inherent features of the product. The type of secondary processes performed on the part depends on its original design and intended application. Below are some of the common secondary processes in metal fabrication.
Heat treatment is a secondary process that modifies the microstructure of the metal parts. This process can make a material have higher ductility or increased strength and hardness. It can also relieve residual stresses caused by primary manufacturing processes and welding.
Coating is a general term used to describe processes of applying a layer of material onto the surface of a part. These materials are typically curable polymers which can be in powder or liquid form. Typical types of coating processes are powder coating and painting. The coating imparts improved surface quality, durability, enhanced appearance, various textures, and chemical resistance.
This process involves coating the surface of a metal part with a layer of zinc to prevent steel from rusting. The most common application method is hot-dip galvanizing where the metal is submerged in a molten zinc bath.
This process promotes the formation of a thicker oxide layer on the surface of a metal. It is done by passing a current through the material while submerged in an electrolyte bath. This is commonly done in aluminum parts.
Deburring enhances the final quality of the product by removing raised edges and unwanted pieces of material, known as burrs, left by the initial machining processes. Burrs are created from shearing, bending, cutting, piercing, and compressing metals.
When speaking of steel, it is very common to interchange it with the word metal since most people believe that metal and steel are the same. Though there are metals that have the same look and feel as steel and may have characteristics and properties that are similar, they are quite different. In many ways, steel is an entity unto itself with traits that exceed other metals.
A metal is made of multiple substances that naturally occur in the Earth’s crust. Common metals are titanium, copper, and nickel. Unlike steel, metals do not have to be blended or mixed with alloys but can be dug up and used. Steel is an alloy made from naturally occurring iron ore, a metal that is necessary for the composition of steel and one of the most abundant metals in the Earth’s crust.
The alloying of steel makes it a far stronger and resilient metal than naturally occurring metals. Natural metals, taken from the earth, are commonly used for jewelry, decorations, and surgical implants because they are so malleable. Processed steel requires far more tooling and working to shape it.
The manufacture of steel requires the purification of iron ore by removing its impurities such as silica, phosphorus, and sulfur. Once the ore is purified, carbon is added to enhance steel’s durability, strength, and machinability.
Metal fabrication is a process that uses flat metal sheets that are formed and shaped. The sheets are about a quarter inch thick or less, which makes them pliable enough to be shaped and configured. Much like steel fabrication, the sheets of metal are subjected to cutting, stamping, folding, welding, and other processes to reach the necessary shape.
To strengthen metals, other processes may be used to enhance the properties of the metal and make it more resilient. The types of things that may be added include plating, expanding, wiring, various types of hardware, fittings, and castings. How these factors are added is dependent on the final application for which the piece is created. In many cases, fabrication shops begin with several types of metals and form them into one piece.
Though metals are more pliable and adaptable than steel, similar fabrication methods are used. Unlike steel, which requires aggressive and forceful operations to form it, metals can be shaped with the same processes but in a less dynamic way.
Precision sheet metal fabrication is a common manufacturing process where the structure of a metal workpiece is cut, bent, and assembled by machining. There are any number of operations that are performed in the creation of a finished sheet metal product...
Sheet metal fabrication is metal that has been formed into thin and flat sheets which is then cut and bent into various shapes. Different metals, brass, steel, copper, tin, titanium, aluminium, etc., can be made into sheet metal...
Stainless steel can be fabricated using any of the traditional forming and shaping methods. Austenitic stainless steel can be rolled, spun, deep drawn, cold forged, hot forged, or stippled using force and stress...
Laser cutting is a non-traditional machining method that uses an intensely focused, coherent stream of light called lasers to cut through the material. This is a type of subtractive machining process where the material is continuously removed during the cutting process...
Water jet cutting is a manufacturing process that uses high pressure jets of water provided by pressurizing pumps that deliver a supersonic stream of water to cut and shape various types of materials. The water in water jet cutting is...