Forging defined ~ For those new to the forging process and the benefits of forged parts here are some Forging FAQs:
What is forging?
Forging is manufacturing process where metal is pressed, pounded or squeezed under great pressure into high strength parts known as forgings. The process is normally (but not always) performed hot by preheating the metal to a desired temperature before it is worked. It is important to note that the forging process is entirely different from the casting (or foundry) process, as metal used to make forged parts is never melted and poured (as in the casting process).
Why use forgings and where are they used?
The forging process can create parts that are stronger than those manufactured by any other metalworking process. This is why forgings are almost always used where reliability and human safety are critical. But you’ll rarely see forgings, as they are normally component parts contained inside assembled items such a airplanes, automobiles, tractors, ships, oil drilling equipment, engines, missiles and all kinds of capital equipment – to name a few.
How FORGINGS compare to Castings
Forgings are stronger. Casting cannot obtain the strengthening effects of hot and cold working. Forging surpasses casting in predictable strength properties – producing superior strength that is assured, part to part. Forging refines defects from cast ingots or continuous cast bar. A casting has neither grain flow nor directional strength and the process cannot prevent formation of certain metallurgical defects. Pre-working forge stock produces a grain flow oriented in directions requiring maximum strength. Dendritic structures, alloy segregation’s and like imperfections are refined in forging.
Forgings are more reliable, less costly. Casting defects occur in a variety of forms. Because hot working refines grain pattern and imparts high strength, ductility and resistance properties, forged products are more reliable. And they are manufactured without the added costs for tighter process controls and inspection that are required for casting. Forgings offer better response to heat treatment. Castings require close control of melting and cooling processes because alloy segregation may occur. This results in non-uniform heat treatment response that can affect straightness of finished parts.
Forgings respond more predictably to heat treatment and offer better dimensional stability. Forgings’ flexible, cost-effective production adapts to demand. Some castings, such as special performance castings, require expensive materials and process controls, and longer lead times. Open-die and ring rolling are examples of forging processes that adapt to various production run lengths and enable shortened lead times.
How FORGINGS compare to Weldments / Fabrications
Forgings offer production economies, material savings. Welded fabrications are more costly in high volume production runs. In fact, fabricated parts are a traditional source of forging conversions as production volume increases. Initial tooling costs for forging can be absorbed by production volume and material savings and forging’s intrinsic production economics lower labor costs, scrap and rework reductions and reduced inspection costs. Forgings are stronger. Welded structures are not usually free of porosity. Any strength benefit gained from welding or fastening standard rolled products can be lost by poor welding or joining practice. The grain orientation achieved in forging makes stronger parts.
Forgings offer cost-effective designs/inspection. A multiple-component welded assembly cannot match the cost-savings gained form a properly designed, one-piece forging. Such part consolidations can result in considerable cost savings. In addition, weldments require costly inspection procedures, especially for highly stressed components. Forgings do not. Forgings offer more consistent, better metallurgical properties. Selective heating and non-uniform cooling that occur in welding can yield such undesirable metallurgical properties as inconsistent grain structure. In use, a welded seam may act as a metallurgical notch that can lead to part failure. Forgings have no internal voids that cause unexpected failure under stress or impact. Forgings offer simplified production. Welding and mechanical fastening require careful selection of joining materials, fastening types and sizes, and close monitoring of tightening practice both of which increase production costs. Forging simplifies production and ensures better quality and consistency part after part.
How FORGINGS compare to Machined Bar / Plate
Forgings offer broader size range of desired material grades. Sizes and shapes of products made from steel bar and plate are limited to the dimensions in which these materials are supplied. Often, forging may be the only metalworking process available with certain grades in desired sizes. Forgings can be economically produced in a wide range of sizes from parts whose largest dimension is less than 1 in. to parts weighing more than 450,000 lbs.
Forgings have grain oriented to shape for greater strength. Machined bar and plate may be more susceptible to fatigue and stress corrosion because machining cuts material grain pattern. In most cases, forging yields a grain structure oriented to the part shape, resulting in optimum strength, ductility and resistance to impact and fatigue. Forgings make better, more economical use of materials. Flame cutting plate is a wasteful process one of several fabricating steps that consumes more material than needed to make such parts as rings or hubs. Even more is lost in subsequent machining. Forgings yield lower scrap; greater, more cost-effective production.
Forgings, especially near-net shapes, make better use of material and generate little scrap. In high-volume production runs, forgings have the decisive cost advantage. forgings require fewer secondary operations. As supplied, some grades of bar and plate require additional operations such as turning, grinding and polishing to remove surface irregularities and achieve desired finish, dimensional accuracy, machine-ability and strength. Often, forgings can be put into service without expensive secondary operations.
How FORGINGS compare to Powder Metal Parts (P/M)
Forgings are stronger. Low standard mechanical properties (e.g. tensile strength) are typical of P/M parts. The grain flow of a forging ensures strength at critical stress points. Forgings offer higher integrity. Costly part-density modification or infiltration is required to prevent P/M defects. Both processes add costs. The grain refinement of forged parts assures metal soundness and absence of defects. Forgings require fewer secondary operations. Special P/M shapes, threads and holes and precision tolerances may require extensive machining. Secondary forging operations can often be reduced to finish machining, hole drilling and other simple steps. The inherent soundness of forgings leads to consistent, excellent machined surface finishes. Forgings offer greater design flexibility. P/M shapes are limited to those that can be ejected in the pressing direction. Forging allows part designs that are not restricted to shapes in this direction. Forgings use less costly materials. The starting materials for high-quality P/M parts are usually water atomized, pre-alloyed and annealed powders that cost significantly more per pound than bar steels.
How FORGINGS compare to Reinforced Plastics/Composite (RP/C)
Forgings offer greater productivity. New advanced-composite part designs may often require long lead times and substantial development costs. The high production rates possible in forging cannot yet be achieved in reinforced plastics and composites.
Forgings have established documentation. RP/C physical property data are scarce and data from material suppliers lack consistency. Even advanced aerospace forgings are established products with well-documented physical, mechanical and performance data. Forgings offer broader service temperature range. RP/C service temperatures are limited and effects of temperature are often complex. Forgings maintain performance over a wider temperature range. Forgings offer more reliable service performance. Deterioration and unpredictable service performance can result from damage to continuous, reinforcing RP/C fibers. Forging materials out-perform composites in almost all physical and mechanical property areas, especially in impact resistance and compression strength.
