{"id":1352,"date":"2017-12-07T07:39:47","date_gmt":"2017-12-07T07:39:47","guid":{"rendered":"http:\/\/www.steelforging.org\/?p=1352"},"modified":"2021-03-25T02:59:17","modified_gmt":"2021-03-25T02:59:17","slug":"differences-between-forging-and-casting","status":"publish","type":"post","link":"https:\/\/www.steelforging.org\/?p=1352","title":{"rendered":"Differences between Forging and Casting"},"content":{"rendered":"

Forging<\/a> and casting are both the techniques used for forming complex shaped metal components by transforming metal materials, but different methods. Although the working way of forging and\u00a0casting is different, sometimes, the same metal components could be produced in either casting or forging. Today, we would like to discuss the differences between forging and casting, so that\u00a0our customers could have a clear understanding on them, and know which process is preferred for their products.<\/p>\n

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Definition & Process<\/h2>\n

Forging<\/strong><\/p>\n

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Forging is the metalworking process by putting pressure on metal billets in solid status. We could generally divide forging into hot forging and cold forging. Hot forging is the forging process that\u00a0the billets is pressed under hot temperature status, in other words, before deforming the billets, they need to be heated by medium frequency furnace first.<\/p>\n

There are also different types of hot forging<\/a>, including open die forging, closed die forging and roll forging. Open die forging, also named as free forging, is the hot forging method that shaping\u00a0metals under the workforce of simple molds. Open die forging is specially used to produce large metal parts in simple shapes, like shafts. Tolerances of open die forging are loose, and the\u00a0components by open die forging are more likely to be further machined. Closed die forging<\/a>, also called impression die forging, is the popular hot forging method for small components different\u00a0from open die forging (refer to open die forging vs. closed die forging<\/a>). This kind of forging way is usually interchangeable with investment casting method for the same metal part, but closed die\u00a0forging is better for its good strength and toughness. Roll forging is the forging process for round shaped parts, like rings, flanges, etc.<\/p>\n

Cold forging is another forging process that deforms the billets to required shapes directly under room temperature, this kind of forging is more suitable for small precision parts, like bolts and nut,\u00a0gears, etc. Cold forging deforms metal while it is below its recrystallization point. Cold forging is generally preferred when the metal is already a soft metal, like aluminum. This process is usually\u00a0less expensive than hot forging and the end product requires little, if any, finishing work. Sometimes, when aluminum is cold forged into a desired shape, it is heat treated to strengthen the piece.\u00a0This is called “tempering.” More on hot forging vs. cold forging<\/a>…<\/p>\n

Casting<\/strong><\/p>\n

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Casting is the metal forming process by pouring liquid metal into molds for shapes. Casting could be generally separated into three types of different methods. They are investment casting, sand\u00a0casting and die casting.<\/p>\n

Investment casting, also called precision casting, is the casting method for precision metal components, whose fuction is similar to closed die forging. Investment casting is a manufacturing\u00a0process in which a wax pattern is coated with a refractory ceramic material. Once the ceramic material is hardened its internal geometry takes the shape of the casting. The wax is melted out and\u00a0molten metal is poured into the cavity where the wax pattern was. The metal solidifies within the ceramic mold and then the metal casting is broken out. This manufacturing technique is also known\u00a0as the lost wax process. Investment casting was developed over 5500 years ago and can trace its roots back to both ancient Egypt and China. Parts manufactured in industry by this process\u00a0include dental fixtures, gears, cams, ratchets, jewelry, turbine blades, machinery components and other parts of complex geometry.<\/p>\n

Sand casting<\/a>, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term “sand casting” can also refer to an object produced via\u00a0the sand casting process. Sand castings are produced in specialized factories called foundries. Over 70% of all metal castings are produced via sand casting process.<\/p>\n

Die casting<\/a> is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies which\u00a0have been machined into shape and work similarly to an injection mold during the process. Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminium, magnesium,\u00a0lead, pewter and tin-based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.<\/p>\n

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Advantages & Disadvantages<\/h2>\n

Forging<\/strong><\/p>\n

Forging have a generally higher strength and are typically tougher than metal processed in castings. The metal is less likely to shatter on contact with other objects for example, making forging\u00a0highly suitable for items such as swords. This increased strength and durability is a result of the way in which the billet is forced into shape \u2014 by pressing or by hammering \u2014 during the forging\u00a0process. The metal\u2019s grain is stretched by this process, and ends up aligned in one direction, as opposed to being random. Following the pressing or hammering, the forging is cooled in water or\u00a0oil. By the end of the process, the metal is stronger than it would have been had it been cast, for example.<\/p>\n

A forging\u2019s strength isn\u2019t consistent all the way through; instead, forgings are anisotropic, which means when the metal is worked on and deformation occurs, the metal\u2019s strength is greatest in the\u00a0direction of the resulting grain flow. This results in metal forgings which are strongest along their longitudinal axis, while in other directions, the forging will be weaker. This differs from castings,\u00a0which are isotropic and therefore have almost identical properties in all directions.<\/p>\n

Since the process of forging is controlled and deliberate, with each forging undergoing the same steps, it\u2019s typically possible to ensure a consistent material over the course of many different\u00a0forgings. This is in contrast to casting, which is more random in nature due to the processes used.<\/p>\n

But forging has limitations on sizes. During the forging process, it\u2019s more difficult to shape the metal, since forging occurs while the steel is still solid, unlike in casting where the metal has been\u00a0reduced to its liquid form as part of the process. Since the metallurgist working with the steel will have more difficulty altering the metal\u2019s shape, there\u2019s a limit on the size and the thickness of the\u00a0steel which can be successfully forged. The larger the metal section being worked on, the harder it is to forge.<\/p>\n

Casting<\/strong><\/a><\/p>\n