Plastic processing - Sosei kakou

In general, when a solid object is deformed by applying force, the shape of the object returns to its original shape when the force is removed as long as the force is small. This property of solids is called elasticity. If the force is gradually increased, the object will no longer return to its original shape even when the force is removed. In other words, it undergoes plastic deformation. This property of solids is called plasticity, and the method of using plasticity to mold materials into products of a given shape and size is called plastic processing. A great many of the metal products we see in our daily lives have been made through a process of plastic processing, and this processing is an important area of ​​metal processing. There are various processing methods for plastic processing, such as rolling, extrusion, forging, drawing, shearing, pressing, and straightening, and the processing is carried out using machines named after each processing method. Rolling, extrusion, and forging can be carried out at high temperatures or at room temperature, but the others are mainly carried out at room temperature. The strength and other properties of metal materials are improved by plastic processing. A method called thermomechanical processing has been developed that further increases product strength by skillfully combining heating temperature and plastic processing. Plastic processing is a method suitable for mass production of products of the same shape and size, and has developed in the direction of efficient production of high-precision products by improving the precision of machinery and tools used. In particular, the introduction of automatic control technology has produced remarkable results in rolling processing. Some shapes of products can be made by cutting, but plastic processing is more advantageous than cutting in terms of effective use of materials because it does not produce shavings. However, it is inferior to cutting in terms of product precision. On the other hand, there are some products that can only be made by plastic processing, such as plates, tubes, and wire rods, but there are many cases where the same product can be made by different types of plastic processing, such as tubes that can be made by rolling or extrusion. Recently, with the diversification of applications, the demand for small-lot production of a wide variety of products has been increasing in the field of plastic processing, and in order to respond to this, computers have been introduced and automation technology that utilizes robots has been adopted in fields other than rolling, with good results and labor savings. Plastic processing is not only performed on metals, but also on plastics and composite materials made of metals and nonmetals. The deformation of soil and rocks is academically treated as plastic deformation, but the molding of clay and china clay is not called plastic processing.

[Takahashi Hiroo]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

一般に固体物体に力を加えて変形させるとき、力が小さいうちはその力を取り除くと物体の形は元に戻る。固体のもつこの性質は弾性とよばれる。力をしだいに大きくしていくと、ついには力を取り除いても物体の形は元に戻らなくなる。すなわち塑性変形する。固体のもつこの性質が塑性であり、塑性を利用して材料を所定の形状、寸法の製品に成形する手段を塑性加工という。日常生活で目に触れる金属製品のきわめて多くのものが塑性加工の工程を経て製品となっており、この加工は金属加工の重要な分野を占める。塑性加工には圧延、押出し、鍛造、引抜き、剪断(せんだん)、プレス加工、矯正とよばれる各種の加工法があり、それぞれの加工名を冠した機械装置によって加工が行われる。圧延、押出しおよび鍛造は高温に加熱した状態でも、また室温でも行われるが、その他は主として室温で行われる。金属材料は塑性加工によって強度その他の性質が改善される。加工熱処理とよばれ、加熱温度と塑性加工をうまく組み合わせることによって一段と製品強度を高める方法も開発されている。塑性加工は同一形状・寸法の品物の多量生産に適した手段であり、機械装置および使用工具の高精度化によって高精度の製品を能率よく生産する方向に発展してきた。とくに圧延加工においては自動制御技術の導入が著しい成果をあげてきた。製品の形状によっては切削加工でつくれるものもあるが、塑性加工は削り屑(くず)を出さない加工なので材料の有効利用の点で切削加工より有利である。しかし、製品精度の点では切削に劣る。一方、板、管、線材のように塑性加工でなければつくれないものもあるが、たとえば管が圧延によっても押出しによってもつくれるように、同じ品物を別種の塑性加工でつくれる場合も多い。近時、用途の多様化で多品種少量生産の要求が塑性加工の分野においても強まってきており、これに即応できるようコンピュータを導入し、ロボットを活用する自動化技術が圧延以外の分野にも取り入れられて成果をあげ、省力化の実もあがっている。塑性加工は金属に対してのみでなく、プラスチックや金属と非金属との複合材料に対しても行われている。土や岩石の変形は学問的には塑性変形として取り扱われるが、粘土や陶土の成形は塑性加工とはいわない。

［高橋裕男］

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