Forging - Tanzo

Japanese: 鍛造 - たんぞう

A type of metal processing, it is the process of applying a compressive load to a raw material through a die tool, reducing its height (or diameter or thickness), and stretching it in a direction perpendicular to the compression to form an item of a specified shape and dimensions. Its history dates back to the Bronze Age (4000-2000 BC), when humans began to make weapons and ornaments from metal. In Japan, it has been used since ancient times as a method of manufacturing swords, farm tools such as hoes and shovels, horseshoes, etc., under the name of fire forging or blacksmithing. These were done by hand using hand-held hammers, but nowadays, using mechanical power such as air hammers and presses, large items such as rotating shafts for ships and nuclear generators weighing several hundred tons, small items such as nails weighing around 1 gram, and various complex-shaped parts for automobiles are made by forging. Forging can be carried out at a range of temperatures ranging from red hot to room temperature, depending on the purpose.

[Takahashi Hiroo]

Hot Forging

Forging involves heating the material to a red-hot state, and the purpose is to improve the mechanical properties of the material by forging while forming it. Ingots, which are made by pouring molten metal into a mold and solidifying it, and slabs made by continuous casting are brittle and have low strength as they are. However, when they are hot forged, their internal structure is improved, they become viscous, and they become more resistant to impact forces. However, some materials, such as mild steel, have a property known as hot brittleness, which makes them very brittle at temperatures between 900 and 1200°C, so it is important to select a small degree of processing in the initial process of ingot and slab forging. Metals whose internal structure has been improved by forging are soft at high temperatures and have sufficient elongation, so they can be formed into complex shapes with a large degree of processing.

[Takahashi Hiroo]

Cold Forging

On the other hand, forging performed at around room temperature is called cold forging. It is not suitable for forming products with complex shapes, but it is possible to obtain high strength due to the work hardening that occurs as the deformation occurs. It can also produce products with a clean surface and high dimensional accuracy.

[Takahashi Hiroo]

Warm Forging

Warm forging is a process that aims to take advantage of the advantages of both hot and cold forging, using a temperature range between them.

Forging is also broadly divided into free forging and die forging depending on the type of die tool used.

[Takahashi Hiroo]

Free Forging

In free forging, a simple shaped tool, i.e. a tool with a flat pressing surface or a simple curved surface such as a cylindrical surface, is used to crush parts of the material one by one, repeatedly compressing them to create the final shape and dimensions. This takes a long time to work with, but the same tool can be used to make products of various shapes, making this forging suitable for high-mix, low-volume production. However, it requires high levels of skill from the worker. Depending on the shape of the tool used, punching and cutting can also be included as part of free forging.

[Takahashi Hiroo]

Die forging

On the other hand, die forging is a forging process that uses a pair of upper and lower dies that carve recesses that match the outer shape of the final or intermediate product. Dies for die forging are very expensive, but the working speed is fast, so it is suitable for mass production of forged products with the same shape and dimensions, such as automobile parts.

[Takahashi Hiroo]

New forging technology

Advances in forging technology are aimed at the economical production of more precise, complex, and highly functional products. To achieve this, various special forging machines have been developed in parallel with efforts to automate and speed up machines. Multi-ram forging machines use multiple reciprocating rams arranged vertically and horizontally, and each ram is fitted with a die tool to simultaneously pressurize multiple points on the material, thereby speeding up the work speed. There are also hot free forging machines that achieve improved work speed and product precision by computerizing everything from the operation of the rams to tool replacement. Rotary forging machines are used for the small-lot production of disc-shaped products. This machine has a holder on top with an upper die (with a cone-shaped pressing surface) attached, and its axis is slightly tilted from the vertical. The holder then rotates and revolves around the vertical axis. In other words, it performs a miso grinding motion. Meanwhile, the lower die is engraved with bumps and grooves that match the shape of the product, and is attached to a hydraulic ram at the bottom, and is pushed up by hydraulic pressure. In this way, the material is continuously pressed part by part on the conical pressure surface of the upper die, filling the recess in the lower die. Because pressure is applied locally, the load required for forming is much smaller than with normal die forging, which compresses the entire material at the same time, and smaller machines are also required. Rotary forging can be considered a combined process of rolling and forging, and because it does not strike the material, there is less vibration and noise. It is also used to form gears.

The development of combined processing methods with other processing methods has been a recent trend. One example is molten metal forging, a combined process of casting and forging, in which molten metal (molten metal) is poured into a mold and high pressure is applied to the molten metal by forcing a punch tool into it, forming and solidifying it at the same time. This process produces homogeneous, high-strength products without the defects typical of cast products. Powder forging is a process that combines powder metallurgy and hot forging to produce high-precision, high-strength products at a relatively low cost, and is also attracting attention as a method for processing titanium alloys and other heat-resistant materials, as well as difficult-to-process materials such as tungsten.

[Takahashi Hiroo]

Rotary forging and squeegee forging
©Shogakukan ">

Rotary forging and squeegee forging

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

金属加工の一種で、金型工具を介して素材材料に圧縮荷重を加え、素材の高さ（または直径もしくは厚さ）を縮め、圧縮と直角の方向に伸ばすことによって所定の形状寸法の品物に成形する作業をいう。その歴史は、人類が金属で武器や装飾品をつくり始めた青銅器時代（前4000～前2000）にさかのぼる。わが国でも古来、火造(ひづく)りまたは鍛冶(かじ)といわれて刀剣類や鋤(すき)・鍬(くわ)などの耕作用農具、馬の蹄鉄(ていてつ)などの製造手段として行われてきた。これらは手持ちハンマーによるいわば手作業の域にとどまるが、現今では空気ハンマーやプレスなど機械力を利用して、大は重さ数百トンに及ぶ船舶用や原子力発電機用回転軸から、小は釘(くぎ)のような1グラム前後の製品、その中間では自動車用の各種複雑形状部品が鍛造でつくられている。鍛造は目的に応じて赤熱の高温から室温に至る間のいろいろな温度範囲で行われる。

［高橋裕男］

熱間鍛造

材料を赤熱状態にまで加熱して行う鍛造であり、その目的は成形と同時に鍛錬によって材料の機械的性質を向上させることにある。溶融金属を鋳型に注入して固めた鋳塊や、連続鋳造でつくった鋳片はそのままではもろく、強度も低い。しかしこれを熱間鍛造すると内部組織が改善されて粘さをもつようになり、衝撃力に対しても強くなるのである。ただし材料によっては、たとえば軟鋼の場合、熱間脆性(ぜいせい)とよばれて900～1200℃の範囲で非常にもろくなる性質があるので、鋳塊・鋳片鍛造の初期工程では加工度は小さく選ぶことが肝要である。鍛錬で内部組織が改善された金属は高温において軟らかく、かつ十分に延びる性質をもつので、大きな加工度でしかも複雑な形状に成形できる。

［高橋裕男］

冷間鍛造

一方、室温付近で行われる鍛造は冷間鍛造とよばれ、複雑形状品の成形には不向きだが、変形に伴っておこる加工硬化のため、高強度を得ることが可能であり、また、表面がきれいで寸法精度の高い製品につくることができる。

［高橋裕男］

温間鍛造

温間鍛造は熱間鍛造と冷間鍛造の中間の温度域で両者の長所を生かすことをねらった作業である。

　鍛造はまた、用いる金型工具の種類によって自由鍛造と型鍛造とに大別される。

［高橋裕男］

自由鍛造

自由鍛造では単純形状工具、すなわち加圧面が平面かまたは円柱面のような単純な曲面の工具を用いて、素材の一部分ずつを圧(お)しつぶす局部圧縮の繰り返しによって最終形状寸法に仕上げていく。したがって作業時間は長くかかるが、同じ工具を用いていろいろな形の製品をつくることができ、多品種少量生産向きの鍛造である。しかし作業者には高度の技能が要求される。なお、使用工具の形状いかんによっては、打抜きや切断も自由鍛造の一環に含まれる。

［高橋裕男］

型鍛造

一方、型鍛造は、最終または中間製品の外形形状にあわせた凹(へこ)みを彫り込んだ、上下一対の金型を用いて行う鍛造である。型鍛造用金型は非常に高価であるが、作業速度は速いので、自動車部品のように同じ形状寸法の鍛造品の大量生産に向いている。

［高橋裕男］

鍛造の新技術

鍛造技術の進歩はより精密・複雑・高機能の製品の経済的生産を指向している。そのために機械の自動化、高速化を図るのと併行して、種々の特殊鍛造機が開発されている。多ラム鍛造機は、往復運動するラムを複数個用いてこれを鉛直および水平方向に配置し、それぞれのラムに金型工具を取り付けて、素材の複数箇所を同時に加圧することによって作業速度の迅速化を図っている。また、ラムの作動から工具交換を含めたすべてを計算機制御することによって、作業速度と製品精度の向上を達成した熱間自由鍛造機もある。円板状製品の少量生産用には回転鍛造機がある。この機械は上部に上型（円錐(えんすい)状加圧面をもつ）を取り付けたホルダーがあり、その軸は鉛直からわずかだけ傾いている。そしてホルダーは自転しながら鉛直軸の周りに公転する。すなわち、みそすり運動をする。一方、下型は製品形状にあわせた凹凸が彫り込まれており、下部の油圧ラムに取り付けられ、油圧によって押し上げられる。こうして素材は上型の円錐状加圧面で一部分ずつ連続的に加圧されて下型凹部に充満していく。局部加圧なので成形に要する荷重は、全体を同時に圧縮する通常の型鍛造よりずっと小さくてすみ、機械も小型ですむ。回転鍛造は圧延と鍛造の複合加工とみることができ、しかも材料を打撃しないので振動・騒音が少ない。歯車の成形にも応用されている。

　他の加工法との複合加工法の発展は近年の傾向であり、その一例として溶湯(ようとう)鍛造は、金型内に注入された溶融金属（溶湯）にパンチ工具を押し込むことによって溶湯に高圧力を加え、成形と凝固を同時に行う作業で、鋳造と鍛造の複合加工である。鋳造品に特有な欠陥を含むことなく、強度の高い均質な成形品が得られる。また、粉末鍛造は、粉末冶金(やきん)と熱間鍛造を複合させて比較的安価に高精度・高強度の製品を得る加工法であり、チタン合金その他の耐熱材料やタングステンなどの難加工性材料の加工法としても注目されている。

［高橋裕男］

回転鍛造法と溶湯鍛造法

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例

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