Forging is a metal shaping process in which a malleable metal part, known as a blank, billet or workpiece, is worked to a predetermined shape by one or more processes such as hammering, upsetting, pressing, rolling and so forth. Cold forming is a precision category of forging which does the same thing without heating of the material (room temperature), or removal of material.
Most of Shimano's products in the bike and fishing business utilize cold forming technology, which was established by the company more than four decades ago. It was in 1963 that Shimano introduced a cold forging plant to press precision parts for bicycles using dies and high pressure in order to form metal at room temperature. Plants such as these use presses, punches and dies that see very high working pressures, upto 1500 N/mm^2.
But why such specialized equipment?
The plasticity of aluminum at room temperature is low. The flow stress of aluminum decreases with increasing temperature. For alloys that are very easy to forge, such as 6061, there is nearly 50% decrease in flow stress between 700 deg F and 900 deg F.
Forgeability and forging temperatures of various aluminum alloys. Note that 810-900 deg F is the recommended forging temperature for 6061 alloy. Credits : Aluminum and Aluminum Alloys (ASM International)
Therefore, at room temperatures , because the flow stresses are higher, large machines capable of ramming and hammering the hell out of these alloys to get accurate shapes are needed. Of course, its more a delicate operation as opposed to the violence I have described above as great care has to be taken to prevent microscopic defects from developing in the cold forged piece, while it works at the upper limit of its strength.
On the other hand, because cold forging allows one to make parts without introducing the need for heat treatment and additional machining processes, it is an economical manufacturing method to produce precision, net-shape parts.
This is exactly what was needed by Shimano back in the day when it started designing integrated shift levers and gears that demanded high precision but which invariably suffered from the disadvantage of having a specialized and small market without much economy of scale. It has been mentioned that Shimano is one of the few companies in the world that can produce cold forged aluminum parts with close tolerances as those needed in the STI mechanism.
So how exactly did Shimano get around to having this precision, cost cutting technology? It turns out that the company has to thank a brilliant electrical engineer who basically re-created the entire company in the 1950's by helping it adopt the cold forging process, way before any other company in Japan at the time, even Toyota!!
Shuzo Matsumoto joined Shimano in 1954 with a dream. A graduate of the electrical engineering department of Osaka Prefecture University, he saw his mission as introducing cold forging technology to the replace hot forging then used. To achieve this goal, he was dispatched to the United States for 2.5 months by the company President, Shozaburo Shimano (died in 1958). In those days, only a limited amount of foreign currency could be taken out of Japan by any individual. Therefore, before departure, he was handed a lot of dollars obtained from the black market by Shozaburo and was simply instructed to "enjoy the trip".
The following snippet from page 76 of the book "Japan : Moving Towards A More Advanced Knowledge Economy, Vol. 2 Advanced Knowledge Creating Companies " describes briefly how Matsumoto went about accomplishing his mission of introducing cold forging technology to Shimano. Zoom in to enjoy the read. If you've anything else to share about Shimano and their production processes, give me a buzz.
ADDITIONAL RESOURCES :
Cold Forging In Bolt Production : A Video From Discovery Channel's How Its Made
Shuzo Matsumoto Patent : Rear Hub With Built-In Three Speed Change Mechanism For A Bicycle
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