Prise winners list

Establishment of energy-saving/high yielding manufacturing technology for metal rings with Benda Method

Kure-City, Hiroshima Prefecture
Benda Kogyo Co., Ltd.
Other award winners
Benda-Kogyo Co., Ltd. / Mamoru Ojika, Kazunari Yashiro, Koji Yashiro, Takashi Yamane
Qingdao Benda Automobile Parts Co., Ltd. / Yukio Yashiro
Benda SunKwang Ind. Co., Ltd. / Kim Teikan, Tei Jyunko, Ryu Gaihan
Recommended by
Kure Industry Promotion Center

Yashiro, Yasuhiro  (68)

Steel materials also have their own characters and insists. We cannot manufacture them properly unless we understand those properties in advance

This company has tackled research and development for cold bending of steels since its establishment. The wide flange beams manufactured by its bending technology are used for the tunnels nationwide and for various purposes. It started development of technology for continuous mass production of ring blanks (material for ring gears) in the early 1970s. It developed its unique technology that combines the cold bending of steels and electric resistance welding, replacing the conventional method that had a problem in production efficiency, and obtained a patent for the technology as "manufacturing method and equipment for metal rings" in nine countries in the world in 1975. With this technology named "Benda Method", the company entered the automobile industry. Currently it manufactures various rings including small ones, having diameter of 10cm or less, for a lawnmower and other ones, having diameter of about 1m, for ocean vessels and construction of buildings. The company's market share accounts for 15% in the world.


We will bend any iron in the world! What is the request from the automobile industry that the professional of cold working accepted?

The work for bending steel materials is called "bending", and there are two types of bending. One is the hot working in which steel materials are heated and bent. The other is cold working in which steel materials are bent at normal temperature. The former requires large-scale equipment, long manufacturing time and high cost. On the other hand, the cold bending, for which we have expertise, is technically difficult to perform because it must be performed while making use of the properties of steel materials such as strength, toughness and resilience.

"When my father started this business, only few companies could perform the cold bending. Therefore we ourselves developed the work method and machines and even obtained patents. 'We will bend any iron in the world!' was our slogan at that time."
We received a request from a carmaker in the early 1970s. The carmaker asked, "Can you mass produce the steel ring blank (a ring before gear teeth are made on it), which is the material for the 'ring gear', by cold bending?" A ring gear is mounted on the flywheel of engine and conveys the revolution of the starter to the crankshaft to start the engine.

"They had so far been using a press-cutting machine, slicing a steel pipe or manufacturing blank rings in rolling forging that was a large-scale method. However, if a press-cutting machine was used, the remaining steel plates after the rings were made could not be used any longer. 80% of the raw materials became scraps. Therefore we decided to manufacture the products by cold bending the square steels and welding them."
This company had to produce a dedicated bending machine for itself, but Mr. Yashiro in his young days started research and development excitedly. Firstly, he milled the round steel bars into the square bars. Then he bent and wound these square bars into a coil in layers with three rollers. However, they could not be coiled uniformly because the cross section of a coiled bar becomes trapezoidal due to the difference in degree of elongation between the outer and inner diameters. Therefore he corrected this distortion by applying force. 
"We modified the shape of roller that mills the round bars to have the cross section of the square bar trapezoidal from the beginning. Then the problem was solved because the cross section became rectangular when the bar was bent and wound. However, this modification was made after the mass production was started. At first, we ground the four surfaces of the ring to correct the distortion. Now such additional work is not necessary."

When the square bar was bent and wound into a coil, the sides of the coil were cut vertically to produce many rings. Subsequently the cut surfaces of a ring were welded together.
"However, the completed ring is not a true circle. It was an irregular one with one side distorted. The circumference of the ring became shorter by the thickness of the cutter's blade and because the cut surfaces were melted in welding."

Make use of the properties of steel material!! Groundbreaking method "Overlapping"

Then we thought that we had to calculate the shrinkage beforehand, have the circumference of ring slightly longer for this shrinkage and "overlap" both cut ends. Just after it is cold worked, a steel material slightly returns to its original state before it is worked. We thought that we might be able to use this "spring back" property. 

We thought as follows, "First, insert a core bar larger than the inner diameter of the coil into the coil to extend it. Cut the coil in that state and then remove the core bar. Then the rings shrink due to spring back and the cut ends are overlapped on each other."
However, if a big core bar was inserted into a coil forcibly, the coil might be damaged. While we were quite at a loss, our former president (my father) found a solution. He thought, "We should produce a hollow core bar and set it into the coil. Subsequently we should insert another jig bar into the hollow core bar and extend the coil together with the core bar. The coil will be extended without any problem!"
"It was a good idea. However, as my father explained his idea while likening this method to a deed between a man and a woman, we all burst into laughter before admiring his idea." 
Although we had difficulties finding a proper material for the core bar, this method was a success. The overlapped section was pushed out as burrs when the ends were welded together, and the ring became a true circle. We later established an equation to determine the overlap distance according to the types of steel ant the ring diameters. Then if we removed the burrs, the rings would be completed, we thought at first  but this was not the case. The steel material and the welded section are different in composition and so the strength was not even among the two.
"Therefore we heated the rings up to 840C and subsequently cooled them with a big fan to normalize them. Then the composition of the steel material returned to its original uniform state."
Having finished normalizing, we thought that we had completed the rings at last!! However, one more work was necessary. We had to use a pressing machine to correct the slight errors caused by the works. The die diameter of straightening pressing machine was made slightly larger. When we checked the rings after they were pressed  they had the correct size due to spring back.

Benda Kogyo Co., Ltd.

Sep. 1964
58.5 million yen
94 (as of Dec. 2009)
Brief information:
The company specializes in cold bending of wide flange beams, square beams and other steels such as a pipe and has obtained a patent for its "Benda method".

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L:1. Raw material is round bars.
R:2. The round bars are worked into the square ones with the rollers.


L:3. The bars are bent and wound into a coil.
R:4. The ends are overlapped when the rings are cut.


L:5. The cuts of rings (top) are welded (middle) and the burrs are removed (bottom).
R:6. Heating/cooling for normalizing the rings


L:7. Straightening press
R:8. Completed ring blanks