2005 巻 (2005) 50 号 p. 63-71
Usually, helical compression spring ends require a grinding process. This process sometimes restricts productivity of the production line and needs countermeasures for dust and noise. Fine steel powder generated from the process contains particles of the abrasive wheel. As the steel powder and the abrasive particles are inseparably mixed, they cannot be handled as steel material for scrap metal. They inevitably become industrial waste. As a result, the grinding process needs additional costs for dust control, noise prevention and waste disposal. This committee was launched for the purpose of investigating the new processing method which can replace grinding operation, and the following results were obtained.
(1) Study on current practices
Springs that have not-ground- ends are widely used for industrial purposes. Wire diameter of the springs range from 0.2mm to 35mm and the spring indexes are higher than 3.5. The production-mix ratio between “ground-ends springs” and “not-ground-ends” springs varies from company to company. It seems that the customers make a decision on necessity of coil-end grinding. When squareness and flatness is essential, the grinding process is employed.
(2) Archive research
The committee members reviewed relevant literatures written from 1975 to August 2003 and could not find any that conforms to their purposes.
(3) Patent research
The committee searched through patents applied in the same period and found that 10 of them met with the requirements.
(4) Finite Element Analysis (FEA)
The committee investigated the applicable range of a spring characteristic formula and a stress formula by applying FEA to the calculation model. Consequently, it seems that the spring characteristic formula is practical. However, when the spring index became less than six, it is necessary to take the influence of contact stress into consideration for the stress calculation formula.
(5) Study on existing manufacturing methods
Bending, rolling or cutting-off method, are mainly used for the manufacturing of “not-ground-ends springs.” The Rolling method has long been utilized for hot-formed springs while it has not been applied to cold-formed springs.