This invention relates to electric switches of the type which have an opposed pair of stationary contacts and a movable contact and are fabricated by pressing, to an apparatus for the manufacture thereof and to a process for said manufacture.
The quality and performance of electric switches have no little effect upon the quality of various electric appliances which these switches serve. In an extreme case, failure in an electric switch can even endanger the safety of a person handling the electric appliance containing that switch. All the electric switches are, therefore, required to possess stable quality, provide quick operation and preclude troubles. For this reason, ordinary electric switches currently manufactured require much time and labor in jobs of inspection and possible readjustment which are performed subsequent to conclusion of the assembly of parts. U.S. Pat. No. 3,189,703 has issued to an invention which relates to a method for providing epochal improvements in the manufacture of electric switches. It provides a method which comprises the steps of punching sets each of three terminals in an interconnected form out of a strip of electroconductive material, mounting on each set an opposed pair of stationary contacts and a leaf spring fitted with a movable contact, embedding them with a molded plastic webbing and thereafter removing the webbing temporarily interconnecting the three terminals. This invention is excellent in that there is no possibility of dimensional error because the three terminals and the conductor are always retained in their relative position acquired at the time of punching and that the switches are suitable for mass-production. Nevertheless, the work of mounting a leaf spring and an opposed pair of contacts on such terminals which are manufactured efficiently by the method of said U.S. patent is not efficient. Particularly, the stationary contacts are formed by a troublesome step of mounting two prefabricated mushroom-shaped silver contacts in the slots and peening the divergent portion of the contact at predetermined positions into the slot. Contacts of the type formed by pressing silver rods into hemicircular slots are not totally reliable in terms of joint strength and electroconductivity. Worse yet, the very low dimensional accuracy of contact gap poses itself as a serious problem.
According to said U.S. patent, each unit of interconnected terminals is embedded by molded plastic webbing. Inclusion of such troublesome and inefficient molding work in the process of switch production can hardly be regarded as an improvement.
The main object of the present invention is to provide electric switches which are suitable for mass-production and which enjoy so precise fabrication as to render the jobs of inspection and readjustment practically unnecessary.
Another object of this invention is to provide electric switches each possessed of an opposed pair of contacts, completed by a sole operation of pressing using a strip of contact material such as of silver which is fed to the electric switch production line.
Still another object of this invention is to provide a process for completing high-quality stationary contacts in electric switches by a sole operation of pressing using a strip of contact material such as of silver.
Yet another object of this invention is to provide electric switches which are completed by a sole operation of pressing using a strip of contact material such as of silver and subsequently enclosed in prefabricated cases with high efficiency.
Another object of this invention is to provide electric switches which, on account of a leaf spring fitted at one end thereof with a movable contact and mounted on the other end thereof around the neck of a common inner end of terminals, enjoy sharp snap action and durability and which, at the same time, enjoy freedom from a conventional disadvantage that the snap action is adversely affected by the degree with which the spring is fastened.