Patent ID: 9255378
Filing Date: 2016-02-09
CPC Classification: E02F

Claim Text:
1. An arm for a construction machine formed as a box-shaped structural body having a square cross sectional surface, having left and right side plates, an upper plate joined to upper end sides of said left and right side plates by welding, a lower plate joined to lower end sides of said left and right side plates by welding, and a rear plate joined to rear end sides of said left and right side plates and a rear end side of said upper plate by welding, comprising: a boom connecting boss located on rear parts on the lower end sides of said left and right side plates and joined to the rear end sides of said left and right side plates and said lower plate and a front end of said rear plate by welding; a bucket connecting boss joined to front ends of said left and right side plates, said upper plate, and said lower plate by welding; and a pair of left and right bucket cylinder brackets joined to an outer surface of said upper plate by welding , characterized in that; said upper plate is formed by joining two members, that is, a rear, thick upper plate located on a rear side of said upper plate and made of a plate material having a large plate thickness and a front, thin upper plate located on a front side of said rear, thick upper plate and made of a plate material having a small plate thickness; said lower plate is formed by joining two members, that is, a rear, thick lower plate located on a rear side of said lower plate and made of a plate material having a large plate thickness and a front, thin lower plate located on a front side of said rear thick lower plate and made of a plate material having a small plate thickness; said left and right side plates are formed by joining two members, that is, a rear, thick side plate located on a rear side of each of said left and right plates and made of a plate material having a large plate thickness and a front, thin side plate located on a front side of each said rear, thick side plate and made of a plate material having a small plate thickness; said pair of said left and right bucket cylinder brackets are configured to be joined to an outer surface of said rear, thick upper plate; said boom connecting boss is configured to be joined to a rear end of said rear, thick lower plate; a joint portion between said rear, thick side plate and said front, thin side plate, said joint portion being configured such that an upper end of said joint portion is joined to said rear, thick upper plate and a lower end of said joint portion is joined to said rear, thick lower plate; an auxiliary welding member having a flat plate shape and provided on an outer surface of the rear part side of said upper plate so as to surround a welded portion between each of said pair of left and right bucket cylinder brackets and said upper plate; and a welding bead formed by applying fillet welding around said auxiliary welding member.