Electric heating – Metal heating – By arc
Reexamination Certificate
1999-05-21
2001-12-11
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C134S001000, C219S121830, C219S121850
Reexamination Certificate
active
06329630
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process of cladding by welding which is advantageous in suppressing defects of cladding.
2. Description of the Related Art
Japanese unexamined patent publication 6 (1994)-257,505discloses a conventional process. Using a cylinder head formed of aluminum alloy having a cladding-scheduled portion for constituting a valve seat, this conventional process irradiates the cladding-scheduled portion with a laser beam to remelt and resolidify all of the surface of the cladding-scheduled portion. After that, this conventional process covers the resolidified portion with a clad layer. Even when the cladding-scheduled portion involves gas therein, this conventional process can release and eliminate gas so as to leave less gas in the cladding-scheduled portion before cladding. Accordingly, this conventional process can suppress expansion of gas in cladding the cladding-scheduled portion by welding.
Japanese unexamined patent publication 64 (1989)-62,282 discloses another conventional process. This another conventional process forms a bead layer by high-frequency welding to produce a seam-welded ferrous pipe. This process irradiates the bead layer with a laser beam after immediately welding, so as to remelt and eliminate weld-defects remaining in the bead layer. In this case, the bead layer is irradiated with the laser beam in such a manner that the bead layer causes little or no molten metal. This process also discloses a technique which detects plasma light generated in eliminating the weld-defects so as to examine the presence of weld-defects in the bead layer.
Japanese unexamined patent publication 6 (1994)-88,120 discloses still another conventional process concerning apparatuses which is to be employed in high temperatures, such as boilers or turbines. This process forms a bead layer by welding, and then irradiates a heat-affected zone in the vicinity of the welded bead layer with a laser beam or an electron beam so as to perform an eliminating step for eliminating the creep-voids remaining in the heat-affected zone.
According to the abovesaid publication 6 (1994)-257,505, almost all of the cladding-scheduled portion constitutes an exposed normal region having a normal surface: the cladding-scheduled portion has very few portions containing gas. In spite of this, this publication technique remelts all of the surface of the cladding-scheduled portion to generate molten metal at the all surface. Accordingly, due to such molten metal and the resultant solidification, this publication technique causes a problem that roughness is generated in all of the surface of the cladding-scheduled portion, thereby causing a problem that the clad layer is unevenness in thickness. Further, remelting all of the surface of the cladding-scheduled portion, this publication technique largely heat-affects the base material constituting the workpiece to rise a problem that balance collapses in strength of the workpiece.
Also, some workpieces have a condition that the cladding-scheduled portion is restricted to be small in thickness. In such workpieces, this publication technique, remelting all of the surface of the cladding-scheduled portion, might cause a problem that some holes unexpectedly are formed in the cladding-scheduled portion. This reason is that control is not necessarily easy in the remelting as production technology.
Since the aforesaid publication technique 64 (1989)-62,282 irradiates all of the surface of the welded bead layer with the laser beam after producing the welded bead layer constituting a clad layer, this publication technique sometimes causes a problem that metallic structure is transformed or deteriorated in all of the surface of the welded bead layer.
Also, since the aforesaid publication technique 6 (1994)-88,120performs the eliminating step after forming the welded bead layer, this publication technique sometimes causes a problem that metallic structure is transformed or deteriorated in all of the welded bead layer.
SUMMARY OF THE INVENTION
The present invention has been developed in view of the above circumstances.
It is a primary object of the present invention to provide a process of cladding by welding, which advantageously suppresses a clad layer on a cladding-scheduled portion from being transformed or deteriorated in metallic structure while eliminating a foreign substance portion to be defects in cladding. It is another object of the present invention to provide a process of cladding by welding, which performs an eliminating step before covering the cladding-scheduled portion with a clad layer, substantially without melting an exposed normal region of the cladding-scheduled portion.
A process of the cladding by welding according to a first aspect of the present invention comprises the steps of: (1) preparing a workpiece having a cladding-scheduled portion including an exposed-normal region, the exposed normal region having a normal surface including a possibility that a foreign substance portion exists, and the foreign substance portion to form a defect in cladding; (2) irradiating the exposed normal region of the cladding-scheduled portion of the workpiece with a high-density energy beam, the high-density energy beam capable of eliminating or decreasing the foreign substance portion, substantially without melting the exposed normal region of the cladding-scheduled portion; and (3) covering the exposed normal region of the cladding-scheduled portion of the workpiece with a clad layer.
The first aspect of the present invention eliminates the foreign substance portion existing in the cladding-scheduled portion of the workpiece, by irradiating the exposed normal region of the cladding-scheduled portion of the workpiece with the high-density energy beam. Thereafter, the first aspect of the present invention covers the cladding-scheduled portion of the workpiece with the clad layer. Therefore, when the cladding by welding is performed, the foreign substance portion in the cladding-scheduled portion is eliminated or decreased for purification. Accordingly, the first aspect of the present invention can suppress defects in cladding, thereby forming an appropriate clad layer to become advantageous in ensuring strength which the clad layer has originally.
Further, the first aspect of the present invention can suppress the melting of the exposed normal region having a normal surface which occupies the majority of the cladding-scheduled portion. Accordingly, the first aspect of the present invention can suppress roughness in the surface constituting the cladding-scheduled portion, thereby suppressing dispersion in thickness of the clad layer, as compared with the conventional technique which remelts all the surface of the exposed normal region and which is disclosed in the aforesaid unexamined patent publications.
Moreover, the first aspect of the present invention can suppress the transforming or the deteriorating of the exposed normal region of the cladding-scheduled portion, thereby advantageously ensuring balance of strength of the workpiece. Also, the first aspect of the present invention can prevent holes from being unexpectedly formed in the cladding-scheduled portion of the workpiece, even when the cladding-scheduled portion of the workpiece is restricted to be thin in thickness.
According to a second aspect of present invention, the irradiating step generates a physical amount in eliminating or decreasing the foreign substance portion, and the irradiating step has a detecting operation for detecting a degree that the foreign substance portion is eliminated or decreased. So, the second aspect can detect the presence of the foreign substance portion, namely the remainder thereof, without destroying the workpiece. The second aspect of the present invention is advantageous in ensuring quality of the workpiece, provided that the information about the presence of the foreign substance portion is supplied with feed-back to production conditions for producing workpieces.
Preferable Mode
The pre
Kawasaki Minoru
Maeda Chikatoshi
Sato Akio
Evans Geoffrey S.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Toyota Jidosha & Kabushiki Kaisha
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