Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
1999-05-13
2001-07-10
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C029S888440
Reexamination Certificate
active
06259054
ABSTRACT:
FIELD OF INVENTION
This invention concerns the forming of valve seatings in metal castings forming parts of internal combustion engines, most commonly cylinder heads of such engines.
BACKGROUND TO THE INVENTION
Conventional techniques for forming valve seats in cylinder heads involve cryogenically freezing sintered alloy iron annular seating rings, force fitting the rings into recesses in the cylinder head, and then machining. Recently it has been proposed to reduce the iron sector of the seating rings and it has now been proposed to electrically weld or otherwise bond the seating rings into position using resistance welding techniques, typically DC current derived from a single or more preferably multiphase AC supply.
Problems have arisen in designing apparatus for achieving this proposal, not least of which involve the handling of the relatively small metal rings which are to constitute the seatings, and the positioning of these reliably for welding.
An ancillary problem arises from the inevitable process spatter which, if not removed from the cylinder head, would cause problems when the resulting engine was run.
In EP-A-0751284 there is disclosed a method of securing a valve seat member to a cylinder head recess, in which the cylinder head is placed on a press machine with the recess facing upwards, the member is pressed down against the recess, and the member is metallurgically bonded to the recess by applying a voltage thereacross via upper and lower electrodes. However, this prior disclosure does not obviate either of the above mentioned problems.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a method of fitting a valve seating ring in a annular recess in an engine component, such as a cylinder head comprises the steps of:
a) supporting the engine component above a workstation so that the recess which is to receive a valve seating ring faces in a generally downward direction;
b) positioning the ring at the upper end of a tool which forms part of the workstation and is adapted to be moved in an upward direction towards a component supported thereabove;
c) moving the tool so upwards so that the upper end enters the recess and positions the seating ring accurately therein;
d) exerting an upward force so as to press the ring uniformly against at least one region of the recess into which it is to be fixed;
e) causing an electric current to flow across the junction between the ring and the component so as to locally heat and cause a plastic deformation of the component material around the ring, to weld-bond the ring to the component;
f) terminating the flow of current to allow the site to cool; and
g) removing the tool and leaving the seating ring bonded to the component, to form the valve seating.
It is an advantage of the present method that any metal spatter which can occur during the heating and bonding process will tend to fall under gravity away from the component and can be collected and conveyed away from the workstation, if desired. This is achieved in accordance with the invention by having the reverse arrangement to that disclosed in EP-A-0751284.
Preferably the component can be indexed so as to present different ones of a plurality of recesses therein in alignment with said tool so as to allow each of the recesses to be fitted with a valve seating ring in the manner aforesaid.
According to another aspect of the invention there is provided apparatus for fitting a valve seating ring in an annular recess in an engine component, comprising component support means positioned adjacent and above a workstation, a tool in the workstation, drive means for moving the tool in an upward and downward direction relative to the component support means, means for aligning the tool axis and the support means so that the up and down movement of the tool is in alignment with a given region of the component support, means for locating onto the upper end of the tool a valve seating ring, control means for controlling the drive means to cause the tool to move upwards and position the ring located thereon in a recess in the component carried by the support means, electrical connections between a supply of electric current and the component and the tool so as to cause an electric current to flow from one to the other when contact is made between the ring and the component, means for exerting a force on the tool or the support means or both to push the tool and the support means towards each other so that the ring on the tool is pressed into contact with said recess in order to resistance weld the seating ring in place, said control means also causing the drive means to withdraw the tool in a downward direction clear of the ring when weld-bonded to the component, permitting relative lateral movement between the component support and the tool to allow the later to be aligned with another region of the component support means or to allow a component carried by the support means to be moved away and replaced by another component for fitting a ring therein.
Since considerable heat is generated during the weld-bonding process, preferably both the tool and the component holding device are fluid cooled, typically using water or glycol solution.
Furthermore, since there will be local temperature rise within the component around each weld bond site at least during and immediately after a ring has been welded into place, the sequence in which rings are fitted to the component is chosen, so that successive rings are located at well spaced apart regions of the component, allowing the heat generated during the previous welding step to dissipate, and prevent an integration of heating in any one region.
The invention also lies in an engine component when fitted with one or more valve seating rings in accordance with the aforementioned method.
The apparatus is of particular use in forming valve-seats in the underside of an aluminium engine cylinder head.
In order to accommodate misalignment between the axis of the tool and the axis of a annular recess into which a valve seating ring is to be fitted, the tool may be formed in two parts, an upper and a lower part, and the upper part is adapted to receive a valve seating ring thereon and is mounted on the lower part so as to be movable relative thereto so as to allow the valve seating ring to fit uniformly and accurately into a recess into which it is introduced.
In a modern internal combustion engine, valve seats are typically arranged in pairs relative to each cylinder and there may be four valves (and corresponding number of valve seats) per cylinder, arranged in two pairs. In some engine cylinder heads the axes of the narrow diameter bores associated with one pair of valve seats, extend in a divergent manner through the cylinder head relative to the axes of the bores of the other pair. The two valve seats of each pair (and therefore the recesses into which the valve seating rings are to be fitted), are in close proximity in the cylinder head, but the valve seating rings of each pair cannot be fitted and bonded simultaneously or even in quick succession due to the cumulative heating which would occur. However it is possible to consider fitting a seating ring to one of the bores in one pair associated with a first cylinder, and one of the pair of bores associated with another cylinder which is remote from the first cylinder, in quick succession.
To achieve this there is provided tool means adapted to support at the upper end thereof a pair of valve seating rings for movement into engagement with and fitting into each of two spaced apart recesses in the cylinder head in the manner described as aforesaid, each of the two valve seating rings being presented to the tooling means in the workstation from a supply of said valve seating rings, and the tooling means being movable to present and insert the valve seating rings located thereon simultaneously into the two recesses, and electric current is caused to flow through the tooling means to weld-bond the valve seating rings in place.
Whilst it is possible to envisag
Evans Geoffrey S.
Lee Mann Smith McWilliams Sweeney & Ohlson
Unova U.K. Limited
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