Electric heating – Metal heating – By arc
Patent
1993-09-24
1995-08-29
Reynolds, Bruce A.
Electric heating
Metal heating
By arc
21912161, 21912173, 21912192, 148565, 148512, B23K 2600, B23K 2608
Patent
active
054462584
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for remelting metal surfaces using a laser to increase the wear resistance of metal surfaces. This is of particular importance in the case of camshafts which are used for the valve timing gear in internal-combustion engines. Due to their rotary movement, the individual cams arranged on the camshaft effect an adjustment of the corresponding cam followers, valve levers or the like. Normally, the wear resistance of the cam running surfaces is increased by remelting. It has already been known for a relatively long time to make use of the so-called TIG process (tungsten inert gas process) for this purpose. A particular disadvantage of this process is, the relatively high time outlay and the long cycle times bound up therewith. German Publication DE 3,916,684 A1 discloses using a rectangular laser beam to carry out remelting of valve lever running surfaces for the valve timing gear of internal-combustion engines. The width of the surfaces to be remelted is subdivided there into a plurality of subregions and a large middle top region is remelted separately in time from outer edge regions. Here, too, the time outlay is still relatively high.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a particularly cost-effective process for remelting by using a laser. The invention provides a process for remelting metal cam running surfaces on a cast iron cam using a laser beam focused to a rectangle. A laser beam is produced which has a rectangle length substantially equal to a width of a cam running surface and a rectangle width between approximately 1 to 3 mm. The laser beam is applied to the cam running surface. The laser beam is controlled such that immediately above the cam running surface the laser beam has a power density between 5.times.10.sup.4 and 1.times.10.sup.5 W/cm.sup.2. Relative movement is effected between the cam running surface and the laser beam approximately transversely to the laser beam at a speed of 2 to 6.5 cm/sec.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in further detail below with reference to the accompanying FIGURE, which illustrates a preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
It has been proved that given a specific parameter setting it is possible to remelt the entire surface width of a workpiece in one operation without the occurrence of undesired phenomena at the surface edge regions. Correspondingly, in the process according to the invention the length of the laser beam rectangle is set approximately as wide as the width of the workpiece surface, that is a rectangle width of approximately 1 to 3 mm. Immediately above the metal surface, a laser beam with a power density of 5.times.10.sup.4 to 1.times.10.sup.5 W/cm.sup.2 is provided. The metal surface moves relatively and approximately transversely to the laser beam at a speed of 2 to 6.5 cm/sec, preferably 4 to 4.5 cm/sec. It is possible to achieve particularly wear-resistant surfaces by means of the process of this invention in a cost-effective way and with a relatively short machining time.
Before remelting using the laser, the workpiece, in particular the camshaft, having the metal surface, is advantageously preheated to 360.degree. to 420.degree. C., preferably to approximately 400.degree. C. The remelting time is further reduced thereby, and the wear resistance is improved overall after termination of the process.
The quality of the surface edge regions corresponds strongly to the remelting depth. Remelting the surface down to a depth of 350 .mu.m is particularly advantageous. Further added to this dimension is a tolerance of preferably 200 .mu.m for grinding of the surface which may optionally be carried out after the remelting.
An example of the process according to the invention is explained in more detail below with the aid of the sole FIGURE. The FIGURE shows a laser 20 and one cam 11 of a plurality of cams which are arranged on a camshaft 10. The running surface of the c
REFERENCES:
patent: 4304978 (1981-12-01), Saunders
patent: 4686349 (1987-08-01), Kawazu et al.
patent: 4692583 (1987-09-01), Kimura et al.
patent: 4714809 (1987-12-01), Hammond et al.
Zechmeister et al., "Bearbeitung mit Hochleistungslasern", Werkstatt und Betrieb, vol. 115:265-267, (1982).
Mills Gregory L.
MLI Lasers
Reynolds Bruce A.
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