Electric heating – Metal heating – By arc
Patent
1998-08-24
2000-11-07
Evans, Geoffrey S.
Electric heating
Metal heating
By arc
21912169, B23K 2636
Patent
active
061440116
DESCRIPTION:
BRIEF SUMMARY
This invention relates to laser marking apparatus and methods and in particular, but not exclusively, the invention is concerned with marking a series of marks or characters on an elongate and/or moving object, such as a wire, cable or tube, or on a series of objects.
Manufacturers of products containing a large number of electrical wires or cables, or other elongate elements such as pipes or tubes, are often obliged to mark them with identification codes for production, maintenance and safety reasons. This is particularly so in the aerospace industry where the outer insulation of wires must be marked at regular intervals along their length (typically every 75 mm). Historically, this has been achieved using hot stamp, ink jet and, more recently, laser technologies. The word "wire" is used to include the electrical conductor, and any insulation or shielding.
For the last several years, ultra violet (U.V.) laser wire markers have been available based on a specific type of pulsed U.V. laser known as an "Excimer" laser which generally induces a colour change in Titanium Dioxide, which is contained as a pigment in many plastics materials used as insulation. These U.V. laser wire markers are quickly becoming the preferred solution in higher volume manufacturing situations because of their speed of operation and particularly because they produce high quality permanent marks on the most advanced, "non-stick", thin-walled fluoropolymer finished wires and cables without damaging or affecting the integrity of the insulation.
In a typical arrangement, radiation from an excimer laser which can be fired on demand is used to illuminate alphanumeric characters on a continuously rotating mask. The laser, being capable of asynchronous operation, is slaved to the mask and fired when the selected character or the mask is in the path of the laser beam. De-magnified images of the mask characters are created on the surface of the wires thereby producing wire or cable identification marks. To allow for the fact that the laser does not fire at regular intervals when a series of characters is printed, a galvanometer mirror is positioned to provide a variable deflection to ensure constant character spacing and to increase effective throughput. This system gives excellent results and has achieved substantial commercial success with major aerospace manufacturers, but the system is sophisticated and the purchase and running costs reflect this. Excimer lasers are large, expensive, use toxic gases to produce the laser radiation and require special services. Thus the site for the laser marking machine requires water or air cooling services, an extraction system, a source of compressed air, a supply of several gases, and a suitable power supply. However, against this these systems do have the advantage that the laser is slaved to the mask and so the mask is only required to rotate at a constant speed.
Naturally, in any machine, particularly those without galvanometers, the wire marking speed is extremely important because this dictates the productivity of the machine, with a typical throughput for marking applications needing a laser firing at 20 Hz. Any slower than this would mean that the throughput rate of wire was unacceptably low. Existing machines using fire-on-demand lasers employ a variety of techniques to maximise this speed, including sweeping the beam to track the wire during printing. To cater for a variety of sizes of wire, and customer requirements, the rotating mask usually needs to carry several print sizes and also to present characters in both vertical and horizontal orientations, and so the mask may carry three or more character sets around its periphery, which in turn dictates the diameter and inertia of the mask.
A need exists for a laser marking machine of simpler construction for lower volume manufacturing and maintenance operations and which does not place such high demands in terms of the services required at the site.
In our first proposal, we investigated the possibility of a marking system which used a pulsed so
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Lau Simon
Moss John
Phillips David Keston
Evans Geoffrey S.
Spectrum Technologies Limited
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