1. Title of Invention
Mechanism for marking locations of holes using laser scribing technique
2. Field of Invention
The present invention generally relates to mechanical engineering process and in particular relates to a combination of Mechanical, NC Programming and Laser marking techniques.
3. Background of Invention
The hole locations on aircraft skins are in general marked using various methods which includes drill templates, layout methods, drilling fixtures or using forming tool on CNC machines. When it comes to aircraft skins with larger surface area, the layout method is very laborious, time consuming and the least accurate which can potentially cause errors in the hole location resulting in part rejections. The other methods use bulky, expensive and long lead time tools. This may not be cost effective if the number of parts required to be produced from these tools is less. In addition to this, the handling of huge bulky tools requires lots of manpower. When it comes to the use of huge forming tools on CNC machines for marking / drilling hole locations, the machine bed should be adequate to accommodate the same.
Along with these limitations, using laser scribing machine directly on bare metal damages the laser probe.
4. Summary of Invention
The present invention provides a methodology for using a Laser scribing technique for marking of locations in general and in particular to marking of pilot hole locations on aircraft skins in the present embodiment.
In this particular case, using an outer surface skin without pilot hole locations on a structural assembly jig can lead to wrong positioning of skin and create redundant holes at unwanted location, which would result in rejection of the part or sub-assembly.
However, there are methods to create pilot hole location by other means such as Layout method, Drill template, drilling fixtures etc., which are bulky, expensive, less accurate and time consuming.

5. Detailed Description of the Invention
A Laser Scribing Machine is used in the present embodiment for marking areas for chemical milling / electrical bonding etc on the maskant. The machine is a 5-axis machine equipped with laser head. The laser from the laser head is designed to scribe only the maskant, and within the thickness range of 20um to 45um. The machine is generally not designed to scribe on bare skin.
The skins were masked with neoprene maskant and then followed with pilot hole marking.
Various trial runs were taken to check the feasibility to mark hole location on the masked test specimens. The test specimens ranged from flat plates to stretched sheets. The parameters such as the laser power, laser distance etc needed to be set at optimum so as to ensure that laser marking did not damage the skin. The optimum parameters were arrived at, after various trials.
Vector locations were taken as input for NC programming and then they were mapped and superimposed on to the individual skins.
The skin was masked in strips with maskant with an appropriate maskant thickness. It was positioned on the machine bed of a laser scribing machine that utilizes a vacuum controlled mechanism. The positioning was adjusted with respect to the model of the skin. The skin was locked at both ends on tooling holes. There were no other tools or fixtures used.
.The marked skin was loaded on the assembly jig. One hole was layout marked from the frame to the skin, to validate the pilot hole marking on the skin. Once confirmed, the complete drilling was taken up and later the maskant was removed. Thus, location of pilot holes was marked on the skin, without any additionally customized production tools.