Still another challenging project came from a request from representatives of the Special Vehicles Group of the Ford Motor Co., who wanted about 4 inches trimmed off the bottom of Ford Thunderbird windshields to be used in NASCAR race cars. This posed an interesting problem, because Ford wanted to uses finished windshields that were already laminated and bent to the contoured windshield shape.

It was necessary to find a way to support the windshields properly as they were being cut and then cut along the bent contour of the windshield. Special fixturing, the addition of a Z axis for raising and lowering the nozzle as it moved over the contour of the windshield, plus a lot of experimentation finally led to a successful result in this project.

My company has been doing waterjet contract cutting for four years. During this time, we have done an enormous amount of experimentation in order to gain the knowledge needed to be able to apply the abrasive waterjet technology to cutting thick glass, borosilicates, polycarbonate glass laminates, wire glass, chemically strengthened glass, and such varied items as parts for CAT scan machines and tank windows.

Some of the most recent and most exciting of such applications have involved the cutting of chemically strengthened glass. Many laminators have had difficulty in cutting notches and drilling holes in chem-strengthened glass, especially when it is laminated with layers of polycarbonate for bullet- and forced-entry resistant products.

Experiments

During the past year, my company has performed extensive experiments with ways to employ the waterjet process with chem-strengthened, glass-clad polycarbonate laminates. In January, we finished developing a series of techniques designed to make these types of cuts both routine and cost effective.

This development is significant not just because holes and notches can now be cut inexpensively from this type of glass with a very low risk of breakage but also because it provides an opportunity to maximize the throughput of the laminating process.

The ability to use the waterjet to cut laminated parts to size from large sheets can make a substantial difference in reducing autoclave cycles.

Continued

Continued from

Let's look at a specific example. If a customer needs 2,400 parts of 9/16-inch thickness chem-strengthened and polycarbonate laminate with dimensions of 6 inches by 24 inches, the laminator can lay up sheets 72 inches by 48 inches and use waterjet cutting to "strip cut" these sheets into 24 pieces per sheet. As a result, he need only send 100 sheets through the autoclave instead of 2,400.

The opportunity for cost savings and improved capacity from this alone is potentially substantial. In some cases, the net effect is equivalent to having extra autoclaves, with the cost of the waterjet cutting about a trade-off with the cutting and laying up of all the individual small pieces.

With waterjet cutting, it is also possible to build an inventory of the most common constructions of laminated glass and then cut them to size based on customer requirements. This allows laminators to provide faster service to their customers by either having waterjet cutting equipment in-house or inventorying material at a contract cutting facility. In either case, product can then be cut and drop-shipped to a customer with a turnaround of less than a week.

One laminated glass application my company had recently was particularly challenging. This involved cutting bullet resistant 2 inch thick laminated glass windows, 12 inches by 12 inches, for military tanks. The biggest challenge was the need to hold a tolerance of +/-.020 inches.

Difficulty

What made this project difficult is the tendency in thick laminated glass applications for the stream of the waterjet to begin to spread out after leaving the nozzle and create a taper of about one to two degrees from the top to the bottom of the glass.

The amount of this taper depends on the cutting speed, pressure, and nozzle and jewel combination, as well as other factors. By balancing all the cutting factors properly, we were able to hold the required tolerances and still make the parts on a cost-effective basis.

Another interesting project has been the cutting of large rings of 3/8 inch glass used in making optical encoders for CAT scan machines. After being cut by waterjet, the rings are then ground, polished, and coated. Eventually, the tiny optical lines used for the encoding are made on the surface, and the finished unit becomes an integral part of the motion control system of a CAT scan machine.