January 9, 2007
Both laser and waterjet cutting systems produce precision parts, and in many applications, either is appropriate. This article, which discusses the benefits and limitations of both technologies, can help you decide which is best-suited for your operation. In some cases, utilizing both can increase manufacturing flexibility and your business capabilities.
Today's laser and waterjet cutting technologies offer flexibility for precision applications in a range of materials. The choice to use either technology is in part determined by the material to be processed, because both technologies are capable of delivering precision cuts. Materials that are difficult to process with a laser, such as aluminum, brass, and copper, are processed easily and economically with a waterjet.
While laser technology offers the distinct advantage of high processing speed in most sheet metal applications, waterjet technology offers flexibility for materials that are difficult to cut with a laser or that require a non-heat-affected surface. Utilizing both technologies offers precision, speed, flexibility, and diversification in manufacturing.
Lasers ( Figure 1) are used widely in manufacturing processes that involve sheet metal and plate components. Laser popularity is due in part to the ever-increasing demand for accuracy, repeatability, speed, and overall quality. Downstream processes, such as robotic welding and press brake operations, benefit from increased accuracy. Producing components to fit into tight-tolerance jigs is a prime example of the benefits derived from using a high-precision cutting tool on the front end of the manufacturing process.
Lasers can process sheet metal at high speeds because of their ability to melt or vaporize material, in addition to requiring little to no setup time. Because the laser is a single tool that can cut almost any shape, the need for expensive hard tooling and the setup time involved for these tools are eliminated. High-speed lasers are capable of high acceleration and deceleration rates, allowing for optimum point-to-point positioning and contour cutting speeds. Sheet metal laser cutting speeds can exceed 1,000 inches per minute, depending on the material's thickness. Lasers offer the added benefit of eliminating secondary finishing operations, and parts can move directly from cutting to other downstream processes.
Typical laser cutting cells comprise the laser machine, along with material management and automated load/unload systems that allow manufacturers to process high volumes of varying material types and thicknesses in an unattended operation. Jobs are sent directly to the laser from the production office.
The system automatically selects the proper material type and thickness to process the job and unloads it onto tables or back-stores it onto shelves within the material tower. Kits or assemblies can be stored on their own shelves, or materials can be stored based on the next process. For example, components moving to bending, welding, and painting areas can be stored on different shelves for easy handling.
While lasers appear to be the optimum tool for manufacturers in many cases, they do have their limitations. The most apparent limitation is their inability to cut a broad range of materials, either because of the material's properties, or because toxic fumes are generated by thermal processing.
Another limitation is the difficulty in processing steel plate materials thicker than 1 in. Special care must be taken not to overheat the metal. Cut sequences must move around the plate to offset heat, and parts generally are spaced apart using the material thickness as the standard offset distance. Aluminum, brass and copper have more process limitations because of their reflective and thermal conductive properties.
The use of lasers in aerospace applications is severely limited because of the laser's effect on the microstructure of the metal, which leads to cracking and hardening; this effect is known as the heat-affected zone (HAZ). Structural components subjected to large load forces, such as wing components, are prohibited from having laser-finished parts because the microstructure change in the cut surface could lead to a catastrophic failure under a load stress.
Waterjets, on the other hand, are used extensively in aerospace and other industries because of the technology's flexibility in processing a range of materials and thicknesses. Also, waterjet processing does not change the microstructure of the cut surface.
The basic erosion characteristics of water are evident in the large canyons and earth carvings that have been created over millions of years. In a waterjet cutting system, when water pressure is generated to 55,000 PSI and accelerated at nearly 3,000 square feet per second, the erosive characteristics are instantaneous and extremely powerful. While pure water erosion is one form of waterjet cutting, another— abrasive waterjet cutting — also exists.
Industries that use nonabrasive waterjets include the food industry, in which some foods are cut or separated (desserts, beef, poultry) using a high-pressure water stream; the textile industry, in which clothes are stack-cut to shape and size requirements (blue jeans); the paper industry for cutting paper rolls into different widths; and the foam industry in trimming products, such as automotive and marine seat foam.
The abrasive waterjet (Figure 2) adds a mineral sand, such as garnet, into the water stream to accelerate the erosion process. This provides a more aggressive medium for hard materials, such as metals, stone, marble, glass, and composites.
Industries that use abrasive waterjets include the metal industry, which processes metals of all types and thicknesses for many industrial and consumer goods; the glass industry for processing special applications, such as notching and multilaminate bulletproof glass; the plastics industry to eliminate environmental concerns associated with thermal processing; the stone and marble industry for architectural applications; and the composite industry, which manufactures resin materials are manufactured for both the aerospace and automotive industries.
Abrasive waterjets are used widely in sheet metal and plate components manufacturing. Waterjet popularity has grown in part because of an ever-increasing demand for processing thicker parts in aluminum, stainless steel, copper, brass; and thinner materials that require no HAZ (Figure 3). Thin materials can be processed almost as efficiently by a waterjet as a laser by adding cutting heads and stacking techniques.
For example, say you are cutting a high volume of 1/8-in. aluminum parts. A 4-kW laser can process this material at a feed rate of 200 IPM, and a single-head waterjet at 120 IPM. Adding a second cutting head to the waterjet and processing with both cutting heads simultaneously increases the net feed rate to 240 IPM.
Another feature of abrasive waterjets is the ability to stack dissimilar materials with varying thicknesses; provided you do not exceed the maximum thickness rating of the system. Stack-cutting with lasers is not a viable option, especially not for varying material types.
Because waterjet plate cutting does not produce heat, part spacing is not a critical consideration and can be close to optimize material utilization.
The waterjet's cold cutting eliminates concerns about releasing toxic fumes that some metals can emit, and most plastic, rubber, and composite materials certainly do that with thermal processes.
Precision waterjets can maintain tight tolerances in the range of +/- 0.002 inch for most applications. Because of this ability, precision waterjets are in the same accuracy category as lasers and other machining processes.
With waterjets, the cut surface has no HAZ, no slag formation, recast layer, or thermal deformation, as are common with laser-cut surfaces. A waterjet also is a single tool capable of cutting almost limitless shapes, eliminating the need for expensive hard tooling and the accompanying setup time.
Waterjets also eliminate secondary finishing operations, because they produce no slag formation or oxidation layer that could affect welds or paint integrity.
In today's environment, with more and more companies needing to reduce their supply chains and vendors, it is even more important to be able to offer a single turnkey manufacturing process for your customers. Suppliers who can deliver multiple products for the same customer will benefit from increased business and profits. Using lasers and waterjets will help you to achieve precision and diversification across an almost limitless range of materials and applications.