Laser stamping takes off

With the advent of laser processing sheet metal, there has been a continuous drive for greater efficiency and tighter tolerances beyond those given for general sheet metal products. According to industry magazines, it becomes evident that this push has manifested itself in the form of hybrid laser/punch tools, as well as laser/punch/folding platforms. These platforms provide production capabilities as well as small-lot fabrication solutions for everyday sheet metal products.

However, there is a niche emerging from traditional punch press stamping in the form of laser formation of precision components utilizing coil-fed metals, where the products must maintain edge quality and dimensional stability from beginning to end of the laser cut. Current market-driven demands can easily be met by a combination of state-of-the-art motion control, laser beam delivery, process gas, and material handling, delivering new digital production capabilities for the stamping industry.

Laser precision cutting application

Digital Laser Stamping technology, developed by BOLD Laser Automation (Bedford, NH), differentiates the concepts of lower-tolerance laser blanking with higher-accuracy laser cutting engineered to mimic high-precision punch stamping. To make this a reality, the use of coil-fed material with mechanical indexing is required. Coil stock material in the form of 300- to 600-pound rolls with a specific width and thickness offers the ability of the laser system to run continuously for hours, producing a product from flat material. Without operator intervention, the payout reel, driven by a DC motor, automatically compensates using a droop sensor for feeding material into the laser process zone, where an x-y-z laser cutting head flies over to create the precision part.

By targeting niche markets, such as higher-precision (±0.001 in.) parts, the laser technique offers substantial opportunities to U.S. manufacturing for supporting small-batch pilot production and small-scale volume, high value-added component manufacturing. Benefiting significantly are U.S. manufacturers within the aerospace, automotive, and medical device industry who want to develop and test new products before committing to the substantial costs of punch tooling for mass manufacturing.

Although the general idea of precision laser cutting is not new, leveraging specialized industrially hardened laser technology offers advantages. One such advantage is small-core (20 and 50 µm), single-mode fiber lasers from SPI Lasers (Southampton, England) in continuous-wave/pulse modulated modes at power levels of 750 W to 2 kW, as well as beam delivery and shaping technology. This method better meets the industry’s needs for prototyping and short-term pilot production needs. FIGURE 1 shows the details that can be cut in a stainless steel part using such lasers when paired to appropriate motion control and beam delivery platform.

Critical motion control system

Motion control has always been a critical part of achieving precision laser cuts—computer numerical control (CNC) motion controllers for precision laser cutting using gantry x-y-z stages are a common approach. These types of stages are produced by companies that specialize in high-precision motion. For laser processing, CNC motion controllers are an option that offers ease of use and expanded operational tools, including an infinite field-of-view technology (IFOV) for synchronizing multiple-axis galvo scanners and lasers. As with most CNC controllers on the market, an integrator can create user-defined G- and M-codes or add unique plug-ins to enhance the software capabilities.  

Within any laser platform, it becomes necessary to provide opportunities for the freedom to develop process-specific servo loops and add in custom digital filters. These possibilities increase precision as well as maintain optimum laser parameters on target, especially when considering small tool path geometries. This level of high-performance coordination and synchronization of the motion controller provides advanced path planning, including sophisticated G-code processing, cubic splines, PVT profiles, and jerk control. Within this particular application, the controller and motor drives perform double floating-point calculations for the highest resolution and dynamic range of any motion control system in the industry. The use of CAD/CAM laser interface provides an automatic generation of paths from CAD files, as well as process monitoring visualization tools.

With coil material processing systems, the material is indexed into the process zone by indexing feeders so that a laser cutting head can fly over the material. The laser cutting head motion and beam delivery become the critical element for achieving consistent cut quality. Based on a precision bearing design, a multiaxis x-y-z gantry system delivers high acceleration and velocities while minimizing adverse effects such as Abbe error and path wobble resulting from high accelerations.  

Higher-precision platforms can utilize linear motors with cross roller bearings or frictionless air bearing guiding systems, both of which provide for excellent repeatability, velocity/acceleration control, and straightness. The motion, coupled with both incremental and absolute encoders, provides precision positional control with precision interpolated laser firing.

Laser cutting optics

Laser beam delivery can be sourced from a variety of vendors, each producing several models for precision cutting as well as welding. These optical heads are ideally suited for integration into precision digital stamping platforms and each are customized. Options can include inline vision modules, height sensors to optimize focus, and work with a variety of lenses, providing selectable focal spots, kerf qualities, working distances, and nozzles. 

These laser process optical heads are rated for handling fiber laser power levels up to 4 kW, providing an opportunity to explore optimized parameters. Simple changes in nozzles from a single orifice, to double or shower designs as well as nozzle diameter or pressure of the cover gas, affect process cut quality. The goal is reducing dross and material recast on precision parts.  Other critical aspects of beam delivery selection are dynamic stability during cutting and focal-point power density of the laser beam on target. FIGURE 2 demonstrates the critical nature of optimized laser process development, gas nozzle settings, and material fixturing or handling.

Safety and debris extraction

In production, there is a need to ensure a safe environment for the plant workers. Delivering Digital Laser Stamping machines with a qualified Class 1 laser enclosure to protect machine operators from laser exposure is vital. Secondarily, protection from the vaporization of metals needs proper mitigation. Of specific concern are the outgassing of both organic and inorganic fumes, particulates and bulk debris generated from the plasma generated during the laser-material interaction. With precision laser cutting, process gases (such as pressurized argon) blow the molten material through the formed cut down to the underside of the material. 

With regard to laser interactions, appropriate debris extraction is required. From above, an extraction system must handle argon overflow and from the underside, it must be able to entrain and evacuate the jetting material, debris, and gases from the plasma. Integration of debris extraction within the fixturing becomes paramount to producing quality parts.

Fixturing technology

Unlike traditional laser cutting systems, where a bed of nails supports the material, precision components must be self-supporting or be precision-fixtured. Bold Laser Automation specializes in high-volume vacuum-assisted chuck surfaces in holding the part securely as well as a mechanism to shuttle the part to a finished bin or conveyor upon completion.  With a vacuum assist, the fixture holds the parts in place during laser processing then, drops in the z-axis, rotates, and drops the part onto a conveyor or parts bin before the coil material is indexed.

No matter what the laser process might be, the most impactful and challenging design of a laser system becomes the fixturing. Over the years, it has become clear that what is achieved under production conditions requires highly skilled fixture design.  Production processes often fail because fixturing was not given equal consideration in the early system design.

Summary

Bringing together: precision lasers, laser beam delivery, high-speed motion control and fixturing techniques into the world of coil-based laser processing offers opportunities to the punch press/stamping industry within the U.S. marketplace. These tools offer solutions to retain existing customers looking for the agility that Digital Laser Stamping can offer. Also, adding this capability to traditional high-volume stamping can bring in low-volume customers whose production economics could not afford traditional punch tooling. 

Some engineers may never consider domestic sources, especially if told that it would cost up to $100,000 to produce the punching or stamping tools during those initial phases of product development. The advantages of leveraging laser tools for cutting smaller-scale parts using Digital Laser Stamping is worth exploring. With a reenergized manufacturing base in the U.S., opportunities exist for adding innovative laser processing capacity to more traditional fabrication organizations to capture further domestic production.  Adding this capability may also lead to newer ways of meeting the needs of lower volume customers as well as providing prototyping services to an existing customer base allowing them to innovate more quickly.

ACKNOWLEDGMENT

Digital Laser Stamping is a trademark of BOLD Laser Automation.