Another challenge: AHSS’ negative effect on edge quality. When stamping AHSS, microfractures form along part edges and often develop into splits during subsequent forming processes. Additionally, manufacturers using laser-cut blanks for tryouts or as bridge parts while waiting for production tools often don’t discover a microfracture problem until it’s too late, after the die enters service. Workhardening brings similar problems. In many cases, stamped edges, unsuitable for downstream processes, must be trimmed ahead of time.
Lasers, however, are material agnostic in terms of tensile or yield strength. The edges of laser-cut blanks don’t manifest the microfracture issues that arise with mechanical shearing of AHSS. And, a laser’s faster cutting speed results in smaller heat-affected zones on the blank edges—the hardness change on the cutting edge is smaller than that found on a mechanically sheared edge.
WSP makes use of the process’ penchant for flexibility.
“As we partner with our automotive customers to develop solutions for reducing the weight of vehicles,” says Adams, “the laser-blanking system gives us the flexibility to run a variety of materials, including AHSS and aluminum.”
|Laser blanking enables optimization of part nesting to reduce costly scrap.
Consider Speed as Part of a Productivity Equation
Yes, laser blanking offers slightly slower speeds than stamping, but the process still runs fast—capable of cutting through 1-mm-thick aluminum, mild steel, AHSS and surface-sensitive materials at speeds to 2 m/sec. This makes laser blanking a viable and competitive choice for part volumes to 100,000/yr.
Laser blanking may seem unsuitable when producing blanks through paid-for dies on a mechanical press running at 30 to 40 strokes/min., with minimal scrap and little tool changeover. But, remember that a laser-blanking line can accommodate multiple cutting heads—two lasers are common, but more are available on custom machine configurations. LaserCoil can accommodate as many as eight heads, for instance.
In addition, stamping requires die maintenance, an important consideration given the increased wear rates common when blanking high-strength steels. For laser blanking, setting up a new job is a matter of loading a new coil and a new program, and pushing cycle start versus the time required for a die change when stamping blanks. A laser setup also makes drop-in orders and test runs simple to accommodate. Work-in-process (WIP) is reduced, and the elimination of dies creates additional floor space.
Laser Blanking Cuts Waste
It’s hard to fathom that scrap from producing automobile bodies-in-white can range from 20 to 40 percent, inclusive of rejected parts. With raw-material costs increasing, and the premium prices attached to some high-strength steels, all steel processors have scrap-reduction goals. Software advancements give laser cutting great potential for cost savings through the ability to maximize raw-material usage and reduce scrap.
Analysis of a 25-part list from an automotive program with an annual volume of 100,000 cars revealed that a laser-blanking manufacturer processing high-strength steels—stamping and shearing various chevrons, trapezoids, rectangles, and some developed and semi-developed pieces—may expect a total 5-yr. material cost of nearly $237 million. However, with the nesting capability offered by laser blanking as well as excellent performance in cutting advanced steels, this figure can be reduced to $217 million. And, don’t forget about fewer trips to the recycling yard.
WSP realized some of these material savings through these advantages, and also found that it could be flexible with its cutting strategy.
“We refer to it as a free-style approach,” says Fred Weddington, WSP vice president of sales. “The nesting opportunities for real-yield savings are incredible.”
This results from the laser-blanking process’ ability to produce fully developed blanks, which are much closer to their final, formed shape than their mechanically produced counterparts. Lasers enable nesting and common-line cutting, and even allow smaller parts to be coproduced from normally unusable pieces of material—window cutouts, for example—that in a conventional stamping operation would be sent for recycling, or stacked and stored for future re-blanking, both of which are wasteful.
Advantages Beyond Throughput Rates
Part makers looking for high volumes of simple-shaped parts out the door may not be inclined toward the laser-blanking process. In our example, the stamping line produced the required number of pieces in just 2300 hr., whereas the dual-headed laser needed 3400 hr. to finish the same job.
But, remember that parts/hr. is not the end-all measurement. Costs to maintain dies and tooling dwarf those for laser-blanking consumables. And, tooling and tooling-maintenance costs have skyrocketed as companies that cut AHSS spend about four times what’s required to maintain tooling for mild steel. Comparing this to $40,000/yr. for maintenance on a dual-head laser blanker, concerns over lower throughput can be put to rest.
In addition, laser-cut blanks better lend themselves for secondary operations. With tolerances of ±0.2 mm achievable, tailored blanks that require joining usually can go directly to the welding department. A LaserCoil customer, for example, prior to laser blanking, had to run each of its stamped blanks through a precision shear prior to the laser-welding process. But, laser cutting these blanks provided an edge that could be welded directly to the other part, eliminating secondary shearing and reducing the width of the coil required for processing.
For established stampers, an investment in laser blanking may seem difficult to justify and undertake. But, operationally, a coil-blanking system requires no complex foundation or high bays—it can be installed on a flat floor. Laser-blanking units also can be integrated into a direct-feed production scenario—coupled to a transfer press, for example. This setup further reduces inventory, WIP and production time. They’re also less expensive than comparably sized mechanical presses, often by 30 percent or more. And, often a system can be retrofitted to an existing coil line with minimal disruption to the production floor.
Given the right software, lasers also can be simple to operate. Custom coil/strip nesting and CAD/CAM-programming software (LaserCoil’s LaserCoilCAM, for example) can help optimize part orientation, common-line cutting, nesting and laser parameters. Users import the CAD files, input the coil width, material and thickness, and the software does most of the rest. The software considers grain constraints, multiple cutting heads and peripheral automation. MF
Industry-Related Terms: Nesting
, Dedicated Tooling
, LASERView Glossary of Metalforming Terms
See also: LaserCoil Technologies, LLC
Technologies: Cutting, Fabrication