Patent Application
20230093862
This disclosure relates to the field of technology associated with laser cutting through metal workpieces and more particular to a laser blast shield and a method of using the same to shield a first wall portion of a workpiece against damage during high speed laser cutting through a second wall portion of the metal tubular structure opposite the first wall portion.
A conventional step in the manufacturing of a vehicle running board having a tubular metal body and rubber or plastic anti-slip step pads and end caps attached to an upper (Class A) surface and ends of the tubular metal body involves cutting attachment holes or apertures into the surface of the tubular metal body. The anti-slip step pads and end caps can include integrally formed pegs that are frictionally fitted into the holes or into anchor sleeves mounted in the holes to securely attach the anti-slip pads to the tubular metal body. It is particularly advantageous to use laser cutting techniques for creating the attachment apertures. Such techniques are amenable to full automation and high-speed production. However, a problem arises from the difficulty of concurrently managing the power to the laser cutter to achieve high-speed cutting without damaging a wall portion of the tubular metal body opposite of a portion through which the apertures are being cut. Specifically, a lower power level that allows cutting of apertures without cutting through or marring a portion of the tubular body opposite the portion being cut has a longer cycle time that results in lower production rates and high manufacturing costs. Higher power levels that facilitate high-speed production can cause marring or undesirable cutting that promotes corrosion, and which can result in undesirable rates of rejected parts.
Described are a laser cutting tool blast shield and method of using the same to facilitate high-speed cutting operations on a tubular metal workpiece without damaging a portion of the workpiece opposite the portion being cut.
The blast shield can include a surface having a micro-textured topology that scatters impinging laser energy along the surface of the blast shield.
The blast shield can include a highly thermally conductive coating. A preferred thermally conductive coating is gold or silver. The thermally conductive coating may be applied to an untreated surface or a micro-textured surface.
The body of the blast shield, which may be micro-textured and/or provided with a thermally conductive coating, can be comprised of a metal having a relatively high thermal conductivity and a relatively low cost, with an aluminum body being preferred.
Shown in
Another advantage is that blast shield 12 captures and collects dross generated during the cutting process. This prevents the dross from being deposited onto the surface of wall 18, which can otherwise promote corrosion. It can also prevent contamination of electrolyte tanks used during subsequent electrolyte deposition of a coating, and redeposition of dross particles onto the workpiece during electrolytic coating (e.g., chrome plating) of the workpiece.
Blast shield 12 includes a metal sheet material having a thermal conductivity and a heat capacity well suited to act as a heat sink for absorption and rapid uniform distribution of the laser energy that impinges on the blast shield, while also being relatively inexpensive. Preferably, the metal sheet material has a thermal conductivity of from about 75 to 240 Wm−1 K−1 at 273.15° K and a heat capacity of from 400 to 950 J Kg−1 K−1. Preferred metal sheet materials for the blast shield include aluminum, aluminum alloys, iron and stainless steel, with aluminum being particularly preferred based on a combination of relatively high heat capacity, thermal conductivity, low cost, and high availability.
The upper surface 20 of blast shield 12 can be provided with a micro-textured topology having random or patterned surface features of a size from about 1 μm to 1000 μm. In certain embodiments, the micro-textured surface exhibits an average surface roughness (Ra), as determined in accordance with procedures provided in ASME B46.1-2009, of from 1 μm to 100 μm. The micro-textured surface can be relatively random as achieved using mechanical (e.g., abrasive) or chemical (e.g., etching) techniques or patterned (controlled) using laser machining techniques. The micro-textured topology of the surface 20 diffracts or scatters laser light impinging on surface 20 to reduce the amount of energy absorbed at the point of impingement and more uniformly distribute the energy along the surface. The micro-textured surfaces may be provided on one or both opposite sides of blast shield 12, along the entire surface or along selected surfaces corresponding to workpiece cutting locations.
Surface 20 can be provided with a highly reflective and highly heat conductive coating to reduce laser energy absorption at the location where the laser light beam impinges upon the surface 20, and to rapidly spread any absorbed energy along the surface and into the metal sheet substrate. Because only a relatively thin coating (e.g., 5 to 10 μm) is needed, scarce and expensive metal coatings can be employed. Preferred metal coatings are gold and silver, each of which are highly reflective and have a thermal conductivity significantly higher than aluminum. The coating can be sputtered or electrochemically deposited.
Blast shields 12, 30 and 32 are preferably curved such that they can be placed into the hollow space or spaces defined between the wall of the workpiece that is to be laser cut and an opposing wall without requiring the use of fasteners or clamps. However, plastic or vulcanized rubber bumpers can be attached to opposite edges 50, 52 of the blast shield, or positioned between the opposite edges and respective side walls 52, 56 of the workpiece to establish a frictional fit between the blast shield and the workpiece. The dross collected on the blast shield is mostly metal (e.g., aluminum) from the workpiece, which can be recycled with the blast shield after repeated use (e.g., about 50 production cycles). For example, as illustrated in
Use of the blast shields 12, 30 and 32 involves positioning of the blast shield or shields within the space or spaces defined between a first wall (e.g., 14 or 38) which is to be cut (such as to form apertures for attachment of plastic or rubber step pads), and a second wall (e.g., 18 or 40) of the workpiece opposite the first wall relative to the direction of the laser light beam of the cutting tool, such that laser light penetrating the wall to be cut impinges on the surface (e.g., 20) of the blast shield. Preferably, the laser beam is focused on the wall to be cut with the power adjusted to facilitate short cycle times without concern for damaging the opposite wall (e.g., wall 18 or 40). The blast shields can be curved or contoured to position a section of surface (e.g., 20) on which laser light beams will impinge approximately midway between the wall to be cut (e.g., 14 or 38) and the second opposite wall (e.g., 18 or 40).
While the present invention is described herein with reference to illustrated embodiments, it should be understood that the invention is not limited hereto. Those having ordinary skill in the art and access to the teachings herein will recognize additional modifications and embodiments within the scope thereof. Therefore, the present invention is limited only by the claims attached herein.
