Direct diode lasers for heat-assisted sheet metal forming

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There is a growing demand for products made from ultra-high strength steels. While traditional “cold” sheet metal forming methods, such as roll forming and stamping, are ideally suited for mild steels, using them for ultra-high strength steels.teles can cause springback, cracking or deformation.1

Image Credit: Shutterstock / Roman Zaiets

These problems can be circumvented by increasing the temperature of the steel before forming, but heating steel sheets can be very energy intensive.

Side-emitting monocrom laser diodes provide precise, efficient and targeted heating. This improves the formability of the sheet without the huge energy losses that come with other heating methods.

The Advantages of Hot Forming High Strength Sheet Metal

A fundamental form of metal from which products and components are created is sheet metal. Applications include household appliances, buildings, and body panels for airplanes and vehicles.

Sheet metal is made into these articles using a variety of stretching and bending processes known collectively as sheet metal forming methods.

Stamping is one such method, whereby sheet metal is formed by pressing it against a die in a stamping press. Roll forming is another technique where the sheet is bent into a specific cross section as it passes through a series of rollers.

While these methods are ideal for shaping a wide range of different sheets, they are of limited utility in processing ultra-high strength steels. The global industry is moving towards an increased use of ultra-high strength steels, especially for automotive applications where weight reduction is crucial.2-4

The relatively high brittleness of these materials and the forces required to shape them means that traditional sheet metal forming methods, such as rolling and stamping, frequently result in springback, cracking or warping of the final product.5

“Hot forming” is the solution to this problem. This involves heating the steel plate before forming it. Heating can dramatically improve the ductility of very high strength steels, allowing large bend angles to be profiled and high strength steel sheets to be stamped without springback.2.4

In industry, there are a variety of heating methods that are commonly used, including the use of electric furnaces and electromagnetic induction (“induction heating”). These heating methods have their own advantages and disadvantages, but they also share some common problems.

The main problem is that they are very energy intensive. Such heating methods usually heat the entire sheet metal, which requires a huge amount of energy and, in turn, increases costs. Additionally, heating certain types of steel (especially ultra-high strength steel) can introduce weaknesses.

Fortunately, these weaknesses are usually overcome by the strain hardening that occurs during the forming process; but unworked areas may remain weakened by the heating process if the entire sheet is heated.2

Laser assisted rolling of high strength steels

By using high efficiency lasers to selectively heat only the areas of steel that need to be worked, Monocrom direct diode lasers offer an alternative solution to hot forming steel.

Monocrom MET series lasers are based on light emitting diode technology and achieve the benefits of hot forming without the associated energy losses and attenuation that occur when unworked areas of the sheet are heated.

The ductility of the part can be refined by simply heating the areas of the sheet to be worked. This allows the formation of complex structures with small radii of curvature and large angles of curvature without springback or cracks.

The service life of forming tools is also increased due to the decrease in forming forces; and the residual stresses in the metal during the forming process can be released, resulting in higher production precision. Controlled energy deposition and high efficiency minimize energy consumption and lifetime costs.

Monocrom supplies two direct diode lasers optimized for forming ultra-high strength steel: the MET R-9 and the MET S-9.

MEET R-9

The MET R-9 is a direct diode laser designed for heat assisted rolling forming. It is made up of numerous stacks of laser bars arranged horizontally. It concentrates up to 5kW of power in a straight line focused well on the room, with customizable line width and length.

MEET S-9

The MET S-9 is also composed of a horizontal array of side-emitting laser diodes and offers more flexibility and power for heat-assisted stamping of ultra-high strength steels. Delivering up to 10 kW of power, the MET S-9 allows full customization of the intensity distribution along the line, allowing greater control of part ductility.

Both R-9 and S-9 offer high electro-optical efficiency and extremely high maximum power density, enabling rapid and controlled heating with low power consumption.

Unique patented solderless mounting technology means Monocrom’s MET series lasers have a lifespan of over 20,000 hours. This equates to more than two years of constant use or more than five years of use at 10 hours per day.

Monocrom MET series lasers

Monocrom’s Met DoForce is a versatile product in this product category and convinces with its long working distance, modularity and depth of field. A single module illuminates an area of ​​40 × 34 mm2 and power densities are as high as 1.2 – 1.5 W / mm2.

It includes two stacks of laser diodes, which are individually controllable and can heat an area of ​​20 × 34 mm2. Depending on the total heated length required, these modules can be mounted side by side, up to 5 in total, increasing it up to 200mm.

Some other semiconductor laser arrays are prone to near-field distortion (known as the “smile” effect), but the MET series lasers provide high power intensity with less than 0.3 microns of smile distortion, allowing precise and reliable power distribution.6

Monocrom MET series lasers offer high performance, customizable dimensions and optical properties and provide a low cost in-line solution for heat-assisted sheet forming.

The references

  1. Halmos, GT Roll Forming Manual. (CRC Presse, 2005).
  2. Lindgren, M., Bexell, U. & Wikström, L. Partially heated cold rolled stainless steel profiling. Journal of Materials Processing Technology 209, 3117-3124 (2009).
  3. Olsson, K. & Sperle, J.-O. New advanced ultra-high strength steels for the automotive industry. AutoTechnology 6, 46-49 (2006).
  4. Mori, K. et al. Hot stamping of ultra high strength steel parts. CIRP Annals 66, 755-777 (2017).
  5. SSAB. Does Roll Forming Work For Advanced High Strength Steel? https://www.youtube.com/watch?v=yDh7Kc6rSmU (2013).
  6. Wang, J. et al. Study of the “smile” mechanism in high power laser diode arrays and near field linearity improvement strategies. in 2009 59th Electronic Components and Technology Conference 837-842 (IEEE, 2009). doi: 10.1109 / ECTC.2009.5074109

This information was obtained, reviewed and adapted from documents provided by Monocrom.

For more information on this source, please visit Monocrom.


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