17 May Improving the Formability of Sheet Metal with Edge-Emitting Laser Diodes

Demand for products made from ultra-high strength steels is increasing. While traditional ‘cold’ sheet metal forming techniques, such as roll forming and stamping, are ideally suited to mild steels, using them for ultra-high strength steels often results in cracking, spring-back or distortion.¹ These problems can be addressed by raising the temperature of the steel prior to forming – but heating steel sheets can be extremely energy-intensive.

Image Credit: Shutterstock/Roman Zaiets

Monocrom edge-emitting laser diodes enable precise, targeted and efficient heating, improving sheet metal formability without the huge energy losses associated with other heating techniques.

The Benefits of Hot Forming High Strength Sheet Metals

Sheet metal is one of the fundamental forms of metal from which products and components are made, with applications including buildings, household appliances and body panels for vehicles and aircraft.

Sheet metal is transformed into such items via a range of stretching and bending processes collectively known as sheet metal forming techniques. These techniques include roll-forming, in which sheet metal is bent into a specific cross-section as it passes through a series of rollers, and stamping, whereby sheet metal is formed by pressing it against a die in a stamping press.

While these techniques are perfect for shaping a wide range of different sheet metals, they are of limited use in processing ultra-high strength steels. Global industry is shifting towards increased use of ultra-high strength steels, particularly for automotive applications where weight reduction is of high importance.^2–4

The relatively high brittleness of such materials and the forces required to shape them mean that traditional sheet metal forming techniques like roll-forming and stamping commonly result in cracking, spring-back or distortion of the end product.⁵

The solution to this problem lies in ‘hot forming’: heating the steel plate before forming it. Heating can drastically improve the ductility of ultra-high strength steels, making it possible to roll-form large bend angles and stamp high strength steel sheets without springback.^2,4 A variety of heating methods are commonly employed in industry, including electromagnetic induction (‘inductive heating’) and the use of electric furnaces.

While these heating techniques have their own benefits and drawbacks, they share some common problems. Primarily, they are highly energy-intensive. Such heating techniques generally heat the entire metal sheet, requiring a huge amount of energy – and raising costs accordingly. In addition to this, heating some steels (especially ultra-high strength steels) can introduce weaknesses.

Fortunately, these weaknesses are often counteracted by work-hardening that occurs during the forming process; but if the entire sheet is heated, then unworked areas can remain weakened from the heating process.²

Laser-Assisted Roll-Forming of High Strength Steels

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

Based on edge-emitting diode technology, Monocrom MET series lasers enable the benefits of hot forming to be realized without the associated energy losses and weakening that occur due to heating of unworked areas of the sheet.

By precisely heating the areas of the sheet that are to be worked, the ductility of the workpiece can be fine-tuned. This enables the formation of complex structures with small bending radii and large bending angles, without cracks or spring-back. In addition, the lifetime of forming tools is increased due to decreased forming forces; and residual stress in the metal during the forming process can be released, leading to higher production accuracy. High efficiency and controlled energy deposition minimize energy usage and lifetime costs.

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

MET R-9

The MET R-9 is a direct diode laser designed for heat-assisted roll forming. Consisting of several laser bar stacks arranged in a horizontal array, the MET R-9 concentrates up to 5kW of power onto a tightly focused straight line on the workpiece, with customizable line-width and length.

MET S-9

The MET S-9, which also consists of a horizontal array of edge-emitting laser diodes, offers additional power and flexibility for heat-assisted stamping of ultra-high strength steels. Offering up to 10kW of power, the MET S-9 allows the intensity distribution along the line to be fully customized, enabling additional control of workpiece ductility.

Both the R-9 and S-9 offer high electro-optical efficiency and extremely high maximum power density, enabling rapid and controlled heating and with low power consumption. Our unique patented solder-free mounting technology means our MET series lasers have a lifetime in excess of 20,000 hours – that’s over two years of non-stop usage or over five years of use at 10 hours per day.

MET DoForce

Our Met DoForce is one of our versatile products in this product category and convinces through its modularity, long workings distance and depth of field. Power densities are as high as 1.2 – 1.5 W/mm² and a single module illuminates an area of 40 × 34 mm². It comprises two laser diode stacks, each of which individually controllable and heating an area of 20 × 34 mm². Depending on the required, total heated length, these modules can be mounted side by side, up to 5 in total, to increase it up to 200 mm.

MET Series Lasers from Monocrom

Where other semiconductor laser arrays are prone to near-field distortion (known as the ‘smile’ effect), our MET series lasers provide high power intensity with less than 0.3 microns of smile distortion, enabling reliable and accurate power distribution.⁶

With customizable dimensions and optical properties, Monocrom MET series lasers offer a high performance and low cost in-line solution for heat-assisted forming of sheet metal. To find out more about our edge-emitting diode laser technology, get in touch with a member of the Monocrom team today.

References

1. Halmos, G. T. Roll Forming Handbook. (CRC Press, 2005).

2. Lindgren, M., Bexell, U. & Wikström, L. Roll forming of partially heated cold rolled stainless steel. 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 mechanism of “Smile” in high power diode laser arrays and strategies in improving near-field linearity. in 2009 59th Electronic Components and Technology Conference 837–842 (IEEE, 2009). doi:10.1109/ECTC.2009.5074109

Would you like to know more? Contact our application expert Dr. Igor Alexander at i.alexander@monocrom.com