Laser – A new Heating, Drying and Curing Solution

Fiber lasers are an industrial tool of choice due to their proven productivity, reliability and affordability. In standard applications, the laser is focused onto a small spot (<1 mm) maximizing its intensity to fulfill cutting, welding, drilling or cleaning applications. Recently, customers began to request lasers configured to cover large surfaces (~1 square meter) with uniform energy to replace conventional ovens to reduce greenhouse gas emissions. A new class of laser products, led by IPG Photonics’ DLS-ECO now fulfills these needs. 
A New Heating, Drying and Curing Solution 
Up to 10% of total energy consumption by industry results from heating, drying and curing processes. At least three quarters of industrial ovens, heaters and furnaces rely on convective heating, while more than half burn fossil fuels. Convection furnaces heat or dry by blowing hot air onto a surface. Convective drying is slow, because only the surface is dried. Normally, about a third of the heat energy generated by a convection oven is transferred to the product. The rest heats the oven walls and atmosphere, or is spilled into the factory environment. When drying or curing, volumes of forced air are required to remove moisture/solvents which adds a substantial operational burden, both to scrub and exhaust the warmed air exiting the oven and to heat the cool air which replaces it.  
Lasers offer a stark and attractive alternative. Radiative heating, such as lasers provide, speeds the process, because near-infrared light penetrates many materials to dry volumetrically. For the same reasons a microwave oven can bake a potato faster than a traditional oven, productivity gains from laser heaters can be large.  

For example, a typical lithium-ion battery cell factory employs gas-fired furnaces of 50-100 meters length to dry slurry applied on metal foils over a ~40 minute drying period. A laser heater neatly replaces these giant ovens requiring only 10-20 meters of factory footprint. Figure 1 is an example of battery electrode drying conducted at IPG Photonics’ European application lab on customer samples. In under one minute, 99% of moisture was removed, which provides huge advantages compared to the customer’s existing 40 minute convection drying process. 

A paradigm shift results from the “cold” nature of a laser oven. The laser is highly directable enabling nearly all of its energy to be transferred to the product, while warming neither the oven interior or atmosphere (Figure 2). The “cold” nature of the laser heater simplifies oven design by eliminating the need for thick, insulating walls, while enabling new instrumentation and metrology to be introduced. 

In the industrial coatings industry, lasers have been successfully applied to dry paint, cure powder coat and fire porcelain ceramic. Figure 3 shows powder coated panels midway through the laser cure process at IPG Photonics’ applications lab in the United States. The images below are captured by a FLIR infrared camera which accurately measures and controls the coating temperature. The laser cures powder coat in <1 min at a temperature of 350°F, while conventional convection oven curing requires 10 min at 400°F. Standard ASTM quality tests (Figure 4) confirm the high quality of laser cured powder coatings. 

Further improvements are available because lasers mainly interact with the surface without wasting energy to heat the underlying substrate. Laser heating is therefore ideal for drying coatings without impacting fragile, temperature sensitive underlying substrates or devices. This feature has attracted interest from industries which apply coatings to temperature sensitive materials such as polymers or wood. 

Semiconductor is another industry seeking to reduce greenhouse gas emissions emissions by replacing inefficient infrared lamp heaters with lasers. Near infrared laser light is strongly absorbed by silicon, enabling fast temperature ramps and low overall energy consumption. Figure 5 shows a 200 mm wafer heated to 800°C in <10 sec by an 8kW DLS-ECO laser emitting at IPG Photonics’ application lab in Japan. We estimate with confidence that <15 kW of laser power is able to heat a 300 mm silicon wafer above 800°C with a fast rise time. 

Among laser heaters, DLS-ECO solutions from IPG provide the highest efficiency and reliability over a portfolio spanning 2 kW to 100 kW lasers (Figure 6) and integrated systems. DLS-ECO converts at least 55% of electrical power input into usable optical energy, while its carefully shaped projector optics can transfer <90% of the optical energy on to the product. DLS-ECO lasers are maintenance free for seven years. In the context of a 500kW laser heater installation at a typical energy cost of $0.15/kW-hr, this corresponds to >$500,000 annual energy savings over an infrared lamp solution, while also eliminating maintenance costs associated with infrared lamp replacement. 

The introduction of laser heaters is engaging many new industries. This creates a need for safe, Class I solution, such as the compact system shown in Figure 7. Systems like these are as safe to operate as a photocopier, while enabling chemists, food scientists and other R&D engineers to safely investigate and qualify laser heating for their proprietary applications.
The requirements across many industries to reduce greenhouse gas emissions has finally created an incentive to explore alternative heating solutions to burning natural gas. To meet this challenge, laser heaters have demonstrated remarkable throughput and efficiency advantages over incumbent and rival solutions (Figure 8). Lasers speed processing by interacting with the material volume during heating, releasing the surface constraints of convection process. Faster processing means lower energy consumption and smaller ovens. The remarkable reliability of fiber lasers promises seven years of maintenance free operation, bringing further OpEx savings.