Lasers Accelerate Powder Coat Curing While Reducing Energy Consumption

By Aidan Freeburg

“Like watching paint dry” is no longer the case for industrial powder coat curing, now that lasers have arrived on the scene as a high speed alternative. Long the industrial tool of choice for precision metal cutting and welding, lasers provide similar advantages to high utilization powder coating operations. Namely, lasers are fast and offer precise control, while saving on energy bills due to their extraordinary curing efficiency.

Powder coat curing can be accomplished with infrared laser light around 970 nanometers. Diode lasers are the ideal laser selection because they combine the lowest cost-per- watt with the highest electrical power conversion efficiency. Their infrared radiation penetrates a few microns beneath the coating surface to provide several benefits over convection furnaces. Foremost, volumetric heating transfers energy rapidly into the powder coat layer, the same way a microwave oven accelerates food preparation by cooking from the inside out. Second, little energy is wasted heating the underlying substrate, which is critical when coatings are applied to temperature sensitive materials like polymer or wood. Third, laser light is highly directable so that only the coated area is illuminated. Finally, because most of the heat input remains in the coating, part cool down time is often seconds instead of minutes.

On Demand Heat Source
Laser curing lowers operating costs and lessens environmental impact. A laser heater consumes energy only when processing parts; there is no idling between batches since the laser is able to turn on at full strength in milliseconds while switching off instantly like a light switch. No energy is wasted heating oven walls or the atmosphere inside the enclosure, or for that matter the factory floor. Because the laser beam is expanded, not focused, eye safety requirements are less stringent than for laser cutting and welding. Generally, less factory floor space needs to be dedicated to a high speed laser curing process which manifests as either a shorter oven length, or the reduction or elimination of offline curing and cool down areas.

Click to see this disruptive technology in action (video):

Powder coated parts cured by laser pass standard ASTM quality tests with flying colors, including crosshatch, solvent, and impact. Practitioners detect no difference in laser cured powder coat versus conventional convection oven or IR lamp processes. This is unsurprising since the laser heater produces a comparable wavelength, so cures via similar mechanisms as lamps.

While lamps and lasers share positive attributes such as high speed infrared light curing and rapid turn-on, lasers provide operating cost advantages. The high directability of laser radiation ensures that 90% of the light can contribute to powder coat curing. While IR lamps begin to degrade immediately and require replacement after one to two years at 24x7 utilization, diode lasers are extremely long-lived. For example, IPG Photonics provides the DLS-ECO diode heater with a 3-year full warranty while anticipating seven plus years of uninterrupted, service free operation. Throughput-focused manufacturers who adopt laser curing will enjoy significantly reduced energy bills and maintenance costs.

Focus on Process Control
Superior process control and endpoint detection are also benefits of laser curing. A room temperature laser enclosure supports metrology to precisely control curing temperature and cycle time. Infrared-based temperature sensors are challenging if not impossible to implement in conventional ovens or amidst IR lamp background emissions. A control loop enables the laser to gel the powder coat in just a few seconds without overshooting the mark. Process data may be archived for quality control. Job files may be stored and modified as needed. A visible light camera enables an operator to observe the finish of fully cured parts. There is no need to apply extra heat and process time for good measure, as can be the case with traditional curing methods.

Lasers are ideal for high throughput processing of parts with flat surfaces. The lightweight projection head may be mounted on a robot arm or swung on a gantry. Just as commonly, coated parts are conveyed beneath a fixed laser head. The high speed of laser curing enables continuous flow parts production by removing the curing bottleneck. Because the laser is projected, not focused, cure quality is insensitive to part topology. Laser curing is also possible without a direct line of sight. In the image above, topside laser illumination heats the upper surface first as is evident by the shiny finish. Eventually, the entire part reaches curing temperature, enabling areas outside the line of sight to fully cure. Curing of backside areas is purely thermal, resembling the convection oven process, but still faster due to the direct heating nature of the laser.

The upfront capital investment needed for laser curing is not a fit for every powder coating operation. For early adopters, a laser heater investment may be four times higher than a comparable gas-fired box oven, or two times that of an IR lamp installation. Throughput focused operators benefit from higher capacity, lower operation expenses, and factory footprint reduction, so are able to quickly recoup the capital expenditure. The trade-offs between laser, IR lamp, and gas- fired convection oven curing are summarized in Table 1. Less throughput focused powder coating operations may likely forego the switch to lasers, just as smaller shops gravitated more slowly towards now-ubiquitous laser cutting and laser welding processes.

Lasers have migrated from James Bond movies into the shop for cutting, welding, and cleaning, and now as a compelling curing process. Large scale powder coaters
who adopt laser curing can expect higher productivity and throughput, benefit from tight process control, and free up valuable shop floor space while enjoying lower energy bills. Those looking to learn more about this new curing process will have the opportunity at Powder Coating Week 2024.

Aidan Freeburg is a laser applications engineer with IPG Photonics. Contributions provided by Vijay Kancharla, laser applications director, and Dan Valcour, diode laser product manager.