Air cooled vs water cooled laser welders

What is the difference between air cooled and water cooled laser welders?

Air-cooled and water-cooled laser welders differ in their heat transfer methods. Air cooling transfers less heat than water cooling, so air-cooled lasers operate at lower power levels than their water-cooled counterparts. Air cooling is used in low-powered pulsed and continuous wave laser welders. Water cooling is necessary for high-powered lasers such as 3000W water-cooled units. Water-cooled laser welders use water as an intermediate heat transfer medium, and their final stage is to reject their heat to atmospheric air.

Why do lasers need cooling systems?

Lasers need cooling systems because high-powered lasers generate waste heat while requiring a stable temperature for optimal operation. Waste heat is generated because their conversion efficiency is less than 100%. Older lasers, such as lasers used in the National Ignition Facility to initiate nuclear fusion reactions, are 13% efficient, meaning 87% of the energy used is rejected as heat. In contrast, the latest fiber lasers are up to 42% efficient. Most industrial fiber lasers are 33% efficient, but that still means 67% of the electricity consumed is lost as heat and must be carried away to keep the laser operating optimally and avoid the laser source overheating. Water cooled laser sources operate best at 25°C, while air cooled models are designed for a larger temperature range, such as fan cooled and heat pipe types where the laser cannot reach a temperature below the ambient air temperature.

What is an air-cooled laser welder?

Air-cooled laser welders are cooled directly by air, without the use of a water chiller system. All industrial or high-powered lasers were water-cooled until recently, so air cooled lasers are notable for not using a water chiller.

What types of air cooling are used for laser welders?

The most common types of air cooling for lasers are listed below.

• Forced Convection or Fan Cooled: Forced convection uses fans to create turbulent flow and maximize cooling. To transfer large amounts of heat, such as from a 2000W laser source, powerful fans and large surface areas are required. All types of laser cooling systems use forced convection to some degree, usually to transfer the final heat to ambient air.

• Heat Pipes: Heat pipes transfer heat from the heat source via copper or aluminum tubes, using the latent heat of evaporation of a liquid as it phase changes to a vapor. Fans are used to magnify the cooling effect, so heat pipe cooling systems also rely on forced convection to transfer the heat from the copper tubes to the surrounding air. This cooling transfers the vapor back to a liquid. At a basic level heat pipes use some of the the principles of heat refrigerant types and forced convection types.

• Heat Pump or Refrigerant types: Heat pump laser welders operate on the same principle as air conditioners, using carefully controlled refrigerant compression and expansion to efficiently transfer heat and maximize the cooling effect. Heat pumps are complicated but have the advantage of a high coefficient of performance, allowing 1 kW of compressor power to pump or transfer 4 or 5 kW of heat out of the laser source. The air-to-air heat pump type is related to the conventional water chiller cooling system but eliminates the water section, conducting heat from the laser to the refrigerant and then to ambient air.

This graph shows the comparative performance of forced convection, heat pipe and heat pump cooling systems. However, in practice the designer can improve performance by fitting large, powerful fans and optimising the heat transfer path. In our air cooled fan forced welders such as G6-2000AC we have greatly increased the contact area, surface area and volume of aluminum heat sinks to achieve 100% duty cycle at 100°F. This far exceeds most MIG welders, is superior to most welders on the market, and is adequate for all but the most extreme use cases.

How does a water cooled laser welder work?

A water-cooled laser welder works by utilizing a refrigerant chiller to carry waste heat away. It uses heat pump principles, with water as a conducting medium to transfer heat to the heat pump. The water stabilizes the temperature by acting as a heat sink or store of heat. The water volume or mass avoids rapid changes in the laser’s temperature.

Advantages of air cooling over water cooled laser welders

Advantages of air cooling over water-cooled laser welders include being cheaper, lighter, simpler, using less electrical power, not requiring warming up, and much less maintenance. The advantage is particularly true for forced convection systems. However, it relies on the assumption that the system is designed correctly. The Generation 6 or G6 laser welder range, such as G6-2000AC, is well designed, with large, powerful yet quiet fans, good cooling paths and heat sinks, and high cooling capacity.

Air cooling avoids the risk of algae, slime, or scale buildup in the cooling passages. Freeze cracking of water-cooled systems is very expensive to repair, and air-cooled units avoid this risk.

When is water cooling better than air cooling?

Water cooling is better when the application requires very stable temperatures or high levels of heat removal, such as high-powered lasers or lasers with low efficiency. Water cooling is currently better for cooling the welding head or gun, but specially-designed welding heads work without it.

What to look for when buying an air cooled laser welder?

Look for the true power output and duty cycle when buying an air-cooled laser welder. Cooling capacity or rate of heat removal are the determinants for the duty cycle. Undersized cooling systems have been incorporated into many models to produce the cheapest product. Many of these have small, low-powered fans designed for computers. These fans are inadequate, as demonstrated by simple calculations: A 1500W air-cooled laser is typically 33% efficient, so the input must be three times as great, or 4500W. 3000W is rejected as heat, and the fans must carry it away. A computer rejects in the order of 150W, so two computer fans reject about 300W. It is only 10% of the necessary heat transfer. Hence, a welder with such fans must be far below 1000W, or it is only welded briefly before the thermal sensor or cutout intervenes to stop welding. The percentage of time that the welder can run in a ten minute period is known as the duty cycle.

What is duty cycle and how do we measure it?

The duty cycle for welders is defined by EN/AS60974-1. The test involves stabilised welding in a high-temperature environment at 100% power for 10 minutes and recording the welding time. The duty cycle is 60% if the welder cuts out and only welds for 6 minutes. The ambient temperature is normally 40°C. Our welders, including the new air-cooled models G6-1500WC and G6-2000WC, are tested to weld at 100% duty cycle at up to 40 degrees C.

What is the best cooling system?

The best cooling system depends on the needs and how well it is designed. High-powered lasers such as 3000W output models need water cooling. The most critical task is cooling of the laser welding head or gun, and gas or air cooling currently lack the heat transfer rate required to cool 3kW welding heads.

2000W and smaller welders are suitable for air cooling, and a well-designed air-cooled model can perform as well as the conventional water-cooled models. Our air cooled, refrigerant cooled and forced convection cooling models have proven this with acceptable noise levels and a duty cycle of 100% at up to 40 degrees C.

What is the best coolant for water cooled lasers?

Demineralized or distilled water is the best coolant for water cooled lasers. Ethylene Glycol (glycol) is inferior to water as a coolant because it does not transfer heat as well, and its heat capacity is less. Water’s heat capacity at constant pressure is 4.20 J/g K while pre-mixed ethylene glycol (50% water) is around 3.5 J/g K. Water’s heat transfer coefficient is also superior to glycol. If changing from 100% water to a 50% glycol, 50% water mixture, to maintain the same cooling effect, the flow rate must be increased by 20%.

Why do you need to change the cooling water in a water cooled laser, and how often?

Water must be changed regularly to avoid the growth of algae or similar microbiological fouling in the cooling system. Water has no inhibitors to prevent algae growth, and we have seen chiller cooling passages blocked by such growth. This requires chiller replacement, and also risks blocking and damage to the laser source.

The recommended change interval for water replacement is one month, as this is frequent enough to avoid significant microbiological growth. Such biological growth is normally exponential, so leaving it too long risks a major build up. Changing it early will limit the growth.

Can you use coolant in a water cooled laser chiller?

Coolants such as ethylene glycol (glycol) are not recommended for use in water cooled lasers. This is because glycol does not transfer heat as well as water. The only situation where glycol is permitted by laser source manufacturers such as Max Photonics or Raycus is when the ambient or room temperature is close to freezing. Freezing temperatures can freeze the water in the laser and water passages, where the freeze expansion will crack the laser’s cooling passages. This can require replacement of the laser source, which is the most expensive component in the laser welder. In Spring or when temperatures climb above freezing the coolant can be drained and flushed, and replaced with pure water.

What maintenance is required for the cooling system on an air cooled laser welder?

The only maintenance required on air cooled laser welders is cleaning of the filters. If operating in a dusty environment, or if cooling seems to have reduced, use compressed air to blow out the fins to remove dust. If the fins are thin, take care not to bend them as this will reduce cooling performance permanently. Follow the machine manufacturer’s guidelines and ask if not sure, particularly if electrical circuits are exposed by removing covers.

What maintenance is required for the cooling system of a water cooled laser welder?

The maintenance required on water cooled laser welders is changing the water every month with fresh demineralized water, and periodic cleaning of the chiller filters and cooling fins. If operating in a dusty environment, or if cooling seems to have reduced, use compressed air to back flush the filters and blow out the fins to remove dust. If the fins are thin, take care not to bend them as this will reduce cooling performance permanently.