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Fall 2011
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Trumpf Inc., Farmington, Conn., offers a range of industrial lasers and metal fabrication machinery. For more information, visit www.us.trumpf.com.

When Selecting a Laser System,
Look Beyond Energy Efficiency

Just because a system uses less energy does not mean it is the most economical for the job.

Discussions about energy consumption are commonplace today as companies strive to be more green and more lean. For those investigating modern laser cutting technologies, the search leads naturally to the question of electrical efficiency. Several styles of laser sources are available from a variety of different manufacturers, and each laser source has its strengths and weaknesses.

The market for sheet metal cutting is dominated by the CO2 laser, the traditional workhorse of laser machining. Solid state laser sources, long a mainstay of the laser welding industry, have become more practical for cutting applications with the help of recent technological advances. With all the information circulating about energy efficiency, it is easy to become focused on the obvious benefits of reducing power consumption. But a singular focus on energy efficiency can sometimes blind users to the complete picture of the cutting process.

When evaluating the efficiency of a system, it is a good idea to start by defining what efficiency is and how to measure it. Simply put, efficiency is the ratio of input to output. In other words, efficiency is the sum of all resources that must be expended to achieve a desired result. When the value of the resources expended is less than the value of the end result, there is a net efficiency. The more we can reduce the expenditure required to achieve the desired output, the higher the efficiency of the system.

That certainly sounds like plain common sense, and yet there are many factors that determine the cost of the end result. For example, consider the cost to produce a given part with a laser. The total cost of the part will include the investment cost of equipment required for the production process (capital expenditure and amortization), the cost of the labor involved (machine operators and programmers), the hourly operating cost of the equipment involved (electrical power, gas, consumables), and the cost of materials (in this case, sheet metal).

Starting with a CO2 laser as the production process, the cost of electrical consumption will be about 3 percent of the total cost to produce each part. The material will be approximately 50 percent of the cost of that part. The machine tool itself will be about 26 percent of the cost, including the hourly cost to operate the laser and the rate of amortization on the original investment. Labor will be about 18 percent, and the gasses required will about 3 percent. Exact values will vary, of course, depending on the situation, but these are good averages.

Taking this broad view of the efficiency of the production system, we can start to see that electrical consumption constitutes about the smallest piece of the puzzle. Even a drastic savings in electrical consumption, say 50 percent, still only results in a cost reduction of around 1.5 percent for each finished part. That’s not to say that saving 1.5 percent on the cost of a part is not a worthy goal, just that the effect of that savings on the total efficiency of the system is very minor. If we can save just 10 percent of our material cost, that works out to be 5 percent of the total efficiency of our production process. Saving a small amount of material creates a greater total efficiency than saving a large amount of electricity.

When selecting a machine tool as an integral part of the production process, the total efficiency of the system needs to be taken into account in order to make the right decision. At the end of the day, what matters most is the ratio of input to output. When comparing two laser cutting systems, one with a CO2 laser source and the other with a solid state laser source, one obvious factor that jumps out immediately is the difference in energy efficiency. A CO2 laser typically achieves an electrical efficiency of around 10 percent, meaning that for every 100 watts of electrical power pumped into the laser, we get about 10 watts of useable energy out. A solid state laser can tout electrical efficiencies of around 25 percent, so for the same 100 watts of input power, we can get 15 additional watts of useable energy. On paper that sounds great, but in the grand scheme of the production process, that equates to half a percentage point of the cost per part. To put this in perspective, the amount of time required for the machine operator to empty a scrap tray once per shift will have a greater impact on productivity. On the other hand, if we can reduce the downtime for maintenance and setup by investing in a machine that is more user-friendly, we manage to reduce two much larger pieces of the efficiency puzzle: machine cost and labor cost.

The laser source is a tool and should be considered in that light. The overall efficiency of the production system hinges on a number of considerations, not just energy consumption. Only by taking them all into account can users ensure the best possible output for their expenditure.

  
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