Don’t Short-Change Your Laser Welding or Cutting System

The following scenario is a common one in the specialty gas field.

An end-user takes great pains to determine the right laser welding machine for his application. He should—after all, he is spending $500,000 to more than one million dollars for this equipment. He has waited at least six months for delivery, but just when the installation is to go into place, he realizes that he does not have the equipment to deliver the gas to the laser.

He is in a panic. A high-priced installation technician is cooling his heels and he sees money going down the drain. It is then that he calls his gas supplier who informs him that the system needed to deliver the laser gas to his new welding equipment is going to cost a minimum of $4,000 to $5,000.

The customer’s reaction: “I don’t have that kind of money in my budget.” But after much hand-wringing, the customer reluctantly comes up with some cash, but just enough to cobble up a minimal system that is full of short cuts and far less than what he really needs to get the most out of his laser welder.

The Solution

If you, Mr. Gas Distributor, knowing that your customer is buying a laser welding machine, should sit down with him and determine the gas requirements for that system — well in advance of its delivery. That pro-active conference will provide the customer with the right gases and gas transfer system for his needs.

Planning ahead allows the customer to budget for the cost of the gas transfer system and to have it on hand when the laser is being installed.

In many systems, the laser is fed carbon dioxide, helium, and nitrogen that are blended dynamically to the right proportions. Of course, it is also possible to use a pre-blended gas mixture. Although this approach is a bit more costly, some laser suppliers recommend the pre-blended mixture.

While some systems require higher purity gas than others, designing the system for high purity gas provides some distinct benefits and ensures a degree of operational assurance that the laser beam generated in the resonator will not be compromised.

Minimum Requirements for a System

The minimum requirements for a system that will deliver high-purity gases to a laser welding system follow:

• Pressure regulators should be brass bar stock units with stainless steel diaphragms. They may be singlestage or two-stage, depending on the degree of the constant delivery pressure required.
• Gas transfer lines should be all metal. If stainless steel, brass, or copper tubing is used, the connection should be compression fittings. Welded or brazed connection can result in oxide build-up and possible laser cavity contamination. If flexible hoses are used as gas transfer lines, only all stainless steel hoses should be used. In no way should Teflon or Kel-F lined hoses be used. All transfer lines should be installed by an experienced gas system installation contractor. Do not hire a plumber—he may be able to install drinking water lines, but usually has no idea what the requirements are for a high-purity gas installation.
• Air should not be allowed to enter the gas supply system during a cylinder change. Moisture destabilizes the laser beam, absorbs into the coating of some optics, and decreases power output. Purge assemblies on the cylinder end of the pigtails are highly recommended. This ensures that no oxygen or moisture contamination will enter the system. Some lasers are more forgiving than others, so if cost is a major issue, check valves can be installed in the cylinder connection to minimize the introduction of atmospheric contamination to the resonator in the throat of the cylinder valve.
• Filters of two microns or less should be installed in the gas lines after the regulators to avoid the risk of damage to the laser mirrors. These filters are generally not provided as part of the laser welder.
• The last item in a well-designed system is a safety relief valve that is set at 100 psig. This ensures that the laser will not be damaged by over pressurization.

The Practical Application

All of the above is quite acceptable, but what does it look like? The bottom line design is a system that meets the above criteria and looks like the system, which includes a single-stage regulator, as shown in Figure 1.

In practice, three of these systems will be needed, one each for helium, carbon dioxide, and nitrogen. This is a manual changeover system that is built on a protocol station platform. It can be further enhanced by adding a pressure switch and alarm module that will alert the user that the cylinder in service is almost empty.

Enhanced Systems

For applications that require additional assurance of unassisted or uninterrupted gas supply during the daily operations, the basic principles above may be applied to a semi-automatic changeover system, such as that shown in Figure 2. This is a fully automatic electronic system, such as the one shown in Figure 3.

If you choose the changeover option, be certain to select a changeover that has regulators with stainless steel diaphragms and all-metal lines connected by compression fittings and/or pipe threads with Teflon tape sealant.

We recommend that any semi-automatic changeover system used in a laser welding application be fitted with an alarm system that will signal the need for a change of gas supply from one side to the other. The empty cylinder can the be replaced immediately and the manifold can be switch back to its original position. Most electronic systems, such as the AUTO-LOGIC shown here have built-in alarms.*

Summary

In specialty gas terms, a laser welding system is to a manufacturing operation what a high end gas chromatograph is to a laboratory. Only the laser costs much more. No lab manager would ever consider using less than the best for his chromatograph. Similarly, the operations manager of a plant should not consider using less than the best for his laser welder.