GOING FOR GREEN LIGHT: REDUCING LASER SETUP TIMES TO KEEP THE BEAM ON

Green light time is the way to make money operating a machine tool, and it never hurts to go back and review some basic principles for improving productivity in a laser fabricating process. With an eye toward keeping that light on longer, let’s look at a few simple strategies that can pay off.

In a perfect fabricating world, all machine tools would operate at a 100 percent utilization rate. Operators would take no time at all to set work and retrieve product, and material would flow like a river through every laser processing cell. It is a nice picture, the kind of thing process engineers and plant managers dream about. As an ideal, it is certainly worth working toward. The rallying cry of continuous improvement means that we strive to refine our expectations and set higher standards all the time. There are always efficiencies that can be gained and opportunities to keep that “laser on” warning lamp lit a little bit longer during every shift.

But in the real fabricating world, day-to-day challenges mean that 100 percent utilization rarely happens. Operators do require time to safely feed material to a machine, as well as to sort and separate the finished product and dispose of scrap. Even fully automated systems require occasional downtime for maintenance. And there is the ever-present need for setup, getting the machine ready to work the next job. Despite our best efforts at root cause analysis, definition and implementation of best practices, and dedication to streamlining processes, that light never seems to stay on as long as we would like it to.

Green light time is the way to make money operating a machine tool, and it never hurts to go back and take a look at some basic principles for improving productivity in a laser fabricating process. With an eye toward keeping that light on longer, let’s look at a few simple strategies that can pay off.

The first way, and generally the most obvious, to reduce the time spent setting work on a laser cutting machine is to stage materials to the machine in the most efficient order. Grouping different jobs together by material type can make shop floor organization a little more complex, but at the same time will result in better throughput at the machine.

This might mean taking product from different product lines or customers and nesting them together, where traditionally your operation would have run these orders separately. Again, from an organizational standpoint it requires a little more legwork. Your machine programmer has to have an overview of the job orders that need filling, and implement programs in an intelligent way in order to take advantage of overlapping material requirements.

Your operator must be aware of special sorting actions that are required for the finished product; it’s no use to have parts from Job A and parts from Job B ending up mixed together. That’s another challenge to overcome, and yet the rewards of higher productivity and reduced downtime can easily justify the effort. Often enough, offline programming software that you are already using to generate NC programs has the ability to help you achieve this goal, even if you are not taking advantage of it presently.

Another tactic for keeping the laser productive is optimizing your machine parameters for the materials that you process regularly. Aside from the time to load and unload material, the most common reason for a laser sitting idle is the setup for the cutting process. Changing cutting heads and cutting nozzles when switching between different materials can take a few minutes of processing time away from the machine. If you are changing over frequently during the course of a single shift, those minutes add up very quickly.

Machine tool manufacturers generally provide cutting data for common materials and thicknesses, and usually these parameters are geared toward providing the end user with a reasonable balance between cut speed and quality. It is possible in many situations to commonize certain cutting heads and nozzles across a range of materials to reduce the number of times that changeover is required.

A machine manufacturer may call for three different nozzle diameters for cutting .25 in mild steel with oxygen, .185 in aluminum with nitrogen, and .06 in stainless with shop air. By sacrificing a few ipm of cut speed or a few extra cubic ft per hour of assist gas, it can be possible to modify cutting parameters to use the same nozzle for all of these applications and reduce the unproductive time in between jobs. This is not going to make sense in every situation, for instance when cutting materials near the thickness limit for your machine. In this case, taking the extra minute to change nozzles is worth the added cutting performance. However, this sort of cutting data optimization can be very cost effective for facilities where lot runs are short and changeover times are frequent.

A final thought to consider when we look into reducing our unproductive time is the amount spent on daily or weekly chores that are required to keep the machine running. Cutting lenses become contaminated and require periodic cleaning. Scrap trays need to be emptied regularly, and the same goes for dust buckets if your machine has an integrated dust collector.

Sometimes investing in some redundancy here can return a significant gain in productivity. Having a spare cutting head so that one can always be in the machine while the other is being serviced is a very good way to eliminate short but regular periods of machine idleness. This can also be applied to scrap trays and dust buckets; if you have a backup ready to go at all times, the machine does not have to be stopped while scrap and dust are disposed of.

These strategies all have up front costs associated, but the benefits usually justify the expenditure. Remember, the idea is to keep the green light on!