A schematic of a typical laser trimming system is shown in Figure 2. Three mechanisms can be involved when laser trimming. The first is simply the material evaporation by the high-power laser beam. Examples include tantalum nitride and polysilicon. The second is the oxidization of the resistor material in the presence of silicon dioxide. Such is the case for sichrome and nichrome thin films. The last mechanism is the so-called island structure change in very thin discontinuous films. The conduction is based on quantum electronic tunneling effect.
Traditionally, the wavelength of 1 micron has been used as it is the wavelength from a commonly used industrial laser based on Nd-doped crystals. It also has the proper characteristics for power, repetition rate, beam quality, and material absorption. Recently, as the dimensions shrink and tolerances tighten, it was discovered the traditional 1-micron laser Nd-doped technology experienced trimming limitations on some of the new materials and so an alternative was developed to more successfully manage the laser material interaction issues. Moreover, the trimming quality and post trim stability of the 1-micron wavelength was compromised by thermal and optical proximity effects. It was found that the heat affected zone (HAZ) generated by the laser beam was mostly responsible for post-process resistance drift and TCR.
Shorter wavelengths have the advantages of being able to generate smaller beam and smaller kerf, thus allowing smaller features to be trimmed. Because most materials absorb more strongly at shorter wavelengths than at 1 micron, fewer thermal effects will be expected. Therefore, HAZ at shorter wavelengths tends to be less. This will in turn give rise to less TCR drift, which is caused by the HAZ around the laser trimming kerf.
In addition to laser sources, the beam positioning accuracy is also important in order to achieve high-precision trimming. This is especially true if the dimensions of the components to be trimmed are very small and so a high precision galvanometer beam positioning system was developed to complement the smaller spot size.1 The difference between actual and nominal beam positions are detected and mapped. The entire galvanometer field is mapped in such a manner and fit with mathematical model so the beam placement can be accurately determined.
Two product test samples were used as the basis for the evaluation, and there were two objectives for each product evaluated. The first was to determine the maximum gain potential for each product under similar conditions (number of cuts, cut length, spacing, etc.). The second was to trim each product to a nominal that reflected a moderate gain, to a tolerance of ±0.1 percent with a standard deviation of less than 0.08 percent. The green W778G Laser Trim System was used for the test with a 3-watt green (532 nanometer) laser with a spot size of 13 microns and kerf widths of 10 microns.
Gain study-To examine the gain potential of each material, a series of serpentine trims using different trim spacing (pitch), was made on a sample quantity of resistors. Trim area was equal-first and last serpentine trim locations, location of the fine trim relative to the serpentine and trim length. The number of trims was changed according to the pitch used so that the last trim location would be as consistent as possible for all samples. Q rate and bite size were kept the same and power adjusted only to maintain a clean and constant kerf. Resistor nominals for each test were selected that would ensure that all resistors trimmed to maximum distance. Six tests were conducted for each material using 25-, 30-, 35-, 40-, 50-, and 65-micron cut spacing. Figure 3 shows the trim pattern for the pitch of 25 microns.
The following data was recorded: pre-trim value, post-trim value, and the time it took to trim the pattern. With that data and the known geometry of the resistor (1.25 squares), the ohms per square, gain, and final square count could be calculated. Tables 1 and 2 show the results for each test group from both resistor materials and the number of cuts used. Table 3 shows the trim parameters used for each test.
For most manufacturers, buying an industrial laser cutting machine is a major investment. It&#;s not just the initial price you pay, but the fact that the purchase will have a great impact on the entire manufacturing process. If the wrong equipment is chosen, you have to live with the decision for quite a long time. It is not unusual to see manufacturers keep a laser for seven to 10 years.
Do you know the best way to go about purchasing a laser cutting machine? Even if you currently own one, how long ago did you buy it, and what has changed since then?
This guide should help you in making a capital purchase decision that will drive your manufacturing operations to new heights.
Perhaps the real question is, &#;Should I even be buying a laser cutting machine?&#; For many reasons, investing in a different cutting system may make more sense for a company&#;s manufacturing activities. Investigating all available options can minimize any possible regrets in the future.
Depending on the part volume, a stamping press may deliver the lowest cost per part. When speaking of metal forming in a press, however, you also are talking about the need to invest in tooling. Stamping also presents the ability to perform multiple tasks, such as forming and tapping, as part of the production process.
A traditional turret punch press can cut out holes and shapes economically, but, again, it involves tooling. A punching machine also can&#;t match the production speeds of laser cutting machines. As with a stamping press, some forming can be done on the punch press.
A high-definition plasma system is good for thick materials and for applications in which the edge quality isn&#;t critical. An abrasive waterjet also is good for thick materials and for applications in which the metal can&#;t have a heat-affected zone, which is a problem with most thermal cutting methods. Both plasma and waterjet cutting systems cost less than laser cutting machines, but many times do not match the laser&#;s cutting speed. Of course, plasma cutting and waterjet systems can boost productivity with the use of multiple heads and the ability to cut stacked blanks; the application obviously would influence what exactly you need.
A company that doesn&#;t have a laser cutting machine generally subcontracts the work to one or several job shops with that capability. This scenario doesn&#;t involve a lot of risk and can work if you have some flexibility with lead times.
But there will come that time when you have to ask yourself if it is time for the company to bring laser cutting in-house. This has to be considered even if the business relationship with the subcontractor is great.
How do you know if it is the right time to own a laser? Look at how much you are spending monthly for laser-cut parts. In the words of Henry Ford, &#;If you need a machine and don&#;t buy it, then you will ultimately find that you have paid for it and don&#;t have it.&#;
If the decision is made to bring laser cutting in-house, you may be put in a position where you need to justify why the investment needs to be made. The costs associated with subcontracting out the laser cutting are just the starting point for the justification. How much more productive will the manufacturing process be with in-house laser cutting? How does this affect lead times? From an expense standpoint, not only do you have the cost of the laser cutting machine, you have labor and consumable costs, such as laser cutting assist gas.
Figuring out these answers will give upper management or even a lending institution an idea about production savings and subsequent return on investment following the initial investment.
Other than monetary issues, when manufacturers offer reasons as to why they are looking at purchasing a laser cutting machine, they mention &#;control.&#; Ask yourself these questions to see if you fall into this category:
As a manufacturer, you have numerous sources to purchase a laser cutting machine. There are dealers that specialize in used equipment and original equipment manufacturers that offer state-of-the-art cutting equipment and even refurbished machines that may not have the production prowess of new machines, but still can perform much more efficiently than machines of a similar age with no rework done to them.
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Ask the OEMs questions about service availability. Today&#;s technology does not require as much maintenance, but when a machine goes down, you&#;ll want it back up and running as soon as possible. Also find out about parts availability and delivery. Again, a laser cutting machine that can&#;t cut because of a damaged part just doesn&#;t cut it.
Be aware that laser cutting machines from OEMs that are recognizable in the industry typically have higher resale values.
Two types of lasers currently make up a majority of the industrial market: traditional CO2 gas lasers and newer solid-state fiber lasers (see Figure 1). CO2 lasers have been the workhorses of the metal fabricating industry for the previous two decades. These lasers operate by running electricity through a gas-filled resonator (which includes CO2) and using mirrors to focus and deliver the beam. In a fiber laser, banks of diodes are used to create the laser, and it is channeled and amplified through fiber-optic cable, similar to that used in the telecommunication industry.
The fiber laser, which made its debut around , has lower operating costs and delivers higher cutting speeds than the CO2 laser. Early on the fiber technology could cut at these higher speeds only on thin materials, but with the advent of more powerful lasers, fiber lasers are demonstrating robust cutting speeds even in 0.5-in.-thick material. As a result, fiber lasers tend to be a popular choice, despite their higher price.
Also, fiber technology may open new opportunities for a fabricator. These machines can cut reflective material, such as brass and copper, whereas it is difficult for CO2 lasers.
Some applications still remain better suited to CO2 lasers, such as applications that require good edge quality on thicker or specialized materials. Also, some manufacturers may feel comfortable with CO2 technology because they&#;ve used it for several years, and the company has in-house maintenance expertise.
After the end of the warranty period, keep in mind that you will have to make a decision about ongoing maintenance. Are you comfortable relying primarily on the OEM for service, or do you like to be self-sufficient, perhaps relying on a third-party source for any maintenance? Because the fiber laser has fewer moving parts or mirrors when it comes to laser generating, unlike a conventional CO2 resonator, it will require less maintenance over its lifetime.
Choosing some level of automatic material handling equipment also is an important consideration. This is even more important today, primarily because of the significantly faster cutting speeds of the fiber laser technology (see Figure 2).
That&#;s why it&#;s necessary to understand just how you will use this new laser cutting capability. Do you plan to run the laser only a few hours each day or multiple shifts? Based on the typical time to process a sheet of material, can your operator keep up with manually loading and unloading the laser, even if it has a second shuttle table? How important is minimizing the labor cost in the part production to making a profit and remaining competitive in your business?
Sometimes metal fabricators choose not to buy material handling automation immediately. If you choose this route, ensure that pallet systems or even an automated storage and retrieval tower can be added easily in the future.
In many instances, manufacturers are already using a software package that everyone is used to. Will that software be able to work efficiently with the new laser cutting machine, or will you be better off purchasing the OEM&#;s software? If the latter, what new capabilities come with the new software?
As more of the manufacturing world is talking about increased interconnectivity among machines and software systems, it behooves you to ask if the new software is capable of running other machines already in place on the shop floor. Additionally, it&#;s worth having a conversation as to how the laser might integrate into the company&#;s network. Laser cutting speeds aren&#;t the only thing increasing at an incredibly fast pace; collecting pertinent manufacturing information in the blink of an eye is leading to more timely and impactful decision making for manufacturers.
With such a large investment, a manufacturer needs to know at what level of efficiency the equipment is operating. You need to know more than just if the machine is running or not running. This is where equipment performance monitoring comes in.
It&#;s important for you to find out if software can measure the laser cutting machine&#;s overall equipment efficiency (OEE) in real time. If so, can the software be used for your other laser cutting machines, if you have them, so that you might discover &#;hidden capacity&#; where you thought there was none?
With the cost of about 1 percent of the equipment price, monitoring software can provide a 10 to 50 percent productivity gain with paybacks of less than four months.
While some manufacturers pay cash for a laser, the majority use some method to finance the purchase. Don&#;t assume that your bank is the best source for funding the laser equipment purchase. Look at other alternatives, including the OEM, many of which own their own financing arms.
Also, don&#;t assume you will receive better service if you choose the OEM&#;s financing option.
Preparation is required for a successful delivery and installation. First, what type of foundation, if any, is going to be required? Second, the laser cutting machine has to be located in the right place in the facility, preferably away from harsh environmental areas. You also should have found the best location for the laser so that it contributes to an efficient flow of laser-cut blanks to downstream manufacturing processes.
For a lot of companies, the delivery of a new piece of major manufacturing equipment is a new experience. The company that supplied the laser cutting machine can answer your questions about shipping and rigging; they do this all the time.
Answering these questions and obtaining quotes based on the feedback can be used to narrow down the selection of the supplier of a laser cutting machine to two to three sources. From there you need to find the right model, ask the right questions during equipment demonstrations, and work toward an acceptable price. Remember, there are many important items to discuss during the final negotiation.
The purchase of such a machine can be an overwhelming task. That&#;s why it might make sense to join an industry association, such as the Fabricators & Manufacturers Association, to network with manufacturing peers to learn from them, or even seek out the assistance of someone that has been through or is familiar with this type of industrial equipment purchase. Such an effort likely would prove to be worthwhile.
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