Laser Die Cutting: “A Guide to Laser Cutting Technology – Part 2”; Screen Printing; March 2009

Figure 26: Laser cutting Technology Comparison Chart

Part II

Technical Guide: How to Match Today’s Laser Cutting Technology to Application Requirements

By Markus Klemm, R&D Software Engineer, Spartanics

Fallacy of the Double Scan Head Advantage

Another area that can get confusing to those who do not understand the specifics of laser scan head design is the use of so-called double scan head systems in hopes of accelerating cutting speed. These higher-priced double scan head laser cutters are actually at times no faster or even a tad slower than single scan head laser cutters that use higher wattage lasers coupled with more sophisticated algorithms in the laser control software. Although it might sound good, i.e. the idea of using two lasers at once to double your production speed, this both creates significant quality issues and cannot truly double speed because of the physical constraints of putting two laser scan heads next to each other and the compromises that this forces one to make.

When you are stitching two halves of the web width together, it is often possible to have more parts on one side of the web as compared to the other side, as shown in Figure 21. In such a scenario, with a double scan head machine you will lose web speed because the laser on the overloaded side will cause a slower web speed. To solve this problem, manufacturers of double scan head systems usually position the two
laser scan heads as close together as possible across the web width to create the greatest possible overlap between their two cutting fields.

However, for wider material there is always an interplay between the size of the scan heads, how closely they are positioned together, the spot size that results, and the extent to which there is overlap in the cutting area of the two scan heads and the related stitching involved. If the scan heads are large such that they cannot be placed very close together, there will be less overlap in the cutting area and more need to stitch, which is an eventual challenge to quality, as shown in Figure 22. Alternately, if small can heads are used and positioned closely together, there might be a greater overlap in cutting area but the spot size would need to be much larger, as much as 280+ microns, which is also an eventual challenge to quality. A third option, which also undermines quality, would be to use small scan heads positioned a distance apart for a smaller spot size, but again creating a need for stitching because there is a much smaller overlap in the cutting area, as in Figure 23.

Another constraint is that there are always areas beyond the reach of the other laser scan head, as shown in Figure 24, which means that you must contend with the difficulties of stitching two objects together that have been cut by different scan heads. This ALWAYS means some compromise in quality, because different scan heads will have different temperatures resulting in different drifts during operation. Realistically, there are very few laser cutting applications that are forgiving enough for the quality issues that such stitching engenders. It is not only applications with stringent cut-to-print registration requirements that are challenged by stitching the cut images from each of the dual scan heads . For example, if there is an offset of the two cut parts by more than +/- 0.1 mm this can create a knick during waste removal due to the misalignment during stitching.

Thus, the higher cost of double scan head systems is not justified especially if one compares these systems to single scan head laser cutters that are designed for cutting at higher speeds. Double scan head systems often cannot use the 200 –210 micron spot size lasers that avoid the excess heat which can cause problems such as burn throughs, adhesives sticking to release papers, etc. Moreover, the costs for higher wattage single scan heads is considerably less than the dual scan head designs, yet the production speed they afford is typically the same or a bit faster.

Systems Integration, User-Friendliness and Production Output

The quality improvements that are possible when high resolution camera systems communicate to scan head control software to determine required X/Y offsets is only one example of the benefits of systems integration in top quality laser cutting machines. The extent of systems integration in one or another laser cutting system can largely determine how user-friendly they are to operate and has great bearing on the production outputs that can be achieved. For example, older systems required users to obtain a separate camera system, and required operators to additionally master the camera control software. In contrast, today’s better quality laser cutting systems come with cameras fully integrated with the laser software. Operators do not have to learn set up of a separate camera system, as this is now done directly from the laser control software, and in the best-in-class systems only takes three simple steps.

The better quality laser cutting systems with full integration of all systems components are in fact the only laser cutting machines one can find in the market today that work seamlessly with variable images from digital printers. These better quality laser cutters allow one to create laser jobs with multiple pictures with different geometries and different step-ups. This is only possible in today’s fully integrated laser cutters where there is ongoing communication between the PLC and the camera system. It’s a good illustration of why laser cutters that do not feature a high level of systems integration are now obsolete machines. They simply can’t keep up with the demands of working with variable data and variable images for which digital printing is so ideally suited.

This same feature of integrating cameras with machine controllers allows today’s high quality systems to automatically compensate for variations in prints, such as those that are created by shrinking as inks dry. These better laser cutters automatically account for variations in step-ups from one part design to the next and can only do so because of that ability for the machine controller to communicate with the camera system. Because these better laser cutting systems feature full communication between the camera system, the laser software and the machine controller they can automatically determine the step up of each job. They are self-calibrating and operator input is not required to measure or input step-ups. Antiquated technology that does not have this level of systems integration simply has no mechanism available to automate the start of jobs, the calculation of step-ups, or to compensate for variations in step-ups created by other steps in the production process.

In today’s systems with a high level of systems integration, there is a new ability to vary the job stop criteria by part count rewound, by rewinder diameter, or the rewinder roll length as shown in Figure 25. Here too, this is only possible because the software that controls inputs, outputs, and the laser cutting per  work in concert and are fully communicating with each other.

This same systems integration feature of top quality systems also facilitates the fastest setup of repeat jobs. This is because ALL the machine parameters needed for a specific job—web speed, dancer arm pressure, camera system settings, etc.—are saved in one file. This means that at the very start of the job you can achieve required cut-to-print accuracy without having to fuss with reloading parameters for different system components separately.

You also can always identify the better laser cutting systems that have full systems integration by their smart stop systems, which are lacking in lower quality laser cutters that are devoid of systems integration. These smart stop systems monitor all possible fault conditions such as web breaks and off-positioning of the dancer arm, or full rewinder rolls. When there is a fault condition anywhere in the system it pauses and the error message is displayed on the operator screen. Such smart error messaging facilitates maximum throughput and is only possible in fully integrated systems where there is seamless communications between operating software for registration, lasers, laminators, slitters and rewinders.

Thus, the upshot of systems integration in the better quality laser cutting machines is a faster throughput. Though throughput varies from one plant to another, and one job to another, a reasonable expectation is that throughput with today’s better quality laser cutting machines will be significantly faster than what is possible with non-integrated technology.

Better yet, estimating production time is now automated by the software in today’s better quality laser cutting machines. These systems’ software creates a database that stores laser settings for various types of cuts (e.g. kisscuts, creases, etc.) for the particular substrate being cut. Using this data, the same software capability that optimizes a job for web speed will calculate this optimum web speed and the production rate that is possible. This job simulation is done by the software, before the job is run, and gives users of today’s better quality laser cutters an ability to make very accurate cost projections of new job runs.

Selecting System Components

You can expect a cost difference of up to 20 % between laser cutting systems made from high-end components and those that are made with components of lesser quality. As a manufacturer of both high-end and more affordable laser cutting systems, Spartanics estimates that nearly four times as many users–but certainly not all– will be adequately served by lower cost systems. It is important to know that your source for laser cutting technology is not married to particular component suppliers. Best-match components for particular applications (laser source, laser scan heads, etc.) can be sourced worldwide. Lower cost systems can produce high quality outputs IF the underlying software engineering and systems integration are expert.

Figure 26 (Laser Cutting Technology Comparison Chart-repeated from Part I) outlines some of the key differences between lower cost and high-end systems, and the obsolete technology that they both replace.

Knowing your real quality requirements is the first step in zeroing in on whether your operation is better served by low cost or higher quality laser cutting systems. However, there is a baseline of quality that should ALWAYS be achieved such as avoiding burn-through marks and ensuring that there is a crisp narrow cut precisely following the artwork geometry. A laser cutting machine must have a high quality laser source with a small spot size to achieve these results. In label applications, this also allows for much better control of the heat transmitted to the release paper on the back of labels. Inferior laser sources with larger spot sizes often make it difficult to remove the cut labels because melted adhesives cause the labels and release paper to stick together. If a laser cutting system presents burn-throughs it usually reflects both a poorer quality of software engineering to operate the laser power and an inferior laser source with a large spot size. The soft marking capabilities of today’s better quality laser cutters should be considered as a non-negotiable feature, whether a system is high-priced or low-priced. There are systems at all price levels that can and cannot achieve this level of quality and thorough investigation is required.

The wattage of the laser should be carefully considered. Many of the commercially available lasers have the best laser beam quality with full power. For lasers of that type, if you end up using only 10% or less of the laser power from your laser source you can expect significantly diminished laser beam quality. For example, a converter making kisscuts with easy-to-cut materials that has a 300 watt laser in their cutting system may be using only a small portion of available laser power and would be better suited by a lower watt laser. A converter making many throughcuts, including more difficult to cut release paper, which also wants to achieve high cutting speeds would need that 300 watt laser.

The smaller the maximum working area the smaller will be the spot size of the laser. Smaller spot size means better cuts because the energy is concentrated and you need less laser power to achieve the same depth of cut. Less heat is transferred to the material being cut is always the desired scenario. One of the differences you will find in lower-priced systems is that they sometimes use lower cost air cooling for lower power lasers, as opposed to the more costly water cooled lasers.

The edge quality that a particular laser cutting system delivers will vary with the spot size of the laser. In systems with smaller working fields (e.g. 200 x 200 mm field size) this is not as much an issue and one can expect both the better high-end and lower-priced systems to have a 210 micron spot size. If the working field is larger, however (e.g. 300 x 300 mm field size) one needs to be able to make due with a 280 micron spot size when considering the lower-priced system. As an example, generic label converters might be well-served by a system with such larger spot sizes but those involved in RFID applications might need the greater precision in cutting edge quality.

Smaller spot sizes not only affect edge quality of the cuts but also will have bearing on cutting speed. It is very important to verify that a system can maintain the desired edge quality and cut-to-print accuracy at the maximum cutting speed of the system. Some of the more poorly designed laser cutting systems cannot maintain cut-to-print accuracy over time. The lower cost laser cutting systems may use sensors for registration, or in more demanding applications use the sophisticated camera technology to deliver the very tight tolerances in cut-to-print registration that are typical of high-end systems. If these camera systems are fully integrated with the laser scan heads they are able to apply the offset values to keep cuts to a precise registration. Here too, it is not only the quality of the camera but the underlying software engineering that has great bearing on the tolerances that are achieved at varying speeds.

Features that bear on user friendliness and ease of operation are found in both the low-priced and high-end better quality laser cutting machines, reflecting the high level of systems integration in better quality laser cutters at all price points. Smart stop systems, job simulation software, automatic image splitting and optimization for web speed, variable job stop criteria, and one step job setups of all operating parameters make these systems straightforward to operate, even for lightly skilled workers. Because the software is handling most operations behind the scenes— registration, web control, laser powering, laminating, slitting—and because there is full communication between different system modules, the operator’s work is relatively simple because the software does the difficult jobs automatically. Obsolete technology does not have these various features for ease-of-operation. Some out-of-date designs do not even give operators the capability to change job settings while the laser cutting machine is operating, nor directly on the machine. These type of laser cutters, that force operators to stop cutting operations entirely and reload a job from scratch saddle users with unnecessary drags on production that today’s better quality laser systems bypass altogether by giving operators numerous ways to amend job parameters without shutting down the production line.

(Note: Spartanics has taken user-friendliness to the next level with the introduction of the only step-by-step instructional video wizards for laser cutting as semi-interactive Help Menu options on all Spartanics Finecut Laser Cutting Systems as shown in Figure 26. These interactive video wizards do not Figure 26: User-friendly instructional software rely on language and are designed to help overcome language barriers that exist in many workplaces around the world and to quickly bring workers at all skill levels up-to-speed in operating sophisticated laser cutting technology. The instructional video wizards cover a range of topics such as camera set up, performing test shots, and job setup. When a topic is selected, a short step-by-step interactive video plays showing the sequence of operational steps required to perform that function. The videos play on one screen while the operator can directly interact with the laser system on another screen while the instructional video wizard is in progress. Lessons are taught by visual example rather than spoken or read-then-do techniques.)

Suggested Method for Sourcing Laser Cutting Technology

To begin sourcing the best laser cutting technology for your operation, you must first determine your application requirements in terms of: complexity of geometries to be cut; production rates required; sheet vs. web; type of materials (PET, ABS, poly-carbonate, etc.). One is best served by contacting several manufacturers that build laser cutting systems to request that samples be run on your materials using a few of your part configurations. The manufacturers should then be able to recommend the model of their laser cutting systems that will be correct for cutting your parts from your materials. Of course, it is very important to ensure that these manufacturers are equally adept at creating lower-priced laser cutting systems AND more sophisticated technology such that they can deliver best-match solutions. If a laser cutting system integrator is married to particular components – whether they are lasers, scan heads, etc.—consider it a red flag that they are not set up to match laser technology to real application requirements.

After receiving your cut samples from the prospective manufacturers of laser cutting systems, and after receiving their recommendations on the proper model of laser cutter and their budgetary pricing, request a personal visit to manufacturers of interest to see actual cutting of your parts and materials. If you spend one day at the individual manufacturers you should be able to get a good feel for the degree of difficulty cutting your parts. A visit also provides an excellent opportunity to see their plant, to understand their people that you could be dealing with in the future, and to examine the ease of use of importing drawings of parts into the laser cutter and converting the drawings into a usable cutting path.

As with any equipment purchase, it’s also advisable to determine the extent of service support that is available from each manufacturer, as this can make the difference between a relatively short period and a much longer period of downtime in the future. Better quality laser cutters, both low-priced and high-end, include complete remote diagnostic capabilities.

The best case scenario of comparative shopping would also include use of laser cutting system manufacturers’ contract manufacturing services. These would provide not only proof of concept but would allow expert software integrators to fine tune operations to your exact application requirements.

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