Category Archives: Laser Editorials

Laser Safety in Entertainment Applications

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By James Stewart, CLSO

High power lasers are routinely used in entertainment environments as a special lighting effect. Historically such lasers could only be used in situations where the budget, infrastructure, (namely power supply and cooling), and space permitted.

In recent years, however, these barriers have disappeared with the proliferation of low-cost solid-state laser light sources that now dominate this sector. This has created new opportunities in how the effects are being used, as well as who is able to now use them.

Business is healthy for the specialist laser effects providers that typically supply lasers for events and music performance tours, using output powers ranging from 1W through to 40W CW, with not a drop of water or three-phase in sight. Dramatic reductions in the purchase cost, physical size, and power supply requirements have influenced how the effects are used. Ten years ago, a typical music concert touring application would employ a single digit number of laser effects projectors, with output powers ranging from 3W to 10W. The same types of installation in 2017 are typically using 30 to 40 fixtures, with a range of output powers up to 30W or more. The greater number of lasers being used on single installations has increased the need for better awareness of the exposure risk, and

The greater number of lasers being used on single installations has increased the need for better awareness of the exposure risk, and requirement for a robust installation protocol. In a change to earlier practice where a dedicated laser operator and control system were used to operate the laser effects, many of the latest generation laser lighting effects are designed to operate directly from the same control systems as normal stage lighting effects. This has benefits from a creative perspective, in that that a lighting designer no longer needs to interface through a third party dedicated laser system operator. But the downside is that the lighting designer may not necessarily be familiar with the risks in using Class 4 laser products.

A lack of familiarity of exposure risk also exists for another new group of users, which with laser projectors costing only a few hundred dollars, and being widely available online through disco / stage lighting distributors, can install laser effects in small venues and for mobile discotheques. At the budget end of the market are multicolour laser effects projectors that produce moving beams and pre-programmed animated graphics and text. These devices typically output 1W – 2W, and operate automatically in sound-to-light mode.

Exposure potential from laser lighting effects can be considered when the characteristics of how the effects are produced is understood. The majority of lighting effects created at laser installations are through movement of two mirrors placed orthogonally, so as to move the beam freely about an imaginary x and y-axis. The maximum extent of beam deflection is typically between 50° – 60° optical.  In practice this leads to typical scan across-the-pupil exposure durations of a few µs to several hundred milliseconds, depending on the content material. Stationary beam creation is also possible if the control signal is held constant, or fails.

The other popular method of creating laser effects is achieved by passing a laser beam through a transmissive diffractive optical element (DOE), (also referred to as a diffraction grating), that splits and deflects the beam creating arrays of lesser-powered beams creating a geometric pattern. The DOE is normally attached to a motorized substrate, typically able to rotate from stationary through to 10rpm – 20rpm. The characteristics of the DOE determine the visual appearance of the laser effect produced. The time it takes a diffracted beam to scan across-the-pupil distance typically varies from a few milliseconds to being stationary.

The majority of exposures occur in the millisecond and microsecond domain, meaning for MPE comparison radiant exposure expressed in J·m-2 is used, however, for the purposes of risk assessment, it is more convenient to consider the exposure having been converted to a peak irradiance.

The hazard distance (NOHD) of most lasers used for lightshow applications normally exceeds the length of the working, (and viewing), space they are being used at. Table 1 shows the NOHD, along with the irradiance at five distances that may be representative for four typical laser output powers used in this sector. For each distance, a 0.25s and 1ms dose are considered, to give an indication of how many times in excess of the MPE such an exposure may be at that distance.

 

Laser Power 3 10 20 30 W
NOHD 387 707 1,000 1,225 m
Exposure Distance 5m Irradiance 60 199 398 597 kW·m-2
250ms dose 2,345 7,815 15,630 23,446 Excess
1ms dose 590 1,966 3,931 5,896 Excess
10m Irradiance 23 75 151 226 kW·m-2
250ms dose 888 2,960 5,919 8,879 Excess
1ms dose 223 744 1,489 2,232 Excess
30m Irradiance 4 12 23 35 kW·m-2
250ms dose 138 459 919 1,378 Excess
1ms dose 35 116 231 347 Excess
50m Irradiance 1.4 5 9 14 kW·m-2
250ms dose 54 178 356 534 Excess
1ms dose 14 45 90 134 Excess
100m Irradiance 0.4 1.2 2.4 3.6 kW·m-2
250ms dose 14 47 94 141 Excess
1ms dose 3.6 12 24 36 Excess

 

Table 1  A comparison of exposure potential of four laser output powers typically used in lightshow applications

The figures in Table 1 demonstrate how the irradiance present at the exposure distances is significantly higher than the 25W·m-2 and 101W·m-2 MPE limits (0.25s and 1ms respectively). Areas within several metres of the source are particularly high risk exceeding the MPE by several hundred, if not, thousand times, depending upon the laser power and duration. Such viewing conditions could occur for lasers positioned on, or directed at the stage from the vicinity during a poorly managed performance or rehearsal. It is also possible that the exposure could occur when the scanning position of the lasers are being lined up during the installation phase, where a stage may be occupied by technicians and crew unaware of the exposure risk.

With laser effects capable of producing exposures with peak irradiances of several kW·m-2 over a considerable distance from the source, controls are necessary to limit exposure to levels considered safe for viewing. In the first instance, the user and those sharing the environment lasers are being used in, need some appreciation of the risk and what precautions should be typically adopted. As with most projects, spending time at the early stages of development helps to identify and address issues that could become more significant if left unchecked. In an ideal world, the laser provider would be contacted early on in a production’s development, be provided with a full brief from the client, and full information about the rest of the production’s implementation. It is recognised that events rarely function like this, which is no fault of the laser provider, but instead the nature of the sector. This means the successful laser provider has to remain alert, and often has to anticipate factors that could affect safe laser use. Even the best planned productions can be dynamic environments with tweaks and changes happening right up to the last moment. Basic rules however help to keep a laser install on track and minimise the risk to workers and audience alike. At no point should users neglect the fact that laser lighting effects are a special effect, and should be regarded as such, needing appropriate precaution to be taken for their safe use.

Presently, two major standards organisations have working groups producing specific guidance for this sector. ANSI through Z136.10 – Safe Use of Lasers in Entertainment, Displays and Exhibitions (currently under development), and IEC through IEC/TR 60825-3 – Guidance for Laser Displays and Shows, will each address the issues that have become apparent as laser light show technology has become more accessible, and is being used in ways that would have just a few years ago been impractical. It is hoped that when the new guidance is available that it will provide end users and safety advisers alike with an authoritative reference to best practice for this application of lasers.

James Stewart works for LVR Optical, based in the UK, as laser safety practitioner with a keen interest and experience in managing entertainment applications using lasers. He is the project lead for IEC/TR 60825-3.

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Interested in Laser Safety? To learn more about Laser Institute of America’s International Laser Safety Conference, visit the conference website. 

 

Setting Up a Laser Lab? Avoid the Pitfalls

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By Jamie J. King, CLSO

The design of a laser laboratory is not only critical to its overall functionality, but more importantly to the safety of those who work in and around it.  The safe planning of a laboratory is no accident.  From conception to commissioning of the laser, safety must be involved in every step of the process.

Each situation presents unique challenges with equally differing solutions.  It is up to, and the responsibility of, the Laser Safety Officer (LSO) to ensure that each Laser Controlled Area (LCA) is fashioned in the safest way possible.  American National Standards Institute (ANSI) Z136.1-2014 states that the total laser hazard evaluation is influenced by:

  1. The laser’s capability of injuring personnel or interfering with task performance.
  2. The environment in which the laser is used.
  3. The personnel who may be exposed to the laser.

The laser part sounds like the simplest problem to solve.  This may have been true in the days before ultrashort pulse lasers, OPAs, nonlinear optics, and high-average power lasers, to name a few.  Today you may be faced with several of these aspects all at once. The LSO must be part of the design phase very early on to ensure all issues are addressed.

The environment in which the laser will be used is probably the biggest variable to deal with.  Being involved in the process early will ensure the crafting of a space that depicts excellence in terms of form, function, and safety.  Coming in late can be a disaster, requiring patchwork fixes that look sloppy and may not be safe.

You can minimize the extent of personnel potentially exposed by controlling the design of the laser space.  Reducing the potential for exposure to personnel decreases the hazard and downgrades the level of safety training required.  This will lessen the overall per annum operational expenses.

In setting up a laser lab, the pitfalls can be a plenty.  Without forethought, you won’t recognize them until the space is completely built out and you are ready to operate.  Any new design or remodel should incorporate the use of a computer-aided design (CAD).  With this, you can start to envision the potential problems that might unfold otherwise.   Working with the end user, you can discuss the intended operation and process flow.  Some of the potential issues you will uncover are:

  • Entryway controls – whether defeatable or non-defeatable Safety Interlock System (SIS) you can determine if you might have potential laser beam outside of the LCA.
  • Ergonomics – what tasks/operations will be performed frequently? Design the height of the optical table accordingly.  Can the worker perform all actions comfortably?
  • Utilities – electrical cables, water lines, fire suppression, and ventilation are best thought out and designed early on. Having these engineered in at the beginning prevents patch work fixes after, which surely will create slip/trip/fall issues.

In looking at the layout of the optical tables, you can determine how best to plan the beam path.  It is never a good idea to direct a laser beam towards the entryway.  If you operate in a seismically active area, you should either brace your tables or locate them such that egress will not be inhibited in the case of an earthquake.  As soon as an optical table is installed in the space you should electrically bond it to ground.  You never know that will be put on the table in the future.  Do not make the mistake of connecting a bonding strap to the bottom of the table unless you ensure there is electrical continuity between the top and bottom plate.

Something to keep in mind in setting up a safe laser operation is that you want to control the hazard as close to the source as possible.  Things to look at here are:

  • Beam Blocks/Barriers/Enclosures – beam blocks are placed at the end of beam lines or behind optics and are expected to take the power/energy of a full beam. Choice of materials is crucial here in that you don’t want to select something that is highly reflective or can’t handle the thermal load of the incident beam.  Remember that the go-to material of black anodized aluminum is very reflective in the near infrared.  Barriers are installed beyond beam blocks, usually around the perimeter of an optical table.  They are only meant to see a diffusely scattered beam.  Barriers can also be used to block an area, preventing line of site into an LCA.  Barrier materials can range from laser curtain material to metal panels or even walls.  When installing these types of barriers, one must ensure that physical stature of the worker is considered.  This will ensure that the height of the barrier is adequate to protect all outside of the LCA.  In more mature and static operations, one can employ an enclosure to take the laser hazard away from the worker.  For truly Class 1, the panels must be either interlocked or require a tool for removal.
  • Shutters – this is one of the most significant components of a safe operating laser. Limit the open space between source and shutter.  Is the shutter in place?  This may seem like a ridiculous question, but if your SIS does not have feedback capabilities, how do you know it is even there?  Shutters should be “fail-safe,” meaning they will close on a failure.  Shutters can and do fail internally and may need to be inspected to ensure proper operation.  Failures may be broken blades, mirrors, levers, and even drilled holes.

Failures may be broken blades, mirrors, levers, and even drilled holes.

The use of multiple wavelengths creates a nightmare when trying to find adequate laser protective eyewear.  Early involvement of the LSO in conjunction with your laser eyewear vendor can help determine what wavelengths can and cannot be blocked.  A safe worker is one who can adequately see what they are doing.

What about high intensity/high power lasers?  This presents another set of unique challenges altogether.  At levels of >1015 W/cm2, the generation of ionizing radiation is possible.  A 25kW laser beam with a peak irradiance of ~10 kW/cm2 can cut through simple drywall in a second.  With diffuse reflections being the main concern for barriers and enclosures, this may become a real issue.  Limited commercially available items rated at these high outputs may necessitate that you become your own tester of materials.  In this realm, you are better off just removing the worker from the hazard and go with remote operations.

The result of a well-planned laser laboratory not only promotes pride in the team that will use it, but it fosters safety.

The result of a well-planned laser laboratory not only promotes pride in the team that will use it, but it fosters safety.

How?  The space will be well engineered from the start with safety built-in.  There is less reliance on administrative controls, and with the LSO input from the start; the worker sees that their safety is the utmost concern.

FDA’s Proposed Change to the Regulation of Laser Pointers

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By Patrick Murphy

In October 2016, the U.S. Food and Drug Administration (FDA) put forth a preliminary proposal to declare green, blue, yellow and violet laser pointers as “defective.” Only orange-red and red laser pointers would be allowed to be manufactured, imported or sold in the U.S.

This proposal was in response to the thousands of illegal and unsafe laser pointers aimed at aircraft in the U.S. According to the Federal Aviation Administration (FAA), pilots reported 7,442 laser incidents in 2016 — more than 20 every night. 91% of the incidents involved green laser light.

Laser Illuminations reported to U.S. FAA, annual total

Safety experts are most concerned about the bright light from laser pointers causing distraction, glare and temporary flash blindness. When visual interference occurs during critical phases of flight such as takeoffs, landings, low altitude maneuvers and emergencies, there is potential for an aircraft accident. Visual interference also has disrupted police and rescue missions.

Pilot groups and lawmakers have called for restrictions on pointers, especially green ones. For example, in February 2016 Sen. Chuck Schumer (D-N.Y.) met with the incoming FDA commissioner, who agreed to consider having FDA ban the sale of green pointers.

To understand FDA’s proposal, it is helpful to describe how FDA can change its regulations, and what a finding of “defective” means.

Under 21 CFR 1040.10 and 1040.11, FDA has limited regulatory authority over laser devices, and over three laser uses. These regulations were written well before laser pointers and thus do not specifically address pointer usage or misuse. (A separate law passed by Congress in 2012 as part of FAA legislation does make it illegal to aim the beam of a laser pointer at an aircraft, or the flight path of an aircraft. The penalty is up to 5 years in prison and/or up to a $250,000 fine.)

To update its regulations, FDA is required to present them first to a permanent statutory committee, the 15-member Technical Electronic Product Radiation Safety Standards Committee. In October 2016 FDA presented TEPRSSC with a wide range of electronic product radiation safety proposals. Two of these dealt with laser pointers.

The first proposal was to define “laser pointer.” The agency suggested the following wording:

Handheld laser products designed for battery-powered operation that are manufactured, designed, intended or promoted to provide illumination, designation of a target or point of origin, or sighting, with no associated technological or scientific purpose for the laser’s emission. Laser products are not excluded as laser pointers when used for visual entertainment, vision disruption, to startle, or novelty purposes.

The second proposal was to restrict laser pointers based on the beam color.

The FDA showed TEPRSSC members the following chart showing the eye’s sensitivity to colors under light-adapted and dark-adapted vision:

Human photopic and scotopic response

The three circled areas show how the dark-adapted human eye (dashed curve) perceives red light as much dimmer than equivalent amounts of blue and green light.

FDA told TEPRSSC that “[t]he hazard from laser aircraft illuminations would be effectively eliminated if green and blue laser pointers were not available. Colors at 615 nm and longer, viewed with night-adapted vision, appear only 1.4% as bright as green at the commonly manufactured 532 [nm].”

FDA then invoked 21 CFR 1003.2. This regulation states that a product is defective if it “… emits electronic product radiation [in this case, visible light] unnecessary to the accomplishment of its primary purpose which creates a risk of injury …”

FDA said there is a risk of injury from visual impairment from laser pointers aimed towards operators of aircraft, vehicles and watercraft, and noted that “pilots are particularly vulnerable to disruptive visual impairment at night.” Based on this risk, FDA would prohibit the manufacture or importation of laser pointers from 400 nm (deep violet) to 609 nm (red-orange). Pointers from 610 nm to 710 nm (deep red) would be permitted.

As with current laser pointers, the power output would be limited to less than 5 milliwatts.

If implemented, FDA’s proposal would not affect individual possession of laser pointers in the 400-609 nm range. It would only restrict manufacture and importation of such pointers.

A key benefit of FDA’s proposal is to make it easier to control the vast majority of pointers — green — that are involved in pilot reports of laser interference. If a pointer’s beam is any color other than red or red-orange, it would not be permitted for sale in the U.S. No additional testing, using expensive power meters, would be necessary.

In addition, state and local authorities could enact color-based restrictions based on FDA’s “defective” determination. This would, for example, allow a police officer to take action such as confiscation based solely on the color of the laser beam. FDA told TERPSSC ” we envision that just like any other hazardous product that has been determined to be defective, that state and local … ordinances and laws would be put in place that would likely deal with the use of green and blue laser pointers.”

Members of the TEPRSSC committee generally agreed with FDA’s laser pointer proposals, while also raising some concerns for further consideration.

The next step is for FDA to review its TEPRSSC proposals in light of the members’ comments, and make any changes FDA feels are appropriate. After this, FDA would publish the official proposed regulations in the Federal Register. The public would have from 30 to 180 days to comment. Based on those comments FDA could drop a proposed rule, change it and resubmit for new comments, or proceed with a final rule if comments were favorable or only required minor changes.

In summary, the FDA has made a first-in-the-world proposal to allow manufacture only of red pointers (610-710 nm). By designating all others (400-609 nm) as “defective”, this would give the agency additional regulatory authority which makes it much easier for authorities to determine which laser pointers may be imported, manufactured or (depending on state and local laws) sold, owned or used.

Additional details about the proposal are in an 11-page paper presented March 21 at the International Laser Safety Conference, available online at http://bit.ly/2pvfwpw.

 

 

Turbine Blade Cladding & Remelting for Single-Crystal Volume Extension

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By Irene Alfred, Boris Rottwinkel, Christian Noelke, Volker Wesling, Stefan Kaierle

Figure 1: Track parameters measured after laser cladding of single tracks while varying laser power, laser travel speed and powder feed rate

Nickel-based superalloys are used extensively in the combustor and turbine sections of aircraft engines due to their ability to withstand temperatures of up to 1100°C, thereby increasing engine efficiency. The microstructure of single-crystal turbine blades show superior creep and fatigue properties when compared to poly-crystal alloys and increase their lifespan. However, the production of such parts remains expensive and extensive as the process involves a thermal gradient to allow for directional solidification to create a single crystal microstructure. Since these parts undergo the most amount of erosion and cracking during their lifetime and no effective repair method exists, these parts must be replaced, which is an expensive process.

Our objective was to achieve a single-crystal clad on a single crystal turbine blade while facing the challenges of maintaining said structure of the substrate as well as the deposit and avoiding solidification cracks. We hypothesized that the combination of laser powder deposition and laser remelting would lead to the reorientation of the polycrystalline area and thereby extend overall single-crystal height. In order to achieve our goals, a diode laser system with a wavelength of 980 nm and a maximum power of 340 W was used. Experiments were carried out on CMSX-4 and PWA 1426 substrates as well as on turbine blades of the latter material.

Laser Cladding

The first step of the process was to carry out a parameter study in order to determine a set of laser process parameters that resulted in tracks that were free of cracks and pores and also did not diminish the crystallographic orientation of the substrate during the process of cladding. In order to do so, the primary laser cladding parameters, namely laser power, laser travel
speed and the powder feed rate, were varied and the track parameters shown in the figure below were measured.

Figure 2: Laser power ramp methodology for the remelting process

The clad height (h) was defined as the height from the surface of the substrate to the highest point, while the single-crystal height, hsx, was measured at the shortest distance between the
surface and the beginning of polycrystalline microstructure. In order to reduce the effect of process instabilities and variations of the melt pool chemical composition, hsx was measured at the
cross-sectional and longitudinal axes. The melt pool depth, h’, and the polycrystalline area, Ap, were also measured, which resulted in five tracks for further testing, the laser parameters
required to create them and the track parameters that were measured.

Laser Remelting

For the process of remelting, we hypothesized that ideal pairs of remelting speeds (vr) and energy inputs (ELI) that resulted in the highest monocrystalline volume would exist. These values were determined by evaluating the results of our power ramp methodology that is depicted in the figure below. The power ramp methodology involved maintaining the remelting speed at a constant value while decreasing the laser power linearly over the course of the track. The laser power was increased to 200 W prior to the start of the track in order to ensure the beginning was not abrupt, after which a short period of constant laser power was maintained to allow for melt pool stabilization prior to the linear drop in power. A descending ramp ensured that unnecessary heat would not be built up in the substrate and disrupt the thermal gradient necessary for the formation of monocrystalline structures.

The remelting process was carried out at 3.3 mm·s-1, 2.5 mm·s-1, 1.7 mm·s-1 and 0.8 mm·s-1 for each of the five tracks. Longitudinal analyses of the microstructure of the tracks were
then carried out. By determining the highest single-crystal cross section and the corresponding laser power, it was possible to determine pairs of vr and ELI values.

It was determined using the method of least squares that a second degree polynomial equation best represented the relationship between the values. In an attempt to define a single
family of equations that would allow for the determination of ELI using track parameters, the polycrystalline area (Ap) was taken into consideration in the equation and the coefficients a’,
b’ and c’ from the general second degree polynomial equation recalculated. The resultant general equation is as follows (Figure 3):

Figure 3: Relationship

 

Using the above equation, a set of remelting parameters was calculated and applied to a single track of CMSX-4 and PWA 1426. As is seen in the figures below, it was possible to extend
the height of monocrystallinity past that which was created during the cladding process.

Figure 4: CMSX-4 (left) and PWA 1426 (right) substrates after cladding and remelting

 

Multi-layer Cladding

In order to create multilayered structures, the substrate orientation and heat drainage effects had to be taken into consideration. The most common strategy of creating such layers is by overlapping one track with the next. However, this could cause a misalignment of the thermal gradient and the formation of an acute angle between the new track and the substrate, which could lead to the formation of cracks and pores. In order to determine an ideal distance between the tracks, the following values were tested: 1.3 mm, 1.5 mm and 1.7 mm and the
resultant tracks depicted.

At 1.7 mm the space between the tracks is not sufficiently filled and a spacing of 1.5 mm shows a polycrystalline area at the overlap of the tracks that could be susceptible to hotcracking
in subsequent steps of the cladding process. Tracks with the spacing of 1.3 mm showed the best results with the gap being filled and the surface creating an ideal substrate for further cladding. The multilayer clad on the right, obtained by the parameters previously deduced, showed a single-crystal structure with a height of 650 μm and a width of 3,700 μm. A complete reorientation of regions that were previously misoriented was also observed. Using the parameters deduced in the previous steps, a process was developed to perform cladding on a turbine blade tip, which
showed no macroscopic cracks as shown below.

Figure 5: Tracks with a spacing of (a) 1.7 mm, (b) 1.5 mm, (c) 1.3 mm and (d) a multilayer CMSX- 4 clad

Summary and Outlook

While our present and future work seeks to further validate this design of experiments, we were able to show that the processes of laser cladding in combination with laser remelting is a capable
tool for improving and simplifying the formation of large single crystal volumes. It was determined that ELI, the energy input per unit length necessary to remelt and reorient a track increases
exponentially with decreasing remelting speed. We were also able to define a relationship between laser parameters and track parameters during the cladding and remelting processes,
which allows us to predict and calculate said parameters.

Figure 6: Cladding on a turbine blade tip

 

This process shows promising results for the repair of single-crystal turbine blades and requires further evaluation with regard to the thermal properties and detailed microstructural analyses of the regenerated parts.

Laser Applications in Battery Production

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By Ruediger Brockmann

The proceeding limitation of CO2 emissions by government as well as expected shortage of oil resources worldwide associated with increasing cost for fuel results in a global requirement for alternative mobile forms of energy. The development of these alternative forms of energy is summarized within the Mega Trend E-Mobility. Within this Mega Trend the main topics are alternative drives, energy storage systems, concepts for lightweight design and infrastructure for the E-Mobility.

As more than 40 percent of the manufacturing cost of an electric vehicle results from the battery, a significant cost reduction of this key component is required to increase the sales. Therefore many technical developments and political framework have been developed within the last few years. On the political side, all around the world governments support the E-Mobility, e.g., in Germany with a premium of $4,300 for the purchase of a battery electric vehicle (BEV) or plug-in hybrid vehicle (PHEV). The Chinese government supports the installation of charging stations and the purchase of PHEV and BEV with several billion dollars. Although the actual number of electrified cars is very small compared to ICE-cars (internal combustion engine), the number increases very fast every year.

On the technical side, there has been much progress in the performance of the battery and in the production technology. Especially, the big efforts in improving production technology leads to a faster decline in prices for batteries and battery packs than expected a few years ago. The actual price for battery cells is below $215/kWh and is expected to become lower than $108/kWh in the year 2030.

In the context of the developments within these main topics, there are some new technological challenges, for example, cutting of electrode foils, welding of different materials, e.g., aluminum and copper, aluminum and steel, and gastight welding of boxes containing heat-sensitive components. The laser with its high flexibility, its high process speed and its possibility to bring in the energy very selective into the material is very suitable for a high productivity and components of highest quality.

The upper part of Fig. 1 (labeled with “step”) shows the full process chain of battery production. In the lower part beneath the production technology (e.g., “welding”), there are the optics and the laser source suitable for this production step.

 

Fig. 1: Production steps of battery cell manufacturing

Overview of the Process Chain

At the beginning of the production chain the aluminum or copper foil is coated and compressed to manufacture the electrode foil. For anodes you use copper, for cathodes aluminum as carrier material. This foil is produced on a coil which needs to be cut in sheets in a process chain called slitting or sheet cutting. The state-of-the-art technology for this production step is mechanical cutting. A major disadvantage of mechanical foil cutting is the very high mechanical abrasion of the cutting tool. Therefore it is necessary to change the tools frequently, which leads to additional tool costs and fluctuations in cut quality.

Within the next step the taps of the electrode foils need to be welded together. Today, the state-of-the-art technology at this step is laser welding or ultrasonic welding. The technological challenge during this production step is welding thin foils in combination with material mixing, like copper-copper, aluminum-aluminum or aluminum-copper joints. Furthermore, a very low electrical resistance in the fusion zone is required for a high quality battery cell.

 

Welding of AI-Cu combinations with the laser, e.g., for cell connectors

 

The electrode foils are packed in the case during the next production step. This can either be a hard or a soft case, also called pouch-cell or coffee-bag. After packaging, the case is closed and sealed. The welding seam must be gas tight. For this reason, there are high requirements for the welding process. As the electrical parts are already in the case, the thermal energy and power density are limited. Therefore, there are only very few welding technologies which can fulfill these requirements – one of this technologies is laser welding.

In the last step of the cell production, the battery case is filled with electrolyte. After filling, the inlet must be closed, using a welding process with nearly the same requirements as in the previous step.

In the last production step, the cells are combined to battery modules and blocks. Also in this step joining technologies are needed for electrically and mechanically connecting the several cells and modules. As the current delivered by the modules is much higher compared to a single cell, the cross section has to be bigger, but the requirements for the weld seam are the same as for the tap welding.

Welding Copper – Spatter Free 

One of the most challenging process steps is the welding of copper without spatters. Especially for welding of the taps made from copper or electric contacts within the electronic parts. To weld this material mostly spatter free, there are two ways – depending on the application. One possibility is the use of a laser with infrared wavelength, high beam quality, and a small spot diameter. The other solution is, to use a laser with green wavelength.

Welding with green wavelength

The benefit of the infrared wavelength laser is, that it is a common technology today. But for realizing larger weld width, an oscillation (wobbling) of the laser spot on the workpiece is needed. This means you have to handle an additional process parameter – and this always means a more complex process. By using the green wavelength, additional wobbling can be avoided, as a small focal diameter as a result of the higher absorption of the green wavelength into copper is not needed. Therefore the process is less complex and much more robust compared to the use of the infrared wavelength – especially in the field of battery and electronic parts production with its high production and volume and complex parts a big benefit for the production.

Benefits of green wavelength for welding copper – same welding quality on every kind of surface

Conclusion

(TruDisk) Lasers are very suitable for welding applications in the field of battery production because they have the ability to machine high-reflecting materials like aluminum or copper. By using an additional scanner focusing optics for remote welding the productivity increases even further. Due to the low total costs of ownership remote welding with (TruDisk) Lasers is an ideal solution for the welding of lithium-ion batteries.

Sealing of battery housing for prismatic battery cells

Advantages like a defect-free and hermetic seal weld without holes and cracks and low thermal heat input make laser welding so essential in the manufacturing process of the battery housings.