Apps

I got a copy of SmartWeld when I was at another company. I found the program is great because we use a number of pulsed YAG lasers for Ti case welding in production. The program can provide very useful information in optimizing welding parameters. I am wondering if you have updated the program, which can calculate the temperature profiles of Ti materials if a set of welding parameters are given. In this way we can compare the difference if we change parameters.

Ti-6Al-4V is now in the SmartWeld materials list.

We are running our laser as follows: Controller power setting: 785 Watts Measured power at the workpiece: 589 Watts (25% less)I believe that to determine the actual power absorbed into the workpiece the power at the workpiece would need to be further reduced by approximately 25% (to 442 Watts) due to reflectivity. Is this correct ?

Yes the power at the workpiece will be significantly reduced due to reflection; deeper welds absorb somewhat more power than shallow welds. The magnitude of these reflected losses is not common knowledge. The best way to estimate the power absorbed is to have SmartWeld determine the power required to obtain a known weld area with a known travel speed. Use ISOEDGE for a sample that is melted all across the top. The power should be less than what was measured at the workpiece. Use that fraction for your next analysis.

Why is melting efficiency important?

Melting efficiency indicates what fraction of the weld energy transferred to the workpiece is used to produce melting rather than undesirable effects, such as thermal damage, base metal annealing, or distortion.

Why is energy transfer efficiency important?

Energy transfer efficiency (ETE) is only an important variable in laser beam welding. For arc welding processes ETE (arc efficiency) is essentially constant. For laser beam welding ETE can vary from 20 to 90%, and can be dependent on the laser wavelength, the base metal, the shielding gas, and the fusion zone dimensions. A high ETE indicates that laser energy is absorbed consistently and that beam power is not wasted.

I am interested in using your software for laser weld joint designs and process development. We are attempting to position an optical element in 2 dimensional tilt and lock it in place with a YAG laser. We have not purchased a laser or built any parts, yet. Glues have proved unreliable on similar products to hold position, especially since we must hold microradians of tilt. Can the software handle butt, lap, corner, and tee joints? I'd prefer to work with low expansion steels, at best Invar, at worst Kovar. Any help would be appreciated.

There now are 14 applications in SmartWeld which can be used to analyze both pulsed and continuous wave laser welding. The joint design affects the type of heat flow. Most joints can be approximated with either 2D or 3D heat flow. Shrinkage after welding is not computed but you can estimate heat input and temperatures with the software. We have Kovar in our material list.

We are principally interested in lap joints of different materials 302, aluminum, copper. What are the chances of getting versions of SmartWeld that can accomodate lap joints of different materials? The application is welding 2-4 mil 302 stainless onto a thick 6061 aluminum plate. This is a lap configuration with the 302 on top. We have the capability to perform the welds but see the value in predictive modeling first and empirical verification.

You probably realize by now that there are many different applicationsin SmartWeld. The accuracy of the model can be improved by choosing the application that is closest to your problem. The only way to incorporate other materials is to make welds under controlled conditions and measure the weld dimensions and the input variables. It can be done by making GTA edge welds (see publication). There is very little reliable data in the open literature that can be used to predict weld response for engineering alloys. 302 should weld almost identical to 304.

Thank you for the software. I have run each of the apps and find the results very useful. I imagine that as a modification to the code you could change the shape of the laser spot or change the focal position?

I am glad to hear that you have tried out all of the SmartWeld apps. We are always interested in user feedback- good and bad. If the laser beam has been characterized with a Prometec laserscope we can input that information into the OSLW model. The laser beam propagation in the version of SmartWeld that you have is for a Photon Sources V1200 slow flow CO2 laser. The NAWC measured spotsize for their 1600W Rofin Sinar fast axial flow laser with the same instrument, we were able to customize the application for his laser. They are happy with OSLW and uses it all of the time for set-up. ote that in the focusing lens selection window, you can select the lens to use and whether you want to defocus or not. In some instances a large beam diameter is recommended and defocusing is one way to achieve that.

What if the alloy we use is not included with SmartWeld?

Many metals will heat up and melt similarly to the metals currently in SmartWeld. It is easy to choose other materials and see what the results are. Often that answer is close enough to improve the procedure or to reduce the base metal heating. For example, 316 stainless steel can be analyzed using 304 stainless steel.

I have been investigating the possibility of using some analytical analysis to determine laser weld parameters for production. In the process of doing literature review I came across the SmartWeld software. I believe that having a quick analytical model has the possibility of saving us a considerable amount of time and money.Therefore, I began researching the available models and creating my own code. I have been using the model based on multiple reflections by Kaplan. I am wondering what SmartWeld's capabilities are. Specifically, what type of laser welding can it simulate? Can it handle pulsed Nd:YAG and continuous wave? If pulsed, does it allow for the user to define multiple laser profile sectors (pulse widths and heights)? How do you account power losses due to plume absorption? Can you modify this power loss? We have also recently purchased a new single mode continuous fiber laser system, produced by IPG, which is both new to us and the market. Have you had any experience using SmartWeld to model this particular type of laser? We are especially interested in simulating this system.Also, I am wondering if you have considered modifying your models for use in electron beam welding? This would also be something I would be interested in expanding upon.

Our first application (OSLW) was for CW CO2 laser welding with a Photon Sources laser. That was a custom model for that system that used  empirical data for lens focus to predict penetration. Later on we realized that SmartWeld would be more useful if it was less specific. So we added applications that are based on conduction heat flow models like Rosenthal developed. It takes an inquisitive engineer to really understand the benefits of SmartWeld. If you look at the Slides 23 and 24  on the website you can get a good idea of the utility of this approach. It really is not complicated but it does take some effort to understand at first. The type of fusion welding heat source is not really important. Conduction heat flow dominates the answer for laser, arc, plasma, electron beam. Spot welding and pulse welding are a little different, that is why we have special apps for spot welding. Pulse YAG and pulse GTA conduction model apps have not yet been developed but they could be.

The idea for our experiment is to laser weld two Al6XN stainless steel substrates together and from that, carve out Compact Tension specimens for fatigue testing. Our interest is in running the crack within the weld metal. We had hopes of having our C(T) specimens 0.5 inches thick, which would require the depth of the weld to be slightly largerthan this so we have some material to machine away. What amount of power would be needed to result in a weld of this depth for such stainless steels?

I looked in the AWS recommended practices for laser beam welding handbook and 0.5 inch welds are really quite rare. It appears that at least 6000 watts would be needed to weld this thickness. I ran a calculation in SmartWeld and it shows that at 4500 watts and 6 mm/s, a weld 12.5 mm deep by 2.45mm wide can be expected in 304 stainless steel. Your 5000 watt CO2 Spectra Physics laser might do it.

I've just run across the SmartWeld web site. Are you working on modeling for GMAW as well?

We are not modeling GMAW specifically. The addition of filler metal complicates the heat flow assumptions in SmartWeld. The additional variables in GMAW such as transfer mode, wire speed, diameter, stickout, gas, etc. can make the problem very complex. But SmartWeld can certainly be used to give approximate values for power, travel speed, melting and temperatures for many different materials. You just need to add the filler metal addtion when you look at weld size.

We have been using SmartWeld lately and trying to explore some of its capabilities in pulse laser welding in YAG program. Some of the laser specifications such as pulse duration and frequency are given as the "best" weld procedure. Is it possible to specify these parameters as the input to the program? What about the laser beam distribution (shape). Looking forward to hear from you.

The YAG model is built around data taken on a Sandia laser with energy and peak power as inputs to the model. YAG wraps an optimization method around the model and finds those inputs to obtain a desired depth for the lowest heat input. Pulse duration and frequency are computed from these computed optimal "inputs" (power and energy). Laser beam distribution is presently not one of the inputs. The YAG model is purely an empirical one taken from a response surface analysis of pulse laser welding that was published in the Welding Journal in March, 1997. Pulsed welding is much different than the quasi-steady state welding that is modeled in the other SmartWeld applications. The best way to use YAG is to compare the results with some of the other SmartWeld applications.

I have just found and read your paper "Weld Procedure Development with OSLW - Optimization Software for Laser Welding" I am excited about the potential of using this type of software for our applications. My company is in the business of contract manufacturing photonic components. We primarily assemble telecommunication packages. We are currently using Nd:YAG laser welders for spot welding Kovar parts together. Can you recommend a source for literature and software to address modeling/predicting necessary weld parameters for our type of system?

OSLW is one of 11 software applications contained in SmartWeld which is described on our website. We now have a spotweld application that is particularly useful for active alignment of fiber optic devices.

I have a question about the 2-D and 3-D isothermal models. It appears that the output from any set of input parameters always produces an area where the melting temperature of the material is exceeded. The only difference is the size of the spot decreases. For example, a weld made at 1 watt traveling at 50-mm/second still shows that the melting point is exceeded in the laser spot. In reality at these parameters the base material would just warm-up.

I suspect the isothermal models break down at 1 watt because the math does not account for the latent heat of fusion. Those SmartWeld applications use theoretical models which are only valid within certain bounds. Infinitely low power is not a realistic condition and therefore does not give a real answer.

I wanted to know if you have experiece laser welding tantalum. I need to weld a round piece of .002" thick tantalum foil to a tantalum washer. I can use either Nd:YAG or CO2. I would like to know what wattage laser I would need (ie. 500, 1000, 2000-watts). If you know approximately what wattage level is needed I would appreciate it. Thanks in advance.

We usually electron beam weld tantalum because that is the easiest way to assure a good atmosphere. We did a lot of work with pulse laser welding of molybdenum in a glove box but found that cracking and porosity were common defects. Proper shielding will be critical with any laser weld on refractory metals. The thin foil of course makes your problem more difficult. Pulse Nd:YAG is great for delivering a precise amount of energy in a small spot in a short duration pulse. Less than one joule should be sufficient for such a shallow weld. If you try continuous wave I would estimate just a 100 watts at a very fast speed. But I haven't done this so I really don't know. I used ISOSPOT2D and ISO-2D to get these estimates. I used titanium and molybdenum as a baseline. Good Luck.

We are interested in both active alignment and passive alignment of fiber optics. The post weld shift (PWS) problem is critical and we are trying to do a better job. Beside the parameters like beam balance, focus length, spot size, weld pool size,etc., how do you characterize your process with different material related to PWS problem? Do you consider also the time-dependent behavior of the material? Is SmartWeld a set of heat transfer analysis modulus? Do you intend to improve the modulus to predict the PWS in the future (For example, calculate residual stresses and deformed geometry.) Do you use finite element analysis for simulation?

SmartWeld does not calculate residual stresses or post weld shift due to welding. SmartWeld uses conduction heat flow equations to predict fusion zone size. Thermal properties are constant in SmartWeld and even that data is very hard to find for common engineering alloys. Temperature dependent data is just not available in the temperature range required. The conduction models can be very accurate in predicting weld size and temperature fields. FEA analysis of welding has been ongoing at Sandia since computers first became available. FEA models require an experienced analyst and a simultaneous experimental program to be useful. Check out the Apps to see what SmartWeld can do, and our recent paper on photonic package alignment to understand post weld shift.

Could you please review the below file attachment and give me a call? I am trying to correlate/calibrate the SmartWeld CD to actual experimental data.

Your weld section indicates that the weld was made in "keyhole" mode. In essence, the laser is creating a vapor cavity that allows the energy to be deposited below the surface. Therefore the weld pool is not formed only from energy deposited on the surface and conducted into the part. Laser welds can be made in conduction mode, keyhole mode, or partial keyhole mode. ISO Edge is a purely conduction model and cannot display weld pools that exhibit keyhole characteristics. The weld cross-sectional area however will be similar in any mode since the overall melting is determined by the energy deposition rate. If your cross-sectional area is similar to the SmartWeld calculated size then your results are reasonably close. Also keep in mind that we do not truly know the energy transfer efficiency but are guessing the magnitude from data generated with another process.

Thanks for the feedback. I think you are now understanding your process a little more. For better process robustness you might consider melting across the edge more uniformly. Then, if the laser alignment varies during welding the joint penetration will not be affected. You can probably melt more uniformly with a larger spotsize, more power, or both.

I noticed the following using the "results file outputting ON" The outfile is being overwritten with the latest results. The reason for the request is to be able to get a temperature history by position (and other parameters) and use in other applications. At this point, my only (??) recourse is to digitize the Figure with all the curves shown provided I kept a log.

Before you hit the "compute" or the "clear and compute", change the label in the Curve Label box -- it's an editable type-in. The name can be as elaborate as you want. It will create a file of that name then when you hit compute. The files that are written pertain to a single curve. Keep changing the names to get as many files as you want. Also if you want to capture the screen,use the PrintScreen button on your keyboard. This acts like a copy <Control-C>. You can then paste this into PowerPoint or Word with <Control-V> and crop it to your taste.

The YAG optimization program has a "solution method" of "minimize temperature.....".   The Temperature contour plot says "minimize Temperature fix P. depth only" when you choose that plot type.  Where on the weld is that temperature referring to? 

YAG is referring to the temperature on a glass to metal seal near the laser weld. It is only optimizing weld procedures to minimize that seal temperature. It is essentially an electronic representation of the data discussed in our March, 97 Welding Journal paper.  

We are planning to laser weld a 304SS housing that is 0.060 in thick. We are concerned that the wall temperature on the inside may get hot enough to damage a heat sensitive material that contacts the housing and is nearby the weld. The continuous wave Nd:YAG weld is made at 150 ipm and 600 W power which gives us a penetration depth of about 0.030 in. When I run ISO-2.5D with these conditions the weld depth is only 0.022 in and the width is larger than we see on our welds. How can I estimate the temperatures at the bottom of the plate more accurately?

Using your same conditions, I ran ISO-2.5D several times, each time I adjusted the magnitude of the number 3 temperature contour until it just touched the bottom side of the plate at the weld joint centerline. For those conditions the simulation gives a maximum temperature at the far side of the joint of 445°C. The ISO-2.5D simulated weld is wider and shallower than the laser weld you described for your application because it is produced by conduction heat transfer from the surface only. In contrast, your laser weld is likely created by the laser beam penetrating the workpiece and depositing energy below the surface (i.e. keyholing). As first applied, ISO-2.5D is too general for this problem. I suspect that the actual laser weld cross-sectional area is less than the simulated area (which is 0.48 sq. mm) since some of the laser energy will be reflected during the weld. If that is the case, the maximum temperature at the bottom side could be lower than the simulated 445°C.

To check this, I ran the laser welding based application OSLW, for 304SS, and mouse clicked on the contour plot until I found the point for the 150 ipm and 600 W power you used. Sure enough, OSLW predicts a deeper but narrower weld than ISO-2.5D. To get the best fit to the penetration depth you observed, I chose different focusing lenses for the simulation. Using a 5.0 in focal length lens, the simulated penetration depth is 0.029 in, which is virtually the same as the 0.030 in depth you measured. We find for that condition in OSLW, that the energy transfer efficiency is only 0.44, which means that the laser power absorbed is much less than the 600W we used for ISO-2.5D. As a result, the weld cross-sectional area is only 0.20 sq. mm which again is much less than the 0.48 sq. mm result of ISO-2.5D.

Now to refine our temperature estimate, we can use either the laser weld area or the net power from OSLW to estimate the temperatures in ISO-2.5D. If we use the net power of 264 W with the travel speed of 150 ipm, we see that the simulation gives a maximum temperature at the root of 162°C. If we adjust the net power to yield the same size weld that OSLW predicts (i.e. 0.20 sq. mm), the power goes up to 360W and the maximum temperature at the root increases to 213°C. It would be nice if SmartWeld would predict just one number, but our models are not that refined yet. The best we can do is bracket the problem in the manner just described. The temperature probably ranges between 162°C and 213°C, and with an uncertainty comparable to the difference. I don’t think we can expect it to be close to the initial ISO-2.5D over-prediction of 445°C since we know with certainty that the actual weld is smaller, and that some laser power must be reflected away. In this way, OSLW helped us to refine the problem statement for ISO-2.5D