High Volume Laser Welding Applications
Fiber Lasers have now matured into exceptionally reliable and stable industrial tools. These Lasers have unique capabilities that enable improvements to a wide range of industrial and manufacturing processes.
This application note looks in particular at high volume welding of thin metallic parts found in the electronics industry (Li-ion mobile phone batteries) and medical markets (pacemakers & welded implantable devices). The key difference between this and our other application notes on the subject of welding is volume. This note recreates real life experiences from users with multi million piece part throughputs where process improvements yielding a 1% scrap reduction can create savings over $100,000k per year and more.
The starting position is taken as an existing Laser user deploying large numbers of YAG based flash lamp or DPSS welding systems for piece parts typically less than 1mm thick and usually thinner. Materials may range from stainless steel to aluminium or nickel coated steels.
The YAG Laser system deployed (typically less than 400W CW power) will suffer from the standard (physics based) limitations of rod Lasers which can lead to time based fluctuations in CW output power, focal point and beam quality. Such time based parameter changes in Laser performance will of course induce time based differences in weld performance. Weld to weld and batch to batch variations in the strength of a weld is not conducive to high volume automated production. Minimizing such time based fluctuations becomes the job of a specialist Laser maintenance crew.
In many industries Lasers are seen as the tool of last resort since the ongoing maintenance required to keep the Laser processes within tight Cpk values is costly in spare parts and involves regularly taking the process off-line. Add to this that most high volume production now takes place across Asia where specialist Laser support skills are rarer than they would be in the USA or Europe, and it can be seen that high volume Laser welding is often a problem looking for a solution within many companies.
Spot or seam welding in thin metallic parts is sensitive to Laser output power stability since variations will alter the depth of weld penetration (seam welds) or cause punch through or weld splatter (spot welds).
Very thin parts such as the welds found on disk drives or on medical device parts are particularly prone to such process variations.
Inside a Fiber Laser
Whereas the YAG Laser is typically a doped glass rod pumped by flash lamps and using mirrors and collimating optics, the Fiber Laser is created within a sub 20um core of doped fiber optic. No mirrors are required since fiber based devices called bragg gratings are used for the mirrors that create the Laser cavity. The entire Fiber Laser cavity is made from glass fiber components spliced together into a monolithic structure that requires no adjustment or periodic maintenance.
Multiple (for redundancy) single emitter diodes, created for sub sea telecom networking (with MTTF rates of over 400,000 hours), are used to pump the doped fiber. So in fact the entire system is created and kept within single mode fiber through to the delivery collimator. This ensures that there is no alignment, thermal lensing or calibration of the optics (since no glass optics) required.
The proof of course is in the application: our Lasers have high volume manufacturing customers running 24/7/365 who have measured Laser downtime at sub 1% including switch on and warm up (Fiber Lasers offer immediate switch on and no warm up).
Process Advantages of Fiber Lasers
The advantages of such a system are as follows:
- The single mode fiber only carries a TEM00 output giving an M2 of 1.1 or less
- The output power is highly stable across a wide environmental temperature range at +/- 0.5%
- The laser gives fiber delivery via a small BDO (beam delivery optic) outputting a 5mm collimated Laser beam into the focusing optics of the welding head
- The pumping scheme requires no maintenance, enabling greater uptime and eliminating consumable materials costs
- The lack of thermal lensing ensures the Lasers cannot drift out of calibration or vary in output power with time
- The lack of optical parts ensures no alignment drift with time or vibration
At this stage some operational assumptions must be made. Please try to estimate your own savings by checking yourself against these typical situations.
We assume a high volume part with a material cost at this stage in its build process of 10 cents (US$) per part. The volume per day is 7,300 units with approximately 11 second cycle time for the full welding and parts handling process (your volume may be far higher and so your savings greater!).
Further assumptions are that the process is operating 24 hours a day and 7 days a week but 50 weeks a year, we assume in our costing a machine utilisation and availability rate of 93%.
The process scrap on the welding process is assumed at 2% and a 50% improvement is assumed to be possible (our customers often report a 1% reduction in scrap when deploying our Lasers) by improving process capability (Cpk).
With 25,550,000 parts welded each year the value of materials passing through the line is approximately $2.55M.
A 1% improvement in yield will therefore save $25,550 in material scrap.
A 5% increase in machine availability will give a further 127,750 additional piece parts per year (or $12,775 additional output per line).
An additional $4,000-$6,000 in flash lamps spares per year would also be saved.
The reduced demand for a specialist maintenance crew could save 1 person across 20 machines and so $2,500 per year.
It is easy to imagine $50,000 a year in tangible savings when compared to a similar YAG based system as well as the increased output per unit of factory space.
Other key product benefits would include stronger and more repeatable welds and reduced batch testing or inspection times. Inspection is typically used in less controlled processing to inspect quality into a part rather than designing it into the production process. Further process savings could be expected from the elimination of set up times and run through scrap at the point of Laser switch on. There is no warm up on the Fiber Laser, turn it on and it is process ready instantly.
With energy efficiencies of up to 10X that of an equivalent YAG Laser the Fiber Laser is ideal in areas where energy costs form an important part of the utilities budget.
Once the decision has been taken to process parts on a Laser based welding system it is clear from the above that advantages and operational savings from choosing a Fiber Laser make it clearly the Laser of choice.
Additionally the Fiber Laser can often be retrofitted into existing stations making the savings even greater. Ask us for further details.
We run a free applications laboratory to process “proof of principle” samples for you. We offer evaluations of our Lasers to allow you to run internal process developments. Once these are completed you can run your own ROI calculations against your own process.
We work globally with Laser integrators of welding stations and are happy to either work with your current selected supplier or suggest new suppliers for you to work with.
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