Manufacturers of electronic cigarettes (e-cigs) are gearing up to meet the huge spike in demand for their product. A key challenge of increasing e-cig manufacturing line volume is welding the atomizer - a heating element comprised of a thin wire wrapped around a wick – to the terminals. Welding solutions have been evolving rapidly. Here’s a look at some of our early investigations helping manufacturers determine which welding technology is best to meet this demand.
Resistance welding or laser welding?
The e-cig manufacturing process requires welding of the heating element (atomizer), which is made up of two stainless steel terminals and a wick wrapped with a thin Ni-chrome wire. Placement of the weld relative to the joint on the part is critical; a tolerance of just +-0.002-inch is required to ensure that the product functions properly and does not become scrap.
A few years ago, a major e-cig manufacturer asked Amada Miyachi America to help them determine the optimal welding/joining/bonding technology for this application. After looking at a variety of metal joining technologies, the team of application engineers determined that either resistance welding (RW) or laser welding (LW) could be utilized for this process, each with pros and cons. Table 1 shows a quick overview of these pros and cons:
Process engineers started with an investigation of the resistance welding process (established, lower cost) which provided a good, solid weld, but didn’t give the manufacturer the throughput they needed. Furthermore, RW requires a consumable item – electrodes – which adds to maintenance and replacement time and expense.
So the investigation shifted to focus on laser welding. It was immeditately clear that laser welding could not only achieve the weld and handle the high volumes manufacturers were looking for, but also could be used to extend production to meet the burgeoning demand. The only downside to laser welding is that as a non-contact process, it requires special tooling to hold the parts in intimate contact.
For high speed, high volume production, reliance on a steady product is vital. For lasers, this means that the pulse energy and peak power must remain constant from shot to shot over the course of millions of shots. Modern, pulsed Nd:YAG lasers have real-time power feedback that maintains a constant output over the lifetime of the flash lamp. Since e-cigarette heating element welding has a very small processing window, this type of feedback is essential; without it, yield would decrease, and scrap would increase. A closed loop laser with feedback is a standard feature on all Amada Miyachi’s pulsed Nd:YAG lasers.
To date, the Amada Miyachi team has worked with about a half dozen e-cig companies in Asia and the United States. Laser sources and optics packages have been tailored to the specific application and throughput demand of each customer. For example, some manufacturers are using a standard laser with multiple output capability, while others, looking for greater throughput, are using a new galvo solution in which the beam can be rapidly steered to provide multiple spots at a higher rate of speed. Yet another manufacturer was looking for a custom solution that included the ability to weld multiple spots simultaneously with a single optical device.
Since e-cigs are still a relatively new product, many process-related questions and issues arise, and Amada Miyachi has provided onsite process development support on a routine basis.