D1: 0.20mm D3: 0.18mm
1. 6 mm
30 Industrial Laser Solutions NOVEMBER/DECEMBER 2016 www.industrial-lasers.com
of formation of
greatly limit weld
ductility is not quan-
tified here, our pre-
liminary results sug-
gest that it is greatly
improved over high-
er-heat-input welding techniques. And
although an inert
cover gas was not
employed in these
trials, these combinations would certainly
benefit from an argon
gas shield to further
reduce intermetallic formation.
Micro keyhole welding
copper and copper alloys
As shown above, we have reported excel-
lent results in welding many different
metals to copper foils, with copper as
the lower layer. Weld strength was ade-
quate to produce parent metal failure if
required and fit-for-purpose weld quality
was observed in all cases. Results weld-
ing alloys of copper such as phosphor
bronze (~95% copper) to other materials
were also good, but it is clear that when
welding with pure copper as the upper
layer of the joint, a modified strategy is
required. Welding two layers of 50µm
copper foils together can be achieved by
localizing heat flows using spiral features.
In this way, weld strengths >150N were
achieved at 2000mm/s with only 100W
CW power. Parent material failure was
readily achieved (FIGURE 6), and a stable
keyhole weld is noted.
To weld through thicker copper or copper alloy foil either to itself or to other metal
foils in the stitch-weld format, more average power is all that is required to produce
stable welds (FIGURE 7). For 150µm-thick
pure copper foil, >300W was used and at
this power level, stable welds were read-
Although not reported in detail here,
we have also shown that this technique
can produce three-layer joints with cop-
per or aluminum as the interlayer or as
the outer materials. We will report more
on this later.
It is widely known that continuous or
semi-continuous welded seams lead to
greatly reduced stress concentrations
and stiffer-welded structures, and the
automotive industry has already moved
away from spot welds to a degree [ 4]. As
consumer devices become smaller and
lighter, welded joints are also required
to be smaller and stronger. The small
welds shown here will enable many dif-
ferent weld shapes such as sawtooth and
sine waves to be used to increase weld
strength and structure stiffness.
The calculated fluence/peak power density at the full power setting used for these
trials was 55 × 106W/cm2—lower than previously reported for micro keyhole welding.
It should also be noted that when micro
keyhole welding 100µm-thick stainless
steel to itself, an average power as low
as 52W was required at 1000mm/s. This
relates to a fluence of only 12 × 106W/cm2—
also lower than previously reported.
It is well accepted that the absorp-
tion of liquid copper by high-brightness
1070nm laser beams increases to ~60%
when molten [ 5]. This helps to explain
why the stable keyhole welding shown
here can be produced in copper once
initial melting has been produced with a
high-intensity fiber laser beam.
When welding aluminum to copper, an
intermetallic layer thickness of <10µm is
considered desirable. A high weld speed
and low heat input are known to reduce
time- and temperature-related diffusion
processes that form the deleterious metallurgical phases that are responsible for
reducing joint ductility [ 3]. By applying weld
speed of 2000mm/s, laser power of 200W,
and interaction time ~50µs, heat input is
only 1J/cm. This is much lower than that
of other laser or non-laser welding techniques. Although metallographic analysis
to confirm our hypothesis is under way, this
is strong evidence that intermetallic formation is reduced significantly. ✺
[ 1] R. Mueller, “Getting close to remote laser welding,” The
Fabricator (Jul. 2009); see http://bit.ly/2dvFjJj.
[ 2] I. Miyamoto, “Precision microwelding of thin metal foil with
single-mode fiber laser,” Proc. SPIE, 5063, 297 (2003).
[ 3] E. Schubert, I. Zerner, and G. Sepold, “Laser beam joining
of material combinations for automotive applications,” Proc.
SPIE, 3097, 212 (Aug. 18, 1997).
[ 4] M. Wiener, “Laser seam stepper takes on conventional
welding,” Industrial Laser Solutions, 30, 4, 17–18 & 22 (Jul/
[ 5] S. Liebl et al., Phys. Procedia, 56, 591–600 (2014).
DR. TON Y HOULT ( email@example.com) is applications manager at the IPG Photonics Silicon Valley
Technology Center, Santa Clara, CA; www.ipgpho-tonics.com.
FIGURE 7. An example of an excellent top bead of a 150µm copper-to-copper foil stitch
FIGURE 6. The upper surface of a spiral-weld failure in 50µm-thick
copper at 180W.