SAMPE Journal - July/August 2023 - 55

analysis, a dedicated unit-cost break-down is used
for this purpose, with the results feeding into an
investment case.
In the example of a wet filament winding
process, the total composite weight is 75 kg.
Assuming an average winding speed of 0.7 m/s, the
total lay-up time is 161 min. Factoring in necessary
set-up and other manual activities for lay-up, total
average production time per vessel amounts to 177
min. For an annual vessel production volume of
30 k units per year (based on 2-shift operation), 28
spindles are necessary. The total cost of the lay-up
operation (before curing) is estimated at € 1,327.91
using material cost of 20 €/kg of fiber (52,4 kg) and
10 €/kg of resin (22 kg) at a fiber weight ratio of
70%. The blended specific material cost is therefore
17 €/kg.
For the FPP dome reinforcement vessel, towpreg
material is used, at 35 €/kg. It is cut into 1,400
patches representing the 14 HAHL orientations
in the dome areas, which were removed from the
winding laminate. This saves 12 kg, or 20% of the
initial material weight for the adjusted winding
laminate. The process to apply these patches takes
48 min lay-up time, assuming an FPP system with
2 placement robots and an individual patch cycle
time of 4 s/patch.
Given the material reduction of the winding
laminate, the overall process time for the adjusted
laminate will scale down to 121 min, which is a
reduction of 20%. This translates into a capacity
increase in the FW line of the same amount, as
the FPP reinforcement process and FW process
can run in parallel in a series production setting.
Overall, the total combined lay-up costs per unit
(before curing) is forecasted to decrease by 9% to
€ 1,209.
The saving potential of FPP leads to a high
positive return on investment as well as a short
payback period. The initial investment delta for
a 30 k p.a. volume production set-up in year 0
amounts to approx. € 11 M including hardware and
software. With a unit-cost difference of € 119 (net
material cost + process time improvement), the
cost savings amount to € 3.6 M p.a. for 30 k units.
In addition to these savings, manufacturers have
a pricing advantage, as they can offer vessels with
significantly better storage efficiency (less weight
and increased volume for the same exterior space).
With an assumed price / margin opportunity of €
105 per unit (1.5% of assumed sales price of 7,000
€/unit), the total benefits (material cost, process
time, margin opportunity) amount to € 6.7 M p.a.
This represents a very fast amortization period of
just 20 months for the initial investment, with an
internal rate of return (IRR) of 58%.
www. sampe.org
Towpreg vs. Wet Winding with FPP
Dome reinforcements are also applicable to
a towpreg winding set-up. The magnitude of
benefits even increases due to the higher specific
material prices for towpreg and the subsequent
effect of material savings. This also considers the
faster winding speeds typical for towpreg lines.
Existing towpreg-wound vessels can be adjusted to
include dome reinforcements; overwinding can be
performed at existing winding stations.
The main economic differences of towpreg
winding compared to a wet winding set-up are the
following:
* Material cost:
o Towpreg: ~ € 35 / kg
o Wet winding: ~ € 17 / kg (incl. cost of resin)
* Winding speed (average across all orientations):
o Towpreg: ~ 1.6 m/s
o Wet winding: ~ 0.7 m/s
The saving per vessel in a towpreg set-up
increases to 14.7%, driven by higher savings on
material reduction. Process time is reduced by 16%,
as compared to 20% in the wet-winding scenario.
Overall, this results in net unit cost improvements
of € 390, and an even faster payback period of just
10 months for the initial investment, representing
an IRR of 126%.
CONCLUSION AND OUTLOOK
This paper describes and quantifies the expected
benefits from using FPP dome reinforcements
for composite pressure vessels. While the general
benefits of this solution were established several
years ago, the industrial equipment to implement it
was not available until now. With FPP-based lay-up
systems, dome reinforcements for composite tanks
can be produced on an industrial scale, combined
with existing filament winding equipment. Most
cylindrical PV can be reinforced by using the FPP
solution. The benefits increase with growing vessel
aspect ratio.
The key benefits are an increase of storage
efficiency - approx. 16% less weight, 6% volume
increase
- and an associated
recurring
cost
reduction of 9 - 15%. It is noteworthy that
implementing dome reinforcements also frees
up almost 16 - 20% capacity on existing winding
equipment, as less material and cycle time are
needed per vessel in the winding process (Figure
15). The resulting investment case is highly positive,
with an amortization period of 10-20 months.
To underpin the presented
approach, an
optimized, full-scale demonstrator was developed
and is currently tested in a joint project with
JULY AUGUST 2023
|
SAMPE JOURNAL |
55
http://www.sampe.org
SAMPE Journal - July/August 2023

Table of Contents for the Digital Edition of SAMPE Journal - July/August 2023
