Choosing the Low Cost Method for Manufacturing

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Lasers for Manufacturing Event
September 28, 2011
Mueller, NuTech Engineering
Choosing the Low Cost Method for Manufacturing
Robert Mueller, Ph.D., CLSO
NuTech Engineering Inc.
Milton, ON
Email: [email protected]
Introduction
When the first lasers were built over 50 years ago, they were described as “a solution looking
for a problem”. In the years since, lasers have solved many problems, and laser cutting,
welding, drilling, and other laser processes are now accepted manufacturing methods for a
number of applications. But there are still many more applications where lasers are not yet
considered to be viable process options. For some of these, laser processes may never be
technically or economically feasible, but for many applications, laser processes are becoming
viable alternatives to traditional processing methods.
Adoption of any new technology requires the demonstration of merit in two areas: technical
proficiency and cost. Technical proficiency means that the process performs a function that
meets or exceeds all technical requirements; everything from accuracy and reproducibility to
meeting cycle time. Cost implies the lowest possible cost to produce the product, including
capital costs, and all operating and material costs.
Laser manufacturers continue to advance the technical capabilities of the lasers themselves,
making more powerful and energy-efficient lasers with better beam quality. These new lasers
are also simpler to operate and maintain, and often cost less than older lasers. Increasing the
technical capability of lasers and lowering the purchase and operating costs moves the
boundary of technical and economic viability, and in many cases, makes laser processing the
low cost method of manufacturing.
This presentation will describe a method for calculating the cost of manufacturing, and compare
the cost of several laser-based methods with traditional methods to determine if, and at what
production volume, the laser method becomes the low cost method of manufacturing. The case
studies to be reviewed are: remote laser welding vs. resistance spot welding, laser blanking vs.
press blanking, and laser hybrid laser welding vs. multi-pass MIG welding.
Cost of Manufacturing
There are several ways to calculate the cost of manufacturing. For this study, we will use a
cash flow method, and not consider the depreciation of capital assets.
The cost of manufacturing is composed of the following cost elements: purchase of the
equipment, labour, building costs, electricity usage, and process consumables. A spreadsheet
may be used to record and calculate the relevant costs for all methods under consideration, and
calculate the production capacity of each system. Several assumptions must be made, and
applied uniformly to the competing processes. These assumptions include: the number of
working hours per shift, the number of shifts in a day (1, 2, or 3), the number of operating days
in the year, and the expected production efficiency or up-time. All these factors affect labour,
electricity and consumables costs, and the total production capacity of the machines.
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Lasers for Manufacturing Event
September 28, 2011
Mueller, NuTech Engineering
Electricity
For the equipment costs, the purchase
price for each machine, and its tooling,
Consumables
is estimated. This cost is amortized
over an assumed loan period, with two
or three years being typical, at a typical
commercial interest rate, and the
annual cost of these loan payments is
Worker costs
included in the annual cost for the
Annual cost of
Capital inc
system. Note that after the loan is paid
Financing
off, this cost element drops to zero. For
labour costs, we consider the number of
operators that each system requires per
shift (usually one), and that all the
operators are paid at the same rate.
Floor space
We also factor in a fraction of the
maintenance personnel cost, and
Figure 1. A typical breakdown of operating costs for a
consider the amount of work required to capital-intensive process. The major cost components are
be performed on each type of machine. the capital equipment and worker costs.
A factory building costs a certain
amount per year, to rent or lease, and to keep the lights on and the space heated. This cost
should be divided up among all the operations taking place in the building, in proportion to the
floor space occupied by each operation. We therefore assume a reasonable annual building
cost of $50/sq.ft., and multiply this by the cell area for each case. The cell area includes space
for the equipment and a safety enclosure, operator workspace and space for racking or other
dunnage for in-process parts. Warehousing of incoming and completed parts is not included.
For electricity utilization, we list the rated electrical consumption of the major components of
each cell, factor in the usage fraction of each component, derive a total consumption, and
multiply by a uniform price for electricity. The consumables category captures all the items, with
cost and lifetime, required to keep a system operational for a year. It includes items such as
spot welding tips, laser gasses, protective windows, even water filter cartridges. The cost of
each item is multiplied by the number of service lifetimes in an operating year. The total costs
for each system are totalled, along with the production capacity.
Other costs could be considered in the analysis, such as rework or the cost of poor quality, and
inspection costs. These costs may be more difficult to quantify, especially for a new or
proposed process. In some cases, these costs can be significant, and a process that minimizes
rework and allows for in-process inspection (such as laser welding) can have an advantage.
Rework and inspection costs are not considered in the examples below.
Note that some cost elements are fixed, such as the cost of the equipment and floor space,
while the other costs are variable, and depend on the usage of the machine. You have to pay
for the equipment, and the floor space it takes up, whether it is used for half a shift per day, or 3
shifts per day. On the other hand, operators can be re-assigned, power can be turned off, and
consumables last longer when the machine is not fully utilized.
The production capacity is an important consideration in these calculations. Competing
processes often have different production capacities, making direct cost comparisons
misleading. A more useful approach is to calculate the cost per part, or per length of process.
Comparing cost per part gives a better indication of the low cost process, but only if you can use
the production capacity of the machine. A more thorough analysis requires determining the
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Lasers for Manufacturing Event
September 28, 2011
Mueller, NuTech Engineering
production cost for a range of production volumes. At low volumes, a machine may not be fully
utilized, while at high production volumes, some processes may need several machines to meet
demand. Plotting production cost against production volume for competing processes clearly
indicates the low cost manufacturing method for each product volume range.
Remote Laser Welding vs. Resistance Spot Welding
Resistance spot welding is a mainstay of sheet-metal
manufacturing. The equipment is relatively
inexpensive and reasonably productive. If higher
productivity is required, additional units can be
installed to work in parallel. A robotic spot welder
typically performs one spot weld every 3 seconds.
Remote laser welding is a relatively new process that
is capable of performing laser stitch welds very
quickly, typically at a rate of 3 or 4 welds per second.
A high-power laser beam is directed by galvo mirrors
and focussed onto the workpiece anywhere within the
work envelope of the remote welding head. The
Figure 2. A resistance spot welding line for
process works on the same concepts as galvo-head
automotive production.
laser markers, just using about 100 times more laser
power. A typical remote welding head and application are shown in Figure 3. One remote laser
welder can replace up to 9 robotic resistance spot welders.
Figure 3. A Fiber laser remote welding system, using a 2 mirror galvanometer scanning head.
Cut-away view courtesy of HighYAG GmbH.
In order to compare the costs of remote laser welding and resistance spot welding, we will
consider three cases: 1) a simple resistance spot welding cell with one robotic spot welding gun,
2) a larger resistance spot welding cell with four robotic spot welding guns, and 3) a remote
laser welding system using a near-IR fiber-delivered laser, with the remote welding head on a
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Lasers for Manufacturing Event
September 28, 2011
Mueller, NuTech Engineering
robot, as shown in Figure 3. For each case, we consider the following cost elements: capital
equipment (the cell, including robot, power source, end effector, and tooling), manpower,
building costs, electricity usage, and process consumables. A spreadsheet was constructed to
record and calculate the relevant costs for each case, and calculate the production capacity of
each system. Table 1 summarizes these costs and production capacities. Note that the remote
welding system uses 2 operators, to keep up with the productivity of the welder.
Table 1. Production Capacity and Annual Costs for Resistance and Remote Welding Systems.
RSW - Single
RSW - 4 Gun
Fiber Remote
Process
Units
Gun
Cell
Laser
Productivity
Weld rate
Hours/shift
Shifts/day
Days/Year
Machine efficiency
Hourly Production
Annual capacity
Spots/s
hr
shifts
days
spots/hr
spots/yr
Cost Summary
Equipment Cost
Loan Period
Annual cost of Capital inc Financing
Floor space
Number of operators per shift
Worker costs
Consumables
Electricity
Total Cost
Cost/Spot
$/yr
$/yr
$/yr
$/yr
$/spot
1.33
7.5
2
240
70%
3360
12,096,000
4
7.5
2
240
70%
10080
36,288,000
232500
3
86000
6500
1
125000
2500
1600
221600
0.0730
667500
3
245000
10500
1
125000
9800
4900
395200
0.0327
1035000
3
381000
8100
2
203000
3400
3700
599200
0.0165
Weld Cost Breakdown Per Spot
(System fully utilized)
0.08
Annual cost of Capital inc Financing
0.07
Electricity
Consumables
0.06
Weld Costs ($/Spot)
Figure 4 shows the cost per spot
weld for the three configurations
described above, and running at
capacity on 2 shifts. For all
configurations, capital and
manpower are the largest
contributors to the total cost.
The total costs per spot for the
remote laser welding system is
significantly less than for the
resistance welding systems, due
mostly to the increased
productivity of the remote
welding system. The remote
welding systems has a
somewhat higher annual cost
than the 4 gun resistance
welding cell, but that cost is
spread over three times the
$
Years
$/yr
$/yr
0.33
7.5
2
240
70%
840
3,024,000
Worker costs
Floor space
0.05
0.04
0.03
0.02
0.01
0.00
RSW - Single Gun
RSW - 4 robot cell
Fiber Remote Laser
Figure 4. Breakdown of weld costs per spot, for a system running
at capacity.
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Lasers for Manufacturing Event
September 28, 2011
production capacity of the
resistance cell.
Mueller, NuTech Engineering
Spot Welding Cost Comparison
$4,000,000
$3,500,000
RSW - Single Gun
Total Annual Cost ($/yr)
Figure 5 shows the result of a
RSW - 4 robot cell
$3,000,000
calculation of total annual cost
Fiber Remote Laser
$2,500,000
(capital and operating)
$2,000,000
against production volume.
$1,500,000
We assume that capital,
manpower, and building costs
$1,000,000
are fixed, and the rest of the
$500,000
costs vary with machine
$0
usage. For example, an idle
0
5
10
15
20
25
30
35
40
45
50
machine does not use
Millions of Spots/Year
consumables or electricity.
Figure 5. Plot of annual cost vs. production volume for resistance
We also assume no overtime,
and remote welding systems. The low cost method of
and if a system reaches its
manufacturing varies with production volume.
production capacity, another
machine must be purchased
in order to increase capacity. The data shows that, at low volume, a single robot resistance
welding cell is the low cost option. But as production demand increases, one must add cells
(and operators), and the single robot cell configuration becomes uncompetitive. At moderate
volumes, the 4 robot resistance cell is the most cost-effective, until this configuration reaches
capacity, and a second cell is required. At that point, the cost of the resistance system takes a
step increase, and is no longer competitive with remote welding. This defines the production
volume threshold for cost-effective remote laser welding. In this case, remote laser welding
would be the most cost effective production method if you require more than 15 million spots to
be produced per year.
Due to the flexibility of remote welding, this volume threshold of 15 million spots/year could be
made up from more than one part. By changing tooling, or interleaving tools in a flexible
manufacturing system, several assemblies could be run through the remote welding cell to
achieve the economic production threshold. Also note that the remote cell is the most
economical method of production, even if the cell is only utilized at half its capacity.
Laser Blanking vs. Press Blanking
Press blanking using cutting dies is the standard method for cutting automotive blanks from coil
stock prior to stamping in forming dies. Blanks are cut to a defined size and shape to provide
the material to draw into the stamping die during deep drawing and to prevent wrinkling from
excess material. Presses and dies are expensive, and cutting dies are subject to wear and
maintenance.
Flat sheet laser cutting is commonly used at the prototype stage to cut blanks, before the blank
shape and die design are finalized and the dies can be manufactured. Flat sheet laser cutting
uses no tooling, and the cutting machine is programmed directly from the part CAD drawing.
This allows designs to be changed and produced quickly for testing.
It has been suggested that laser cutting could be cost competitive with press blanking for
moderate volume production, up to about 60,000 parts per year, if a coil-fed laser blanking line
were to be constructed. Laser blanking would allow tighter nesting of parts, increasing coil
utilization and reducing scrap, and would completely eliminate hard tooling, with its cost and
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Lasers for Manufacturing Event
Mueller, NuTech Engineering
Cost Comparison
Laser Blanking vs. Press Blanking
$15,000,000
Laser Blanking
Press blanking
Annual Cost, $/yr
maintenance
requirements.
Laser blanking
would not be as fast
as press blanking
while in production,
but change-over
time between part
runs would be
reduced to the time
required to call up a
new program.
September 28, 2011
$10,000,000
$5,000,000
$0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Performing an
Production per job, Million pc/yr
analysis similar to
the previous
Figure 6. Comparison of cost and production volume for laser and press
example, with the
blanking, assuming each system is running at capacity with jobs of the sizes
indicated. At low volume/job, tooling costs for many jobs hurts the press
assumption that
blanking cost structure. Laser blanking is efficient for multiple small jobs.
each machine is run
near capacity, and
filled with jobs of
equal size, we get the result shown in Figure 6. For small job sizes, press blanking has high
costs, due to the cost of many tools for all the jobs that fit into the machine capacity. Laser
blanking has no hard tooling cost, only some programming for each part path. In this example,
laser processing is the low-cost manufacturing solution for low to moderate volume production,
and traditional press blanking technology has the lowest cost at high volumes.
Laser Hybrid Welding vs. Multi-Pass MIG Welding
Multi-pass MIG welding is the standard method for fusion welding carbon steel plate structures.
Examples of this type of weld would be joining steel pipeline sections, or rolled plate sections for
a large oil storage tank. In both cases, we would expect the butt joints to be about 1/2“ thick,
and these would require several MIG welding passes to fill the joint groove.
Laser hybrid welding combines the welding speed and penetration of high power laser welding
with the stability, filling and gap-bridging capability of MIG welding. Using high powered lasers,
up to 15 kW, welds up to 3/4” deep have been full-penetration welded in a single pass. Single
pass laser hybrid welding does not require any special joint preparation, like a V-groove, and
laser cut plate edges are usually sufficient.
For this example, we will consider manual MIG welding, robotic MIG, robotic twin-wire MIG, and
laser-MIG hybrid welding. The analysis will be carried out using the same procedure as the
remote welding case, with the addition that the cost of edge preparation for the weld was
considered. The results are shown in Figures 7 and 8.
Laser hybrid welding is a high productivity process; single-pass welding joints that would
traditionally take 3 or 4 passes to fill. Hybrid welding also does not require any special edge
preparation; perpendicular laser cut edges are sufficient. Being a single-pass, narrow fusionzone process, hybrid welding imparts much less heat into the part, reducing distortion. Hybrid
welded parts often require less post-weld rework to straighten the parts. This cost saving has
not been included in this analysis.
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Lasers for Manufacturing Event
Discussion and
Conclusions
2.5000
Annual cost of Capital inc Financing
2.0000
Preparation
Electricity
Consumables
1.5000
Worker costs
Floor space
1.0000
0.5000
0.0000
Manual MIG
Robotic MIG
Tw in-Wire MIG
Laser Hybrid
Figure 7. Breakdown of weld costs per length of weld, for
systems running at capacity. Laser hybrid welding has a
low cost due to its productivity and lack of preparation
requirement.
Annual Cost vs Annual Production
1/2" Butt Joint
$10,000,000
Manual MIG
Robotic MIG
Annual Cost, $/yr
The cost models shown
here use values for
individual costs deemed
appropriate and
representative. Each
user’s actual costs may
vary, and prospective
users should perform
this type of study using
their own data before
selecting the appropriate
manufacturing method
for a specific situation.
Mueller, NuTech Engineering
Welding Costs Per Length of Weld
1/2" Butt Weld, Including Edge Prep.
Weld Costs, $/Inch
Laser hybrid welding of thick
parts requires a powerful
laser to achieve full
penetration, which requires a
substantial capital
investment. Figure 9 shows
that the capital investment
required for hybrid welding
only makes sense if you
require over 100,000 feet of
weld length per year. Many
small shops would not
approach this value, but
large shops should consider
hybrid welding, and the
benefits that it brings.
September 28, 2011
Twin-Wire MIG
Laser Hybrid
$1,000,000
Laser processing is a
$100,000
viable technology for a
1000
10000
100000
1000000
10000000
wide range of industrial
Annual Weld Production, foot/yr
applications. The
Figure 8. Plot of cost vs production for several MIG welding methods
productivity, efficiency
and laser hybrid welding. The low cost manufacturing method
and price of lasers now
depends on the production demand.
make laser processes
economically competitive
in many areas, including applications that have not, up until now, been considered for laser
processing. Companies that can identify a novel low-cost laser processing application can gain
a significant competitive advantage in the global market.
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