I presented the results of a study comparing AM methods to create patterns for investment casting last year at the Investment Casting Institute Fall Technical Conference. The ICI then printed the study in a series of three articles in their InCast magazine. This is the second of three articles.

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14 ❘ April 2017
A Comparison of 3D Printing Technologies
Used to Make Investment Casting Patterns –
Part 2: Operating Cost
by Tom Mueller, Mueller Additive Manufacturing Solutions
T
his is the second of three sections
of a detailed comparison of the
four leading methods to print
investment casting patterns. The four
methods are QuickCast, CastForm, Projet
Wax, and Voxeljet Any comparison
must compare the performance in three
separate areas; printer performance,
pattern performance and operating
cost. In the first section, the printer
performance of the four methods was
compared. In this section, operating
cost will be compared.
Each of the manufacturers sells
multiple models of printers with
different build envelopes and build
speeds. To limit the scope of the
analysis, we selected the model most
commonly used to print investment
casting pattern. Table 1 shows the
printer models used in this study and the
materials printed.A printer with great
performance that builds patterns that are
easily and reliably cast is of little value if
the cost of creating patterns makes them
economically unfeasible. In this section
of the comparison, the purchase price
of printers as well as operating cost will
be examined. Some of the prices have
changed since this information was first
presented at the 2016 ICI Fall Technical
Conference. As a result, some of the
operating costs have changed.
Printer Price
The four printers in this comparison have
a wide range of prices, from $100,000
to more than $700,000. Table 2 lists the
price of each of the four printers. The
price of the Voxeljet printer is based on
currency exchange rates at the time of
publication.
In reality, few buyers of these printers
pay the list price for the machine.
Prices are often discounted, sometimes
heavily. Determining average actual
purchase prices, however, would be
extremely difficult.
In addition, all of the printers offer
several pieces of auxiliary equipment
in addition to the printer. Some of
the auxiliary equipment is necessary
to the operation of the printer and
some is optional. For simplicity, this
analysis uses only the list price of the
printer without auxiliary equipment for
comparison.
Capacity Cost
Comparing printer simply on the basis
of price can be very misleading. As
shown in the previous article in the
series, the four printers have widely
varying build rates. Expensive printers
build much faster. Might it be better to
buy several low cost printers? To answer
that question, we need to compare the
printers on the bases of equivalent build
rates.
We can calculate Capacity cost,
which is the cost of one cubic inch per
hour of build capacity. Capacity Cost
is easily determined by dividing the
printer cost by the average build rate
as determined in the previous article.
Figure 1 compares the capacity cost of
Technical Article
Table 1: Printer models used for comparison.
Technology Printer Model Material
QuickCast ProX 800 Accura® CastPro
CastForm S-Pro 60 CastForm™ PS
Projet Wax 3510 CPX VisiJet® M3 Hi-Cast
Voxeljet VX1000 PMMA/Polypor B
Figure 1: Capacity Cost of the Printers

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April 2017 ❘ 15
the four printers.
Surprisingly, the least expensive
printer has the highest capacity cost. The
Voxeljet printer has the lowest capacity
cost followed by the QuickCast printer.
Elements of Pattern Cost
Capacity cost only measures the cost of
obtaining build capacity. Operating cost
is how much it costs to run the printer
after acquisition. Other than labor, there
are three major elements of pattern cost;
the cost of materials, depreciation and
the cost of maintenance.
• Material Cost - For purposes of this
analysis, list prices of the materials
supplied by the manufacturer of the
printer were used. Manufacturers
often sell at a discount and
aftermarket material suppliers
often supply less expensive
materials. Given the difficulty of
determining actual average prices,
manufacturers’ list prices are used.
Material cost for QuickCast patterns
varies widely with the geometry of the
pattern and has four components:
1. Resin used to build the internal
support structure – the volume
of resin used for internal support
structure is approximately 13% of
the pattern volume.
2. Resin used to build the skin – the
volume of resin used to build the
skin of the pattern is the surface area
times the skin thickness
3. Resin used to build supports – the
stereolithography process builds
supports which attach the part to the
build platform and act as a fixture.
The amount of supports required
varies dramatically from pattern to
pattern and can vary significantly
depending on how the part to be
built is oriented in the build.
4. Resin undrained from the interior of
the pattern – In the build process,
liquid resin is trapped within the
pattern. Drain and vent holes
allow that liquid resin to be drained
out after the build is complete.
Draining is further encouraged by
placing in the pattern in a centrifuge
for several minutes. Nonetheless, it
is virtually impossible to completely
drain the pattern and some liquid
resin will remain inside. It will
be cured in place in the post cure
process. It could easily be a percent
or two of the pattern volume and for
patterns with thin walls, it could be
significantly higher
For this analysis, it was assumed that
resin volume consumed averaged 40%
of pattern volume, although the actual
percentage is likely higher.
CastForm is the easiest material cost
Table 2: Printer List Price
System List Price
3D Systems ProX 800 $550,000
3D Systems S Pro 230 $475,000
3D Systems ProJet 3510 CPX $100,000
Voxeljet VX1000 PPB $735,625
Figure 2: Material Cost for the Printers
Figure 3: Depreciation Cost per Cubic Inch of Patterns

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16 ❘ April 2017
Technical Article
to calculate. It is simply the volume of
the pattern times the cost per cubic inch
of polystyrene powder. Any unused
powder in the build is recycled.
The Voxeljet analysis considered
the price of PMMA powder, binder,
and cleaner used to clean the print
head during the build. The amount of
wax required for infiltration depends
on the surface area of the pattern. For
this analysis, it was assumed that wax
volume was 5% of the pattern volume.
The Projet Wax system uses two
different waxes, one for the pattern
and one for the supports. The ratio of
support wax to pattern wax varies with
the geometry of the pattern and the
build orientation. For this analysis, it
was assumed that the amount of support
wax used was 50% of the volume of
pattern wax. Users have stated that this
number is conservative.
Figure 2 shows the cost per cubic
inch of pattern volume for each of the
four technologies.
At $6.70 per cubic inch, the
Projet Wax printer had by far the most
expensive material cost, more than triple
the cost of the next highest cost material,
QuickCast. The least expensive material
cost was PMMA from Voxeljet with a
cost of $0.81 per cubic inch.
• Depreciation – Depreciation is
a significant expense in building
patterns. More expensive printers
will have a higher total depreciation
cost, but they also will print more
patterns. To get a true comparison,
the depreciation cost per cubic
inch built was calculated. For this
analysis we will assume a straight
line seven year depreciation. The
monthly depreciation cost is then
the printer cost divided by 84
(number of months in seven years).
To compare from printer to printer,
it is necessary to compensate for the
volume of patterns built. For this
analysis, it was assumed that each
printer would be operated 16 hours
per day for five days a week, or
320 hours per month. Multiplying
the 320 hours by the average build
rate will yield the total volume of
parts built per month. The monthly
depreciation is then divided by the
volume of parts per month to get a
depreciation cost per cubic inch.
Figure 3 shows the depreciation
cost per cubic inch of pattern for
each of the four printers. Note that
the cost depends on the number
of hours per month the printer is
used. As printing hours increase,
cost per cubic inch decreases. The
Project Wax printer has the highest
depreciation per cubic inch of
pattern built.
• Maintenance Cost – A significant
cost of running a pattern printing
operation is the cost of maintenance.
Determining actual maintenance
costs would be extremely
difficult. However, a reasonable
approximation can be obtained by
looking at the cost of the highest
level maintenance contract offered
by each manufacturer. For those
customers who purchase the
contract, it covers most if not all of
their maintenance cost. To calculate
Figure 4: Maintenance Cost per cubic inch of Pattern
Figure 5: Total Non-labor operating cost per cubic inch of pattern.

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April 2017 ❘ 17
the cost of maintenance per cubic inch, the monthly
cost of the maintenance contract is divided by the
total volume of patterns built per month (320 hours
per month as calculated above). The result of those
calculations is shown in Figure 4. Like depreciation
cost, the more hours per month the printer is used,
the lower the maintenance cost per cubic inch will
be. CastForm has the highest maintenance costs.
• Total Non-Labor Pattern Cost – To obtain total non-
labor pattern cost, we can simply add the three
previous costs together and is shown in Figure 5.
The Projet has the highest cost per cubic inch of
part volume followed by Castform, QuickCast, and
Voxeljet. Note that the highest cost is more than 7
times the lowest cost.
Observations
Several observations can be made
1. The least expensive printer, the ProJet 3510 CPX has
both the highest capacity cost and operating cost.
2. The most expensive printer, Voxeljet VX1000 has
both the lowest capacity cost and operating cost.
3. Capacity cost, depreciation cost, and maintenance
cost (but not material cost) are all dependent on the
build rate. An increase in build rate will lower both
capacity cost and operating cost.
Build rate varies significantly depending on the
number of parts being built, build orientation and the
geometry of the parts being built. As was explained in the
first article, average build rates is determined from actual
data gathered on a number of machine runs. As more
data is gathered, better estimates of average build rates
will be determined. As a result, cost data may change.
A great printer with low costs will be of no value if
the patterns it creates cannot reliably be converted into
acceptable castings. The ability to convert the patterns
into acceptable castings is dependent on characteristics
of the patterns. In the next issue, those characteristics
will be examined.