Technical Article


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


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 18 ❘ April 2017 ® Figure 5: Total Non-labor operating cost per cubic inch of pattern.


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.


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 For this


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


Figure 4: Maintenance Cost per cubic inch of Pattern


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