3 versions of the same model were printed using 3 different printers and materials. This is a cost/quality comparison. The object was modeled with a number of details that would effectively measure the precision of each of the printers.
Aside from reproduction of the details in the model, another test was done to determine the surface smoothness of each model. Aside from a visual inspection, a more scientific test was conducted using a digital light meter.
The dimensions of the printed models are CM: 4.84 w x 4.84 d x 5.68 h.
The modeling was done in Maya and contains a number of details that were specifically examined in the printed models. One was the vertical ribs that ring the object. Also visible in the wireframe are a number of grooves that ring around the top third of the model on the outside. These groves are "V" shaped and are progressively smaller the higher up that they appear on the object.
Z650
The first examination was conducted on the Gypsum based model printed with a Z Corp Z650 using SLS printing technology. It was the roughest to the touch and seemed to leave a fine powder residue when being handled. It also got dirty very quickly but was able to be cleaned with bleach. Most of the details were visible, with the exception of the top, smallest, horizontal groove. Small details can be somewhat difficult to make out due to the heavy texture of the printed model.
A detailed close up of the horizontal ribs shows that the top few can be hard to make out even at close range. Also visible is the bumpy texture and a wavy type of grain resulting from the printing process.The top of the model with the stepped indentations appeared very well.
PA2200
The next model to be inspected was from a PA2200 printer in Nylon 12. Like the Z650, the PA2200 printer used an SLS printing method. This model had far noticeably smoother surface texture than the first. It also preserved a high degree of surface detail as it was the only of the three to display the top horizontal rib without the need for very close examination. The details for this model were most problematic around the vertical ribs area. The top of the vertical ribs did not indent properly and the inner wall of the vertical ribs was sometimes rough.
The top horizontal rib was most easily visible in this model vs. the other two prints.
Some parts of the inner wall on the vertical rib appeared rough.
Objet
The last of the models was the acrylic photopolymer using an Objet printer with Polyjet printing technology. This had the smoothest surface of all of the models and preserved most details very well including the indentations at the top of the vertical ribs. The top horizontal rib was not easily visible however and there was a strong plastic smell exhibited by the model. The model was somewhat shiny, while the other two were flat, and the material itself looked almost gel-like and thus some of the details in shaded areas were difficult to make out.
Top details were well preserved but may not be apparent at first because of the low contrast shading caused by the objects material.
The top horizontal rib is difficult to make out as it runs the same direction as the horizontal banding that is an artifact from the printing process.
Again, the lack of contrast in the shaded areas makes it difficult to determine how far indented the vertical ribs are and whether they converge with each other or if there is an inner wall.
Rakings from Visual and Physical Inspection (lower value is better)
Z650 Gypsum model PA2200 Nylon model Objet Polymatrix acrylic model
Smoothness 3 2 1
Detail level 3 1 2
Light Meter Test
While the visual inspection provided a good reading on the surface smoothness of each of the prints, a more scientific method was used to quantify this attribute. A laser was pointed at each model and reflected onto a digital might meter. The assumption for this test is that smoother the surface, the more concentrated the reflected light will appear to the light meter. Meanwhile, the rougher the surface, the more the light will scatter and thus the light reflected onto the light meter will have less of an intensity.
The test was conducted in a dark room and the laser, object and printed model were placed at equal distances for each of the tests.
Results from light meter test (measured in foot candles)
Z650 Gypsum model PA2200 Nylon model Objet Polymatrix acrylic model
Base reading 1.0 1.0 1.0
Conclusions
Z650 Gypsum model PA2200 Nylon model Objet Polymatrix acrylic model
Min. Wall 1mm 1mm 2mm
Min. Detail .2mm .2mm .4mm
Watertight no yes no
Recyclable no no no
Max Temp 60 C 80 C 48 C
Max Size 66 x 35 x 55 cm 49 x 39 x 20 cm 25 x 38 x 20 cm
All print were an accurate representation of the original 3D model, given their size (cm: 4.84 x 4.84 x 5.68), though there was a variance in detail level and surface texture. Taking cost into account and print quality, the PA2200 print in Nylon 12 using Synthetic Laser Sintering technology provides the best value. The Polyjet model had the smoothest surface texture, but the details were sometimes difficult to make out and it was by far the most expensive method. The Z650 model preserved the least amount of detail and had the roughest texture, but was the cheapest to print and is better suited for larger printing jobs where texture and fine detail may not be as important as the overall cost.
Further Research Recommendation
More printing methods and materials exist, and an expanded comparison may provide better recommendations as to which is the better from a cost vs. quality perspective.
A strength test may also provide useful as it would allow the durability of a model to be factored into its evaluation. Prototype models may be handled by many people or may be transported multiple times and durability could be an important factor.
Flexibility testing would also be useful, as it can affect the durability of an object and also may be useful for certain prototypes that are meant to have flexible parts.
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