Note: This is Part-2, Click Here To Read Part-1
Last time we touched on building from the foundation of a good CAD file, this entry deals with orientation of the part during the build as a factor in making a good part. This orientation may be different in PolyJet versus Fused Deposition Modeling and also varies on the end use of the part that you are building. However there are few good guidelines.
In general if you are building a part with a cylinder shape, hollow tube, or circular ductwork, you will want to build the part in a vertical orientation. In other words, you want to build the parts so that the open area of the tube faces upward. This orientation allows you to minimize the amount of support used, maximize the stress resistance from forces from the side and minimize the stepping that can be seen when the part is built on the side. This build orientation may be a factor when looking at whether you can get the part into the build envelope, but in general, if you can get the part into the build area vertically, try to go that route.
In parts where you using PolyJet and building the part out of Rigur or Durus, if the part is going to be flexed across a thin wall area (such as a prototype of a living hinge) you will want to build the part with the thin section in the x and Y axis with the longest side of the hinge area getting the longest paths on the material laydown. Try avoiding doing short pathways of material build where the layers will be at the flexure points.
Note that the parts with living hinge prototyping will not have the same lifetime as an injection molding part with the same feature due to difference in material tear strength.
In prototyping a flat part, if the flat area exceeds 4 inches, remember that getting a similar part in injection molding would mean developing geometry to assure flatness. In end of arm tooling, thin flat areas with tips that must be accommodating to robotics with precision placement should have “v’s” or ribs to assist in keeping the parts from defecting, much like an injection molding part. In contrast, in injection molding achieving a flat surface is difficult due to material shrinkage and internal stresses in the part due to material flow and knit lines where the material fronts meet together during processing.
In 3D printing, you can often get the desired flatness on the part, but then have problems reproducing the flat feature in the production part. In FDM Ultem for example, you can print low volume production parts that have the flat feature, but in injection molding would not be abler to produce the same flatness.