Rapid Prototyping and TEOTWAWKI, by PMN

If there is a breakdown in the normal manufacturing system because of TEOTWAWKI, the usual supply of parts may be unavailable to replace the broken pieces of our machines. However, 3d printing might provide a solution by allowing us to make whatever we need as we need it, but we’d need to exercise caution. There are problems of strength, accuracy, and technical ability involved in this process, and it isn’t “Beam me up Scottie” quite yet.

Some of you guys/girls may have heard of rapid prototyping, which is also called 3d printing. If you haven’t, it is roughly equivalent to 21st century blacksmithing. First, you make a computer model, and then you make a part from the computer model. The materials and processes vary. I will try and give a general non-technical description of the major materials and processes.

I will append a couple of links, to help in your understanding of the processes and physical properties of the printed model.

BACKGROUND

The first article that I read about rapid prototyping was published in the late 1980’s, and it involved what is called photo reactive polymers. The article didn’t mention “3D systems”, and it didn’t mention the term stereo-lithography. However, it did talk about multiple lasers curing the photo reactive polymer material in a vat. That is turning a fluid into a solid.

In about 1995 I learned about the two companies involved– 3d Systems and Stratasys. 3D Systems produced the first commercial stereo lithography machines, and Stratasys did the first commercial fused deposition modelers, or “FDM”.

STEREO-LITHOGRAPHY: A light-protected machine with a vat of photo reactive polymer that uses a laser and actuating equipment to create a model by turning a liquid plastic into a solid plastic part.

Youtube example.

FUSED DEPOSITION MODELING: A heated nozzle in a machine extrudes a plastic filament onto a platen in a molten bead. This process also works with wax for lost wax molding.

Youtube example.

In both processes/machines, the 3d computer model is cut, with the use of software, into thin x-y plane slices. The slices are then printed on a platen, which displaces on the z axis, allowing an additional layer to be deposited and so on until the entire 3d model has been produced. In most machines, the x and y axes movement are done by movement of the platen or the head. The machines are varied as to which part moves which axis, but the process is roughly the same. Sometimes the platten goes down, and sometimes the head goes up.

Several additional technologies need to be mentioned, although this is an abbreviated list.

POWDER SINTERING: May be either a plastic or metal powder in which the powder is fused into a solid product.

Metal products may then also be infused with additional alloys.

POWDER JET ADHESIVE: An adhesive spray creates a solid out of plastic, metal, or ceramic powder.

Metal products may be fused with heat and then also be infused with additional alloys.

LAMINATE OBJECT MANUFACTURING: Paper is used to create a wood-like object adhesive sheet

SPRAY METAL DEPOSITION: A process in which a molten metal is sprayed in to mold solidifying into a part. Today there are a number of major and minor companies in production with a number of these different technologies.

SOFTWARE

All of the parts are created in what are called solid modelers. There are two major modeling software companies–Autodesk and Dassault Systems– with computer software programs in the $3,000-$4,000 range that account for most of the production. Autodesk’s products include Autocad and Inventor, though AutoCAD is much more popular than Inventor. Dassault Systems offers Solidworks. In addition, there are several older or smaller companies with products that are worth mentioning, such as Cadence, Turbocad, ProE, Siemens NX/solidedge, Cadkey, Intellicad, and Rhino. Some of these are available at quite reasonable prices.

Google Sketchup is a new kid on the block and for the basic version it is a free download. Freecad is a free modeler under development. However, my personal software is Autocad, because it is good for both 2d and 3d drawing.

The general file type for 3d printing is the STL file, which comes from 3DSystems, because it was one of the first in the field. Commercial machines usually include slicing software in the machine as a part of the product you buy, which makes the production process much simpler. However, all of the machines must section the 3d model into flat slices for printing. The slicing software produces a tool path for the machine to use in making the model.

REPRAP

For those of us who don’t have the money to invest in a production machine, costing tens or hundreds of thousands of dollars, there is an independent group of modeling machines that can be bought or kit-built and are quite reasonably priced. I have built several of these machines and recommend the ones made by “makertoolworks”. I really like the MendelMax 2.0. Yes, this is a clear plug for the company, because they went the extra mile to help me get my kit machine working.

These machines are not for the faint of heart hobbyist, but they are the coolest thing around. You have to use several software programs to actually make a model with a reprap machine function– a program for slicing and then a control program. I have found “Gslicer” and “Pronterface” easiest to use but would suggest you do research in the other software available. So all in all that’s three programs and a fairly complex machine to get from broken part to new part; it is the modeler, the slicer, and the machine control program.

A good resource of information is: http://reprap.org/ Resolution is a magnitude better in the commercial machines than it is in the Reprap machines. Here is a picture of a set of handles I did for a friend’s S38 auto 1911 on my Mendelmax 2-0 and a picture of the product done on a commercial machine. The black model is done in 1.75mm black PLA on a Mendelmax 2.0, and the white model is done in white nylon at Shapeways.

As you can see, the Shapeway’s object is much higher resolution. Information about the reproduction company’s product and shameless plug for the product is online.

MECHANICAL PROPERTIES

Engineering properties is beyond the scope of this post, but in general Sintered or Polyjet plastic powder models can be thought of as having a homogeneous or isomorphic structure, where as fused deposition models should be thought of as having a grain somewhat similar to a piece of wood. Metal Sintered models may also be thought of as having a homogeneous or isomorphic structure and are of course much stronger.

With Sintered or Polyjet powdered models, which are going to be produced on commercial machines, it isn’t as necessary to think about the relationship of the shape of the model to the platen or XY plane. With fused deposition models it is absolutely necessary to think about the shape of the model relative to the platen or XY plane. This is because overhang shape is a very important consideration in printing FDM 3d models.

In most commercial machines using laser sintering or Polyjet glue with a powder medium, the material is self-supporting layer by layer, because the non-printed material is deposited along with the hardened material. When the model is finished the extra powder material is vacuumed out of the model and may be reused, after sifting or cleaning. Consideration of hollows and enclosed spaces is important in this respect.

Photo reactive polymer machines use software to create their own overhang support material, which is dissolved or cleaned away after the model is finished. With these machines, care should be taken in the orientation of the models to provide a stable base for the model as it is grown in the medium.

With FDM models, overhangs are a limiting constraint. With these machines a support structure may be created by the slicing tool path software for the first extrusion head, or a second extrusion head may be used to provide a support structure of different material more easily removable for the model. I have found that anything less than 45 degrees of slope is difficult to achieve without support structure, and the support material done of the main extrusion material is difficult to remove. So far I have found it impractical to use the main material for support structure, because it’s hard to remove, and I haven’t wanted to go to the additional complication of a 2nd, more easily removed support material and head. With FDM, it is easiest to use a constant section or orient the shape so that it will get smaller as the model is printed.

FUTURE

I remember in the early 1990’s, when I was first trying to produce ray traced renderings from 3d models and had to use a 386 Intel chip-based machine that would take 48 hours to produce a 2k x 4k pixel image. I can now produce a similar image in 10 or 15 minutes. In the same vain, it can take several hours to produce a 3d print of reasonable size and complexity. I am sure that similar progress will be coming in the future, if we manage to avoid the kind of mistakes we all worry about here. But even with current limits to the technology you can do amazing things with 3d printing right in your own basement.

Other cautions:

I use a mechanical air filter machine and a filter face mask when I’m tending my prints, as I have found that the PLA fumes are a little irritating.
I have also mounted a fire alarm above the 3d printer, and
I never let it run unattended. It will be running at 195 to 220 degrees centigrade and should be considered a fire hazard.
The multitude of settings make the configuration of the software difficult. I found the configuration provided by Makers Tool Works very helpful. I will append a couple of links to help in understanding of the physical properties of the printed model.