Printer Types

I have seen videos of several different designs, in so far as how the model is build up. The support problem is described at the bottom of this page.

Squirting Plastic (or something)

A head is moved along a flat bed (in the X and Y direction) and squirts molten plastic on a flat surface. After it has hardened the head moves up (the Z axis) and another layer is added to previous. There are variations on the mechanical arrangement; the head stands still and the flat surface moves, or some combinations of these. You might liken it to a robot moving a glue-gun in concept.

It is possible to have a changing or multi head variation so you can have several types or colour of plastics in the same model. The extruder can also use other materials as long as they can be squirted and harden afterwards.

The support problem is handled by printing with at least two heads – one with the real plastic, the other with a weak, soluble plastic that is washed away.

Home model

It seems this is the type used for the small and home models. The material (long plastic wire) is safe before and after, relatively cheap, no after treatment required, no waste. In addition you can use a dough, or jelly or any “fun” material.

Building Sandcastles

A thin layer of sand is placed on a flat surface. A head (moving along X and Y axis) then selectively squirts glue where the part is to form. Another layer sand is placed on top and is also selectively glued. The un-glued sand acts as support for the shape being made and afterwards is simply brushed off and recycled. The method thus requires no special handling for supports.

Home models

Have not found any, but seen some video show a kind of proof of concept, using a mutilated (not just modified) ink jet printer (ie the ink was the glue)

Liquids and Lasers

A thin layer of liquid is in a tank. A laser draws on the liquid surface, and this hardens the liquid. A little more liquid is added (or the platform lowered) and the laser draws the next layer. This method was the first method I heard about many years ago.

Supports are made in the same material, and broken off afterwards.

Multi jet with liquid

The head has many jets, and is more like an ink jet printer than a glue gun. The layer thickness is an order of magnitude thinner than the plastic extrusion systems. The liquid is hardened by UV light immediately for each layer. The jets and the thin layers give a much higher precision. The increase in primttime is mitigated by the number of jets.

I think the systems have a few jets use a different material which builds the supports and is “easily” removed/dissolved.

Print with metal

This is the same technique, but the extrusion material is a mixture of metalparticles and some liquid.  The resulting model is then put in an oven where the metal particles fuse. Not sure how the support problem is solved (just very hard to break away the temporary structures if they are in metal?).

Laminate layers

This uses a sheets of plastic. The machine glues the successive sheets together where the model is formed, and uses a knife to cut the edges. No care need be taken for supports. After the print job is done it requires that you “dig it out” of the near solid block of plastic, and that includes any “insides” , like a hole through a block.

The support problem

Imagine you print the letter M, from the bottom. It is easy as you print the two columns. Halfway up you need to start laying down the middle of the “v”-part. But is not yet connected to either column… plop… the first bit falls to the bottom. You could solve it for the M by printing it lying down, but some shapes will have that problem whichever way you turn it for printing.

The printer needs to build a support, which later is removed. In our case the M starts with three columns, the third is under the “v”-point. There are two ways to handle that: You modify the computer model to include the supporting column, and make the place where the support joins the real part so thin it is easily broken off after the model is done. This material is thus wasted, and it requires some hand finishing to remove the marks from the support. In complex models it may be hard to place the support so they can be removed.

The other method presumes that you can use two materials at the same time when printing. Support structures are made of this material. After the print is done, the whole model is put in some bath which dissolves the support material. The advantage here is that the supports can be anywhere, in particular inside the model, and removal is easy and does not leave marks. The downside is that the printer needs to be more complex, you need a second material.

The software that transforms the 3D model to slices for the printer may be able to generate and place supports automatically.

How big?!

The model must fit inside the printer, but there is no real size limit to a printer. I think the relative accuracy probably remains a constant. Some artist made a 3D printer (link missing) several meters on each axis of the sandcastle kind to make sculptures. This had a lot less accuracy and the “print head” was that much coarser (Otherwise each print would take months…). One could make a very small but hyperaccurate model  to make tiny casts.

The width of the printhead limits the size of the model because of the time it takes to fill in the volume.

See the Wikipedia Solid freeform fabrication Category for lots more info

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