Today, I'm going to talk about StackMold.
StackMold is actually a result of a [INAUDIBLE]..
He's from the University of Hasselt.
But he unfortunately couldn't make it
because he's working in the industry right now.
This work is also done in collaboration
with Dan Ashbrook and [INAUDIBLE]..
So let me tell you what StackMold is.
With StackMold, we can build really multi-material objects.
For example, this functional multi-material
headphone with embedded speakers.
Let me start off with a simpler example--
a multi-material turtle with embedded LEDs.
So how does it work?
We have the software tool that allows
us to annotate different material regions,
and StackMold generates a laser-cuttable mold.
The user then embeds electronics and casts different materials
in a mold, according to the manual.
Once done casting, the user removes the mold
and reveals the multi-material turtle
with embedded electronics.
All right.
So now let me motivate why we did this.
So I will discuss three processes
that are readily available that got used
for multi-material prototyping.
First, let me start with CNC milling.
CNC milling is traditionally done with a single material
type.
Making a truly multi-material object
requires milling separate parts out
of different materials that need to be assembled or glued.
But this process of assembly and gluing
takes a great deal of precision and can be highly
challenging for novice makers.
Then we have the additive manufacturing processes,
like this industrial printers, like [INAUDIBLE] connects.
But these printers are limited in the materials
that they can print, depending on their print heads.
Also, the cost of these printers and the prints
are also very high, especially for novice makers.
In contrast, we have this inexpensive multi-material IDM
printers, but they're also often limited by dual extrusion
or single extrusion machines.
But single extrusion machines can
have these add-ons like Mosaic that combine multiple filaments
into a single strand to print a multi-material object.
Some research has also been done with rotating [INAUDIBLE]
to realize multi-material as lay prints,
but approaches like this are not yet mainstream.
Last, we have the formative processes.
Some research also has been done in optimizing the casting
process, like Flex-Mold or metal mold,
but none of these techniques actually
support the creation of multi-material or multicolored
objects.
In industry, there's a multi-material injection
molding technique that's called over-molding.
This approach requires a new mold
for every material present in the object,
and is very expensive.
We took inspiration from these techniques
and devised a new concept that we
call multi-stage molding that allows makers to cast
truly multi-material objects.
With StackMold, we facilitate the casting
of different materials and different colors
by using a novel concept we refer to as multi-stage molds.
These molds consist out of different compartments
for casting different materials over time.
So here, we can see the manual instructing the user
to remove temporary props and add layers,
creating a new casting compartment.
As you can see, the inner layers of the multi-stage mold
exist out of individually layers cut and the [INAUDIBLE] pieces
of wood.
Optimizing the build-up of this mold and the casting
steps as complicated as a complicated computational
problem.
To illustrate this, I will walk you through a simple example.
Let's say we want to cast this figurine in two
different colors.
We cannot make this mold into two casting,
because if we fill up the model with temporary props--
that you can see as dark gray--
and we cast only the blue part, the undercut of the neck
prevents the removal of the mold.
If you can read it, it's from layer 14
and above will not be removed.
Therefore, the temporary props inserted in the left region
can never be removed if the blue part is casted.
So how do we solve this?
We fill the green part with temporary props,
but we leave the head out of it.
So then we cast the other side with the blue material,
and then remove the temporary props.
And then the mold, because we open the mold,
we can move the temporary gray props out of there,
and we create this new casting compartment.
Then we build up the mold further,
and we fill the blue head with other parts of the props,
enabling us to cast the new compartment
with green material.
After we remove the temporary props of the blue head,
creating yet again another compartment
for the last casting operations of the figurine.
We now can fill this compartment with the blue material,
and the casting process is done.
The only thing left to do is to remove all more
layers to reveal the figurine.
Even for such a simple figurine, this is a very complex problem.
Therefore, we built a software tool
for optimizing the mold build-up that facilitates
and streamlines the workflow.
Let me now go into more detail on how this interface works.
By applying the brush, we can define different material
regions.
Regions that are not annotated have the base material
properties.
In this example, the blue material.
Once sliced, the StackMold generates a multi-stage mold
that is ready for laser cutting.
So now, let me tell you how this mold is built up.
The mold consists out of laser-cut layers and a box
to facilitate their alignment.
Layers can have temporary props that
can be removed over time to realize the casting
compartments.
At every step, a bracket can be pressed into the slot,
keeping layers together to avoid leakages.
Every layer has brake lines engraved into them
to facilitate removal of the mold layers after casting.
StackMold also generates a custom manual,
guides the placement of all laser-cut parts and layers.
These parts are marked with an ID
using the laser cutter so that the user can easily
assemble the mold.
For smaller parts with no marking,
or they're too small to mark, we use this paper
with the corresponding shape and ID.
For removing the mold, some layers come apart very easily,
but others are destructively removed
from the mold facilitated by the brake lines mentioned earlier.
So hopefully, now we have a general idea
of how multi-stage molding works.
Now I will explain some additional features
of StackMold.
StackMold allows for seamlessly embedding electronics
into casted objects.
During the generation of the multi-stage mold,
fixtures are added to hold electrical component in place
during the casting.
Another feature of StackMold is that it
can optimize the level of details in the cast object.
Because of the sliced model layers,
objects have staircase effects, and therefore have less detail
in different regions.
To mitigate this problem, our software has three approaches.
First, the user can specify the direction in which
the details are rendered.
Second, the user can control the mode layer thickness.
Adjusting the mode layer thickness gives more detail,
and also increases the amount of layers.
In future versions, we could also
adopt an adaptive slicing technique.
Last, we can define higher fidelity regions,
and StackMold will generate 3D-printed parts
that can be inserted into the mold and after casting.
Objects in these regions have much more detail.
This last option leverages the insight
that prototypes do not need the same level of precision
in every region.
The object as presented in the [INAUDIBLE] system at GUI 2015.
This technique significantly speeds up
fabrication time, as it only renders regions
in high fidelity where it's needed.
So now I want to talk a bit about the multi-stage mold
optimization.
StackMold optimizes the order in which all compartments
are casted to minimize the number of casting and curing
steps.
Here, you can see a representation of four layers,
from M1 to M4.
And you can see six compartments.
That's A1 to A4, and B2, and B3.
A1 to A4 needs to be casted in the blue material,
and B2 and B3 in the green material.
So now we want to optimize the order in which
these compartments are casted.
To minimize the number of casting and curing steps,
if we try to cast every layer individually,
the casting order would be A1, then B2, then A2, B3, A3,
and A4, like a zigzag pattern.
In this approach, only layers A3 and A4
could be casted together, as well as all other blue casting
regions, followed by a [INAUDIBLE] casting steps.
Therefore, in this case, we have five casting steps.
So if we want to cast it with lesser steps,
the normal approach would be, let's cast A1 to A4,
and then B2 and B3.
But we end up with an invalid solution,
and we'll ask why is this--
for casting the blue compartment,
we have props in the green casting compartments B2 and B3.
If we cast A1 till A4, we're unable to remove B2.
This is because [INAUDIBLE] is blocked by layer A4 that's
sticking out.
So how do we solve this?
First, a material volume can only
be casted when all volumes below that are in direct contact
are already casted.
For example, A3 can be casted before B2,
but B2 cannot be casted before A2 because it's not in direct
contact.
Because A1 is not casted yet, sorry.
So in this model, the model--
these relations, we build up the volume dependency table.
Here, for example, in this table,
you can see that B3 is in direct contact with B2 and A2.
We now can build up a casting tree.
When using this tree, all possibilities are considered.
The most optimal solution that we thought of before
is still in the tree, and is still
invalid because we didn't consider
replacement and removal of the temporary props.
So to model the placement and removal of temporary props,
StackMold verifies all viable sequences
of the casting tree using an algorithm we described
in detail in the paper.
In short, this algorithm considers the following four
relations between casting volumes.
First, volumes in the same layer that are in direct contact,
like A2 and B2 are connected together.
Second, the second rule, it checks for volumes on top
that are in direct contact, like B2 and B3, in this case.
Then as the third option, mold layers on top
locks the volume material from B2.
So B3 is on top of B2, so it cannot be casted.
And then fourth, the material and volume above
locks the mold layer below.
So these four parameters are considered in the algorithm.
By considering all these relations,
the following result is the most optimal and valid
involving three casting steps.
First, we need to cast A1, then A2, then A3.
These are cast in blue.
And then we can cast B2, B3 in green.
And lastly, we can cast A4 in blue.
So for the last part of this presentation,
we'll give you some more details how we implemented
some interesting features.
First, StackMold has support for two types
of annotating [INAUDIBLE].
If we want a 3D volume selected, we
use the endpoints to determine the region.
If we only want to annotate a surface,
we implemented an eroding selection technique.
To use the eroding selection, the user
can set the inclusion depth of the brush.
What do we do if we have overhanging structures?
If temporary props cannot be removed,
we use temporary casts of beeswax to provide support.
After all casting steps are completed,
we heat up the mold, allowing the beeswax to melt,
and we can pour out the beeswax.
So here, you can see that we cast temporary beeswax.
After this is hard, we disassemble the mold,
and we reassemble it to make a casting volume for the plaster.
Once we casted the plaster and it's fully hardened,
we can heat up the mold in an oven,
and therefore melting the beeswax,
and just pour it out as a support structure.
So now the vase is fully hollow in between.
So for-- I'm going to skip that ones.
So let me briefly talk about limitations and the future work
of StackMold.
Although we use some heuristics for pruning the solution space,
the solution space sometimes can be large for complex problems.
What are the solutions for that?
We can use more heuristics for pruning the casting tree.
For example, processing materials,
volumes with the same material properties first,
or prioritizing material volumes that
are connected across mold layers.
As a third option, what we can do is optimize groups of layers
individually.
When it takes too long or it's too expensive
to calculate the most optimal solution,
we optimize for groups, as you can
see in the image on your right.
This approach is significantly faster,
as it optimizes the build-up of groups of layers,
and thus approximates optimal solution in which the build-up
of all the layers is optimized.
And lastly, what we could do is use
some data heuristics to optimize the pruning of the casting
tree.
So for some objects, an optimal solution is still impractical.
For example, this checkerboard.
We cannot optimize more for this--
or this Christmas tree.
It's going to be a lot of steps, and it's
going to be labor-intensive because you
have to cast all separate layers in a different color.
We have also some material limitations.
First, some casting materials are incompatible.
Some components in one casting material
can have influence on other previously-casted materials,
deteriorating it.
And secondly, some materials are hard to adhere to each other.
So an interesting way to solve this is using mechanical hooks.
So to sum up, in this paper, we contribute
the concept of multi-stage molds consist of multiple casting
compartments over time that allow for casting
multi-material objects.
One of the most interesting qualities of this project
is embedding of existing components, objects,
and electronics that are very convenient.
With alternative fabrication techniques,
such as 3D printers, this is oftentimes
much more cumbersome.
With this, I would like to open the floor for questions.
[APPLAUSE]
Stephanie Miller from MIT [INAUDIBLE]..
Hey, I'm here.
Great talk.
I really loved the new fabrication technique.
So you talked a lot about the geometry,
and how to cast everything, but can you also
talk more about which types of materials
we can now maybe cast together that enable
some new interactive device applications?
So these are mainly different colors, right?
Which you could also do with 3D printing.
But what's maybe some materials that cannot be 3D printed,
but now you have this new multi-material fabrication
process?
Thank you.
What's interesting is these examples
are silicon-based, as you said.
But they're different [INAUDIBLE] harnesses,
so that's the first thing where you can experiment with.
But then if you want to go further,
you could go and do some acrylic casting.
That's very hard to 3D print.
Or just in that [INAUDIBLE] parts of some carbon fiber.
Or everything that can go into a mold,
and you can cost something that's liquid on top,
could be used in this mold.
For example, in the headphone, there
is a metal structure inside of it just attached
if it's springy enough.
So you could use different materials.
All materials that are castable, you can use,
but also existing materials.
And I think that's very exciting.
I cast a hinge inside of an object.
That's more difficult with 3D printing, I think.
Or I don't know, electronics in different layers
on top of each other.
You can just have different compartments
where you can route the cables in between,
and you don't have to wait for the printer
to reach the stage where you can put in there.
Awesome.
Thank you.
So to keep us on time, we're going
to go to the next presentation, but if you
do have more questions for Danny,
you can find him at the--