Week-17 Wildcard week
‘Heroshot: My hot-wiring cut foam profiles to enhance the system integration of my project’
This is my 17th week at FabAcademy. This week we had the wildcard so I learnt about hot wire cutting, something that has been completely new to me (as all other lessons of the FabAcademy). The assignment of the week consisted of:
- Design and produce something with a digital process (incorporating computer-aided design and manufacturing) not covered in another assignment, documenting the requirements that your assignment meets, and including everything necessary to reproduce it.
So in the following I explain the process, design and fabrication of what I have done, including a description of the facilites in where the job was done.
Design of the foam profile for system integration of my project
The only machine left to use in my lab was the how wiring cutting machine, therefore I used that machine, which I never used before, for the wildcard. My intention was designing a foam profile that can serve to enhance the system integration of my project. First of all I designed the profile in VCarve and exported the resulting profile in DXF to subsequently using the geometrical model in Cenecé - the software used for implementation in the hot wire machine. The profile consisted of a simple terminal edge that has to chamberings and is slotted to accomodate in the edges of my metacrylate ventilation gates. The metacrylate is 3 mm in thickness so I decided to slot with about 2,5 mm to assure rigidity of the joints. In the following images you can see the design in VCarve and the corresponding files can be downloaded in the download section for reproduction purposes.
The overall starting size of the profile was about 5 x 5 mm, but as you will see latter, that was just a reference size, as the real size needs to be further scaled in CENECÉ software.
Hot wiring CNC cutting in CENECÉ
The exported .dxf model that is got out of VCarve is then opened in the CENECÉ software:
It is worth noting that when opening the dxf file in CENECÉ the software asks for the number of points to consider, which is useful for being able to capture the smothness of curves (high number of points) or not. In my case the curves where not important for achieving the function of the system, which is intended to be used as system integration component.
The next step consists of defining the original cutting point from which the hot wire will start melding the foam. This can be done by right-clicking the corresponding point and selecting the menu:
Also it is very important that the models in CENECÉ work like .DAT files, and as such they must be normalized to unity. At the beginning that sound strange but latter one realizes that actually that is very usefull for scaling the model as desired, something that is very common in hot wiring cutting. In fact, in my case I needed to scale the profile several times until being sure that it perfectly fits with the metacrylate gates. In the next image it is shown how to command the normalization:
Next step is creating a project (top left menu) as well as reviewing the configuration of the system:
As you can see in the latter image, our machine has several preset configurations for cutting, in my case I chose that the cut was from left to right.
Once the overall configuration is selected, I created a new project giving a name:
Next I defined the dimensions of the foam block I had for the cutting. It is worth noting that first I did some tests just to see the results with styrofoam, and latter I made the final pieces with polyretane foam.
Once defined the project, I could load my project as a DAT family:
Which is illustrated here
Then I started a process of testing different scalings of the pieces to make sure that they will be properly hot-wired as well as generate a good fit with the ventilation gates. That can be adjusted in the cut menu as shown here:
As you can see in the latter image, I made the first tests with relatively large pieces, as I scaled them by a factor of x10 keeping the x-y relationship.
Also at this point it is important to define the depth of the hot-wire travel before cutting, in my case I defined 10 mm, but depending of the test I needed to adjust it in a range of about 10 to 20 mm to make sure that all the cutting profile was drawn within the foam block.
There is also one additional menu for cutting that defines the base material and the setting up of several cutting parameters such as wire temperature, velocity, etc. In my case I let that as deafult parameters, and the temperature, and speed, which are very important parameters were then tested in situ at different ranges. Before cutting it is very important to give a good heating of the wire until red and then decreaseing the temperature before cutting. The sound of the cut during the process is also an important indicator: the cut should be silent not noisy. The observed thickness of the cut is also an important indicator, if the wire is too hot the thickness of the cut will be too large. Here you can see the paremeters I let by deafult:
Once, the cutting set up was defined, the next step was setting up the foam block in place well aligned with the wire and set up the right height of the wire. At this point is care is very important because in our machine we do not have limit switch, so the wire can never surpass the down limit or everything will need to be rearanged.
And with all that defined the cut can start, when gouin left down in the menus to cut of profile a recall of all selected parameters is shown
After reviewing that the cutting can start when left clicking cut off:
And I started the trial cutting, in this video you can see the cutting process:
That worked relatively well but I realized that the slot was way too large for adjusting with the metacrylate gates. So I satarted the resizing process, this can be done directly in CENECÉ by rightclicking each point and setting a new relative possition in where X=1 and Y=1 are the maximum limits (it is normalized to unity). Also it is convenient to normalize to unity again after each scaling in case the boundary postitions have changed.
In my case I essentially needed to scale the X direction (width) to about 0,5 factor because the slot was too large for the metacrylate. After adjusting the dimensions and making some tests I got the right shape, and in this video you can see the cutting process of my profiles:
This resulted in the following pofiles:
That can be latter be used as system integration of my project, in this illustration you can see the first fits of the profiles:
Files for download and reproduction
Here you can download the relevant files of the week for the design and fabrication of the foam profiles Wildcard_Pablo