Task:
INDIVIDUAL assignment
- design a 3D mold around the stock and tooling that you'll be using,
- machine it, and use it to cast parts
GROUP assignment:
- review the safety data sheets for each of your molding and casting materials,
- then make and compare test casts with each of them
Review the safety data sheets for each of your molding and casting materials, then make and compare test casts with each of them
DESIGN A 3D MOLD
I live in Münster, a beautiful city in Germany. The city center has historical buildings, which are representative for Münster. Therefore I would like to cast a telephone stand or a pendant for a key ring in the shape of a gabled building.
This assignment consists of these steps:
- Drawing the 3D model and setting up the CAM software for the milling process.
- Milling the form in two steps 'Rough Cut' and 'Finishing Cut' to cast the flexible material.
- Mixing and pouring the flexible material (silicone) and casting the silicone.
- Using the silicone parts to cast the final material (resin).
- Removing the cast and trim it.
In Inkscape, I vectorize an image file with three buildings and export it as DXF file. In Rhino, I open the DXF file and extrude the curves straight as solid (closed) volumes and move the solids volumes in the Z-axis.
Don’t forget to add the registration points (one side positive and one side negative) to put the two silicone parts in the right position. Also add a pouring tube that is large enough to vent. I use the commands ‘Boolean Union’ and ‘Boolean Difference’ to create a closed volume for the STL export file.
Model 01, the phone stand: After I have drawn the first 3D model, I test the settings in the CAM software. I notice that the milling process is extremely long (8 hours for one half), so I decide to reduce the size of the 3D model and abstract it.
Model 02, the pendant for a key ring: Now I have both halves on one board. I also draw the size of the milling bed. For the milling process I use a flat end-mill with 3 mm diameter and 4 flutes. I simplify the 3D model again and used the commands ‘Fillet Curves’ or ‘Fillet Edges’ with 3 mm or 5 mm radius. I also check the distance between the volumes like windows and the cutting depth (max. 19 mm). Finally, I export the volume as an STL file.
Link to Carbide end-mill, flat, item # CU 136596
Flute length 19 mm
Diameter cutting 3 mm
Note: it is important that you check the operation (machining) dimensions X, Y and Z of the CNC milling bed and the block you are milling. I did not check this at the beginning and had to adjust the 3D model. In the topic ‘SDS’ I link the materials I use.
- Operation dimensions for the Roland SRM-20 machine:
203.2 (X) x 152.4 (Y) x 60.5 (Z) mm.
Link to Download Roland Software
PUR board: 500 x 245 x 50 mm (X x Y x Z): I cut the board with a handsaw so that it fits into the CNC machine.
Link to PUR board, ordered in modulor (Germany)
More information about the materials in → Group Assignment → Data Sheets
Sketches
Sketches in Inkscape
Phone stand, extrude in Rhino
Phone stand, closed volume
Pendant for a key ring, version 01
Pendant for a key ring, version 02
Pendant for a key ring, version 02CAM-SOFTWARE | MILLING THE MOLD
CAM: computer-aided manufacturing
For this assignment I will use the Roland SRM-20, which I already used in the assignments Electronics Production and Electronics Design. I have learned to mill the PCB, but I have no experience with the Roland CAM Software ‘SRP Player’.
Our instructor showed us how to use the Fusion360 CAM module. I did this assignment in Münster, where I live and used the Roland SRM-20 in the FabLab Münster. The Roland CAM software does not have as many setting options as the Fusion360 CAM module.
SRP Player toolbarSRP Player (CAM software)
Before I started with the Step 1, it is important to register the cutting tool:
> Menu options > Register Cutting Tool > Click on New and enter: Tool Name, Tool Type, Material, Flute diameter and Flute length.
STEP 1: Determine the size and orientation of the model:
- Open the software and import the STL file, check that the size of the model is correct.
- Functions in the toolbar: See screenshot on the right. You can also choose between Perspective, Top, Front or Side from the View menu.
STEP 2: Determine what to do: Type of milling:
- Better surface finish, model with many curved surfaces and block workpiece only cut on top.
STEP 3: Create the cutting Data: create the toolpath:
- Important: Choose the right material, SRP has default cutting parameters for each material. You can also add a material.
- Then set the workpiece size: The minimum values for the material appear in parentheses.
- Click on Edit: A new (green) windows opens: here you can select the settings for Roughing >Go to Top Side >Model form > Uncheck the box Add Edge (we don’t need an edge around the model… you save time).
- I repeat these steps for 'Finishing' and then select 'Close'.
- Back in the settings for the STEP 3 (yellow) window: Select 'Create toolpath' and a new window with processing bars appears. You can see the different toolpaths on the screenshots → with and without an edge around the model.
SRP Player Register cutting tool
SRP Player Step 1
SRP Player step 2
SRP Player step 3
SRP Player step 3 Edit
SRP Player step 3: with edge
SRP Player step 3: without edge
STEP 4: Preview the Result of Cutting:
- You can see the result of the cutting simulation, e.g. the inner corners are round, and the estimated cutting time.
STEP 5: Perform Cutting:
- Check the box 'Save the cutting Data' and click on 'Start Cutting'.... SRV Player creates one file for 'Roughing' and a second file for 'Finishing'. Save these files. You also select the starting point for the toolpath, it should be the same point on the machine, in this case " in this case “Lower Left”.
SRP Player step 4
SRP Player step 5VPanel (PART 2)
- I decide to use the PUR board for this assignment and fix it to the milling table with double-sided adhesive tape. Then I turn on the CNC machine and open the VPanel.
- Set the Origin Point: with the cursor buttons X and Y I move the end-mill to the atart position (Lower Left). The end-mill is 1-2 mm above the board. Using an hexagonal wrench, I loosen the screw in the collet, so that the tip touches the surface of the board, then I tighten the set screw in the collet.
- Set the Origin: click on the X/Y and Z buttons. All values are set to 0.00 in the User Coordinate System.
- Select the Cut button, a new window opens. Delete all files and add the first file 'Roughing'. Select Output and the milling process STARTS.
You can Adjust the speed to 30%: the speed changes to 432 mm/min as in the Data Sheet for the board I+m using (SIKABLOCK M450).
- When the milling process 'Roughing' has finished, select Move To Origin X/ Y and Z. Select Cut and repeat the steps for the Finishing file. When both milling steps are finished, remove the dust with a vacuum cleaner and clean the CNC machine.
VPanel Set Origin
VPanel Cut Speed
VPanel Set Origin
'Roughing'
'Roughing'
Mold after 'Finishing'GROUP ASSIGNMENT
MILLING AND CASTING TESTS
Link to the group assignment site
I run two tests to check if the CAM settings are correct: one with a 3D model I found in Thingiverse and the second one with the pendant for a key ring, which I scaled to 50%. Above I already described the steps for the CAM software and the milling process. After finishing the test, I realized that I had to change the ball end-mill to a flat end-mill.
Link Darth Vader cookie cutter
The PUR board has a high dimensional stability with a very dense fine surface. It has a good milling behavior and it is easy to seal. The manufacturer has recommended milling parameter for each product:
Link to Milling Parameters, Page 8
After the milling process is completed, I apply the mold release wax with a brush and wait 15 minutes.
Then I mix the two components of the silicone, one part of each component (1:1) and pour it into the mold. It is easy to mix and the silicone cast has no bubbles. .
Mixing time: 1 min., Processing time: 14-17 min., Curing time: 90 min.
The next step is to mix the two components of the acrylic resin (1:2.5). One part of the component A (liquid) to 2.5 parts of the component B (powder).
You have 8-10 minutes to mix and pour it into the silicone mold. The cast is small, so I can remove it after 30 minutes.
The acrylic resin cast is very soft, so you can trim the part you do not need. The curing process takes 6 hours to 3 days. It depends on the size of the cast.
Mold release wax
Mixing the silicone
Cast test with the silicone
Mixing the acrylic resin
Cast test with the resin
Tests resultsITEMS
Before you start mixing the components, check if you have everything you need:
- Syringes
- Stirring Stick Spatulas
- Funnel
- Plastic Container
- Digital Scale
- Good air ventilation in the room
- Hand protection: protective gloves
- Respiratory protection: for dust or aerosol formation use a respirator with an approved filter.
- It is recommend to use: eye protection (safety goggles),
Skin protection (long-sleeved working clothing and trousers).
.CASTING THE PARTS
Mold release wax
Pouring the silicone
Silicone castThe first step is to apply the mold release wax into the mold (PUR board).
- Flash-off time: 15-20 minutes.
Then I mix the two components of the silicone. It is easy to mix as you need one part of each component (1:1). I calculate how much silicone is needed and use a digital scale to check the 1:1 ratio. The silicone has low viscosity and can be poured easily and without bubbles.
- Mixing time: 1 min., Processing time: 14-17 min., Curing time: 90 min.
Removing the silicone
Silicone cast
Silicone cast
After 90 minutes I remove the silicone cast and trim the parts I do not need. I prove that the two silicone parts fit and fix them with rubber bands.
Mixing the acrylic resin
Mixing the acrylic resin
Pouring the acrylic resin
Before I mix the acrylic resin, I check the parts of each component (1:2.5) on a digital scale.
To get a homogeneous and bubble-free mixture, the mixture should be stirred for another 1 to 2 minute. After pouring the casting mixture into the mold, any resulting air pockets can be removed by shaking the mixture gently or by tapping the mold.
- Working life: 8-10 min, Curing time to remove the object from the mold: 20-120 min,
extra curing time at room temperature: 6 hours (90%)up to 3 days.
Removing the cast
Results
Pendant for a key ring
After 60 minutes, I remove the resin cast. There are some tiny bubbles in the edges, but the result is very good.
The cast is still soft, so I can cut off the cast pipe and other residues.
GROUP ASSIGNMENT
REVIEW THE SAFETY DATA SHEETS (SDS)
Link to the group assignment site
This is a summary of the SDS for each product I use. Before you use the product/material, it is important that you read the SDS. Make sure that you have the latest version. This summary has no guarantee of correctness and completeness.
PUR BOARD: SIKABLOCK M450 (Polyurethane)
- High dimensional stability and low density 0.45 g/cm³,
- With a very dense fine surface and good milling behavior. Easy to seal.
- Precautions for safe handling: no special handling advice required, normal measures for preventive fire protection. Do not eat, drink or smoke while working. Handle in accordance with good industrial hygiene and safety practice.
- Hazards identification: As an article the product does not need to be labeled in accordance with EC-directives or respective national laws.
Link to Product Website, SIKABLOCK M450
Link to Product Data Sheet, SIKABLOCK M450
MOLD RELEASE WAX (liquid in glass bottle)
- Silicone-free, halogen-free
- Ready for application with a brush or a rag. Apply it to the master form before the casting process or to the finished mold before starting your reproduction work.
- Flash-off time: 15-20 minutes. Multiple applications are advisable. After the flash-off time you can polish the wax smoothly with a brush for an optimal surface.
- Wax residues can be removed with hot water and soap.
TFC SILICONE RUBBER Type 2-1, two component set
Silicone rubber type, low viscosity, for larger, self-supporting molds. Suitable for shapes with undercuts, multi-part molds or impressions of an original model.
- Self releasing and non-adhesive
- Easy mixing of components (1:1) and pouring, with a high level of detail.
- Mixing time: 1 min., Processing time: 14-17 min., curing time: 90 min.
- For solvent-containing casting compounds, e.g. resin and epoxy resin, the mold should be pretreated with a release agent (for example Mold release wax).
- This product is not classified as hazardous. First aid measures: After eye contact: rinse under running water for 15 minutes. After skin contact: rinse immediately with warm water. After inhalation, supply fresh air.
- Use protective equipment and clothing. Wash hands during breaks and at the end of the work. A good ventilation of the workplace is important.
- Suitable extinguishing agents: CO2 extinguishing powder or foam.
ACRYSTAL PRIMA ACRYLIC RESIN, Type Component A (liquid) and B (powder)
Two component water-based acrylic resin system, low density, for casting indoors or protected outdoor areas, with high mechanical stability and impact strength.
- Final-State: material is opaque white, can be colored with any acrylic-based inks.
- Working life: 8-10 min, curing time for demoulding the object: 20-120 min, additional curing time at room temperature: 6 hours (90%) - 3 days
- Mixing of components 1 part acrylic resin to 2.5 parts powder (1:2.5)
- Does not contains solvents and generates a moderate amount of heat during curing, it does not shrink and is an excellent material for casting in silicone molds.
- Combustion behavior: flame retardant, self-extinguishing. In case of fire: CO2 extinguishing powder or water jet.
- It is comparable to synthetic resin based casting materials but has the advantage over them that it contains no hazardous materials. The product does not have to be labeled.
- As long as the resin has not yet dried, the tools can be easily cleaned with water.
- First aid measures: no special measures required. After skin contact: rinse with warm water. After eye contact: rinse under running water.
- Protective equipment and clothing is recommended. Wash hands during breaks and at the end of the work.
Link to the Product Site, Acrystal Acrylic Resin Component A and B
Link to the Data Sheet, Acrystal Acrylic Resin Component A and B
Link to the Users Guide, Acrystal Acrylic Resin, Component A and B
Link to Safety Data Sheet, Acrystal Prima Component A (liquid)
Link to Safety Data Sheet, Basic Crystal Component B (powder)
Download
| Rhino, STL and PRM(CAM) files (zip) | Download |