14. Moulding and Casting

Assignments

Here you can find a recording of the lecture from the 23rd of April.

This week's assignments and learning outcomes, see here:

Group assignment:

Review the safety data sheets for each of your molding and casting materials
Make and compare test casts with each of them
Compare printing vs milling molds

Individual assignment:

Design a mold around the process you'll be using, produce it with a smooth surface finish that does not show the production process, and use it to cast parts

Questions to be answered/from Nueval:

Have you answered these questions?

Linked to the group assignment page and reflected on your individual page what you have learned
Reviewed the safety data sheets for each of your molding and casting materials, then made and compared test casts with each of them
Documented how you designed and created your 3D mold, including machine settings
Ensured your mold has smooth surface finish, that does not show the production process (by postprocessing if necessary)
Shown how you safely made your mold and cast the parts
Described problems and how you fixed them
Included your design files and ‘hero shot’ of the mold and the final object

Link to group page

Here you can find the documentation of our group assignment.

Hero shots

Hero shots from group assignment

3D printed mould and casting

I designed a mould and 3D printed it. Then I made two casts of moulds with Zhermack HT 33 Transparent and Zhermack ZA 22 in blue. After that I made casts out of Jesmonite AC100 and Acrystal Prima.

Hero shots from individual assignment

Mould for buttons

Here you can see the model for casting buttons.

Mould and casts

Here you can see the final mould with smooth surface finish and the casts I made. The HT 33 silicone buttons came out very good but the polyurethane buttons are stuck in the mould.

Summary

Tips

Neil gave us some tips in the lecture.

Important to sheer and absolutely not to scoop, because scooping can add airbubbles to the material.
Pour in a thin bead. It can be a good idea to paint the first layer of resin and then the other layers will stick to the first layer.
Wait for all the bubbles to come out.
A poor mix will not get warm and will not harden completely.
If you are working with big moulds the heat can damage the mould.
Remember to slightly angle all faces (draft angle) for easy release.
Hydrostone and silicone will not stick but check if you need a release agent if you are using another materials.
Test the materials before beginning.
Caution! If there is a warning that says the material is not suitable for home use, we should not use them.
Caution! Read the safety precautions on the datasheet.
Let material set before disposing.

Some tips from Adrián Torres:

Add an offset at the top of the mould for easy removal.
First do a rough milling and then use a finish stepover.
Make sure that the endmill is long enough not to collide with the walls.
Use a ball nose.
You can recycle the wax shavings.
Use 3D milling settings in Fab Mods or Fab Modules
Remember that you need a hole to pour in and also a hole/holes for air to excape.

Work process detail

Group assignment

Link to group page

You can find the documentation for our group assignments here. On the group page I documented making the moulds and casting process. Here below is the documentation on designing the 3D mould.

A 3D mould designed in Fusion

I began by drawing a center rectangle and extruding it to 5mm thickness.

Datasheet and pinout for Raspberry Pi Pico

Then I created a new sketch and drew a rectangle on top of the box and extruded it downwards. By using the Cut option under Extrude I made a hole in the cube.

The next step was to create a new sketch and draw another rectangle on top of the box.

Then I chose the outer rectangle and extruded it to create a step around the hole.

Datasheet and pinout for Raspberry Pi Pico

After this I created a new sketch on the bottom inside. There I drew a center circle.

Then I extruded this circle.

Importing a sketch from Inkscape into Fusion

I wanted to put the Fab Lab logo on top of the cylinder. I had the logo ready in my Fab Lab Austurland logo. I saved a copy of that file and deleted Fab Lab Austurland from the file.

I saw that Luc Hanneuse said that he used a .svg sketch and added it to his Fusion file. I tested if I could add the .svg file but it didn't work. Then I thought of how I had exported .dxf files from Fusion in Machine week and imported it into Inkscape. Maybe it would work the other way around. Yes it worked and that is probably what Luc Hanneuse was talking about.

Using a sketch from Inkscape

I exported the logo as a .dxf file and imported it into a new Fusion file. For some reason I could not import it directly into the Fusion drawing I was designing the box in. But I could copy it and paste it into my box file. Then I just had to move it a little bit.

Then I extruded the image and saved the file as a .stl file to use for 3D printing.

3D printing the mould

3D printer and material / filament

Bambu Lab X1 Carbon

I used the Bambu Lab X1 Carbon with a 0.4mm nozzle to print the mould. I used pink PLA filament. Here below you can see the model in the Bambu Studio slicer.

Slicing

Here below you can see the sliced model and that the model did not need any support.

Bed adhesion

Here on the left you can see settings for bed adhesion.

Strength of print

Here on your left you can see the settings for the strenght of the 3D print. I used the preset settings and it worked fine.

Speed

Here on your left you can see the settings for the speed of the print. These settings were preset and I did not change anything.

Using the 3D printed moulds to cast silicone moulds

I used the moulds to cast two silicone moulds. I used the Zhermack HT 33 Transparent and the Zhermack ZA 22 in blue. I wasn't sure if the moulds would hold the silicone so I let them set with a bowl placed under them.

Very hard to release casts from moulds

When I wanted to remove the casts from the moulds, I ran into problems. It was very hard to remove them. I tried to use my fingers but that was impossible. I knew that I should not use sharp objects so I decided to use a plastic brush to help me. I began with the Zhermack ZA 22 in blue, which is softer with 22 Shore A. This took time but I managed to release it without damage.

I should have used a taper angle when designing the mould. It was not enough to use a fillet to soften the corners.

Then I tried to get the Zhermack HT 33 Transparent out of the mould. It was even harder. I really thought that I wouldn't be able to do it, but it worked after quite some time of hard work and to my surprise it wasn't damaged.

Here you can see the 3D printed moulds and the cast silicone moulds:

As you can see in the image below, the lines from the 3D printed moulds are quite apparent. This is a big minus.

Using the silicone moulds to cast small objects

The final step was to see how the silicone moulds would work for casting small objects.

I added Jesmonite colours to the two sets of Jesmonite AC100 that I casted. The cast objects came easily loose from both the Zhermack HT 33 Transparent and the Zhermack ZA 22 in blue.

Bubbles in Jesmonite AC100 and Acrystal Prima

Here you can see the final cast parts. The two on the left are made of Acrystal Prima. The pink and the blue ones are Jesmonite AC100. There are small bubbles in all these casts, even though I tried my best to pour the material from good height, let it run in a thin line and tried to let the material run into cavities without closing air in. I also tapped the moulds against the table for some time after pouring the material in. One more thing; When I designed the mould I thought about whether to make the Fab Lab logo stand out or be engraved. In the final casts I can see that it would have been much better to make the logo stand out in the final cast, so I should have had the logo stand out in the Fusion design mould.

Individual assignment

Buttons

I decided to make a button for my final project. I I made four different versions that varied in size and form. I used Fusion to design the model. I wanted to use Renshape Tooling Board to mill the negative of the button to create a mould and then cast the buttons into it.

I had a small cube of the Renshape Tooling Board began by drawing the size of the material I had. Then I created a new sketch and drew four center rectangles of different size. Then I extruded these rectangles downwards into the cube and had the Taper angle set at 5°. I used the Cut option to create a hole.

Then I drew another sketch on the face (bottom) of the holes. I drew two rectangles of different sizes and two circles of different sizes. Then I extruded them and again I set the Taper angle at 5°, as you can see in the image below.

I used the Fillet option under Solid to soften all corners of the buttons. I was planning on using the 1/8 endmill (which is 1/8th of an inch in diameter) so I used the formula 1in/16 for the size of the fillet (1/16 but not 1/8 because the fillet was equal to the radius, not the diameter).

Section analyzis

Under Utilities you can find Inspect and then Section analyzis. You can use this option to inspect the model. You begin by choosing where you want to slice through the model (see image below). Then you can see if everything looks okay (second image below).

3D Fusion model for mould

Mould for buttons

Here you can see the model for casting buttons.

Exporting the model as a 3D model from Fusion

Importing model into Vcarve did not work

This was the first time that I exported a 3D model from Fusion and I ran into problems. Before, in other projects, I only needed the cutting lines. Then I had created sketches an used Project/Include and included the lines I wanted and then exported them as .dxf. I tried to use a similar workflow to export a 3D model. I created a New sketch. Then I chose Project/include and then Project and in it I chose Bodies. Finally, I right-clicked on it and exported it as .dxf. When I tried to import it into Vcarve, I got an Error notification.

Then I asked for assistance and Svavar Konráðsson and he told me that under Utilites you choose Make and then 3D print and save it as .stl file.

Importing .stl to Vcarve

Working with 3D models

The first thing to do was to click on Create new file

Working with 3D models

Next step was to set up the job. I chose to work on one side of material. Then I put in the size of the material. I set the Z zero position to surface of material. Then I chose the xy datum position. Finally, I clicked on OK.

Import 3D model

I clicked on File and then Import. Then I chose the Body1.stl file that I wanted to use.

3D model

Here you can see the 3D model in Fusion. Note that I was doing this for the first time and this was not sure how to do things, but wanted to see if it would work. I asked Svavar Konráðsson for assistance and he did his best to help me, but he had not done this before either.

I made sure that the sizes were the same in Fusion and in VCarve.

Making model fit

I tried to change the orientation until the model was fitting well inside the red outlines of the material setup. I also had to go into Edit and then Job setup to change the size of the material, because I had the size set up the wrong way, or at least something I did was not done the right way. Then I moved the Zero plane position in model down until it was under the holes.

modeling resolution

I changed the modeling resolution to standard for more speed.

A rough toolpath to begin with

Roughing toolpath

I made a rough toolpath to begin with by clicking on the symbol for Roughing toolpath.

Area machine strategy changed

I changed the Area Machine Strategy from Climb to Raster.

Choosing the right endmill

Here the 1/8 inch straight endmill was chosen for the rough paths. It is important not to change settings here. You do it in the next step.

Changing settings for tool

If you want to change settings you do it by clicking on Edit tool.

Warning

Then I got a warning that the Large machining allowance selected was more than 20% of the tool diameter and that might lead to finishing tool breakages.

Machiningin allowance

I changed the machining allowance from 1.0 to 0.5mm.

A finishing toolpath with finer detail

Finishing toolpath

I made a new toolpath for the finishing job. The 1/8" ballnose was already in the presettings and I did not change that.

Moving the design

Job setup still not fitting well

When I opened the Edit and Job size and position and clicked on the 2D view I could see that the material was still not fitting well.

Design moved

I decided to move the design by dragging it with the mouse.

Recalculating paths

Then I choose the toolpaths and then Recalculate paths.

Preview of paths in Vcarve

Preview of paths

When I looked at the preview of the paths, I thought that everything looked okay. I decided to perform the job in the Shopbot.

Preview of both paths in Vcarve

Performing the job with the ShopBot

Information on the ShopBot

The ShopBot

We have an ShopBot PRS-alpha with 1440 x 2190 x 150 mm working area. You can read the brochure for the ShopBot here. In this brochure it is noted that to get good quality CNC cuts it is vital to choose the best cutting speed (feed rate) and router/spindle RPM. The ShopBot has two speed modes which are pre assigned. Move speed is used when cutting og machining, in other words Feed rate. Jog speed is when the tool is moved and is not machining or cutting material. In the brochure they recommend checking out Onsrud.com for good information on cutting and machining different types of material. This is an image from the ShopBot brochure with some basic information on which settings and tools to use.

Following is a description of how to turn on and operate the ShopBot.

Turning the ShopBot on

Turn on the ShopBot

You begin by using this button to turn the ShopBot on.

Press the Reset button

Then you press the blue Reset button.

Open the ShopBot program

Click on the icon for the ShopBot program.

Overview of the ShopBot interface

Interface the ShopBot program

Here you can see the interface of the ShopBot program.

The warmup routine

Important to run a warmup routine

Before performing any job in the ShopBot it is important to do a warmup routine. It is also important that you click on Tools and then Spindle control before doing the warmup. Then this window opens up and there you can see the speed of the spindle.

Important to open Spindle control

It is important to open up the Spindle control under the Cut.

Opening up the keypad

At this point you need to open up the keypad to be able to move the tool to a safe place while the warmup routine runs. You find the Show keypad as a small icon in the Shopbot position window. Then you use the arrow keys to move the tool. Find a place for it where the tool won't touch anything in its surroundings (make sure that it is high enough).

The warmup routine

Choose Cut and then Spindle warmup routine. In the image below you can see the window that pops up. You begin by pushing the Start button which is beside the Reset button (that you pushed in the beginning). Then you click on the OK on the screen. Now the machine goes through the routine.

Changing the tool

After the warmup routine is finished you can change the tool. You could also have changed the tool before the warmup routine. You begin by loosening the screw that holds the dust collection skirt. The screw is on the backside. Then you lower the dust collection skirt. Now you have good access to the tool. To loosen the endmill that is in the collet you have to use a wrench and the Collet wrench that is fastened to the machine with a key. Knock the collet against the table and blow in it, just to make sure that there is no material/dust collected in it.

Note! Make sure that you are using a collet that fits the endmill you are using.

Tools

Here below you can see the dust collection skirt, the collet wrench, the wrench and the endmill in the collet.

Material fastened

Here you can see how the material was fastened in the ShopBot. We have wooden pieces of different size designed to hold down material. I used it on two sides and then two pieces of wood fastened on each end.

Zeroing the X- and Y-axis

Move the tool to the point over your material where you want the zero point to be. Make sure that it is the same X- and Y- point that you used in job setup in VCarve. Click on the small blue button on the Yellow keypad, marked as Zero axis. Then you put a checkmark in the boxes in front of the X- and Y- axis (NOT the z-axis!). Then you click on Zero.

Zeroing the Z-axis

Alligator clip

Here you can see the alligator clip that is used to zero the Z-axis.

Info

You begin by letting the alligator clip touch the endmill and check if a green light appears in input nr. 1.

Zeroing the Z-axis

Then you click on the small symbol that shows Z and arrows.

Place alligator clip under endmill

The program will ask you if the alligator clip is placed under the bit. Make sure it is! Then you follow the directions on the screen and hit the right button. The tool will move down and when the endmill touches the alligator clip, it will go up again. Note! The tool will repeat this process so keep the alligator clip until the endmill has lowered and touched the clip TWO TIMES! I used the top of the material when zeroing the Z-axis.

Is Zero for Z-axis supposed to be on top of material on or machine bed?

Before you begin with zeroing the Z-axis, think carefully about whether you are supposed to zero the Z-axis on top of the material or on the machine bed. Make sure that you are choosing the same as you used as in the job setup in VCarve.

Performing the cut

Ready to perform the job

Now the machine is ready to start machining or cutting. Close the yellow keypad. Then you click on the Cut Part button, find the job you want to do and double-click on it. Then you click on the Green Start button.

Turn on the dust collector

After pushing the start button you give the tool a little time to spin while you turn the dust collector on. My co-teacher, Viðar Guðmundsson, told me once that Bas Withagen this was a good time to prey to the ShopBot God that everything will work out fine.

Click on start

Finally, you click on the Start on the screen.

Watching the cut performed in the air

Cutting in the air

It can be a good idea to perform the job a few centimeters above the material if you are not sure if everything is correct. Then you begin by setting the zero point for the x-, y- and z- axis. Then you raise the endmill for a few centimeters up and set the z-axis to zero. When you watch the machine performing the job in the air, you can check out what the path looks like and whether the machine seems to follow the boundaries of the material. When this is done, you use the alligator clip and zero the Z-axis again.

Cutting in the air

Machining the rough paths

First a rough job, then finer details

Since everything looked good when cutting in the air, I began by performing the roughing paths and used a flat 1/8 endmill for the job.

Cutting the rough paths

Machining the finishing paths

Failure in performing the finishing paths

I was happy with the rough parts and wanted to do the finishin paths quickly. I changed the endmill to a ballnose 1/8". I made a mistake and did not zero the Z-axis again even though the machine asked if I had zeroed the axes before performing the job. I should have thought carefully about what the machine was asking about. When the machine began with the job, it went in a straight line quickly into the material in a completely wrong place! I was ready to pause the job, so I acted quickly and hit the Space bar.

I realized that I had forgotten that changing the tool will change the zero point. I zeroed it again and checked if the X- and Y- axis was in the right place and it was correct. After zeroing the Z-axis I tried again, but the tool followed a wrong path again. It was obvious that I had made other mistakes as well when setting the job up.

What caused this failure?

I am not sure what caused this mistake but I think it is very likely that when I went into job setup again and moved the job by dragging it here, the mistake was made. Most likely, since I moved the design after calculating the paths, I moved one path but not the other one.

When I looked at the finishing paths in VCarve, it seems that the machine was following the red line that it was intended to follow before beginning to machine the material, as you can see in the image below. So, the setup for the final path was much lower on the Z-axis than for the rough paths. The final path was also lower on the Y-axis than the roughing paths, as you can see on the image of the job in the image here above.

I have to set everything up again from beginning and make sure that I am doing it the right way.

The solution

To choose the area to be milled

I contacted Jón Þór Sigurðsson and he looked into my VCarve files. He noticed that the finishing path was covering all the surface of the small cube (my material) and since I had fastened it with wood that went a little bit over the top, the endmill ran into it. I thought that since the roughing path was only where the holes were, the finishing path would also only be placed there, but I was wrong. Jón Þór gave me a tip on how to avoid this, and this is what I did:

Creating a new layer

I double-clicked on the Finishing path. I clicked on the layers tab and created a new layer.

Moving layer to 3D layer

Then I moved the layer to 3D layer.

Drawing one rectangle around areas

I clicked on the rectangle tool and drew a rectangle around all holes.

Drawing rectangles around all areas

Then Jón Þór Sigurðsson showed me that I could use many vectors around areas and I did that around all the holes, right at the edge of each hole. I could control how much I rounded the corners and there I only rounded them by 1.

Machining limited boundaries

Then I double-clicked on the Finishing toolpath and under Machine limit boundaries I changed the selection to Selected vector(s).

Recalculate paths

It is very important to recalculate all paths after changes.

Finishing path only on selected areas

Here you can see the preview of the paths and that they are only where the holes are.

Smooth surface finish

Here you can see the surface finish of one hole. Not perfect but quite good.

Casting

Material

Cast with HT 33 clear silicone and Polyurethane

I made a cast out of two different materials.

Zhermack Silicone HT 33

Zhermack HT 33 Transparent

You can read the datasheet for Zhermack HT 33 Transparent here.

The HT 33 is a bicomponent addition RTV silicon rubber, you mix base and catalyst and it sets at room temperature. When vulcanized it has a high chemical resistance to addressive components of certain types of resin. It has high resistance to wear and tear and can be used for casting fine details. It is heat resistant and withstands aging well. This material has high anti-stick effect.

The mixing ratio is 1:1

Specifications:

Hardness: 33 Shore A
Working time: 20-22 min
Curing time: 3 hours
Tear strength: 16 N/mm
Viscosity: 7000-8000 cP

Precautions and personal safety

Zhermack HT 33 Transparent is not classified as hazardous but you should only use it in a well ventilated area. When working with the material it is adviced to use protective clothing, glasses and mask. Keep material away from food.

Rampf Polyurethan

You can read information on Polyurethan here and the datasheet here.

Polyurethan is made of two components: Polyol (component A) + isocyanate (component B). Raw materials can be added to casting and thus create products with difference in hardness/softness or elasticity. The cast that I made has much hardness.

The mixing ratio is 1:1

Precautions when casting

I mixed the material and made the casts in good ventilation. I used glasses, wore a mask and had on a shirt with long sleeves. I also wore gloves.

Casting results

Moulds and casts

Here you can see the mould and the casts I made. The silicone buttons were released easily and the result was very good, but the polyurethan is stuck in the mould and will probably stay there forever. When I told Svavar Konráðsson about this he said that it might be good to keep in mind a basic rule that if you want to cast a piece with a hard material, you should use a soft mould (f.ex. silicone) and if you are casting a piece made of soft material, then you can use a mould made of hard material.

Fortunately, I can use either of the silicone buttons that I casted in my final project, so I am happy with the results.

Learning outcome from group project

Conclusions

3D printed mould works very well but the lines from the 3D printed object are visible on the cast.
You have to think carefully about how you are going to release your cast object from the mould. It would have been much easier to release the casts from my 3D printed moulds if I had made Taper angle.
It is hard to get rid of bubbles if you don't have a vacuum chamber and I do not have such one in Fab Lab Austurland, but the small bubbles did not make much difference in the cast mould.
You have to work fast with materials that have a short pot time/working time.
Make moulds that do not use more material than needed. I made my moulds from more material than needed and could have made them smaller.
Create a step at the top of the mould. This thinner edge makes it easier to get the cast out of the mould.
Be careful when you pour the material into the mould. Bubbles can easily get trapped in the cast. This was not easy and all my casts from Acrystal and Jesmonite had small bubbles/failures in them.

Learning outcome from individual assignment

Learnings from individual assignment

I learned how to export a 3D model as an .stl file from Fusion to use in VCarve
I learned how to import a 3D model into VCarve
I learned how to create areas on material that I wanted to be machined.
I learned how to create a mould from Renshape Tooling Board.
I learned the basic rule that basic rule that if you want to cast a piece with a hard material, you should use a soft mould (f.ex. silicone) and if you are casting a piece made of soft material, then you can use a mould made of hard material.

Design files

Design files for group assignment

3D printed mould - .f3d file

3D printed mould - .stl file

Fab Lab logo - .dxf file

Fab Lab logo - .svg file

Design files for individual assignment

Mould with too large finishing paths

Mould for buttons - .f3d file

Mould - .stl file used in Vcarve

Mould - .crv file

Mould Rough path - .spb file

Mould Finishing path - .spb file

Mould with smaller finishing paths

I used the same .stl and .f3d file as here above

Mould - .crv file

Mould Roughing path - .spb file

Mould Finishing path - .spb file