3D Printed Mold Shell

Hi everyone this is my first tutorial so please don't do not judge strictly.

English is not my first language so I apologize for the mistakes :D

I work with silicone molds since 2012 and I made a lot of them, but I am still learning and trying to find interesting solutions, 3D printed Mold shell is one of them.

1. 3D Printer
2. Filament
3. Screws and nut
4. Two component silicone
5. Release agent
6. Sculpture Clay (Monsterclay is perfect)
7. Computer
8. Blender program
9. Netfabb program

Many propmakers are familiar with the process of creating shells for matrix silicone molds, this is a very hard and "dirty" process: future silicone surface sculpted with clay right on the product, then it is covered with fiberglass and epoxy or polyester resin.

Classic method require a lot of time, skills and different materials. Working with fiberglass and resins is hazardous to skin and breathing. But you get a very light and solid shell. Mistakes are very difficult to fix.

3D printed shell save your time, money and health, plus it is pretty beautiful) You can plan all mold details at the modeling stage. The 3D printer will do most of the hard work while you can do other things. With 3D printed shells you can do very complex mold shells with many parts.

All right, let's start!

To model the casing, you will need only two programs: Blender, Netfabb and the 3d model of your product.

Blender is a free program, you can buy it in Steam.

Netfabb is quite expensive, so you can use a student license or download from a torrent.

As an example of my product, I will use Smoke mask from Mortal Kombat from bkzthunder.

Open Blender and import the mask model. The first thing we need to do is to figure out where pouring hole and air vents will be located. Keep in mind that you need to put air vents wherever the air can be blocked.

In the case of Smoke's mask, I decided to place poring hole on the upper point of the nose and two air vents at the ends of the mask near the ears. Air vents should not be wide, about 2-3 mm is enough. Pouring hole - the larger the better, but we must remember that the plastic will harden in these channels and they will have to be trimmed. I made the pouring hole the same size as air vents - 3 mm and this was my mistake, then I had to cut silicone, since the plastic did not have time to pass through such a small hole, it is better to do 6 mm and larger.

Shift + A - add an object, select a cylinder, press the letter N (in the window that appears you will see the size of the selected object in meters, 1 meter is 1 mm by default. I tried to set the correct units in the program, but I still haven't figured out how it works, so it's easier to leave it as it is) and scale with the letter S (press X, Y, or Z if you want to scale with regard to a specific axis). Select the pouring hole and air vents through Shift, press the right mouse button and select "join".

As soon as pouring hole and air vents are placed, we can start to create shell parts borders for separating the two halves of the shell, it is also very important to pay attention to the location of this border, because its location will also depend on how easy it will be to connect and separate the halves.

In some cases, it is necessary to make shell out of 3-4 or more parts. In case of Smoke it was necessary to make three parts, but I made two, this was my mistake, I will show you how to fix such problem later.

Add the plane model through the same Shift + A operation, enter the editing mode through TAB, select Face in the upper left corner, right-click on the face and press subdivide.

Select two polygons on one side of the Y axis and delete through the X key by selecting Face (depends on the axis on which your object is symmetrical).

Next, in the panel on the right, select the wrench icon and press Add Modifier, select the mirror modifier, and choose axis to mirror your plane (If that won't work add another model and choose it with pipette in modifier window). Also in the modifier you need to tick Clipping this will stitch original and mirrored planes.

Now all actions with one half of the polygon will be repeated on the other half.

At this stage, you can remove the edge in the middle (select the edge, press X and choose Dissolve edges).

Using the S (scale), G (move) and R (twist) keys with X, Y, Z move plane to the place where the border will be, it is important to position it in right way so that one edge enters the model, and the other edge locate in about 10+ centimeters away from the model.

Select the edge between the edge that enters the model and the opposite and extrude it with the letter E. Make sure that that the border passes in the middle of the pouring hole and air vents, and its lower part is always inside the model. Extrude this border until it connects to itself.

After that, press Ctrl + R and place the yellow line about 1-1.5 cm from the mask where will be the future length of the silicone border. I recommend you exit edit mode, click Apply in the mirror modifier and copy border through Shift + D, but do not move it. Select a copy of the border, press TAB and delete all long polygons. Exit edit mode and add the Solidify modifier to both of our sides, setting the offset parameter to 0.

Now we can export our models individually in stl format to a separate folder through File - Export - stl (do not forget to press "selection only" in the window on the right) and sign accordingly.

Open Netfabb, add mask, pouring hole, air vents and small silicone border .

First you need to "treat" (red cross on the toolbar, follow the pictures actions) each imported object, including the mask.

When all models are treated, you need to select all models and perform a Boolean operation (merge) (merged Red and green balls on the toolbar).

So we got one solid object and now we need to imitate a silicone shell. Select the mask and then the right mouse button - Extras - Create Shell, in the opened window in Shell thickness we set 5 mm (optimal silicone thickness), on the right we choose Outer offset, below in Accuracy we put 1 mm, I do not recommend putting less, other way it will be too heavy model.

As a result we get this beautiful silicone shell)))

Choose silicone shell - Right mouse button - Export Part - as STL, sign as "Silicon shell without locks and poring hole" (Yes there will be another pouring hole but for silicone)

Go back to Blender, import our silicone shell model, hide everything on the top right, pressing the eye icon.

Now we need to make mold "keys" (keys are needed to keep the mold in the same position at each casting cycle) and pouring hole for silicone.

The Pouring hole for silicone must be pretty large, at least 3-4 cm in diameter. It can be located on the silicone shell border, or on each side separately, in my case it can be located on the border.

Make sure that the part that enters the silicone shell enters it completely and smoothly, without sharp angles, for this you can extrude the lower circle in editing mode and arrange it inside the silicone shell, scaling and moving.

You can also "pull" the silicone shell on the pouring hole tube by using the Sculpting mode (optional). I recommend to watch some training videos on the YouTube, otherwise this long tutorial will become even longer.

I advise you to make trapezoidal-shaped keys from cylinders: add a cylinder, scale to the right size and scale the top cover in edit mode, extrude bottom for a few millimeters.

I also recommend to add a "mirror" modifier - there will be half less work. Place keys on the surface of a silicone shell so that they drown a little in it, distribute evenly over the surface and do not forget about the reverse side of the silicone shell.

Select keys, pouring hole tube, big border (don't forget to use solidify modifier as we did with smaller border before) and combine into one file through the right mouse button - "Join", export them as a separate file and combine them with a silicone shell in Netfabb.

Don't forget to treat all models.

Now we can use Create shell as we did before, but the thickness should be 3 mm (with such thickness, mold shell will be strong and light, you can make it thicker, but as for me it is needless).

We get the Mold shell, but it is still raw, we need to finalize it.

First we need to cut the extra border, follow the instructions on the pictures. I forgot to tick "Only selected parts", so tick it to cut only mold shell. Remove cut part by right mouse click - remove.

Use a Boolean operation and "subtract" a silicone shell with a big border from the mold shell. Using the arrows below the parts list, we transfer the silicone shell file to the right column, the shape will be painted red, so it will be subtracted from green shell when we press minus.

Now we need to divide the shell into two separate files, right mouse button - Extended - Shells to parts.

Do not move it apart, I just did it for example.

Export models to Blender.

We still need to make holes for screws that will tighten two halves to each other and holes for air to exit.

I use screws М6, so the diameter of the holes I made is 6.2mm. We add cylinders with a 6.2mm diameter and 3-4 cm length, we set them along the perimeter of the border using the mirror modifier. Make sure that the cylinders are perpendicular to the border.

We also should make cylinders with a 2 mm diameter and locate them throughout the entire area of the shell, in places where air can get stuck.

Then we combine screws holes and vent holes separately, export and subtract from the shells in Netfabb.

Hurray! The mold shell is ready!

So this is a finished Mold shell ready to use) I recommend to use PLA filament. You can also use transparent filament to monitor the silicone filling.

As I told you in the beginning I should make it out of 3 parts but I made only 2, that's why it was very difficult to pull out prototype from mold after pouring silicone. To solve such problem you can do this way: model additional borders, 3d print them, connect them with screws, solder one of the border to the main shell (I used 3d pen), cut the shell trough but not completely, left a bit material to save position of the shell parts, then connect borders with a screws and solder other bolder to the main shell, finish cutting the main shell, done!

Now you need to pour silicone in mold.

Make flat sheet with a thickness of 5 mm out of monster clay and put between prototype and mold shell, this will help position the prototype at the correct distance from the shell.

Then feel all gaps on sides and sculpt border with keys.

You can use Netfabb and split the silicone shell just like the mold shell, so you can find out the amount of needed silicone.

Connect mold shell with screws, make several clay balls and long clay stripes. Push clay stripes on borders seam.

Mix some silicone and start to pour it in the pouring hole, use clay balls to plug holes from which silicone starts to flow. It is better to do this with four hands, because you need to pour silicone continuously. If the flow is interrupted, an air bubble may form.

Wait for the silicone to cure, separate the mold shell, remove the clay, apply the release agent, close the mold and now you can pour the second part.

It's done!

I hope this tutorial was helpful for you))

You can visit my Instagram page if you interested to see my other projects - Gear_props