For us to get started with the HD Pattern System we're first going to have to make a clear silicone mold.  I know most of you are probably familiar with making vulcanized rubber molds in a traditional way, but we're going to show you how to make clear silicone RTV molds that are going to have an exact duplication of cavity from the master. There's going to be no shrink and they can be used either for wax injection or for the HD pattern process.  Traditional molds and mold frames are very very large and they waste a lot of silicone. It's not necessary to make a mold this large.  What we're going to do is show how we can make molds for wax injection or HD using a much smaller micro frame, using much less silicone, but still have the long life we've come to expect from traditional mold making processes.

When using silicone clear RTV you can basically use anything as a master.  You can use a traditional silver master, you can use a milled wax master, you can use a mastering compound that HD provides and we'll explain this later, or you could use any of the RP outputs from rapid prototyping machines.  In this case we're going to be using models that have been produced in the EnvisionTEC machine.  This is one of their materials called HTM.  It's moldable but not castable.  This is another one of their materials and this is called photo silver.  It is also non-castable however we have the benefit of being able to detail these in other words sand these down, make them perfect and high polish like we would normally do with a silver master to go into mold making.  And of course we can use the traditional metal master as our master to make the mold.

We're going to move now to the preparation of the mold frame, the mixing of the silicone, and the production of those silicone molds are going to be using again for either wax injection or the HD process.   Traditionally when some of you have made silicone RTV molds or RTVs that are not silicone you've used the very large and somewhat cumbersome frame and the reason you've used these tall frames is that you would mix the silicone by weighing it, blending it, and then pouring it into the mold frame around the master.  This frame is so tall because when you vacuum to remove air bubbles, you have to allow for the expansion of the material.  And again we're producing a heavier mold and it's really necessary.  What I'm going to explain is that you really don't have to have a tall frame.  We do not need to vacuum to produce a perfect bubble-free mold using only overpressure.  So after we've mixed the silicone, we're going to pour it in the mold frame and we're going to put pressure only on it and it was going to remain under pressure through the entire curing process and again there'll be no bubbles inside.  

So now we're going to be talking about placing the masters into the mold frame and to use that we're going to be using the micro frames.  Now the micro frames again are going to save a great deal on silicone consumption.  This to produce this size mold we're going to spend about a dollar fifty to make this mold.  We can expect to get as many as a thousand injections in wax or somewhere between one and two hundred in the HD patterning process.  

Let's look at what's in the micro frame mold kit.  First of all you're going to have the frame itself, stainless steel, you're going to have two glass plates that we're going to sandwich against the frame, and then you've got the sprue former which is how we're going to attach the master to the sprue forming base, put it into the mold frame, you're going to have what I call a hinge bar in this kit and I'll get to that later.  This will go above the pattern which means that when we make the mold we can cut to this and create a mold that actually opens more like a wallet than the traditional two-part.  This keeps the mold in very good registration and never allows the mold to lay open on the countertop work and can be contaminated.   There's also rubber bands and a short sprue that's used to put the master model into the mold frame.  So let's get started building some frames.  

We've talked about the various components that come in the micro frame kits and just to refresh you, these are available in five sizes.  They range from half-inch, which I actually consider to be my most popular size to use for virtually everything, all the way up to an inch and a quarter for things like award rings.  In making molds in clear silicone using the micro frames, remember this you only need to have about two millimeters of free space between the outside of the master pattern and the glass plate of the mold so we're able to make very thin molds and our strategy here is that we want a very flexible mold.  So rather than trying to work inside the confines of a frame like this in this sprue base, we're going to actually set our patterns up with the sprue former and screw in it separately, then put it back into the mold frame and set it up from there.  So let's get started.

I've got a couple of little elephants that we've made that are very very thin.  These were produced on the EnvisionTEC machine in this material called HTM.  Again it's a material for mastering but not for direct casting.  So I'm going to set up this pattern inside the sprue former and to seal it in place I'm going to be using yellow sticky wax.  Yellow sticky wax as most of you know is something that we use around the bench a fair amount, we'll use it also for attaching these parts to the tree when they move into casting.  So find yourself a little bit of sticky wax and use your wax pen.  You're going to melt the sticky wax and you're going to secure the model to the sprue base.  

I'm just finishing up on preparing the masters that are going to be in the micro frames and then we're going to start pouring silicone.  You may see me put the addition of what I call the hinge bar and this is going to come into micro fame kits.  The hinge bar serves several functions.  It basically is a way to keep the silicone from hitting directly on to the master that may be fragilely set in wax into the mold frame and it also creates a hinge when it's molded in place in the mold it's going to create a hinge in the mold when we're done which means that we have to not cut as much in heavy registration like we would normally do and we're always going to go back in perfect registration.  A great way to store the molds,  If you're wax injecting you're going to find that by putting the hinge bar just above the prongs or the highest portion of a ring, you can then cut those lines directly to this and this will be a manifold so the hinge bar, the hinge that is formed, actually is a way for the gas to escape because venting silicone sometimes can be a tricky operation.  So I'm just going to put in this hinge bar by using again a little bit more of the sticky wax and I'm going to put a drop underneath the bar to keep it from shifting when I pour the silicone in.  And from here we're going to move on to assembly of the mold frames so that they can fit in either the NoVac unit or the Firefly unit for curing.  If we had a long bar clamp and wanted to make up to 20 we could use that in the silver bullet unit so we can cure again under pressure in the silver bullet unit, in the NoVac unit, which actually has no heat to it at all so you'll have to do an overnight curing of RTV silicone, or the Firefly.  And the Firefly we're going to use the heat that's generated from the LED lights to bring this up to 120 degrees, which is the absolute perfect temperature for rapidly curing silicone, in which case the silicone molds are going to be made in about an hour and a half to two hours.  So now I'm assembling the frames and I do that by keeping them basically upright and I'm stacking them in two because I can get up to six in the Firefly and that's what we're using today to cure the molds.  And I'm going to separate by a piece of glass in between and make kind of a sandwich between the two molds.  So I've got my masters are in the mold frames, I've got three pieces of glass, I'm going to put a common glass in between, making kind of a sandwich, and then I'm going to cover with rubber bands.  I'm going to hold them together with rubber bands.  Now it's really important to always use a minimum of three rubber bands and the reason I'm telling you that is if one should happen to break you don't want to have a mess in any of your curing units.  The silicone will cure and you'll be able to peel it away you just might have wasted the time that it took to prepare these individual molds.  

Now you want to be concerned when you put these mold frames together that you don't make them and stack them too wide to fit into the Firefly unit if that's what you're using for curing.  So you'll see here I put a five-eighths with a half-inch, I can put a three quarter with a half inch.  So I can put up to six molds in for curing at one time.  I'm going to talk a little bit about the silicone law and preparing these.  The most important feature of silicone RTV is how long you mix it and what the room temperature is that you started with to affect the time of curing.  If your silicone is set up in a warm part of the country and it's been acclimated to room temperature over the weekend without air conditioning, it might be in the upper 80s by the time you go to mix it.  The difference from a normal room temperature of around 70 degrees to 85 to 90 degrees in the silicone is probably going to change the curing time by half.  Now the way silicone RTV works is it's very much like two part epoxy.  You're going to put two pieces two separate components together one is a base material and one is a catalyst.  When they're stirred together they begin to cure on their own.  We can accelerate the curing again by the addition of heat, but be very careful if you want to use something like an old wax pot, be very careful that you limit the heat to 120 degrees Fahrenheit during the curing cycle.  Okay so I've got two more molds to set up.  Now again I'll refresh your memory a little bit about the masters that we're using to make molds.  We can use masters from the Digiwaxx machine, the new Pico machine, the EnvisionTEC machine if you're making your masters in solid scape and want to mold those directly you can do it, they're going to crumble like a cookie but before you pour the silicone around them, you want to spray them down with a little bit of silicone mold release to make sure you seal them well.  They'll break when you cut the mold but you will be able to produce a mold from a solid scape pattern.  Milled wax of course is always an option.  Now you're going to be seeing more and more tooling board things like chorion to be used as a material to put inside the mill and have your pattern directly done in to that material.  Now the advantage to that is that you'll be able to take the chorion or tooling board and remove any sort of machine lines that may be put on during the manufacturing process of the milling machine from the STL file.  Okay we're about ready to make silicone we're going to move on to the weighing and the mixing of the silicone RTV compound to make these molds.