Tuesday, July 2, 2013

mold reading

this article I hope to explain, in terms a lay-person might understand, the way that I make all my Master-moulds. It will hopefully be of use to sculptors who wish to understand the nature of what I do to their beautiful little green sculptings. It may also prove of interest to others who are considering making moulds for themselves, I wish you the best of luck.  Those who have made moulds before may find that this article asks more questions than it answers. If you would like to talk further on any of the matters raised, then I would be delighted to here from you.

1)      Plan the work.

This is basically a good look at the work in front of me, how many moulds I plan, how I intend to space and angle them on the rubber. I make sure all the parts that are necessary are present and correct and that there is no damage to greens before I start working. Also I look for potential weaknesses on the models that need to be taken in to consideration.
The minis that I am using to illustrate the process are some of the Frothers Unite UK 2007 Sculpting contest entrants.
These 6 items were made as personal miniatures as additions to the Asylum game.

They represent various level of technical difficulty, and all present issues that I deal with on a day to day basis, for all minis that pass through my care.

2)      Prepare rubber.

Preparation work necessary before the miniatures see the mould, reducing the amount of rubber in the "Can", encouraging the rubber to move and seating the core nicely.
This is a pair of 9” (227mm) organic rubber disc's.
Firstly I remove any excess rubber; I want as little material in the mould as I can manage. I measure the thickness of the rubbers and consider the depth of the miniatures compared to the capacity of the moulding Can.
Rubbers can be easily separated into their laminated layers
Then I cut the rubber to seat it correctly in the Can, removing V’s of rubber to allow some give.

Cutting away an area to seat the central steel "Core" in the Can.
3)      Cut cavities.
Showing how each individual mini is catered for in the mould, why things are cut in and in what direction they face.

OK, from the start I have to work from two assumptions, one, that we can get anything to cast. Metal flows like water when it is hot and getting it to flow in to all the right areas is only a matter of applying a few basic physical laws. Secondly that the sculptor in question has done everything possible to protect the miniature from the necessary stresses of the moulding press.
Casting is the easy part.
What is more difficult is building up a relationship with the sculptor where they know what is necessary for the successful moulding and I can be trusted to do as little damage to every piece that passes through my hands.

What I initially assess when I consider a miniature is the “natural plane” of the piece. Almost all miniatures sit on a natural plane that they were made on. Some miniatures like this Asylum beast, the natural plane is obvious,
but on others like this Idol, it is less so.
I always try and work against this natural plane on Master moulds, minis need to sit on the Production mould in the easiest way possible and pressing most minis on the same plane twice, leads to distortion of the mini in its final stages.

Rubber is cut in the following way, the item (in this case a base for the slotted miniatures used in the game) is placed on the rubber.
Pressure is applied, *hard*, with my thumbs and fingers.
This leaves a mark in the rubber to act as a guide to the cutting
The final rough cavity should leave the piece neatly seated in anticipation of the pressure the vulcanisation process needs.
Like so.

This is how I chose to cut the minis concerned for this mould.
This has moved as much as possible off the natural plane, dropping the piece on a 45 degree angle. Separate small parts concerned with the miniatures are seated closely near-by.
This idol has been turned a full 90 degrees off the natural, a perfect way to ensure that the pressure of both mouldings is shared equally across the mini.
This very two dimensional “Green creature” has been seated to take as much pressure as possible away from the natural plane, but the issues are compounded by the width of the mini.
Things sticking out a long distance from the central body of the piece, in this case the out-stretched arms, reduce the chances of movement off the plain.

This on the other hand, was very nicely formed on a central core of the mini and I was able to move the piece 60 degrees from the natural to preserve more bulk in the miniature.
As you can see (on this, the previous and next picture) small amounts of rubber are added to support areas where pressure may damage delicate items.

The final piece was the most technically challenging.

Moving metal in three separate directions away from the body of the piece is never easy, but can be done by careful placement of the mini in relation the final spinning metal. This item also presented issues with “depth” I can normal allow about 23mm as a maximum depth, this piece is bigger than that. When this occurs extra layers of rubber added to the out-side of the mould to thicken those areas
4)      Prepare for vulcanisation.
Showing the care that is taken in the pre-press stage. Making sure that the mould goes in as planned, that everything is present and that no damage is done in the vulcanizer.
The mould is emptied of everything and talc is then applied, the blank disks are then warmed for a while to ensure that the rubber is nice and soft before the miniatures are re-introduced.
The warm disks are place in the moulding can and the minis returned to their prepared places. The steal core which forms the centre of the finished mould is put in place and some locating studs are added to the outside to hold the finished rubbers in place.

the top piece of rubber is then carefully placed on and the steal lid of the can lifted into place.

5)      Press.
It’s in the can, the pressure is on and we sit and hope.
The process of Vulcanisation changes the soft, raw rubber that is shown earlier, into the tough, durable finished item which is able to with-stand the heat and stresses exerted by casting using white metal alloys.
Unfortunately rubber needs heat and high pressure to make this chemical transformation, which is why fragile minis need to be protected as much as is possible.

This is the vulcanising “press”, two steal heating elements with the pressure controlled by an hydraulic jack.
The temperature is set at 150 degrees and the pressure could be as much as 25 tonnes per sq cm.
When vulcanisation is complete the mould is removed and cooled.

6)      Open & pre-cut.
the next stage is all about opening with care, removing miniatures, locating missing parts, and pre-cutting of vents.
All master mould are opened with care, much effort is put into ensuring that as little damage is done to the original sculpts, after there moulding, as to ensuring that they get through the press successfully.
This is the mould when opened and the sculpts carefully removed.
As much as possible is collected and returned to the sculptor. Sculptors who have access to good existing pre-moulded parts are much more prolific and productive, when compared to those starved of usable parts.

Much of what is shown could easily be re-moulded at any time.

At this stage I also cut the vents which draw air away from the extremities of the moulded cavity. Surface Vents are those on the internal surface of the mould, most surface vents are not vented directly out of the mould.  Drill Vents are those drilled through the depth of the mould to release trapped air.

7)      Cut, the major cuts.

Finally the mould is cut to allow the metal to flow through it. Large channels are cut to open the cavities to the core of the mould where the hot metal will fall during casting. Most minis have only one opening to the metal flow, but occasionally more are needed.
Metal is encouraged to fill the whole cavity in one even stream, with a back-vent taking away most of the expelled air/gasses.

8)      Casting.

I will write a full description of our casting process at another time but needless to say the mould is spun in a centrifugal casting machine, hot white metal is poured into the core and the miniatures cast, like this.


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