Moulding ABS rod

[bernardgreen]

I am trying to mould ( or thermo form ) a simple foot shape at the end of 4 mm diameter ABS plastic rod but am not getting good results with my trials.

The aim is make legs for clay models of Sean the Sheep that a friend like to make.

I am putting the rod through a hole in the back of the mould and then softening the protruding end at the front of the mould. When the rod is soft I am pressing it into the mould.

If the mould is cold the then the material skins before it fills the mould and the shape is malformed.

If the mould it hot enough to prevent that then the rod softens behind the mould and deforms.

Any other ideas ?

 

[ColJack]

injection mould it?

 

[Trazor]

I presume you have a split mould.
The first thing I would look at, is drilling a very fine hole in the split line, to allow air to escape.
If you drill anywhere else, you will have trouble removing the excess plastic pushed up the hole.

I would then ream the hole in your die to 4 m/m dia, to obtain a smooth hole.
A piece of 4 m/m silver steel will then be a nice sliding fit into it.
You then need to arrange a method of forcing the 4 m/m silver steel, in behind your 4 m/m plastic, as you heat it up, perhaps some sort of toggle clamp arrangement.

If your inlet hole is too short you will need to extend it....Hope that gives you some ideas......

 

[bernardgreen]

No I had not been using a split mould as I had thought that moulding a near cone shape could be achieved with a solid mould.

That does release when moulding at low temperature but the poor flow into the narrow end of the cone prevents good shape being formed.

At higher temperatures shape is good but release is difficult.

So tomorrow I will bite the bullet and create a split mould out of brass.

Thanks

Bernard

 

[Trazor]

Did not realise it was conical, can you not drill a venting hole in your existing tool, at the point.

You would need to clean the vent hole each time with a drill.

Good luck.

 

[bernardgreen]

A trial split mould made out of plastic ( no brass in the junk box ) with a vent hole worked well. But as expected it distorted when the ABS was hot enough to be very fluid.