Metal Casting or Mold Making?

[kb18951452]

I don't know the correct terms for this stuff, and that mostly of the reason for this post.

A friend of mine does Fire Hydrant Repair. He knows about my homebuilt CNC machine and asked me if i were interested in making some parts for him to send to the foundry(?) I usually deal with cabinetry, but these things are made from wood and plastic, as he showed me.

He explained to me that a shape is made on two wides of a board. Half of the shape on one side, and half on the other. The boards are framed, and "green sand" is packed ontop, then its tuened over and the sand cavity is left. The same is done for the other side. The part i would be making is removed off to the side, and metal is poured into the cavity of the sand molds when placed together.

So here is my question.

What is this actually called? Casting? Forging?

Where might i go to begin my journey of understanding on making the mold part? He is a machinest, so these parts are made a bit larger so he can machine them down to the right size, and put threads on them.

Anyone?

Thanks allot.

[Geof]

Try Googling 'pattern making' or 'moldboard'.

What you describe is a mold board with half the pattern on each side. As you mention the pattern has to be made oversize for a machining allowance in certain areas and also to compensate for shrinkage. It also needs 'draft' which is a taper on ends that would otherwise be square so that these can be drawn out of the sand mold withou pulling away the corners. Then it includes other thoings like 'feeders', 'risers' and 'sprues'. These are to create channels in the sand mold for the molten metal to pass throu and allow the trapped air in the mold to escape and to provide a reservoir of molten metal adjacent to large cross-sectional areas in the casting allowing metal to flow in as these areas cool and shrink.

Google all the words in ' ' and you should dig up plenty of information. Pattern making is as much an art as a technology and it can take a lot of experience to make good patterns.

EDIT: corrected typo, pattern not patter. Google would have come up with something very different.

[beone]

It's 'pattern making' not patter. a pattern is an object the size and shape of what you want to mold. When it is mounted to a board this way it is called a 'matchplate'. The majority of casting made in the world are made from matchplates. This is exactly why I made my cnc- to make patterns for my foundry. Pattern making is a great if dying specialty. Remember, the patternmaker is the highest paid carpenter

[kb18951452]

Beone and Geof

Would you mind sharing your knowledge with me?

I'd like to get into the patterns making field with my CNC. I live in SE Texas and there is a great demand for it around here. The closest pattern maker i know of has a 2-6 month turnaround time. There's room for me, but i don't really know where to star. I've been running my CNC for a while and feel quite comfortable around it. My problem seems to be that those who make them now have lots of experience because they did it in a machine shop for ears before breaking out solo.

The first job looks simple enough for me to make from wood on my CNC, nothing fancy in it at all, the tricky part, however, seems to be knowing how to do all the other things i never would have realized without seeing a complete one in person, like the channels, and the reservoirs.

Any suggestions on where i might begin? This first job is for a friend of mine, and he doesnt mind me "learning" on this project. He said he'd be able to show it to the foundry and get it "approved" before it was cast to make sure it would work without wasting the effort.

A machinest friend of mine told me i should get into the metal business because thats where the money is. This might allow me to stick with wood and get into metal.

I'de love to talk to you more about this.

[Geof]

I cannot tell you much more than I did. My experience with casting was doing a Machinist apprenticeship with a company making brass and aluminum parts which had their own foundry. I did get involved in pattern design, also since then I have made patterns for my own products and had them cast but all that was 20 amd more years ago.

If you have the opportunity to learn as you go with a first project I would say go for it. You should see if the foundry people are willing to give you advice and assistance; maybe in return for some low cost work.

Good luck.

[advt001]

Depending on size 2-6 month leadtime is about right, but carpenters we are not.

[svenakela]

Here are some sites to look at for a start.
http://www.efunda.com/processes/meta...ting_intro.cfm
http://en.wikipedia.org/wiki/Sand_casting


There are also heaps of books on the subject, but if the object to be moulded is simple it's not that hard to make a mould. Ask a smaller foundry company for some tips and howtos and you are on your way.
On good thing with sand and plaster moulding is that if the part needs changes it's easy to add extramaterial if needed (such as 2K filler or extra pieces of wood) then you simply re-mill the cores.

[Geof]

Depending on size 2-6 month leadtime is about right, but carpenters we are not.

I wondered if someone would pick up on that. Sculptors maybe? I think I am a very good Machinist but I have seen stuff made by a top notch Patternmaker I wondered how they did it.

[advt001]

KB ask away, I admire you for trying this and my first suggestion would be to actually go to the foundry and watch them make some of your friends castings.Geof I used to work with a man that could do as much with a Buck chisel as I could do with a Bridgeport and he was quicker.

[Kipper]

KB ask away, I admire you for trying this and my first suggestion would be to actually go to the foundry and watch them make some of your friends castings.Geof I used to work with a man that could do as much with a Buck chisel as I could do with a Bridgeport and he was quicker.

I'll second that...or see if there's a metalcasting group that meets up near you.

[SPEEDRE]

Hi I'm a first class journeyman pattern maker and I'll share my knowledge with you. Yes this is called " board mounting ". It make it easier to mold and pour. If the shape is an easy one you'll have to consider the shrink percentage, i.e , what is the metal to be poured. Each metal to be poured has a different percentage of shrink, such as 1/10th or 1/8th per foot for cast iron. The usual sequence is, to submit the drawing for a quote, if you accept the price the foundry will specify dimensions for runners, gates and basins, if needed and send you the instructions. Sometimes, the foundry will do the rigging as it's called, and the gating themselves. Being as a hydrant may be made of Brass or Bronze you must find a foundry that cast said material. They seldom cast both at one foundry. Is this good for a start? send my a PM if you need more info.

[wudbutcher]

I've been a patternmaker for 32 years and no one has every called me a carpenter...just a sign of the times I suppose. Looks like another lesson in patternmaking isn't needed. Glad to see some of you guys out there. We're getting a large Onsrud router soon so things are gonna change around here, another sign of the times!