Joining Metals      

There are many ways of joining metals but I am sticking to the most common types, welding, brazing, soldering and soft soldering along with nuts and bolts and riveting. I have also decided to include casting because it is a way of forming metal and is used when you want to make complicated shapes (a bit similar to injection moulding in plastic).

Look at the animation below to see a few ways of joining.

Riveting

Welding

Sand Casting

In its simplest terms sand casting is when a wooden pattern is made which is identical to the item you are making. The wooden pattern is then pressed into a special type of sand (green sand) and the result is an impression in the sand of your pattern (imagine pressing your hand in wet sand). The pattern is then removed and hot metal poured into the shape you made. Once you have the pattern you can press it into the sand as often as you like to make as many of the item as you like. The expensive part of this process is making the original wooden pattern and keep preparing the sand mould. This method of casting allows very large numbers of large items to me made (mass production) or reasonable numbers (batch production). Take a look below at the process in a more detailed way.

If you print this page the writing is clearer.

The wooden pattern is placed on the floor and sand rammed round it. The box which surrounds the pattern is called a drag,	The pattern is first coated with powder (parting sand to make it easier to take the pattern out of the sand.	Another box is placed over the drag (called a cope) Which is also rammed with sand. Into this little holes are left so you pour the metal into the drag.	These holes are made by placing sprue pins in the cope sand. Little ventilation holes are put into the sand so steam can escape when the wet sand gets hot.
The cope in now removed from the drag and the pattern taken out. This leaves an imprint where the pattern was.	Small channels are cut from the mould (hole where the pattern was) to the sprue pin holes. All loose particles of sand are blown away.	The cope is now placed back on top of the drag and hot metal poured down the sprue hole. It fills the mould and eventually comes up the riser hole at the other end of the mould.	When cool the sand is broken away and the parts which are not needed (shown in red) are sawn off and used again in the next melt.

Die Casting

This is similar to injection moulding in plastic. A metal mould is made (die) and metal is run into it producing an item the same as the inside of the die (not unlike a jelly mould). Usually small models are made using this method. Unlike above the sand does not need to be prepared because the die is all that is required. As with sand casting, the die is the expensive item and once this is made any number of the items required can be made using the die. Mass production makes an enormous number and batch production makes about 1000 or so.