This post covers the production of an aluminium last. Surpringly, as I saw in this last factory in Taiwan, it is a really intense, old school hand made process. Even the molten aluminium is poured by hand from the super hot over.
Click the Read More link below for all the pics and info on the process.
NEW- Aluminum Last Making Video
see post: http://www.firstpullover.com/2010/05/aluminum-last-making-video.html
As mentioned in part 1 (how to make a plastic last), aluminium last are every common in mass production of shoes because they can be made fairly cheaply (even though there is lots of labor involved), and they can also be recycled after use. As you'll see later in future posts of factory visits, the amount of lasts a factory has in inventory can quickly accumulate, and storage is big problem. In this respect, being able to recycle an alumimum last is a big advantage. All things considered however, plastic lasts are still more common in quality athletic footwear production because the fit, sizing and shape is more accurate. A solid plastic last will change shape less in different temperatures compared to a hollow aluminium last.
The process of making an aluminium last is called sandcasting. This is a common mass production process for aluminium and metal products including faucets and some things that dont need too much detail.
The first step of sandcasting to to make a positive core from sand that is the same as the shape of the last required, only differening in dimension a little bit to account for shrinkage of the final aluminium part (the hot aluminium after cast will shrink when it cools down).
This core is made using two halfs of a pattern made from aluminium. Like making sand castles on the beach. The sand is a special kind of sand that packs well and has some sort of binder material in it to help it stick together.
The second part of the process, is to prepare the mold. The mold is a 4 sided aluminium box called a flask. There is a top and bottm mold parts. The top is called the cope flask, and the bootom is the drag flask. The process starts with what will be the top part of the mold, flipped upside down. Sand is put into the bottom container (cope flask) until it is about halfway filled.
At this point a plastic last that is the same shape as the aluminium last they are trying to make is buried halfway into the sandfilled box. It is used to make a cavity in the sand. Here you can see the lastmaker using the other part of the mold (drag flask) to scrape of the excess sand so the filled box is perfectly level to the top. The sand is packed well into the box and around the last.
The white powder on top is some sort of release powder so that that the sand in the other half of the mold wont stick to it when it is put together.
The plastic last is then removed from the box of tightly packed sand, and small foam spacers (the little white squares in the picture) are put in place where the plastic last was. These spacers are will create a space where the aluminim will go. When the hot molten aluminium is poured into the mold, these spacers will melt away and disappear.
The sand core that was made in the first part is then carefully placed into the cavity on top of the spacers.
The bottom half of the mold is then added on top (the drag flask) and filled up with sand and packed tight.
The whole thing is then flipped over and the can be filled with hot molten aluminium that is poured into the mold through a small that is put into the sand that goes into the space inside where between the sand core and the sand all around it. This is the casting process.
The result is a hollow aluminium last. For production typcially at least a few thousand lasts are needed depending on how many shoes are being made at one time.