Production Method of Light Alloy Wheels
Light alloy wheel production methods are broadly divided into two categories - Casting where melted materials are made solid in dies and Forging where materials are pressed with a high pressure.
Melted aluminum alloy is injected by natural gravity into dies – also called GD (Gravity Die Casting) method. This method is most spread in Japan and the method is called as such due to its procedure of only using natural gravity to inject melted material into dies. There are dies of different types called respectively upper, lower, and horizontal molds to which melted material is injected through casting runners and sprues
Low-Pressure Casting Method
Although gravity casting method is easiest way of producing wheels, as the melted alloy is injected only by natural gravity, there is a tendency of its molecular structure leaning toward the bottom of dies.
Low-pressure casting method is used to make the procedure a perfect one.
The unique feature of this method is that there are closed crucible set under dies to hold melted alloy. The melted aluminum alloy is injected through conduits called stoke while added low-pressured gas in the crucibles.
Die Casting Method
In this category, what is mainly used for production of light alloy wheels is the nonporous die casting method which is also called PF (Power Free) die casting method. More specifically, in this method, air is ejected from dies before melted aluminum alloy is spray-injected directly.
Squeeze Production Method
This is a method that has realized a level of strength by using casting method that can be compared with that of forging method. Inject melted aluminum alloy into dies and apply a high pressure of 700 to 1000 kg/cm2 while it is not yet fully solidified to forge the aluminum alloy for homogenization. With this method, it is possible to build out products of a fine metallographic structure without pores or vapor in it.
Products made through this method have higher strength, toughness and ductility and can save weight of 10 to 15% compared with one-piece wheels in the same size produced through low-pressure casting.
Hot forging method
Generally speaking, forging represents a method where a metallic material is pressed with a high pressure to be made into an intended form and it is divided into certain categories by its processing.
Out of them, what is used for light alloy wheels is the one called hot forging where an aluminum alloy material called billet is pressed with a high pressure while heated to 400 to 500 degrees C. This process is repeated several times to form the material into an intended shape.
Molten Metal Forging Process
Literally, melted aluminum alloy is formed into an intended shape while being pressed. Molten metal is injected into dies and pressed with a high pressure of 300 to 1500 kg/cm2 in its solidification process, which has earned another name (high pressure forging method) for the method.
SSF (Semi-Solid Forging Method)
The unique feature of this method lies in the fact that electromagnetically-stirred aluminum alloy called MHD-A357 is used.
MHD-A357 alloy has better-balanced non-dendritic solid phase and liquid phase compared to the conventional A-357 aluminum alloy.
The process begins with cutting A-357 billets into fragments in an appropriate shape to form slags and then preliminarily heat them in a hot-air oven to 500 degrees C or so. Preliminarily heated slags are then exposed to the final heating in a high frequency electric induction furnace.
Heated slags are automatically set onto the metal injection gate at the upper part of the dies in the pressing machine. They are then stored in the shot sleeve before pressure-shot by a hydraulic piston into an intended form.
The SSF method draws a lot of attention as it can provide both detailed expression of the conventional casting method and a high rigidity of forging. It is also very effective in weight saving that is one of the basic requirements for light alloy wheel production.