Aluminum mold shells

These molds can be made from CNC-milled or casted aluminum mold shells (a combination between both methods is possible as well). A mold made from a combined cast aluminum and CNC-milled shells can be manufactured. In addition, a lot of different materials in a mold (aluminum with steel) can be used for the manufacture of mold shells. 

Most molds are thin shell-like structures made from metals. Molds made from other materials (plaster casting, reinforced plastics, wood, etc.) are used for special applications. Lightweight cast aluminum and electroformed or vaporformed nickel molds, which are light in weight and low in cost, can be used. Aluminum molds are very popular especially for small to medium-size products. Aluminum has better heat... 

This cast aluminum rotational mold can be modified using inserts so that either a BBQ-Donut Half (Figure 1.175) with steps of invert or a half with motor and umbrella holder can be molded. The mold consists of 10 mold shells. 

The production steps of both applications differ from each other significantly. The complete construction of the mold shells and the design of the form separation and flanges have to be determined for the production of a machined aluminum mold. The manufacture of a mold begins mostly with the production of a positive model (per sample, drawing, or 3D data). 

The use of mold shells manufactured in an aluminum casting is advantageous for large and deep mold shells or for necessary follow-on molds. For the manufacture of aluminum casting mold shells, the casting molds made from sand or sand/ceramic molds have to be manufactured first. The aluminum casting process, shown in Figure 1.179, is done by hand. 

The wall thicknesses of the aluminum molds are very thick in comparison to the thin-walled sheet steel molds (1.5 to 3 mm). Wall thicknesses between 7 and 15 mm are used for casting molds (depending on the quality of the casting process). In the mold shells that are CNC milled out of an aluminum block material, a standardized wall thickness of 7 mm is established. 

Since the in-mold pressures in RIM are generally relatively low [50 to 150 psi (0.4 to 1.1 MPa)] a variety of tooling constructions have been used. These include machined steel or aluminum, cast aluminum or kirksite, sprayed metal or electroplated shells, and reinforced or aluminum filled epoxy (Chapter 17). With mold pressures usually below 100 psi (0.7 MPa), mold-clamp-pressure requirements can accordingly be low when compared to injection and compression molding. 

The aluminum bore tube is made vacuum tight so that it can be used as part of the vacuum impregnation mold. (A vacuum tight mold is essential.) The outer shell of the vacuum mold consists of sheet steel, which is wrapped and clamped around the coil. The... 

The AMPCO alloys recommended for process applications are essentially aluminum bronzes and nickel-aluminum bronzes. They can be produced in a wide range of forms-sand, centrifugal and shell mold castings forgings rolled sheet and plate extruded and continuous cast rod, tube and shapes. 

---