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Creation of Aluminium Moulds
Some useful indications on the proper use of selected Aluminium alloys in the design and creation of the mould:
 Differences in the thermal expansion coefficient in comparison to steel
Possibility of producing undercuts
Design with equal stiffness and possible oversizing
Possibility of superficial treatments
Exceptionality of burrs (mould sealing line)
Differences in the thermal expansion coefficient with respect to steel
The difference between the thermal expansion coefficients of aluminium and steel is something that is often underlined by toolmakers who broaden their sector by passing from steel to aluminium alloys.
However if the mould is entirely of aluminium alloy, an alternative which in most cases constitutes the best constructive solution, this aspect does not create any particular problems, in either injection moulds, blown moulds or moulds made with other technologies.
Possibility of producing undercuts
Given a drawing for a moulded part in order to construct the aluminium alloy mould, the same methods are followed.
From the mathematics of the moulded part comes the dimensioning of the mould. The typical thicknesses will be greater than the case of traditional steel moulding. In general, Al Thickness = Steel Thickness x 1.8 for the walls of the form, and Al Thickness = Steel Thickness x 1.4 for the bottom of the mould and for the mould carrier attachment area.
Design with equal stiffness and possible oversizing
Given a drawing for a moulded part in order to construct the aluminium alloy mould, the same methods are followed.
From the mathematics of the moulded part comes the dimensioning of the mould. The typical thicknesses will be greater than the case of traditional steel moulding. In general, Al Thickness = Steel Thickness x 1.8 for the walls of the form, and Al Thickness = Steel Thickness x 1.4 for the bottom of the mould and for the mould carrier attachment area.
Possibility of superficial treatments
Though the choice of superficial treatments for Aluminium alloys is very broad (chrome-plating, nickel-plating, anodic oxidation, chemical nickel-plating and derivatives), superficial treatments are resorted to only in exceptional cases: e.g. the chrome-plating of the moulding of transparent parts featuring optic qualities (windscreens, large protective masks).
Exceptionality of burrs (mould sealing line)
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The starting (the adjustment immediately before the first mouldings) of Aluminium alloy moulding must be performed with great care. The moulded piece card should contain precise information regarding the injection volumes necessary for correctly filling the cavity.
The procedure is the approximation by degrees when writing the 'mould card', 90% 95% 97.5% filling.
Excess volumes create burrs, and likewise burrs are caused by the improper operation of the press. In nine out of ten cases examined, the burr was caused by the wrong moulding cycle and only one by the mould.
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