The primary criterion of good design for die-casting is that it shall provide for rapid production with a low reject rate. The design should also allow for easy removal/trimming of flash. Diecastings to be used for decorative applications should be simple to polish – and clear of polishing residues – before plating. These requirements reinforce one another: smoothly faired contours and an absence of sharp edges, for example, promote easy cavity filling and good casting quality as well as aiding secondary machining operations.
Though components with hard edges and ‘squared-up’ forms do not present any real production problems to the die caster, it is unrealistic to expect the same quality of surface finish on such parts as is attainable with the more rounded form. Furthermore, rejects will certainly be higher with sharp edged forms and maximum strength will not be developed because stresses set up during contraction are localised at the angles instead of being spread evenly throughout the structure. Also, sharp outside corners are stress raisers and are prone to cracking so that the die life is reduced.
Generous radii and the provision of the maximum draft allowances compatible with the function of the component, are among the most valuable contributions the designer can make to the economical production of any die cast component. Well-radiused corners reduce stress concentrations, and adequate draft minimizes the risk of distortion, or further stressing, when the casting is ejected. Given these two essentials, the most intricate castings can be produced successfully; without them, the simplest part is troublesome to maunfacture.
Diecastings can be produced which are excellent in surface finish, dimensional precision and minimum draft. All such requirements in maximum degree combined in one die casting will rarely if ever be required. For this reason, these guidelines cover values consistent with speed, uninterrupted production, reasonable die and tool life and maintenance cost, normal inspection packing and shipping costs. Conformity to these guidelines assures dependable service and lowest cost. Special requirements for finish, dimensional accuracy, etc., beyond the guidelines may be specified when required. Consultation with NORFRAN may result in these requirements being incorporated with little addition in cost.