Design Specifications For Die Castings
The design of die castings must consider seven aspects: wall thickness, casting fillets and draft angles, reinforcing ribs, casting holes and minimum distance from holes to edges, rectangular holes and slots, inserts, and machining allowances.
Design Specifications for Casting Fillets
Generally, all parts of a die casting should have fillets (except at parting surfaces) to ensure smooth metal flow during filling, facilitate gas escape, and prevent cracks caused by sharp angles. For die castings requiring electroplating and coating, fillets allow for uniform plating and prevent paint buildup at sharp corners. The fillet radius R of die castings should generally not be less than 1 mm, with a minimum fillet radius of 0.5 mm.
Design Specifications for Inserts in Die Castings
First, the number of inserts in a die casting should not be excessive. Second, the connection between the insert and the die casting must be firm, and grooves, protrusions, knurling, etc., are required on the insert. Third, inserts must avoid sharp corners to facilitate placement and prevent stress concentration in the casting. If there is severe electrochemical corrosion between the casting and the insert, the insert surface needs a protective coating. Finally, castings with inserts should avoid heat treatment to prevent volume changes caused by phase transformation of the two metals, which could loosen the insert.
Design Specifications for Die Casting Wall Thickness
Thin-walled die castings have higher strength and better density than thick-walled ones. Therefore, the design principle for die castings should be: while ensuring sufficient strength and rigidity, the wall thickness should be minimized and kept uniform. Practice has shown that a wall thickness of 2.5-4mm is generally suitable for die castings; parts with a wall thickness exceeding 6mm should not be produced using die casting. The impact of excessively thick or thin walls on casting quality: If the casting wall is too thin in the design, it will result in poor metal welding, directly affecting the casting strength and making forming difficult. Excessively thick or severely uneven walls are prone to shrinkage and cracks. Furthermore, as the wall thickness increases, internal defects such as porosity and shrinkage also increase, similarly reducing casting strength and affecting quality.
Design Specifications for Machining Allowances in Die Castings
Generally, due to the limitations of the die casting process, when certain dimensional accuracy, surface roughness, or geometric tolerances of die castings do not meet the requirements of the product drawings, companies should first consider using finishing methods such as straightening, polishing, extrusion, and shaping to repair them. If finishing cannot completely solve these problems, certain parts of the die casting should be machined. It is important to note that when machining, a smaller machining allowance should be selected, and the surface unaffected by the parting line and moving parts should be used as the blank reference surface as much as possible to avoid affecting machining accuracy.
Design Specifications for Draft Angles of Die Castings
When designing die castings, structural draft angles should be included in the structure. If no structural draft angles are available, process draft angles for demolding must be provided where necessary. The direction of the draft angle must be consistent with the demolding direction of the casting.
