Understanding customer and part requirements is key to achieving a design that maximizes part performance while minimizing part and assembly manufacturing costs. A good product design considers part function, application, application environment, die casting capabilities, ease of assembly and good tolerance practices. Rapid prototyping parts are very useful in discovering part design and tooling problems, are often used for new part designs. Sometimes early involvement of potential suppliers will help optimize product and mold designs, help reduce part costs.

 

Maintaining uniform wall thickness throughout part is critical. When a uniform wall thickness transitions to other structural features of product, transition area needs to be gradual to avoid abrupt transitions. Uneven wall thickness can lead to poor molding quality and part fit issues.

 

Uniform cross-section improves metal flow in mold to speed up casting cycle. Excessive differences in cross-section can cause turbulence in flow of molten metal. This can trap air, causing porosity. In addition, castings with large differences in cross-section tend to experience irregular shrinkage.

 

Wall thickness is highly dependent on part size, part geometry and supplier capabilities. Typical die castings for electronic control products usually have a basic wall thickness of 2.5~3.0mm. Thin walls are usually only suitable for smaller parts, such as products around 100mm*100mm, which can be designed with a wall thickness of 1.5mm. Reason for this is that when molten metal hits relatively cool mold, it immediately begins to solidify. This happens faster in parts with thinner walls, so metal can't flow very far before solidifying, therefore product size won't be too large.
Minimum thickness of wall should be consistent with practical capabilities of good casting, still provide adequate strength and stiffness. Cost-effective designs are those that use the least amount of material, have the fewest casting and product performance issues. Metal flows in different directions as it enters mold, and when mold is filled, metal must hold together. If walls are too thin or metal moves too far, when metals meet they won't be hot enough to join together properly. Result is a "cold seal," which creates seams in casting that can lead to leaks or weaknesses. If metals don't meet and leave a hole, it's called underforming, a short shot, or a short shot. It is therefore important to evaluate mold filling during mold flow analysis.

 

It is also important to avoid parts designed in a structure that makes mold susceptible to thin walls, which will increase mold maintenance costs and shorten mold life.
In the early stages of design, when preliminary structural design plan is completed, mold supplier needs to be consulted as soon as possible to achieve the best design and process trade-off.

Draft angle refers to need to give mold core or other parts of mold cavity a certain taper or slope to facilitate demoulding of casting. Die casting surface, which is usually perpendicular to mold parting line, requires a draft to allow good ejection of casting from mold.
Draft depends on many factors: wall thickness or type of draft surface; height of ribs/ribs or side walls, etc.; die cast alloy material.
Casting with zero draft can be specified in local areas to eliminate final machining operations, subject to supplier approval or agreement. Manufacturing capabilities of these molds can be leveraged by us when necessary to gain economic advantages and reduce product weight. In other cases, a standard draft angle can be used to facilitate release from mold and reduce mold maintenance.
Almost all structures perpendicular to parting plane require draft. Because casting shrinks, draft of inside walls is more important than draft of outside walls.

 

Standard draft angle range for die-cast aluminum alloy inner walls is usually 1.5~2°. Drawing notes usually specify draft angle, except for individual features. Design always defaults to maximum draft value allowed. Each draft angle will add 0.017 mm/mm to dimensions. Lower walls should have a steeper draft. If design permits, a draft angle of 3 to 15 degrees may be used for walls with a height less than 12.7 mm.