As you know, An excellent die casting designer should be familiar with the die casting mold manufacturing process and the production process, So that the design of the die casting parts, can very easily made out, and easy to manufacture, and reduce manual operation. also save cost.
High Pressure die casting part design is the most fundamental link to ensure the quality of die casting, The rationality of the structural design and process directly determines the degree of difficulty in mold making, product dimensional accuracy, die casting process parameters, production and installation efficiency. Today we will discuss the points to note in the design process of aluminum alloy die casting, so as to reduced design changes, machining difficulties, cost savings and increased strength.
High Pressure aluminum die casting molding principle
Aluminum alloy die casting should have die casting mold, die casting machine, aluminum alloy material three elements work together. The principle of die-casting process is to use high pressure to flow metal liquid into a precision metal mold cavity at high speed, and the metal liquid cools and solidifies into casting under pressure. Cold and hot chamber die casting are the two basic ways of die casting process. In cold chamber die casting, Robots poured metal liquid into chamber, and then the pressure plunger advances and presses the metal into the cavity. In the hot chamber die casting process, the chamber is perpendicular to the crucible and the liquid flows automatically into the chamber through the feed port on the chamber. After the liquid solidified, the die open and ejector pin push the casting parts out, completing the entire die-casting formation process.
High pressure die casting material selection
|Easy to die-cast metal, economical for making small parts, easy to coat, strong pressure resistance, high plasticity, long service life of cast parts.
|light weight, high dimensional stability when making complex and thin-walled castings, corrosion resistance, strong weather resistance, good mechanical properties, high thermal and electrical conductivity, good strength in high temperature environment.
|easy to carry out mechanical processing, high strength to weight ratio, is the lightest material in die-casting metal.
|high hardness, strong corrosion resistance, the best mechanical properties of commonly used die-casting metals, anti-wear, strength close to steel.
|Lead and tin alloy
|high density, high dimensional accuracy, can be used as special anti-corrosion parts. Due to public health considerations, they cannot be used as food processing and storage equipment.
Aluminum die casting Characteristics
|Aluminum die-casting parts
|high production efficiency
low processing cost
easy to achieve mechanical automation in the production process.
high dimensional accuracy of the casting
good surface quality
good overall mechanical properties
|easy to produce defects such as porosity, flow marks, abrasions, depressions, cracks, under-casting, etc. These defects make the die-casting appearance quality and mechanical properties decline
in order to avoid the above problems, the die casting parts design is very important. we need to optimizing the structure, and reduce the defects.
Aluminum die casting design key-points
Die casting parts design is base.it will effect mold and manufacturing, such as parting line, branch runner, ejector pin, mold structure, and manufacturing difficulties; also will effect alloy shrinkage, casting accuracy, the type of defects, etc.
1.Uniform Wall Thickness
The wall thickness of die casting has a great influence on the quality of the casting. Take aluminum alloy as an example, thin wall has higher strength and good denseness than thick wall. Therefore, in order to ensure that the casting has sufficient strength and rigidity, the wall thickness should be reduced as much as possible, and keep the wall thickness uniform.
A. Casting wall is too thin, so that the metal fusion is not good, affecting the strength of the casting, while bringing difficulties to the molding.
B. wall thickness is too thick or seriously uneven is easy to produce shrinkage and cracking. With the increase in wall thickness, casting internal pores, shrinkage and other defects also increased, also reduce the strength of the casting.
Die-casting wall thickness is generally ~ 4mm appropriate, over 6mm parts should not be used die-casting.
The intersection of the die casting parts should have radius (except parting surface area), so that material flow smooth for filling, easily vent air, and can avoid cracks due to sharp corners. For those plating and finishing die castings parts, radiu area can coating easily, and prevent the accumulation of paint at sharp corners. Generally, radius should not be too large or too small, too small die-casting easy to cracking, too large will be shrinkage, Normally we take: 1/2 wall thickness ≤ R ≤ wall thickness
|Thickness of 2 connected walls
|Equal wall thickness
|Unequal wall thickness
Remark: For zinc alloy castings, K=1/4; for aluminum, magnesium and alloy castings, K=1/2
In order to eject parts out of the mold smoothly, reduce the push-out force, core extraction force, increase mold life, in the design of die casting, should have enough draft angle in the structure. So as to reduce the friction between the die casting parts and the mold, easy to take out the casting, also make the casting surface is not scratched, to ensure the surface finish.
|Minimum draft angle for the assembling surface
|Minimum draft angle for non-assembly surfaces
|Outer surface α
|Inner surface β
|Outer surface α
|Inner surface β
|Aluminum magnesium Alloy
Bigger draft angle, easier to eject part out die casting tooling, it will be more important for those parts with deep wall.
tanθ=X/H; θ=draft angle; H=wall height or rib height; X=the reduced wall thickness (or the amount of tilt deviation).
Usually products with more precise design will require smaller draft angle, that is, when the product is deeper (higher), its tilt amount X needs to be controlled within a certain range, for example, for a product of 100mm high, if it is a product requiring precision, the upper and lower deviation amount is expected to be controlled within 0.15 mm, tanθ=0.005, θ≈0.25.
The setting of rib can increase the strength and rigidity of the part, and at the same time improve die casting process. However, attention must be paid to.
A.The distribution should be even and symmetrical;
B.The root of the connection with the casting should have rounded corners;
C.Avoid crossing ribs;
D.The width of the ribs should not exceed the wall thickness.
E.Rib draft angle should be bigger than the casting cavity draft angle.
generally; we take 2/3~3/4 of the wall thickness for rib.
5.Die Casting Hole
Die casting holes should be cast as far as possible, which not only can make the wall thickness uniform, save material, also can reduce machining hours.
|Minium hole diameter d(mm)
|Maxium hole depth(mm)
|Min Draft angle for hole
6.Text, logo, pattern
Logo or Text can directly made on tooling or die. use convex pattern. The height of convex pattern is bigger than 0.3mm, it will be easy for mold manufacturing and extend tooling life.
After die-casting out the casting, can use laser for text, logo. it will be very nice effect.
Shrinkage is the percentage reduction in size when the alloy solidifies from liquid to solid ; and cools to room temperature; the shrinkage formula as below.
K=(L mold – L piece)/L piece
Remark: L die is the cavity size, L piece is the casting size.
shrinkage is related to the structural ,wall thickness, chemical composition of the alloy and process factors. such as, Zinc alloy shrinkage is generally: 0.6%~0.8%
A. The external thread can be cast out, need keep 0.2~0.3mm machining allowance.
B. Although the internal thread can be cast, the core in the die casting mold is rotated by a mechanical device, which makes the mold structure more complicated and increases the cost. Therefore, the base hole is usually cast first, and then machined into internal threads.
|Minimum thread outside diameter
|Max. thread length