Casting metal, like any other industrial method, requires a significant amount of accuracy and fidelity towards the design that was intended for the product. However, things are rarely as simple as executing a method of production because uncalculated variables can rear their heads and ruin a design with bumps, tiny gaps, and the topic we will be discussing today: shrinkage.
For the finished product to have the desired degree of precision, the rate of shrinkage must fall within a predetermined range
The most that can be done in situations like these is to maintain a controlled amount of change and put appropriate measures in place to prevent such changes from spiraling out of control
Before beginning the process of die casting, there are a few fundamental safeguards that one can put into place as well as a few things that person should keep in mind
Investigate the Levels of Shrinkage and Expansion.
The first thing one needs to keep in mind is the characteristics of the material that has been selected. This may appear to be an obvious point, but things quickly become more complicated when one has to take into account the various strains of alloys, the levels of shrinkage versus contraction, and the properties of materials contained within the alloy. It is essential to conduct research on the materials in question to determine how they adapt to different temperatures.
There are three distinct types of material shrinkage that can occur with molten metals: the contraction that occurs during liquid cooling, the shrinkage that occurs during solidification, and the contraction that occurs during solidification. There is a general rule that applies to metals, despite the fact that every material experiences these in different degrees of expansion and contraction as well as different boiling and solidification temperatures. When temperatures get close to the liquefying range, liquids start to contract, which can change the rate at which their densities shift quite rapidly. In this section, it is essential to apply as little superheat as is humanly possible in order to reduce the amount of shrinkage and micro-cavities.
The next thing to keep an eye on is the shrinkage that occurs during solidification. The amount that die-cast alloys contract is significant, but it is important to keep in mind that aluminum contracts the most during the solidification process, at an astounding 6.5%, while magnesium and zinc only contract by approximately 4% or 3% respectively. It is important to note that aluminum with a higher percentage of silicon can lead to a decrease in the overall part volume shrinkage. This is something that should be taken into consideration. Because the shrinkage that occurs during solidification is the primary cause of porosity in the finished product, it is essential to have an accurate estimate of the amount of size shifting that will occur before selecting the material and establishing the temperature.
The most notoriously difficult aspect of solid mechanics to calculate is solid contraction. In this regard, the amount of shrinkage that occurs is proportional to the volume of the material that was used to make it; more specifically, the volume decreases by one inch for every inch of the material. There is a very helpful summary of the calculations on diecasting-mould.
Keeping an Eye on the Temperatures
Again, this might sound obvious at first, but when you consider all of the things that you have to keep in mind when properly monitoring the temperature flow, there are some major tricks of the trade that one should remember to keep in mind.
Heating the metal to achieve appropriate molten characteristics is necessary when die-casting; however, this should be done without the metal completely reaching its liquid state. In extreme cases, overheating can cause the material to contract unnecessarily, which in turn can result in imperfections in the part. Casting metal requires careful monitoring of the cooling process, which is the other side of the coin. Because metals can lose as much as 100 degrees Celsius in temperature every minute, CNC machining services is best practice for certain CNC aluminum die casting services methods, such as vacuum assisted die casting, to keep treating equipment ready to shape the object before it becomes completely solid.
