Deciding on a metal casting process can be complicated, and is impacted by a number of things such as budget, volume, and the type of object being cast.
Two common methods of casting are sand casting and permanent mold or “chill” casting. Both of these methods work by pouring the molten metal into a three-dimensional mold. However, the nature of the mold is very different.
What is Sand Casting?
Sand casting is characterized by using sand as the mold material. A pattern is used, around which the sand is compacted. This forms a cavity in the form of the component to be cast. The sand used is a blend of silica grains with five to 20% clay or bentonite and two to eight percent water. Sand can be shaped by hand or by machine.
Sand casting can be used for cast iron, copper alloy, and aluminum alloy, and steel. It is commonly used for some automotive parts.
Advantages of Sand Casting
The primary advantage of sand casting is lower production costs. Other advantages include:
- The ability to fabricate very large components.
- Works for both ferrous and non-ferrous materials.
- Low cost of post-casting tooling.
Disadvantages of Sand Casting
However, sand casting also has some disadvantages:
- It yields a lower degree of accuracy and, thus, is not good for precision parts with predetermined size and weight.
- It carries additional material to be machined and as a result, also weighs more. Both in which increases costs for the parts.
- Products tend to have a rough surface finish.
- The cooling rate is slow, which results in a looser grain boundary, due to the fact that the mass of sand has to cool.
- The sand mold is broken open after the cast, meaning you have to make a new mold for each object cast.
What is Permanent Mold Casting?
Permanent mold casting, on the other hand, uses a reusable mold made out of steel or copper alloy. The mold is then coated with a graphite mix to ensure that the cast metal does not stick to the mold.
Advantages of Permanent Mold Casting
The primary advantage of permanent mold casting is the much greater accuracy of the cast. Other advantages include:
- More environmentally friendly. The mold itself does not produce waste and molds can generally be reused or recycled once the run is over.
- The casting chills very fast, with the part often ready in seconds. Which makes the grain boundary much tighter. In fact, we can guarantee a minimum conductivity level of 98% IACS, and casts will routinely exceed this.
- The part is more homogenous, eliminating hot spots or poor connections.
- The part tends to have higher strength.
Disadvantages of Permanent Mold Casting
- Permanent mold casting has one specific disadvantage, namely the high cost of the mold. This makes it not effective for small production runs, and it is often only used when accuracy is critical.
Conclusion: Permanent Mold is Better
If you are producing parts that need to be made with a high degree of accuracy and within tight tolerances, permanent mold chill casting is your friend. Despite the initial cost, permanent mold casting can provide parts with high strength, superior surface finish, and better dimensional tolerances.
Although permanent mold casting is not suitable for prototypes or small quantities due to the cost of the molds, the cost is well worth it when looking at larger runs. With the high conductivity levels and lack of poor connections, permanent mold cast parts can handle anything you want to throw at them.
Burnstein Von Seelen does high-quality permanent mold casting, using virgin metals to provide you with the best parts for applications which require strength, conductivity, and precision.