The process of casting manufacturing involves the pouring of a molten metal into the cavity of a mold designed to produce a specific shape, which is then allowed to cool and harden. After the molten material solidifies, the newly-formed workpiece is extracted from the mold and subjected to finishing processes that results in the final product. Metal casting, including aluminum casting, is often used to create complex hollow and solid shapes. Casting is used for various industrial applications, including those in the aerospace and automotive industries.
Below we cover three popular casting processes – Sand Casting, Die Casting, and Investment Casting. The choice of casting must be made based on various considerations related to engineering, design, manufacturing, and cost.
Sand Casting
Sand casting usually depends on materials that are silica-based. These can include naturally-bonded or synthetic sand. The sand used for casting is typically spherical, finely ground grains that are packed together tightly into a smooth molding surface. This form of casting tends to reduce the possibility of cracking, tearing, and other defects by introducing shrinkage and flexibility into the cooling process. Clay may be added to strengthen the sand, helping to strengthen the bond between particles. Sand casting is often used to produce engine blocks.
The level of accuracy produced with sand casting is generally lower than with other methods. The products yielded from this process, including aluminum casting with the sand casting method, also tend to have a comparatively rougher surface finish.
Die Casting
The die casting process molds materials under high pressure and is often used for non-ferrous metals and alloys such as aluminum, copper, zinc, and tin. A lubricant is coated onto the surface of the mold to keep the temperature of the die under control and make material extraction from the mold easier. With this casting method, molten metal is placed into the die under high pressure, which is maintained until the solidification of the workpiece occurs.
The benefits of die casting, including when performed for aluminum casting needs, such as uniform design, high components dimensional consistency, closer near net shape and size tolerances, and less of a need for machining after the casting phase.
Die casting does have high tool costs, which means high volume production runs will increase its cost-efficiency. Also, products made with die casting are not often structural in nature since it is challenging to ensure the mechanical properties of a die-cast product.
Investment Casting
Investment casting utilizes a disposable wax pattern for each part cast. The wax is placed into a mold. It is then removed and covered with refractory material and a binding agent. This is often done in multiple stages to create a thicker and thicker shell. Various patterns are put together onto common sprues. After the shells have hardened, the patterns are inverted and then placed into ovens for heating to remove the wax. Then, the molten metal is emptied into the remaining shells. The resulting piece which has hardened reflects the wax pattern shape. The refractory shell is then removed to display the hardened casting. This method of casting is often utilized in the power generation, automotive, and aerospace industries, including for turbine blades.
Investment casting benefits include:
- Exceptionally precise and accurate dimensional results.
- Ability to cast ferrous and non-ferrous metals
- Produces exceptional quality surface finish and component details
- Can produce parts with complex geometries and thin walls
The quality surface finish produced through investment casting (for metal and aluminum casting) can compensate at times for the higher expense associated with this casting method.
Sand Casting vs. Die Casting
The mold types used for each method are different. Sand casting uses sand mold, while die casting uses metal molds. Dies casting is more ideal for parts that require dimensional accuracy and is ideal for higher production runs.
Sand Casting vs. Investment Casting
Sand casting produces a rougher surface finish and can produce net shapes within 1/4 of an inch. Investment casting produces excellent surface finishing and is the optimal choice for highly complex designs. Sand casting offers greater versatility with weight and size capabilities than investment casting.
Die Casting vs. Investment Casting
The differences between die casting and investment casting include:
- Die casting uses reusable molds while investment casting uses disposable molds for each new cast.
- Die cast parts may require some post-processing in order to achieve desired finishes and dimensions, while investment casting generally requires little to no additional processing.
- Investment casting is ideal for production runs in the low to medium volume range, while die casting is more suitable for production runs in the high volume range.
- Die casting may only be used for non-ferrous metal casting, while investment casting can be used on both ferrous and non-ferrous metals.
When it comes to aluminum casting and other metal casting, the casting methods mentioned above have their own unique benefits and drawbacks that make them ideal for certain manufacturing requirements.
The significant benefit to using any casting method is you end up with a part that is close in size and weight to the end product of your part. Yes, it will involve finish machining but it saves you a both machining time and metal over machining your part from a solid piece of Aluminum, whether from a wrought or cast aluminum plate.
At Howard Precision Metals we often get asked what is more cost effective, machining a part from a solid block or from a casting? As mentioned above the tooling for a cast part needs to be amortized over the run quantities. If your quantities are low, it normally does not justify tooling up a mold for casting. However, if you have high run quantities that will keep increasing over the lifetime of a part, a casting should always be considered. Should you need Aluminum cast or wrought blocks to machine your prototypes from prior to casting Howard Precision Metals is here to help.
To learn about the standard and custom aluminum products we offer, including custom aluminum extrusions, give us a call today at 800.444.0311 or request a quote.
