Volumes of production
High-pressure die-casting is strictly for high-volume production.
Unit price vs. capital investment
Economical unit price is obtained by mass-producing highly complex parts, which eventually drives down the relative cost of the expensive tooling that has to be designed to withstand repeated injection of molten metal at high pressure.
Speed
Fast, although the removal of flash as a separate process adds to the time.
Surface
Excellent.
Types/complexity of shape
Ideal for producing complex, open-walled parts in metal, especially those with thin wall sections. Unlike investment casting (see p.224), high-pressure die-casting requires draft angles.
Scale
Up to a maximum weight of approximately 100 pounds for an aluminum component.
Tolerances
Reasonably high level of tolerance, but shrinkage can sometimes be problematic.
Relevant materials
Metals with a low melting temperature, such as aluminum and zinc, which are by far the most commonly used materials. Others include brass and magnesium alloys.
Typical products
Chassis for a range of electrical products such as PCs, cameras, DVD players, furniture components, and wet-shaver handles.
Similar methods
Investment casting (p.224) and sand casting (p.228), which allow the casting of larger parts and require less capital investment, but demand higher tolerances. Gravity die-casting is a much older process and is employed on a much smaller scale of production than high-pressure die-casting.
Sustainability issues
The low melting points of the metals used in high-pressure die-casting require lower temperatures and quicker cycles than some other processes, such as MIM, so the process consumes less energy and releases fewer emissions. However, excess flash material after casting requires additional trimming, which adds to energy use and waste. At the end of their use, this can be reclaimed and recycled to reduce the use of virgin metals.
Further information
www.castmetalsfederation.com
www.diecasting.org
Ceramic Injection Molding (CIM)
Product |
Dental bracket used in braces [pencil sharpener is for scale] |
Materials |
99 percent Alumina |
Manufacturer |
Small Precision Tools |
Country |
US |
Date |
2010 |
The image illustrates a specific technology from Small Precision Tools that allows for molding ceramics such as dental brackets for braces at a micro scale.
Ceramics provide a hard, wear- and corrosion-resistant solution for many engineering challenges that other materials are rarely able to meet. The injection molding of ceramics allows for complex shapes to be created in a process that borrows a great deal from the injection molding of plastics. The technique is suitable for scales of production from one-off research prototypes to mass-produced components for commercial products. Ceramic injection molding (CIM) has been especially effective within the medical field, to make components for pacemakers and surgical instruments that need to be micro-miniature, with exceptional tolerances, as well as being biocompatible.
The most suitable type of ceramic powder is chosen and mixed with a binder that allows the mixture to flow and become moldable. The binder is a key aspect of the molding process and is used because it has a lower melting point than the ceramic powder, which enables the two materials to be separated at a later stage. A specially made machine with greater corrosion strength than traditional injection molding machines is used to feed the ceramic and binder mix into the mold cavity. The corrosion strength is required because of the abrasiveness of the ceramic that is being molded.
Once the component has cooled the mold is heated until it is just high enough to melt the binder material (but not the ceramic), causing it to evaporate and leave behind just the ceramic material. The finished part can be sintered or undergo hot isostatic pressing (HIP) in order to remove any stresses caused during molding and provide further strengthening.
– Complex and intricate parts that would otherwise be difficult or even impossible to produce in ceramics can be achieved.
– Production of molds can be costly and time consuming.