Die casting is a method which is used to produce complex and predominantly thin-walled components, using low-melting light metals such as aluminum, magnesium, copper or zinc and their alloys. The complexity of the shape is achieved by the high pressure applied when injecting the material into the tool (die casting mold) and the resulting high flow rate.
Coolable and heatable tools can be used to achieve high dimensional accuracy and surface quality along with good mechanical and physical properties through relatively homogeneous microstructures. An important factor is the controlled cooling of the die cast parts in the mold and the positioning of the sprue. Typical casting defects such as gas inclusions, blowholes and hot cracks might occur in components produced by die casting. Die cast parts are mainly used for metallic lightweight design, for example in the automotive industry.
Casting Only Profitable in Large Quantities
However, die casting molds are very expensive and the production process is time-consuming. This is mainly due to the fact that, after design and simulation on the computer, the molds often have to be produced from the solid block of material using machining processes such as milling in order to achieve the required high surface quality. In most cases, cooling channels and holes for the suspension and mechanics have to be added later. As die casting tools are very expensive, their use is only economically worthwhile above a quantity of about 30,000 parts.
Additive manufacturing is currently mainly used to produce individual parts and small series. However, there are now numerous processes that are included in the definition of additive manufacturing. To produce metallic parts, powder bed-based processes such as laser beam melting, electron beam melting or binder jetting are widely used. Methods with higher construction rates include wire-arc additive manufacturing (WAAM) or laser deposition welding. Processes that are typically used to produce polymer components are also adapted by the addition of metal powders for the manufacture of metallic components (for example, the BMD process from Desktop Metal, or the ADAM process from Mark3D). The parts are subsequently compacted like metallic sintered ones. In principle, the light metals used in die casting can also be processed by additive processes. Laser-based processes with green instead of the usual red lasers have been developed for copper alloys and above all pure copper can also be processed by electron beam melting.
AM Offers Several Advantages
Depending on the desired component properties and general conditions (cost, complexity, post-processing effort, process speed, component size, etc.), different processes must be used. Additive manufacturing offers the following advantages over conventional processes such as die casting:
- Almost any complexity without additional costs
- Small batch sizes without additional costs
- Easy and quick adaption/modification of the component
- Flexible production on demand
However, even the fastest additive manufacturing process cannot (yet) keep up with the process rates of die casting. Especially large numbers of complex components that can be produced in die casting cannot be economically produced with additive manufacturing.
Nevertheless, additive manufacturing is attractive for die casting foundries. As the production of specialized tools is extremely expensive, the potential of additive manufacturing can be fully exploited. The high degree of design freedom offered by additive processes allows the integration of holes and holders during the construction process. Moreover, 3D printing allows complex shapes and better functions to be mapped. Internal, complex and near-surface cooling channels - which were previously not possible - can now be realized. Worn tools can also be repaired by processes such as WAAM or laser deposition welding, which eliminates the need for expensive re-production. It is particularly useful to manufacture tool inserts by means of additive manufacturing, as this significantly reduces the construction time compared to complete tools, but still allows the advantages of the high complexity and internal cooling channels to be exploited.
Additive manufacturing with plastics can also be an interesting option for die casting foundries. These processes are often less expensive than those for metals and, above all, allow prototypes and models to be realized quickly and easily. This reduces the development time for new tools and products.
New Customers and Markets
Finally, the direct production of small series and individual parts, which is uneconomical for die casting foundries due to the costly tool production, is a possibility to gain new customers and markets through additive processes. The existing know-how about processing and properties of light metals as well as the correlation between microstructure and mechanical and physical properties can be adapted to additive manufacturing. This enables companies to develop new expertise and expand their portfolio.
However, it should be considered that, given the current state of development of machines, a lot of process-specific know-how must also be developed and applied. In order to control the processes, many parameters must usually be defined and their effect on the component must be known in order to predict the component’s properties. Especially if individual parts are to be manufactured, non-destructive testing of the components is necessary to avoid the cost-intensive production of samples.
