Design for additive manufacturing (DfAM)

DfAM is a strategy that challenges industrial and mechanical designers to transcend the existing design paradigms, which guide and constrain designers when they design for traditional manufacturing technologies. Sometimes DfAM only involves redesign of existing parts for additive manufacturing (AM), for example, to reduce the mass or to consolidate several parts into one. However, one should not stop there, and should think in the direction of changing the internal and external geometry of products to improve the function or to customize their shape and function to needs of individuals or groups of users.

Optimization of product geometry based on the DfAM methodologies refers to specific design techniques that need to be developed to maximize the potentials of AM. These techniques are:

• Light-weight design (Complex design)
  • Topology optimization
  • Application of bionic principles and transformation of shapes from nature
  • Lattice and cellular structures
• Component consolidation (design of integrated geometries - several parts connected into one functional unit)
• Design for functional integration - multifunctionality achieved by shape
• Design to improve the function and performance of the work
• Tool optimization
• Customization

The freedom in creating the geometry offered by AM enables design of the parts according to the same functional requirements as conventional parts, but with less material, which is called “lightweight design”.

Topological optimization of parts for AM is done to achieve the following goals: mass reduction, stress reduction (i.e., elimination or reduction of stress concentration), obtain a uniform voltage distribution and reduce waste during production.

Designing products by emulating shapes from nature goes a step further in topology optimization. After the phase of topological optimization using mathematical methods, the shaping of parts follows by mimicking structures from nature.

Lattice and cellular structures represent a type of complex designs used for topological optimization for AM. These are structures that consist of unit cells made of nodes and rods (or load-bearing walls) that periodically repeat in space. By combining different densities of nets, distances between nodes, wall thicknesses and cell shapes, one may adjust the mechanical characteristics of these structures.

Conventional technologies often impose on designers the need to simplify parts of complex geometry by dividing them into several simpler elements. The final shape is then obtained only after the assembly or welding process. AM, on contrary, allows integration of geometries, i.e. combining of elements adjusted for traditional production technologies to obtain a more complex part, which will be produced as a whole in a single process. This means that the geometry and function of a single AM part will correspond to the geometry and function of a whole set of elements after assembly or welding. This process is called “component consolidation” or “consolidation of parts” in the literature. The consolidated part is also lighter than the assembly for two reasons: first, due to the omission of additional connecting elements (screws, nuts, etc.), and second, due to the possibility for topology optimization during the redesign.

“Functional design” mainly means unification of multiple kinematic functions in an assembly, which can be produced as a single part in one AM process, but requires production of several parts, assembly and adjustment when it is produced by traditional technologies. In most cases, the design for functional integration comprises the design for AM of moving parts with joints, such as various assemblies with hinges, sliders, guides and similar components that are, by redesign, joined in a single part.

The important property of AM to produce objects of almost arbitrary shapes enables the creation of machine parts of complex geometry, with thin walls and internal channels and cavities. Such mechanical structures have superior fluid flow properties because they offer the ability to control direction that other technologies cannot achieve, which is of great importance for the flow of fuel, air or coolant.

Another important application of design for function and performance improvement is the production of plastic injection tools or blowing tools with conformal cooling channels.

With these tools, it is necessary to provide additional cooling, i.e. tempering (setting the optimal, uniform temperature filed over the surface of a tool), which is achieved by introducing internal channels through which the coolant liquid flows at the appropriate temperature. When this type of tool is made with conventional technologies, the shape of these channels is limited to combinations of straight lines. Additive technologies enable production of tool inserts with internal channels for conformal cooling, in which the channels follow the contour of the tool at an optimal distance from the surface of the tool. Conformal channels, in addition to being able to follow the contour of the mold, are not limited to circular cross section, but can be optimized according to the requirements of mold temperature control, so they may have oval, triangular or any other shape. Such channels allow the coolant to pass through the mold in accordance with the shape of the mold cavity, which further ensures uniform and faster cooling. The process of design of a tool is based on combination of standard components (using the traditional technologies of making tools) and innovative components (inserts) made by AM.

Customization design means adapting the product to the needs (requirements) of a specific user (customer) or a specific group of customers. One of the most important advantages of AM technology is that they can manufacture different parts in one production process without additional costs, which makes them the optimal solution for production of customized products. In this way, these technologies make are transforming the concept of mass production of identical parts into mass production of customized, mutually different, parts.

Individual design has the most important and the greatest role medical and dentistry applications. AM is used to directly manufacture personalized prostheses, splints and fixators that provide better comfort to the patient, because the shape is adapted to his constitution and body shape.