Image Credit: Oakridgelab
Design for Additive Manufacturing (DFAM)
When designing for 3D-printing (AM), it is important but also difficult to free the mind from ordinary construction constraints (freedom of design) in order to create new improved designs that utilizes the advantages of the new construction method.
When producing the digital component, one method is to disregard any production details and rethink upon the constraints and purpose of the component. Using Topology optimization is one example of rethinking.
“Topology optimization finds the best distribution of material given an optimization goal and a set of constraints” – Steven Hale
As an example in the figure below, constraints are set and direction and strength of forces are set. Softwares (e.g. ParetoWorks or Solid works) often have plugins to calculate the required geometry of a part. This geometry can then be adapted to a CAD (3D-computer drawing) model that also can be used for simulations (soft testing) and printing. If there is some local part of the component that seems sensitive to failure, it is possible to locally overdimension that particular part to ensure component durability.
Other aspects of DFAM are manufacturability, reliability and cost optimization. These aspects are process related and expert knowledge is required during the component design and preparation for 3D-printing. 3D-printing offers unique capabilities, e.g. customization, improvement in product performance and multi-functionality, but also possibly lower overall manufacturing costs and spare part production in remote locations.
A guide for using the SLM machine and the design steps preceding the printout can be found here: 2_1 Guide for metal printing_English
In order to illustrate advantages of 3D-printing, the following demonstrators were designed. A full report for these can be found here:
1. Clamp (for robots) – topology optimization
DfAM is here used to design a clamp in aluminium (AlSi10Mg) for demonstration purposes (topology optimization), with the aim to reduce weight enabling higher payload. Design process include:
- Creating a mass model with constraints
- Generating a preliminary 3D geometry using ParetoWorks
- Design of final geometry (based on previous topology optimization), taking manufacturing method into account and numerically pre-test the model using Finite element analysis and printability. Support structures are also added
After these steps, 3D-printing and post-treatment ensues. In this case, the component in volume is 0.033 dm³ and support structures are 0.005 dm³ (15%). Time and costs for printing four parts simultaneously is 16.5 hours at a cost of 1320€. Post treatment involve removing from build plate, milling bottom surface and glass ball blasting at ~25 minutes/piece.
2. Gas mixer – part consolidation
This demonstrator part (reduced assembly) was especially designed for 3D-printing and has only 2.2% support material. Design time was about 12 hours, including eight components consolidated into one piece. Four feet to stand, three channels combine gas into one nozzle outlet, with cooling/heating channels that spirals around the part.
For four components printed simultaneously, printing was made with 30 µm thickness at took 29 h at a cost of 580€ per piece. It required 30 minutes of post processing per part: 5 minutes to unfasten from platform, 20 min machining and 5 min blasting.
More on DfAM
“DFAM is the synthesis of shapes, sizes, geometric mesostructures, and material compositions and microstructures to best utilize manufacturing process capabilities to achieve desired performance and other life-cycle objectives.” -David W. Rosen
The steps during DFAM is roughly divided into:
- Manufacturing method and material
- Guidelines for process
- Material specific guidelines and restrictions
- Optimization of geometry
- Topology optimization
- Taking into account the special features of the manufacturing process
- Part orientation, support structures, tolerances, geometric feature min/max sizes, residual stress etc
- Minimizing post-processing
- Industrial design
When 3D-printing, advanced inner structures are possible to make, e.g;
- channels for gas or liquid flows
- channels for insertion of electronics such as sensors or lighting
- inner structures
Preparation for printing
When adjusting the CAD design and preparing for printing, some knowledge of the AM process is required since the final result and build cost may depend upon build orientation and design of support structures.
In this preparation step in DFAM, we will either give support or directly help to prepare the components for printing. Further guidelines will later be produced and put here for your convenience.
There are many ideas on how to reduce time needed during the design phase of parts and how to make it more automatic/supportive.
ISO / ASTM52910-17: Standard Guidelines for Design for Additive Manufacturing
VDI 3405 Part 3: Additive manufacturing processes, rapid prototyping – Design rules for part production using laser sintering and laser beam melting