Additive Manufacturing Teaches Designers New Tricks
Considering what is required to design additive parts can illuminate the value of understanding all manufacturing processes, including subtractive ones.
Design methods directly affect manufacturing costs. Every component characteristic has an impact on manufacturing. Consider size and shape, complexity/intricacy, surface finish/coatings, hardness, dimensional tolerances and geometric tolerances. For each of these aspects, it is easy to spot distinctions that govern the related manufacturing cost. Generally, large, complex components are more difficult to produce than small, simple components. Fine finishes commonly require longer machining times than coarse finishes. Hard workpieces are more difficult to machine than soft ones. Workpieces made to less stringent tolerances require more elaborate processes than those requiring exacting precision.
Given these realities, design engineers must make every effort to ensure that designs are appropriate to the manufacturing equipment being used. Unfortunately, many design engineers have little or no manufacturing experience, so they may not fully understand the processes involved. Most, for example, have not actually worked on a shop floor, so they have no first-hand knowledge of the negative impact an inappropriate design decision can have on manufacturing costs.
Most machine tools used today fall into the category of subtractive manufacturing. This methodology has existed since we first pounded a stone into the shape of a wheel. With subtractive manufacturing, bits and pieces are removed from a chunk of material to shape it into a finished component.
Design engineers have always had the benefit of extreme diversity in subtractive manufacturing methods. There is a subtractive manufacturing process for even the most obscure design technique. While just about anything is possible with subtractive manufacturing, inappropriate design expectations always come with a higher price.
Additionally, design engineers have traditionally depended on someone else—a manufacturing person—to figure out how to produce designed workpiece attributes. This means the design engineer may not be aware that a design technique is increasing manufacturing costs.
Designing for additive manufacturing is very different. These are the first machines that require design engineers to understand the process to create successful designs. In fact, it may be the design engineer, especially for prototyping, that sets up and runs additive manufacturing equipment – and these machines often reside in or close to the design engineering department. Here are a few examples of what a design engineer needs to understand for a fused filament fabrication (FFF) 3D printing process versus a CNC machining process:
- Creating a printing profile (determining printing temperatures, layer height and infill, among other settings) can be compared to understanding basic machining practices for creating successful machining processes.
- Creating a slicing program for the 3D printer can be compared to using a computer aided manufacturing (CAM) system to create CNC machining programs in G-code
- Calibrating the 3D printer (bed leveling and nozzle height) can be compared to assigning program zero
- Determining the need for brims and rafts can be compared to determining the need for special workholding devices
- Ensuring model adhesion to the build surface can be likened to what it takes to make a workholding setup
- Considerations surrounding support structures (and how to limit the need for them) can be compared to considerations surrounding work-support devices like tailstocks and steady rests
- Changing the filament can be compared to preparing and measuring tool assemblies and entering offsets
- Determining and applying clearances for mating components can be compared to sizing adjustments for machined parts
Although these comparisons are limited to FFF 3D printers, similar issues impact other forms of additive manufacturing (such as resin and metal types). Admittedly, some of the comparisons are a bit far-fetched, but they should nicely illustrate the kinds of things a typical design engineer does not know about CNC technology.
If a design engineer does not fully understand the technologies surrounding the type of additive manufacturing equipment being used, they are in for a lot of failed prints. In similar fashion, if a design engineer does not fully understand the technologies surrounding any kind of subtractive manufacturing equipment, manufacturing costs are probably higher than they should be.
If the approach required for additive manufacturing could be applied to subtractive manufacturing, a design engineer would specify exactly how the required machine tools must be used to produce their designs. This would require a design engineer to know as much about subtractive manufacturing methods as they must know about additive manufacturing methods.
Educating design engineers to this extent may be an unrealistic goal. It should, however, illuminate the need for design engineers to know more about all manufacturing processes, subtractive as well as additive. At the very least, design engineers exposed to additive manufacturing for the first time should gain an appreciation for the efforts made by manufacturing people.
A video from Pratt & Whitney illustrates the steps needed to additively manufacture an aerospace component.
A fourth-generation family machine shop integrates metal additive manufacturing as another production operation.
Machining a large 3D-printed part for aerospace composite tooling is fundamentally different than manufacturing the part traditionally. Baker Industries knows this first-hand.