In product design and engineering, it is one half to design a part that would be good in CAD. It is only after the design leaves the screen that the real challenge starts when it becomes a shop floor challenge. Here is where Design for Manufacturing (DFM) and Design for Assembly (DFA) are involved.
In as much as these two concepts are used interchangeably, they are not synonymous and mixing these two concepts may result in increased costs of manufacturing, delay in production and assembly problems. Most designers unwittingly optimize one and totally ignore the other; to produce designs that are simple to create and hard to put together, or simple to put together and very costly to create.
In this blog, the differences between DFM and DFA are broken down, the pitfalls designers usually fall into, and both methods are demonstrated to achieve efficient design that is production worthy.
Understanding Design for Manufacturing (DFM)
Design for Manufacturing (DFM) is the design of parts so that they can be easily and cheaply and dependably manufactured with the available processes, typically CNC machining, laser cutting, sheet metal fabrication, injection molding, or 3D printing.
The fundamental objective that DFM tries to achieve is to minimize manufacturing complexity without losing functions. When properly implemented, a DFM strategy will make sure that the manufacture of parts can be handled in an efficient and stable way with limited levels of waste, reworking, and trouble with tools.
CAD wise, be it SolidWorks, Inventor or any other parametric modelling package, DFM affects such decisions as geometry simplicity, feature choice, material choice, tolerances, and surface finishes.
Key Principles of DFM
- Reduce complicated geometries which demand special tooling.
- Use conventional material profiles and thicknesses.
- Unnecessary tight tolerances should be avoided.
- Design characteristics that are congruent with production.
DFM worksheet, when designers neglect to observe DFM, manufacturers are required to make alterations to the design – a cost, time and risk addition to the project.
Understanding Design for Assembly (DFA)
Design for Assembly (DFA) emphasizes on the ease and efficiency with which the assembly of a product can be done, instead. It also goes beyond the individual components and takes into account the way that the components come together to produce a finished product.
DFA aims to:
- Reduce the number of parts
- Streamline assembly line procedures.
- Limit the work of handling, rotating and fastening.
- Enhance completeness and reproducibility of assembly.
Good DFA design will allow a design to save on labor costs and assembly time significantly, particularly during high-volume production.
DFM vs DFA: The Key Difference Designers Miss
The greatest error that designers commit is to believe that DFM automatically refers to DFA- or vice versa. As a matter of fact, one design may be good in one aspect and bad in the other.
For example:
- One component could be very simple to machine and have five fasteners and difficult to align in the process of an assembly.
- Another component may assemble perfectly but it may need costly tooling or complicated machining operations.
DFM is concerned with efficient production of parts. DFA concerns assembling parts in an effective manner. The two are both indispensable and should not be made to look optional.
Common Mistakes Designers Make with DFM and DFA
- Designing Only for CAD, Not for Manufacturing
Among the most typical ones is the design with visual symmetry or CAD convenience in mind. Such items as unnecessary fillets, decorative cut-outs or fancy contours might appear impressive in SolidWorks or Inventor, but will just add time and cost in machining.
Aesthetic attributes not considerably functional to the manufacturer do not earn the manufacturer any pay. Each additional toolpath, setup or operation adds cost.
- Overusing Tight Tolerances
Among cost drivers in manufacturing, tight tolerances take up the greatest share. Tight tolerances have been used by designers as a safety measure, when they are not even aware of the actual effect they can have.
From a DFM standpoint:
- Narrow tolerances are slow to machine.
- They make inspection time more.
- They might necessitate special machinery.
This is actually damaging to assembly in a DFA perspective because too many tolerances may be detrimental, particularly when tolerance stack-up is ignored.
Good design implies to make tight tolerances where they are necessary.
- Ignoring Assembly Sequence During Design
Most designers design parts without even considering how they would be assembling.
This leads to issues like:
- Components that require bending or coercion.
- Hardly reachable fasteners.
- Assemblies possessing several reorientations.
The design could go through all the checks of DFM, and fail in actual assembly. DFA has the designers walk through the assembly step-by-step mentally (or digitally).
- Excessive Part Count
The spinning part count is a traditional DFA failure. Designers tend to divide parts in a number of sections to make them easier to model or produce without factoring in the assembly effect.
Each additional part:
- Adds handling time
- Enhances the possibility of errors in assembling.
- Increases complexity of inventory and logistics.
The combination of parts or designing of multi-functional parts is better to enhance the efficiency of assembly as well as improve the long-term reliability whenever possible.
- Poor Fastener Strategy
The fasteners are sometimes perceived as a second thought. The Designers combine various forms of screws, lengths, and tools-increasing the time and errors made in assembly.
Good practice in DFA promotes:
- Standardizing types of fasteners.
- Reducing fastener count
- Applying self-locating or snap-fit where necessary.
It does not only enhance the process of assembly, but also minimizes procurement and maintenance.
How DFM and DFA Work Together in Practice
The most successful products would strike a balance between DFM and DFA in parallel, and not as two different stages.
For example:
- The machined part (DFM) may be simplified in order to be self-locating during assembly (DFA).
- DFM may be avoided by reducing the number of parts (DFA).
With the help of the modern CAD, such as SolidWorks and Inventor, it is becoming less difficult to consider the two aspects during the early design stage using the parametric modelling, assembly simulation, and interference checks.
Early design in CAD influences the manufacturing cost and assembly efficiency in a gigantic way in the future.
Role of CAD Tools in DFM and DFA
CAD software plays a critical role in supporting both DFM and DFA when used correctly.
SolidWorks & Inventor Best Practices
- Use parametric design to adapt designs quickly to manufacturing feedback
- Create manufacturing-ready drawings with clear tolerances and notes
- Validate assembly sequences using digital mockups
- Avoid unnecessary features that don’t add functional value
However, software alone cannot fix poor design thinking. DFM and DFA are mind-sets, not just checklists.
Why Designers Often Learn DFM and DFA Too Late
A lot of designers undergo much training in the CAD modelling tools but they have limited exposure to the actual manufacturing environment. Consequently, the concepts such as Design for Manufacturing (DFM) and Design for Assembly (DFA) are usually acquired when the issues with the product are detected in the course of production. This lack of harmony between design and manufacturing is often seen to result in re-work and re-design of the design, and miscommunication with the suppliers and extra cost and time to produce. The only way to fill this gap is to work closely with manufacturers, machinists, assembly teams in the initial design stages and ensure that design choices are made based on some practical manufacturing and assembly limitations early in the design process.
Practical Tips to Improve DFM and DFA in Your Designs
The following are some of the practical things that the designers can put into place at any given time:
- Consult manufacturers regarding the review design.
- Challenge all the features: Does it provide functional value?
- Assemble at an early stage in the design process.
- Minimise the number of parts used where feasible.
- Intent in manufacturing and assembly of documents in drawings.
Even minor design enhancements can produce a huge saving in the cost in the future.
Conclusion: Designing Beyond the Screen
Design for Manufacturing and Design for Assembly are not pathos–they are core to good engineering design. When designers solely embark on CAD beauties or performance in theory only, they tend to produce prototypes that do not succeed in the real production process.
Knowing the distinction between DFM vs DFA and considering both at the initial design phase, engineers will have an opportunity to design products, which are not only functional, appealing, but efficient, economical and scalable.
Ultimately, the most desirable designs are not the most elaborate ones, but those that can be made with little difficulty, assembled with little difficulty and work found to be reliable.
