Mechanical design engineers, sheet metal fabricators and building product manufacturers may call it design for manufacturing (DFM) and design for assembly (DFA), or combine it into design for manufacturing and assembly (DFMA). Whatever the moniker, the principles of DFM and DFA have been long accepted as thumb rules of designing sheet metal fabricators, fabricators of engineer-to-order products, furniture manufacturers, etc. to incur minimum cost in manufacturing and eliminate unnecessary features that pose hurdles in assembly.
However, there are multiple reasons why design engineers and manufacturing companies adopt DFM and DFA. Although 3D design using a suitable CAD platform, such as SolidWorks for example, has ensured proper downstream communication, DFMA lets the engineers get down to the fundamentals when it comes to quality performance and operations of final components.
Signals from the Manufacturing Floor
It is a myth that when all the design features are explained correctly from design teams to manufacturing teams, machining and fabrication becomes seamless. The shop floor challenges come in form of inappropriate fabrication drawings, engineering change orders (ECOs), re-designing, request for information, and many other interruptions that prevent continuous and consistent manufacturing.
Some of the most common error signals found during initial manufacturing can range from incapacitated machine tools on shop floor to misaligned holes when stacked and much more. Later on, when the parts are assembled into sub-assemblies and assemblies, the shortcomings of mismatching limits, fits and tolerances, errors in fixtures and components, and parts that could have been consolidated into a single component are encountered.
The manufacturing process then has to go backward by dismantling the assembly, fixing the part or remanufacturing it, and then reassembling it. Time, money, raw material and man power is wasted due to design mistakes. In a typical collaboration between the design engineer, CAD drafter and the manufacturer, the entire case would result in drawings and revisions moving back and forth.
DFMA to Decrypt Signals
When the foremen on shop floor start the process of dismantling, design inconsistencies come to light and are sent for correction. Even if the design intent is conveyed correctly, but design features are inappropriate or the designs do not complement the shop floor capabilities, the shop floor will keep flashing error signals.
Designing the component geometry and features by keeping manufacturing process and assembly at the center will automatically help eliminate ECOs, mismatched geometries, and incorrect tolerances. DFMA confirms the “rightness” of the component manufacturing and assembly.
Accounting for Better DFMA
In its most simplistic form, DFMA accounts for both designing and machining factors—with the utmost importance given to cost, rework, material usage, the least number of manual joints, minimum parts, workflow, and part performance. All the unnecessary features are consciously eliminated so that manufacturing is seamless. Secondly, when the parts are reduced in numbers, their operational failure risks are reduced due to joint failure—which is a big challenge for machine components.
Another major factor that DFMA covers is accessibility of various features in any CAD model, which may otherwise cause hurdles. For example, it is common knowledge that when any mating part has multiple through-holes for fasteners, slots and holes are provided. But challenges are encountered when holes are drilled or parts are assembled with fasteners. This is where DFMA comes into picture. Using holes or slots of oversized clearance will compensate for misalignment and provide quick assembly. Similarly, using the right kind of fasteners will allow easy access and clearance during assembly.
Like accessibility, there are many other features for sheet metal part orientation that explains indexing and positioning of parts to eliminate the issues of misalignment. DFMA emphasizes simplified designs and proper tooling guides, especially in case of multi-component assemblies.
In short, DFMA actually differentiates good designs from bad designs and stops the manufacturing shop floor from sending error signals. Even if the design engineer is inexperienced, DFMA will help them understand the error signals from manufacturer’s end and allow the designs achieve new heights.
Usha B. Trivedi is an engineer who focuses on enabling engineering professionals, furniture manufacturers and fabricators to optimize design outcomes through CAD and CAE tools.
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