Design for Manufacturing/Design for Assembly - By Omnex
Even though as a system Design for Manufacturing/Design for Assembly (DFMA) has been evolving in industry for well over a decade now, the evidence suggests that only a few organizations have achieved significant benefit from systemic application and use. While the emerging ideology arose in 1970’s, it only took real shape as a system in the 1980’s when Geoffrey Boothroyd provided what had been basically conceptual with substantial form and structure by incorporating specific tools and methods.
In this article we discuss how DFMA can be of substantial benefit to organizations, and how implementation of the process can be effectively planned and executed.
The concept “Design” is often misunderstood or misconstrued. While some in the field would say “design must be strong enough to be robust,” and others insist it must be “conceptually strong,” somehow the results always seem to involve complexities that challenge efficient and capable realization.
Design has been described as “the art of transforming the customer / user requirements into product specifications.”
Ideally, Innovation and Engineering converge during the Design Process to provide maximum value to the customer. The more the designer understands the requirements of the product, the more the design will be close to achieving a robust solution. A robust design can be characterized, perhaps, as the “Simplest Design,” where Simple means:
• Easy to manufacture & assemble
• Not compromising on functionality
• User friendly
• Cost effective / economical to produce (high value)
Simplicity should be a paramount goal for design. Without it, the product will lack competitive advantage in the marketplace due, at least in part, due to the risk of high costs for manufacturing and assembly.
Nonetheless, simplicity of design cannot sacrifice function. Functional requirements are the key inputs for successful design, not just to meet customer requirements, but to do so by accomplishing a robust design solution.
Omnex strongly recommends the concurrent, cooperative engineering approach, integrating product & process design and incorporating improvement initiatives with FMEAs. By the same token, DFMA needs to be incorporated for enabling simple, cost effective and robust designs for both the product and the production processes. overhaul facilities and the maintenance repair for the aircraft industry at all levels of the MRO (Maintenance, Repair & Overhaul) process.
Although the most common acronym is DFMA, Design for Assembly (DFA) is performed first, followed by Design for Manufacturing (DFM) next, because DFA helps to optimize the assembly design and ideally reduces the number of sub-assemblies / components and their complexity from the perspective of the assembly process. Once the part count is reduced / optimized, then DFM focuses on selecting suitable manufacturing processes and optimizing component / part designs which are optimally producible.
Starting with the functional inputs from the FMEA process, a cross functional, multidisciplinary team is assigned responsibility for DFMA, starting with the three phases of the DFA process:
• First phase - design simplicity in general
• Second phase - to evaluation and optimize the design
• Third phase - optimizing the design for the specific assembly process
Phase 1 is used to question the concept design and to optimize it, so that general design errors are avoided. This helps bring basic initial simplicity to the design. In Phase 1, 10 General Design Rules are used to evaluate the concept.
Phase 2 is focused on optimizing the design by evaluating its design efficiency. A Design Efficiency calculation developed by Boothroyd & Dewhurst provides a relatively simple and effective tool to evaluate the relative efficiency of the design. The DFMA Team’s effort should result in improvements to design efficiency by applying Design Rules.
3 common methods for evaluating design efficiency:
• Boothroyd Dewhurst Technique (mostly widely used)
• Lucas DFA Method
• Hitachi Assembly Evaluation Method
Phase 3 involves choosing the assembly process(es) based primarily on considerations of production volumes and throughput rates required to ensure meeting customer and program requirements. Choices can be Manual, Robotic or Hard Automation assembly processes, or some combination thereof. The DFMA team should impart more knowledge, experience and efforts in each phase of DFA, to enable fewer iterations of Design improvements at the concept.
With a finalized Assembly Design, the team initiates DFM to enhance design robustness.
DFM guidelines are often well defined conditions / recommendations, by process technology, associated with dimensional / part-topographical requirements suitable for specific raw materials, and for the various features/characteristics of the detail part / component. These guidelines have been established (and generally followed) to enhance the manufacturability of individual parts, and to reduce the defects due to part design.
The team chooses the appropriate manufacturing process for each part based on the design outcome from DFA. For each of the manufacturing processes, DFM guidelines are applied to optimize the manufacturability of the design. These guidelines are also employed in verifying the part design before initiating tooling fabrication. If any product design modifications are required based on these guidelines, the DFMA cycle should be repeated.
Once optimized for the manufacturing process(es), the part design is ready for producing the detailed Product Definition (3D model, 2D CAD, print). In this stage the DFMA Team should apply GD&T concepts and Tolerance Stack-up Analyses to further optimize the robustness of the design. The final outcome will be prints for production, incorporating a design result optimized through the use of the DFMA approach.
Benefits of implementing DFM DFA:
1) Product design becomes simpler, with fewer parts, and easy assembly methods
2) Product design incorporates simple error-proofing solutions like asymmetrical mating parts, assured orientation features, auto alignment features, elimination of “blind” assembly tasks, etc.
3) Best assembly sequence is established
4) Design is optimized for the selected assembly method
5) Design is optimized for the parameters of the selected manufacturing process as a process driven activity, and to implement the process by following these steps:
• Assign a DFMA champion at the Corporate Leadership Team level
• Form teams at various levels, e.g. product groups / plants
• Ensure the competency of the teams in employing these approaches
• Identify the commodity / product for performing initial application of DFMA
• Assign each project team with a product / assembly
• Start with Design FMEA, and close the 1st level gaps in design process
• Using the input from Design FMEA, start with DFMA
• Conduct evaluation of progress after every stage of DFMA
• Evaluate the results achieved by each project team. Achieving even a modest 3-4% improvement is a good start
• Implement recommendations and verify the results achieved
• Start the next cycle
To achieve maximum gain from DFMA, Omnex recommends the initiative be adopted as a corporate strategy rather than
This DFMA article has been submitted by Omnex, republished from their own original newsletter. Omnex is an international consulting, training and software development organization that specializes in management systems.
The article was written by G. Mani, Senior Consultant for Omnex, and S. Prabhu, Principle Consultant for Omnex India.