Design for “excellence” (also known as DFX) is a general term used in the engineering world that serves as a placeholder for different design objectives. In reality, the term DFX is better thought of as Design For “x” where the variable x is interchangeable with one of many values depending on the particular objectives of the venture. Some of the most common substitutes for x include assembly (DfA), cost (DfC), logistics (DfL), manufacturability (DfM), reliability (DfR), serviceability and/or repairability (DfS).
Design for x
Designs can vary wildly depending on which items you prioritize over others and the degree to which you make them your focus. Here is a little more about each design and their associated principles:
DfA: Design For Assembly (read detail on DfA)
DfA focuses on maximizing the ease with which a product can or will be assembled. Major considerations include whether human labor or automation will be used to join subcomponents together. When a process is highly automated, considerations like part orientation, techniques for segmentation amongst different part types, and spacing between units on the line become a higher priority. When an assembly process is more manual (i.e. dependent on human labor) then important things to incorporate into your designs include human accessibility to small spaces, a logical layering sequence for subcomponents and subassemblies to fit together into the larger product, and designing mistake proofing into the parts themselves. Mistake proofing is essentially the idea that you ought to make sure there is only one way to assemble a product. If the assembler makes a mistake regarding orientation, fastener size or type, or a number of other issues that might come up in the course of assembly, mistake proofing prevents them from making it by ensuring the part simply cannot be assembled with the wrong accessories and/or in the wrong manner. Think of designing mechanical limits into your products (e.g. square pegs that fit in square holes but simply cannot fit into a round hole even if the assembler thinks they’re supposed to). A well designed product has safeguards against mistakes that are intended to prevent costly outcomes farther down the production line.
DfC: Design For Cost
DfC needs to be a consideration in every design because a product that costs more to produce than it can be sold for doesn’t have a future. Designs must be profitable and cost reduction on the design and development side of things is a large piece of that puzzle. DfC combines a lot of other design principles into one. A design that is easily assembled, logistically efficient, manufacturable, reliable, and serviceable is also likely to be lower cost. Choice of materials is also a major influencer Other relevant DfC principles include simplification (reducing the total number of parts and fasteners in your design), modularization (the idea that parts ought to be somewhat interchangeable and/or of logically standardized size and dimension), and parallel processing (minimizing bottlenecks and inefficiencies in assembly).
Pro Tip: In the world of plastic parts one of the most beneficial things you can do is to use a single mold tool for multiple parts. Adjust orientation of different pieces to maximize the number of distinct mold cavities that are useful on a single tool.
DfL: Design For Logistics
DfL is also known as Design for Supply Chain. The concept involves incorporating design considerations like economizing on packaging and transportation, modularization (standardization) of parts, and parallel production processes that minimize lead time and inventory requirements.
- Packaging and Transportation: Work on designing your finished assemblies to fit standardized sizes for shipping and retail distribution. For example, UPS measures packaging using the following formula: L*2W*2H where L = length, W= width, and H = height. This is the measurement that is multiplied by package weight to determine your shipping costs. Minimizing the quantity L*2W*2H will minimize shipping costs. Also consider the fact that this measurement needs to be less than 165 inches total to qualify for regular shipping in the first place. Any larger and you’ll have to use freight services in lieu of UPS. Additionally, using the same example (UPS), packages need to be less than 150 lbs and less than 108 inches in length. Another DfL consideration might include designing your product with “retail ready packaging” in mind. Retail ready packaging means more than simply fitting on the 14” Walmart shelf. Make sure your product packaging is easy to identify, simple to open, that the interior product is easy to shop for, that the technicians can stock the shelves without much heartache, and that the left over packaging is easy to dispose of once the product is gone.
- Modularity: An example of modularity in a design would be using the same type of fastener (such as a screw) used in a design. If it is not possible to use only one type of screw then focus on minimizing the different type of screws used in the design.
- Parallel processing involves eliminating bottlenecks where a single fallout can hold up the entire operation. The objective of parallel processing is to achieve “just-in-time” (JIT) manufacturing in the shortest amount of total time possible.
DfM: Design For Manufacturability (read detail on DfM)
DfM involves technical expertise in the particular manufacturing process being used. One of the most common manufacturing processes is known as injection molding. Designs that minimize defects during injection mold manufacturing will take into account technical specifications like mold temperature, cycle time, and even larger ticket items like facility humidity. Designers will also incorporate techniques like designing small draft angles into vertical surfaces and rounded corners within mold cavities. Other important design considerations include items like gate location and its relative location to different part geometries. Designers should aim to avoid flow issues as this will ultimately prevent weakness in the final output.
Solidworks Plastics Mold Flow Simulation From a Single Gate Location
When molten plastic flows through a mold cavity it has to wind its way through the part. Making sure that the turns along its path are smooth (rather than abrupt and/or full of acute angles) help it to flow evenly and thus maximize the odds of uniform parts. This will help prevent defects like weld lines that can lead to hairline fractures and eventually propagate into bigger cracks and potentially completely ruin the part. Take it from Creative Mechanisms president Tony Rogers who identified the mold design as “the most important part of a molding project.” He noted that a lot of thought needs to go into it and “getting things right the first time is critical to the success of the injection molding venture.” Here is an example of a multicavity tool from Creative Mechanisms:
Read more design tips for injection molding here. Consider contacting Creative Mechanisms if you need help designing parts that can be reliably injection molded or developing working prototypes prior to investing in the expensive and time consuming tool creation process.
DfR: Design For Reliability
DfR is an engineering focus item that aims to prevent failure for a known quantity of time (typically greater than or equal to the product’s lifecycle). Product lifecycle is influenced by a number of factors but in many 21st century cases is driven principally by the pace at which the next generation of a product can be produced. Principles include redundancy, preemptive failure analysis and prevention, as well as lifespan and warranty predictions. The idea is really to ensure the product will work consistently and be maintainable in the modern production environment with generally shorter product lifecycles and rapid innovation.
Related to DfR is the well known Failure Modes and Effects Analysis (FMEA). FMEA is a good way to retroactively analyze failures and determine root causes while pre-emptive failure testing like tensile testing, trial and error, and functionality testing (“burn in”) are all good ways to set your product up for success ahead of time (i.e. make it reliable). Design for reliability should also not be confused with Design for Six Sigma which is similar but slightly different and focuses more on quality assurance tools and tolerance development.
DfS: Design For Serviceability (Repairability)
What happens when parts break and repairs need to be made? Does the entire product need to be taken apart? Do entire subassemblies need to be scrapped? Can you make “DIY” fixes? Although it is more common than ever to scrap old products for completely new replacements, there are still a number of industries where repair is incredibly relevant to designers. Long lifespan products like vehicles, refrigerators, and HVAC systems all benefit from simplicity of design that maximizes serviceability. Generally speaking, the easier a product is to repair, the lower your prices can be and the more competitive your company will be in the marketplace. Relevant DfS principles include simplifying designs by minimizing total parts, providing logical component labeling and technical user guides, and making spare parts readily available. This all translates directly to repeat and happy customers.
There are a great number of factors to consider and balance when designing a new product. In all cases it’s important to realize that there is no such thing as a “perfect design.” Everything involves tradeoffs and mechanical design is no exception. Cheaper material generally means lower costs but also lower reliability. The question is typically how much to prioritize cost savings at the expense of other things like quality, reliability, or manufacturability. Prior planning and accurate predictions about product lifecycle, sales expectations, and ROI analysis will help to prioritize the various “x” items you can design for.