Design is defined as a visual communication of the intent, form, materials, functions, dimensions, and qualities thereof of a product. Nearly all physical products that are used or seen in the daily lives, for example, a mobile phone, a chair, or even the pen, were once just a concept in a designer’s mind. An interesting thing, however, is that while the designer’s mind runs carefree on creativity, there are often barriers to making the product idea manufacturable in a practical sense. Consider the design of an everyday product for the sake of stripping down the different areas of design and manufacture — say a water container. What would you think from the perspective of design and manufacturability? What are the questions you would ask or consider from the point of view of form/shape, purpose, function, dimension, durability, cost, quantity, material, etc?
All of the questions above, and probably an equal number more, are what would cross an engineer’s mind when they adopt the Design for Manufacture process, usually at the ideation stage. But why for manufacturing? Why not something else?
Practical design – Heart of DFM
It is vital to understand that the manufacturing process for the water container that we discussed above can be as simple as hammering a rectangular tin foil into a cylinder and closing the open ends with a lid, or chopping a hollow bamboo and tying the end with an oilcloth, or developing an efficient blow mould tool that produces a thousand PET bottles an hour! What we notice here is that manufacturing plays an essential and central role in controlling the time, cost, and quality of the product that is being manufactured. This is an elastic band, depending largely on the interplay between many characteristics that we will discuss ahead.
While we can imagine many things and make most of them, often the most successful designs are those, that are also practical — scalable, adaptable, and economically viable. What then is practicality or practical design?
Well, practicality is at the heart of Design for Manufacturing, or DFM, as it is often abbreviated.
Influencing factors during product lifecycle
Considering that there are different verticals or heads within what practicality means to different people, the majority of these characteristics can be broadly classified under: the design idea, the material, the quality or durability of the product, the process of making the product, and finally, the cost of making the product.
It is important to understand that all of the above heads influence one or all other heads at some time or the other during the lifecycle of the product. In essence, the final product, after being duly considered for its many different characteristics, will more often be an optimal output of the core rules (or the minimum acceptability criteria) laid down for each of the individual heads. One can also call it an acceptable compromise, but then again, we will end up with the glass half-full or half-empty analogy. Further, the Design for Manufacturing process is not linear but rather circular in nature. What this means is that each iterative step keeps improving the collective process until the system has reached an optimal state. DFM, which is an integral part of concurrent engineering, as a concept is at least 100 years old, drawing roots from the first production line!
Design idea stage
This stage is all about the problem statement or the answer to a problem statement in sometimes vague but relatable terms. It also includes a large part of visualisation such as preparing sketches, drawings, CAD models, and more often than none, physical prototypes. At this stage, a minimum number of acceptable characteristics is defined, typically using the age-old must haves and good to haves of each head. Interestingly, this is also one of the critical stages responsible for the standardisation aspect that we see in nearly every product. This process also considers the aspects of tool & auxiliary design, Design of implements and sub-processes, test and reliability design as well as end-of-life design. In mechanical designs, some of the core design features are likely to be wall thickness, fillet radii, chamfers, length to diameter ratio, overhang, support ribs, surface flow, fastening and joining mechanisms, sliding and rotating mechanisms, suspension mechanisms, and sealing mechanisms, amongst many other critical features. This process also includes a simulation or validation phase, which starts with assumed inputs and refines the design based on inputs from the remaining heads in the DFM process, often in the analysis of strength, fatigue, flow characteristics, thermal effect, chemical reactivity, efficiency, etc.
Selection of material
The next head, selection of material is based on the desired physical properties of the end product. This stage considers mechanical, optical, aesthetic, electrical, thermal, chemical, and a host of other related properties. Starting with how strong, flexible or stiff a material should be, or what colour, how lustrous or not, transparent, translucent or opaque the material should be or what patterns, lines or texture the material should have, to how the material must handle moisture, chemical exposure, electricity, and also the feel and touch of it, while being handled or used. As mentioned earlier, each of the above comes at the cost of one or more characteristics, in what is commonly referred to as trade-offs. Historically, materials are known to be one of the biggest cost components of the final product costs. It is due to this factor that there has been so much innovation in material technology. To appreciate this, let’s just wonder for a moment on how small microchip processors have become since the time they were used on the first computer!
Quality of product
Having established the material characteristics, we are now left with understanding that durability, weatherability, fit and finish, looks and appeal, conformance to dimensional specifications, etc, are what comprise quality. In certain ways, this head also has a strong influence on the material at times. While quality has undergone several definitions since the industrial revolution, the core aspects of functional durability at reasonable cost have arguably been prevalent since the stone age. This process also draws from the sub-processes in the design phase to test and certify that the product conforms to the design specifications. Until a few decades ago, quality was considered a cost. However, with PLM and DFM processes, it has been demonstrated that quality actually saves huge costs over the lifecycle of the product.
The process of making the product is normally a function of the demand that exists for the product (or how much of the products are to be made in one go), the time required to make it (how soon is the product needed) and the available equipment to make the product efficiently and accurately (eg, moulding, stamping, milling, spinning, welding, 3D Printing, casting, turning and the list goes on!). This process also depends on what kind of material will be used, as the same process can yield different timing and costs for different materials! To add to the decision-making chaos, a simple tweak in the design may significantly reduce the manufacturing process or get rid of some sub-processes entirely. This is not all; the expectation of quality from the consumers of the product in question also alters the manufacturing process and methods at times.
Reducing costs with effective DFM
The sum total of all of the previous processes creates a minimum cost for the product, without which the product cannot be made as per set or defined standards. This has, since time immemorial, been the key to defining what we have come to understand as a value proposition. Of course, there are other costs related to people, administration, logistics, marketing, and statutory taxes, among others, but somehow manufacturing has been able to reduce costs in the core processes. How is that? One may ask, and the answer will point to effective DFM.
What if the design could not be manufactured? Or worse, it could be manufactured, but at a cost that will make it unaffordable. What if it could be manufactured economically but wouldn’t last a day? What if it could be manufactured economically, last for a reasonable time, but not be transported easily? What if it could be transported easily but did not have aesthetic appeal? What if it had aesthetic appeal but lacked the necessary grip and ergonomics to handle it while performing other tasks?
These questions can go on until they start looping back – eventually towards manufacturability and efficient manufacturing.