What is product Design For Manufacturing?


Designing products with a view to their ease of manufacture and assembly, it really is that straight forward!

Why? Reduce production cost, improve quality and reduce lead time. There are many more indirect benefits but basically it is the big three, the reason behind any improvement – cost, quality and time.

Why improve with DFM, why not line balancing, 5S or other lean manufacturing actions? If a product contains 1 ton of steel which requires 10 processes and that takes 5 hours, lean manufacturing may only reduce the 5 hours slightly. A design change could reduce the amount of steel, the number of processes and the lead time. In terms of improving product cost, quality and lead time, the gains are highest with Design For Manufacturing.

DFM approaches started to be used in the 60s. In the 70s, analytical evaluation tools started to get developed such as the Assembly Evaluation Method (AEM) developed at Hitachi and the Design for Assembly Method developed by Geoff Boothroyd. Further advancements and variations of these methods happened during the 80s and 90s.

An important point to bear in mind with these tools is that they are evaluation tools – to evaluate a design you first must create a design. Granted, through continued use of these tools, the user will most likely learn what works and doesn’t work and feed that into their initial design. A competent DFM designer however will have an understanding of the principles that under pin these tools and apply that knowledge in their initial designs. The ultimate goal in Design For Manufacturing within a lean organisation should be to design it right first time. After all it is ‘Design For Manufacturing’, not ‘Re-Design For Manufacturing’

An example of a Design For Manufacturing principle is to design for vertical assembly where parts are assembled in a straight down motion. This means gravity can be taken advantage of to provide positive location rather than a fixture. This also future proofs the design for a move from manual to robotic assembly.

Another example is zero drawings design where the assembly or fabrication of a product is intuitive and mistake proof without the need for production drawings. This could be with assembly features like multi-sized tabs, used to create parts that will only fit in the correct location. An everyday example of this is if you have ever changed a flat wheel on your car. You may have noticed that the holes on the wheels are quite a bit larger than the wheel studs, this allows the wheel to be easily located on the hub and the wheel studs started. The studs then have a taper at their head that centres the hole as it is tightened ensuring the wheel is centred. The wheel is easy to fit but impossible to fit off centre.

There are many theories, methods, tools, software packages and opinions on effective design for manufacturing. Taking a step back however and considering the big picture there are 2 key points that must be considered before embarking on DFM improvement.

Firstly DFM needs to be a balanced design perspective. What that means is your design engineers are already designing for a budget, designing for a timescale, designing for a customer, designing for a duty cycle, designing for a . . . the list goes on. Design For Manufacturing is another perspective that needs to be considered from the start along-side all these other perspectives but balanced against them depending on your priorities.

Leading on from that is the second key point, as with any improvement, your company is different from every other company and one size does not fit all. For that reason successful improvement relies on company culture, buy in at all levels and working out what works for you based on your own priorities.

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