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Design for Manufacturing and Assembly: The Ultimate Guide

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Question everything, assume nothing, believe only that which can be measured and validated. It’s a hard road we all must travel, but the right road to bring your ideas through to mass production.

DFMA or DFM is the ‘head’ of the engineering design process, balancing the ‘heart’ of knowledge, brilliance and inspiration. Product design without inspiration is generally terrible, product design without DFMA is liable to be miserable, and unlikely to make a return on investment. 

The principles embodied in DFM can be quite varied, because of the diverse nature of products. DFM for a PCB looks very different from the same analysis for a stent or an oil-well drill bit. But the principles are simple enough, even if the execution needs considerable tailoring.

The seven core principles of DFMA are:

  1. Minimize part count
  2. Standardize parts, materials and processes
  3. Design for ease of assembly
  4. Use a modular design approach
  5. Integrate multiple functions into parts
  6. Optimize for manufacturing processes
  7. Design to comply with regulation and meet standards

The right time for a DFM process to start is NOW. If now is at the concept stage, all the better. The sooner that your product accommodates the optimizations that DFM imposes, the less the cost and time influence it’ll suffer.

DFM, at its best, will challenge the design and the designers’ foundational thinking, to look beyond simply solving the functional execution of parts, sub-assemblies and the product construction/assembly. It will drive the entire process from go-to-whoa towards excellence.

This illustration offers a clear visualization as to why DFM should be a co-driver in the design process. Early changes are frictionless and low cost, but once the design becomes crystalized and tooled, it gets MUCH harder, slower and more expensive to alter the outcome in significant ways.

Your acquiring early input from stakeholders that continues throughout the design process is key to a good outcome. It’s the designers job to hear and collate a diversity of views – from factory engineers, services suppliers like tool designers/makers, materials supply chain and production management. Not everyone will be right – but as the author of the design, you need to figure out who is most right for each element you’ll have to tackle.

Here at Jiga we have seen a lot of ideas come to fruition, so we have a pretty good feel for what makes good mass production outcomes, so here’s a brief summary of our thoughts. If you want more detail, then maybe you’re ready for our video series and our white paper that delves deep into the DFM maze. Sign up for our newsletter for updates.

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The six drivers of DFM

Process and Material

As a starting point for any component, it’s best to narrow down the core manufacturing process. If you want only one, things look very different than if you expect to make a million a year! 

The DFM influence on process selection starts with the planned volume, then quickly homes in on the materials, the complexity of the surfaces, the tolerances required and whether there were secondary processes required. These are intrinsic design decisions, but often design execution has to be driven by indicative process and materials selections.

Supplier selection

While it may seem a long way off, getting your general supplier options at least indicatively made early in the development of a product can be invaluable. A supplier who has been familiar with the product since the kick-off, or at least the mid-concept stage will develop ownership and will want to support you, in order to support themselves. Helping you prepare for manufacture when the product is little more than a specification and a twinkle in your eye is how they a) cement themselves in your process and b) help you drive towards outcomes that they know will work!

We at Jiga exist to serve in making these connections to help you on your product road. We will introduce the right options of suppliers, facilitate your communication with them and support you at your right hand every step of the way . Check out how we do it here.

Component and Sub-Assembly Design

Effective design is pivotal in making good parts, good assemblies and easy to build products. 

  • If your part is to be CNC machined, is that 3 axis? More?
 
  • If it’s to be polymer is that rubber, rigid, injection molded, thermoformed etc?
 
  • If it’s an exotic material or process, do you have the right suppliers on speed-dial?
 

Discuss the design with the expected manufacturer, get them to confirm your thoughts (or put you straight) early.

Material

While you’ll likely know the general class of material – steels, aluminum, engineering polymers etc. – homing in on the grade early will inform your design process and direct you to the right supply chain. Questions that will drive material choices are:-

  • How strong must the part be?
 
  • How much heat must it tolerate?
 
  • What chemical or thermal attacks might it suffer?
 
  • What electrical, magnetic, optical and processing properties are needed?
 
  • Is weight more important than cost?
 

Keep an open channel to the material supplier and contract manufacturer, who can very likely give you better options that you’ll find quickly on your own.

Environmental Considerations

Whatever the part or assembly, there will be normal usage conditions that it must endure, and exceptional conditions that may need to be allowed for. These might be handling and skin oils, food acids, stronger acids, cleaning agents, aggressive atmospheres, radiation or even zombie apocalypse. Yes, ok maybe the last one isn’t generally required.

Compliance and Regulatory requirements

Every product has market expectations it must meet, some have regulated requirements in terms of function and a few – mostly medical or flight related – must follow a design process/methodology and documentation/retention, the lack of which will make the product unsaleable in developed markets. Be sure you have these details right.

Look for ISO-certified manufacturers and product validation facilities. Keep good records. Design to the requirements, to avoid trying to modify later to meet them.

The seven levers we hold to drive DFM

Minimize part count

Part count is king. If your product is a spoon, and your component supply chain is full service, then you have no final assembly and all you need to do is sell spoons.

The aim with any more complex product is to tend-towards spoon simplicity. Merge parts into each other, integrate functions into fewer parts and make the product simple. Do this and you win in makeability terms, but also in function and product longevity as well

Standardize parts, materials and processes

Consistency is the mother of simplicity. Never use 2 fastener types if one will do the job

Choose materials and processes that suit your product, keep production streamlined and simplify the production line and supply chain, as much as you can.

Design for ease of assembly

Think about the hands, jigs and machines that will build the product. Make the product fall together – read all about the bucket test in the white paper that sits here backing up this blog.

This assembly is a prime example of complexity without purpose. It’s a 3D printable COVID19 breathing mask. As an emergency response it had a place, but in production?

Use a modular design approach

Make your product out of distinct sub-assemblies that can be built and tested before final assembly. These can be as simple as integrated fasteners, like insert-molded threads in a molded plastic housing. They can be wiring harnesses built into a chassis to be ready for quick connection.

Integrate Multiple Functions Into Parts

Modular design can also push you to integrate functions and parts to reduce stock complexity and improve assembly. A good example is a snap closed lid with a living hinge. Fewer parts, no assembly and very Industry 4.0.

Design for jointing

Can the parts interlock or clip together without need for screws or adhesives? If fasteners are required, these are some rules to follow in designing them in:

  • Reduce the number and variance of types as much as possible
 
  • Use standard fixings.
 
  • Use one-sided fasteners like thread forming screws, or overmolded inserts.
 
  • Remember that factories HATE wet processes – particularly glues. Use them only where you MUST.
 
  • Avoid complexity, washers, long fixings, double sided fixings and pre-assembly.
 

It’s worth considering that while fixings add typically 5% to a BOM cost in parts, they often account for 70% of the labor cost!

Minimize adjustments during assembly

Products should be designed without options, adjustments and possible alignment errors so all the parts fall into place and are finished as they’re fitted.

Ten results from effective DFM

You know you’re winning if:

1. You’ve minimized the number of parts in your product to restrain the cost of parts and assembly. This simple aim reduces the engineering, production, labor and shipping costs.

 

2. Customization is not your friend – it’s expensive and it’s time consuming. Standard parts that are already made mean less logistics, easier QA and less engineering effort. You save costs and remove uncertainties.

 

3. Using sub-assemblies and modules will simplify assembly and maintenance and allow staged testing during assembly, rather than fully relying on all-or-nothing final QA. Also future engineering costs can be lowered by re-use of modules in later products.

 

4. Designing multi-functional parts may seem like a given, but it’s a method that’s often not fully exploited. It can reduce part count, ease assembly and make a better product – every junction between functions is a potential failure point.

 

5. Designing for multi-use products and assemblies allows the sharing of elements that have been designed for adaptability. Can your product cannibalize prior designs and subassemblies that are already validated?

 

6. Design for easy fabrication, exploiting the material selection and manufacturing process to minimize production costs. Make your assemblies obvious and logical, so assembly requires less thought and goes faster.

 

7. Join without fasteners or adhesives. They’re often overkill. Screws typically boost material costs by 5%, but assembly labor by 70-80%. Use them sparingly, and make sure all of them use the same driver/torque where possible.

 

8. Design your parts and assemblies to minimize handling and orientation decisions during production and assembly. Handling and orientation mean there’s probably decisions to be made – and potentially errors that can result. Fewer decisions means an easier build.

 

9. If at all possible, build your product from only one direction. Ideally, parts should be added from above, using gravity as the feed mechanism, as this will reduce handling errors.

 

10. Design to maximize compliance, using tapers, chamfers, radii and keys to allow precise engagement to occur during fitting, rather than as a basis for fitting.

What's the effort required for DFM?

If you’re new to the concept of DFM, you’re thinking this all sounds like hard work that makes every stage a chore of self examination and decision review. Yes. But that self examination is MUCH easier when

  • a) it’s an intrinsic part of design (which it is for good design).
 
  • b) it’s tackled from the get-go, so you’re not having to step back and rework to correct a difficulty that could have been ironed out earlier.
 

When DFM hurts in both cost and project schedule is when it’s an afterthought. DFM exists to reduce the complexity of the design in both part manufacture and assembly, it builds in lower costs and higher reliability and it improves the odds on meeting the market demand for price, spec, material and schedule.

DFM enables design that is manufacturable, cost minimized and ready for mass production.

Jon
Jon
Jon is a dynamic and accomplished professional with a rich and diverse background. He is an engineer, scientist, team leader, and writer with expertise in several fields. His educational background includes degrees in Mechanical Engineering and Smart Materials. With a career spanning over 30 years, Jon has worked in various sectors such as robotics, audio technology, marine instruments, machine tools, advanced sensors, and medical devices. His professional journey also includes experiences in oil and gas exploration and a stint as a high school teacher. Jon is actively involved in the growth of technology businesses and currently leads a family investment office. In addition to his business pursuits, he is a writer who shares his knowledge on engineering topics. Balancing his professional achievements, Jon is also a dedicated father to a young child. His story is a remarkable blend of passion, versatility, and a constant pursuit of new challenges.

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