Posted on 20 Aug, 2015 by Russell Poppe
In previous blogs we’ve discussed the value of involving your electronics manufacturing services (EMS) provider in design for manufacture (DFM), and some of the common mistakes that can occur when it comes to electronic assemblies.
However, electrical and mechanical assembly is not always as defined and precise as it is for electronics. Due to the greater number of bespoke items that are involved, optimising the DFM process could be said to be even more critical.
Here’s a simple 10 point guide to check against when it comes to outsourcing your next electro-mechanical product:
1. Selecting the right material suppliers
When it comes to drawn items, such as metalwork, you may well have a favourite supplier. But for each part have they really understood what you need - and can they make it to specification? As "nearly right" items won’t be good enough, this is where you should leverage your EMS provider’s expertise in the supply chain.
2. Materials finish
Do ensure this is clearly defined, communicated and understood; particularly with regards to cosmetic finish standards, as these can very subjective.
3. Check your tolerances
Firstly make sure each part – be it a piece of metalwork or a length of wire – has a defined tolerance. Then check that even in the worst cases of tolerance build up everything will still fit together. Remember, too, that sub-assemblies made separately will need to fit into the "top level" final assembly. It may sound obvious, but making sure these then fit back through the opening of the enclosure will save you costly headaches occurring out on the assembly line.
4. Avoid too many parts
Boothroyd Dewhurst, for example, suggest a very simple but effective way of assessing design for manufacture by reducing the number of parts. This, in turn, reduces the number of assembly operations, and therefore makes the assembly operation easier. The number of parts could be reduced by considering whether the part moves relative to another part, if it needs to have specific material properties, or if it needs to be separate to make it possible to assemble. If not, then it may be possible to combine parts.
5. Leave enough space to work in
Your electro-mechanical product might fit together when you look at the finished drawing, but remember that space is needed for the assembly staff to get their hands and tools in there to put it together. This can also be an important consideration for future servicing.
6. Don’t forget the finer details
Nuts, bolts, washers, tie-wraps and the like are often overlooked in the bill of materials (BOM) and may not be considered during the initial design of the assembly. Naturally, an experienced EMS partner will help you decide on the best assembly methods and parts to use, but anything critical should be considered beforehand if possible and then added to the BOM.
7. Produce wiring schedules
For wired assemblies consider providing a wiring schedule along with the schematic, containing details of cable type/size/colour/length/identifier, as well as termination points and contacts. This will assist the assembly partner in ensuring accurate and repeatable (i.e. cost-effective) manufacture, and also helps design in efficient use of components.
8. Think about test
Consider how the unit will be tested, both for safety and functionality, and how the test operator will get access to critical points. Remember to include the necessary connections for earth bond testing.
9. Leaving it too late
Involve your EMS partner as soon as possible, ideally when the very first draft of the design is available. Similarly, give yourself time to make changes after prototype and pilot builds, and certainly before committing to formal design testing and approvals.
Try to use "standard" parts where possible, as items such as crimp tools and torque screwdrivers for special or unusual parts can be surprisingly expensive and are often on long lead-times.
Hopefully, you have found this quick DFM checklist for electro-mechanical products useful. Getting this process right often helps ensure a cost-effective product build, shorter lead times, and greater product quality and reliability. Particularly when a number of drawn items are involved, getting it wrong can be costly, which is why it’s recommended to talk through the details of your project with your chosen EMS partner, so they can advise you on the best approach.
Image by Dave Crosby