START with the FINISH
Some Practical Advice for Design Engineers by Dr Russell House
Surface Engineering Consulting SEC
SEC has spent many years going in an out of companies to assist
them with their process finishing problems. Those companies could
be finishers, OEMs with a finishing capability or electronics/engineering
companies who require assistance regarding the correct finish and
who subcontract their work to outside finishers.
We work with the end user and the finisher and in all cases our
objective is to resolve the situation as quickly as possible. The
outcome of this activity is that the company profitability increases,
because the whole of our approach is to “Get it right, first
As far as engineers are concerned, we have no influence on their
basic design, but we know, as with most manufactured items, that
in the final analysis the designed item will require finishing.
The finish may be aesthetic or it may have some functional role
to play such as corrosion protection, wear resistance, or some other
feature. All will be designed to make the item operate more effectively
over a considerably extended lifetime.
In this guide we look at what factors need to be considered by
the engineer, from the basic substrate, the surface properties required,
the operating environment, the goal to be achieved and how the engineer
and the finisher can work together to mutual advantage.
My concern is that it is often assumed that the Finisher understands
and knows all about the finishing and therefore the engineer leaves
it to the Finisher to decide what to do. The alternative is that
the engineer passes the responsibility to the purchasing department
to procure the correct finish. Both methods could work to your satisfaction.
Both could be recipes for disaster and, if this guide does nothing
more, it will show you the engineer how to “Get it right,
the first time.”
I am assuming that you have engineering drawings showing precisely
the shape and size of the item to be finished. Somewhere on the
same drawing will be an indication of the material used to make
the item concerned. Every tiny detail should be present; thickness,
length, width, diameter, hole sizes, thread sizes, angles, heat
treatments, hardness, alloy specification, etc.
The plan now is to turn the drawing into a real item and then get
the item plated or finished with some coating appropriate to the
base material, the environment in which it will finally work and
at the lowest possible cost. The item will then be ready for testing.
This all sounds very plausible and often it is the route taken.
It is certainly not the best route. There is no problem in creating
the correct shaped item. However, you are now presenting the finisher
with a kind of ultimatum. “Here it is. See what you can do
with that. Oh! by the way, the plating mustn’t cost more than
6 pence per item!” That last statement has locked the finish.
Functionality no longer rules the roost; only the cost.
So what would be a better approach? - Start with the Finish
There are several matters to consider.
- WHAT will be the optimum substrate and surface finish?
- WHY is this the best selection?
- WHEN are you likely to be ready?
- WHERE will the item operate?
- HOW will it be processed?
- WHO will be the most suitable finisher for you?
One thing is becoming abundantly clear. Perhaps it would be wise,
before you go too far down the road, to involve a suitable finisher
and allow them to be part of the team. If necessary, get some formal
Confidentiality Agreement between your company and the Finisher.
That point could be important.
WHAT Substrate? WHICH Finish?
There are another host of questions to ask:
- Does the component have to have a good strength?
- Does it need mass?
- Must it be as light as possible?
- Does it need to be metallic?
- Must it be machined?
- Should you incorporate features to assist the finishing?
- Can it be cast or extruded?
- Where will it operate?
- What is the approximate life time required?
- Will it need corrosion protection?
- Will it be likely to wear?
- Is it possible that it will be shipped through the tropics?
- Are there any peculiar features or functional properties required,
(e.g. lubricity, solderability, thermal conduction, EMI/RFI shielding,
- Are dimensional tolerances important?
- Are some areas more critical than others?
- Do some areas need masking?
- Could your choice of finish have any environmental implications?
If so, is there a suitable alternative?
- Will it need thermal treatments to reduce stresses?
- Are there any cost issues?
It might be a good idea to create some form of checklist, the above
isn’t necessarily complete. That way some crucial point wont
The answers will determine whether the substrate can be made from
aluminium alloy, titanium, magnesium; copper, brass, bronze; mild
steel, stainless steel; zinc; plastics such as ABS, Polycarbonate,
ABS/PC mixtures, PEEK, etc. Is your choice going to have serious
implications for the finisher? You may need a specialist Finisher.
Create the item on paper. That way we know the size and shape of
the item concerned, but then take some advice on the best substrates
to use and the optimum finish. For that you could use independent
advice or ask a suitable finisher.