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Welcome to my blog for all things related to business quality (processes, systems and ways of working), products and product quality, manufacturing and operations management.

This blog is a mixture of real-world experience, ideas, comments and observations that I hope you'll find interesting.

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July 2010
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Control your cosmetics – “because you’re worth it”!

No, I’m not talking about lipstick and blusher despite the tongue-in-cheek introduction. Cosmetic Inspection refers to the quality of the surfaces of products or equipment, especially those surfaces that are visible to the customer.

Nothing is perfect; no material is entirely defect-free (especially if you look hard enough), so what scratches or blemishes or discolouration or badly-formed edges are acceptable to your company and its customers? What defects are unacceptable? How do you decide?

This is somewhat of a minefield for the Quality Inspector and the supplier alike, because you are trying to quantify and form a go / no-go decision on something that is highly subjective.

So how do you decide what cosmetic quality is acceptable versus unacceptable? I suggest that you write, then evolve and continuously improve, a Cosmetic Inspection Specification or Standard.

Now, I can’t simply write one for you here and now because (a) I haven’t got the space and (b) I don’t know what products you produce for what markets. What I can do is to give some guidelines about the things that you should think about putting in this document to make it as useful – and as consistently applicable – as possible.

Materials

You will have different requirements for self-coloured plastics as opposed to clear plastic windows or sheet or cast metal. Plated surfaces can have discolouration and can show underlying flaws, paint can have blemishes, runs, different textures and embedded specks.

Different materials and surface finishes can show defects in different ways so it’s unlikely that one simple rule will suffice; be prepared to have different sections of the specification for different materials.

Surfaces

Although no-one likes defects anywhere, surfaces that face the user are usually more critical than bottoms or back panels. You can categorise your surfaces and allow more blemishes on the less important faces whilst imposing higher standards on front panels or display windows or anything frequently seen by the user.

For many types of surface it is common to permit certain specified minor defects so long as the integrity of the coating isn’t breached, e.g. so that you don’t let moisture in which could lead to corrosion.

Time, distance and lighting

Given enough time, light and a magnifying glass you’d be astonished what defects you can find, but that’s hardly a fair test. Will your customers apply the same techniques? (If they will, you should too.)

It is usual to have a standard inspection distance – perhaps 1 metre, specified lighting of a certain luminous intensity, and a time limit (such as 10 seconds) for finding the blemishes; these can all vary depending on the products, surfaces and materials involved.

Size

Which is worse, a deep, short scratch or a very fine long one, a patch of noticeably different texture on a surface or a fine scratch across it? You will want to quantify what is acceptable and what is not acceptable; how many defects of what size will you permit?

Defect density and orientation

Very fine marks parallel to a panel edge (often caused by tooling) are often less objectionable than scratches at random angles; a group of small scratches concentrated in a limited area can be more noticeable than a few very fine hairline defects distributed over a large panel. You will need to specify what is acceptable for your products, surfaces and customers.

Colour and Texture

These are some of the most difficult parameters to get right because colour and texture often interact and can be greatly affected by lighting conditions. Getting dissimilar materials to match in colour, or plastics to match with metals, can reduce even the best engineers to tears; often the answer is not to try – deliberately use different textures or colours for the different materials, although sometimes you have no choice and detailed specifications and samples… and tenacity… are required.

Burrs, dents and manufacturing marks

Will you allow weld or solder marks to show? Glue seepage? Dents where spot welding has been done? What about the finish of edges, how much trimming or burrs or grinding marks will you let show and will you allow any sharp edges to be present even on normally hidden surfaces?

What about sink marks, or flow or ejector marks, or voids? What marking or burring of screw or bolt heads, or the surfaces they mate up against, will you allow?

At what point will you decide there have been lapses in workmanship and the defect is unacceptable?

Alignment

What misalignment will you allow between panels or other mating surfaces? What gaps? How straight must labels be, and will you allow any bubbles under them or curling, overlaps or smudges?

Examples and photographs

In the end, you can follow all these guidelines in great detail and write a really thorough, objective, detailed specification but still end up with ambiguous results. Why not take a leaf out of well-established standards such as the electronics workmanship standard IPC-A-610 and include photographs of what is acceptable and unacceptable to clarify your requirements?

‘Golden samples’ i.e. reference parts that are used to define exactly what you require, can also form a useful part of your standard.

How you define cosmetic defect acceptability depends on your products, your markets and your customers. But, if you haven’t got a written specification already, wouldn’t it be useful to have an agreed cosmetic standard to work to? Of course it will have to change over time, and sometimes you will have to concess or deviate from it, but at least you and your suppliers and customers can all be ‘singing from the same hymn sheet’ and that has to be a good place to start.

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