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for ppm levels, with and without sorting the parts. The tolerance
levels are not stated, so it is assumed that these are the ppm they
may see in manufacturing automotive parts, with whatever
tolerances they may have. Clearly, to achieve low levels of ppm
defectives, in many cases sorting will be needed.
PPM In Fastener Manufacturing
By Dr John Newnham
Confederation of British Metalforming
−4 σ − 3σ − 2 σ −1 σ μ 1 σ 2σ 3 σ 4 σ
68%
95%
9 9.7%
0.135% 0.135%
3 4 . 1 3 % 3 4 . 1 3 %
1 3 . 5 9 % 1 3 . 5 9 %
2 . 1 4 5 % 2 . 1 45 %
99.993%
4 .3 2
Figure 1. Normal distribution curve with standard
deviation intervals
−6σ −5σ −4σ −3σ −2σ −1σ +1σ +2σ +3σ +4σ +5σ +6σ
LSL USL
± ppm Yie ld Cp
1 320,000 68% 0.33
2 50,000 95% 0.67
3 2,700 99.73 1.00
4 64 99,9936 1.33
5 0.6 99.99994 1.67
6 0.002 99.9999998 2.00
Table 1. Relationship between sigma, ppm, yield, and Cpk
Process without sorting
Process capabilities
Forging 500 ppm
Stamping 250 ppm
Plastic injection moulding 100 ppm
Assembly 100 ppm
Table 3. Possible process capabilities without
subsequent sorting
Figure 2. Normal distribution with “six sigma” between
specification limits
ASSOCIATIONS
Issue 49 – January 2008 – Fastener & Fixing Europe – www.fastenerfair.com
104
The AFFIX document has been taken for discussion to French
automotive OEMs in order to establish mutual understanding of
the issues. The AFFIX committee contends that in many situations,
the fastener users could implement mechanical devices such as
‘poka-a-yoke’ to catch defective parts, with little or no cost. In
situations where substantial fines are automatically imposed for
non-conformities, there needs to be recognition that some
parameters have very little influence on the assembly process, so
should not cause large fines. They are also using the document for
trying to promote some standardisation within the OEMs of the
documentation for dealing with non-conformities, in order to
minimise costs incurred by the manufacturers.
In Germany, DSV, the German fastener manufacturers’ trade
association, is following a similar approach, and their document is
expected to be published soon. It is hoped that between the two
approaches, there will be a common European document that all
of the European manufacturers can support via EIFI. It is not
expected that the request for zero ppm will go away as a result, but
there may be a more reasonable and rational attitude if all
manufacturers are supporting the same data.
Anew format was adopted for the Confederation of British
Metalformers - Fastener Sector meeting at the end of
November 2007. The meeting was held away from the CBM
offices, in the St David’s Park Hotel in North Wales, a venue chosen
for its proximity to the Airbus wing assembly factory in Broughton.
At the meeting, the primary speaker was Phil Matten, Editor of
“Fastener & Fixing Europe” magazine, who provided an analysis of
the EIFI complaint to the European Commission on the alleged
dumping of standard fasteners by the People’s Republic of China,
now the subject of an EC investigation. Phil outlined the key details
of the complaint, including the product ranges involved, assessing
that there was a high probability antidumping tariffs would be
imposed on the cited fastener ranges. Other speakers were Dr Ken
Campbell of CBM talking about the Government changes to the
administration of the Climate Change Levy reduction, and Roger
Doo of Henrob presenting the history and products of the Deeside
specialised rivet manufacturer.
After the sector meeting, the attendees were escorted around the
main Airbus wing build factory. Over 5000 people work at the
Broughton site, which currently operates 168 hours each week to
keep up with demand. The factory tour included visiting the “jigs”
where the wing skins are attached to the structure for both the
single-aisle A320 variants and the A330/340 aircraft. Some time
was spent viewing the operations in the single-aisle flow line,
which is based on automobile production line concepts, although
everything moves more slowly, and the degree of automation is not
as high. CBM members were able to see the types of fasteners
currently being used in the construction of the wings, and their
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