First Edition Dated September, 2000 44
components are assembled together in the same build position, the groups
feeding that build position should work together to create the reference
drawing.
The minimum requirement is for the drawing tree and build tree to match.
World class suppliers focus on the process that ensures that the two trees do
match. The goal is to avoid having to rework the drawing tree after the fact, in
order to make it match the build tree. Whatever process is developed, it
should result in concurrent design and build definition.
Section 4.5.4 Reference points (datums) on the product
design shall account for the way the product is fabricated,
assembled, used, or functionally tested.
Previous paragraphs (4.5.1, 4.5.2 and 4.5.3) discussed customer/supplier
relationships, flowdown of requirements and coordination of the drawings with
the build process. Paragraph 4.5.4 supplements these requirements with a
requirement for logical design datums. There are two important elements in
meeting this requirement.
The first element is that of matching the datums of the product in a specific
build position to the corresponding manufacturing indexes (part-to-part and
part-to-tool). This concept, known as functional datuming, may seem very
basic, but it is often violated. When this concept is violated, tolerances stack
up and the variation monitored at the build position will not match that
experienced by the customer of the product. Much time can be wasted
improving product characteristics defined on the drawing that have no bearing
on the quality of the product passed on to the customer.
The second element of the requirement is that the datums be related to
functional manufacturing features that flow down through the drawing/build
trees. Ideally, using the same feature throughout the flowdown from
installation through assembly to detail would ensure this. But as each
assembly and detail part is split off in lower levels of the drawing and build
tree, different features have to be picked for the datums/indices. Therefore, in
order to have functional flowdown of datums/indices, key characteristic
features are used to connect datums.
