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1. precedencediagram along with assembly tree for
Electric motor clutch Assembly
Precedence Diagram
Precedence Diagram is designed to show all the possible assembly sequences of a product. To
develop the precedence diagram for a product, each individual assembly operation is assigned a
number and is represented by an appropriate circle with the number inscribed. The circles are
connected by arrows showing the precedence diagram is usually organised into coloums .All the
Operations that can be carried out first are placed in the first column, and so on .usually one
operation appears in the first column: the placing of the base part (the host) on the work carrier
where assembling takes place.
To draw the precedence diagram, one places the base part in column-I. Assembly operations
that can only be performed when the operation in column I has been performed are placed in column
II. Lines are then drawn to connect operations in columns I and II. Third- stage operations are
placed in column Ill with appropriate connecting lines, and so on until the diagram is complete. -
following all the lines from a given operation to the left indicates all the operations that must be
completed before the operation under consideration can be per-formed.
Figure shows the precedence diagram for the clutch assembly. The frame is chosen as the base part.
The precedence diagram (a) is based on the individual parts of the clutch. This means that all these
parts are assembled on a single assembling machine.
In the assembly of the clutch shown in (a) there are 14 operations, and it is probably impractical to
carry out all these on a single assembling machine for the simple reason that it would be difficult to
design all the proper fixtures, and fixtures may be in the way of assembling some parts. Therefore, it
is probably better to treat groups of parts as subassemblies. This is indicated in Fig (a) by the dashed
lines enclosing the proper operations. Thus, if a product is broken down into a number of
subassemblies, all assembly sequences for each one can be easily studied and evaluated. In addition,
if these subassem blies can be mechanically assembled, separate assembling machines may be used.
Figure 14-20b shows the precedence diagram for the subassemblies of th clutch assembly. The clutch
is divided into four subassemblies. It can be seen tha no flexibility exists in the ordering of
operations 1, 4, 2, 6, and 7. Operations and 5, however, can be carried out in any order except that
they can not