A company may be already committed to a certain manufacturing system if there is prvious investment in capital equipment and tooling. Additionally, the external dimensions, performance or appearance of the product may be unchangeable. If a product is only part of a much larger assembly, the effect of changing a critical dimension may have expensive consequences for the rest of the much larger assembly. The performance of the re-designed product must be as good as, if not better than, the original design. The product may be one where visual appearance plays an important part in it’s acceptability in the market place. All of these factors place limitations on the engineer being able to specify the optimum product design and production system for that design.
It is easier to design the most economic assembly system for a product
prior to commercial manufacture. In this case, there won’t be an
inherited investment in manufacturing equipment or tooling, and the
product design won’t have been finalised. If the product is well
established, and has been produced for many years, the assembly systems
engineer may be limited to a re-design of the assembly system alone.
This is because a re-designed product may require expensive design
modifications to the tooling used for the manufacture of the product
parts. In these situations, a hybrid assembly system is required to
meet the product requirements. A hybrid assembly system uses a mixture
of methods during assembly of the product.
THE COMPONENTS OF A HYBRID FLEXIBLE ASSEMBLY SYSTEM
There are six methods of assembly and the simplest form is MANUAL
ASSEMBLY. For high volume production, the operatives usually work
on an assembly line. Other forms of manual assembly are a single worker
assembling a complete product and groups of workers assembling a
portion of the product.
For a more limited product range, a MANUAL ASSISTED method may be used,
whereby workers are assisted by mechanical devices, such as automated
parts feeders. The feeders present the parts to the worker in an
ordered manner and the assembly time is reduced by eliminating the time
taken to separate the parts from bulk random orientation. The reduction
in assembly time is the basis for the economic justification of these
The third form of assembly uses AUTOMATIC INDEXING assembly machines.
These are rotary or in-line systems with a number of
workstations. Automatic feeders supply components to workheads
and they assemble the part to the fixture or part-built assembly. The
workstations are ‘special-purpose’ and are dedicated to the assembly of
only one product. Production volumes need to be high for the economic
justification of these machines. Component quality must also be high to
avoid excessive downtime caused by components jamming, etc.
The efficiency of an AUTOMATIC FREE-FLOW assembly machine is less
dependent upon component quality. Transfer of work pieces
between workstations is non-synchronous. There are
small buffer stocks between each workstation and other workstations may
operate whilst one is stopped due to a fault caused by, for example, a
The AUTOMATIC PROGRAMMABLE assembly machine has a non-synchronous
transfer line and programmable workstations to assemble the parts,
which are presented to the workheads by automatic feeders or, in the
case of difficult components, part magazines may be used. The workheads
execute one, or a number of, operation(s). Different computer programs,
for each series of assembly processes, give the flexibility to assemble
a variety of product styles on one assembly machine.
Robotic assembly is used for the assembly of products with large
product variety, required in low volumes. Assembly operations are
carried out by a robot which, itself, transfers the completed product
onto the next operation.