The efficiency of an automatic free-flow assembly machine is less dependent on parts quality. The transfer of work pieces between each workstation is non-synchronous. Small buffer stocks are held between each workstation and the other workstations still operate even if one is stopped because of a fault, e.g. a defective part jammed in the escapement mechanism.
The programmable automatic assembly machine has a non-synchronous
transfer line with a series of programmable or robotic workstations to
assemble components. Parts are presented to the workheads by automatic
feeders or, in the case of difficult components, magazines may be used.
The workheads can execute one or a number of operations. Flexibility is
acheived by using different programs for each product to be assembled.
The final type of assembly system is robotic assembly and it is used
for the assembly of products manufactured in low production volumes.
This method can also be used when there is large product variety. Work
transfer is not by conveyor, as all the assembly operations are carried
out by a single robot. Transfer of the completed sub-assembly
onto the next operation may also be done by the same robot.
The direct labour content in assembly is reduced in the progression
from manual assembly to robotic assembly. However, the complexity of
the equipment increases as workers are replaced by machines.
Indirect labour also increases for the maintenance and computer control
of the equipment.
The application of technology to manufacturing is used to increase
productivity and the selection of a system for the economic assembly of
a product depends upon a number of factors. The final selection must
take into account the following:
- Market life of product - influences the decision of the company on
investing in capital equipment. Products with short market lives are
usually assembled manually.
- Variations in demand - Automatic assembly machines are designed to
operate with fixed cycle times. Low demand leads to increasing stock
levels or the machine has to be stopped. Both of these actions are
expensive. Flexibility to assemble different types of products is
needed if there are large demand variations. This flexibility can only
be provided by manual assembly or programmable machines.
- Parts quality- Automatic assembly machines are intolerant of
defective parts and they can cause a station to breakdown. Whilst
inter-station buffers will reduce the effect on efficiency, manual
assembly is necessary for products that use low quality parts.
- Number of products - to be assembled by a system determines how
flexible it needs to be. Different products manufactured in high
volumes can be assembled using programmable workheads. Smaller volumes
require manual assembly.
- Major design changes - Products subject to frequent design changes
need flexible assembly systems, in a similar way to systems used to
assemble a variety of products.