Hybrid Assembly (5/5)

The two parts to be handled by multiple vibratory feeders are the second worm gear and the third worm gear. These parts are changed to produce the various gear ratios used to create different product styles. The disruption to production, during product changeover, is minimised by using a group of vibratory feeders which deliver one particular second or third worm. The pick up point of the workhead is thus quickly changed to the output of a particular feeder for the assembly of a different style.

The jewel--plate sub-assembly is a large and delicate part which cannot be fed by an automatic feeder.  It can, however, be palletised.  A robot picks up the jewel-plate sub-assembly from the pallet and inserts it into the part-built assembly.  The operation is relatively complex and an operator has been retained at this station to assist the robot when difficulties arise.

The hairspring is a delicate part that can’t be handled by an automatic feeder. The insertion process is also difficult because the end of the spring is welded to a stub on the jewel plate. This part is assembled manually by two workers in parallel, because of these difficulties.

The second worm gear retaining pin is manufactured from wire and it is most cost effective to manufacture this part on the final assembly line by a guillotining operation. The bending of the pin is carried out simultaneously to the part being inserted and secured.

CONCLUSIONS

1) Product re-design for ease of assembly creates worthwhile savings in assembly costs.  However, particularly for large products, these cost savings must be offset against the additional tooling modification costs for the manufacture of re-designed components.

2 ) When assembling a product which has :
a) Many parts
b) Many variants in the product family
c) A large annual production volume
d) Many common sub-assemblies

a hybrid flexible assembly system is required and it will combine manual, automatic and robotic assembly methods.

3) Sub-assemblies, having a fixed content, are always best assembled on dedicated automatic assembly machines.

4 ) Variable content sub-assemblies are most economically assembled using either
a) Assembly robots
b) Flexible free-transfer machines

5) Transfer between sub-assembly production units and final assembly need large buffers to de-couple these two activities and reduce downtime.