Digital Signal Processing Reference
In-Depth Information
Granule
hopper
Injection molded parts
hot runner
nozzles
Distributor
Cylinder heaters
Nozzle Backflow valve Screw Cylindrical container
Linear drive
and actuator
Injection unit
Tools
Illustration 297:
The principle of the plastic injection molding process
Plastic injection molding is a primary forming process, where nearly any part can be formed out of plastic
granules. At first, the granule is melted at ca. 160 - 300 degrees (material dependent) and injected in the
moulds (so called cavities) of the tool at a pressure of several hundreds of bar. After a certain cool- down
phase, the tool is opened and the parts are taken out. Most of the information about procedures in the
process and occurring fluctuations are included in signals directly taken from the cavity where the part
was created. Because of this, mostly pressure- and temperature signals from the tool are used for process
monitoring.
The latter are demanded mainly for safety relevant parts or for simple (low priced)
products, e.g. thread pins, that later are used in big assemblies and that, in case of defect,
would cause costly rework or lead to a complete breakdown of the assembly. Despite
more and more inspections are automatized e.g. by the use of industrial image processing,
many inspection procedures are carried out by specially trained personal in production.
Inspecting parts at the end of the production is always very costly. If defective parts occur
in bigger masses at the inspection, this mostly leads to a shutdown of the production
process and as a result to a further loss of production. The necessary “corrections” of the
production process mostly require several tests and inspections that can last for hours.
Non- detected and as a result delivered errors can lead to customer complaints, in the
worst case they can provoke accidents with personal injuries leading to damages or
expensive product recalls.
The aim of every producer thus has to be the production of quality
without having to expensively inspect it!
The best way to achieve this leads over a direct monitoring of the
production processes.
