Tooling for Injection
Molds
Overview:
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Parts
Design (client may provide completed 3D files)
The tooling process begins with a completed and checked part design.
CNMOULDING can optionally optimize your design before tooling in order to lower your costs and ensure that your design will work well.
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Parts Prototyping (if necessary)
If you would like to validate your parts design with a machined piece that
you can see and feel, cnmoulding can use Computer Numerical Control (CNC)
techniques to prototype your parts.
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Tool
Design
At this stage the tool is designed, using the information from your
completed tools and moulds design
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Tool
Check and Mold Flow Analysis
The tool design is validated for correctness.
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Tool
Fabrication (including use of Computerized Numerical Control (CNC)
and Electrical Discharge Machining (EDM) technologies)
The tool is precisely fabricated according to the validated design.
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First
Shots To Client
Once the
injection molds are made, the first test shot samples will be sent out soon
after via international courier. Once sent, these usually take around 2-5
days to arrive.
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Tool
Modifications and Texturing
At this stage cnmoulding completes the tool and makes any required
changes to bring the tool into the approved spec. Changes made to bring the
tool to spec (specifically excluding design changes, which are always
charged for) are made free of charge by us.
At this stage, texturing also takes place, which is normally the last stage
before mass production.
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Mass
Production Run or Export
At this stage
parts are produced and delivered to the customer, or the tool is released
for export use.
Technical
Topics:
Molding begins with tooling. No matter how good
the design, if the tooling is not up to the task, the quality of the parts will
suffer.
The Molding Machine
Achieving
consistent dimensions and quality requires up-to-date molding machines,
operating to specifications, with precise position and pressure control
capabilities. The basic construction of a molding machine is fairly straightforward.
Material is fed
in through a hopper into a screw and barrel where it is heated to a molten
condition. The melt is then injected under high pressure into the mold while the
mold is held closed with the high force of a toggle or hydraulic ram. The goal
is to melt resin in a very uniform and repeatable fashion, inject it into the
mold under very precise and repeatable pressure conditions, and hold the steel
temperatures in the entire flow system very stable. After the molten plastic is
solidified, the mold is opened and the gear is ejected. It then continues to
cool in the open air.
There are
many handling and pre-processing requirements for injection molding materials.
Engineering polymers quite often must be dried to a specific dew point prior to
use. When parts are made, runners are formed that some shops regrind and put
back in the melt. This quite often raises more quality concerns than the slight
savings in material expense may justify, and CPIM uses only virgin material.
Injection
The
method of injecting the plastic into the mold is very important. In most cases the plastic should be injected under high pressure very quickly in order to maintain the
good characteristics of the melt completely during injection. As the mold cavity
fills, the injection pressure should be held at the same high value and the speed of injection slowed
to maintain that pressure. At the moment when the part is filled, and the mold
machine switches over from injection to a pack & hold condition, the plastic
melt is held at the same high pressure. This pressure is held for as long as it
takes to freeze the gates and achieve the highest weight possible for the molded
part. |