Plastic Injection Molding Service For Low Volume Manufacturing
Medical Parts
Overview of Injection Molding:
Injection moulding enables complex shapes to be mass-produced with
a high level of efficiency and manageable costs. A wide selection
of materials allows engineers to exactly match the physical
properties they require for any given product. Additionally, the
application of multi-shot moulding techniques allows one to secure
an appealing visual appearance, as well as incorporating additional
functionality to the final product using materials that give high
mechanical properties.
Injection Moulding is highly repeatable; this means that all the
parts that are produced will be identical, which is especially
convenient for brand consistency and part reliability in high
volume production.
Injection Moulding Process:
Plastic injection moulding allows to produce large numbers of parts
with great accuracy and A quick cycle times from multi-cavity
tools. The process of injection mould involves a certain amount of
polymer materials being heated, melted, and injected into a mould
under high pressure. Further into the process, main units of the
injection moulding machine are:
- feed hopper;
- heated barrel;
- crew (known as the injection unit);
- clamp unit (which holds the mould together under the injection
pressures);
- ejection unit (which removes the part from the mould).
Plastic Material Comparison Chart
Material | Approximate Tensile Strength | Impact Strength | Electrical Insulation | Temperature Resistance | Chemical Resistance | FDA Compliant | Cost (low to high) |
Acrylic (PMMA) | 8200 psi | low | no | high | strong | no | medium |
Acrylonitrile Butadiene Styrene (ABS) | 5800 psi | high | no | low | medium | no | medium |
Nylon Polyamide (PA12) | 12500 psi | high | yes | high | strong | yes | high |
Polycarbonate (PC) | 9700 psi | high | no | high | weak | yes (can contain bisphenol A, or BPA) | high |
Polyethylene (PE) | 1300 psi (LDPE)
3580 – 6530 psi (HDPE)
800 – 13100 psi (PET) | high (LDPE)
high (HDPE)
low (PET) | yes | low | strong (LDPE)
strong (HDPE)
strong (PET) | yes | low |
Polyoxymethylene (POM) | 6400 – 10600 psi | high | yes | high | strong | yes | high |
Polypropylene (PP) | 4900 psi | medium | yes | medium | strong | yes | low |
Polystyrene (PS) | 2570 – 7690 psi | high | no |
| medium | yes | low |
Thermoplastic Elastomer (TPE) | 280 – 8100 psi | high | no | low | strong | no | high |
The moulding process could be described by the following steps:
1. Thermoplastic granules are prepared according to the
manufacturer’s guidelines. In some cases,
this may mean that the material is dried in a desiccant dryer to
remove moisture.
The material enters the throat of the barrel via the hopper. The
plastic granules are collected
by the helix of the rotating screw — the feeding zone of the screw;
2. The barrel is heated along its length using heater bands. There
are a number of zones depending
on the machine size. The zones have different temperatures along
the length of the barrel.
The temperatures are set in conjunction with the material
supplier’s specification sheet;
3. The screw rotates, which moves the material forward with the
pressure and determined rotational
speed towards the compression zone. This zone of the screw is
designed to put a shear heat into the plastic
and to push the material against the barrel wall, giving it a
consistent melt. As the material is pushed through,
it enters the metering zone of the screw and fills the front of the
barrel;
4. Once the material is injected via the nozzle at the end of the
barrel, it enters the runner system of the mould tool;
5. The runner system allows the material to flow through a gate into
the cavity of the mould tool, which forms the shape of
the finished product;
6. The mould tool is held at a constant temperature, which, again, is
defined by the material’s specification sheet.
Keeping the tool at a constant temperature allows heat to be drawn
from the plastic until it reaches its heat deflection
temperature (HDT). The HDT is also defined via the material’s
specification sheet;
7. Once the parts have reached the HDT, they will remain in a solid
state. The mould tool can be opened;
8. Once ejected, the components fall into a boss. Parts also could be
collected from the mould via a robot or a conveyor belt;
The tool closes and the whole process repeats.
Amorphous vs Semi-crystalline Thermoplastics:
There are two types of thermoplastic materials that we commonly use
at Integrated Molding Solutions,
amorphous and semicrystalline. Amorphous thermoplastic material can
be highly transparent and
has good formability with a lower melting temperature range. While
amorphous thermoplastics have
poor chemical resistance, this provides an easier bond to other
materials using adhesives or solvents.
On the other hand, semicrystalline thermoplastic material has great
fatigue and stress cracking
resistance making it the perfect material for bearing and wear.
However, semicrystalline thermoplastic
material can have high chemical resistance and difficulty bonding
to other parts using adhesives or solvents.
Amorphous and Semi-crystalline thermoplastic material comparison
chart:
| Amorphous Thermoplastics | Semi-crystalline Thermoplastics |
| Soften over a wide temperature range | Sharp melting point |
| Good formability | Poor form ability |
| Transparency | Opaque |
| Poor chemical resistance | Good chemical resistance |
| Bonds well using adhesives or solvents | Difficult to bond using adhesives or solvents |
| Prone to stress cracking | Resistant to stress cracking |
| Poor fatigue resistance | Good fatigue resistance |
| Structural applications only | Good for bearing and wear |
| Acrylic, PC, ABS, PS | LDPE, HDPE, PP, PET |
When comparing plastic materials, use this plastic materials
comparison chart to identify which injection molding materials
will meet the product specifications. One of the many benefits of
working with a professional plastic fabrication company
is their knowledge of plastic material alloys, fillers, and
additives. Custom plastic injection molding materials can be
engineered
to meet required product properties that common plastic molding
materials cannot.
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Plastic Injection Molding Service For Low Volume Manufacturing
Medical Parts,JYH is your best injection mold supplier!
Injection Moulding is highly repeatable; this means that all the
parts that are produced will be identical,
which is especially convenient for brand consistency and part
reliability in high volume production.
