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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:
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) | high (LDPE) | yes | low | strong (LDPE) | 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.
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.