Injection molding is one of the most common manufacturing processes used today. This versatile technique can produce everything from plastic toy building blocks to automobile body panels.
What is Injection Molding
Simply put, injection molding is a manufacturing process for making parts by injecting molten material into a mold. The molten plastic then cools and solidifies into the final product shape.
But what exactly is injection molding and how does this process work? Keep reading, as a professional moulage par injection de plastique manufacturer, I will help you to find out.
Comment fonctionne le moulage par injection ?
The injection molding process can be broken down into the following key stages:
1. Making the Mold
The first step is to create the injection mold itself. This two-piece metal mold forms the shape that the molten plastic will take.
Molds are typically CNC machined out of steel or aluminum. The two halves fit together to form the plastic part’s shape once clamped together in the injection molding machine.
2. Clamping
Next, the two halves of the mold are securely clamped together by the injection molding machine. This essential step ensures molten plastic does not leak out between the two mold halves during the high-pressure injection stage.
3. Injecting
With the mold securely clamped, the injection process can begin. The injection unit of the molding machine melts plastic pellets using heat and pressure. It then forces the molten plastic into the mold through sprues and runners that feed material directly into cavities that form the molded parts.
4. Cooling and Solidifying
During this stage, cooling channels built into the metal mold draw heat away from the molten plastic, causing it to solidify into the final plastic part shape. This cooling time cycle typically lasts between 15 seconds to half a minute before opening the mold.
5. Ejecting
Once cooled fully, the two mold halves separate and metal pins eject the solid plastic parts off the mold core, dropping into a basket or conveyor below the injection press.
Lather, rinse, repeat! The mold then closes again ready for the next injection shot to start a new molding cycle.
And just like that, you’ve created an injection molded plastic part. Apart from the upfront cost of the machined mold tooling, per-part cost using injection molding is very affordable, making it ideal for large production runs.
Now that we’ve covered the basics, let’s look at some key injection molding design principles to follow and different types of injection molding processes.
Injection Molding Design Basics
Properly designing parts for injection molding is critical for defect-free, cost-effective plastic part production.
Here are some fundamental design principles to follow:
Uniform Wall Stock – Strive to maintain uniform thickness wherever possible. Sudden changes from thick to thin walls makes parts prone to defects like sink marks or warpage.
Draft Angles – Taper vertical surfaces slightly to improve moldability and ejection. A minimum draft angle of 1-degree works for general applications (0.5-degrees for core pins).
Avoid Undercuts – Any surface details or geometries that prevent straight mold opening without slider mechanisms will increase costs.
Rounded Corners – Sharp corners act as stress concentrators in plastic parts as well as make molds wear quickly. Radius all edges for better flow and durability.
Boss Reinforcement – Enlarge boss diameters or add gussets whenever threading or fasteners needed for strength.
Ejector Pins – Place ejector pins onto inner flat areas of the part, avoiding highly cosmetic outer surfaces.
Gate Location – Locate injection gates along the parting line without affecting cosmetic surfaces to minimize finishing work.
Types of Injection Molding
Beyond standard thermoplastic injection molding, there are also some specialized injection molding process types, including:
Insert Molding
Insert molding combines two different materials by inserting a pre-formed component into the injection mold tool before injecting molten plastic around it.
Common inserts include metal components like brass threaded inserts to allow for molding-in fastening points or other higher performance parts.
Multi-Shot Molding
Multi-shot injection molding produces plastic parts using two or more different materials layered onto each other in stages. Each material shot occurs in different stages of the injection molding cycle.
Often used to combine different plastic polymers or colors, multi-shot techniques create durable, soft-touch, or ergonomic grips and finishes.
Surmoulage
Similar to multi-shot molding, overmolding bonds two different materials together into one plastic part, often combining a rigid plastic base covered by a flexible rubberized material.
This overmolding technique allows parts to be both rigid and impact resistant, making it popular for tool and consumer product handles.
Matériaux de moulage par injection
Engineers can select from thousands of plastic materials for injection molding tailored to application requirements.
Most fall under two main categories:
Thermoplastic Polymers – The most common type, thermoplastics include materials like acrylic, ABS, nylon, polyethylene, and polypropylene. Thermoplastics melt when heated and solidify upon cooling.
Thermosetting Polymers – Thermosets use heat or chemical reactions to solidify into final shapes. Common thermoset materials include epoxy, silicone, polyurethane, polyester resin and vulcanized rubber. They cannot melt and reshape after initial forming.
Beyond basic polymers, many advanced injection molding material options exist, including:
- Composites – Fiber or particle-reinforced materials for added strength/stiffness
- High Temp Plastics – Can withstand over 500°F for automotive applications
- Conductive Polymers – Static dissipative and electromagnetic shielding
- Biopolymers – Eco-friendly plant-based plastic materials
Choosing the optimum material that meets mechanical property, temperature, chemical compatibility, cosmetics, and other performance requirements is an essential first step toward quality injection molded parts.
Key Benefits of Injection Molding
Now that you know the basics behind the injection molding process, let’s recap some of the key benefits that make it the most popular mass production method globally:
Low Cost – High volume part price using injection molding is very affordable
High Production Speeds – Molding cycles can produce parts in seconds
Design Flexibility – Complex geometries with tight tolerances are achievable
Polyvalence des matériaux – Thousands of plastic material options to suit specifications
Consolidation de l'assemblée – Parts can integrate multiple components and fastening hardware
Clearly, for manufacturing industries from medical devices to consumer goods and automotive, injection molding offers an efficient, versatile and cost-competitive plastic parts production solution.
Conclusion
I hope this beginner’s guide gave you a helpful injection molding overview explanation. The basic injection molding process steps are relatively straightforward, but mastering plastic part design and production optimization develops over years of molding experience.
If you’re looking to have custom plastic parts manufactured, using injection molding for volumes over 1,000 units is a good benchmark quantity where it becomes the most viable option. Under this amount, CNC machining or 3D printing can make more economic sense.
To recap, injection molding offers unparalleled design flexibility, precision, and value for producing plastic components at scale. It rightfully deserves the title as manufacturing’s mass production workhorse worldwide across countless industries.
Have you used injection molding before or are you just starting out? I’d be curious to hear your experiences or questions in the comments below!
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