Injection Moulding Parts Manufacturer
Injection molding is an economical and efficient way to produce plastic parts. With a wide selection of materials and finishes available, it is suitable for many applications.
Injection machines, such as Milacron’s hydraulic Magnas and all-electric Elektron series, are designed for consistency, precision, and reliability. They are capable of handling high-volume production runs.
Material Selection
Material selection is a vital part of the injection molding process. It determines the final product’s properties and performance, its cost, and whether or not it meets industry standards and regulations.
Different plastic resin materials have different physical characteristics, so selecting the best one for a particular application depends on several factors. For example, the material used to produce a kid’s toy must be able to resist blunt impacts, while shoe soles must be flexible and cushioning to prevent injury to the foot and leg. Injection molding is capable of producing a wide variety of aesthetic options as well, including translucent and opaque colors.
Proper storage of the material is also important, as exposure to heat and moisture can degrade or change the mechanical properties of the plastic. Keeping the material stored in an isolated environment can help to minimize this effect. Moreover, it’s important to use draft angles on the walls of the mould to avoid sink marks as the melted plastic cools down. This helps to ensure that the parts come out of the mould easily.
Design
Injection molding is a great option for manufacturing plastic parts because it requires minimal labor and produces very little waste. However, the design of an injection-molded part is a crucial factor to consider when considering this manufacturing process. Failure to design for the injection molding process can result in significant costs, delays, and even rejection of the final product by your customer.
One of the biggest factors in injection moulding parts manufacturer designing an injection-molded part is managing wall thickness. Non-uniform walls can lead to warping and sink marks as the thermoplastic cools and shrinks. Recommended wall thickness varies depending on the material used, so it is important to consult with your machinist for recommendations on your specific application.
Another important consideration is minimizing stress in the injection-molded part. This can be accomplished by adding smooth transitions between features and using rounded corners whenever possible. This helps limit stresses that are induced when sharp corners melt or burn in the injection mold. Stresses can also cause warping, sink marks, and premature part failure. By reducing the amount of stress in a plastic part, you can ensure it will remain stable and functional throughout its lifespan.
Tooling
When making plastic injection parts, the tooling is crucial. The tool is the negative cavity where molten plastic resin is injected to create a finished part. The quality of the tool will directly impact the quality of the resulting molded plastic product. Properly designing the tool will save time and money during production.
The type of thermoplastic used is crucial, as it will affect the mold’s performance. Thermoplastics such as polycarbonate (PC) and polypropylene (PP) have high strength, stability and good fatigue properties. These materials also have electrical characteristics that can be beneficial for certain applications.
Other important aspects of a good plastic injection mold design are draft and undercuts. Draft is when a part is designed with a tapered profile, typically 1-2 degrees. This reduces stress and makes the molded part easier to eject from the two-plate mold. Undercuts are protrusions that prevent a part from being ejected, and can be dealt with by techniques like shutoffs, bumpoffs or multi-part molding. Using ribs to support thick areas of the plastic, rather than having them completely solid, will also help with undercut problems.
Injection Process
Injection molding involves the high-pressure injection of raw material into a mould that shapes the polymer into the final product. Initially, the thermoplastic plastic pellets are fed into the injection machine’s barrel where they are heated until they melt to a low viscosity liquid. Then they injection moulding parts manufacturer are mechanically forced through a nozzle into the mold, where they reside until they cool below their freezing point.
During the injection process, pressures build up due to the shear force applied between the molten plastic and the cavity walls. This creates part stresses that can lead to warpage, sink marks and cracking. The stress can be reduced by adding smooth transitions between features and using rounds or fillets in possible high-stress areas of the finished plastic product.
The nozzles of the injection machine’s injection barrel seal tightly against the sprue bushing, which directs the melted plastic into the part-forming cavity images that are machined on the A and B plates of the mould. The sprue bushing also contains channels that connect the melt-delivery sections (sprue and runner) with the part-forming cavity, called gates. Nozzles come in a variety of designs, such as open, shut-off or mixing screw.
Finishing
Once the injection molding process is complete, finishing will help the final product achieve its functionality and enhance its appearance. While some finishing processes are purely cosmetic others serve a practical purpose, such as improving paint adhesion or creating grip.
The right surface finish or texture can also hide tooling marks created during the injection molding process. For example, flow lines, weld marks, sink marks and shadow markings will be less visible with a polished or matte surface finish.
If you are unsure what surface finish is best for your injection molded part, it’s always a good idea to work with an expert. Xometry’s team has a wide range of manufacturing experiences and can help you determine the right surface finish based on your design and materials. This will help you avoid unnecessary expenses and ensure your parts are fabricated to your specifications.
