ABOUT LOW-MID VOLUME INJECTION MOLDING
Low volume injection molding refers to creating a “low” number of parts using the injection molding services and where that number begins depends on the manufacturer. We at Seaway classify batches ranging between 100 and 10,000 pieces as “low volume”. However, our average production lot is 1,000 pieces and progresses upwards from there.
In contrast to Seaway, other plastic injection molders will usually not consider projects that fall under 10,000 pieces. Our definition stands ideal for several companies in different fields. Those with limited production needs, such as specialized intensive medical equipment and defense armaments, find Seaway’s capabilities desirable. For these situations, companies don’t need more than 10,000 parts made. To add, some companies may need short-run manufacturing abilities to complete projects quickly.
The world does not stop moving: Seaway keeps up with that continuous movement no matter how many pieces.
Types of Injection Molding
Several different types of injection molding exist, and the right options vary. Factors based on the project, the type of part you need, and the volume you need will affect which is best to use. Engineers and designers also consider the material of the mold itself when it comes to volume. Aluminum molds, for example, are best used for lower volume runs while hardened steel provides more security with higher volumes. Tooling costs vary between the two.
Those include but are not limited to:
- Mid volume (10,000 – 500,000) to high volume production (≥1,000,000 parts)
- Two shot molding
- Silicone injection molding (LSR)
- Single cavity, multi-cavity, and family molds
Based on their requirements, budget, and time frame, Seaway can meet expectations with samples in as little as 3 weeks, depending on market conditions.
This differs from additive manufacturing techniques like 3D printing.
How Does Plastic Injection Molding Work?
Plastic injection mold works by melting, molding by machine, and cooling thermoplastics to create parts. The process starts by loading resin pellets into a barrel. Then, machines melt, compress, and inject the plastic into the mold’s runner system. The melted thermoplastics then wait until the previous mold is complete and ejected. Through the now open gates, the melted thermoplastics fill the mold’s cavity. After filling, operators track factors like fill pressure and heat distribution throughout the process. This ensures that blemishes and other imperfections don’t appear. If they do, then operators or engineers can address them immediately.
When the thermoplastic is firm and solid, the mold opens, and ejector pins push the item out of the mold. Then, the mold closes, fills with another shot of thermoplastics, and the process continues to repeat until the batch is complete.
Customers can choose from several different types of thermoplastics available to Seaway. In addition to the typical variety of plastic injection resins, Seaway also offers the option to make products out of highly engineered thermoplastic resins. With Seaway’s experience with over 700+ different types of resins, the possibilities are seemingly endless. Those resin types include but are not limited to:
- Glass Filled Nylon
- Silicone (LSR)
- And many others
When choosing resin, customers need to consider a few different factors when making a selection. They need to think first about the necessary mechanical and physical uses and properties of the part or assembly. They would need to consider that product’s need for resistance to different types of exposure. Those include (but not limited to) chemicals, heat, electricity, flames, and UV rays. Each factor may call for a different type of resin. In additions, each material has different features fit for different uses. Those include cost, pliability, density, impact resistance, susceptibility to sink, dimensional accuracy, and water absorption rates.
Customers may also need to consider resin additives. Several different options exist including glass and carbon fibers. These can strengthen composites, increase hardness, reduce creep, lower costs, make parts self-lubricating, control EMI/RFI interference, or achieve other project goals. Again, each part might need a different resin that fits within the part’s purpose.
Product Designs and Moldability
The right design is critical when using injection molding to create a part. While developing the design, customers need to ensure the design meets the needs of the project. At the same time, you also want to choose a design that lends itself to accurate, high-quality molding. Consider the following:
- Wall thickness: Consistent wall thickness helps to cut the risk of warping or distortion.
- Core geometry: Coring out parts eliminates unnecessary thickness. This can alter dimensions, reduce the strength of the part, and eliminate the need for post-process machining.
- Material-specific designs: The design needs to complement the material you are using. For instance, ideal wall thickness varies based on molding material.
- Ramps: Ramps and slopes reduce the stress risks caused by sharp transitions.
- Radii: Using radii to smooth out sharp corners also helps to drop molded-in stress.
- Bosses: Avoiding thick sections around screw bosses or they may cause voids in the molded part.
- Ribs: Ribs should be less than 60% of the thickness of the walls.
- Core-cavity: When possible, core-cavity stands superior to ribs. It gives a constant wall thickness, a better surface finish, and a faster molding time.
- Fillets: Fillets are design part features that strengthen the design by supporting themselves.
- Draft: Drafting refers to sloping vertical walls. It allows the molding machine to eject the part without making any marks or blemishes.
- Logos and tests: If you have to add logos or parts numbers, consider a few things first. Choose a mill-friendly font, limit the depth to between 0.010 and 0.015 inches, and think about increasing the draft as needed. The increase in draft supports easy ejection from the mold.
Engineers can help with other design considerations that would complement the molding process. Consult with a Seaway engineer today!
Applications for Injection Molding
Injection molding makes parts for a variety of industries. This includes aerospace, healthcare, defense, consumer and many others that require specialized plastic parts.
Companies use injection molding in many applications due to its many benefits:
- Rapid prototypes
- Ability to make tight tolerances
- Fast parts manufacturing
- Ability to test product functionality using CAD models during the development stage
- Ability to create hundreds of thousands of parts in a short time
- Low volume production options
- Supports quick and agile shifts in their manufacturing process
Featured Case Study
Low Volume Injection Molding
This detection device company had designed a detection device for use in identifying airborne explosives, chemicals, and drugs (including fentanyl). With this in mind, manufacturers for the device had to keep to the strict specifications with little room for error. Their need for a highly engineered plastic resin that could withstand extreme environments and use without compromising the machine. However, most manufacturers when dealing with these types of highly engineered plastics either lack the experience to mold them properly or simply will refuse to use them due to their complicated nature.