Plastic Injection Molding

Suited for manufacturing parts in large volumes, plastic injection molding is often used for mass production. Thousands, even millions, of parts can be produced in the same production run. One of the most important aspects of injection molding is the material used. There are hundreds of resins to choose from. We will explore some of these, the uses and benefits of plastic injection molding, and other considerations below.

Plastic Resin Injection Molding Benefits

Manufacturing, in general, tends to be expensive. Injection molding is one of the most cost-effective techniques, but there are a wide range of benefits. Here are some reasons why your facility should consider it:

• Cost-Efficiency at High Volumes: The price per unit is set early in the process. Injection molding can then be scaled to meet any need; the more parts produced, generally the lower the price, as the same equipment is used to continue producing more parts.
• Less Waste Material: Although scrap rates aren’t as low as 3D printing, injection molding doesn’t cut away nearly as much material as CNC machining. In addition, thermoplastic materials lost during the process can be melted and re-formed, so they can be constantly recycled.

In many cases, the recycling process is integrated into the production chain. For example, excess material and rejected parts are introduced to the injection molding press with raw materials. Called re-grind, the amount of reused material used is limited by quality control departments.

• Repeatability: Despite volume, each part will be identical to the next. The performance of the plastic is also consistent; therefore, all items produced in a lot are consistent with the quality and expectations of a particular brand.

Disadvantages of Plastic Injection Molding

There are some downsides that make injection molding more complicated than most people realize. It’s important to get a product design right the first time. Prototype development is an important stage requiring a different material, set of tools, and even facility than the final product. You may need many prototypes to develop and refine the injection mold tool.

This can lead to disadvantages such as:

• High Tooling Costs: Tools are usually made of steel or aluminum and must be produced using CNC or 3D printing. Creating the tooling is, essentially, its own project.
• Uniform Wall Thickness: Not only must a mold be consistent in thickness. If the walls are too thick, cooling can lead to inconsistencies and defects; thin walls can make it hard to fill the mold tool—the ideal wall thickness is around 4 mm.
• Size Limitations: Mold tools and injection mold machines often limit part sizes, so multiple pieces often need to be created. Machinery for producing very large parts is available but expensive to use.

Common Plastic Resins

As mentioned earlier, the type of resin is among the most important considerations. For example, food-grade plastic molding must yield products that are antimicrobial and food-safe. Other materials must tolerate friction, heat, chemical exposure, impact forces, and other elements. Here are some of the most frequently used resins:

• Celcon® (Acetal): Resistant to wear, creep, and chemical solvents, acetal is also preferred for its dimensional stability, stiffness, and low moisture-absorption properties. Stability is crucial for utensils, straws, containers, wraps, and other items that come in direct contact with food, but Celcon® is also suited for plastic gears, bearings, wear pads, guitar picks, and other parts that endure contact-related friction.
• ABS: Acrylonitrile butadiene styrene (ABS) is strong and impact-resistant, and it tolerates a wide range of temperatures. It is used in piping and for automotive parts. The versatility of ABS is, in part, due to its ability to adhere to itself and similar plastics, as well as metal coatings. You’ll find ABS in appliances, computers, medical devices, toys, showerheads, motorcycle helmets, and musical instruments.
• Polypropylene: One of the most widely produced plastics, polypropylene (PP) is tough, elastic, and chemically resistant. Its insulating properties, fatigue resistance, and resistance to electricity suit it for manufacturing, automotive, packaging, household appliances, and construction applications. However, PP tends to be flammable, and it deteriorates when exposed to ultraviolet radiation.
• High-Impact Polystyrene (HIPS): Easily glued, bonded, printed, and decorated, HIPS is also regarded for its impact resistance, machinability, and dimensional stability. It is also highly customizable. HIPS is often used for promotional signs and displays, retail packaging, and posters. In addition to electronic housings and toys, it’s preferred for various graphic arts applications.
• LDPE: Low-density polyethylene (LDPE) has high-impact strength, chemical resistance, and moisture resistance. It is also translucent and weatherproof. Numerous consumer goods are made with LDPE, including bottles and containers, shopping bags, computer components, and juice boxes, as are agricultural and medical products. Recycled LDPE is often used in furniture, garbage can liners, shipping envelopes, floor tiles, and other items.

Considerations

The primary considerations of plastic injection molding include the initial investment in manufacturing capabilities. The cost of design, testing, production, assembly, and marketing and distribution must be factored as well. With the numbers in hand, you can then determine a part quantity that makes injection molding cost-effective.

Design considerations factor in parts and tools. The geometry and complexity of the part should be as simplified as possible. The mold tool must be designed carefully to prevent production defects. There are also important considerations for production. These include minimizing cycle time by, for example, using machines with hot runner technology and designing parts to reduce the need for assembly.

Contact Laszeray for Custom Plastic Injection Molding

If you need custom injection molding services, you can depend on Laszeray Technology, LLC. Our equipment can process over 250 different resins and create plastic parts in a wide range of sizes and complexities. Molds are produced and maintained at our in-house tool shop. We specialize in a wide range of plastic molding processes; our specialists help you determine the best one for your project and guide you every step of the way. Call us at 440-582-8430 to learn more.