What Is a Plastic Injection Mold? An injection mold forms molten plastic into a specific shape for various uses. The mold is designed by an engineer or industrial designer then the specifications are given to a tool or mold maker to implement. Plastic injection molds are typically made from steel, or aluminum precision machined to conform to the exact product design specifications. Injection molding can be used to create a wide variety of product sizes and applications from an automobile body to small components used in a vast number of industries.
How Are Plastic Molds Made?
Tooling that is made for plastic injection molding companies to manufacture custom plastic parts is manufactured in multiple steps or stages.
1. Manufacturability and Feasibility
The first step requires manufacturing specialists to collaborate and establish the product specifications, appropriate materials, and component functionality. The team of engineers and production technicians identify any potential design constraints, geometries that could introduce technical issues, or features that require special tooling requirements such as slides, lifters, or threading. They determine the desired plastic material for the product before selecting the optimal metal for the mold to ensure it facilitates the physical, chemical, and cooling properties of the injection molding material. Several tests are done, including mold flow evaluation, a manufacturability review, and a PFMEA or process failure mode effects analysis.
2. Preliminary Design
The preliminary design stage uses models to determine the ideal mold and steel concept for the product. The design is marked up with changes to be finalized after review and approval.
3. Final Design Specifications
At this stage of plastic injection molding manufacturing, the mold builder gets the final design specifications. The mold maker can then implement any final adjustments or modifications to ensure it conforms to dimensional and manufacturability requirements.
4. Construction of The Injection Mold Tooling
At the start of the mold construction the team has completed the tool drawings and reviewed the manufacturing standards. The plastic mold manufacturer creates a detailed plan for ordering the proper components and employs highly skilled mold making staff and precision machinery to create every detail of the new plastic injection mold. The mold construction timeline can range from 5 days to 16 weeks depending on the complexity of the product and mold design.
5. In-House Initial Samples
Before the initial samples are created, the team establishes a molding process that the manufacturing department approves. The manufacturing process will go through a rigorous series of trials to find the optimal temperatures, times, pressures and speeds for the final approved injection molding process. The sampling process can take several hours or days depending on the dimensional or appearance requirements of the final product.
6. Make Any Final Tool Corrections
The final step in the plastic injection molding manufacturing process involves verifying the mold construction did not have any trouble producing parts to the product specifications and documenting the detailed procedure for future use. The parts that conform to the customer specifications are then submitted to the customer. Once the customer approves the sample, the full production process can commence.
Common Types of Plastic Used for Molded Parts
Choosing the right material for your injection molded products is one of the most critical aspects of product development and injection mold design. It not only determines a lot of the molding cost, but also the part performance. Many material choices are available depending upon the application that impacts the part’s strength, flexibility, durability, color, and cost. Some of the most common include:
- Nylon (Polyamide) – Nylon is often used for mechanical parts requiring strength, toughness, high melting points, as well as good chemical and wear resistance. Examples include automotive components such as bearings, bushings, gears, and quick-release buckles.
- Acrylic – Acrylic is used in applications that require transparent parts. Because of its excellent clarity and weight advantage, it is ideal as a glass alternative.
- Polycarbonate – This durable thermoplastic is approximately 200 times tougher than glass and has excellent clarity.. It is used as a much stronger alternative to acrylic.
- Polyoxymethylene (POM) – POM is a strong, tough, and rigid acetal material that serves as an alternative to metal in some cases where high resistance to solvents is required, such as automotive parts like gears and bearings.
- Polystyrene (PS) – There are two commonly used types of PS: High Impact Polystyrene (HIPS) and General Purpose Polystyrene (GPPS). GPPS is transparent, and HIPS is opaque. They are inexpensive and sturdy enough for toolboxes and power tools.
- Acrylonitrile Butadiene Styrene (ABS) – ABS is an opaque engineering-grade thermoplastic that is very tough with impact, scratch, break, and tear resistance. Because of its low melting point and price, it is often used for keyboards, phone adapters, and wall socket guards.
- Polypropylene (PP) – Polypropylene is a thermoplastic most commonly used for food storage and packaging due to its ability to prevent chemicals from contaminating food. It does not degrade in hot water and has high elasticity, toughness, moisture, impact, and chemical resistance.
- Polyethylene (PE) – This lightweight thermoplastic is water-resistant with high elasticity and chemical resistance, as well as electrical insulating properties. It is used for various products, such as fuel tanks, childrens toys, and trash cans.
- Thermoplastic Polyurethane (TPU) – TPU has excellent elasticity, high tensile and tear strength, and withstands a wide range of temperatures, making it ideal for power tools, sporting goods, cable insulation, and seals.
- Thermoplastic Rubber (TPR) – TPR is a recyclable mixture of rubber and plastic with high impact strength and superior chemical and weather resistance. It is often used for headphone cables, medical catheters, and suspension bushings.
Calculating the Cost of a Plastic Injection Mold
When it comes to injection molding cost, several factors can influence the cost of a plastic injection mold, including:
- Mold construction
- Number of mold cavities
- Part complexity
- Part size
- Plastic Material choice
Low Volume vs. High Volume Production Runs: What To Consider
Within the injection molding industry there are several niche groups of manufacturers. A low-volume injection molding manufacturer is normally a fast and low-cost way to produce part orders less than 100,000 parts per year. A mid-volume plastic molded parts manufacturer routinely produces runs of 100,000-1,000,000 components. For orders above 1,000,000, high-volume injection molding manufacturers are best equipped.
Advantages of Plastic Injection Molding Manufacturing
Plastic injection molding manufacturing provides numerous advantages over other production methods like machining, including but not limited to:
- Accommodates insert molding
- Design flexibility
- Fast, efficient production
- High consistency and repeatability
- High-output production with minimal tooling maintenance required
- Large selection of materials
- Low finishing requirements
- Low waste and high recyclability
- Multiple color options
- Reduced labor costs due to automation
China Molds vs. USA Molds
China has been a popular alternative to USA plastic mold manufacturing. Chosen normally for low costs for initial tooling, China often proves to be a bad decision in the long run. Disadvantages include long lead times, high down payments, inconsistent quality, communication challenges, and cash in advance payment terms. In contrast, U.S. injection molding suppliers and manufacturers have the advantages of low part pricing, fast response times, lower-order minimums,, net 30 day terms, great communication, and reliable delivery . There are tremendous advantages for USA companies to support each other in the plastics manufacturing industry.
Custom Plastic Mold Manufacturing
Custom injection molding produces precision parts in complex geometries that contain numerous custom features. At MSI Mold, our highly experienced engineers and process technicians can design and manufacture plastic injection molds for your most challenging thermoplastic part specifications. The MSI Mold team creates all of our molds in-house, and our proprietary rapid tooling systems provide reasonable mold costs and fast lead times for high quality parts. Contact MSI Mold today or submit an RFQ to get started with MSI Mold, a USA plastic injection molding company.