Plastic injection molding is a popular process that produces identical plastic parts and goods. A mold is created and then filled with a molten plastic material to take on the design of the product once it hardens. This process is fast, precise, and cost-effective, especially for high-volume orders. D&M Plastics has nearly 50 years of experience in the production of high-precision injection-molded parts with the durability, design flexibility, and reduced assembly costs that our customers have come to expect.
The Plastic Injection Process
Plastic injection molding follows a precise set of steps to ensure every workpiece is created with consistent quality and structural integrity. Once the mold is created and manufacturing is about to begin, the process goes through the following:
1. The Material Enters the Barrel
Granular or powderized plastic material is poured into the barrel of an injection molding machine down a hopper. Because the material is granular, it can be premixed with other plastics and additives to create a custom substrate for the products. Granular plastics also have a high degree of surface area for easy heating and control.
2. The Material Melts and Mixes
Injection molding machines use two different mechanisms (sometimes in combination) to melt the granular plastics into a molten fluid. The first is the direct application of heat. The second is heat through friction. To melt plastic through the second mechanism, a corkscrew twists through the filled barrel, raising the temperature and pressure as it drives the melting material toward the mold. This ensures the material is well-mixed and evenly heated.
3. The Shot Sizes Are Measured
Each mold needs a precise amount of molten plastic to fill the mold completely without running the risk of errors, air bubbles, or excess material going to waste. This precise amount is called the shot. Factors such as the shot size and injection pressure impact the speed of injection, which ultimately determines the consistency of the material quality throughout the workpiece.
4. The Mold Closes
Molds are made of two pieces that sandwich together, with the internal cavities making up the dimensions of product the mold will produce. The mold must close with enough pressure and strength to resist movement once the pressurized plastic is injected into the mold. Manufacturers must also keep the mold closed for long enough to allow for thorough cooling and hardening but not so long it holds up the production process.
5. The Plastic Is Injected Into the Mold Cavity
The injection machine pushes the molten plastic fluid into the mold’s cavity. The material is injected with enough pressure to ensure it reaches all of the pathways and edges of the mold cavity and the mold is filled before the material can cool and harden. Both the speed and pressure of the injection determine the quality of the finished part.
6. The Molten Material Cools
Once the molten material leaves the heat nozzle barrel of the injection machine or the hot runner system, it immediately starts to cool and solidify. It will take on the shape of the mold cavity and start to gain its permanent characteristics of hardness, bendability, and color.
7. The Mold Opens
Professional manufacturers will ensure the mold is closed for enough time to set the plastic and no longer. Once the determined time has elapsed, the mold will automatically open.
8. The Part Is Ejected
Mechanisms within the mold or injection machine will push the newly created workpiece out of the mold and onto an assembly line below. From there, the piece can be taken for any smoothing, finishing, and packaging steps that are part of its total production process.
The Cycle Begins Again at Step #4
Now that the mold is empty, the injection process can begin again. Professional systems move from step to step quickly for a seamless cycle of production.
Choose D&M for High-Quality Plastic Injection Molding
At D&M Plastics, we specialize in high-quality molding services from start to finish. We maintain over 30 presses and a cleanroom to produce an extensive array of standard and custom plastic parts. We’ve been an industry leader in reliable production and excellent customer service for almost five decades. Contact us today to learn more about our capabilities or request a quote to start your order.
Plastic injection molding is a popular process that produces identical plastic parts and goods. A mold is created and then filled with a molten plastic material to take on the design of the product once it hardens. This process is fast, precise, and cost-effective, especially for high-volume orders. D&M Plastics has nearly 50 years of […]
Injection molding is a manufacturing process used for mass production of plastic parts and components. A press injects molten plastic resins into carefully engineered mold cavities under high pressure to yield large volumes of consistent pieces. The process is highly versatile as molds and materials can be adapted to meet specifications for unique applications across many industries.
D&M Plastics boasts over five decades as an industry leader in injection molding. Our ISO 9001 and ISO 13485 certified facility houses 30 presses, a cleanroom, and a tool room. We perform injection molding using a variety of high-performance plastics to create parts horizontally and vertically with tolerances as close as ±0.001″. In addition to standard injection molding services, we offer overmolding, insert molding, two-shot molding, and mold labeling, which positions us as a single-source injection molding provider for partners across many industries, including aerospace, electronics, and medical.
Best Practices and Considerations
The injection molding process is a cost-effective and highly customizable approach for mass producing plastic components. The design process requires close collaboration between designers, molders, and other stakeholders, each of which should follow best practices and make important considerations to deliver the best value.
Material Options and Consequences
Stakeholders must consider specific tolerance requirements, strength, electrical resistances, flexibility, durability, thermal properties, flammability, and weight when selecting the appropriate plastic for a job. Though they may be easy or inexpensive to source, some plastic varieties may be challenging to mold, so molders and designers must agree on material selection.
Injection molded parts have an average tolerance of ± 0.250 mm (0.010″), and while tighter tolerances are possible, they come at an additional cost. To minimize impacts on finances or production time, designers and molders can add extra clearance to account for tolerance variations and create plans for post-machining, fixturing, adjusting gate locations, and more.
The appearance of sink marks depends on various factors such as gate location, nominal wall thickness, and material. To address the issue of sink marks, it is important to ensure wall thicknesses at the base of a rib or boss do not exceed 60% of the perpendicular or nominal wall, core out solid sections to reduce thickness, or add additional design features like ribbing.
Steel Safe Areas
To address tight tolerance requirements, some designers and molders add steel safe areas to complex sections of a design before mold production to provide clearance for easy machining after initial test shots. These design features can prevent further delays and tooling expenses later in the process.
Proper gate location ensures the flow of molten plastic through the mold. Factors, such as where the heaviest cross-sections of a component exist and the necessary flow path needed to maintain design aesthetic and function, are essential in determining the most suitable gate locations for an application.
A minimum shutoff angle of 3° to 5° and optimally 7° is often required by a molder to leave adequate space between the core and cavity of components that include snap-fits, holes, or handles.
Draft Angle Orientation
Tapering the sides of the vertical walls in a mold allows for quicker, easier ejection of components and reduces the risk of surface blemishes. Feature height, surface finish, parting lines, and part geometry are necessary considerations when determining the correct angle to minimize these effects. Optimal part design would involve allowing 2° minimum draft throughout the part except for areas where draft is detrimental to fit and function.
Texturing and Draft
Texture can play a role in both the aesthetic and function of a part, but larger relief angles are required for these surfaces. Draft angles should be increased by 1° to 3° depending on the extent of the surface texture.
Scheduling of Critical Startup Phases
Close collaboration between designer, molder, and other business stakeholders is necessary to ensure that project timelines are coordinated effectively and that milestones are met. From ordering materials to establishing quality standards, these partnerships help drive product development and manufacturing.
Secondary Operations and Fixtures
Upfront discussions about the possibility for further machining or finishing can align goals and investment expectations ahead of production, while minimizing production problems and delays.
Injection Molding by D&M Plastics
By working closely together from the start, stakeholders involved in the injection molding process can avoid costly production delays associated with materials or component design. D&M Plastics has been an industry leader for decades, and our highly skilled team has extensive injection molding experience and can guide you through the entire injection molding process from design to production. To learn more about our capabilities, contact us or request a quote today.
Injection molding is a manufacturing process used for mass production of plastic parts and components. A press injects molten plastic resins into carefully engineered mold cavities under high pressure to yield large volumes of consistent pieces. The process is highly versatile as molds and materials can be adapted to meet specifications for unique applications across many […]