The most common process used in manufacturing plastic components is injection molding. This manufacturing process uses specialized machines that melt, inject, and shape thermoplastic into specific shapes. As with any manufacturing process, it’s prone to unique molding defects or low-quality products if not properly managed. Here you’ll learn more about injection molding, six common injection molding defects, and how to avoid them.
Any successful injection molding project must take multiple factors at once into consideration.
Materials play a significant role in injection molding. A skilled injection molding provider can help you choose a thermoplastic that fits your budget and performance requirements. Because molders often get discounts on the large quantities of thermoplastic grades they purchase, they can pass on those savings to you.
Every product made through injection molding should have specific tolerances to fit their intended application. Certain materials may be difficult to mold or hold to required tolerances, and the design of the tooling can also affect the final part’s tolerance. Always discuss with your injection molder the acceptance tolerance range for specific products.
Molders must maintain specific barrel and nozzle temperatures in injection molding because they affect the ability of the resin to flow throughout the mold. Barrel and nozzle temperatures must be precisely set between thermo-decomposition and melting temperatures. Otherwise, it may result in overflow, flash, slow flow, or unfilled parts.
Molders must maintain an optimal flow rate to ensure that the heated plastic is injected as fast as possible into the mold’s cavity until it is 95% to 99% full. Having the proper flow rate ensures that the plastic retains the right viscosity level to flow into the cavity.
Other factors that should be considered in any injection molding operation are:
The injection molding process involves six main steps, and issues can arise at any of these stages if not carried out properly.
In this process, the two halves of the mold are tightly secured using a clamping unit, which uses hydraulic power to exert sufficient force to close the mold. Without adequate clamping force, the process can lead to uneven wall sections, inconsistent weights, and varying sizes. Excessive clamping force can result in short shots, burns, and gloss level changes.
Molders inject melted thermoplastic material into the mold with a ramming device or screw under high pressure. Then, the part must be allowed to cool at a uniform rate. If not, the final part can have flow lines or unwanted patterns that affect its aesthetic.
Once the thermoplastic material has been injected into the mold, molders exert more pressure to fill the cavities fully. They usually hold the molten thermoplastic material until the mold’s gate freezes. The dwelling period must apply the correct pressure—too low and it can leave sink marks on the finished product. Excess pressure can cause burrs, enlarged dimensions, or trouble releasing the part from the mold.
After dwelling, the mold is filled, but it is likely still too hot to remove from the mold. Therefore, molders allocate a certain amount of time for the mold to absorb heat from the plastic. Molders must maintain sufficient, uniform cooling of the thermoplastic material or will risk warping of the final product.
The movable plates of the mold injection machine open. Some molds have air blast control or core pulls, and the molding machine controls the level of force used to open the mold while protecting the part.
The final product is ejected from the injection mold with a pulse from the ejection system, rods, or robotics. Nano release coatings on the mold surface helps prevent rips or tears during ejection.
There are several molding defects associated with injection molding, such as:
The Rodon Group, a high volume, custom injection molding specialist, has a long history of injection molding. Since our founding in 1956, we have been dedicated to providing our customers with the highest quality injection molded parts available. Today, our defect rate is less than 1 part per million, a number few other large volume injection molding manufacturers, if any, can offer.
To learn more about The Rodon Group, including our capabilities and extensive quality control efforts, contact us or request a quote today.