Creating custom plastics through injection molding requires precision, attention to detail, and an in-depth system of checks and balances before manufacturing even begins to make sure the end result is exactly what the customer needs. Whether custom plastics are used as components within an item or our customers need a finished piece, what we deliver must be accurate to the design, consistent, and look flawless, and mistakes or errors that compromise those things can lead to expensive setbacks. Our injection molding company is dedicated to supplying an excellent product with a low per-unit cost and a fast turnaround time, so we know the common problems that can occur and how to prevent them. We’re sharing some of these issues to show how we get the best possible product without setbacks.
Flow Lines on the Plastic
Flow lines are one of the most common problems with injection molding. These are off-tone streaks or lines on the surface of the plastic, and while they don’t affect the structural integrity, they are unattractive and prevent a uniform and consistent appearance.
Typically, flow lines are caused by the liquid plastic cooling at different rates as it flows within the mold. Often, this is because the injection rate is too slow so it takes a “long” time for the melted plastic to reach the bottom or the corners and has cooled by that point, but it can also be caused by the starting temperature set too low.
How We Prevent Flow Lines
We make sure to round areas within the mold in places of varying thickness to improve the flow path of the plastic, and our team ensures the speed and pressure of the injectors are optimized to fill evenly and quickly.
Bubbles Within Completed Pieces
Bubbles and voids within the plastic can affect the structural integrity by creating weak spots in the piece. This can reduce durability and even be a safety issue, especially in automotive injection molding and medical injection molding when precision is absolutely essential.
Bubbles are generaly caused by either trapped gases within the mold due to poor venting, flow problems, or overheating the plastic so it breaks down and releases gases. They can also be caused by vacuum voids in which air pockets get trapped near the surface caused by the center of the part cooling at a slower rate than the surface, causing uneven shrinking or not using enough plastic to fill the mold.
How We Prevent Bubbles
Our design team takes great care in designing the mold to ensure it is vented and the plastic flows properly through it, and our manufacturing team is experienced in setting proper temperatures and pressure and configuring the ideal amount of plastic needed to fill the void completely to avoid gaps and spaces. The end result is a smooth, solid piece of plastic throughout the component.
Sink Marks Marring Smooth Areas of Plastic
While vacuum voids are often the result of the plastic cooling to quicky close to the mold walls, sink marks are the opposite. Sink marks are small depressions or “dents” in a flat or smooth section of an injection molded plastic. The inner part of the component cools faster than the outside and shrinks while the still-liquid material at the outside sinks inward toward the center of the mold. The dents and sink marks are more cosmetic than structural, but they are still flaws that need to be avoided.
How We Prevent Sink Marks
Like many of the other problems found with injection molding, using the right holding pressure and cooling time is key to creating a consistent cool through the part. Also, we make sure the walls of the tooling are designed to achieve the right balance of allowing the center and surface to cool at even speeds.
Weld Lines Can Compromise Strength
Weld lines are thin seams or lines that appear where two streams of melted plastic meet when flowing through the mold and don’t bond well together. Because of the poor bond between the lines of plastic, these can actually weaken the component and making it less durable.
How We Prevent Weld Lines in Injection Molding
Choosing the right thermoplastic and ensuring the temperature and pressure being used to heat and inject it is key to avoiding weld lines. The faster and hotter the plastic is as it flows into the mold, the less likely it is to have a bond issue when two flow lines meet, but going too hot or using too high of a pressure can cause problems, too. Our design, engineering, and manufacturing teams work together to ensure the best possible outcome of the component by making sure temperatures, pressure settings, and other factors are properly optimized.
Rely On Advanced Plastiform for High-Quality Injection Molding
Since 1988, customers have relied on us for injection molding and thermoforming custom plastics. We are dedicated to providing a high-quality product that also is produced at a low cost per unit and with a quick lead time. If you’re interested in having custom plastics manufactured for your company, reach out to our team today. Our injection molding company works with all types of industries in the Southeast and Mid-Atlantic, including North Carolina, South Carolina, Pennsylvania, Maryland, Tennessee, Georgia, and Virginia.