Author Archives: Anna Kwong

  1. Identifying Plastic Injection Molding Defects

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    D&M Plastics utilizes the latest plastic injection molding technology to create high quality parts for a diverse range of industries. Typically used for mass production, plastic injection molding is a process which allows manufacturers to create immensely high volumes of the same part within tight tolerances. While this process has numerous advantages, errors in the plastic injection molding process or tooling setup may cause defects that impact the appearance or functionality of the final product. Understanding these potential issues makes it easier to avoid them in future projects.

    plastic injection molding defectsIdentifying Plastic Injection Molding Defects

    Here are some of the most common defects to watch for during the plastic injection molding process:

    Burn marks

    These discolorations appear on the outer surface of the component and may be black or rust-colored. They are often caused by trapped air or resin overheating within the mold. Shorten the mold cycle time or lower the mold temperature to avoid burn marks. Adding venting can help with trapped gas.

    Flow lines

    Although they typically do not impact the functionality of a product, flow lines—off-color streaks or patterns across a product’s surface—may look unprofessional when visible to consumers. This defect is caused when plastic cools too rapidly during the injection molding process. Increasing the nozzle diameter and injection speed will help prevent flow lines.

    Short shots

    Short shots weaken the part and are commonly caused by a lack of molding pressure, which results in trapped air within the product.

    Sink marks/voids

    When the plastic does not have enough time to cool within the mold, the surface material may shrink inward. This results in surface depressions known as sink marks. Increasing pressure and cooling time can help avoid this defect. Proper part design is necessary to avoid sink marks, i.e. uniform wall stock rather than uneven/thick walls. Uneven cooling speeds may also create voids (internal sink marks) within the part. Limit the risk of this defect by increasing the injection pressure or choosing low-viscosity materials.

    Weld lines

    Weld lines are caused by multiple molten materials colliding at too low a temperature, resulting in a thin line where the materials did not properly bond. This defect can weaken a component. To help plastic injection molding materials bond properly, increase material temperature and injection speed or eliminate partitions within the mold. Proper gate location can help to avoid weld lines.


    Often caused when residual resin is left in a mold from a previous project, discoloration impacts the aesthetics of a part. Occasionally, discoloration may also occur when the coloring agent is unstable. Utilizing a high-quality coloring agent and thoroughly cleaning the production equipment between production runs helps reduce the risk of discoloration.


    One of the more serious defects is delamination, which presents as a flaking surface layer that separates from the surfaces beneath it. Generally caused when the resin is contaminated or exposed to excess moisture, delamination will negatively impact the strength of the part. It can be avoided by properly storing the resin pellets and increasing the temperature of the mold.


    Jetting appears as a distinctive snaking spray line on the product’s surface. It typically occurs when the molten material is injected too quickly without contacting the mold’s wall. Jetting ultimately weakens the part but may be avoided by increasing the temperature of the material and lowering the injection pressure. Proper gate location can help to avoid jetting.

    Eject marks

    When a part is ejected too early or with too much force, it can be left with unattractive markings. Waiting until the part is fully cooled and reducing the force of the ejector rods can reduce the likelihood of eject marks.

    About D&M Plastics

    At D&M plastics, our experienced team crafts high quality molded products at competitive prices from our ISO 9001 and ISO 13485 certified facility. We can mold parts in both vertical and horizontal molding machines at tolerances as low as ±0.001 inches and offer insert molding, overmolding, and cleanroom molding to meet specialized needs. Visit our injection molding services page to learn more, or request a quote to see how we can help with your next project.

  2. Most Common Materials for Plastic Injection Molding

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    At D&M Plastics, we specialize in performing high-volume injection molding using state-of-the-art equipment and technology to create tight-tolerance precision parts down to 0.001 inches. Our capabilities include:

    We also offer many value-added and secondary services, full service support, and real-time production analysis.

    plastic injection molding materialsCommon Materials for Plastic Injection Molding

    Depending on the end-product’s desired properties, there are a multitude of plastic injection molding material options.


    This material offers very predictable shrinkage, making it ideal for projects which require particularly tight tolerances. Polycarbonate is naturally transparent, strong, and durable, and is a popular choice for protective gear, eyewear, and window parts; however, it is not safe for food applications.

    Nylon (Polyamide)

    Nylon’s strength makes it an ideal material for mechanical parts, sports equipment, and medical products. It is highly resistant to wear and chemicals, has a high melting temperature, and is durable against impacts.


    Acrylic is transparent, and manufacturers often use it in place of glass as it is scratch resistant and has high tensile strength. This material is tasteless, odorless, and free of BPA, making it ideal for food applications.

    Polyoxymethylene (POM)

    This acetal resin commonly replaces metal in automotive or mechanical parts, such as gears or ball bearings. It has high levels of strength and rigidity, and is resistant to alcohols, motor oils, and many other solvents. However, POM cannot withstand nitric acid or hydrochloric acid.

    Polystyrene (PS)

    Polystyrene is budget friendly and available in two types: High Impact Polystyrene (HIPS), which is opaque, and General Purpose Polystyrene (GPPS), which is transparent. Polystyrene is popular for single-use items such as petri dishes and food packaging, but it is not environmentally friendly and does not offer significant strength or heat resistance.

    Acrylonitrile Butadiene Styrene (ABS)

    ABS is a flexible and affordable engineering grade plastic with high amounts of strength and toughness. It is resistant to scratches, offers good impact resistance, and is lightweight. Common uses include electronic casings, phone adapters, and wall socket plastic guards.

    Polypropylene (PP)

    Popular for food packaging, PP is highly resistant to moisture and chemicals. This thermoplastic has a high melting point and is durable, with good impact resistance and flexibility. In addition to its use in the food industry, PP can be found in automotive components, athletic apparel, and many household objects.

    Polyethylene (PE)

    Polyethylene is available in two types: High-Density Polyethylene (HDPE) and Low-Density Polyethylene (LDPE). It is affordable, lightweight, flexible, and moisture-resistant, making it one of the most popular plastic injection molding materials. PE can be found in a wide array of products, including prescription bottles, plastic bags, trash cans, and geomembranes.

    Thermoplastic Polyurethane (TPU)

    TPU provides high levels of tensile and tear strength, withstands high temperatures, and replicates the elasticity of rubber. Manufacturers commonly utilize this material in cable insulation and power tools.

    Thermoplastic Rubber (TPR)

    TPR combines plastic and rubber, resulting in a material that can withstand harsh environments and chemicals. It is highly impact resistant and is commonly used in catheters and headphone cables.

    D&M Plastics for Your Plastic Injection Molding Needs

    For over four decades, D&M Plastics has provided our clients with industry-leading custom injection molding solutions. If you have further questions about the best plastic injection molding material for your needs, our team of experts is here to assist you. Learn more about our services, or request a quote to get started on your next project with us.