Injection Molding Services

Simplicity is Important:

There are many factors that can quickly complicate an injection molding project. By keeping your design simple you can avoid many complications that may arise in the manufacturing process. Some examples of simplicity in design are avoiding sharp inside corners, undercuts, and deep recessed cavities, which can all hinder the ejection process from the mold cavity and quality of the final product.

Use proper draft angles:

Designing proper draft angles is an important part of injection molding design because it allows easier and more efficient part removal from the mold. If a part design does not account for removal from the mold, the part can stick to the mold making it difficult to remove and potentially damage the parts upon removal. Both of these setbacks increase manufacturing costs and a lower yield of parts within the intended tolerance.

In general, it is best to avoid 90 degree angles in injection molding designs since they are not practical with the manufacturing process. However, a proper draft angle can be used to avoid these complications. A draft angle is a small incline of the surface of the part that makes it easier to remove from the mold. Even a one degree adjustment to a vertical surface of the part can prevent parts from sticking to the mold, prevent warping, and minimize unwanted flashing on surfaces.

Plan for shrinkage:

Since the plastic injection molding process involves heating plastic to fill a pre-existing mold, it is important to keep in mind that plastic decreases in volume as it cools and solidifies. This process is called shrinkage. Shrinkage rates will vary based on the type of plastic material that is being used, wall thickness of the part, and the overall temperature of the mold.

Shrinkage can create numerous issues during the injection molding process, such as warping, cracking, or flashing. Warping occurs when parts cool unevenly causing unwanted bends or twists. Cracking occurs when parts cool too quickly which creates stress points that are severely weakened. Flashing occurs when plastic leaks out of the mold cavity and cools along the parting line.

In order to minimize complications that come with shrinkage, part designers must take many factors into account, such as the shrinkage rate of the intended plastic material and designing the mold cavity with slightly oversized dimensions. Both of these considerations allow for the part to shrink to its correct size once it has cooled and solidified.

Think about the gate location:

Gate location is where the melted plastic is injected into the mold in injection molding. Since the gate is the point of entry of plastic in a mold, it needs to be designed and placed carefully to ensure a smooth and efficient molding process.

Gate location is important because it affects the quality and consistency of the final part. A poorly placed gate location can result in defects such as uneven cavity filling, sink marks, or flashing. Poor gate positioning may also result in cosmetic flaws or imperfections if not properly taken into account. Typically gates are located in non-visible areas to avoid any cosmetic issues with the outer surfaces.

Another important factor of designing a gate location is understanding that it affects the flow of plastic into molds, the filling time, the cooling time, and accommodating pressure releases from the heating and cooling processes. An optimally designed gate location would ensure that the melted plastic is evenly and efficiently distributed throughout the mold which would result in a consistent and high-quality final product.

Consider the material:

When designing a part for an injection molding project, choosing the proper material can have a significant effect on the outcome of the final part. Since injection molding can utilize a large array of different plastic materials, it is important to consider which plastic material is suited for your design, both functionally and cosmetically. The properties of a plastic material can determine its longevity and functionality in various chemical, temperature, and pressure environments, as well as dimensional stability, surface finish, and overall aesthetics.

Some important factors to consider when choosing the proper plastic material for your injection molding project are mechanical properties, temperature resistances, chemical resistances, dimensional stability, surface finishes, and even recyclability. Before choosing a material to be molded, it is important to confirm whether or not the functionality of the final part would be hindered by particular properties of the base plastic material.

Make use of ribs and bosses:

Ribs and bosses are typically used in injection molding designs to add strength and rigidity to parts and reduce the chances of having it warp or break. When ribs or bosses are placed correctly, they can increase the structural integrity of a part and distribute pressure points more evenly across a part.

Ribs are raised features which are added to increase the stiffness and strength of a part. They are typically added to walls or other thin sections of a part to prevent warping or other deformations. These ribs also allow for even distribution of loads across a part which reduces the formation of stress points and cracks.

Bosses are another raised feature that are added to designs to provide locations for fasteners, screws, bolts, or other mating surfaces for other parts.

Both of these features have the capabilities of adding to the overall structural integrity of a part but also to produce a more aesthetically pleasing and functional design. When designing these features, it is important to keep in mind the thickness, size, and location of their placement. When properly designed, ribs and bosses can minimize the chances of warping, cracking, and flashing while also improving the overall quality and consistency of the part.

Wall thickness should be consistent:

When designing a part for plastic injection molding, consistency among wall thicknesses is important because it helps ensure that the plastic will cool and solidify evenly, which reduces the risk of defects, such as warping or cracking. When a part has an uneven or inconsistent wall thickness, the thicker sections cool and solidify more slowly compared to thinner wall sections. This design flaw can lead these thicker walls to warp or crack as they cool since the thinner sections have already been solidified and molded.

Having consistent wall thickness also helps provide the final parts with dimensional stability and reduces the risk of shrinkage or warping. Consistent wall thickness typically results in better surface finish and overall consistency in terms of dimensions and shape. Features such as ribs and bosses can also be used to strengthen certain sections so the walls can stay consistent, provide structural integrity and improve the overall quality of the molded parts.

Consider post-molding operations:

Not all parts are designed to be used as produced. Many parts undergo secondary machining services to make the final product, such as trimming, sanding, polishing, painting, assembling, and packaging. Even if a part is not meant for a secondary machining service, it might become necessary due to short-sighted design mistakes. For example, if a part is affected by flashing due to shrinkage or inconsistent wall thickness, it may have to undergo trimming or sanding to remove excess materials which adds to manufacturing costs and delays production.

By considering post-molding operations in the design or prototyping process, it makes it possible to optimize the engineering of the parts and the molds, to minimize the need for additional machining services and steps.