Injection Molding: Design Guide and Application

Injection molding is a manufacturing procedure for manufacturing components by injecting molten materials into a mold, or mold.

Injection molding allows parts or components to be manufactured in enormous quantities. This is done by injecting molten materials into a mold. It is often used for producing identical items in large quantities.

Factors to consider before designing a molding

No matter how confident you are about the injection mold, there are a few factors to consider before actually starting the process. This would help in reducing cost, and minimizing any problems that might crop up in the process of manufacturing. There is a process called “Partnering with your molder”. Having a close bond with your preferred molder would help you manufacture perfect parts.


Below are some of the factors to consider before commencing injection molding. These factors are important because they can potentially affect any injection molded part.


Material Options and consequences

The type of material to be used is often started early before the molding process commences and should be agreed upon by the molder and the designer. Often, molders purchase enormous amounts of specific resins at huge discounts. These discounts are sometimes passed on to customers. For instance, if a designer can indicate an ABS grade that has the same characteristics as one bought in large quantities by a molder, lots of money can be saved. A designer might also find out that a particular high-performance resin may not be suitable for a molder because of its viscosity, high volume of glass, or crystallinity.

Texturing and Draft

Experienced designers and engineers teams that are conversant with injection molding service are aware of the impact surface finish has on draft angles, such as RapidDirect who has a professional injection molding service team to control on this part. High gloss smooth surfaces can be removed from a mold with more ease when compared to rough or textured surfaces. Oftentimes, components are designed with characteristics that could be created from the core or cavity side of the mold. It is best to discuss features with the molder to avoid mistakes and optimize the part for manufacturing. On external surfaces, certain textures are normally engraved or imprinted into the steel to a particular depth. Deep textures are also occasionally stated for the desired effect.


One of the greatest challenges a designer tasked with designing an injection molded part might face is the provision of sufficient clearance in the design for tolerance variation. Tolerance variation often depends on lots of variables, such as materials used, process control, and the design of the tool. Designers must review acceptable significant tolerance specifications with a molder and assess different options for possible mold revisions if it is needed. This may need specific design features to be purposely designed with extra clearance, which will be tightened later by discarding the steel from the mold. Nobody would add steel with welding to repair interference issues.

Gate location

Gate location should normally be stated by the designer, molder, and toolmaker. Gate location is very important to nearly every aspect of an injection molded part. It determines appearance, warpage, tolerances, surface finish, wall thickness, molded-in stresses and physical properties, and much more. Designers often make use of mold flow simulations to direct gate design and location. This can only work if the molder agrees with the recommendation. Molders often advise the designer about what type of gate and characteristics have to be included in the part geometry based on gate design. Types of gates include; fan gates, edge gates, or spree gates.

Shut-off angles

A lot of people will be familiar with the terms “shutoff angle” and “bypass”. These terms simply mean the minimum angle between the core and the cavity, which generally creates an opening in a part that would normally require a slide or cam. Characteristics such as circular holes, snap locks, or large rectangular openings can usually be molded in walls perpendicular to the line of the draw by designing features for a bypass in the mold. Every molder wants as much angle between the core and cavity as possible, while designers generally would want zero or minimal angle in these features. However, the compromise always lies between a minimum of 3 degrees to 5 degrees in most cases.


Injection molding products used in human’s daily life

Injection molding is important in our daily lives as it is used to create some of the tools, accessories, and appliances we use in our day-to-day operations.


Beauty accessories: Injection molding is used in creating accessories such as variety plastic combs, hairbrushes, casing for blow dryers, hair curler and hand dryers are products of injection molding.

Outdoor appliances: Outdoor equipment such as picnic tables, chairs, and chaise lounges are gotten from injection molding

It is also used to manufacture toys, computer keyboard, mouse and casing for small household equipment, parts of automobiles such as dashboard panels.


Injection molding is an indispensable part of human lives, as it is used to manufacture things we use. From industrial components to household appliances, and also casing for computer hardware. The importance of injection molding cannot be overemphasized.


Injection molding is also used in prototyping, this is known as prototype injection molding. It is used to create parts for prototypes. It also helps in modifying the existing mold, which saves cost and reduces the cost of production.


The above factors should also be followed to avoid mistakes that would result in the creation of a defective mold. The designer, molder, and toolmaker should have a close relationship and share ideas. The designer should also endeavor to tell the molder if he has any requirements or special tweaks for the mold being created.

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