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Plastic Injection Molding Guide - From Design to Materials

October 15th, 2020

Thermoplastics are what most people think about when they think of plastic injection molding. Many common products, such as telephones, computers, auto parts and appliances are made this way. Additionally, some highly-specialized industrial components are made this way as well. Regardless of the part, the goal is to optimize cost and time efficiencies while producing superior quality, meeting regulatory compliance, and ensuring end-user satisfaction. With such high standards, plastic injection molding requires technical expertise, which is why partnering with an experienced molder is essential. Working with a company that has a true understanding of design for manufacturing has a plethora of benefits including confidence and results-driven, efficient design decisions.


Design for Manufacturing

Design for manufacturing is the process of consciously and proactively designing products to optimize all facets of manufacturing. This methodology brings together engineering and production into the design phase; there should be a symbiotic relationship between part design and mold design. It encompasses material selection, mold design, and process optimization. 


The basic process of injection molding beings when a polymer is heated and forced through a nozzle or sprue. In the mold, this polymer passes through runners and gates. Then, when the part is ready, the mold is opened, and the part is taken out.  


Thus, the following factors are especially important to consider in injection molding: materials, wall thickness, angles, gates, vents, structural reinforcements, cycle times, and undercuts.  



It’s critical to choose the right material, as this decision affects not only the molding operation, but the products performance. One should consider strength, durability, flexibility, color and cost when choosing materials. At Southwest Plastics, our working knowledge of engineered plastic and molding compounds ensures that your parts deliver optimal performance. Forming solid partnerships with all our material vendors enables us to be up to date on the latest engineered materials and ensures our customers top priority when supplies are short. There are dozens of plastic material options to choose from when working with Southwest Plastics, and we will work with you to make sure you select the right one for each part.  


Wall Thickness

Walls that are too thick can make a part too heavy, expensive, or esthetically unattractive. Walls that are too thin can weaken and cause parts to fail. The part wall’s thickness will also Affect the thermal, electrical, and acoustic insulation, as well as impact the corner radius and resistance. 


Draft Angles

Applying draft to the faces of the part is critical to improving the moldability of your part. Otherwise, parts run the risk of poor cosmetic finishes, and may bend, break, or warp due to molding stresses caused by the plastic cooling. Equally important, an absence of draft may prevent parts from ejecting from the mold, damaging not only the parts, but possibly the mold itself—which can be costly and time-consuming.


Vents and Gates

Vents release air that’s displaced during the in-flow of molten material. Gates are transitional areas between the molded part and the runner system that should be large enough to allow uninterrupted material flow, but small enough to separate the runner from the part easily. 


Structural Reinforcements

Some parts may need added strength through the use of reinforcements instead of thicker walls. 



Undercuts are part features that can complicate the ejection of injection molded parts. Examples of these protrusions and indentations include locking tabs, slots for switches, and screw threads. They add cost and complexity to the mold. 


Cycle Times

A faster cycle time means the products will get to market faster, while simultaneously reducing manufacturing costs by decreasing production time. Decisions like material selection will impact cycle times.


The benefits of design for manufacturing can be appreciated across industries and throughout companies, from new product development to the mass production of specialized industrial items. At Southwest Plastics we will work with you throughout the entire experience of plastic injection molding, from design and material to production and execution. We put your unique needs first, while always protecting your company’s intellectual property. Contact us now to find out how we can make injection molding work for you. 

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