Injection Molding Part Design
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Injection Molding Part Design

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Injection Molding Part:

Size: 211cm * 145cm * 8.2cm

Material: PA6 + 15% GF

Finish: Texture VDI23

Tooling Materials: P20

Cavity: 2 Cavities

Injection Molding Part Design


Injection molding as one of those technologies, it is so centrally in nearly all the industries. Almost everything is made from plastics! We are surrounded by the objects created through injection molding process in the daily live. As a product designer, it’s important to understand injection molding , and how injection molding part design!


What is injection molding process?

Injection molding is a process to manufacture a wide ranges of items from small part to large components. It uses a granular plastic that is gravity fed from a hopper, forced into the mold cavity, then cooling and ejecting out as a solid part. The manufacturers apply Injection molding process to make custom parts in any volume.


Firstly, we need to have a injection mold. 

Here are the 3 types of molding in manufacturing field.

Prototype molding by aluminum molds to get hundreds of prototypes injection molded parts.

Rapid injection molding by steel molds to get small to medium volume injection molded parts.

Mass production by hardening steel molds to produce parts in large volumes.

Selecting the best tooling and molding methods can allow the designers and customers get qualified injection molded parts with less investments. Needs injection mold for your new projects, send us inquiry at today

Secondly, we can summarized the injection molding process to 4 major steps. 

The full cycle time of injection molding typically takes 30 seconds to 2 minutes.



The manufacturer clamps the core side and cavity side on the injection molding machine. Hydraulic power may be involved for sliders.



Raw materials are fed into the injection machine, then melted and pushed into the mold cavity though barrel.



Cooling is the stage to allows the molten plastic to solidify and take the shape of the cavity. A series of cooling channels on the mold, the cold water goes through the cooling channel in order to cool down the plastic.



The molded parts are ejected out by ejectors after cooling. Some manufacturers usually spray mold release agent on the cavity for better de-mold and improve drag.


Thirdly, why injection molding?


1. Low production costs

The unit part cost is extremely low even if for the low volume injection molded parts, the most significant costs for low volume molding comes from setup costs. Furthermore, the more parts you produce, the less unit price is! Injection molding cost competitively among the traditional manufacturing processes, especially on the large volume runs.


2. Low scrap rates

The molding materials is in pellet. Comparing to the block or sheet cutting, injection molding can reduce the waste plastics maximum from the principle, even though there are waste plastic comes from runners, gate, and sprue, they can be recycled.


3. Repeatable and consistent quality

Injection molding is an idea process, it is particularly suitable to run identical parts from low volume manufacturing to mass production. Each part can in the same quality as the first one approved sample, the manufacturers can get consistency and reliability quality injection molded parts.


Injection molding benefits quite a lot to manufacturers and designers, but it is not perfect. It has disadvantages as well. The major challenge of injection molding is in how to design the injection molded parts to get a good quality injection mold! The mold is the database of parts! You can never get nice products if the mold has problem. Injection molding part design is the topic on the following article.



Injection Molding Part Design Considerations

Injection molding part design involves lots of factors. The part not only functional well but also well to manufacture. Part design always effects on the tool design, product’s quality. The right tooling way is critical, we need to take into considerations of the factors such as entry cost, production quality,  demanded quantities, cycle time, finish, assembly etc.


Injection_Molding_MaterialsMaterial Selection

There are thousands of material options on the market. Choosing the right injection material for your molded part is critical! First of all, as a designer, you need to confirm the function of your products? Will it works under harsh conditions? Will it waterproof? Thinking about all these then pick up the scope of injection materials.


There are two major categories of plastics for injection molding—Thermosets and Thermoplastics, we will look at the major characteristics of plastics and some design considerations.



Thermoplastics become soft with heat and are easy to injection mold. They do not go through a chemical change like thermosets. Because of this, reprocessing after the initial manufacturing process is possible. There are two different types of Thermoplastics—Semi-Crystalline and Amorphous.  



When processed, a thermoset plastic goes through a chemical reaction. This reaction creates bonds in the polymer chains. The chemical reaction is not reversible and can only happen once, so the use of regrind is impossible. The tradeoff is the potential for high-strength and high-temperature resistance. Common types of thermoset plastics are epoxy, silicone, polyurethane, and phenolic.


Popular materials for injection molding:

ABS; Acrylic; Polycarbonate; PVC; Acetal; Nylon; PBT; HDPE; LDPE; PET; Polypropylene.

You can contact our team at for more details.


Additives and Fillers

It’s common to use additives and fillers in injection molding. For a simple example, the injection molder coloring the molding material in expected color through adding pigments or colorants, these pigments or colorants belongs to additives. Also, the material manufacturer modify the material’s properties through adding additives and fillers. Taking the nylon 12 and glass filling material for example, the nylon 12 after adding glass performs much stronger, it is far more harden than raw material nylon. Furthermore, the manufacturer can get modify materials include UV protectants, antioxidants, antistatics, antimicrobials, lubricants, and so on through adding additives and fillers.


Parting_Lines_AnalysisSelecting a Parting Line

The first consideration of injection molding part design is parting line selection, it is directly define the parting surfaces where the two halves of the mold come together. For some applications, it is obvious choice to set the parting lines, but not for all the cases.

Firstly, deciding which direction of mold open(the line of draw will be for the mold). You can have a good reference on the below image.

Exploded View for Injection Mold

1. The parting line should be as simple as possible to avoid adding cam actions and lifters.

2. Choosing the A side and B side for your part,  appearance and cosmetic surfaces for A side on cavity side, other non-cosmetic surfaces for B side on core side. As ejectors always setting on core side, it will have visible ejector pin marks on the part of core side.

3. As plastic has shrinkage, it should have more features on B side to avoid part sticking issue.


Adding Draft

To avoid part stick and drag issue, draft is necessary for injection molded parts. Generally speaking, the surfaces parallel to the mold open and close direction should have drafts angle.

The draft angle can be verified depends on molding material, surface finish, part structures.

The general rule is to have at least one degree for every inch of depth. Below is a list of suggestions for different finishes.

Further considerations for draft

1. Draft on A side typically should be smaller than B side, this is a way to avoid stick issue.

2. The more aggressive texture, the more draft you need.

3. More draft on deep or thin ribs to avoid drag issue.


Uniform Wall Thickness

The consistent wall thickness throughout a part is the key to injection molding. The injection material can flow into the cavity smoothly and cools down evenly. The uneven wall thickness usually leads to injection defects such as sinks, stress marks, short shot etc. The pressure and temperature drop too much from first side to the end side in unevenly wall.


Coring & Ribbing to avoid thick sections

To avoid thick sections leads to injection molding defects, coring and ribbing should be way to improve this issue. The part with ribs can reduce the cycle time, reduce the part weight, and can make the part even stronger. The ribs are usually added on core side, adding on cavity side will affect the part’s cosmetic and geometry. Depending on the injection molding materials, the ribs should be 1/2 of wall thickness, but not less than 0.8mm. The thinner ribs leads to short shot, and the thicker ribs lead to shrinkage.


Looking for a reliable manufacture to assist with injection molding

Given the many design considerations for injection molding, it takes special skills, training, and knowledge to implement all of them and get the part right. This is something takes lots of costs. As a experienced manufacturer in China, TEAM MFG can provide you with an individual or a team of professionals who can help you develop injection molded parts from scratch. We will match you with pre-vetted and highly qualified design professionals.



Contact us to get a free quote today, and tell us about your project!


TEAM MFG is a rapid manufacturing company who specializes in ODM and OEM starts in 2015.

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