How Draft Angles Affect Mold Release: Essential Guide for Mold Design

Table of Contents

Part with and without draft angle
Part with and without draft angle


One major objective of every manufacturer of injection molded parts is to ensure a perfect cycle of parts production. Thankfully, introducing draft angles to the design process often increases the probability of a successful production.

Now this begs the question, what are draft angles?

A draft angle is a mold design consideration for areas in the mold like corners and intricate shapes that make it difficult to remove the plastic part from the mold. Its primary job is to ensure the safe and seamless removal of molded parts. It doesn’t end there.

Draft angles also reduce the possibility of defective parts often caused by difficult demolding processes.

By the end of this post, you’ll not only know the function of draft angles but also how it influences mold release and its many benefits. Shall we begin?

Draft Angle Injection Molding 2
Internal Draft Angle

Understanding Draft Angles

To begin with, draft angles are incorporated into mold design so that the friction between the mold and the molded part is eliminated. Furthermore, a crucial assignment of the draft angle is to ensure the part maintains its structural integrity. Here is how it carries out this assignment.

When the injection molding process reaches its optimal cooling temperature and the molded part is solidified, the next operation is to eject it from the mold. However, ejection can be challenging for parts with intricate details or complex geometries. However, the placement of draft angles reduces the possibility of the molded part getting stuck to the mold.

As a bonus, draft angles are responsible for one additional role.

If the detachment of the molded part is successful, the mold is saved from frequent damage due to reduced friction. In addition, an efficient production cycle is achieved and the component maintains its structural form.

However, you may encounter terms such as positive and negative drafts when dealing with mould designs and draft angles.

What do these mean?

Positive drafts are the narrow parts of the draft that extend to the outer sections. They are the real MVPs of the ejection process. Meanwhile, the negative drafts as their name suggests do not assist much with the ejection.

draft in core and cavity
Draft in core and cavity

Mechanics of Mold Release

Like a referee in a football match who ensures the match abides by the game’s rules, so does the draft angle function in the interaction between the mold’s surface and the molded component.

The draft angle in its bid to minimize the occurrence of abrasion between the two players controls the level of contact between the mold’s surface area and the molded part. The goal here is to ensure the removal process is risk-free and easy.

Consequently, the placement of the draft angle is crucial for this phase to be successful.

Let’s picture it from this angle. The complete absence of draft angles puts the mold and the component at a high risk of damage. This helps nobody especially the mold itself as production efficiency is significantly reduced.

With that said the proper placement of draft angles creates a frictionless ejection. This is because as the component cools down within the mold, it shrinks. This helps the draft angle limit the ejection force required with the outcome being a seamless ejection. Thus, ensuring both players come off unscathed.

On top of that, draft angles share the ejection force evenly over the component to avoid cracks and flaws which is why its impact is huge in maintaining top-quality manufacturing.

Draft Angle in molds
Draft Angle in molds

Optimal Draft Angles

The quality of every component begins with selecting the right materials. Likewise, choosing the right draft angles often depends on the material selected for the part production.

The applications of draft angles on different injection molding materials are important as each material possesses differing qualities which is essential in knowing how to apply draft angles.

Thermoplastics: In the case of thermoplastics, these materials have an excellent malleable quality about them. With that, the degree of draft angle that makes it effective to eject is between 1 and 2 degrees.

Thermosets: The same conditions do not apply to thermosets, largely due to their high chemical bonding properties. This means that once formed it is difficult to remold by reheating it. However, draft angles for this material increase from about two to three degrees. This will ensure there are no cracks in the component after solidification.

Elastomers: Elastomers being the third member that completes the group are pretty malleable as well just like the thermoplastics. This makes such materials require a lower draft angle of about one degree. Its elastic quality makes it easier to detach from the mold without compromising its integrity.

These recommendations are based on the selected material. Since part geometry also plays a significant role in the selection of draft angles, it is important to always consider this in mold design. Hence, where complex shapes and designs are involved special considerations are required.

From extensive experience in injection molding, the deeper or more complex the design, the more draft angle to be applied. That sounds more like the laws of supply as well but never mind.

Furthermore, the shape extensively determines what draft angle is to be applied as well. For instance, cylindrical parts or components with undercuts may require different degrees of draft angle at different points in the ejection process.

Above all, meticulous considerations must be implemented before deploying the various draft angles in the cookbook. This will yield more benefits than complications.

Complex Part Geometry is Crucial to Draft Design
Complex Part Geometry is Crucial to Draft Design

Design Considerations

From the foregoing discussion on part geometry and depth as considerations for applying draft angle, well that’s just the captain of the team. Let’s introduce the other members of the team. Other factors make up the design considerations for draft angle including the following.

●  Part complexity: When the part to be manufactured carries some complexity with it, then the regular measure of draft angles may change, requiring more unconventional mold release mechanisms. Part complexity entails complex designs that are accompanied by textured surfaces, threads, and undercuts. This may necessitate wider degrees of draft angles or extra split mold mechanisms.

●   Surface finish requirements: This is the co-captain of the team. Designs with special surface finish requirements will ensure the appropriate draft angle is used. Textured surface finish for example will consider the perfect draft angle to ensure zero flaws in the quality of the final product.

●    Wall thickness: The wall thickness is another determinant of the degree of draft angle required. In this case, the thinner the wall, the higher the degree of draft angle needed to counter defects when ejecting from the mold. On the contrary, a lesser draft angle is needed for designs with thicker walls.

As surprising as it might sound, other design features play minute but essential parts in considering the draft angle requirements. Balancing them is of utmost importance.

Let’s take cooling rates and material shrinkage as part of the other design features. Mold designers have to balance these with the necessary draft angle applications.

Nevertheless, with a consistent wall thickness, cooling and shrinkage rates could be monitored and guarantee they are uniformly controlled. Then the accurate draft angles can be applied. Additionally, material flow must likewise be controlled for even distribution of material. The essence of that is to further aid the proper cooling of the molded part for an efficient mold release.

Draft Angle Injection Molding 1
Parts without draft angle are hard to remove

Consequences of Inadequate Draft Angles

Inadequacies often breed challenges and this is no different. The errors of deploying the right draft angles lead to potential issues. You can probably guess what these potential issues might be, but in case you guess wrong don’t sweat it.

  • Part sticking: You are right if you guessed part sticking is the first potential issue for errors in draft angles. Where drat angle is lacking, the molded part sticks to the mold. This is every manufacturer’s incubus because production time is stretched owing to extra measures employed to pull out the stuck component. Production efficiency also diminishes, and additional cost is incurred, let’s not forget the potential damage to the mold itself.
  • Surface defects: A perfect surface finish is paramount to every production cycle. Some other products require extra top-quality surface finish. Imagine the disappointment when a lack of adequate draft angle diminishes the quality of the surface finish. Due to inadequate draft angles, drag marks and scratches impair the quality of the surface finish anticipated. In some cases, they are redeemable by adopting post-processing routines and in other cases, nothing can be done to salvage the part.
  • Increased wear on molds: The overall health of the mold is dependent on applying the appropriate draft angle. When the reverse is the case, the mold suffers as much as the component suffers. The forceful removal of parts from the mold wears on it and the quality of the parts produced might be questioned due to wear and tear. The mold will then require constant replacement or maintenance which drives up the cost of production.

These potential issues put production efficiency and quality of parts produced on the negative side. We might be hard on the increase in the cost of production, but while necessary corrective measures are being implemented production is halted completely. The quality of the parts produced goes under strict review to be certain it meets industry standards. All these are negatives for both production efficiency and part quality.

Effective draft angle
Effective Draft angle

Best Practices for Implementing Draft Angles

With the knowledge gained from the consequences of inadequate draft angles, best practices that can mitigate those potential issues have been discovered. A few of these best practices include

  • Using CAD software for draft analysis: The use of Computer-Aided Design (CAD) software has been developed to help analyze the best way to implement adequate draft angles even in complex designs. This software predicts potential issues during draft analysis, thus tackling the problem before it arrives. The CAD software ensures that precise draft angles are incorporated into the mold design before fabricating the mold.
  • Consulting with mold designers and engineers: Consulting the biggest brains with the technical know-how is another practice that aids proper draft angle implementation in mold production. Experienced mold designers and engineers can spot a draft angle inconsistency with their wealth of industry knowledge hence their involvement in the implementation of draft angles.

An effective draft angle design is achievable when all factors are considered. Part geometry, wall thickness, material types, and qualities all play an essential role in reaching an effective draft angle design.

A typical example is an automotive part manufacturer that considered increasing the draft angle from two to three degrees due to the undercut in the part to be manufactured. The ejection force is largely reduced, the part ejection is seamless, and the aesthetic is intact.


In a nutshell, it is crucial to note that for an optimal draft angle, the types of materials and their qualities will aid the accurate implementation of the draft angle. In addition, factors such as part complexity, surface finish, and wall thickness are essential in identifying the degree of draft angle to select.

Ultimately, understanding the importance, effect, and best practices required for an adequate implementation of draft angle is paramount for effective mold design and production efficiency. However, as advancement in injection molding technology continues, there is no doubt that more advanced ways of implementing a draft angle to boost production efficiency will be developed.


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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