Understanding Draft Angle in Injection Molding for Effective Molds

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Draft angles often come up in discussions that pertain to plastic injection molding. It is so because it is essential to the successful production of parts when the preferred manufacturing method is injection molding. With that said design considerations in injection molding go beyond selecting the right material and optimizing machine settings. Understanding draft angle is as important as these options mentioned.

injection mold

However, as a professional the inclusion of draft angles consideration eliminates moldability concerns to a large extent, assists in the final appearance of molded parts, reduces risks posed by ejection, and offers top quality to users of these molded parts. 

So, if you’re new to plastic injection molding, we suggest you sit back and relax as we take you on a journey through the world of draft angles and their importance to injection molding.

1. Understanding Draft Angle in Injection Molding

1.1 What is Draft Angle?

Often when a manufacturer of plastic parts embarks on a part production, factors such as draft angles are infused in the production process. Draft angles are like oiling a key to seamlessly fit into a keyhole and foster easy removal as well. But in the case of draft angles, they are measures created as part of the mold that allows the easy and fast removal of parts produced. 

The vertical walls of the mold need to be tapered to allow the smooth ejection of parts from the mold. The introduction of draft angles saves both the part and the mold. The mold is vulnerable to rapid wear and tear, while the part likewise is subject to defects from getting stuck to the mold.

Furthermore, the lack of a draft angle increases the risk of friction to both the mold and the part. In the event this occurs, the part loses its structural and aesthetic properties. This in turn reduces the parts functionality and increases the production cycle times. 

With slight slopes applied, the frictional impact is reduced saving the mold and the part. This is the reason draft angles are typically infused in the design phase to ensure optimal injection molding outcomes. 

1.2 Importance of Draft Angle

The importance of draft angles cannot be overemphasized. Draft angles, if carefully considered and implemented, play a crucial role in any injection molding process. But let’s note a few reasons injection molding cannot do without draft angles. 

First is improved moldability. As a result of the slight slope infused into the mold, the ability to easily remove the part formed from the mold without physical force that dents the part and the mold, production runs are increased and efficiency in part production is also increased. 

In addition to improved moldability, draft angles assist in reducing the friction that would have been detrimental to both the mold and the product. More importantly, draft angles limit the occurrence of surface flaws that can lead to post processes which in turn increases the cost of production and cycle times. 

The performance of your product is likely to be compromised due to distortions or warping in the product. Now who wants that? You are right, nobody. 

On top of all that, draft angles increase the mold’s lifespan and further reduce the costs of production – another result draft angles offer the high-quality mold manufacturing industry. 

The mold can be severely damaged within a short space of time if excessive force is applied during part removal from the mold. That shortens the lifespan of the mold and replacement will be necessary. Now imagine replacing molds intermittently, that isn’t good for injection molding.

Lego injection mold

2. Effects of Insufficient Draft Angle

2.1 Moldability Issues

When the provisions made for draft angles in a mold are insufficient, this can lead to a host of production challenges in injection molding, one such being moldability issues. 

In some cases, draft angles might be completely lacking. And when such occurs, there is no preventing the friction that follows. It is no longer news as to what that does to the parts. You as a manufacturer are left with a distorted part with deformities all around it. 

The functionality is reduced as the structural balance of the part is minimized, while production costs will be inflated. As the costs increase so does the cycle time. 

It’s like a chain reaction of events with one problem leading to another and all accounting for the challenges posed by the lack of one thing – an insufficient or missing draft angle. 

A more consequential effect of the lack of draft angles or its inadequacy is the challenge of a more difficult ejection process of parts from the mold. This automatically means the part becomes stuck to the mold and makes proper and easier ejection impossible. 

The result of this is a forceful ejection that can damage the part or render it completely useless by breakage and the possibility of that happening is huge. Visible blemishes are conspicuous and the reduction in parts marketability is further depleted. It’s no wonder high-quality mold manufacturing companies never fail to put draft angle into consideration at the design stage. 

2.2 Manufacturing Constraints

The lack of draft angles or its inadequacy doesn’t stop with moldability issues. It further poses certain manufacturing constraints. These constraints are not limited to but include increased injection pressure. The pressure applied when injecting the molten plastic into the mold must be increased to compensate for the lack of taper that will help in ejecting the molded part. 

And for this reason, higher energy is consumed. The increased consumption of energy by the injection molding machine results in greater wear and tear on the machine, and this impairs the efficiency of the process. 

Additionally, the lack of draft angle means longer production runs and longer cycles partly because it now takes longer to separate the part from the mold. This reduces production efficiency and cycle time simultaneously. 

Moreover, the application of excessive force in detaching the part produced from the mold likewise results in extensive damage to the old components. When damage to the mold occurs, production is halted for possible repairs. This results in increased downtime and reduced output while increasing tooling costs due to the repairs. 

It is glaring the vicious cycle of failures and inefficiencies that a lack of draft angle brings. It is safe to say then that draft angle is essential to limiting complications, ensuring seamless and budget-friendly production while optimizing the injection molding process.

draft angle design

3. Determining the Appropriate Draft Angle

3.1 Part Design Considerations

After examining the possibilities of draft angles and the setbacks of not adopting draft angles, it is paramount to determine the accurate appropriation of draft angles during designing. And the necessary design considerations to be critically factored in the part’s design itself includes

  • Part geometry: The intricate dimensions of a part’s design are essential to determining the type of draft angle to be included. The more intricate the design, the higher the draft angle. Consequently, if the dimensions are quite simpler, then a lower draft angle should be included in the design.
  • Material selection: At every stage of the injection molding process, material selection has been an important consideration. For draft angle considerations, the shrinkage properties of the material are highly regarded in determining the draft angle. Materials that possess flexible properties will require higher draft angles and vice versa. This is to make up for their different shrinkage properties.
  • Surface finish: The surface finish requirements are crucial as certain part designs require a very smooth surface finish akin to sophisticated production methods like high-quality CNC Machining. These types of designs will adopt higher draft angles to eliminate marks that may have been created during ejection.

Further determinants of draft angles include the fusion of text and logos, undercuts, and wall thickness must ensure the proper number of draft angles in part design considerations. 

3.2 Mold Design and Tooling Considerations

Part design is crucial to determining the appropriate draft angles from injection molding, but what’s also important is mold design and tooling considerations. Parameters for consideration in mold design and tooling include

  • Mold release: The ejection of parts from the mold can only be successful with the right mold release mechanisms. The mold release mechanisms such as lifter, pins, etc., are pivotal in maintaining the perfect release of parts from molds without jeopardizing the integrity of the part and the mold. 
  • Sliders and side actions: For designs with intricate geometries or undercuts, side actions, and sliders may be needed to keep the design integrity while ejecting the part, making room for the draft angles on different parts to ensure smooth ejection. 
  • Cooling channels: It is confirmed that without proper cooling warping and distortions can occur. It is, for this reason, cooling channels should be properly and meticulously positioned in the molds to eliminate these risks. 

And where there are insufficient draft angles, these cooling channels compensate for the remaining lags. What’s more, the intricacies in part layouts and cavities should be in tandem with the number of draft angles appropriated for them to ensure optimized production runs and efficiency. 

4. Draft Angle Guidelines and Best Practices

4.1 General Draft Angle Recommendations

In an attempt to determine the best draft angle recommendations to work with, it is noteworthy to understand the general rules and tips as to what standard is adopted for draft angles in injection molding. 

However, it is also useful to know that draft angles may differ in terms of the design considerations and the material properties that are also deployed. About that, here are a few general guidelines to integrate into your designs. 

The typically recommended draft angle dimensions for most applications irrespective of what material is selected are between one to three degrees. Thus, providing ample taper and facilitating the seamless ejection of parts from the mold

Furthermore, when employing materials such as elastomers and specific thermoplastics that possess more flexible properties, a draft angle in the range of three to five may be wise to adopt. This will enable the draft angle to fit in with the properties of such materials. 

In addition, for aesthetic purposes such as finely textured surfaces, draft angles within the same three to five degrees or more would be required. This ensures any marks from ejection-based frictions are duly catered to, and the desired smooth, eye-catching surface finish is attained. 

Material suppliers and mold designers are the best practitioners to assist in determining the best draft angle option that can be applied relating to the materials in use as well. 

4.2 Case Studies and Examples

What better way to demonstrate the impact of draft angle in injection molding if not by showcasing real-world case studies? These applications expand more on the scope and provide tangible insights in terms of moldability, part quality, and production efficiency of injection molding over new innovations like 3D printing technology

A typical example is in automotive part manufacturing where the challenge of part ejection surface defects of a complex interior trim component is common. With an increase in the draft angle from 1.5 to 3 degrees, the result is often phenomenal. Reduced friction, elimination of visible marks, smoother ejection, and an outstanding surface finish that takes the aesthetics to a different level are usually the outcomes of such draft angle adjustments. 

By the same token, a company in the consumer electronics industry also experienced a sticking and part deformation problem while manufacturing plastic housing. By adopting an increased draft angle of 2.5 degrees and integrating a proper mold release mechanism, part ejection was enhanced while the sticking challenge was massively curtailed. 

These are a few case studies amongst many where a tweak in the draft angle and implementation of other mold design and tooling considerations have expressly elucidated the impact of draft angles in injection molding.


In closing, it is imperative to note that the inclusion of draft angles in achieving a successful part production in injection molding is pivotal. Nonetheless, the effects of neglecting the adoption of this parameter would result in moldability issues and manufacturing constraints. 

Despite that, determining the appropriate draft angle will require you to take into account the part and mold designs and tooling. And in addition to that, general draft angle recommendations stipulate a one to three degrees draft angle be infused into the part design to foster easy ejection, complete part integrity, and production efficiency. 

Ultimately, draft angles are useful to many if not all industries, especially the automotive and consumer electric sectors. So, if you were ever in doubt, this is a guideline for understanding the impact of draft angles in injection molding and its contribution to successful molds.


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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