Understanding Undercuts, Side-Actions, and Cams in Mold Design

Table of Contents

Injection mold undercuts
Injection mold undercuts


Injection molding as a manufacturing technique presents manufacturers with the best of both worlds. And the reason is simple. Injection molding offers precision, performance, and efficiency. However, the road to these impressive milestones is rocked by some bumps Some of these bumps including undercuts, cams, and side actions are not entirely villains because they assist in the manufacturing of complex parts.

The injection molding process starts from the melting of plastic to the ejection stage, but then that’s where these complexities show up. Undercuts prevent the easy ejection of injection molded parts from the mold, hence the superheroes that save the day in side-actions and cams.

Let’s take you on a magic carpet ride as we unveil a whole new world of undercuts, side-actions, and cams. Let’s go.

Undercuts in injection molding
Undercuts in injection molding

Section 1: Understanding Undercuts

When designing a mold for injection molding, undercuts offer a dimensional complexity responsible for the forming of parts that cannot be achieved any other way. However, as brilliant as the idea of undercuts is in mold design, its ability to create complex geometrical designs also comes with difficulty in ejection. Owing to the protrusion that hinders simple ejection caused by undercuts, designers, and engineers develop other means of removing the molded part via other creative ways. Meanwhile, ensuring the part is unaffected while ejecting it from the mold remains paramount.

To a novice, undercuts might be seen as a feature that brings problems and headaches. But to engineers, designers, and manufacturers, it allows them to create some of the most sophisticated parts the manufacturing world has ever seen. On top of that, it also serves as a channel where manufacturers incorporate other features such as custom inserts, threads, side holes, and snap fits. These features further improve the natural performance of a molded part.  So, under the right circumstances, undercuts could have different views for different viewers. It could be seen as a challenge, or an opportunity to tip the scales of innovation towards manufacturing advancements.

On the flip side, it is not deficient in challenges. In fact, its challenges are the driving energy for creative solutions. Topmost among these pitfalls include the impending damage to the molded part. The presence of undercuts poses an immense risk to ejecting the perfectly molded part from the mold. Thus, manufacturers must ensure and designers must ensure the easy removal of the parts produced. In addition, undercuts require post-processes that are liable to increase the cost of production. Hence, the proper positioning of undercuts in the mold design is essential to efficiently minimize costs.

Injection Mold Side Action
Injection Mold Side Action

Section 2: Side-Actions in Mold Design

Having considered undercuts and the role they play in mold design, side actions offer a solution to the struggles undercuts pose to manufacturers. Side actions are crucial to the existence of undercuts as it solves the problem of undercuts without damaging the molded part. The creativity of designers and engineers spurs the idea of side actions in combating the stress and issues undercuts pose. Its working principle entails placing the sliders and lifters adjacent to the parting line of the mold. With that, pulling out the molded part with undercuts becomes a walk in the park.

Since the development of side actions as a tool to eliminate the threat undercuts pose, there has been no limit to the design possibilities available to manufacturers in crafting and molding complex parts. The efficacy of side actions reveals the capacity to create unorthodox designs and shapes and the manufacturability of these shapes. This guides them in accurately incorporating undercuts into designs to raise the bar on the complexities of the design. On that note, some considerations are necessary to effectively employ the powers of side actions in manufacturing high-performing and aesthetically appealing components.

To garner the full competence of side actions, manufacturers are saddled with the responsibilities of factoring in design considerations such as part geometry. This is crucial to understanding how complex the design is and how to place the side actions. Furthermore, material characteristics are likewise essential. The behavior of the plastic materials to be employed during injection molding will determine how to optimize the use of side actions. One last consideration would be the molding process requirements. Yet, manufacturers have to be wary of the occurrence of wear and tear of the side actions, hence adequate maintenance protocols must be implemented for an effective side action procedure.

Cams in molds
Cams in Molds

Section 3: The Functionality of Cams in Molds

Similar to side actions, cams in mold design are also a mechanism channelled toward safely ejecting molded components from the mold. Nonetheless, cams are dynamic in their modes of application and quite versatile as well. The role of cams in mold design is displayed in their mechanical movements in ensuring molded parts are precisely and accurately ejected without blemish. For this reason, manufacturers of complex features such as threaded or locking mechanisms are the biggest beneficiaries of this ejection method. On the back of that, cams work in unique movements and with certain accessories that aid its effective use. The use of cams in mold design also offers numerous advantages that have made it a go-to solution for precise and controlled ejection for manufacturers.

Cams offer a more sophisticated way of seamlessly ejecting complex components with undercuts, but a major difference between cams and side actions is the movement. Cams operate with a rotational or linear movement ejection technique. Additionally, cams work alongside sliders and ejector pins to attain optimal efficiency in the ejection of complex parts. The controlled movement translated from rotary to linear aids in achieving precision. Beyond that, cams foster alignment while molding is ongoing to ensure the undercuts are precisely positioned.

One of the major benefits of cams in injection molding is the ability to use controlled movements to ensure precise ejection that increases the functionality and finesse of the component. In addition, it helps in manufacturing a consistent and precisely molded component which improves part quality especially when manufacturing a large volume. Meanwhile, specific limitations are likewise encountered. For instance, the maintenance of cams application in manufacturing can be more expensive than other ejection techniques. It may require contracting the services of a trained professional with vast knowledge and expertise. Also, designing cam profiles for complex designs can be daunting.

 Injection molding Design
Injection molding Design

Section 4: Designing with Undercuts, Side-Actions, and Cams

The mold in injection molding takes responsibility for the outcome of any component. Thus, for projects with undercuts, ensuring they are ejected without damage is the goal. Nevertheless, incorporating these features into the mold will require in-depth knowledge of its principles. Undercuts as we now know hinder the smooth ejection of injection molded parts. With that in mind, the most important principle is ensuring its corrective measures are adequately implemented. That requires that side actions and cams are strategically placed to ensure they work as a union in achieving optimal production efficiency. The only way that happens is by employing the side action and cams where appropriate in ejecting components without flaws.

Besides incorporating undercuts, side actions, and cams, designing complex mold mechanisms can be taxing. But to make these designs easier, the adoption of software such as computer-aided design (CAD) software is encouraged to foster designing for efficiency and manufacturability. This software fosters visualization and simulations of behavioral tendencies of undercuts, side actions, and cams. Additionally, this tool assists in proactively anticipating errors and also seeking potential ways to tackle such impending errors. This will in turn limit costs, reduce production time, and guarantee efficiency.

Practical knowledge of these mold design techniques can only be obtained from successful case studies. These case studies highlight how manufacturers work together with the designing team to craft molds with undercuts, side actions, and cams. For example, an electronic manufacturer that wants to manufacture a lustrous speaker. It begins with a CAD-developed 3D model where the side actions were placed at an elevated angle to the parting line. Furthermore, cams were infused into the mold design to accommodate movements that will aid the ejection of the parts with undercuts. The mold designer chose a steel material for the mold crafting, and the close communication between both parties ensured the mold was fabricated to perfection.

Molding Cost Consideration
Molding Cost Consideration

Section 5: Troubleshooting Common Issues

For every problem, there’s a solution. That brings us to the common pitfalls related to undercuts, side action, and cams and their corresponding remedies. They include

  • Undercut Interference: Sometimes, interference between the molded parts and undercuts could cause drawbacks leading to mold damage, production delays, or even part sticking. This could be detrimental to the quality of the part.
  • Mechanism Failure: Cams and side actions if not properly maintained will fail over time. These mechanisms are mechanical components that are subject to wear and tear in the long run.
  • Production Variability: Variability or differences in part dimensions and shapes can affect the part’s quality. This results from improper placement of undercuts, side actions, and cams.
  • Cost Considerations: The existence of undercuts signifies increased production costs. Then, corrective mechanisms in side actions and cams further incur additional costs. Hence, the adoption of these mechanisms can be pocket-draining.

With the common problems identified, here are some troubleshooting systems that can help mitigate these challenges

  • Undercut Interference:  The best solution to part sticking from undercut interference is the modification of ejection force or the application of more ejection pins to aid seamless ejection. Additionally, the mold can be frequently maintained by cleaning and lubrication to avoid part sticking.
  • Mechanism Failure: To eliminate the possibility of this occurrence, regular maintenance is quite necessary. This entails swapping worn parts with new parts which will guarantee smooth operation.
  • Production Variability: Careful placements of side actions and cams in tackling undercuts and process optimization will ensure parts uniformity. This may also require modifying process specifications.
  • Cost Considerations: when the costs outweigh the benefits of adopting these mechanisms, it will be prudent to optimize the mold design phase. This removes any extra cost that would have been incurred with the use of undercuts, side actions, and cams.


In a nutshell, undercuts can either be a blessing or a curse. But with the aid of corrective mechanisms such as side actions and cams, it becomes more advantageous for creating complex components. Undercuts on their own are a nightmare to manufacturers that eventually require creative ways to mitigate. However, the corrective steps, birth side actions, and cams that then make undercuts seem awesome.

Conclusively, the strategic placement of side actions and cams in creating a win-win situation comes as a blessing in disguise. The employment of CAD software will enable designers and manufacturers to determine potential challenges and adequately deploy corrective measures. Through it all, undercuts, side actions, and cams are an inseparable bunch that ultimately ensures efficiency and productivity.


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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