--- title: "Mastering Undercuts in Injection Molding: Solving External Undercuts" description: Asaclean's Purging Expert Jerry Weddell helps you solve undercut issues in injection molding. He offers tips and tricks to get back to running good parts. image: https://www.asaclean.com/hubfs/Undercut%20Blog%202.jpg --- [ Order Online ](https://asaclean.my.site.com/b2bstore) [ Free Sample ](https://offers.asaclean.com/free-sample) ## [ Asaclean Blog ](https://www.asaclean.com/blog) Browse by Topic " aerospace asaclean asaclean news Asaclean® benefits asahi kasei automotive Best Practices black specks blisters blow molding blown-film extrusion buyers caps and closures carbon contamination cast-film extrusion Chemical Purging Compounds clear applications Color Changeovers Company News compounding consumer products contamination Cost savings custom molders Customer Success Story decreasing scrap defects electronics Energy Efficiency EX Grade extruder cleaning Extrusion fillament glass filled Glitter Grade Selection HDPE High and Low Temp Changeovers hold a bubble Hot Runners Injection Molding Injection Molding Tips LDPE Lightweight automotive components LLDPE low residue maintenance Material Changeovers Mechanical Purging Compounds medical Melt Flow Index NPE 24 nylons on the fly packaging PCR PEEK Polypropylene Post Consumer Resins preventative preventative purging processing tips profile extrusion Purge Program purge programs Purge Training Purge Trial purging purging compounds purging concentrates purging procedures Purging Tips quality recycled resins residue issues scrap reduction Screw Pulls sheet extrusion shutdown and sealing start-up super engineering resins Sustainability Tech Day technical support training trials Troubleshooting Twin Screw twin screw extrusion two step purging U Grade ULTEM venting Viscosity webinars wire extrusion - 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This post is the second installment in our 4-part series, Mastering Undercuts in Injection Molding, where we’re breaking down practical solutions step by step: Part 1: What Are Undercuts in Injection Molding? Part 2: Solving External Undercuts (Parting Lines & Cam/Slide Systems) (you’re here) Part 3: Solving Internal Undercuts (Lifters, Unscrewing Molds & Collapsible Cores) Part 4: Draft Angles & Best Practices for Complex Part Design In this article, we’ll focus on external undercuts—features like clips, hooks, or snap assemblies that appear on the outside of a part. These are extremely common in industries like automotive, electronics, and packaging. We’ll explore two proven solutions: parting line adjustments and cam/slide systems. **Why External Undercuts Are a Challenge** External undercuts are found on the outside surface of a molded part. Unlike internal undercuts, they’re visible—but that doesn’t make them easier to deal with. If you’ve ever worked with parts that include: - Snap-fit assemblies for consumer products - Side clips for automotive interiors - Tamper-evident features in closures - External hooks or protrusions for assembly …then you’ve encountered external undercuts. The challenge is simple: when the mold opens, these features block the part’s ejection path. Without a solution, the part either gets stuck in the mold or the feature breaks off, leading to scrap. **Solution 1: Using Parting Lines to Eliminate External Undercuts** A parting line is where the two halves of the mold meet. With clever design, the parting line can sometimes be positioned in such a way that the undercut is split, allowing the part to be ejected without the need for additional tooling. **How It Works** - By shifting the parting line to intersect the undercut, the mold can release the feature naturally. - This method essentially “splits” the geometry across the mold halves, freeing the part on opening. **Advantages** - Cost-Effective: Avoids the expense of additional mechanisms. - Simple to Maintain: With fewer moving parts, there is less wear and tear. - Efficient: No added cycle time from cams or slides. **Limitations** - Aesthetic Impact: The parting line may leave visible marks, which could be an issue for cosmetic parts. - Geometry Restrictions: Not all features can be split by a parting line; complex or deep undercuts usually require alternative solutions. **Example Applications** - Packaging parts where parting lines aren’t visually critical - Industrial housings where function outweighs appearance - Clips and side features that can be aligned with mold separation **Solution 2: Cam/Slide Systems for Complex External Features** When the parting line can’t eliminate the undercut, cam/slide systems step in. These are one of the most widely used solutions for external undercuts. **How They Work** - Slides move into position as the mold closes, guided by angled pins. - Once in place, they form the undercut feature during the molding process. - As the mold opens, the slides retract, pulling away from the undercut before ejection. This ensures the part can be released without breaking clips or hooks. **Advantages of Cam/Slide Systems** - Handles Complex Features: Perfect for snap assemblies, external holes, or side details. - Fully Automated: The process is built into the mold’s opening and closing cycle. - High Repeatability: Ensures consistent part quality in high-volume production. **Considerations** - Cost: Adding slides increases mold cost and complexity. - Maintenance: Slides require lubrication, inspection, and precise alignment to avoid failures. - Cycle Time: In some cases, the added movement increases cycle time. **Example Applications** - **Automotive:** Dashboard clips, air vent assemblies, or cable housings - **Consumer Electronics:** Side hooks or snap-fit connectors in housings - **Closures**: Tamper-evident packaging with side locking features **Comparing Parting Lines vs. Cam/Slide Systems** | **Factor** | **Parting Line Adjustment** | **Cam/Slide System** | | --- | --- | --- | | **Cost** | Low | High | | **Complexity** | Simple | Complex | | **Best For** | Straightforward features | Complex external features | | **Cycle Time Impact** | None | Possible slight increase | | **Maintenance** | Minimal | Requires regular care | | **Aesthetic Impact** | Visible parting line | Clean Surfaces |   **Best Practices for External Undercuts** - Evaluate early in design: The earlier you decide between a parting line adjustment or slides, the more cost-effective your mold will be. - Prioritize simplicity: If a parting line solution works, it’s almost always better than adding slides. - Balance appearance vs. cost: For cosmetic parts, slides may be worth the added expense to avoid visible parting lines. - Maintenance plan: If using slides, build a maintenance schedule to keep them running smoothly. ** ** **Conclusion** External undercuts are common in injection molding, especially in parts that require clips, hooks, or snap features. Fortunately, there are reliable ways to solve them. Parting line adjustments offer a simple and cost-effective solution, while cam/slide systems handle more complex geometries with precision. By understanding these options, molders and designers can improve ejection, reduce scrap, and maintain part quality. Key Takeaway: For external undercuts, always explore parting line adjustments first for simplicity and ease of use. When the geometry demands more, cam/slide systems are the industry standard for reliable results. In Part 3, we’ll turn to internal undercuts—looking at how lifters, unscrewing molds, and collapsible cores allow molders to produce complex internal features without compromising efficiency. *Are undercuts giving you trouble in production? Our team has helped hundreds of processors improve cycle times and reduce scrap. **C[ontact us ](https://offers.asaclean.com/free-purge-consultation)**[with your questions—we’re here to help](https://offers.asaclean.com/free-purge-consultation).* [![](https://no-cache.hubspot.com/cta/default/468726/interactive-161630774182.png) ](https://www.asaclean.com/hs/cta/wi/redirect?encryptedPayload=AVxigLJVWMZem3DFLC12eXEAdO34Waqe5NJeM6feXVr4FBRMTu0YzSj69BEt7dekS0XCqcjj%2F8tzgMrl1L0OfNtM3VSiNZedgHJ9gl0umEF%2BmVQ%2BbRxEcL0s5dYpDotkTqbJ044zAwOnCPLSnPReO%2FPQI9C5ZuA2KcWAHHi2floJh9YggZOYVdiYYxSDoAOIaEbkk8rWZUJpcR1mBE63E2gz3eMTBYXzAycguQJQzNbTZXbKjFRgWxKDqL5h&webInteractiveContentId=161630774182&portalId=468726) ![Jerry Weddell](https://www.asaclean.com/hs-fs/hubfs/1713568728231.jpg?width=150&name=1713568728231.jpg) #### [ Jerry Weddell ](https://www.asaclean.com/blog/author/jerry-weddell) With over 30 years in the field, Jerry Weddell is a Technical Sales Representative with a wealth of knowledge in mold-making and purging compounds. While his expertise spans injection molding, extrusion, and blow molding, he is particularly distinguished in injection molding. Jerry's profound understanding of these processes enables him to offer targeted, practical solutions, especially in the nuanced aspects of injection molding. His commitment to providing exceptional guidance and support to clients has made him a respected and trusted figure in the industry. - [Share On LinkedIn ](https://www.linkedin.com/in/jerry-weddell-b0747538) ## Related Posts [![Two process engineers reviewing injection molding part quality.](https://www.asaclean.com/hs-fs/hubfs/AI-Generated%20Media/Images/The%20image%20depicts%20two%20injection%20molding%20process%20engineers%20on%20the%20floor%20of%20an%20injection%20molding%20shop-1.png?width=450&height=250&name=The%20image%20depicts%20two%20injection%20molding%20process%20engineers%20on%20the%20floor%20of%20an%20injection%20molding%20shop-1.png) Mastering Undercuts in Injection Molding: Solving Internal Undercuts Troubleshooting / 17 min read / March 03, 2026 ](https://www.asaclean.com/blog/mastering-undercuts-in-injection-molding-solving-internal-undercuts) [![Engineers in front of an Injection Molding Machine.](https://www.asaclean.com/hs-fs/hubfs/AI-Generated%20Media/Images/the%20image%20shows%20two%20plastics%20process%20engineers%20standing%20in%20front%20of%20an%20injection%20molding%20machine%20on%20a%20plant%20floor-1.jpeg?width=450&height=250&name=the%20image%20shows%20two%20plastics%20process%20engineers%20standing%20in%20front%20of%20an%20injection%20molding%20machine%20on%20a%20plant%20floor-1.jpeg) Mastering Undercuts in Injection Molding: What You Need to Know Troubleshooting / 7 min read / February 17, 2026 ](https://www.asaclean.com/blog/mastering-undercuts-in-injection-molding-what-you-need-to-know) ## Comments Get Started ## Ready to start improving your efficiency and increasing your profitability? - [Request a Consultation](https://www.asaclean.com/blog/mastering-undercuts-in-injection-molding-solving-external-undercuts#) - [Contact Sales](https://www.asaclean.com/blog/mastering-undercuts-in-injection-molding-solving-external-undercuts#) ![](https://www.asaclean.com/hubfs/assets/images/icons/icon-layers.svg) #### Free Sample Request a free sample of Asaclean® Purging Compounds for your plant and start saving today. 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[See your savings](https://www.asaclean.com/cost-savings-calculator) [ Back to Top ](https://www.asaclean.com/blog/mastering-undercuts-in-injection-molding-solving-external-undercuts#top) ```json { "@context" : "https://schema.org", "@type" : "BlogPosting", "author" : { "@type" : "Person", "name" : "Jerry Weddell", "url" : "https://www.asaclean.com/blog/author/jerry-weddell" }, "dateModified" : "2026-02-24T17:40:50.754Z", "datePublished" : "2026-02-24T17:40:50.000Z", "headline" : "Mastering Undercuts in Injection Molding: Solving External Undercuts", "image" : [ "https://www.asaclean.com/hubfs/Undercut%20Blog%202.jpg" ], "mainEntityOfPage" : { "@id" : "https://www.asaclean.com/blog/mastering-undercuts-in-injection-molding-solving-external-undercuts", "@type" : "WebPage" }, "publisher" : { "@type" : "Organization", "logo" : { "@type" : "ImageObject", "url" : "https://www.asaclean.com/hubfs/Asaclean%20Logo%20TM.jpg" }, "name" : "Asahi Kasei Plastics North America" } } ``` ```json { "@context" : "http://schema.org", "@type" : "Article", "articleBody" : "In Part 1 of our series, we introduced undercuts in injection molding, explained the difference between internal and external undercuts, and discussed why they matter in complex part design. This post is the second installment in our 4-part series, Mastering Undercuts in Injection Molding, where we’re breaking down practical solutions step by step: Part 1: What Are Undercuts in Injection Molding? Part 2: Solving External Undercuts (Parting Lines & Cam/Slide Systems) (you’re here) Part 3: Solving Internal Undercuts (Lifters, Unscrewing Molds & Collapsible Cores) Part 4: Draft Angles & Best Practices for Complex Part Design In this article, we’ll focus on external undercuts—features like clips, hooks, or snap assemblies that appear on the outside of a part. These are extremely common in industries like automotive, electronics, and packaging. We’ll explore two proven solutions: parting line adjustments and cam/slide systems. Why External Undercuts Are a Challenge External undercuts are found on the outside surface of a molded part. Unlike internal undercuts, they’re visible—but that doesn’t make them easier to deal with. If you’ve ever worked with parts that include: Snap-fit assemblies for consumer products Side clips for automotive interiors Tamper-evident features in closures External hooks or protrusions for assembly …then you’ve encountered external undercuts. The challenge is simple: when the mold opens, these features block the part’s ejection path. Without a solution, the part either gets stuck in the mold or the feature breaks off, leading to scrap.", "author" : { "@type" : "Person", "name" : "Jerry Weddell" }, "datePublished" : "February 24, 2026", "headline" : "Mastering Undercuts in Injection Molding: Solving External Undercuts", "image" : "https://468726.fs1.hubspotusercontent-na1.net/hubfs/468726/Undercut%20Blog%202.jpg", "name" : "Mastering Undercuts in Injection Molding: Solving External Undercuts", "url" : "https://www.asaclean.com/blog/mastering-undercuts-in-injection-molding-solving-external-undercuts" } ```