Adding Undercut and Side Action Complexity without Sacrificing Speed
About Xcentric Mold & Engineering Xcentric Mold & Engineering provides the fastest, most affordable quick-turn low-volume injection molding, CNC machining and rapid prototyping services within 15 days or less. Xcentric can manufacture complex parts without compromising the engineers design or time-to-market. Features: Simple and Complex Insert Molding Simple and Complex Overmolding Unlimited Undercuts Internal & External Threading Free Manufacturability Review Xcentric complement s their automated manufacturing through a skilled sales engineering team who works with design engineers to optimize their parts. In addition, we achieve tighter tolerances through our quality control tooling process. 24541 Maplehurst Drive Clinton Twp., MI 48036 (586) 598-4636 sales@xcentricmold.com Highlights: 20 years in business Two Highly Advanced Manufacturing Facilities Located in South East Michigan All molds are built and run onsite at each facility Over 10,000 tooling orders placed Life Time Mold Guarantee 1,000 s of different engineered grade materials processed 50+ industries served Proprietary advanced manufacturing processes and automation Manufactured in the USA
Our Story In the mid 90 s, two Michigan-bred brothers working for other companies as mold makers realized that all the mold shops in the Detroit area lacked technology and relied primarily on traditional and more manual processes. In 1995, they decided that the only way to differentiate from their peers in the trade was to learn and apply technology on their own and Xcentric Mold & Engineering was born. They built a proprietary advanced technology platform focused on software, automation, systems, and custom standardization and processes it would become the foundation that would surpass all other traditional manufacturing companies. Employees were hand-picked and trained through a rigorous advanced mold making program that the founders created so each individual could speak technically and with confidence to customers on the fly. The art of mold making was transformed into the science of custom quick-turn manufacturing and Xcentric Mold & Engineering of today where quality, design and speed are not compromised. The brothers knew they created something special. Because of their vision and strong belief in utilizing and creating technology, processes and systems along with building a team of professionals, Xcentric was able to compete even when jobs were being lost to lower labor countries overseas. And when the bottom fell out in the economy in 2009 it had very little effect on the company. A story of two brothers, a vision realized through courage and innovation combining the art and science of mold making, leading to over 20 years of experience as Xcentric Mold & Engineering. Copyright Xcentric Mold & Engineering 3
What is an Undercut? Draw Cavity An undercut is any indentation or protrusion that prohibits the ejection of a part from a mold. Core An undercut is a feature that cannot be captured with the cavity and core alone. It is dielocked which prevents the part from being ejected from the cavity. Undercut Undercuts can be used to carry out complex forms of molding such as the overmolding process and insert molding process. Parting Line Copyright Xcentric Mold & Engineering 4
Purposes of Undercuts Some of the more common ways to use undercuts are to create interlocking or snap and latch features. This allows for clamshell or housing designs to come together for quick and easy assembly. Another way to use undercuts are to capture side holes or ports for wiring, button features or assembly. Snap & Latch More common ways to use undercuts are to capture vertical threads and barb fittings typically used in medical device products. Holes or Ports Undercuts can also be used to core out thick sections that cannot be captured by the core and cavity alone. This prevents the possibility for sink and warp. Finally, undercuts can be used to provide threaded and custom inserts that are not in the line of draw. The insert itself can sometimes create undercuts. Vertical Threads Barb Fittings A thorough DFM can be provided by your manufacturer to identify problematic areas within the undercut features. Therefore, it s best to design it as you intend it and to keep the functionality of your design. Copyright Xcentric Mold & Engineering 5
Undercut Example - Medical Undercuts are commonly used in medical parts. At left, is a medical part with some key features. Vertical Threads The internal threads on this part uses a side action to unscrew from the part after the injection process to create these threads. Be sure to continue threads throughout the entire interior of the part so the interior hand load will not be dielocked and can be easily removed. Internal threads must be captured by a hand load that is removed manually from the part after molding. Core-out Keep in mind, the space between the inlet ports also require a special undercut called a core-out. Core-outs are used to keep wall thickness even and are a planned aspect of the design. Barb Fittings The barb features are another classic yet complex undercut feature for medical parts because they are necessary for tubing. Most manufacturers will mold this so that the barb is parrallel to the parting line. At Xcentric, we use a rather complex undercut that includes a pin assembly to allow for venting and capture the barbs perpendicular to the parting line. The venting will prevent gas trapping and air burning which creates short shots at the tip of the barb feature. Copyright Xcentric Mold & Engineering 6
Undercut Example - Consumer Electronics At left is a cell phone housing that contains many undercuts. All the holes located on the side of the housing are considered to be undercuts. These functional features include buttons, port holes and hinges. However, each undercut adds to the complexity of the mold. There are also some recessed areas that we call internal undercuts which are areas inside the part that cannot be captured from outside the part. Core Internal undercuts can be the most difficult type of undercut for a manufacturer to capture. Special considerations must be made for allowing enough space for the removal of these. Draw Cavity Internal Undercut Copyright Xcentric Mold & Engineering 7
Undercut Requirements Part Hand Load Part features that can only be captured by hand loads or side actions have design requirements. Ejector Pins Mold The first requirement is space. Design your undercut feature (button, port hole, etc.) with enough space so that the hand load can be removed without obstruction. If there is not enough space, the hand load will be die locked and will not be able to be removed. Secondly, design your part so that the molder is able to effectively pinch the hand load or side action with the cavity and core. This will result in a tight shut-off which is imperative to reducing parting line flash. Part Hand Load A final requirement is to add enough draft to your undercut feature so that it can be removed from the mold easily. Copyright Xcentric Mold & Engineering 8
Undercut Challenges Part Some of the challenges involved with molding parts with undercuts are that non-drafted areas can be difficult to remove. Demolding parts with insufficient draft will make it difficult to remove the side action manually. Hand Load However, if the draft cannot be increased, the hand load can be coated with nickel-plating which allows for a more non-abrasive connection between the part and the hand load making removal easier. Part Certain materials can also be challenging when incorporating undercut features. Some materials, like glass filled plastics, are more difficult to pull from the mold. In general, the harder the material, the harder the pull. So, it is essential to put as much draft as possible when using these harder materials. Hand Load Finally, cosmetic surfaces with undercuts will be hard to maintain due to increase parting line exposure from the hand load. When designing undercut features that lie on the cosmetic side, it s recommended to reduce the amount of parting lines on the outside by utlizing an internal undercut. Copyright Xcentric Mold & Engineering 9
Overcoming Undercuts As undercuts add complexity to the mold, it also adds cost. It s recommended to try eliminate unnecessary undercuts when possible by designing part features that are perpendicular to the draw line. Below are some drawings to help you visualize ways to avoid an unneccessary undercut. Draw Copyright Xcentric Mold & Engineering 10
Summary Example Features - Some of the more common features that undercuts can capture: Interlocking snap or latch features Holes or ports Vertical threads and barb fittings Coring out thick part sections Threaded and custom inserts. Design Requirements - Undercuts have three main design requirements that should be noted. 1. Space - The undercut should have enough space for removal without obstruction 2. Tight shut-off - the undercut should have a tight shut-off within the core and cavity 3. Draft - the undercut must be designed with sufficient draft to facilitate easy, manual removal. Hard materials can cause difficulty in removing the undercut. The harder the material, the harder it is to remove. Also, on cosmetic surfaces, it s recommended to use an internal undercut to reduce the appearance of parting lines. When possible, it s best to avoid undercuts to keep costs down. Designing undercut features perpendicular to the draw line will help reduce the amount of overall undercuts needed. Copyright Xcentric Mold & Engineering 11
Answers to Common Questions Q: Why do you use hand loads instead of slide cams? A: We use hand loads for speed and time to market. This also depends on the part geometry or whether or not it is an external or internal undercut. The auto-slide is implemented based on a longer cycle production to reduce overall per part cost. If speed is essential, we use manual hand loads. Q: On average, how much time is added to the process for every undercut in the design? A: This will depend on how many hand loads are needed and also the complexity of the hand loads, whether internal hand loads or threading. Typically a couple hand loads will not increase timing, at least not for us. However, we conclude this will depend on overall design and complexity. Q: How do you keep the hand load in its place? A: Hand loads are held in place by the clamp of cavity or core and also by press fit into either cavity or the core. This is critical with keeping parting lines and reducing flash. The more we can hold them in place, the better your overall part molding. Q: Would it be helpful for a part designer to go ahead and model in what he had in mind for actions/hand loads, or just leave it to you guys? A: Always model your part the way you need and intend for it to be. Keep in mind the tips outlined in this book, but build your model with good molding intent. From there, a good manufacturer can help tweak the design to function well in the tool building and molding process including those undercuts. If they can be removed, we can provide that information. Copyright Xcentric Mold & Engineering 12
Additional Resources Xcentric can provide you additional resources to increase your level of understanding of injection molding and manufacturability. Click the images to view in your browser. Webinar Series Video Tour What is and Undercut? An animation About Injection Molding White Paper: The Smart Guide to Designing for Manufacturability Material Data Sheets Consider us for a project you are working on today. We will provide a quote within 24 hours or less. Get a Quote Copyright Xcentric Mold & Engineering 13
Glossary Undercut - An undercut is any indentation or protusion that prohibits the ejection of a part from a mold. Side Action - a separate piece within the mold used to capture the undercut feature in the molding process. These can be manually or automatically removed. Hand Load - a manual side action used to capture the undercut feature that is removed by hand after the injection. Parting Line - the point where the core and cavity of the mold meet. Draw - the direction in which the core and cavity are pulled apart from the parting line Die Locked - any part or undercut feature that cannot be removed due to an obstruction Demolding - the process of removing a part from a mold after the injection process Draft - the angle in which walls are designed to ease the demolding process (removal of part from the mold) Copyright Xcentric Mold & Engineering 14