{"id":1867,"date":"2017-02-12T10:00:25","date_gmt":"2017-02-12T16:00:25","guid":{"rendered":"https:\/\/www.cadcrowd.com\/blog\/?p=1867"},"modified":"2021-12-16T02:43:44","modified_gmt":"2021-12-16T08:43:44","slug":"how-to-design-for-injection-molding","status":"publish","type":"post","link":"https:\/\/www.cadcrowd.com\/blog\/how-to-design-for-injection-molding\/","title":{"rendered":"How to Design Products for Injection Molding & Prototyping Firms"},"content":{"rendered":"

Injection molding is one of those technologies that is so central to our everyday lives that we hardly notice it. We are surrounded all the time by objects created through this process. Almost everything made from plastic (which is almost everything) is made with injection molding. As a product designer, it’s important to understand this process! So let’s get to it.<\/p>\n

What is injection molding?<\/h3>\n

It a process used for manufacturing a wide variety of items from small components to large ones. It uses a granular plastic that is gravity fed from a hopper, forced into a heated chamber by a screw-type plunger, melted, and then pressed against the mold. It then cools and is removed as a solid part. Rapid injection molding uses aluminum molds that are quick to make, while large-scale production typically uses steel molds.<\/p>\n

Injection fabrication makes it possible to produce parts in large volumes. This is why it is typically used in mass-production processes, where thousands or even millions of parts are needed. The biggest drawback, really, is that the tooling time and costs required to set up for the molding process make the technique inappropriate for small batch production runs (luckily we have 3D printing<\/a> for that now).<\/p>\n

The injection molding process cycle follows 4 stages<\/span> and typically takes between two seconds and two minutes per part<\/p>\n

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  1. \n

    Clamping\"injection<\/h4>\n<\/li>\n<\/ol>\n

    This is the part where two halves of the molds are securely closed by the clamping unit. Hydraulic power is used to keep the clamping unit in place while the specific material is injected (typically a thermoplastic<\/a>).<\/p>\n

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    1. \n

      Injection<\/h4>\n<\/li>\n<\/ol>\n

      At this stage, raw plastic material or pellets are fed into the injection molding machine, pushed into the injection unit, melted and then injected into the mold.<\/p>\n

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      1. \n

        Cooling<\/h4>\n<\/li>\n<\/ol>\n

        Cooling allows the molten plastic to solidify and take the shape of the mold. There are specific cooling times for different parts and components, depending on the maximum wall thickness of the part and the thermodynamic properties of the plastic material<\/p>\n

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        1. \n

          Ejection<\/h4>\n<\/li>\n<\/ol>\n

          An ejection system is used to push the molded part out of the clamping unit. A mold release agent may be sprayed onto the surface of the mold cavity before injection to facilitate easy ejection and prevent damage to the new part.<\/p>\n

          What are the benefits of injection molding?<\/p>\n

          Low production costs<\/h4>\n

          In injection molded manufacturing, the price per unit is extremely low. The most significant costs are the setup costs. As more parts are produced, the price tends to drop drastically. Once the initial costs of fabrication have been paid, the profit margin can be quite wide. This makes financial sense in the business front, so long as there is a demand to satisfy the production.<\/p>\n

          Low scrap rates<\/h4>\n

          Unlike traditional manufacturing processes, where a substantial percentage of an original block or sheet is cut away during production, injection molding cuts with accuracy and waste plastic usually come<\/span> from overflow material that leaks out of the cavity. It can also come from runners, sprue, and gate locations.<\/p>\n

          Repeatable and consistent<\/h4>\n

          As a process used in high-volume production, injection molding is ideal for producing practically identical parts. Each part produced is going to be the same as the first one, which is important for<\/span> consistency and reliability.<\/p>\n

          Of course, injection molding is not perfect. But its benefits often outweigh the disadvantages.<\/p>\n

          A major challenge in injection molding is designing a mold. The main focus is usually on the finished products, but no part would be made without the mold from which it is formed. The design aspect of a component is often overlooked, but it is the most important.<\/p>\n

          Design Considerations for Injection Molding<\/h3>\n

          There are many factors to consider for injection molding, but the part<\/span> design and tool design are two of the most important.Getting them right could mean lower entry cost, high production quality, shorter cycle time, and quick assembly. Getting them wrong, on the other hand, can be very costly indeed.<\/p>\n

          Wall thickness<\/h4>\n

          The thinner it is the easier the injection molding process. Parts with thin wall thickness cool faster, weigh less<\/span>\u00a0and use less plastic per part. This means shorter cycle times, resulting in more parts produced per hour and lower production cost.<\/p>\n

          On average, injection molded parts should have a wall thickness that ranges from 0.08″ (2mm) to 0.16″ (4mm), but thin wall injection molding can go as thin as 0.02″ (0.5mm). But wall thickness also depends on the material used. The recommended wall thickness of an ABS resin, for example, is between 0.045 and 0.140 inches, Acrylic is at 0.025 \u20130.150, Liquid crystal polymer at 0.030 -0.120, Nylon at 0.030\u20130.115, Polycarbonate at 0.040 \u2013 0.150, Polyester at 0.025 \u20130.125 and Polypropylene at 0.025\u2013 0.150.<\/p>\n

          Wall thickness must be consistent to reduce if not eliminate warping. If consistency is hard to achieve due to design limitations, the change in thickness should be done gradually. The use of a coring<\/span> method will help eliminate such problems,<\/span> while adding gussets will reduce warping.<\/p>\n

          Ribs<\/h4>\n

          Instead of increasing the thickness of the wall, ribs are often used to increase the bending stiffness of a part, which is a result of an increase in the moment of inertia.<\/p>\n

          When adding ribs, follow the recommendations below.<\/p>\n