Injection molding has been around for decades. It’s in in almost every industry around the globe, but it still isn’t fully understood. There are a lot of myths about what it can do, how cheap it can be, and what happens after the process. We’re going to dispel eight common rumors we see asked frequently to cast some light on injection molding.
Myth 1: Injection Molding Can Do Any Shape Possible
We often are asked how complex a shape can be before it isn’t manufacturable. The myth is that anything can be injection molded. While injection molding is capable of many shapes, there are certainly limitations. One key element that is done in a design review is a ‘moldability check’, and your part should have a minimum target of 90%. That target allows enough flexibility to make changes and increase the moldability for a more balanced melt flow, heat exchange, as well as uniform cooling inside the injection mold as the cycle completes.
Myth 2: Injection Molding Shouldn’t Be Used for Prototypes
Plastic injection molding can be used to create many things, but not prototypes. Does that sound familiar? Plastic injection molding can absolutely be used for prototyping. You might say that 3D Printing or Additive Manufacturing has become more common for prototypes in some cases, but using a simple injection mold may be a more cost-effective and faster option depending on the situation. It will come down to how many prototypes are being made, how often changes need to be made, and the material your prototype needs to be made from.
Myth 3: Plastic Injection Molding Can’t Utilize In-Mold Customization
Many plastic injection molded products have enhancements to increase functionality or visual aesthetics, but many customers think it involves extra process steps after the molding. That ‘extra’ usually translates to increased cost and time to develop the products. In reality, plastic injection molding can support in-mold customization to add extra colors, textures, and finishes. Great examples of potential option include toothbrushes and hairbrushes with rubber grips and multiple color toys.
Myth 4: Injection Molds Can Be Made in Days
The timing to manufacture plastic injection molds seems to vary wildly based on the myths floating around. Some say they only take days to complete. Others say it could take a year. The truth is that injection molds can take weeks to complete depending on factors including their design intricacy and the material they are made from. Simple plastic injection molds that have no moving parts such as slides or details can be made from a softer material like aluminum quickly. Add in extra moving details and parts, then make the injection mold from a hard steel, and it can dramatically increase the time it takes to complete the mold. It may take up to 16 weeks to complete a complicated design ready to mold a million parts annually. The up to a year timing may be a little too far-fetched though.
Myth 5: Plastic Injection Molding Doesn’t Have Many Material Options Available
We’ve heard some comments centered around the myth that injection molding only has a handful of options. If you were to count with your fingers for the number of options available, you may have to bring the neighborhood in to help. There are 1000s of resins available for all methods of plastic injection molding. While there are basic resins commonly used such a nylon, polypropylene, and more, each can vary to include a broad range of characteristics. More flexibility, a harder surface, corrosion and temperature resistance, and more are just a formulation away from a perfect engineered resin that can handle the harshest environments available.
Myth 6: Your Molded Part Weight Determines Which Molding Machine to Use
This myth may be discussed more between molders and employees than the general public, but part weight isn’t the determining criteria of which machine to use. It shouldn’t also be the criteria for deciding what molding company to partner with on a new project. Injection molds have a physical size that needs to fit inside the machine, but the characteristic of the machine that is critical is the maximum injection rate. If the machine can inject molten plastic at the rate needed to fill the cavities completely, size of the mold isn’t a concern. Too small or too large is only relative, but the machine must be able to fill the mold completely in the time allotted. Too slow of an injection rate may allow the resin to start cooling and not fill the cavities completely.
Myth 7: Only Injection Molding Machine Parameters Influence Product Quality
Some injection molders have too much faith in their ability to push buttons and turn knobs. The myth that anything can be fixed by adjusting parameters isn’t always true. Can it influence quality? Yes, but it’s not a guaranteed outcome. Your products may be facing a strict consumer demand that won’t tolerate sink marks, dimensional differences, and quality variances. You may need more focus on plastic injection mold design to counteract product quality concerns that just fiddling with parameters day after day.
Myth 8: Plastic Injection Molding Produces an Immense Amount of Scrap
You’ve seen that one picture of a bad day at work where the molding machine doesn’t give many good shots. It perpetuates the myth that injection molding is wasteful, and it just piles up the waste going out the door. Don’t let one bad day influence your perception of injection molding. It does produce scrap at the inject gate locations, the sprue, runners, and anything that leaks out from the mold cavities, but it isn’t a lot. Most of the material can be ground into small pellets and reused in the future. While injection molding does produce some scrap, very little actually leaves the facility to be put in a landfill. What does leave can also be utilized in other ways to be productive rather than polluting.
The myths about plastic injection molding are very interesting because it can paint the whole industry in a positive or negative light. If you want to know the truth of what can and can’t be done, have a frank discuss with a leading expert. SEA-LECT Plastics has an elite team that produces world-class prototypes and products, and we have decades of experience with plastic injection molding. We can offer support to determine what type of mold you need, what resin to choose, and how to invest in your future. Give us a call at (425) 339-0288 or email us at mattp@sealectplastics.com. We’ll help to dig through the myths that have you nervous about your next project.
Matthias Poischbeg was born and raised in Hamburg, Germany. Matt moved to Everett, Wash., after finishing his bachelor’s degree in business in 1995 to work for Sea-Dog Corporation, a manufacturer, and distributor of marine and rigging hardware established in 1923.
In 1999, Matt took over the reins at Sea-Lect Plastics Corporation, a sister company of Sea-Dog and a manufacturer of plastic injection molded products with an in-house tool & die shop. Matthias Poischbeg is also a contributor to Grit Daily.