We have covered in previous posts the many reasons companies are switching from metal formed products to plastic injection molded products and components. One of those reasons is weight reduction, and it can be a big reason to make the switch. Once you have decided to base your products on plastic injection molding, keeping the weight down or reducing the weight further has many additional benefits. If you’re not sure how to start the process of weight reduction, we’re going to get you off on the right foot to meet your goals.
Why Part Weight Matters
When making the switch over to plastic injection molded parts, your part weight is going to matter. There are two main reasons that you want to track your part weight: to track associated material cost and to reduce component fatigue or increase durability.
Reducing your associated material cost should always be on your mind as reduced cost could attribute to a better profit margin. Your designer should be able to generate an approximate weight target for each component based on the material density and volume of material used. Tracking your part weight can ensure that you know the exact material cost your business sees on each component produced. From the point of generating a baseline cost you can start to monitor trends for weight on each part as an individual and also monitor weight on an overall volume per run. That run may consist of a few pieces or a few thousand pieces, but you can verify the consistency in each part and determine what adjustments need to be made to ensure quality products are being produced.
Switching from metal to plastic may also help with reducing component fatigue or by increasing the durability of components. Forming metal components through stamping and welding can induce stresses from bending, cutting, or forming holes. Those stresses may be reduced or alleviated by switching to a plastic injection molded part. Reducing the weight of components, without affecting their strength, may also reduce fatigue on other supporting parts and increase the durability of the assembly as less weight overall must be supported.
How to Reduce Plastic Molded Part Weight
If you want to reduce your plastic molded part weight on an individual basis, there are typically five ways to start:
- Make parts thinner – This seems easy to do, but you will need to verify that thinner parts still incorporate the other qualities required for the design. You will need to monitor heat tolerance, strength, fatigue resistance, etc. to ensure you don’t lose the value of the product by moving to a thinner component.
- Change materials – Changing materials may not be a simple task, but it can greatly benefit the parts over time. Assuming your part must stay the same size, you can change the molding resin to a material with less density per volume. The molded component will then stay the same shape and size (keeping the same volume of material used), but it will be lighter. This again will need to be verified that it does not affect the other qualities required of the component.
- Redesign the part – There are ways to redesign the part and keep key characteristics required by the design. You may be able to reduce the wall thickness of the part and add features such as strengthening ribs to keep the required strength of the part. Beyond that you may adjust or add radii on corners to slightly reduce the volume of the material in the part. One last way to reduce material use, and reduce the weight of the component, is to add holes in the component in areas that would affect the part for strength. Less material volume reduces weight.
- Adjust the cycle time and parameters – Adjusting the cycle time and molding parameters will take some testing and validation to ensure the part weight is being reduced while other characteristics are staying within their design range. Every molding material is slightly different, but changing the barrel temperature, increasing or decreasing the injection pressure, and varying the temperature within the injection mold may yield slight reductions in part weight that can add up to significant savings in a long run of parts.
- Change the molding process – You may consider this change close to changing the material, but you may be able to change the process from a standard injection molding to a foaming co-injection molding process. Your part may change from a uniform solid density to a foam core with a solid skin. A second process method to consider could be gas or fluid assisted molding. This could offer hollow parts with a solid outer skin. Fluid assisted parts could also benefit from reduced cycle times as the fluid can assist with part cooling inside the injection mold.
Conclusion
Part weight may just be one of the factors that should be discussed at the beginning of your next project whether that is creating a part from scratch or converting from metal to plastic. Many resins have excellent strength, and some can have strength beyond steel with a reduction in part weight. Finding the correct material to meet your needs, whether that is strength, budget, or somewhere in-between, is a complicated process. At SEA-LECT Plastics we pride ourselves in tool and die manufacturing that allows us to deliver high quality products free from defects. You should be including discussion points on the function, environment, quantity, and recycling of your product to ensure the best resin is chosen for your product. SEA-LECT Plastics has an elite team that produces world-class prototypes and products, and we have decades of experience with plastic injection molding operations and creating tooling for perfect parts. We can offer support to determine what type of mold you need, what resin to choose, and how to best invest in your future. Give us a call at (425) 339-0288 or email us at mattp@sealectplastics.mystagingwebsite.com. We’ll help to determine the best manufacturing for 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.