Injection Molding Tonnage, Explained
Achieving the right injection molding tonnage is one step in the complex process. This measurement — also known as the clamping force — determines the size and strength of the injection molding machine needed to create your part or component. You can also think of it as the measure of power required to keep the tool closed during the injection process.
Injection molding machines typically range in tonnage from less than five tons to over 4,000 tons of clamping force. But, how do you know which injection molding tonnage is right for your part? Choosing the correct force is imperative, or you’ll face costly defects. Here, we break down how to choose the right tonnage and what issues you’ll see if you choose incorrectly.
How Do You Determine What Injection Molding Tonnage is Right for Your Product?
The engineer who designs your part will also determine the correct force. However, it’s a relatively simple calculation to do on your own. The engineer measures the square inch area at the parting line and compares it to the tonnage factor given by the material supplier. Then, they’ll add a safety factor to leave room for error, resulting in the final calculation.
Of course, this calculation would be more complicated with parts that have intricate details, as the area would be harder to calculate. That’s why it’s crucial to work with an experienced injection molder who regularly creates complex plastic components.
What Happens if You Don’t Use the Correct Tonnage?
Whether you use too much or too little force, it will result in easily avoidable defects. Here, we’ll go into detail about each issue you might see. If your products display these issues when they leave the injection molding floor, it might be time to talk to your engineer about fixing the tonnage.
Too Much Force
Short Shots
A short shot means the mold was insufficiently filled during the injection molding process. In this case, the plastic does not fill the entire cavity, as the flow freezes off before the flow paths have filled. In addition to insufficient injection molding tonnage, this could be caused by flow restrictions, complex flow paths, inadequate venting, or another issue.
Gloss Level Changes
You’ll likely see poor surface glossiness if the injection force is too high. In this case, increasing the force should eradicate the issue.
Burns
Burn marks are one of the most common quality issues on injection molded parts. Burns can be created by a number of issues, but you’ll likely want to check your tonnage if this happens often.
Machine and Mold Degradation
Too much force will result in sub-par parts, but it will also cause the injection molding machine and mold to degrade quickly. You might experience broken inserts, a cracked core or cavity block, cracked plates, or fractured machine frames.
Not Enough Force
Parts with Varying Weights and Sizes
Too little force won’t allow the plastic to completely fill the mold. Therefore, you’ll end up with inconsistent parts and not properly serve your customers with the quality they expect.
Poor Surface Finishes
You’ll often see low glossiness when you’re not using enough force for your products. Usually, this is caused because the insufficient force couldn’t push the molten plastic against the surface of the cavity.
Variability in Wall Sections
Just like you’ll get parts with varying weights and sizes, your components will also have variability in wall sections. Some may have thicker walls than others, which can cause issues for your end-users.
Advantages of Completing a Moldflow Analysis
SEA-LECT’s expert engineers, mold makers, and analysts use Moldflow® software to simulate the process before your mold goes onto the injection molding floor. That way, they’re able to improve plastic part designs, mold designs, and manufacturing processes early on, avoiding costly mistakes that lead to wasted material, longer production times and subpar final products.
Do You Need Help with Injection Molding Tonnage Calculations? Get it Right with Expert Support
For decades, SEA-LECT Plastics has been manufacturing high-quality injection molded parts for companies all over the world. We strive to stay on the cutting edge of new and emerging technologies, offering the best products for you and your customers. We’d love to hear about your injection molding project and help you come up with a cost-effective plan that suits your needs. Contact us today to get started.