Plastic injection molding pressures are classified based on the clamping pressure that the molding presses exert. This is the reason why it’s important to check the size of the press, which is often referred to as the tonnage. The clamping pressure exerted by the press can range anywhere from 5 tons to more than 4,000 tons.
Classification of Plastic Injection Molding Presses
When you get in touch with the plastic injection molding press vendor, you will get a list of the presses. Usually, the list will display the ton of each machine. So, if a machine has a tonnage of 123 tons, it means it has the ability to exert 123 tons of clamping pressure. When this pressure is exerted, the mold stays closed throughout the injection process. If the machine exerts too much or too little pressure, it could result in quality problems.
It also is prudent to remember, too much or little pressure leads to flashing, wherein the excessive raw material injected into the mold will appear on the part edge. Pressure also has a profound effect on the viscosity of the resin or plastic that is being used. Any type of plastic has a Melt Flow Index (MFI) and each type reacts and behaves differently to pressure depending on its MFI. If a plastic or resin has a high Melt Flow Index, it will require more pressure compared to a resin with a lower MFI.
How Much Clamping Pressure to Exert
When you’re trying to determine the amount of clamping pressure required, you need to take into consideration several factors. You should know the type of resin being used for the injection molding process as well as the safety fact added to the final calculation, (which is a numerical percentage that functions as a buffer) to prevent flaws in the final product. You may have some experts suggesting you take into consideration mold size, final product size and the platen size. Typically, you have to add 10 percent to account for the safety factor.
As a general rule, you should be looking to use 2.5 times the surface square inches of the product that you intend producing to get an estimate of the clamping pressure that you need to exert. Once you have this calculation in place, you will know exactly the size of the press that needs to be used.
Finding the Right Plastic Injection Molding Company
Even if you know how much pressure is required during the molding process, it is imperative you find the right plastic injection molding company to suit your requirements. It is best to opt for a company that has a wide array of press sizes, as such a company will be able to offer any pressure and is best suited to meet your requirements.
This said, the last word on the appropriate plastic injection molding pressure rests on the molding company. They will determine the right pressure and press size for your production needs. Larger presses often are more cost-effective, as you can use multi-cavity molds simultaneously.