How much tonnage you should apply for the mold during the injection molding operations will determine the success of it. Tonnage is required during the injection molding operations to hold the mold in its place, so you need to apply the tonnage that is not too soft or too excessive.
In this guide, you will learn about how to calculate the required tonnage for injection molding mold.
What is Tonnage Requirement in Injection Molding?
Tonnage requirement is the required tonnage or clamping force you need to apply for the injection molding mold during the injection molding process. This is the force that will keep the mold in its place during the injection molding operations. To keep the injection molding process working smoothly, you will need to apply the tonnage force that is not too soft nor too hard.
There’s a formula you can follow to determine how much tonnage you can apply for the injection molding process. The strength of the clamping force will depend on various factors.
Steps to Calculate the Required Tonnage for Injection Molding Mold
Here are some steps you will need to go through to calculate the required tonnage for injection molding mold:
- Calculating the surface area. The first thing you need to do is to calculate the surface area of the mold by multiplying its length and its width. This is a simple calculation to determine the projected surface area you will be working on in the injection molding process. Surface Area = Length x Width.
- Calculating the Melt Flow Rate (MFR). Each material will have their own melt flow rate, which calculates the material viscosity. You need to calculate the weight of the material and multiply it with 600 and divide it with total extrusion time. Melt Flow Rate = Material Weight x 600 / Extrusion Time. Please note that this mold flow analysis is an optional factor to determine the best tonnage requirement with more accuracy. You can skip this process if you don’t need it.
- Calculating the safety factor. For the safety factor, it is necessary for you to calculate it as you don’t want to apply excess tonnage for the injection molding operation. The rule is simple. For the part depth dimension of more than 1 inch, you will need to apply the 10% safety factor for the injection molding operation.
The general empirical formula to calculate the required tonnage for injection molding mold is Tonnage = Tonnage/Clamping Force Constant x Surface Area x Safety Factor. This is a formula that will allow you to calculate the tonnage requirement fast.
Factors that Affect the Tonnage Requirement in Injection Molding Process
There are some important factors that will affect the required tonnage you will need to apply for your injection molding mold. Each factor will determine whether you will need to apply higher or lower tonnage for the mold.
Here are some factors that affect the tonnage requirement in injection molding process:
- The surface area of the mold. The first factor that will affect the tonnage requirement in injection molding is the surface area of the mold. The bigger the surface area, the more tonnage you will need to apply.
- The depth of the placement unit. The depth of the placement unit in injection molding will also affect the safety factor you need to use. You will need to apply a 10% safety factor for the depth measurement of more than 1 inch. This will keep the tonnage or clamping force in the best range and avoid any excess force.
- Mold cavity. The size and shape of the mold cavity will also affect the tonnage you will need to apply to the mold during the injection molding process. The more cavities the mold has, the higher the required tonnage will be. This is because you will need to handle the pressure inside the mold cavity with enough tonnage during the injection molding process.
- Injection molding materials. The plastic molding materials you are using will also affect the tonnage requirement for the injection molding process. Each material will have their own mold flow rate, which can then affect the required clamping force or tonnage you will need to apply in your injection molding process.
- Tonnage capability of the injection molding equipment. Each injection molding equipment has their own maximum tonnage capability, meaning that they can only produce the tonnage or clamping force up to a certain level. You will need to use a stronger injection molding machine if your required tonnage is higher than the tonnage capability of the machine.
What Will Happen If You Apply Too Much Tonnage?
- Cracking in the mold core. Core cracking is one of the most common results of too much tonnage. This can happen because the core can’t stand the excessive tonnage force during use. Thus, it will get cracked or damaged, which might even result in the core becoming unusable in the long run.
- Damaged inserts. Too much tonnage can also result in damaged inserts during the injection molding process. The insert might not be able to handle the excessive clamp force, which can weaken its structure and damage it.
- Cracked machine frames. The frames of the injection molding machine can also get damaged with too much tonnage force, especially if you are applying the excessive tonnage for too long. This can also damage the machine internals as well, so be sure to keep the tonnage force at the right level.
- Bad quality of the final products. The excessive tonnage force can also affect the quality of the final products you are manufacturing using the injection molding method. Product defects can also happen, as they get deformed by too much force during the injection molding process. You might need to pay for more expensive injection molding costs when this happens.
- Injection molding equipment failures. Failures in your injection molding equipment can also happen when you put too much tonnage on the mold. The equipment will tell you there’s something wrong you need to fix, and it might not continue the injection molding operations before you fix the issue.
It is important to calculate the tonnage requirement before starting your injection molding operations, as it can help ensure a smooth injection molding process. There are various factors that can affect the required tonnage you need to apply in your injection molding process.
It is very important not to apply excess tonnage, as it can result in various damages in your injection molding equipment.