Clamping force is an important factor in the injection molding process. It is basically a safety measure implemented to operate the injection molding setup. A close mold is used to achieve the desired results. This mold is clamped in place during the operation using a clamping unit. Although there are various types of clamping units available for consideration, it is important to know the clamping force before choosing them. This is because the end result of the process depends on the right amount of clamping force applied. Slightly less clamping force can cause defective production where slightly extra clamping force on mold can damage it. Therefore, it is important to perform precise clamping force calculations. If you don’t know how to calculate clamping force for injection molding, then this post introduces you to the clamping force, its importance in injection molding, and calculation.
Introduction to Clamping Force
Clamping force is the force exerted by the clamping unit of an injection molding machine on the mold. The clamping force is also known as clamping tonnage because the force is measured in tons. The injection molding machine of 200 tons can exert 200 tons of clamping force. This force basically pressurizes the mold against separating the force or swelling force of the molding material. There are several factors that make an impact on clamping force calculations. Let us discuss different factors that impact on the clamping force.
Factors impacting Clamping Force in Injection Molding
The clamping force may be affected by any of these factors:
- Injection Pressure: Injection pressure is the amount of pressure exerted by the injection unit on the molding material. It varies according to viscosity, temperature, and other fluid properties of the molding material.
- Melt Flow Index (MFI): Melt flow index is the rate of spreading molding material per unit area, inside the heated mold. The melt flow index is partially responsible for separating force applied by the molding material, therefore it is an important factor of consideration in clamping force calculation.
- Resin Volume and Density: Clamping force helps keep the resin inside the mold. Other than that, resin density is directly proportional to the packing bond of the molding material. High-density resins pack easily, therefore application measures and time of clamping force reduce and vice versa.
- Aspect Ratio: Aspect ratio is a numeric value for the ratio of flow length to wall thickness. The aspect ratio is directly proportional to the clamping force. Low aspect ratio means low packing pressure, eventually, it means low clamp tonnage.
What is the Importance of Clamping Force in Injection Molding?
Clamping force in injection molding is an important factor because it acts against the separation or swelling force of molding liquid. In order to shape the product in the desired manner, the material must pack against the mold walls. Clamping force serves the purpose of material packing. If less than required clamping force is applied, it may cause hotshots, air bubbles, loose packing, etc in the product. Similarly, if extra clamp tonnage is applied then it can cause cracked cores, cavities, wall cracks, parting lines and cracked vents, etc.
As the importance of clamping force is now easily understood, you may be eager to know how to calculate clamping force for molding? Isn’t it? If yes, read the next section on clamping force calculation.
How to Calculate the Clamping Force for Injection Molding?
Clamping force depends on the force projection area and injection pressure. Therefore, the calculation of the clamping force is done by a simple formula. The formula for clamping force is as follows.
Clamping Force (N) = Injection Pressure (MPA) X the Pressure Projection Area (mm²)
The clamping force can be applied by using two different types of clamping units. The clamping units are as follows.
- Toggle System: It uses a toggle link to exert pressure by a mechanical application.
- Direct Pressure System: It uses hydraulic power to exert clamping pressure.
However, proper operational understanding of clamping force calculation comes with on-hand experience. Therefore, you must source the injection molding services to industry experts like Veejay Plastic. This company has been offering plastic injection molding services for several years. Their precise calculations and effective application of technology can give you desired results.
