3 Tips For Calculating The Correct Press Size For Your Plastic Injection Project

Update:18-03-2021
Summary:

  Are you a product designer or engineer looking for mo […]

  Are you a product designer or engineer looking for more information on how to improve the design efficiency of plastic parts in terms of cost and production time? An important consideration in the part design process is to have a full understanding of the basic knowledge of injection molding machines, including the machine dimensions required for the parts.

 

  When determining the required press size, it is not always "bigger is better." During the molding process, the plastic is injected into the mold at an abnormally high pressure, which creates a natural pulling force to force the mold to open. The press is designed to close the mold. Larger parts require more tonnage and force, while smaller parts require less force. The general calculation to determine the required printing press size is as follows:

 

  Pressure (lb / in2) x projected area (in2) = force (lb.)

 

  Here are some other important tips to calculate the appropriate press size for your plastic injection part.

 

  1. Understand the press tonnage.

 

  Your plastic injection molding machine should help you determine the size of the machine you need to help you achieve the best results for your product. Knowing the approximate size of the required size can help you determine the best injection molding partner based on the available press capacity. For example, large presses cannot close smaller molds because they cannot close far enough and the injection process will not proceed.

 

  In addition, the tie rod spacing of smaller presses is too narrow to accommodate larger products. If the mold does not fit in the horizontal or vertical direction, the press size must be increased. Many injection molding machines offer press sizes ranging from 68 tons to 400 tons.

 

  2. Calculate your estimated total closed area and injection volume.

 

  When sizing presses for plastic parts, it is important to calculate the estimated total closed area. This area only contains the space at a 90-degree angle to the direction of the platen of the injection molding machine. Thickness has no effect on the tonnage of the fixture. The general rule is that there are 2 to 5 tons of fixture tonnage per square inch of projected area.

 

  Calculate the injection volume to ensure that your barrel has sufficient capacity, which can be done by performing mold flow analysis together with the injection molding machine. In some engineering materials, the increase in the retention of the material in the barrel will cause the material to degrade, which will lead to the deterioration of the quality of the parts. Mold flow analysis will help you determine the volume of parts and runners, as well as any factors that may cause safety issues.

 

  3. Know how much clamping force or pressure is needed.

 

  Pressure plays an important role in the overall quality of plastic parts. During the injection process, the pressure keeps the mold closed. Too much or too little pressure can cause various problems, such as flash and viscosity. An important consideration regarding pressure is that plastic compounds react differently with each other according to their melt flow index (MFI). MFI measures the fluidity of thermoplastic polymers. The higher the MFI, the higher the pressure required to make a successful part.

 

  The "safety factor" is an additional percentage added to your calculations as a buffer to help reduce defects in the part. Most injection molders recommend using 2.5 times the square inch of the surface of the part, and add 10% as a safety factor. If the area of ​​the part is 120 square inches, a press size with a pressure of 300 tons is required. When you add a 10% safety factor, the required press size will have a clamping force of 330 tons.

 

  A general understanding of how to calculate press dimensions is a good first step in determining which injection molding partners you can use. A strong partner will provide advice on how to properly adjust the parts to ensure that the final design meets your manufacturing needs and reduce the cost of the up-front mold.

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