Flash Injection Molding: Causes And How to Solve Them

Go4Mould is an injection molding company that has come forth to reduce the amount of flash produced during the injection molding process. We are a certified company with on-hand experienced workers that provide you a free consultation and operational videos.

We have designed this blog to highlight the causes and cures of flash injection molding. Stick-on to know further.

Mold flashing – An overview

Mold flash occurs when water seeps behind siding or trim and causes mold to grow. Flashing is a thin, waterproof material installed behind siding or trim to prevent water from seeping in.

Figure 1 Flash Injection Molding

Figure 1: Flash injection molding

5 effective ways to control flash in injection molding

There are a few practical ways you can control flash in injection molding:

  •  Design for manufacturability

It is the general engineering practice of designing products that are easy to manufacture. It helps with flash injection molding and avoiding undercuts to reduce flash.

  • Clamping pressure in the packing

It is necessary to apply the right amount of pressure during the packing and holding phases to prevent flash. The clamping force should be high enough to compress the material but not so high that it damages the mold or causes flash injection molding.

  •   Barrel and nozzle temperatures

If the barrel and nozzle of your injection molding machine are too cold, the plastic material will solidify before it reaches the mold cavity. Conversely, if the barrel and nozzle are too hot, the plastic material will become too soft and flow too quickly, resulting in an excessive flash.

  •  Specify a flash-free mold design

A flash-free mold design can be achieved by creating draft angles on all mold surfaces that come into contact with plastic during the injection molding process. It will ensure that the molded part will release quickly from the mold and minimize the amount of flash produced.

flash injection molding

Figure 1: Flash injection molding

Flash injection molding causes

There are several reasons for controlling flash defects in injection molding, which are as below:

  •   Improper venting 

When the mold is not properly vented, the molten plastic has nowhere to go but out through the sides of the mold. It can cause the plastic to cool too quickly and result in a flash.

  •  Parting lines 

Parting line or flash lines occurs when the two halves of the mold separate during the injection molding process, causing a small amount of plastic to be forced out and creating a thin “flash” on the edge of the part.

  • Low clamping pressure 

One of the primary causes of flash during injection molding is low clamping pressure. When there isn’t enough pressure holding the two halves of the mold together, molten plastic can seep out from the edges, causing a flash.

  •  Viscosity 

Viscosity is the primary cause of flash injection molding. The molten plastic cannot flow evenly throughout the mold cavity, which can cause areas of the mold to cool prematurely. It can result in the plastic becoming too dense and not filling the mold.

  • Flash gates 

A flash gate is a small opening in the injection mold through which molten plastic can flow during the injection molding process. If the flash gate is not correctly aligned with the mold cavity, it can cause the plastic to leak out and create flash injection molding.

  • Burrs 

Burrs and flash can be caused by various factors in the injection molding process. Common causes include incorrect mold design, poor mold maintenance, poor raw material quality, and incorrect process parameters.

  •  Sink marks

Sink marks are one of the most common causes of flash in injection molding. Sink marks occur when the molten plastic cools and shrinks faster.

Flash free molding at Go4Mould

Flash-free molding is a process that we use at Go4Mould to create high-quality, consistent plastic parts.

  • First, we create a preform, or a net-shape part, using an injection molding machine to avoid any defect
  • Then, we use a proprietary process to stretch and form the preform into the final shape of the molded part.

Go4Mould is your one-stop shop for all your flash-free molding needs. Contact us today to learn more about our services.

Frequently asked questions-flash injection molding

1. What is deflashing?

Deflashing is the process of removing flash or injection molding defects from a molded or extruded product. Deflashing is necessary to ensure that products are of the highest quality and meet customer expectations.

2. How to fix short shot injection molding?

Here’s what you should do

  • Check the Barrel temperature and make sure it’s set correctly. 
  • Second, check the Injection pressure and make sure it’s not too high or too low.
  • Finally, check the Mold temperature and make sure it’s not too high or too low. 

If any of these is not balanced, you will likely run into short shot injection molding.

3. What is parting line flash in injection molding?

When it comes to injection molding, the parting line is where the two halves of the mold meet. This line is also known as a “mold seam.” When the mold is closed, molten plastic is injected into the cavity. As the plastic cools and hardens, it forms around the mold. When the mold is opened, the plastic part is ejected.

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