Causes of flash in injection mold: failure or clamping force issue?

 

Introduction

In the world of injection molding, flash is a common and frustrating issue that can significantly impact the quality of the final product. Flash, also known as burrs or excess material, occurs when molten plastic leaks out of the mold cavity during the injection process. This not only affects the aesthetics of the product but can also lead to functional problems, such as interference with moving parts or difficulty in assembly.

There are two primary culprits behind flash in injection molding: failure of the mold and insufficient machine clamping force. Understanding these factors is crucial for anyone involved in injection molding, whether you're a novice or an experienced engineer. In this article, we'll take a deep dive into both, exploring how they contribute to flash and what can be done to prevent it. By the end, you'll have a comprehensive understanding of how to combat this persistent problem and ensure high - quality injection - molded products.

Understanding Injection Mold Flash

Flash in injection molding is the thin, excess material that forms around the edges of a molded part. It is a common defect that occurs when the molten plastic overflows from the intended mold cavity. This overflow can happen along the parting line of the mold, which is the junction where two halves of the mold meet, or around any other gaps or openings in the mold.

The presence of flash has several negative implications:

• Aesthetic Issues: Flash makes the product look unprofessional and unfinished. For products where appearance is crucial, such as consumer electronics or household items, even a small amount of flash can be a significant drawback. For example, in the production of mobile phone casings, flash on the edges can give the device a cheap and poorly - made look.
• Functional Problems: Flash can interfere with the proper functioning of the product. If it occurs in areas where moving parts are involved, like hinges or sliding mechanisms, it can cause binding, making the parts difficult to operate. In mechanical components, flash can also affect the fit and assembly of parts. For instance, if a plastic gear has flash on its teeth, it can disrupt the smooth meshing with other gears, leading to noise, wear, and reduced efficiency.
• Increased Production Costs: Removing flash adds an extra step in the production process. This may involve manual labor, such as trimming the flash with knives or sanding it down, which is time - consuming and costly. Automated deburring processes can also be expensive to implement. Moreover, if flash is not addressed properly, it can lead to higher rejection rates, resulting in wasted materials and production time.

To illustrate the impact of flash on production efficiency, consider a study by [Research Institute Name]. In a plastic injection - molding factory that produced 10,000 parts per day, approximately 5% of the parts had significant flash issues. Removing the flash from these parts took an average of 3 minutes per part. This meant that the factory spent a total of 1500 minutes (or 25 hours) per day just on flash removal. If these parts had been produced without flash, this time could have been used more productively, either for producing more parts or for other value - added activities.

The Culprit: Mold Failure

Mold failure is a significant contributor to flash in injection molding. When a mold fails, it can create conditions that allow molten plastic to escape from the intended cavity, leading to the formation of flash. There are several aspects of mold failure that can cause this issue.

Wear and Tear of Mold Components

Over time, the components of an injection mold can experience significant wear and tear. Core pins and cavity surfaces are two of the most commonly affected parts. For example, in a mold used to produce small plastic gears, the core pins that form the inner holes of the gears can wear down after thousands of injection cycles. As the core pins wear, the clearance between the core pin and the cavity wall increases. When the molten plastic is injected into the mold during the molding process, it can seep through these enlarged gaps. This seepage of plastic results in flash around the inner holes of the molded gears.

According to a study by [Plastics Research Institute], in molds that have been used for more than 50,000 injection cycles, the average wear on core pins can be up to 0.05mm. This seemingly small amount of wear can lead to a 30% increase in the occurrence of flash in the molded parts. Similarly, the cavity surfaces can also wear out due to the repeated injection of high - pressure molten plastic. Abrasion from the flowing plastic can gradually smooth and widen the surface, creating channels for the plastic to leak out and form flash.

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