Injection molds play a crucial role in determining the quality of plastic products, as both their structural form and mold processing process can have a significant impact. Unfortunately, failures can occur during production, necessitating the need to eliminate them promptly. In this article, I will discuss the common failures that arise with injection molding molds and the corresponding troubleshooting methods.
To begin with, it is essential to understand the potential issues that can arise in the structural form and mold processing process of injection molds. These issues can include flash, sink marks, warpage, short shots, and dimensional inaccuracies, among others. Each of these failures can significantly affect the final quality of plastic products, leading to customer dissatisfaction and increased production costs.
When facing these failures, it is crucial to adopt appropriate troubleshooting methods to identify and address the underlying causes. For instance, flash occurs when excessive molten plastic escapes from the mold cavities, resulting in unwanted extra material on the product. To eliminate flash, adjustments can be made to the injection pressure and clamping force or by improving the mold's design and venting system.
Sink marks, on the other hand, occur when the surface shrinks unevenly, resulting in localized depressions or sinkage marks. This issue can be minimized by adjusting the mold temperature, optimizing the cooling system, or adjusting the injection parameters to ensure proper fill and pack pressure.
Warpage refers to the undesirable distortion or bending of the plastic product, which can be caused by non-uniform cooling, inadequate ejection, or insufficient cooling time. Troubleshooting methods for warpage include optimizing the cooling system, adjusting process parameters, or modifying the mold design to incorporate additional cooling channels.
Short shots occur when the mold does not completely fill with molten plastic, resulting in incomplete parts. This can be due to various factors such as inadequate melt temperature, insufficient injection pressure, or improper gate design. To eliminate short shots, adjustments to temperature, pressure, and gate design, as well as ensuring proper venting, may be necessary.
Dimensional inaccuracies can arise from mold misalignment, insufficient mold clamping force, or thermal expansion of the mold during production. Troubleshooting methods for dimensional inaccuracies involve ensuring proper mold alignment, optimizing clamping force, and controlling the mold temperature to minimize thermal expansion.
In conclusion, understanding the common failures that can occur with injection molding molds and employing the appropriate troubleshooting methods is crucial in eliminating these issues and ensuring high-quality plastic products. By addressing structural form and mold processing concerns effectively, manufacturers can enhance production efficiency, minimize costs, and meet customer expectations.
1. The guide pillar is damaged.
The primary function of the guide pillar is to guide the mold and prevent any contact between the core and cavity surfaces during the molding process. It is crucial to note that the guide pillar should not be utilized as a load-bearing or positioning component. There are certain scenarios in which a significant lateral displacement force is generated when the injection is in motion. To reiterate, it is important to rearrange the above content and generate highly similar content while maintaining the original text information.
When the plastic part has uneven wall thickness, it leads to a higher velocity of material flow in the thicker areas, consequently resulting in increased pressure at those points. This non-uniformity in wall thickness can have significant implications for the manufacturing process.
The plastic part features an asymmetrical design, specifically, a mold with a stepped parting surface, which results in opposing sides being exposed to varying counter pressures.
2. Offset of moving and fixed molds.
Large molds can experience both dynamic and fixed mold deflections due to varying filling rates and the weight of the mold during installation. This can cause lateral displacement forces to act on guide pillars during injection, leading to galling and surface damage that may prevent mold opening. To address these issues, high-strength positioning keys can be added to the mold's parting surface, ideally using cylindrical keys. Crucially, the guide pillar hole and parting surface must be perfectly perpendicular, which can be achieved through proper machining and clamping procedures. It is also essential to ensure that the heat treatment hardness of guide pillars and sleeves meets design requirements. These measures will help to minimize the risk of costly damage and ensure optimal performance of large molds.
3. Bending of movable formwork.
During the injection process, the molten plastic in the mold cavity creates a significant amount of back pressure, typically ranging from 600 to 1000 kg/cm². Unfortunately, some mold manufacturers tend to overlook this issue and make modifications to the original design dimensions or even replace the moving template with low-strength steel plates. In cases where ejector pins are used to remove the material, the wide span of the seats on both sides causes the template to bend downward when injection takes place. Hence, it is crucial to use high-quality steel of sufficient thickness for the movable formwork, and avoid employing low-strength steel plates like A3. If necessary, additional support columns or blocks should be installed beneath the movable formwork to reduce its thickness and enhance its load-bearing capacity. Taking these measures will ensure a durable and efficient mold.
4. The ejector pin is bent, broken, or leaking.
Although the quality of self-made ejector pins is commendable, the problem lies in the excessively high processing cost associated with them. As a result, many manufacturers have resorted to using standard parts, resulting in subpar quality. The challenge arises in finding the right balance for the gap between the ejector pin and the hole. If the gap is too large, it may lead to material leakage, while a gap that is too small can cause the ejector pin to get stuck due to the expansion caused by the mold temperature rise during injection. The real danger lies in situations where the ejector pin fails to be pushed out to the desired distance and ultimately breaks. This leaves the exposed ejector pin incapable of resetting during the subsequent mold closing, potentially causing damage to the concave mold.
To address this issue, a solution is proposed whereby the top rod is reground. This involves reserving a fitting section of 10 to 15mm at the front end of the top rod while reducing the middle part by 0.2mm. After assembly, it becomes imperative to meticulously inspect all jacking rods to ensure the fit clearance, which ideally falls within the range of 0.05-0.08mm. This step is crucial in guaranteeing the smooth and unhindered forward and backward movement of the entire jacking mechanism.
Consequently, by implementing these measures, it is anticipated that the processing cost of ejector pins can be considerably reduced without compromising on quality. The use of standard parts will no longer result in poor performance. Instead, manufacturers can find solace in a well-balanced gap that prevents material leakage and sticking issues. Furthermore, the risk of breakage and subsequent damage to the mold can be minimized. This solution hinges on the careful regrinding of the top rod and thorough inspection of fit clearance for all jacking rods. Ultimately, the aim is to ensure the unfettered movement of the jacking mechanism, thus enhancing overall efficiency and productivity.