XavierAdvantages and Limitations of Compression Molding
It is a specialized polymer molding process that creates the desired shape by compressing the material in a closed mold. This manufacturing method is popular for thermoset composites with excellent properties.
The compression molding process requires a multi-cavity compression mold to accurately obtain the negative geometry of the desired shape. Meanwhile, the mold consists of two halves (the fixed lower half and the removable upper half). First, a precalculated amount of material is placed into a heated mold cavity, and then the mold is heated and compressed. Here, compression and mold heating force material to flow through the cavity and fill it. However, it is critical to set the proper pressure, temperature rate, and cure time during the compression process. Next, the mold is opened to expose the cooled, solidified part.
Advantages of compression molding
Here are the recognized benefits of compression molding in a variety of manufacturing applications.
1.Mass production efficiency
Throughput is the most valuable advantage, especially when comparing compression molding and 3D printing. Once the mold is made, you can reuse it to make the same parts in large quantities, up to thousands of times. However, the life of the mold depends on the mold material, charge abrasiveness and other factors. In the long run, this high-volume production efficiency can significantly reduce the cost of each part. On the other hand, the cost per part does not decrease with 3D printing for mass production.
2.Excellent part strength and durability
Molded parts are not structured layer by layer, but in a compact and extruded form. Therefore, compression molding provides excellent part strength. As a result, there is little chance of voids forming, helping the part have excellent structural integrity. According to related research, during testing, the strength, hardness, tensile strength and elasticity of compression molded samples were higher than those of 3D printed parts.
3.good surface finish
Parts formed by this molding method have good surface finish. This is because compression causes the material to conform tightly to the mold surface. Closely adheres to the mold surface. Through highly polished molds and optimal processing conditions, it can achieve Ra values as low as 0.1 microns (μm). At the same time, the surface finish of the cavity wall is critical to the finish of the compression molded part.
4.Suitable for large parts
The dimensions achievable with compression molded parts depend on the mold size. Therefore, you can make larger parts by designing the right mold and using high compression tonnage. For example, aircraft wing skins can be implemented using CM. Subsequently, the charge is pre-placed in the mold rather than using injection methods, which facilitates large-size molding. The reason is that compression enables the material to be evenly distributed within a large mold cavity without being limited by flow and pressure requirements.
Limitations of Compression Molding
Although compression molding offers many advantages, it has limitations in terms of design flexibility, tooling cost, production time, and tight accuracy. Understanding this limitation can help you avoid possible defects in the final molded part and make better decisions. Below is a description of each limitation.
1.Limited design complexity
Compression molding is more suitable for large and relatively simple designs. Here, the limited design flexibility is mainly due to the material flow patterns in the complex cavity of the compression mold. If the design has complex features, such as strong tilt angles and small details on corners, the flow of material cannot accurately fill these cavities. Additionally, material flow restrictions can trap compressed air, causing voids to form. Designers, on the other hand, gain a wide range of freedom through 3D printing.
2.Higher mold costs
If we compare the cost of molds for 3D printing versus compression molding, we see that the mold costs are quite high. This is because of the high upfront cost of molds and other ancillary tools. Additionally, small changes in design require significant investments in tooling. In contrast, 3D printing does not involve such expensive mold costs.
3.longer cycle times
Compression molding processes generally have longer cycle times, even for compression molding and injection molding. It involves preheating the mold and charging, preloading, and relatively long curing times, all of which contribute to improved production times. Subsequently, the process of removing flash and burrs from the molded surface after production also adds time.
4.Quality and accuracy issues
Finally, it is difficult to achieve the same high precision and quality with plastic compression molding as other advanced manufacturing technologies. This is preliminary because the material flow is not as uniform as other molding methods. Second, other quality issues may be shrinkage and warping, as all thermoset and thermoplastic materials shrink to some extent during the cooling process. Regarding accuracy, compression molding tolerances typically range from ±0.127 to ±0.508 mm. Here, tolerances vary depending on the surface quality of the mold cavity, process parameters and characteristics of the charging material.