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Compression Molds<\/h2>\n\n\n\n
Compression molds have a movable top half (the core) and a fixed bottom half (the cavity) that are usually made of aluminum or steel. The parting line is where the two mold halves meet. Some compression molds have a single cavity, but most have multiple cavities to help offset the longer cycle times associated with compression molding. To facilitate part release, molds can also use ejector pins and sliders<\/a> but many are manually removed from the tooling by hand.<\/p>\n\n\n\n Typically, compression molds are machined from hardened steel blocks. Manual machining with milling and drilling, or automated machining are used. Compression molds can be die-cast instead, but the dies still require CNC machining. 3D-printed inserts can be used to reduce tooling costs, but they won\u2019t last as long and can\u2019t match the tolerances of metal molds, especially hardened steel ones.<\/p>\n\n\n\n There are three main types, or styles, of compression molds.<\/p>\n\n\n\n Flash molds are the most common mold because they\u2019re the simplest and least expensive to produce. Before molding, an operator loads the cavity with an excessive amount of charge. When the mold is compressed, material fills the mold completely but flash escapes between the parting line. To control costs associated with waste, flash molds are often used with less expensive materials. <\/p>\n\n\n\n Positive molds cost more than flash molds and require an accurately measured charge. Often, positive molds are used when it\u2019s important to control part density, or if a part is molded from expensive materials. Positive molds are also used when parts have a deep draw, meaning that the depth of the compression molded part exceeds its diameter.<\/p>\n\n\n\n Semi-positive molds are the most expensive compression mold, but they combine the advantages of flash molds and positive molds. Although semi-positive molds don\u2019t require extremely accurate charge measurements, using an excessive amount of charge can cause the material to escape between the parting line during mold compression.<\/p>\n\n\n\n There are three main types of compression molding materials<\/p>\n\n\n\n Compression-molded plastics can be divided into thermosetting and thermoplastic materials.<\/p>\n\n\n\n Thermosets have low shrinkage rates and high durability. They tend to have better mechanical properties, but can only be liquefied once. Consequently, they can\u2019t be remolded. Examples of compression-molded thermosets include:<\/p>\n\n\n\n Thermoplastics can be melted repeatedly and are re-moldable. However, they\u2019re generally not as hard and strong as thermosets. Examples of compression-molded thermoplastics include: <\/p>\n\n\n\n Compression-molded rubber is stretchy and elastic. Depending on the specific compound, it can also provide oil, temperature, or chemical resistance. Examples of compression-molded rubber include:<\/p>\n\n\n\n Thermosets and thermoplastic materials can contain fibers for added strength. For example, bulk molding compound (BMC) is a thermoset composite that\u2019s supplied as a dough-like combination of polymer resins, chopped fibers, and a hardening agent. Nylon, a thermoplastic, can be filled with glass fibers and compression-molded into strong but lightweight parts.Rubber-based composites are also supported by compression molding. For example, silicones and fluorosilicones that contain metal, metal-coated, or bimetallic particles provide electrical conductivity and shielding against electromagnetic interference (EMI). These composite materials don\u2019t flow readily enough for injection molding, but they can be compression-molded. <\/p>\n\n\n\n Compression molding is a relatively simple process, but it still involves a series of steps:<\/p>\n\n\n\n Preparing the charge involves measurement. The compression mold type helps determine the charge’s size, but molders still want to avoid excessive trimming or de-flashing. If the charge is too large, compressing the mold will cause excess material to escape between the parting line and produce flash. If the charge is too small, there won\u2019t be enough material to fill the mold completely.<\/p>\n\n\n\n Loading the mold involves placing the charge in the cavity, the bottom half of the tool. With flat, rectangular parts, the cavity usually has a flat, rectangular opening that approximates the size of the part. For compression molded parts that require a hollow interior, the core combines with the cavity and creates the interior section. <\/p>\n\n\n\n With rubber materials, compression molds are usually pre-heated to soften the charge and reduce its viscosity, or resistance to flow. With plastics, the pellets put into a mold might not be heated until the mold is compressed. Regardless, the top of the mold (the core) is closed on the bottom half of the mold (the cavity). Heat and pressure are then applied so the charge flows and fills the tool.<\/p>\n\n\n\n With thermoplastic materials, lowering the mold temperature causes the molten charge to harden into the final part. With rubber materials, catalysts are used to promote curing, a process that\u2019s also used with thermosetting plastics. With rubber compression molding, there are two main curing systems: condensation curing uses a tin catalyst, and addition curing uses a platinum catalyst.<\/p>\n\n\n\n After the part is cooled or cured, the compression mold is opened and the part is released. Depending on part complexity and volumes, part ejection can be manual or automated. Manual ejection is fine for simpler parts and low-volume applications. Automated ejection is used for more complex parts and higher volumes. Typically, a plunger-style ejector pin that telescopes from the underside of the mold is used. Some mold flash is expected, but excessive flashing needs to be removed so that it won\u2019t detract from the part\u2019s appearance or interfere with assembly or performance.<\/p>\n\n\n\n After compression molding is complete, it\u2019s essential to clean the core and cavity to remove any residual material. Regular cleaning is usually done with a handheld tool, but more thorough periodic cleanings are also required. Technologies include <\/a>dry ice blasting and cleaning with chemicals, lasers, or ultrasonic immersion. Finally, a release agent is applied to help prevent sticking during future molding cycles.<\/p>\n\n\n\n Compression molding also supports insert molding and overmolding, processes that eliminate post-molding part assembly.<\/p>\n\n\n\n Insert molding compresses a charge over a prefabricated component. The charge then encapsulates some or all of the insert. For example, a metal knife blade (the insert) can be placed into a compression mold with a plastic charge. When the plastic is heated and compressed, it forms a handle around the blade. Insert molding is also used with electrical contacts such as plugs. <\/p>\n\n\n\n Overmolding compresses a charge over a previously molded component. This provides the advantages of two separate molding materials. For example, a harder material can be compression molded to form a strong, durable handle. A softer material can then be compression molded over the handle to improve its ergonomics and aesthetics.<\/p>\n\n\n\n The advantages of compression molding begin with lower tooling costs but don\u2019t end there. Because compression-molded materials are placed directly into a mold, they don\u2019t need to flow through a complex series of channels and openings as with injection molding. Consequently, compression molding supports the use of heavier and harder-to-flow materials. Because the charge is placed directly in the cavity, compression-molded parts are free of flow lines and residual stresses that can cause defects<\/a>.<\/p>\n\n\n\n Compression molding isn\u2019t used for fine part tolerances, but compression-molded parts still have good dimensional accuracy. Compression-molded parts also have a smooth, attractive surface finish and can achieve a good level of detail. Because they\u2019re strong and lightweight, compression-molded parts can replace metal ones in structural components and assemblies. Compression molding support for insert molding, overmolding, and a wide range of materials underscores its versatility.<\/p>\n\n\n\n Compression molding is not a good choice for complex parts with sharp edges, steep angles, or intricate details despite its many advantages. Generally, the part geometries are relatively simple so compression molds don\u2019t need to include ejection mechanisms that increase the cost of tooling. Longer cycle times are also a disadvantage, and activities such as preparing the charge, filling the cavity, and trimming finished parts all add costs.<\/p>\n\n\n\n Compression molding is used in many industries and applications. Here are a few examples.<\/p>\n\n\n\n Aircraft manufacturers are replacing heavier aluminum parts with compression-molded C-channels, H-beams, U-sections, L-stringers, and T-strings. Aerospace compression molding is also used to produce O-Rings<\/a>.<\/p>\n\n\n\n The automotive industry uses compression molding to produce fenders and large vehicle panels. Compression-molded plastic parts are also used in automotive interiors to protect engine components. Related applications include housings for LED lighting. <\/p>\n\n\n\n Medical compression molding is used to produce plastic syringe stoppers and silicone respirator masks. Because this molding process is cost-effective at low volumes, it can also be used to produce dentures for individual patients. <\/strong><\/p>\n\n\n\n Compression molding for consumer products is used to produce kitchenware such as utensils, boots, scuba gear, and appliance housings. Household electrical components such as sockets, switches, faceplates, and metering devices are also compression molded. <\/p>\n\n\n\n DFM is about designing your part so that it\u2019s easy to manufacture and, therefore, less expensive and faster to produce. Here are four things to avoid when designing a part for compression molding.<\/p>\n\n\n\n If your part design is still in development, you may not have considered parting line locations yet. That\u2019s why it helps to partner with Fictiv, a provider of compression molding services<\/a> that provides DFM assistance. You\u2019ll also gain access to a carefully vetted network of compression molders.<\/p>\n\n\n\n Is your project a good fit for compression molding? Are you considering 3D printing or maybe even low-volume injection molding<\/a> instead? Fictiv provides all these services and more, so consider us for your next project. Getting started is as simple as creating a free account and uploading your part design. Let\u2019s get started<\/a>.<\/p>\n\n\n\n <\/p>\n","protected":false},"excerpt":{"rendered":" Compression molding produces parts by placing a pre-measured amount of material into a mold, closing the tool, and applying heat and pressure. This pre-measured material is called a charge or load, and the mold is usually pre-heated so that the material flows more readily and fills the tool as it\u2019s compressed. When molding is complete, […]<\/p>\n","protected":false},"author":145,"featured_media":14370,"parent":0,"menu_order":0,"template":"page-article-form.php","fictiv_role":[],"fictiv_topic":[],"fictiv_industry":[],"fictiv_manufacturing_process":[51],"coauthors":[159],"class_list":["post-14369","cpt_blog","type-cpt_blog","status-publish","has-post-thumbnail","hentry"],"aioseo_notices":[],"yoast_head":"\nHow Compression Molds are Made<\/h3>\n\n\n\n
Types of Compression Molds<\/h3>\n\n\n\n
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Flash molds<\/h4>\n\n\n\n
Positive Molds<\/h4>\n\n\n\n
Semi-Positive Molds<\/h4>\n\n\n\n
![\"Compression](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/12\/Compression-molds.jpg\")
Compression Molding Materials<\/h2>\n\n\n\n
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Compression Molded Plastic Materials<\/h3>\n\n\n\n
Thermosets<\/h4>\n\n\n\n
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Thermoplastics<\/h4>\n\n\n\n
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Compression Molded Rubber Materials<\/h3>\n\n\n\n
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Compression Molded Composite Materials<\/h3>\n\n\n\n
![\"Compression](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/12\/Compression-molding-process.png\")
The Compression Molding Process<\/h2>\n\n\n\n
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Prepare the Charge<\/h3>\n\n\n\n
Load the Mold<\/h3>\n\n\n\n
Apply Heat and Pressure<\/h3>\n\n\n\n
Cool or Cure the Part<\/h3>\n\n\n\n
Release the Part from the Mold<\/h3>\n\n\n\n
<\/p>\n\n\n\nTrim or De-Flash the Part <\/h3>\n\n\n\n
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Clean the Mold<\/h3>\n\n\n\n
![\"Cryogenic](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/12\/Cryogenic-deflashing-jpg.webp\")
Compression Molding with Insert Molding and Overmolding<\/h2>\n\n\n\n
Insert Molding<\/h3>\n\n\n\n
Overmolding<\/h3>\n\n\n\n
Compression Molding Advantages and Disadvantages<\/h2>\n\n\n\n
![\"Compression](\"https:\/\/www.fictiv.com\/wp-content\/uploads\/2023\/12\/Compression-molding-1-jpg.webp\")
Compression Molding Industries and Applications<\/h2>\n\n\n\n
Aerospace Compression Molding<\/h3>\n\n\n\n
Automotive Compression Molding<\/h3>\n\n\n\n
Medical Compression Molding<\/h3>\n\n\n\n
Compression Molding for Consumer Products<\/h3>\n\n\n\n
Designing Compression Molded Parts<\/h2>\n\n\n\n
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Compression Molding Services from Fictiv<\/h2>\n\n\n\n