{"id":3542,"date":"2026-10-21T13:58:34","date_gmt":"2026-10-21T05:58:34","guid":{"rendered":"http:\/\/www.spagirardot.com\/blog\/?p=3542"},"modified":"2026-10-21T13:58:34","modified_gmt":"2026-10-21T05:58:34","slug":"what-is-the-dielectric-strength-of-vacuum-cast-parts-495a-a729e2","status":"publish","type":"post","link":"http:\/\/www.spagirardot.com\/blog\/2026\/10\/21\/what-is-the-dielectric-strength-of-vacuum-cast-parts-495a-a729e2\/","title":{"rendered":"What is the dielectric strength of vacuum – cast parts?"},"content":{"rendered":"

If you\u2019ve ever worked with prototype development or low-volume production, you\u2019ve probably heard the phrase \u201cvacuum casting\u201d thrown around for making tight, high-quality parts. As someone who\u2019s run a small vacuum casting supply shop for the last 12 years, one question comes up at least once a week from engineers, designers, and even product managers who are new to the process: \u201cWhat\u2019s the dielectric strength of vacuum-cast parts?\u201d It\u2019s not just a random technical detail\u2014it\u2019s the kind of thing that can make or break a project, especially for electronics, aerospace, or medical devices where electrical insulation is non-negotiable. Vacuum Casting<\/a><\/p>\n

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I get it, though. Dielectric strength sounds like something straight out of a college physics lecture, not a conversation with a supplier. Let me break it down simply: dielectric strength is the maximum electric field a material can withstand before it breaks down and starts conducting electricity. For vacuum-cast parts, that number isn\u2019t one-size-fits-all. It depends on the material we use, the part\u2019s thickness, how we prepare the mold, and even the conditions it ends up in.<\/p>\n

First, let\u2019s talk about why this matters for your parts. Last year, I had a customer come to us mid-project with a prototype for a wearable medical device. They\u2019d tried 3D printing their casings, but the parts kept arcing when they tested the built-in sensors. Their 3D printed parts had tiny, invisible voids from the printing process that lowered their dielectric strength, and they couldn\u2019t fix that easily. We switched them to vacuum casting, and their parts went from failing insulation tests on every trial to hitting 18 kV\/mm right out of the mold. That\u2019s the kind of difference getting this right makes\u2014no one wants a product that stops working (or worse, poses a safety risk) because of a material property they didn\u2019t account for.<\/p>\n

Now, let\u2019s get into what vacuum-cast parts are made of, because that\u2019s the biggest factor in their dielectric strength. Most of our customers use two main types of materials for vacuum casting: urethane resins, which are the workhorse of the process, and silicone rubbers, which we use for more flexible or high-temperature applications. Urethanes generally have higher dielectric strength than silicones, but even within urethanes, there\u2019s a range. The standard general-purpose urethane we use, for example, is our E840 series, which has a dielectric strength of around 20 to 22 kV\/mm when cast to a 1mm thickness. That\u2019s way higher than most common engineering plastics like ABS, which clocks in at around 14 kV\/mm for the same thickness.<\/p>\n

Wait, thickness matters a lot here, too. A lot of new customers ask, \u201cIf I cast a 5mm thick part, will its dielectric strength be five times higher?\u201d Nope, that\u2019s a common mistake. Dielectric strength isn\u2019t linear. For vacuum-cast urethanes, as thickness increases, the dielectric strength per millimeter actually drops a little. A 1mm part hits ~21 kV\/mm, a 3mm part is around 17 kV\/mm, and a 5mm part is around 15 kV\/mm. Why? Because as the material gets thicker, there\u2019s a higher chance of micro-voids or inconsistencies that create weak points in the electric field. That\u2019s another reason why our process is so reliable: we run each cast in a vacuum chamber of 29.5 inches of mercury, which eliminates almost all those tiny voids before the resin cures. No voids means no weak points, so the dielectric strength stays consistent across every part, even for thicker sections.<\/p>\n

Silicones are a different story. We use silicone primarily for things like gaskets, seals, and flexible electronic housings. Their dielectric strength is lower than urethanes\u2014usually around 10 to 12 kV\/mm for 1mm thickness\u2014but they have other benefits, like resistance to extreme temperatures, which makes them useful for aerospace or automotive under-hood applications where insulation still matters. It\u2019s not that one is better than the other; it\u2019s about matching the material to your project\u2019s needs.<\/p>\n

Now, what factors can lower the dielectric strength of a vacuum-cast part, even if you pick the right material? Contamination is the big one. If there\u2019s dust, oil, or even leftover residue from a previous cast in the mold, that can create a conductive path in the cured part. That\u2019s why we take extra steps to clean and prepare every mold before casting: we wipe them down with isopropyl alcohol, run a test cast of a scrap part to make sure there\u2019s no residue, and even inspect every part under a magnifying glass before we send it out. Another thing: moisture. Urethane resins absorb a tiny bit of moisture over time, and high humidity can lower dielectric strength slightly. That\u2019s why we recommend storing parts in a cool, dry place if they\u2019re not going to be used right away, and for projects that need long-term stability, we can offer a post-curing process that removes residual moisture and locks in the material\u2019s properties.<\/p>\n

I\u2019ve seen this play out too many times. A few years back, we had a customer making power tool housings. They initially sourced from a different supplier who cut corners on mold prep, and the parts kept failing insulation tests because of hidden voids. When they switched to our vacuum casting service, we did a dielectric strength test on each batch before shipping, and every part hit their required 18 kV\/mm mark. That consistency is the biggest advantage of vacuum casting over other processes for electrical applications: with injection molding, you might have more defects, and 3D printing just can\u2019t match the low void content that comes from casting in a vacuum.<\/p>\n

Let\u2019s also talk about industry standards, because if you\u2019re working on a regulated project, you can\u2019t just go by numbers\u2014you need to make sure your parts meet specific requirements. For example, medical device parts often need to comply with IEC 60601 standards for electrical safety, which require a minimum dielectric strength of 20 kV\/mm for insulation parts. Aerospace parts might follow NASA standards, which can have different thresholds depending on the application. We do dielectric strength testing for every batch we produce, so we can provide test reports that match whatever standard you need. That\u2019s not something every vacuum casting supplier offers, but for customers working on high-stakes projects, it\u2019s non-negotiable.<\/p>\n

I\u2019ve had engineers ask me before, \u201cWhat if I need higher dielectric strength than what standard urethanes offer?\u201d There are options. We have specialty urethanes that are formulated specifically for high insulation applications, with dielectric strength up to 28 kV\/mm for 1mm thickness. These are used for things like transformer components, high-voltage connectors, and battery enclosures where extra insulation is critical. They\u2019re a bit more expensive than general-purpose urethanes, but for the right project, the payoff is worth it\u2014no failed tests, no rework, no lost time.<\/p>\n

Another point that\u2019s easy to overlook: surface finish. If a part has a rough, uneven surface, that can create electric field concentration points, which lower the effective dielectric strength. Our vacuum casting process gives parts a smooth, consistent surface, which helps with insulation performance. If you need a textured surface, we can add that to the mold, but we recommend a smooth finish for electrical applications to maximize dielectric strength.<\/p>\n

Let\u2019s wrap this up with a real example that shows how all this comes together. Last year, a startup came to us to develop a low-voltage transformer for portable solar chargers. They needed parts that could handle 500V of electricity without arcing, and they were prototyping for a product launch in 6 months. Their initial 3D printed parts had a dielectric strength of only 12 kV\/mm, which meant they had to make the casings twice as thick just to reach their required insulation, adding unnecessary weight to the charger. We suggested our high-insulation urethane (28 kV\/mm for 1mm thickness), cast the parts in our high-vacuum chamber to eliminate voids, and did a dielectric strength test on the first batch: 27.8 kV\/mm. That meant they could make the casings thinner, lighter, and still meet their electrical requirements. They went from 3D printing 10 prototypes a week to ordering 5000 parts from us for their first production run. That\u2019s exactly why I love this work\u2014helping customers solve problems with material knowledge that makes their products better.<\/p>\n

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If you\u2019re working on a project that requires reliable dielectric strength, whether it\u2019s electronics, medical devices, aerospace, or industrial parts, you don\u2019t have to guess about these numbers. Every project is different, and we can help you pick the right material, adjust part thickness, and ensure your parts meet all your electrical requirements. We test every batch, so you can be confident in the performance of your vacuum-cast parts. Don\u2019t leave insulation properties to chance\u2014reach out to us to discuss your project and get the details you need to move forward.<\/p>\n

Rapid Prototyping Services<\/a> References
\nASTM D149 – Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies
\nIEC 60601-1:2018 – Medical electrical equipment – Part 1: General requirements for basic safety and essential performance
\nBrydson, J. A. (1999). Plastic Materials (7th ed.). Butterworth-Heinemann.
\nVacuum Casting: A Guide for Prototyping and Low-Volume Production. Society of Manufacturing Engineers, 2021.<\/p>\n

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Dongguan Xinchuan Precision Manufacturing Co., Ltd.<\/a>
As one of the most professional vacuum casting manufacturers and suppliers in China, we offer a quick lead time for customized orders. Please feel free to buy precision vacuum casting made in China here from our factory. Contact us for quotation.
Address: #16 Gangjian Road, Changping Town, Dongguan City, Guangdong, China. 523000
E-mail: FreeQuote@xcprecision.com
WebSite: https:\/\/www.xcprecisions.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

If you\u2019ve ever worked with prototype development or low-volume production, you\u2019ve probably heard the phrase \u201cvacuum … What is the dielectric strength of vacuum – cast parts?<\/span>Read more<\/a><\/p>\n","protected":false},"author":63,"featured_media":3542,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3505],"class_list":["post-3542","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-vacuum-casting-4ef8-a768c6"],"_links":{"self":[{"href":"http:\/\/www.spagirardot.com\/blog\/wp-json\/wp\/v2\/posts\/3542","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.spagirardot.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.spagirardot.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.spagirardot.com\/blog\/wp-json\/wp\/v2\/users\/63"}],"replies":[{"embeddable":true,"href":"http:\/\/www.spagirardot.com\/blog\/wp-json\/wp\/v2\/comments?post=3542"}],"version-history":[{"count":0,"href":"http:\/\/www.spagirardot.com\/blog\/wp-json\/wp\/v2\/posts\/3542\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.spagirardot.com\/blog\/wp-json\/wp\/v2\/posts\/3542"}],"wp:attachment":[{"href":"http:\/\/www.spagirardot.com\/blog\/wp-json\/wp\/v2\/media?parent=3542"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.spagirardot.com\/blog\/wp-json\/wp\/v2\/categories?post=3542"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.spagirardot.com\/blog\/wp-json\/wp\/v2\/tags?post=3542"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}