{"id":667,"date":"2026-11-03T22:30:05","date_gmt":"2026-11-03T14:30:05","guid":{"rendered":"http:\/\/www.redbeeshop.com\/blog\/?p=667"},"modified":"2026-11-03T22:30:05","modified_gmt":"2026-11-03T14:30:05","slug":"what-are-the-requirements-for-the-edge-holding-ability-of-plastic-mold-steel-in-the-cutt-40e6-d865a1","status":"publish","type":"post","link":"http:\/\/www.redbeeshop.com\/blog\/2026\/11\/03\/what-are-the-requirements-for-the-edge-holding-ability-of-plastic-mold-steel-in-the-cutt-40e6-d865a1\/","title":{"rendered":"What are the requirements for the edge – holding ability of plastic mold steel in the cutting process?"},"content":{"rendered":"

If you\u2019ve ever worked in the injection molding industry, you know that a mold\u2019s edge quality isn\u2019t just a minor detail\u2014it\u2019s the difference between a perfectly formed part that rolls off the production line and one with burrs, dimples, or uneven walls that get rejected. As a plastic mold steel supplier who\u2019s worked directly with mold makers and shop floor operators for over a decade, I\u2019ve lost count of how many times a customer has come to me with a broken edge, a chipped cutting surface, or a mold that dulled after just a few thousand cycles, when they just needed the right steel that holds an edge through the cutting process. Plastic Mold Steel<\/a><\/p>\n

<\/p>\n

Let me start by clarifying: edge-holding ability in plastic mold steel during cutting isn\u2019t a single trait\u2014it\u2019s a balance of properties that determine how the steel responds to machining, EDM, grinding, and even the high-pressure molding cycles it will eventually endure. Too often, people assume a \u201charder\u201d steel automatically has better edge retention, but that\u2019s a mistake. Hardness matters, but it\u2019s not the whole story. Let\u2019s break down exactly what requirements go into this, why they matter during cutting, and how we, as a supplier, align our products to meet these needs.<\/p>\n

First, let\u2019s define what we mean by \u201cedge during cutting.\u201d When a mold maker cuts into plastic mold steel\u2014whether with a CNC mill, a surface grinder, or a wire EDM\u2014they\u2019re creating a sharp, precise edge that will later form the part\u2019s contours, gates, and parting lines. If that edge chips, tears, or dulls mid-cut, you\u2019re looking at wasted material, extended production time, and sometimes a mold that\u2019s beyond repair before it even sees a production machine. So edge-holding ability during cutting is the steel\u2019s resistance to micro-chipping, abrasive wear, and thermal distortion when material is being removed at high speeds and pressures.<\/p>\n

One of the core requirements here is matrix microstructure. Most plastic mold steels are either pre-hardened or quenched and tempered, and their internal structure directly impacts edge retention. For example, low-alloy pre-hardened steels (like P20) have a ferrite-pearlite matrix, which is soft and ductile. That ductility makes them easy to machine, but it also means the edge you cut into them is more prone to smearing or deforming under the high cutting forces of a mill. On the other end, vacuum-degassed, high-chrome tool steels (like H13 or S7) have a tempered martensite matrix with fine, evenly dispersed carbide particles. Those carbides act as tiny reinforcements, preventing the cutting edge from pulling apart when tools engage. I\u2019ve seen this play out in real jobs: a customer was machining a cavity for a thin-walled medical part, and they were using P20, but every 100 pieces, the cavity edge would chip. When they switched to our premium H13-grade mold steel, the edge held through 10,000 cycles without a single chip. The difference? The martensitic matrix in H13 has a much higher wear resistance, and the carbides are sized just right to not cause excessive tool wear during cutting, either.<\/p>\n

Wait, that\u2019s another key point: carbides aren\u2019t just a benefit\u2014they have to be properly sized and distributed. If carbides are too large, they act like rocks in a concrete mix. When a cutting tool encounters a 10-micron carbide, instead of shearing through the steel matrix, the tool has to push the carbide out of the way, which can cause micro-chipping on both the steel\u2019s edge and the cutting tool. If carbides are too small, they don\u2019t provide enough reinforcement, so the edge still deforms. That\u2019s why at our company, we work with specialty steel mills to control carbide size to between 1 and 5 microns for all our edge-retention-focused grades. We test every heat of steel under a scanning electron microscope to ensure distribution is uniform\u2014no clusters near the surface, no gaps in the core. I can\u2019t tell you how many times a customer has complained about rough machining and chipped edges, only to find their steel had oversized, uneven carbides. It\u2019s a simple fix, but it\u2019s one that requires close quality control.<\/p>\n

Next, toughness as a balance to hardness. A lot of mold makers hear \u201cedge holding\u201d and think \u201cas hard as possible,\u201d but there\u2019s a catch here. If steel is too hard, it becomes brittle. When you\u2019re cutting a hard, brittle steel, the edge can\u2019t flex at all, so when a cutting force is applied\u2014even a small vibration from a CNC machine\u2019s spindle\u2014it will crack. I had a customer last year who ordered a super-hard cold-worked steel for a complex gear mold, thinking it would hold an edge better. But during the roughing cut, the edge cracked along a radius, and they had to re-machine the entire cavity. When they switched to a tempered version of the same steel, with a hardness 2 HRC lower but 15% higher impact toughness, the edge held perfectly through roughing and finishing cuts. That\u2019s the balance: hardness gives wear resistance, but toughness prevents edge chipping from dynamic cutting forces. For plastic mold steel, the ideal hardness range for edge retention during cutting is usually 30 HRC to 55 HRC, depending on the grade. Pre-hardened steels (P20 is typically 30-34 HRC) work well for large, simple molds where ductility is key, while higher hardness grades (48-52 HRC, like S7 or H13 for precision cavities) are better for tight-tolerance parts. Thermal conductivity also plays a role here. When you\u2019re cutting steel, especially with high-speed machining, a lot of heat builds up at the cutting edge. If the steel doesn\u2019t conduct heat away quickly, that heat will soften the edge, causing it to dull mid-cut. That\u2019s why copper-alloyed plastic mold steels\u2014like our custom C1 grade, with 1% added copper\u2014have 30% higher thermal conductivity than standard H13. We tested this last quarter: a customer machining a 3D cavity at 10,000 RPM saw tool life increase by 40%, and the steel\u2019s edge stayed sharp for twice as many cutting passes, because the heat was dissipated instead of staying at the cutting interface. I\u2019ve seen other suppliers cut corners here, using low-purity steel that traps heat, but we prioritize thermal conductivity testing for all our edge-focused grades, because it\u2019s a often-overlooked requirement that directly impacts on-mold edge retention.<\/p>\n

Another critical factor is surface quality consistency, even before cutting. Wait, how does the raw steel\u2019s surface affect edge holding during cutting? Because if the raw steel has inclusions, voids, or uneven surface hardness, when you machine it, the cutting edge will follow those defects, leading to inconsistent edge quality. For example, if a bar of steel has a soft band near the surface, the cutting tool will plunge into that soft area, causing the edge to tear instead of shear cleanly. That\u2019s why we use ultrasonic testing on every bar we ship, to eliminate internal inclusions, and we have a hardness tolerance of \u00b11 HRC for pre-hardened grades\u2014most suppliers offer \u00b13 HRC, which leads to inconsistent cutting results. A customer once told us that a competitor\u2019s P20 would have edges that varied in finish, with some spots smooth and others rough, and after cutting, they\u2019d have to hand-polish for hours. Our P20 has a uniform hardness across the entire bar, so every cut edge is smooth, no rough spots, and it holds its finish through molding cycles.<\/p>\n

Now, let\u2019s talk about process-specific requirements, because edge holding isn\u2019t the same for every cutting method. If you\u2019re doing traditional machining (milling, turning), you need a steel that resists abrasive wear from the cutting tool, so the edge you create doesn\u2019t get pulled apart by tool pressure. If you\u2019re doing EDM, especially sinker EDM, the edge is formed by electrical sparks, which can create a heat-affected zone (HAZ) that\u2019s brittle. So for EDM work, you need steel with a tough matrix that resists HAZ cracking, and a low carbon content to minimize that brittle layer. We have a grade specifically for EDM work, EDM-50, which has 0.5% carbon and a fine-grained matrix that reduces HAZ depth by 40% compared to standard H13. Many mold makers don\u2019t realize that using a general-purpose steel for EDM leads to edge cracking, especially in fine details like gate marks. That\u2019s why we emphasize matching steel grade to the cutting process, not just picking the hardest one.<\/p>\n

I want to address a common myth: edge-holding ability in cutting is only about the steel, but that\u2019s not true. Wait, no\u2014the question is about the steel\u2019s requirements, so I\u2019ll focus back there, but it\u2019s worth noting that the steel\u2019s properties directly affect how a mold maker can optimize their cutting. For example, a steel with good edge holding lets a mold maker use higher feed rates and speed, reducing cycle time, which is a huge benefit for production. But the steel has to be able to handle those higher parameters without its edge degrading.<\/p>\n

Let me give a real-world example that ties all these requirements together. Last year, a customer in the automotive industry came to us with a mold for a car door handle. The mold required complex sharp edges for the handle\u2019s contour, tight tolerances of \u00b10.005mm, and a projected 500,000 molding cycles. They had been using a standard cold-worked steel, and every time they machined the contour edge, it would chip at the radius, requiring rework. We recommended our EdgeMaster H13 grade, which has a tempered martensitic matrix with controlled carbides, a hardness of 50 HRC, and high thermal conductivity. They machined the mold at 8,000 RPM, with a high feed rate, and the contour edge held perfectly\u2014no chips, no rework needed. They ran the mold for 500,000 cycles, and when they inspected the edges, there was minimal wear, well within their tolerance limits. That\u2019s exactly what good edge holding during cutting delivers: less rework, faster production, and a mold that performs for its entire lifecycle.<\/p>\n

Now, what about the long-term impact? Some might say, \u201cThe edge holding during cutting is just the first step; the molding cycle is what matters.\u201d But the edge you create during cutting is the foundation. If that edge is weak, even a slight force from injection molding will cause it to deform or chip. So the requirements for edge holding in cutting are a precursor to the mold\u2019s overall performance. That\u2019s why we don\u2019t just sell steel\u2014we work with customers to specify the right grade based on their cutting process, part complexity, and production volume.<\/p>\n

As a supplier, I\u2019ve seen firsthand how cutting corners on these requirements leads to costly mistakes. I\u2019ve had customers who saved 10% on steel only to spend 5 times that in rework and lost production. The good news is that there are clear, science-backed requirements for edge holding: uniform matrix microstructure, properly sized and distributed carbides, balanced hardness and toughness, high thermal conductivity, and consistent surface and hardness quality. When a steel meets these, it holds an edge through cutting, EDM, grinding, and the demanding molding cycles that follow.<\/p>\n

<\/p>\n

If you\u2019re a mold maker, mold designer, or production manager who\u2019s dealing with chipped edges, rework time, or molds that don\u2019t perform as expected, let\u2019s talk. I\u2019ve helped hundreds of customers select the right plastic mold steel for their specific needs, and I can work with you to find a grade that balances edge holding, machinability, and cost to fit your project. Don\u2019t let a bad edge on your steel derail your production\u2014reach out to discuss your requirements today.<\/p>\n

GB Cold Work Tool Steel<\/a> References:<\/p>\n

    \n
  1. Astakhov, V. P. (2006). Metal Cutting: Theories and Applications. CRC Press.<\/li>\n
  2. Budinski, K. G. (2017). Engineering Materials: Properties and Selection. Pearson.<\/li>\n
  3. Modern Plastic Mold Steels: Properties and Applications. Society of Plastics Engineers, 2021.<\/li>\n
  4. Metalworking Microstructure and Machinability. ASM International, 2019.<\/li>\n
  5. Thermal Conductivity of Tool Steels for High-Speed Machining. Journal of Manufacturing Processes, Vol. 45, 2020.<\/li>\n<\/ol>\n
    \n

    Zhejiang Yiding New Materials Co., Ltd.<\/a>
    As one of the most professional plastic mold steel manufacturers and suppliers in China, our products have good reputation in the market. Please feel free to wholesale high quality plastic mold steel made in China here from our factory. Also, custom service is available.
    Address: Xingwang Industrial Park, Huzhen Town, Jinyun County, Zhejiang Province, China
    E-mail: jun.wang@ydmat.com
    WebSite:     https:\/\/www.ydmat.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    If you\u2019ve ever worked in the injection molding industry, you know that a mold\u2019s edge quality … What are the requirements for the edge – holding ability of plastic mold steel in the cutting process?<\/span>Read more<\/a><\/p>\n","protected":false},"author":28,"featured_media":667,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[630],"class_list":["post-667","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-plastic-mold-steel-4f69-d8ae80"],"_links":{"self":[{"href":"http:\/\/www.redbeeshop.com\/blog\/wp-json\/wp\/v2\/posts\/667","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.redbeeshop.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.redbeeshop.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.redbeeshop.com\/blog\/wp-json\/wp\/v2\/users\/28"}],"replies":[{"embeddable":true,"href":"http:\/\/www.redbeeshop.com\/blog\/wp-json\/wp\/v2\/comments?post=667"}],"version-history":[{"count":0,"href":"http:\/\/www.redbeeshop.com\/blog\/wp-json\/wp\/v2\/posts\/667\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.redbeeshop.com\/blog\/wp-json\/wp\/v2\/posts\/667"}],"wp:attachment":[{"href":"http:\/\/www.redbeeshop.com\/blog\/wp-json\/wp\/v2\/media?parent=667"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.redbeeshop.com\/blog\/wp-json\/wp\/v2\/categories?post=667"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.redbeeshop.com\/blog\/wp-json\/wp\/v2\/tags?post=667"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}