{"id":7986,"date":"2025-12-28T09:00:00","date_gmt":"2025-12-28T09:00:00","guid":{"rendered":"https:\/\/uplastech.com\/thermoforming-demolding\/"},"modified":"2025-12-28T09:00:00","modified_gmt":"2025-12-28T09:00:00","slug":"thermoforming-demolding","status":"publish","type":"post","link":"https:\/\/uplastech.com\/it\/thermoforming-demolding\/","title":{"rendered":"Demoulding: Draft, Ejection and the Part That Sticks at Temperature"},"content":{"rendered":"<style>\n.upl-blog{font-size:17px;line-height:1.78;color:#1f2937}\n.upl-blog p{margin:0 0 18px}\n.upl-blog h2{font-size:26px;line-height:1.3;color:#0b2b33;margin:46px 0 14px;font-weight:700;letter-spacing:-.015em}\n.upl-blog h3{font-size:19.5px;color:#0d3b47;margin:28px 0 10px;font-weight:700}\n.upl-blog ul,.upl-blog ol{margin:0 0 20px;padding-left:22px}\n.upl-blog li{margin:0 0 9px}\n.upl-blog figure{margin:0 0 34px}\n.upl-blog figure img{width:100%;height:auto;display:block;border-radius:10px}\n.upl-blog figcaption{font-size:13px;color:#6b7280;margin-top:10px;line-height:1.5}\n.upl-blog .toc{background:none;border:0;border-radius:0;padding:0;margin:0 0 34px}\n.upl-blog .toc .lwptoc{margin:0}\n.upl-blog .toc h4{margin:0 0 10px;font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#0d5563}\n.upl-blog .toc ol{margin:0;padding-left:18px;font-size:14.5px}\n.upl-blog .toc li{margin-bottom:6px}\n.upl-blog table{width:100%;border-collapse:collapse;font-size:14.5px;margin:0 0 10px}\n.upl-blog th{background:#0d3b47;color:#fff;text-align:left;padding:11px 13px;font-weight:600;font-size:13.5px;border:0}\n.upl-blog td{padding:11px 13px;border:0;border-bottom:1px solid #e8ebed;vertical-align:top}\n.upl-blog tbody tr:nth-child(even){background:#fafbfc}\n.upl-blog .tablecap{font-size:12.5px;color:#6b7280;margin:0 0 30px}\n.upl-blog .myth{background:#fff8ef;border:1px solid #f6ddbd;border-radius:8px;padding:16px 20px;margin:0 0 26px;font-size:15.5px}\n.upl-blog .myth b{color:#a85c10}\n.upl-blog .callout{background:#f2f8f9;border-radius:8px;padding:18px 22px;margin:0 0 26px;font-size:15.5px;border-left:3px solid #14707f}\n.upl-blog .faq h3{border-top:1px solid #eceff1;padding-top:22px;margin-top:0;font-size:18px}\n.upl-blog .faq h3:first-of-type{border-top:0;padding-top:0}\n.upl-blog .cta{background:linear-gradient(135deg,#0b2b33,#0d5563);color:#fff;border-radius:12px;padding:34px;margin:48px 0 30px}\n.upl-blog .cta h2,.upl-blog .cta .cta-h{color:#fff;margin:0 0 10px;font-size:24px;font-weight:700;line-height:1.3}\n.upl-blog .cta p{color:#c9dee3;margin:0 0 20px;font-size:16px}\n.upl-blog .btn{display:inline-block;background:#e07a1f;color:#fff;text-decoration:none;font-weight:700;padding:13px 26px;border-radius:8px;font-size:15.5px}\n.upl-blog .rel{border-top:1px solid #e8ebed;margin-top:40px;padding-top:26px}\n.upl-blog .rel h4{font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#6b7280;margin:0 0 14px}\n.upl-blog .rel ul{list-style:none;padding:0;margin:0}\n.upl-blog .rel li{padding:11px 0;border-bottom:1px dashed #e8ebed}\n.upl-blog .rel a{text-decoration:none;font-weight:600;font-size:15.5px}\n@media(max-width:640px){.upl-blog h2{font-size:22px}.upl-blog table{font-size:13px}.upl-blog .cta{padding:24px}}\n\/* \u5355\u7bc7\u9875\u9690\u85cf WhatsApp \u95ee\u5019\u5361\uff0c\u53ea\u4fdd\u7559\u5706\u5f62\u6c14\u6ce1\uff0c\u907f\u514d\u906e\u6321\u4fa7\u680f\u8be2\u76d8\u63d0\u4ea4\u6309\u94ae\u3002\n   \u6ce8\u610f\uff1aClick to Chat \u7684\u70b9\u51fb\u903b\u8f91\u662f\u300c\u95ee\u5019\u5361\u5143\u7d20\u5b58\u5728\u5c31\u4e0d\u8df3\u8f6c\u300d\uff0c\u53ea\u9760 CSS \u9690\u85cf\u4f1a\u8ba9\u6c14\u6ce1\u53d8\u6210\u6b7b\u94fe\u63a5\u3002\n   Code Snippets #9\u300cUPL single post: WhatsApp bubble jumps straight to chat\u300d\u8d1f\u8d23\u628a\u8be5\u8282\u70b9\u4ece DOM \u79fb\u9664\uff0c\n   \u4e0b\u9762\u8fd9\u6761 CSS \u53ea\u662f\u79fb\u9664\u524d\u7684\u89c6\u89c9\u515c\u5e95\u3002\u5220 #9 \u524d\u5fc5\u987b\u5148\u5220\u8fd9\u6761\u89c4\u5219\u3002 *\/\nbody.single-post .ht_ctc_chat_greetings_box{display:none !important}\n<\/style>\n<div class=\"upl-blog\">\n<figure>\n<img fetchpriority=\"high\" decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/10\/thermoforming-demolding.jpg\" alt=\"Release force against draft angle, and release force against air assist pressure\" width=\"1536\" height=\"909\"><figcaption>Release force drops from 120 N at zero draft to 40 N at two degrees, and air assist takes the same part down to 25 N at 400 kPa.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"force\">Why a formed part sticks<\/h2>\n<p>A thermoformed part sticks to its mould for three reasons: shrink, friction and vacuum. Shrink is the dominant one. As the part cools it contracts onto a male mould or away from a female one, and on a male mould the contraction wraps the part around the tool.<\/p>\n<p>Friction is the second. The part is pressed against the tool by the shrink, and the coefficient of friction between hot polymer and an aluminium mould is high, so the force needed to slide it off is the normal force multiplied by that coefficient. A textured tool multiplies it again.<\/p>\n<p>Vacuum is the third and the most easily overlooked. If the part is still under vacuum when ejection starts, the atmosphere is holding it on. Releasing the vacuum before ejection is the first thing to check when a part that used to come off easily suddenly will not.<\/p>\n<h2 id=\"draft\">Draft is the whole force<\/h2>\n<p>Draft angle is the taper on the mould walls, and it is the single largest lever on release force. With no draft, a 1.5 mm ABS part over a 40 mm core needs about 120 N to release. At one degree it needs 70, at two degrees 40, at three 25 and at four 18.<\/p>\n<p>The reason is that draft converts a friction problem into a wedging problem. A tapered wall means the part only has to move a small distance before it is free of contact, and the normal force falls as it moves. A parallel wall keeps full contact for the whole length of the draw.<\/p>\n<p>The practical minimum is one degree per side for a smooth tool and two degrees for a textured one, because texture adds depth that has to be cleared. Below one degree, the part may release but it will scuff, and the scuff shows as a dull streak on the wall.<\/p>\n<table>\n<thead>\n<tr>\n<th>Draft<\/th>\n<th>Release force<\/th>\n<th>Il rischio<\/th>\n<th>Comment<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>0 degrees<\/td>\n<td>120 N<\/td>\n<td>Scuffing, sticking<\/td>\n<td>Only for a shrink-free female tool<\/td>\n<\/tr>\n<tr>\n<td>1 degree<\/td>\n<td>70 N<\/td>\n<td>Occasional sticking<\/td>\n<td>Minimum for a smooth male tool<\/td>\n<\/tr>\n<tr>\n<td>2 degrees<\/td>\n<td>40 N<\/td>\n<td>Basso<\/td>\n<td>The usual specification<\/td>\n<\/tr>\n<tr>\n<td>3 degrees<\/td>\n<td>25 N<\/td>\n<td>Very low<\/td>\n<td>Textured tools<\/td>\n<\/tr>\n<tr>\n<td>4 degrees<\/td>\n<td>18 N<\/td>\n<td>Negligible<\/td>\n<td>Deep draws and heavy gauge<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 Release force against draft, on a 1.5 mm ABS part over a 40 mm core.<\/p>\n<h2 id=\"air\">Air assist is cheaper than a new tool<\/h2>\n<p>Air assist blows compressed air between the part and the tool as ejection starts. The air breaks the contact, equalises the pressure and lets the part come off with a fraction of the force. On the same part, 100 kPa takes the release force from 120 N to 85, 200 kPa to 55, 300 to 35 and 400 to 25.<\/p>\n<p>It works because the failure mode is adhesive rather than structural. The part is not held on by a mechanical interlock, it is held by contact over a large area, and a thin film of air removes that contact. Once the film is established the part slides off.<\/p>\n<p>The hardware is a ring of small holes or a porous insert at the base of the mould, fed from a solenoid through a regulator. It is a few hundred euros on a small tool and it can rescue a tool that was cut without enough draft. That is why it is the first thing to try before re-cutting.<\/p>\n<div class=\"callout\">Sequence matters: release the vacuum, then apply air, then eject. Air applied while vacuum is still on does nothing, and ejecting before either is how parts get torn.<\/div>\n<h2 id=\"temperature\">The part that sticks at temperature<\/h2>\n<p>A part that releases cleanly at 60 C can stick hard at 90 C, and the reason is not the draft. At the higher temperature the polymer is softer, the shrink has not completed, and the surface is tacky enough to wet the tool. The contact area is larger and the friction coefficient is higher.<\/p>\n<p>This is why demoulding temperature and release force are linked, and why a cycle-time reduction often produces a sticking problem. The part comes off sooner, at a higher temperature, and the ejection system that was sized for a cool part is now marginal.<\/p>\n<p>The fix is either more cooling, more draft, more air, or a release agent. Release agents are the least attractive because they have to be reapplied, they contaminate the part and they build up on the tool. On a part that will be bonded or printed, a release agent is often a defect source rather than a solution.<\/p>\n<h2 id=\"ejection\">Ejection hardware<\/h2>\n<p>Thermoformed parts are ejected by pins, by a stripper plate or by air alone. Pins are simple and put the force on a small area, which is fine on a stiff part and bad on a thin one. A stripper plate pushes on the rim, which is where the part is strongest, and it is the better choice for a thin-wall part.<\/p>\n<p>Air alone works for shallow parts with good draft, where the part will lift off once the contact is broken. It is the gentlest method and the least controllable, because the part can fly off and land anywhere.<\/p>\n<table>\n<thead>\n<tr>\n<th>Ejection method<\/th>\n<th>Loads<\/th>\n<th>Il migliore per<\/th>\n<th>Il rischio<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Pins<\/td>\n<td>A small area<\/td>\n<td>Stiff parts, thick walls<\/td>\n<td>Pin marks on a soft part<\/td>\n<\/tr>\n<tr>\n<td>Stripper plate<\/td>\n<td>The rim<\/td>\n<td>Thin walls, cosmetic faces<\/td>\n<td>Needs a flat rim to push on<\/td>\n<\/tr>\n<tr>\n<td>Air only<\/td>\n<td>The whole face<\/td>\n<td>Shallow parts with good draft<\/td>\n<td>Part leaves uncontrolled<\/td>\n<\/tr>\n<tr>\n<td>Air plus pins<\/td>\n<td>Face then rim<\/td>\n<td>Deep draws, sticky parts<\/td>\n<td>Needs a sequence, not a switch<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 Ejection methods, what each one loads, and what it risks.<\/p>\n<p>Undercuts are the fourth case and they need a moving tool. A snap feature on a thermoformed part has to be formed by a slide or a collapsible insert, and the part has to deflect over it on ejection. The deflection is limited by the material's strain at demould temperature, which is much lower than at forming temperature, and that is why undercuts on formed parts are usually small.<\/p>\n<h2 id=\"specify\">What to specify<\/h2>\n<p>Demoulding is a tool feature, so it belongs on the tool drawing rather than on the part drawing.<\/p>\n<ul>\n<li>Draft angle per side, separately for smooth and textured surfaces.<\/li>\n<li>Air assist: hole pattern, pressure and the solenoid sequence.<\/li>\n<li>Ejection method, and the contact area it loads.<\/li>\n<li>Demould temperature, and whether a cooling jig is used.<\/li>\n<li>Undercut allowance, if the part has a snap feature.<\/li>\n<li>Release agent, only if nothing else works, and then with a cleaning step.<\/li>\n<\/ul>\n<p>Draft and demould temperature are the two that decide whether the part comes off at all. Both are cheap at the tool design stage and expensive afterwards, which is why a formed part should be reviewed for draft before the tool is cut rather than after the first trial.<\/p>\n<div class=\"faq\">\n<h3>How much draft does a thermoformed part need?<\/h3>\n<p>One degree per side minimum for a smooth tool and two degrees for a textured one. Release force falls from 120 N at zero draft to 40 N at two degrees.<\/p>\n<h3>Why does my part stick even with draft?<\/h3>\n<p>Usually because it is being demoulded too hot, or because the vacuum is still on. Release the vacuum first, then apply air, then eject.<\/p>\n<h3>Does air assist work on any tool?<\/h3>\n<p>It works on most, provided there is somewhere to put the holes. A ring of small holes or a porous insert at the base of the mould is enough, and it can rescue a tool cut without enough draft.<\/p>\n<h3>What is the difference between pin ejection and a stripper plate?<\/h3>\n<p>Pins load a small area and suit stiff parts; a stripper plate pushes on the rim and suits thin walls. On a 1 mm part, a stripper plate is usually the only option.<\/p>\n<h3>Can thermoformed parts have undercuts?<\/h3>\n<p>Yes, small ones, formed by a slide or a collapsible insert. The allowable deflection is set by the material's strain at demould temperature, which is much lower than at forming temperature.<\/p>\n<h3>Should I use a release agent?<\/h3>\n<p>Only as a last resort. It has to be reapplied, it contaminates the part and it builds up on the tool. More draft, more cooling or air assist is almost always better.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Part sticking or scuffing on ejection?<\/p>\n<p>Send the mould drawing and the demould temperature. We will tell you whether draft, air assist or cooling is the answer, and what each one costs.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/it\/custom-vacuum-forming\/\">Ask about thermoforming tooling<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/it\/thermoforming-cooling-cycle\/\">Cooling in Thermoforming: The Half of the Cycle That Sets the Shape<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/it\/thermoforming-tolerances\/\">Thermoforming Tolerances: What a Formed Part Can Hold<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/it\/thermoforming-match-mold\/\">Match-Mould Forming: Two Halves for Parts That Need Both Faces<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/it\/thermoforming-drape-forming\/\">Drape Forming: The Oldest Method and Where It Still Wins<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/it\/custom-vacuum-forming\/\">Custom Vacuum Forming: Tooling, Materials and Tolerances<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Release force falls from 120 N with no draft to 70 N at one degree and 40 at two. Air assist then takes the same part from 120 N to 25, which is why it is cheaper than re-cutting a tool.<\/p>","protected":false},"author":1,"featured_media":7985,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"Thermoforming Demoulding: Draft and Ejection","_seopress_titles_desc":"Demoulding thermoformed parts: release force against draft angle, air assist against release force, stripper plates, undercuts, sticking at temperature and what","_seopress_robots_index":"","_seopress_robots_follow":"","_seopress_robots_imageindex":"","_seopress_robots_snippet":"","_seopress_robots_primary_cat":"29","_seopress_robots_breadcrumbs":"","_seopress_robots_freeze_modified_date":"","_seopress_robots_custom_modified_date":"","_seopress_robots_canonical":"","_seopress_social_fb_title":"","_seopress_social_fb_desc":"","_seopress_social_fb_img":"","_seopress_social_fb_img_attachment_id":0,"_seopress_social_fb_img_width":0,"_seopress_social_fb_img_height":0,"_seopress_social_twitter_title":"","_seopress_social_twitter_desc":"","_seopress_social_twitter_img":"","_seopress_social_twitter_img_attachment_id":0,"_seopress_social_twitter_img_width":0,"_seopress_social_twitter_img_height":0,"_seopress_redirections_value":"","_seopress_redirections_enabled":"","_seopress_redirections_enabled_regex":"","_seopress_redirections_logged_status":"","_seopress_redirections_param":"","_seopress_redirections_type":0,"_seopress_analysis_target_kw":"","footnotes":""},"categories":[29],"tags":[],"class_list":["post-7986","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-vacuum-forming"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/posts\/7986","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/comments?post=7986"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/posts\/7986\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/media\/7985"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/media?parent=7986"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/categories?post=7986"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/tags?post=7986"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}