{"id":7886,"date":"2025-11-08T09:00:00","date_gmt":"2025-11-08T09:00:00","guid":{"rendered":"https:\/\/uplastech.com\/short-shot-injection-molding\/"},"modified":"2025-11-08T09:00:00","modified_gmt":"2025-11-08T09:00:00","slug":"short-shot-injection-molding","status":"publish","type":"post","link":"https:\/\/uplastech.com\/ru\/short-shot-injection-molding\/","title":{"rendered":"Short Shot in Injection Molding: Ten Causes Ranked by How Often They Are the Answer"},"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\/short-shot-injection-molding.jpg\" alt=\"Share of short shot cases by cause and fill pressure against wall thickness\" width=\"1536\" height=\"909\"><figcaption>Six causes cover almost all short shots, and fill pressure rises with the square of the wall thickness falling.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"what-it-looks-like\">What a short shot tells you<\/h2>\n<p>A short shot is a cavity that did not fill. The part is incomplete, with a rounded or torn edge where the flow stopped, and the location of that edge is the most useful piece of information in the whole diagnosis.<\/p>\n<p>A short shot at the end of flow, far from the gate, is a pressure or a temperature problem. A short shot close to the gate, or in one cavity of a multi-cavity tool, is a restriction or a balance problem. A short shot that moves from shot to shot is a feed or a vent problem.<\/p>\n<p>That single observation eliminates half the list before any setting is touched, and it is the step most often skipped in favour of trying things.<\/p>\n<h2 id=\"pressure-chain\">The pressure chain<\/h2>\n<p>Filling a cavity is a pressure budget. The machine supplies a pressure at the nozzle, and the melt spends it on the runner, the gate, and the flow through the cavity. If the budget runs out before the cavity is full, the part is short.<\/p>\n<ul>\n<li>Machine: is the injection pressure limit reached? If the pressure peak sits on the limit, the machine is the constraint and no setting will help.<\/li>\n<li>Shot size: is the cushion at zero? A shot that is too small runs out of material before it runs out of pressure, and the two look identical on the part.<\/li>\n<li>Runner and gate: a gate that is too small consumes a disproportionate share of the budget, and it does so at the highest shear.<\/li>\n<li>Cavity: a thin wall, a long flow path or a tight tolerance all raise the pressure needed.<\/li>\n<li>Vent: trapped gas resists fill and produces a short shot at the last point to fill, which is where the vent should have been.<\/li>\n<\/ul>\n<p>The pressure needed to fill a wall scales roughly with the inverse square of the thickness. Halving the wall from 1.2 to 0.6 mm takes the fill pressure from 31 MPa to 180, which is beyond most machines and most tools.<\/p>\n<h2 id=\"ranked\">The ten causes, ranked<\/h2>\n<p>The ranking below comes from the pattern of what actually turns out to be the answer, not from a list of possibilities. It is worth reading in order, because the first three account for more than half.<\/p>\n<table>\n<thead>\n<tr>\n<th>Rank<\/th>\n<th>\u041f\u0440\u0438\u0447\u0438\u043d\u0430<\/th>\n<th>How to confirm it in one shot<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>1<\/td>\n<td>Injection pressure or shot size insufficient<\/td>\n<td>Pressure peak on the limit, or cushion at zero<\/td>\n<\/tr>\n<tr>\n<td>2<\/td>\n<td>Melt temperature too low<\/td>\n<td>Short shot moves closer to full as the barrel heats up<\/td>\n<\/tr>\n<tr>\n<td>3<\/td>\n<td>Gate or runner too small<\/td>\n<td>Short shot in the same place every time, pressure peak high<\/td>\n<\/tr>\n<tr>\n<td>4<\/td>\n<td>Trapped air at the last point to fill<\/td>\n<td>Short shot has a dark or burnt edge, and moves with venting<\/td>\n<\/tr>\n<tr>\n<td>5<\/td>\n<td>Vent blocked or missing<\/td>\n<td>Short shot at a corner or a blind boss<\/td>\n<\/tr>\n<tr>\n<td>6<\/td>\n<td>Injection speed too low<\/td>\n<td>Melt freezes before it arrives, short shot far from the gate<\/td>\n<\/tr>\n<tr>\n<td>7<\/td>\n<td>Mould temperature too low<\/td>\n<td>Short shot near the cold insert or the thin core<\/td>\n<\/tr>\n<tr>\n<td>8<\/td>\n<td>Material with too high a viscosity<\/td>\n<td>New lot or new grade, same tool, suddenly short<\/td>\n<\/tr>\n<tr>\n<td>9<\/td>\n<td>Machine capacity<\/td>\n<td>Pressure limit reached at any speed, hydraulic or electric<\/td>\n<\/tr>\n<tr>\n<td>10<\/td>\n<td>Tool defect<\/td>\n<td>One cavity only, or a flash line blocking a runner<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 - The ten causes in the order they turn out to be the answer, with the single observation that confirms each one.<\/p>\n<p>The first three account for about three quarters of cases in a shop that is running an established tool. A tool that is new accounts for a different distribution, where gate size and venting dominate, and a tool that has run for years accounts for a third, where wear and blocked vents dominate.<\/p>\n<h2 id=\"diagnosis\">The diagnosis sequence<\/h2>\n<p>The sequence is designed so that each step eliminates a group of causes rather than testing one hypothesis at a time.<\/p>\n<ol>\n<li>Look at where the short shot is. Far from the gate means pressure, temperature or speed. Near the gate or in one cavity means restriction or balance.<\/li>\n<li>Look at the pressure peak. On the limit means the machine or the tool is the constraint. Well below the limit means the shot ended for another reason.<\/li>\n<li>Look at the cushion. Zero means the shot size is the problem, and no amount of pressure will fix it.<\/li>\n<li>Look at the trend over five shots. Getting better means a thermal problem. Constant means a restriction. Random means feed or venting.<\/li>\n<li>Only then change one setting, and change it in the direction the first four steps indicated.<\/li>\n<\/ol>\n<p>The most common wasted hour in a moulding shop is raising the injection pressure on a machine that is already at its limit, or on a shot that has run out of material. Both look like a pressure problem on the part and neither is.<\/p>\n<h2 id=\"thin-wall\">Thin wall: where short shots are structural<\/h2>\n<p>Below about 1 mm the fill pressure requirement rises so steeply that the process window closes. A 1 mm wall needs about 45 MPa, a 0.8 mm wall 70, and a 0.5 mm wall 180. At that point the machine, the tool steel and the material are all at their limits at once.<\/p>\n<table>\n<thead>\n<tr>\n<th>Wall, mm<\/th>\n<th>Fill pressure, MPa<\/th>\n<th>Practical flow length ratio<\/th>\n<th>Material that will do it<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>0.5<\/td>\n<td>180<\/td>\n<td>120<\/td>\n<td>Thin-wall PP or PS only<\/td>\n<\/tr>\n<tr>\n<td>0.8<\/td>\n<td>70<\/td>\n<td>180<\/td>\n<td>High-flow PP, ABS, PS<\/td>\n<\/tr>\n<tr>\n<td>1.2<\/td>\n<td>31<\/td>\n<td>250<\/td>\n<td>Most commodity resins<\/td>\n<\/tr>\n<tr>\n<td>1.8<\/td>\n<td>14<\/td>\n<td>300<\/td>\n<td>Any moulding grade<\/td>\n<\/tr>\n<tr>\n<td>2.5<\/td>\n<td>7<\/td>\n<td>350<\/td>\n<td>Any moulding grade<\/td>\n<\/tr>\n<tr>\n<td>3.5<\/td>\n<td>4<\/td>\n<td>400<\/td>\n<td>Any moulding grade<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 - Fill pressure and practical flow length ratio against wall thickness. The flow length ratio is the longest flow divided by the wall, and it is the design number that predicts a short shot.<\/p>\n<p>Thin-wall parts need high injection speed, a hot melt, a hot tool and a gate that is large relative to the wall. They also need a material with a low viscosity at high shear, which is why thin-wall grades exist and why substituting a standard grade produces a short shot that no setting will fix.<\/p>\n<p>The flow length to thickness ratio is the design number: a wall of 1 mm with a flow length of 200 mm is a ratio of 200, which is achievable in polypropylene and marginal in polycarbonate. Above about 250, the part needs a different gate position or a thicker wall.<\/p>\n<h2 id=\"fixes-that-fail\">Fixes that make it worse<\/h2>\n<ul>\n<li>Raising the packing pressure. Packing happens after the cavity is full, so it cannot fill a cavity that did not fill. It only adds flash and stress.<\/li>\n<li>Increasing the injection speed without checking the gate. A higher speed through a small gate raises the shear and the melt temperature locally, which can degrade the material at the gate while the cavity is still short.<\/li>\n<li>Raising the melt temperature to the top of the window to compensate for a cold tool. It works, and it produces a part with degraded properties and a longer cycle.<\/li>\n<li>Adding a release agent or a lubricant to the compound. It improves flow and it changes the material, which is not acceptable on a qualified part.<\/li>\n<li>Opening the vent by machining the parting line. It fixes the vent and creates a flash problem, and the flash is harder to remove than the vent was to clean.<\/li>\n<\/ul>\n<div class=\"callout\">A short shot is the tool telling you where the pressure ran out. Fix the place it ran out, not the pressure gauge.<\/div>\n<h2 id=\"prevention\">Prevention<\/h2>\n<ul>\n<li>Simulate the fill before the tool is cut, and look at the pressure at the end of fill as a fraction of the machine capacity. Above 80 percent, the process has no margin.<\/li>\n<li>Size the gate from the wall and the flow length, not from what fits. A gate of 60 to 80 percent of the wall thickness is the starting point for most materials.<\/li>\n<li>Vent at the last point to fill, and vent the runner as well as the cavity.<\/li>\n<li>Record the process window at the first trial: the melt temperature range, the speed range and the pressure range in which the part is good. A tool with a narrow window will produce short shots on a hot day.<\/li>\n<li>Clean the vents on a schedule, not when a part goes short. A blocked vent is a slow failure that looks sudden.<\/li>\n<\/ul>\n<p>The best predictor of a short shot in production is a first trial that needed more than 80 percent of the available pressure to fill. That tool will run, and it will run short on the day the ambient temperature rises or the material lot changes.<\/p>\n<div class=\"faq\">\n<h3>What is the most common cause of a short shot?<\/h3>\n<p>Insufficient injection pressure or shot size, which together account for about a third of cases. Check the cushion and the pressure peak before changing anything else.<\/p>\n<h3>Why does my short shot come and go?<\/h3>\n<p>A moving short shot is usually thermal, because the barrel or the tool is still stabilising, or it is a feed problem such as bridging in the hopper. A constant short shot is a restriction.<\/p>\n<h3>Can packing pressure fix a short shot?<\/h3>\n<p>No. Packing happens after the cavity is full, so it cannot fill a cavity that did not fill. If raising the pack pressure changes the part, the problem was not a short shot.<\/p>\n<h3>Why is my thin-wall part short at 0.8 mm?<\/h3>\n<p>Fill pressure scales with the inverse square of thickness. A 0.8 mm wall needs about 70 MPa where a 1.2 mm wall needs 31, and that is often beyond the machine or the tool.<\/p>\n<h3>Does melt temperature fix a short shot?<\/h3>\n<p>It can, and it is the second most common answer. Raise it within the material window, and check whether the short shot improves over the first few shots, which confirms a thermal cause.<\/p>\n<h3>How do I know if the vent is the problem?<\/h3>\n<p>The short shot sits at the last point to fill and has a dark or burnt edge. Clean the vent and the part fills; that is the confirmation, and it takes one shot.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Chasing a short shot that will not go away?<\/p>\n<p>Send us the part, the gate layout and the process sheet. We will tell you whether it is a tool, a machine or a material problem, and which one to change first.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/ru\/custom-injection-molding\/\">Talk to an injection engineer<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/ru\/injection-molding-defects\/\">Injection Molding Defects: Causes and Fixes<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/injection-mold-venting\/\">Injection Mold Venting<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/hot-runner-vs-cold-runner\/\">Hot Runner vs Cold Runner<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/packing-pressure-hold-time\/\">Packing Pressure and Hold Time<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/clamping-force-tonnage-selection\/\">Clamping Force and Tonnage Selection<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>A third of short shots are pressure or shot size, a quarter are cold melt, and the rest are a short list of restrictions. The diagnosis is a sequence, not a list of things to try.<\/p>","protected":false},"author":1,"featured_media":7885,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"Short Shot in Injection Molding: Causes Ranked","_seopress_titles_desc":"Short shot troubleshooting in injection moulding: the ten causes ranked by frequency, the pressure chain, thin-wall fill pressure, the diagnosis sequence and th","_seopress_robots_index":"","_seopress_robots_follow":"","_seopress_robots_imageindex":"","_seopress_robots_snippet":"","_seopress_robots_primary_cat":"35","_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":[35],"tags":[],"class_list":["post-7886","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-injection-molding"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/posts\/7886","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/comments?post=7886"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/posts\/7886\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/media\/7885"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/media?parent=7886"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/categories?post=7886"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/tags?post=7886"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}