{"id":9105,"date":"2024-01-02T01:00:00","date_gmt":"2024-01-02T01:00:00","guid":{"rendered":"https:\/\/uplastech.com\/shrink-allowance-dispute-crystalline-amorphous\/"},"modified":"2026-11-08T08:09:38","modified_gmt":"2026-11-08T08:09:38","slug":"shrink-allowance-dispute-crystalline-amorphous","status":"publish","type":"post","link":"https:\/\/uplastech.com\/ko\/shrink-allowance-dispute-crystalline-amorphous\/","title":{"rendered":"Shrink Allowance Disputes: When One Tool Is Cut for the Wrong Grade"},"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 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ul.cta-need li{color:#e4f0f2;font-size:14.5px;padding-left:18px;position:relative;margin:0}\n.upl-blog ul.cta-need li::before{content:\"\\2713\";position:absolute;left:0;color:#e07a1f;font-weight:700}\n\/* ==UPL-CONVERSION-MODULES-END== *\/\n@media(max-width:640px){.upl-blog h2{font-size:22px}.upl-blog table{font-size:13px}.upl-blog .cta{padding:24px}.upl-blog ul.conv-need,.upl-blog ul.cta-need{grid-template-columns:1fr}.upl-blog .problem,.upl-blog .steps,.upl-blog .conv,.upl-blog .checklist{padding:18px}}\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\/11\/2024-shrink-allowance-dispute-crystalline-amorphous-hero.jpg\" alt=\"Real production view of an injection moulding machine and moulded parts\" width=\"1536\" height=\"909\"><figcaption>Real injection molding production context. Photo: Pexels.<\/figcaption><\/figure>\n<div class=\"problem\">\n<p class=\"mod-h\">The problem<\/p>\n<p><b>Symptom.<\/b> A 120 mm housing that measured to size at first article now reads 1.44 mm undersize, and the moulder and the buyer each hold a valid dimensional report.<\/p>\n<p><b>What it costs.<\/b> A tool cut for a 0.6 % amorphous allowance cannot hold tolerance on a 1.8 % crystalline grade, so a whole batch is disputed and a launch waits on a re-cut or a requalification.<\/p>\n<p class=\"problem-promise\">This guide separates a grade swap from the measurement condition, gives the shrink figures that belong on the drawing, and sets a dimensional acceptance test to agree before tooling.<\/p>\n<\/div>\n<div class=\"toc\"><\/div>\n<h2 id=\"what-a-shrink-allowance-dispute-looks-like\">What a shrink-allowance dispute looks like<\/h2>\n<p>A tool enlarged by a 0.6 % shrink allowance for ABS returns a 120 mm housing to size; mould a 1.8 % crystalline PP in that same cavity and the part comes out about 1.44 mm undersize.<\/p>\n<table>\n<thead>\n<tr>\n<th>Observed result<\/th>\n<th>Most likely cause<\/th>\n<th>First check on the order<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>120 mm feature reads 1.44 mm undersize<\/td>\n<td>Grade shrink above the tool allowance<\/td>\n<td>Compare the quoted grade with the moulding lot<\/td>\n<\/tr>\n<tr>\n<td>Parts grow after 48 h in stores<\/td>\n<td>Conditioning time not defined in the spec<\/td>\n<td>Re-measure retained samples at 1 h and 48 h<\/td>\n<\/tr>\n<tr>\n<td>One cavity out, others in tolerance<\/td>\n<td>Local wall or packing difference<\/td>\n<td>Log the dimension by cavity number<\/td>\n<\/tr>\n<tr>\n<td>Offset appears after a lot change<\/td>\n<td>Resin grade swapped on the order<\/td>\n<td>Check the grade and lot on the delivery note<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 - Reading a dimensional dispute before re-cutting<\/p>\n<div class=\"callout\">Record which of these you are actually seeing before changing any setting. Two faults can look identical on the line and need opposite corrections.<\/div>\n<p><!-- upl-conv-v1 quickcta --><\/p>\n<div class=\"quickcta\">\n<p class=\"mod-h\">Need a fixed price for this moulded part?<\/p>\n<p>Send the 2D drawing, resin grade and annual volume. Our engineers return a DFM review, a material recommendation and a written quotation you can compare line by line.<\/p>\n<p class=\"quickcta-act\"><a class=\"quickcta-btn\" href=\"https:\/\/uplastech.com\/injection-molding\/\">Get a moulding quotation<\/a><a class=\"quickcta-alt\" href=\"mailto:john@uplastech.com\">Email john@uplastech.com<\/a><a class=\"quickcta-alt\" href=\"https:\/\/wa.me\/8617717529949\">WhatsApp<\/a><\/p>\n<\/div>\n<h2 id=\"separate-a-grade-change-from-the-measurement-condition\">Separate a grade change from the measurement condition<\/h2>\n<p>Measure five numbered housings at 1 h and again after 48 h at 23 C \/ 50 % RH. A fixed 1.44 mm offset is the grade allowance; a 0.2 mm drift is the measurement condition, not a new tool fault.<\/p>\n<div class=\"steps\">\n<p class=\"mod-h\">A five-step diagnostic sequence<\/p>\n<ol>\n<li><b>Pull the order, the drawing and the lot label.<\/b><br \/>Confirm which grade was quoted and which was moulded; a 0.6 % ABS allowance with 1.8 % PP is the classic 1.44 mm error.<\/li>\n<li><b>Measure the same five parts at 1 h and 48 h.<\/b><br \/>A fixed 1.44 mm offset is the grade; a 0.2 mm drift is conditioning at 23 C \/ 50 % RH.<\/li>\n<li><b>Check the wall and the allowance on the drawing.<\/b><br \/>Confirm the 2.5-3.0 mm wall at the measured feature and that the allowance is named with a grade, not a bare percentage.<\/li>\n<li><b>Log the dimension by cavity and by lot.<\/b><br \/>A single-cavity outlier is filling; a whole-batch step follows the resin delivery note.<\/li>\n<li><b>Re-cut or re-qualify, then re-measure after 48 h.<\/b><br \/>Tuning moves shrink by 0.1-0.2 points, so a 1.2 point mismatch needs steel or the quoted grade.<\/li>\n<\/ol>\n<\/div>\n<p>The chart below is a typical result from that measurement step. Use it to separate a design limit from a setting that can still be recovered.<\/p>\n<figure>\n<img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/11\/shrink-allowance-dispute-crystalline-amorphous-chart3.jpg\" alt=\"Shrink Allowance Disputes: When One Tool Is Cut for the Wrong Grade: calculated response trend and an illustrative root-cause split\" width=\"1536\" height=\"909\"><figcaption>Figure 1 \u2014 Calculated response trend and an illustrative root-cause split. Values are engineering guidance for diagnosis, not a measured survey; confirm them on your own line before changing a drawing or a specification.<\/figcaption><\/figure>\n<h2 id=\"shrink-figures-that-belong-on-the-drawing\">Shrink figures that belong on the drawing<\/h2>\n<p>Put the grade, the shrink allowance, the nominal wall and the tolerance on the drawing. A 1.2 percentage-point mismatch moves a 120 mm feature by 1.44 mm, almost six times a +\/- 0.25 mm limit.<\/p>\n<table class=\"spec\">\n<thead>\n<tr>\n<th>Parameter<\/th>\n<th>Typical target<\/th>\n<th>What goes wrong outside it<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Shrink allowance on the tool drawing<\/td>\n<td>Named with grade, e.g. 0.6 % ABS or 1.8 % PP<\/td>\n<td>A bare percentage without a grade is untestable<\/td>\n<\/tr>\n<tr>\n<td>Conditioning before inspection<\/td>\n<td>48 h at 23 C \/ 50 % RH<\/td>\n<td>Crystalline parts keep moving for up to 48 h<\/td>\n<\/tr>\n<tr>\n<td>Nominal wall at the measured feature<\/td>\n<td>2.5-3.0 mm, stated on the drawing<\/td>\n<td>Shrink rises with wall thickness<\/td>\n<\/tr>\n<tr>\n<td>Tolerance on the 120 mm feature<\/td>\n<td>+\/- 0.25 mm<\/td>\n<td>A 1.2 point mismatch already gives 1.44 mm error<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 - Shrink parameters for the part drawing<\/p>\n<h2 id=\"grade-and-wall-choices-that-move-the-dimension\">Grade and wall choices that move the dimension<\/h2>\n<p>Amorphous ABS shrinks 0.4-0.7 % and PC 0.5-0.7 %; crystalline PP shrinks 1.5-2.2 % and POM about 2.0 %. Packing and mould temperature shift shrink by only 0.1-0.2 points.<\/p>\n<table>\n<thead>\n<tr>\n<th>Decision<\/th>\n<th>Effect on the dimension<\/th>\n<th>Trade-off<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Re-cut cavity for the production grade<\/td>\n<td>Removes the full 1.44 mm offset<\/td>\n<td>Tool change, dimensional requalification<\/td>\n<\/tr>\n<tr>\n<td>Revert to the quoted amorphous grade<\/td>\n<td>Restores the 0.6 % allowance<\/td>\n<td>May lose the stiffness the buyer wanted<\/td>\n<\/tr>\n<tr>\n<td>Tune packing and mould temperature<\/td>\n<td>Shifts shrink by only 0.1-0.2 points<\/td>\n<td>Cannot absorb a 1.2 point mismatch<\/td>\n<\/tr>\n<tr>\n<td>Sort and ship under concession<\/td>\n<td>Clears a borderline batch<\/td>\n<td>Leaves the next run out of tolerance<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 3 - Decisions ranked by what they actually fix<\/p>\n<div class=\"myth\"><b>Myth:<\/b> \"A process adjustment will fix it.\" Once a design limit is reached, more tuning only adds cost and variation. Confirm the limit with a measurement, then change the drawing or the specification.<\/div>\n<h2 id=\"write-dimensional-acceptance-into-the-order\">Write dimensional acceptance into the order<\/h2>\n<p>Agree acceptance before first article: name the grade and lot, the allowance with wall thickness, a 48 h conditioning at 23 C \/ 50 % RH, and a +\/- 0.25 mm tolerance on 120 mm.<\/p>\n<div class=\"conv\">\n<p class=\"mod-h\">Not sure whether the fault is in the tool or the process?<\/p>\n<p>Send us the drawing, the process window and a few sample parts. We will tell you which change fixes the fault before you commit to a tool modification.<\/p>\n<p class=\"conv-lbl\">What to send us<\/p>\n<ul class=\"conv-need\">\n<li>Part drawing with the affected dimension<\/li>\n<li>Current process settings<\/li>\n<li>Sample parts from a good and a bad batch<\/li>\n<li>Annual volume<\/li>\n<\/ul>\n<p><a class=\"conv-btn\" href=\"\/injection-molding\/\">Send the part for review<\/a>\n<\/div>\n<h2 id=\"recovery-actions-ranked-by-requalification-cost\">Recovery actions ranked by requalification cost<\/h2>\n<p>When a batch is already out, sorting is the short-term option. Tuning cannot absorb a 1.2 point mismatch, so re-cut the cavity for the production grade or revert to the quoted lot.<\/p>\n<div class=\"callout\">Validate one change at a time and keep the measurement record. A supplier discussion backed by data is resolved in days, not weeks.<\/div>\n<div class=\"checklist\">\n<p class=\"mod-h\">Before you release this injection moulding job<\/p>\n<ul>\n<li>The resin grade and an agreed lot are named on the part drawing and the purchase order<\/li>\n<li>The tool shrink allowance is stated with the grade and the wall thickness, not as a bare percentage<\/li>\n<li>A conditioning time of 48 h at 23 C \/ 50 % RH is written into the inspection method<\/li>\n<li>A +\/- 0.25 mm tolerance and the measurement temperature are defined on the 120 mm feature<\/li>\n<li>First-article dimensions are reported per cavity at 1 h and again after 48 h<\/li>\n<\/ul>\n<p class=\"cl-note\">Attach this list to the RFQ. Most moulding faults are decided at the drawing stage.<\/p>\n<\/div>\n<div class=\"faq\">\n<h3>Why is a part undersize when the tool was qualified?<\/h3>\n<p>The tool was cut to a shrink allowance for one grade. Mould a 1.8 % crystalline PP in a cavity enlarged for 0.6 % ABS and a 120 mm feature comes out about 1.44 mm short.<\/p>\n<h3>Can process settings absorb a wrong shrink allowance?<\/h3>\n<p>No. Packing and mould temperature shift shrink by only 0.1-0.2 percentage points, so a 1.2 point mismatch needs a re-cut cavity or the quoted grade.<\/p>\n<h3>Why do parts keep moving for two days?<\/h3>\n<p>Crystalline grades continue to crystallise after ejection. Measure after a defined 48 h at 23 C \/ 50 % RH, or the moulder and the buyer hold two valid but different numbers.<\/p>\n<h3>Which grades need the largest allowance?<\/h3>\n<p>Semi-crystalline PP at 1.5-2.2 % and POM near 2.0 % need far more than amorphous ABS at 0.4-0.7 % or PC at 0.5-0.7 %.<\/p>\n<h3>Who owns the dispute?<\/h3>\n<p>Put it in the order. Name the grade and lot, the shrink allowance with wall thickness, the conditioning time and the tolerance so a rejected batch is settled by the drawing.<\/p>\n<h3>Should the tool be re-cut or the grade reverted?<\/h3>\n<p>Compare cost and performance. Reverting to the quoted ABS restores size but loses PP stiffness; re-cutting keeps the grade but needs full dimensional requalification.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Get a mouldable part and a fixed quotation<\/p>\n<p>Send us the part file and the failure history. Our engineers will return a DFM review, a material recommendation and a fixed quotation with a defined first-article acceptance test.<\/p>\n<p class=\"cta-lbl\">To get an accurate quote, send:<\/p>\n<ul class=\"cta-need\">\n<li>3D file or 2D part drawing<\/li>\n<li>Resin grade and any regrind limit<\/li>\n<li>Annual volume and target unit price<\/li>\n<li>The failed sample or defect photos<\/li>\n<\/ul>\n<p><a class=\"btn\" href=\"\/injection-molding\/\">Request a DFM review and quote<\/a><br \/>\n<!-- upl-conv-v1 contact --><\/p>\n<div class=\"contactbar\">\n<p class=\"contactbar-h\">Prefer to talk it through first?<\/p>\n<p>Email <a href=\"mailto:john@uplastech.com\">john@uplastech.com<\/a> or message us on <a href=\"https:\/\/wa.me\/8617717529949\">WhatsApp +86 177 1752 9949<\/a>. Send a drawing, a sample or a specification and an engineer will reply.<\/p>\n<\/div>\n<p><!-- upl-conv-v1 trust --><\/p>\n<div class=\"trust\">\n<p class=\"trust-h\">Why buyers work with Uplastech<\/p>\n<p>ISO 9001, ISO 14001 and ISO 45001 certified. Founded in 2016, with injection moulding lines in Shanghai and an extrusion plant in Jiangsu. Moulding machines from 90T to 1100T and a maximum shot weight of 5100 g. Samples and a written quotation are available on request.<\/p>\n<\/div>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/injection-molding-tolerances\/\">Injection molding tolerances: what to specify<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/snap-fit-design\/\">Snap-fit design: strain, deflection and retention<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/plastic-part-assembly-design\/\">Plastic part assembly design<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/dfm-review-checklist\/\">DFM review checklist<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/injection-molding-material-selection\/\">Injection molding material selection<\/a><\/li>\n<\/ul>\n<p><!-- upl-conv-v1 service --><\/p>\n<p class=\"rel-svc\">Ready to specify? See our <a href=\"https:\/\/uplastech.com\/injection-molding\/\">injection moulding services<\/a> or <a href=\"mailto:john@uplastech.com\">request a written quotation<\/a>.<\/p>\n<\/div>\n<\/div>\n<p><script type=\"application\/ld+json\">{\"@context\": \"https:\/\/schema.org\", \"@type\": \"FAQPage\", \"mainEntity\": [{\"@type\": \"Question\", \"name\": \"Why is a part undersize when the tool was qualified?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"The tool was cut to a shrink allowance for one grade. Mould a 1.8 % crystalline PP in a cavity enlarged for 0.6 % ABS and a 120 mm feature comes out about 1.44 mm short.\"}}, {\"@type\": \"Question\", \"name\": \"Can process settings absorb a wrong shrink allowance?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"No. Packing and mould temperature shift shrink by only 0.1-0.2 percentage points, so a 1.2 point mismatch needs a re-cut cavity or the quoted grade.\"}}, {\"@type\": \"Question\", \"name\": \"Why do parts keep moving for two days?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Crystalline grades continue to crystallise after ejection. Measure after a defined 48 h at 23 C \/ 50 % RH, or the moulder and the buyer hold two valid but different numbers.\"}}, {\"@type\": \"Question\", \"name\": \"Which grades need the largest allowance?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Semi-crystalline PP at 1.5-2.2 % and POM near 2.0 % need far more than amorphous ABS at 0.4-0.7 % or PC at 0.5-0.7 %.\"}}, {\"@type\": \"Question\", \"name\": \"Who owns the dispute?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Put it in the order. Name the grade and lot, the shrink allowance with wall thickness, the conditioning time and the tolerance so a rejected batch is settled by the drawing.\"}}, {\"@type\": \"Question\", \"name\": \"Should the tool be re-cut or the grade reverted?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Compare cost and performance. Reverting to the quoted ABS restores size but loses PP stiffness; re-cutting keeps the grade but needs full dimensional requalification.\"}}]}<\/script><\/p>\n","protected":false},"excerpt":{"rendered":"<p>This guide separates a grade swap from the measurement condition, gives the shrink figures that belong on the drawing, and sets a dimensional acceptance test to agree before tooling.<\/p>","protected":false},"author":1,"featured_media":9103,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[35],"tags":[],"class_list":["post-9105","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\/ko\/wp-json\/wp\/v2\/posts\/9105","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/ko\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/ko\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ko\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ko\/wp-json\/wp\/v2\/comments?post=9105"}],"version-history":[{"count":1,"href":"https:\/\/uplastech.com\/ko\/wp-json\/wp\/v2\/posts\/9105\/revisions"}],"predecessor-version":[{"id":9221,"href":"https:\/\/uplastech.com\/ko\/wp-json\/wp\/v2\/posts\/9105\/revisions\/9221"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ko\/wp-json\/wp\/v2\/media\/9103"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/ko\/wp-json\/wp\/v2\/media?parent=9105"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/ko\/wp-json\/wp\/v2\/categories?post=9105"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/ko\/wp-json\/wp\/v2\/tags?post=9105"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}