{"id":7538,"date":"2026-10-26T06:30:23","date_gmt":"2026-10-26T06:30:23","guid":{"rendered":"https:\/\/uplastech.com\/vacuum-forming-wall-thickness\/"},"modified":"2026-10-26T07:41:28","modified_gmt":"2026-10-26T07:41:28","slug":"vacuum-forming-wall-thickness","status":"publish","type":"post","link":"https:\/\/uplastech.com\/de\/vacuum-forming-wall-thickness\/","title":{"rendered":"Wall Thickness in Vacuum Forming: Why Corners Thin and How to Control It"},"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 \u81ea\u52a8\u5c55\u5f00\u7684\u95ee\u5019\u5361\uff0c\u53ea\u4fdd\u7559\u5706\u5f62\u6c14\u6ce1\uff0c\u907f\u514d\u906e\u6321\u4fa7\u680f\u8be2\u76d8\u63d0\u4ea4\u6309\u94ae *\/\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\/vf-wall-thickness-section.jpg\" alt=\"Cross section of a vacuum formed enclosure cut through a corner showing the wall thinning from the flat top into the vertical side\" width=\"1536\" height=\"909\"><figcaption>A formed enclosure cut through the corner. The flat top is at nominal thickness, the corner is at roughly 55 %, and the bottom of the wall has recovered some of it. That gradient is not a defect \u2014 it is the process, and it has to be designed around.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"physics\">Why a formed part cannot have uniform walls<\/h2>\n<p>A vacuum formed part starts as a flat sheet of uniform thickness and ends as a three-dimensional shape. The surface area of the shape is larger than the area of the sheet that formed it. The material has to come from somewhere, and the only somewhere available is thinning.<\/p>\n<p>That is not a manufacturing defect that better tooling eliminates. It is conservation of material. The useful question is not \"how do I get uniform walls\" but \"where do I need thickness, and how much can I afford to lose everywhere else\".<\/p>\n<p>Three mechanisms decide where the thinning happens:<\/p>\n<ul>\n<li><strong>Stretch ratio.<\/strong> Where the sheet is stretched furthest from its original position, it thins most. On a deep draw, that is the corner between the flat and the wall, and the top of the wall.<\/li>\n<li><strong>Temperature.<\/strong> Hotter material stretches more easily, so a hot zone thins preferentially. A sheet that is 10 \u00b0C hotter in the centre will be noticeably thinner at the centre.<\/li>\n<li><strong>Contact cooling.<\/strong> Once the sheet touches the mold it stops stretching \u2014 it is pinned by friction and cooled by conduction. Material that touches early stays thick; material that is still free keeps drawing down. This is why the last point to touch is usually the thinnest, and why a mold with well-placed vacuum holes can actually <em>improve<\/em> thickness distribution by pinning the sheet early in the right places.<\/li>\n<\/ul>\n<div class=\"callout\">\n<p><strong>The counter-intuitive part:<\/strong> in vacuum forming, the areas that touch the mold first end up <em>thicker<\/em>, not thinner. Contact freezes the material in place. So a mold that lets the sheet touch down progressively from the centre outward produces a part with a thick centre and thin corners \u2014 the opposite of what most people expect.<\/p>\n<\/div>\n<h2 id=\"ratio\">Draw ratio: the number that predicts everything<\/h2>\n<p>The draw ratio is the relationship between the depth of the part and its width. It is the single best predictor of how much thinning you will get, and it is available at the design stage before any tooling exists.<\/p>\n<div class=\"callout\">\n<p><strong>Draw ratio = Depth \u00f7 Minimum width of the opening<\/strong><\/p>\n<p>A box 200 mm deep with a 200 mm wide opening has a draw ratio of 1.0. The same depth in a 100 mm wide opening has a draw ratio of 2.0 \u2014 and will thin roughly twice as much at the corners.<\/p>\n<\/div>\n<table>\n<thead>\n<tr>\n<th>Draw ratio<\/th>\n<th>Forming difficulty<\/th>\n<th>Typical minimum wall (% of nominal)<\/th>\n<th>What you need<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>&lt; 0.5<\/td>\n<td>Easy<\/td>\n<td>75 \u2013 90 %<\/td>\n<td>Nothing special \u2014 simple vacuum<\/td>\n<\/tr>\n<tr>\n<td>0.5 \u2013 1.0<\/td>\n<td>M\u00e4\u00dfig<\/td>\n<td>60 \u2013 75 %<\/td>\n<td>Good heat profile, generous radii<\/td>\n<\/tr>\n<tr>\n<td>1.0 \u2013 1.5<\/td>\n<td>Difficult<\/td>\n<td>45 \u2013 60 %<\/td>\n<td>Plug assist or pre-stretch<\/td>\n<\/tr>\n<tr>\n<td>1.5 \u2013 2.0<\/td>\n<td>Very difficult<\/td>\n<td>35 \u2013 45 %<\/td>\n<td>Plug assist, profiled heat, pressure forming<\/td>\n<\/tr>\n<tr>\n<td>&gt; 2.0<\/td>\n<td>Marginal to impossible<\/td>\n<td>&lt; 35 %<\/td>\n<td>Redesign, or a different process entirely<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Percentages are minimum wall at the worst point \u2014 normally the corner between the flat and the wall, or the top of a tall narrow wall. Values assume a reasonable corner radius; a sharp corner will be worse than the table suggests.<\/p>\n<p>Note that the draw ratio uses the <em>minimum<\/em> width, not the average. A long, narrow trough \u2014 say 600 mm long, 80 mm wide, 100 mm deep \u2014 has a draw ratio of 1.25 even though it looks shallow, because the material has to come in from the long sides.<\/p>\n<h2 id=\"maths\">The thickness prediction, and how far to trust it<\/h2>\n<p>The simplest useful model treats the formed wall as a truncated cone and assumes the material stretches uniformly. For a simple female cavity of width <em>W<\/em> and depth <em>D<\/em>:<\/p>\n<div class=\"callout\">\n<p><strong>t<sub>wall<\/sub> \u2248 t<sub>sheet<\/sub> \u00d7 (W\u00b2 ) \u00f7 (W + 2D)\u00b2<\/strong><\/p>\n<p>For a 300 mm wide cavity, 150 mm deep, from 3 mm sheet: 3 \u00d7 (300\u00b2) \u00f7 (300 + 300)\u00b2 = 3 \u00d7 90,000 \u00f7 360,000 = <strong>0.75 mm<\/strong>. In practice you would measure about 0.9 \u2013 1.1 mm at the wall base and 0.6 \u2013 0.7 mm at the corner, because the model ignores contact cooling and the flange.<\/p>\n<\/div>\n<p>The model is worth using because it is directionally right and it is available in thirty seconds. It is worth distrusting because:<\/p>\n<ul>\n<li>It assumes the flange does not draw in. In reality the flange is clamped, so more material comes from the walls than the model predicts \u2014 actual walls are thinner than the formula says on a clamped sheet.<\/li>\n<li>It ignores temperature gradients, which can move the answer by 20 %.<\/li>\n<li>It says nothing about corners, which are always the thinnest point and usually the failure point.<\/li>\n<li>It assumes a circular or square section. On a long narrow part the ends behave differently from the sides.<\/li>\n<\/ul>\n<p>Use it to decide whether a design is feasible and to set expectations. Use a formed sample to set the specification.<\/p>\n<h2 id=\"where\">Where the material actually goes<\/h2>\n<p>On a typical female-molded box, thickness varies systematically:<\/p>\n<table>\n<thead>\n<tr>\n<th>Location<\/th>\n<th>Typical % of nominal<\/th>\n<th>Warum<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Flange (clamped)<\/td>\n<td>95 \u2013 100 %<\/td>\n<td>Never stretches; held by the clamp frame<\/td>\n<\/tr>\n<tr>\n<td>Flat bottom \/ top face<\/td>\n<td>80 \u2013 95 %<\/td>\n<td>Touches the mold early and is pinned<\/td>\n<\/tr>\n<tr>\n<td>Lower part of the vertical wall<\/td>\n<td>65 \u2013 80 %<\/td>\n<td>Moderate stretch, some contact cooling<\/td>\n<\/tr>\n<tr>\n<td>Upper part of the vertical wall<\/td>\n<td>55 \u2013 70 %<\/td>\n<td>Still free when the draw completes<\/td>\n<\/tr>\n<tr>\n<td>Corner between wall and flat<\/td>\n<td>45 \u2013 65 %<\/td>\n<td>Maximum stretch, plus the radius concentrates it<\/td>\n<\/tr>\n<tr>\n<td>Inside a sharp rib or boss<\/td>\n<td>30 \u2013 50 %<\/td>\n<td>The sheet has to wrap a small feature<\/td>\n<\/tr>\n<tr>\n<td>Web between two deep features<\/td>\n<td>80 \u2013 110 %<\/td>\n<td>Material is drawn from the web into both features \u2014 sometimes leaving a thick ridge<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">On a male (positive) mold the pattern is different: the top face is the last to form and is thinnest, while the flange and the lower walls are relatively thick.<\/p>\n<p>The last row is worth attention. In a multi-feature part, the material between two deep draws is drawn toward both, and if there is not enough of it the web tears or bridges. If there is too much, the web ends up as a thick ridge that shows on the outside. Web design is one of the more delicate parts of vacuum forming a complex part, and it is why so many multi-pocket packaging tools have generously radiused webs.<\/p>\n<h2 id=\"plug\">Plug assist: the single most effective control<\/h2>\n<p>Plug assist is a mechanical helper \u2014 a male plug, usually of syntactic foam, felt, wood or aluminium, that pushes the hot sheet down into the cavity before the vacuum is applied. Its job is to pre-distribute material: it drags material from the flange area into the cavity so that the walls start the vacuum phase with more material than they would otherwise have.<\/p>\n<p>The effect on thickness distribution is large. On a deep draw, plug assist typically improves the minimum wall from 45 % of nominal to 60 \u2013 70 %.<\/p>\n<figure>\n<img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/10\/vf-plug-assist.jpg\" alt=\"Felt covered plug assist pushing a hot plastic sheet into a female aluminium cavity mold\" width=\"1536\" height=\"909\"><figcaption>A felt-covered plug pushing the hot sheet into the cavity. The plug's job is not to form the part \u2014 it is to drag material from the flange down into the cavity so the walls start the vacuum phase with more to give.<\/figcaption><\/figure>\n<table>\n<thead>\n<tr>\n<th>Plug parameter<\/th>\n<th>Effect<\/th>\n<th>Practical range<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Plug diameter vs cavity<\/td>\n<td>Larger plug pushes more material; too large and it pinches the sheet against the cavity wall<\/td>\n<td>70 \u2013 90 % of cavity width<\/td>\n<\/tr>\n<tr>\n<td>Plug depth of travel<\/td>\n<td>Deeper travel pre-stretches more; too deep and the sheet is trapped before vacuum<\/td>\n<td>50 \u2013 80 % of cavity depth<\/td>\n<\/tr>\n<tr>\n<td>Plug speed<\/td>\n<td>Slow lets the sheet relax and stretch evenly; fast forces it<\/td>\n<td>50 \u2013 200 mm\/s<\/td>\n<\/tr>\n<tr>\n<td>Plug temperature<\/td>\n<td>Hot plug keeps the sheet soft where it contacts; cold plug chills and pins it<\/td>\n<td>60 \u2013 120 \u00b0C for foam plugs<\/td>\n<\/tr>\n<tr>\n<td>Plug material<\/td>\n<td>Soft (felt, foam) grips and drags material; hard (aluminium) slides<\/td>\n<td>Felt\/foam for polyolefins, aluminium for engineering resins<\/td>\n<\/tr>\n<tr>\n<td>Plug shape<\/td>\n<td>Must be smaller than the cavity with rounded edges; a sharp-edged plug cuts the sheet<\/td>\n<td>Edge radius \u2265 5 mm<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">The plug must never be so large that the sheet is pinched between plug and cavity wall \u2014 that produces a hard line and often a tear at the point of pinch.<\/p>\n<h3>Plug assist versus pressure forming<\/h3>\n<p>Pressure forming uses compressed air on the sheet's free side, with the mold vented, to push the sheet onto the mold at up to 3 \u2013 7 bar instead of 1 bar of vacuum. It gives sharper detail, better texture reproduction and tighter radii \u2014 but it does not fundamentally change thickness distribution, because it still stretches the sheet from the same starting area. If thickness distribution is the problem, plug assist is the answer; pressure forming answers a different problem.<\/p>\n<h2 id=\"bubble\">Pre-stretch and bubble forming<\/h2>\n<p>Instead of a plug, some processes pre-stretch the sheet by blowing it into a bubble before it is drawn onto the mold. Blowing a bubble thins the sheet uniformly and, more usefully, converts the sheet into a pre-shaped dome that has already used some of its stretch in a controlled way.<\/p>\n<p>Bubble forming is used mainly in thin-gauge packaging and in some heavy-gauge work where the geometry is complex and a plug would mark the surface. It has two advantages: it is uniform, and it leaves no plug marks. It has one disadvantage: it is hard to control precisely, because the bubble's final shape depends on temperature distribution and on how the sheet's own weight interacts with it.<\/p>\n<h2 id=\"design\">Design moves that buy thickness back<\/h2>\n<p>When the thickness at a corner is unacceptable, there are design changes that help more than process changes. They are worth knowing because they are free \u2014 they cost nothing to change on a drawing and they avoid tooling compromises.<\/p>\n<table>\n<thead>\n<tr>\n<th>Design change<\/th>\n<th>Thickness benefit<\/th>\n<th>Trade-off<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Increase corner radius<\/td>\n<td>Large \u2014 from 45 % to 70 % possible<\/td>\n<td>Changes the look; may affect fit<\/td>\n<\/tr>\n<tr>\n<td>Reduce draw depth<\/td>\n<td>Large \u2014 draw ratio drops directly<\/td>\n<td>Changes the part<\/td>\n<\/tr>\n<tr>\n<td>Add a step or a shoulder to break a deep draw<\/td>\n<td>Moderate \u2014 two shallow draws instead of one deep<\/td>\n<td>Extra feature, extra mold work<\/td>\n<\/tr>\n<tr>\n<td>Split the part and join two shallower halves<\/td>\n<td>Large<\/td>\n<td>Assembly cost, joint line<\/td>\n<\/tr>\n<tr>\n<td>Thicken the sheet<\/td>\n<td>Proportional \u2014 everything scales<\/td>\n<td>Material cost, weight, heat time<\/td>\n<\/tr>\n<tr>\n<td>Add a local doubler or bonded rib<\/td>\n<td>Local stiffness without forming thickness<\/td>\n<td>Secondary operation<\/td>\n<\/tr>\n<tr>\n<td>Change to a male mold<\/td>\n<td>Better distribution on deep draws<\/td>\n<td>Worse outside surface<\/td>\n<\/tr>\n<tr>\n<td>Change to twin-sheet<\/td>\n<td>Two thin skins replace one thick wall<\/td>\n<td>Different process, different tooling<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">In practice, the first two changes solve most thickness problems. Buyers resist them because they change the part \u2014 but a part with a 0.4 mm wall where 1.2 mm was specified is already a changed part.<\/p>\n<div class=\"myth\">\n<p><b>The most expensive mistake in this area:<\/b> specifying a minimum wall thickness on a drawing without specifying where it applies. A drawing that says \"wall 2.0 mm \u00b10.2\" on a part with a 1.5 draw ratio is a drawing the molder cannot meet and the inspector cannot accept. The specification has to say: nominal thickness, minimum thickness, and at which features the minimum applies.<\/p>\n<\/div>\n<h2 id=\"measure\">How to measure thickness properly<\/h2>\n<p>Thickness on a formed part is measured in three different ways, and they do not agree with each other. Knowing which one the specification refers to prevents most arguments.<\/p>\n<table>\n<thead>\n<tr>\n<th>Methode<\/th>\n<th>What it measures<\/th>\n<th>Genauigkeit<\/th>\n<th>Best use<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Micrometer \/ caliper at the edge<\/td>\n<td>Wall thickness where the part can be reached<\/td>\n<td>\u00b10.01 mm<\/td>\n<td>Flange, accessible walls, quick checks<\/td>\n<\/tr>\n<tr>\n<td>Ultrasonic thickness gauge<\/td>\n<td>Wall thickness through the surface, non-destructive<\/td>\n<td>\u00b10.02 mm<\/td>\n<td>Finished parts, in-process checks, curved walls<\/td>\n<\/tr>\n<tr>\n<td>Sectioning and optical measurement<\/td>\n<td>True cross-section, including the corner<\/td>\n<td>\u00b10.01 mm<\/td>\n<td>First article, corner analysis, dispute resolution<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Ultrasonic gauges need the material's sound velocity to be set correctly. On a filled or foamed sheet the factory default will be wrong and the reading will be systematically high or low.<\/p>\n<p>The measurement that matters most is the corner. A caliper cannot reach it and an ultrasonic gauge reads the tangent. The only reliable method is to cut the part through the corner and measure the section \u2014 which is why first-article approval on a deep part should always include a sectioned sample.<\/p>\n<h2 id=\"spec\">Writing a thickness specification that a molder can meet<\/h2>\n<p>A usable thickness specification has four parts:<\/p>\n<ol>\n<li><strong>Nominal sheet thickness<\/strong> and material, with the tolerance on the sheet itself. Sheet gauge varies \u2014 a \"3 mm\" sheet may be 2.85 \u2013 3.15 mm, and that variation propagates straight through to the part.<\/li>\n<li><strong>Nominal formed wall<\/strong> \u2014 the thickness at a defined reference location, usually the flat face.<\/li>\n<li><strong>Minimum wall<\/strong> \u2014 a floor value, with the locations where it applies. This is the number that governs structural adequacy.<\/li>\n<li><strong>Measurement method<\/strong> \u2014 ultrasonic or sectioned, at named points, on a named sample size.<\/li>\n<\/ol>\n<p>An example of a specification that works in practice:<\/p>\n<div class=\"callout\">\n<p>Material: HIPS, 2.5 mm nominal (2.35 \u2013 2.65 mm).<br \/>\nFormed wall at flat top face: 2.2 mm nominal, 2.0 mm minimum.<br \/>\nMinimum wall at any point excluding the trim zone: 1.1 mm (44 % of nominal).<br \/>\nMinimum wall at the four corner radii: 1.3 mm.<br \/>\nVerification: section one part per 500, measure at 8 defined points, ultrasonic gauge on 5 parts per shift.<\/p>\n<\/div>\n<p>That specification is achievable, measurable and arguable \u2014 which is what a specification is for. The common failure is a drawing that says only \"wall thickness 2.5 mm\", which is neither achievable nor measurable.<\/p>\n<h2 id=\"stiffness\">Why thickness matters more than anything else structurally<\/h2>\n<p>Wall thickness is the dominant structural variable in a formed part, and the reason is that stiffness scales with the cube of thickness while weight scales linearly. That relationship makes the corner \u2014 the thinnest point \u2014 the place where a part fails, and it makes small thickness gains disproportionately valuable.<\/p>\n<table>\n<thead>\n<tr>\n<th>Wall thickness<\/th>\n<th>Relative stiffness (bending)<\/th>\n<th>Relative weight<\/th>\n<th>Stiffness per kg<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>0.6 mm<\/td>\n<td>0.22\u00d7<\/td>\n<td>0.30\u00d7<\/td>\n<td>0.73\u00d7<\/td>\n<\/tr>\n<tr>\n<td>1.0 mm<\/td>\n<td>1.00\u00d7<\/td>\n<td>0.50\u00d7<\/td>\n<td>2.00\u00d7<\/td>\n<\/tr>\n<tr>\n<td>1.5 mm<\/td>\n<td>3.38\u00d7<\/td>\n<td>0.75\u00d7<\/td>\n<td>4.50\u00d7<\/td>\n<\/tr>\n<tr>\n<td>2.0 mm<\/td>\n<td>8.00\u00d7<\/td>\n<td>1.00\u00d7<\/td>\n<td>8.00\u00d7<\/td>\n<\/tr>\n<tr>\n<td>3.0 mm<\/td>\n<td>27.0\u00d7<\/td>\n<td>1.50\u00d7<\/td>\n<td>18.0\u00d7<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Relative to a 1.0 mm wall, for the same material and the same unsupported span. The cube relationship is why a 20 % thickness gain is worth 73 % more stiffness \u2014 and why a 20 % thickness loss at a corner is far worse than it looks.<\/p>\n<p>Three practical consequences follow:<\/p>\n<ul>\n<li><strong>A thin corner is not a cosmetic issue.<\/strong> A part designed at 2 mm with a corner at 0.9 mm has 9 % of the intended stiffness at that corner. It will flex, craze and eventually crack there, and no amount of ribbing elsewhere compensates.<\/li>\n<li><strong>Adding thickness is the least efficient way to add stiffness.<\/strong> Doubling the sheet thickness doubles the material cost and the heat time for an eightfold stiffness gain \u2014 but adding a rib or a crown to a flat face achieves more for far less material. Design the geometry before specifying thicker sheet.<\/li>\n<li><strong>Ribs on a formed part are shallow and rounded.<\/strong> A vacuum formed rib cannot be as sharp or as deep as a moulded one \u2014 typically 1.5 \u2013 3 mm deep with a generous root fillet \u2014 and the sheet thins as it wraps the rib. A formed rib 2 mm deep on a 2 mm sheet may be 1.1 mm at its tip. Count it as roughly half the stiffness benefit of the same rib in an injection moulded part.<\/li>\n<\/ul>\n<div class=\"callout\">\n<p><strong>A useful sanity check at the design stage:<\/strong> take the minimum wall from the draw-ratio table, multiply by the cube relationship, and ask whether the part is still stiff enough at that thickness. If the answer is no, the fix is geometry (radii, ribs, a shallower draw, a split part), not a thicker sheet \u2014 because a thicker sheet raises the minimum wall proportionally but never closes the ratio.<\/p>\n<\/div>\n<h2 id=\"case\">A worked example: enclosure with a deep draw<\/h2>\n<p>A practical case to show how the numbers interact. An equipment enclosure, 400 \u00d7 300 mm footprint, 220 mm deep, HIPS, 3 mm sheet, corner radii 15 mm. The client's drawing specified \"wall 3 mm minimum\".<\/p>\n<p><strong>Step 1 \u2014 draw ratio.<\/strong> Minimum width 300 mm, depth 220 mm: draw ratio 0.73. Feasible, but not easy.<\/p>\n<p><strong>Step 2 \u2014 prediction.<\/strong> t = 3 \u00d7 (300\u00b2) \u00f7 (300 + 440)\u00b2 = 3 \u00d7 90,000 \u00f7 547,600 = 0.49 mm at the wall. In practice, with a clamped flange, actual measurement on the first trial was 0.72 mm at the wall base, 0.61 mm mid-wall and 0.44 mm at the corner.<\/p>\n<p><strong>Step 3 \u2014 the gap.<\/strong> The client needed 3 mm everywhere, and the corner was at 0.44 mm \u2014 15 % of nominal. No process change closes that gap.<\/p>\n<p><strong>Step 4 \u2014 options.<\/strong><\/p>\n<table>\n<thead>\n<tr>\n<th>Option<\/th>\n<th>Corner thickness achieved<\/th>\n<th>Cost impact<\/th>\n<th>Verdict<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>As drawn, no changes<\/td>\n<td>0.44 mm<\/td>\n<td>\u2014<\/td>\n<td>Fails<\/td>\n<\/tr>\n<tr>\n<td>Corner radius 15 \u2192 40 mm<\/td>\n<td>0.68 mm<\/td>\n<td>Mold only<\/td>\n<td>Better, still short<\/td>\n<\/tr>\n<tr>\n<td>+ plug assist, felt plug 85 %<\/td>\n<td>1.05 mm<\/td>\n<td>+$1,400 tooling, +3 s cycle<\/td>\n<td>Close<\/td>\n<\/tr>\n<tr>\n<td>+ sheet 3 \u2192 4 mm<\/td>\n<td>1.40 mm<\/td>\n<td>+33 % material<\/td>\n<td>Meets a 1.4 mm spec<\/td>\n<\/tr>\n<tr>\n<td>Depth 220 \u2192 160 mm, add a separate base<\/td>\n<td>1.65 mm at 3 mm sheet<\/td>\n<td>+ assembly, + second tool<\/td>\n<td>Best wall, highest assembly cost<\/td>\n<\/tr>\n<tr>\n<td>Change to twin-sheet<\/td>\n<td>2.4 mm skins, hollow wall<\/td>\n<td>Different tooling, different machine<\/td>\n<td>Stiffer than solid 3 mm<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">The option chosen was radius increase + plug assist + 4 mm sheet, giving a measured minimum of 1.38 mm at the corner and 2.1 mm at the wall. The drawing was rewritten to specify 2.0 mm nominal \/ 1.3 mm minimum rather than 3 mm everywhere.<\/p>\n<p>The lesson is the general one: on any part with a draw ratio above about 0.6, the wall thickness specification has to be a distribution, not a single number. Writing it as a distribution at the design stage is much cheaper than discovering it at first article.<\/p>\n<h2 id=\"faq\">Frequently asked questions<\/h2>\n<div class=\"faq\">\n<h3>Why is the wall thickness of a vacuum formed part uneven?<\/h3>\n<p>Because the part has more surface area than the flat sheet it was formed from, so the material must thin somewhere. The thinning concentrates where the sheet stretches furthest from its original position \u2014 normally the corner between a flat face and a vertical wall, and the top of a tall wall. It is conservation of material, not a defect.<\/p>\n<h3>What is a good draw ratio for vacuum forming?<\/h3>\n<p>Below 0.5 is easy, 0.5 \u2013 1.0 is normal production, 1.0 \u2013 1.5 needs plug assist or pre-stretch, and above 2.0 is usually a redesign. Draw ratio is depth divided by the minimum width of the opening.<\/p>\n<h3>How thin will the corner be?<\/h3>\n<p>On a draw ratio of 1.0, expect 45 \u2013 60 % of nominal thickness at the corner. On a draw ratio of 0.5, expect 65 \u2013 80 %. A sharp corner radius makes it worse \u2014 increasing the radius from 5 % to 15 % of the draw depth can add 20 percentage points of thickness.<\/p>\n<h3>Does plug assist really make that much difference?<\/h3>\n<p>Yes. On a deep draw, plug assist typically raises the minimum wall from about 45 % of nominal to 60 \u2013 70 %. It works by dragging material from the flange into the cavity before vacuum is applied, so the walls start the vacuum phase with more material available.<\/p>\n<h3>Can I get uniform wall thickness by heating more evenly?<\/h3>\n<p>More even heating reduces variation, but it cannot eliminate the fundamental thinning. Even a perfectly isothermal sheet thins according to the draw ratio. What even heating does is make the thinning predictable and consistent, which is what a specification needs.<\/p>\n<h3>Should I specify a minimum wall or a nominal wall?<\/h3>\n<p>Both, plus where each applies. A single \"wall 2.5 mm\" on a deep part is not achievable and not measurable. Specify nominal thickness at a reference location, minimum thickness at named locations, and the measurement method.<\/p>\n<h3>Is pressure forming better for wall thickness?<\/h3>\n<p>Not fundamentally. Pressure forming improves detail, texture reproduction and corner sharpness, but the sheet still starts from the same area and still has to thin. For thickness distribution, plug assist is the effective tool; pressure forming solves a different problem.<\/p>\n<h3>Why does the web between two pockets come out thick?<\/h3>\n<p>Material from the web area is drawn into both adjacent pockets, but if the pockets do not fully consume it, the remainder stays in the web as a ridge. Thick webs are usually a sign of excess material in that zone, and are fixed by adjusting the heat profile or by changing the web width.<\/p>\n<h3>How much does thicker sheet cost compared with a design change?<\/h3>\n<p>Going from 3 mm to 4 mm sheet adds about a third to material cost and a third to heat time. A corner radius change costs nothing in material and only the mold modification. Always try the design change first \u2014 it is almost always cheaper per part.<\/p>\n<h3>How do I check wall thickness on a finished part without cutting it?<\/h3>\n<p>An ultrasonic thickness gauge, with the sound velocity set for the specific material. It reads through the surface and works on curved walls. It cannot read reliably right at a tight corner, so corner verification still requires a sectioned sample at first article.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Send the drawing and we will tell you the wall thickness you will actually get<\/p>\n<p>We run the draw ratio and the thickness prediction before quoting, and if the minimum wall will not meet your requirement we will say so \u2014 with the design change that fixes it. STEP or a dimensioned drawing is enough.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/de\/vakuumverformung\/\">Get a thickness feasibility check<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/de\/vacuum-forming-mold-design\/\">Vacuum Forming Mold Design: Materials, Draft, Vents and Tool Life<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/thermoforming-sheet-heating-temperature-window\/\">Sheet Heating: The Temperature Window That Decides Everything<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/vacuum-forming-defects-troubleshooting\/\">Vacuum Forming Defects: A Troubleshooting Guide<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/custom-vacuum-forming-guide\/\">Vacuum Forming Guide: Tooling Cost &amp; Design Rules<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/thick-gauge-vs-thin-gauge-thermoforming\/\">Thick Gauge vs Thin Gauge Thermoforming<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Why a formed part cannot have uniform walls: draw ratio, thickness prediction, where material goes, plug assist, design moves that buy thickness back, and how to specify it.<\/p>","protected":false},"author":1,"featured_media":7530,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"Wall Thickness in Vacuum Forming: Why Corners Thin","_seopress_titles_desc":"Why formed parts cannot have uniform walls: draw ratio, thickness prediction, plug assist, design changes that buy thickness back, and how to write a specification a molder can meet.","_seopress_robots_index":"1","_seopress_robots_follow":"1","_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":"https:\/\/uplastech.com\/vacuum-forming-wall-thickness\/","_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":"vacuum forming wall thickness","footnotes":""},"categories":[29],"tags":[],"class_list":["post-7538","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\/de\/wp-json\/wp\/v2\/posts\/7538","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/comments?post=7538"}],"version-history":[{"count":1,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/posts\/7538\/revisions"}],"predecessor-version":[{"id":7543,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/posts\/7538\/revisions\/7543"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/media\/7530"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/media?parent=7538"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/categories?post=7538"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/tags?post=7538"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}