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      <title>Flat pattern tips and techniques</title>
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      <div class="title_topic2" id="xps10_pagetitle">Flat pattern tips and techniques</div>
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               <p class="para_td"><a class="links" href="javascript:void(0)" onclick="top.openFile('sheetmetaldes/flpat_ov.html');return(false);">Flat Pattern Overview</a></p>
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               <p class="para_td"><a class="links" href="javascript:void(0)" onclick="top.openFile('sheetmetaldes/flpat_terms.html');return(false);">How To</a></p>
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               <p class="para_td"><a class="links" href="javascript:void(0)" onclick="top.openFile('sheetmetaldes/flpat_create.html');return(false);">Options</a></p>
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      </table><br><div class="title_division">Non&ndash;sheet metal features</div>
      <p class="para_division"><b class="uiTerm">Flat Pattern</b> works best when you model the part with Sheet Metal features. It will usually handle straight brake (for example, straight bend lines) parts correctly, regardless of the modeling technique. The best way to handle non&ndash;developable surfaces when modeled is with Sheet Metal features (for example, general flanges). When possible, use Sheet Metal features to model your parts.
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      <div class="title_division">Unform features</div>
      <p class="para_division">Always unform any general flanges in your model prior to creating a flat pattern. You can select the unformed general flange faces as area preserving faces and will yield better results. The system will automatically unform the General Flanges whenever an automatic update occurs.</p>
      <p class="para_division">For best results, you should produce the flat pattern using unformed Sheet Metal features, when possible.</p>
      <div class="title_division">Non&ndash;developable faces</div>
      <p class="para_division">Non&ndash;developable faces can be processed as either area preserving or distortion faces. Neither algorithm guarantees satisfactory results. If area preserving does not give good results try selecting the problem faces as distortion faces. Remember that each distortion face must have three edges mapped by previous faces. You may have to remove some faces from the flat pattern. Occasionally, it is best to remodel the part using general flanges or other Sheet Metal features. You may also use the <b class="uiTerm">MetaForm</b> feature to unform the part.
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      <div class="title_division">Geodesics algorithm</div>
      <p class="para_division">To flatten b&ndash;surfaces, the area preserving algorithm uses geodesic curves, for example, minimum distance curves on the surface. You may choose from three geodesics algorithms under <b class="uiTerm">Preferences&rarr;Flat Pattern</b>. Usually, the default method, <b class="uiTerm">Parametric</b>, will suffice. If it gives undesirable results, try using the other algorithms.
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      <div class="title_division">Face sequencing</div>
      <p class="para_division">When creating a flat pattern, the system begins with the starting face it then flattens each connected face. This process repeats for all area preserving faces. Upon completion of the area preserving faces, the distortion faces are processed. The order in which the faces are processed can have a significant impact on the resulting flat pattern. The system does not supply a way for you to control the order in which the faces are processed. When you see the results of one face adversely affect another, you can attempt to change the order in which the faces process by selecting a new starting face, adding cutting edges, or simply eliminating some faces from the flat pattern.</p>
      <div class="title_division">Start face must be area preserving</div>
      <p class="para_division"><b class="uiTerm">Flat Pattern</b> requires that the starting face be an area preserving face. This means that in order to create a flat pattern, there must be at least one area preserving face in a solid body.
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      <div class="title_division">Self intersecting body</div>
      <p class="para_division"><b class="uiTerm">Flat Pattern</b> is able to correctly flatten a self&ndash;intersecting body. If you give <b class="uiTerm">Flat Pattern</b> a self&ndash;intersecting body, it does create a flat pattern. However, the flat pattern intersects itself. A warning message also indicates an intersecting flat pattern. An example of such an object is a locking washer as shown in below.
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         <p align="center"><img align="bottom" src="graphics/self_inter.gif"></p>
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      <div class="title_figure">Self intersecting body when flattened</div>
      <p class="para_division">Other bodies that have faces that form loops in the body could either self intersect or fail to come back together due to tolerances. <b class="uiTerm">Flat Pattern</b> addresses intersections or gaps smaller than the grid size by bridging them with a curve. Larger gaps may still create a flat pattern; however, a warning message appears.
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      <div class="title_division">Disconnected faces</div>
      <p class="para_division"><b class="uiTerm">Flat Pattern</b> cannot create a flat pattern if the selected faces are not connected. An error message displays if the faces are not connected.
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      <div class="title_division">Bend lines</div>
      <p class="para_division">When you create a center line for a bend, bend line data places on the center line(s). The bend line data contains information about the bend, which includes bend allowance formula, angle, radius, thickness, developed length and direction of bend. For some bends, the bend angle and developed length may not be applicable. An example of this would be when a cone surface, selected as a bend face, flattens. The developed length of the bend varies. Therefore, when you encounter this, the bend angle and developed length are set to zero.</p>
      <div class="title_division">Unmodeled bends</div>
      <p class="para_division">You can generate a flat pattern from a solid body, which does not contain sheet metal features or a forming table. The bends on the body do not need to model explicitly. An unmodeled bend is where a sharp edge is used to transition from one face to the next adjacent face, rather than using a cylindrical face or blending the common edge. The figure below gives an example of a body with an unmodeled bend, and its associated flat pattern.</p>
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         <p align="center"><img align="bottom" src="graphics/body_unmodel.gif"></p>
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      <div class="title_figure">Body with unmodeled bend</div>
      <p class="para_division">Flat patterns created from solid models with unmodeled bends have varied dimensions depending on the material side you select the base face from. A geometric transformation about the common edge performs rather than using the developed length of the unmodeled bend to produce the flat pattern.</p>
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                  <p class="para_note_body">To create a flat pattern with the expected developed length, blend the common edge.</p>
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      <div class="title_division">B&ndash;surfaces aspect ratios</div>
      <p class="para_division"><b class="uiTerm">Flat Pattern</b> can almost always do a good job flattening cylindrical faces (or conical faces), since there is a pure analytical solution. When a part contains other surface types, flat pattern uses an iterative technique based on geodesic curves. This approach is an approximation. The algorithms works best if the face has an aspect ratio close to one (such as the face is nearly square). When the faces have very high aspect ratios (long, narrow faces) the algorithm breaks down. Small errors in the angles of the geodesic curve will magnify. This can cause the flat pattern of such faces to curve, self&ndash;intersect, or flip directions. 
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      <p class="para_division">When you see problems due to long, narrow faces, try using a different geodesic algorithm under <b class="uiTerm">Preferences&rarr;Flat Pattern</b>. If that doesn't correct the problem, you may have to remodel the part in order to improve the aspect ratio of the face in question.
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      <div class="title_division">General tips</div>
      <p class="para_division">You should always perform an <b class="uiTerm">Unform</b> on all of the Sheet Metal features before creating a flat pattern. &nbsp;If there is a Sheet Metal feature that is on the bend face of a self&ndash;forming feature the result curve(s) in the <b class="uiTerm">Flat Pattern</b> may not be what you want if the flat pattern is created while the self&ndash;forming features are formed. &nbsp;If a Sheet Metal feature is on the bend face of a formed self&ndash;forming feature, the edge will be a distorted edge and flat pattern will create a spline from that edge, then simplify the spline into several analytical curves. &nbsp;If the self&ndash;forming feature, in which the sheet metal feature is on is unformed, then this edge that was a <b class="uiTerm">Distorted Edge</b> will now be an <b class="uiTerm">Analytical Edge</b> and will convert to the same <b class="uiTerm">Analytical Curve</b>.
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      <p class="para_division">If your part has embosses you will need to deselect these faces because the <b class="uiTerm">Distortion Face Solver</b> does not adequately handle these types of faces. We recommend that you deselect these faces by using  <a class="links" href="javascript:void(0)" onclick="top.openFile('sheetmetaldes/flpat_layout_cutedge.html');return(false);">Cutting Edges</a>. Select the edge formed from the <b class="uiTerm">Area Preserving Face</b> and the <b class="uiTerm">Emboss</b> as your <b class="uiTerm">Cut Edge</b>. When <b class="uiTerm">Cut Edge</b> is selected <b class="uiTerm">Flat Pattern</b> will not use any face past the cut edge to calculate the flat pattern. This technique does not deselect the face, it only stops <b class="uiTerm">Flat Pattern</b> from using the face.
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      <p class="para_division">If you have a <b class="uiTerm">Solid Punch</b> feature in the Model you should unform the solid punch by using the <b class="uiTerm">Unform/Form</b> dialog box or the <b class="uiTerm">Unform Sheet Metal Features</b> button in <b class="uiTerm">Flat Pattern</b> before creating the flat pattern. &nbsp;When you unform the <b class="uiTerm">Solid Punch</b> feature it is converted to a wireframe outline of the solid punch. These curves will then be added to the flat pattern as additional curves.
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