Reading Precision Sheet Metal Prints

Learning Objectives Describe the methods used to display precision sheet metal fabrication drawings on prints Read precision sheet metal fabrication prints Answer questions related to material bending, seams, chassis layout, and other precision sheet metal fabrication practices

Learning Objectives Calculate bend allowance Describe undimensioned drawing practices found on prints Read prints using undimensioned drawing practices

Sheet Metal Definitions Foil or leaf Plate Gauge Flat pattern Cut Bent or bend

Common Sheet Metal Materials Carbon steel Aluminum Stainless steel Copper Brass

Precision Sheet Metal Prints Tighter tolerances than sheet metal parts used in construction Formed from a flat pattern Common industries: Automotive Electronic Product chassis Aircraft industries

Multiview Drawing and Flat Pattern

Multiview Drawing with Flat Pattern Reference Using Phantom Lines

Flat Pattern, Rectangular Coordinate Dimensioning Without Dimension Lines

Flat Pattern Using Tabular Dimensioning

Formed Sheet Metal Part Model and Flat Pattern

Flat Pattern with Manufacturing Information Extracted to a Table

Bend Representation Bend lines: Bend extents: Often drawn as centerlines Sometimes drawn as phantom lines Bend extents: Sometimes shown, usually as phantom lines

Bend Instructions Number of degrees of the bend Bend direction from the principal plane Note Meaning UP 90°R.120 Bend up 90°with a .120 bend radius DOWN 90°R.120 Bend down 90°with a .120 bend radius DN 90°R.120 Bend down (DN) 90°with a .120 bend radius BUP 90°X R. 250 Bend up (BUP) 90°with a .250 bend radius BDN 90°X R. 250 Bend down (BDN) 90°with a .250 bend radius

Additional Bend Information Bend tangent line Center line of bend (CLB) Inside mold line (IML) Outside mold line (OML)

Bend Allowance Different formulas based on: Material type and thickness Bending process Dies or machine used Bend angle and radius Grain of material Surface condition Amount of lubrication used

Bend Transition Helps ensure manufacturability Common examples: Spline Radius Straight

Bending a Corner to a Round May require bend facets when formed using a press break Smooth when formed in a die

Bend Relief

Corner Relief

Flanges Contour flange May require mitered corners

Seams Tight joint Specific gap Lapped Single-lap seam Double-lap seam Welding Lapped Mechanical fasteners Single-lap seam Double-lap seam

Hems

Roll Forming Linear or revolved around an axis Rolled surfaces Contoured rolls Beads

Lancing Stamping press operation Does not remove material

Metal Grain Structure

Blanking Nesting blanks

Undimensioned Drawings Often full scale Part and tooling produced by photographic or other processes Requires stable media CAD model sent directly to CAM machine tool ASME Y14.31-2008, Undimensioned Drawings standard

Undimensioned Drawings Dimensional accuracy applications: Grid lines Dimensional accuracy points Registration marks Artwork alignment in the place of grid lines

Grid Lines

Dimensional Accuracy Points

Registration Marks

Sheet Metal Punch Identification Standard dimensioning practices Punch identification (ID)