What does CAD mean in fabrication?

CAD covers two kinds of work:

• 2D drafting: flat drawings made of lines, arcs and circles, in programs such as AutoCAD or DraftSight. Most laser and plasma parts start as a 2D profile.
• 3D modelling: solid models built from features, in programs such as SolidWorks, Inventor, Fusion or Solid Edge. Their sheet metal tools add flanges and bends, then unfold the model into a flat pattern.

The files a shop receives fall into three groups:

• 2D exchange files: DXF and DWG
• 3D exchange files: STEP and IGES
• native files from one program, such as SolidWorks (.sldprt) or Inventor (.ipt), which open fully only in that program

Customers also send PDFs. A vector PDF holds real line geometry that can be converted to CAD. A scanned PDF holds only pixels and has to be redrawn.

How is CAD used?

Customers design parts in CAD and send the files with their RFQ. The shop uses them three ways:

• quoting: measuring cut length, pierces, part size and bends from the geometry
• fixing: removing title blocks and duplicate lines, closing gaps, and redrawing parts that arrive as sketches or scans
• programming: passing the geometry to CAM software, which nests the parts and writes the machine program

Many small shops also draw parts themselves, for their own products or for customers who arrive with a hand sketch.

Why does CAD matter?

The CAD file is the only source of the part's geometry. If it's accurate and clean, quoting and cutting run straight from it. If it's at the wrong scale, has duplicate lines or shows several views of one part, every step after it inherits the problem.

For bent parts, the CAD model also decides the flat pattern. A model unfolded with a K-factor or bend radius that doesn't match the shop's press brake gives parts that come out the wrong size.

2D drawings vs 3D models for sheet metal

For flat laser-cut parts, a clean 2D DXF is all a shop needs. For bent parts, a 3D model is better:

• the shop can unfold it with its own bend data instead of relying on the designer's
• bend lines, flange lengths and hole positions relative to bends are unambiguous
• the same file shows what the finished part looks like

STEP is the safest 3D format to ask for, because almost every CAD and quoting program can read it.

CAD and quoting

Quoting from the CAD file takes the numbers straight from the geometry. Tempus Tools quotes from 2D DXF and DWG files and from 3D models in STEP, IGES, SolidWorks and Inventor formats, and unfolds the sheet metal parts in a 3D model automatically. For customers who only have a PDF, its PDF to CAD converter extracts parts from vector PDFs.

Further reading: What is a DXF file? A practical guide for laser cutting and fabrication