Much of the fabrication equipment in our shop is CNC, which means each machine needs programming. That can be done at the machine, but in most cases, we prefer to do it with our computer-aided manufacturing, or CAM, software.
CAM works out the best way to produce a part or parts from the input material, but to do that it needs to know the required geometry. That comes from a part file generated by computer-aided design, CAD, and software. So, if you haven’t figured it out already, computers play a big role in fabrication, from part design through to manufacture.
In this blog, we’re going to look at the upstream aspects – the CAM and the CAD – and explain how they contribute to accuracy, efficiency, and faster product development. For any of that to make sense though, we must first talk about CNC.
A Short Introduction to Computer Numerical Control (CNC)
Numerical Control (NC) arrived late in the 1940s. The idea was to replace a machinist operating a lathe or milling machine with a program, coded on punched cards, that would tell the motors on the machine tool where and how quickly to move the axes.
After the pioneering work by John T. Parsons, MIT, and Cincinnati Milacron both developed Computer Numerical Control or CNC. This used the power of a computer to interpolate the motions of multiple axes, thereby machining complex geometries that would be very difficult for even a highly skilled machinist to achieve.
This is one benefit of CNC. Two others are increased accuracy and repeatability, and faster machining because the computer can drive the axes at the highest possible speeds.
CNC machines, that is, machine tools equipped with a computer controller, use a language called G-code to control the movements of axes and spindles. It’s possible to type G-code instructions directly into the machine controller, and for simple jobs, particularly in a toolroom environment, you’ll see that done. More often though, an engineer will use a CAM program and a post-processor to develop an optimized G-code program.
CAM, Post-Processing, and G-Code
A CAM program imports the geometry data from a part design and works out how it will be made. In the case of machines like a CNC router or laser cutter, this means determining the optimal sequence of X-Y moves to cut the shape or shapes from sheet material. Typically, this is governed by constraints imposed by the programmer. They may want to cut as quickly as possible, to minimize floor-to-floor time, or to maximize material utilization by optimizing how parts are nested on a sheet.
Another machine where nesting is part of the CAM process is CNC turret punching. Again though, the CAM programmer must balance material utilization with cycle time.
Once a toolpath or cutting sequence is generated, the programmer/engineer will check for any errors or incorrect assumptions. When the toolpath looks good the programmer moves to the post-processing step. This is where a program applies instructions to the toolpath that are specific to the machine on which the job will run. You can think of it as interpreting the toolpath for a specific machine controller.
To explain why this is necessary, a program written for a CNC router can’t be transferred to a laser cutting machine, because the machine controllers are looking for different instructions or G-code.
Drafting, CAD, and Parametric CAD
The CAM program gets the part geometry from an electronic drawing file. This is generated by a CAD program. CAD first appeared in the 1970s as a form of electronic drafting, and by the 90s had almost completely replaced drawing boards and pencils. Initially, CAD was two-dimensional, and essentially just replicated what an engineer would produce on paper. 3D CAD soon followed though, with the ability to produce complex shapes and view them from any direction, and this led to parametric CAD.
In parametric CAD, which is what engineers use today, geometry is created as a combination of 3D shapes and features. Parameters and constraints are defined, such as a diameter being half the length of a feature, or holes being spaced at a set pitch, so changes made in one part of the design propagate through every feature affected. By capturing the logic of the design and the relationship between various features, changes are made much faster and there’s far less risk of mistakes.
Once the engineer is happy with the design, with most CAD programs it’s now possible to produce almost photo-realistic rendered pictures that make it easy to communicate the design. The programs will also produce 2D prints for use in manufacturing, just like the old drawings painstakingly created on a board.
Benefits of CAD/CAM in Fabrication
CAD/CAM wasn’t essential for CNC, but applying the three technologies together yields dramatic improvements in productivity, efficiency and quality throughout product design and manufacture. For fabricators like Wiley Metal, benefits include:
- Faster design: CAD is faster than working on a drawing board and lets the designer explore more options in less time.
- Easier sharing of design information: CAD files are usually held on a server so they’re available to everyone who needs them. Cloud storage opens up access to customers and suppliers too, if desired.
- Fewer errors: With parametric CAD a change to a single component automatically flows through an entire design. In addition, using electronic files eliminates the risk of people working with outdated versions.
- Higher accuracy in cutting and forming: CAD ensures dimensions are calculated and tolerances applied correctly. CAM ensures those same dimensions are carried through to the part program, avoiding transcription errors. And CNC provides higher repeatability in manufacturing.
- Less waste: Automated nesting capabilities in CAM maximize yield from sheet material. Plus, fewer setup pieces and fewer mistakes mean fewer parts going into the scrap bin.
- Greater flexibility: There’s more volume flexibility in that once a CNC program exists it’s as easy to produce 100 parts as one. There’s also more design flexibility because changes, as when a customer needs customization, are made very quickly.
The Future of CAD/CAM
Perhaps you’re familiar with digital twins. These are virtual recreations of physical entities that go beyond being 3D CAD models. By modeling kinematics and other physical properties, and exchanging data with their real-world equivalents, they replicate the real world inside a computer. This enables accurate simulation, evaluation of alternatives, diagnosis of problems, and remote commissioning and training.
Several machine tool manufacturers are developing virtual machining capabilities that behave as digital twins. These use models of the specific machine tool a job will run on, along with all the fixturing and tooling and will run the CNC part program to show the results achieved.
Virtual fabrication in this manner promises to reduce waste, improve accuracy, and enable the production of complex forms on even just a one-off basis. The technology is still largely in development, but it promises to be the next big advance in CAD/CAM and CNC.
Your Source for Quality Fabrication Work
As experts in the field of metal fabrication, we at Wiley make it our business to use the latest technologies whenever they can help us do our job better. We adopted CAD/CAM and CNC a long time ago, because it makes us more productive, and it improves the quality of the work we do. If you have a metal fabrication project you’d like to discuss, we’d love to talk. Contact us today.