Quality fabrication work starts with accuracy and repeatability in cutting operations. Whether cutting blanks from a sheet or sawing extrusion, angle, or tube, dimensions must fall within the tolerances on the drawing. At Wiley, we take pride in the precision of our work. We believe it results in metal fabrications that fit better, function better, and look better. It enables interchangeability between supposedly identical parts, and it eliminates the need to trim parts that should fit together straight off the saw, punch press, or laser cutter. In short, we pay a lot of attention to metal precision. Here’s how we go about achieving it.
Making Sense of the Terminology
When we talk about precision we’re usually referring to the number of decimal places we’re working with. Cutting a length of aluminum extrusion to 12.000” implies higher precision than saying we’ll make it 12” long.
Left unsaid is the tolerance accompanying that length. When we state a dimension to three decimal places it’s because the tolerance needs that level of precision. A piece 12.000” long with a tolerance of +/- 0.062” requires an accurate cut, whereas if there are no decimal places it doesn’t make sense to apply such tight limits.
“Accuracy” is a measure of how close to the target dimension we get. If our cut piece measures 12.010” it’s quite accurate, and if it’s 12.060” it’s less accurate.
More important than accuracy though is repeatability. This is the spread between repeated attempts to achieve a 12.000” cut length. Providing our cutting process is repeatable, meaning little spread between a series of pieces, we can adjust to improve accuracy. But if our cut lengths take up the whole tolerance band we can’t “dial it in”.
Precision Begins With Design
Applying appropriate tolerances is an important part of metal fabrication design. Tighter tolerances are in general harder and therefore more expensive to achieve. Our designers only apply the precision needed for the cut parts to go together, for the product to function correctly, and to ensure the appearance is satisfactory.
Our CAD systems play an important role in dimensioning and tolerancing drawings. They help our designers apply good Geometric Design and Tolerancing (GD&T) practices that ensure parts go together as intended at welding fit-up and in assembly. CAD also helps avoid any mistakes, like overlooking sheet thickness and bending radii. (Those are rookie mistakes we’ve all made.)
Another aspect is knowing the tolerances our cutting machines can hold. It’s hard to do this without direct knowledge, which is why we like designers to have plenty of metal fabrication experience. It helps them determine appropriate manufacturing processes, and to design for those machines, which is all part of managing cost and maximizing quality.
CNC Brings Precision to the Floor
Many of our machines have CNC, which helps achieve high accuracy and repeatability. When the cutting requirements are straightforward we sometimes program directly on the machine. For more complex parts a part program is developed from the CAD file and sent to the machine’s controller.
Whichever method we use, we can be confident the machine is going to move almost exactly to the required positions. (We say “almost” because there’s a very small amount of variation, far smaller than the limits we put on key dimensions.)
Expertise is Essential
CAD and CNC help us achieve high accuracy and repeatability in our cutting processes, but there’s still a human factor. Machines need setting up, which demands a lot of expertise and attention to detail. Material needs loading correctly, and it takes an experienced eye, (or sometimes ear), to sense when a tool or cutter is starting to wear and should be replaced.
All this is why we value the experience of the people who work here in the shop. They know the materials we use and the machines we have, and they can and do spot when something isn’t quite right. We believe in training too, so people know how to measure, how to set up machines, how to change tools, and more.
We also train people in our quality procedures, so they can do each job the best way, and do it that way every time. Our quality system plays an important role in achieving accuracy and repeatability.
Achieving Quality With our Quality System
In our pursuit of precision, we’re trying to drive out variation, and that’s where our Quality Management System (QMS) comes in. This has procedures for everything, from designing and purchasing to setting up machines and shipping finished products. Then we audit what we’re doing to check we’re following the procedures.
A significant portion of our QMS addresses inspection, measurement, and calibration. We’ve defined and documented standards and operate a calibration system, so when we make a measurement we know it’s correct. And, back to training, everyone working in our Quality function knows the procedures and what’s expected from them every day.
We produce a lot of metal fabrications where precision is critical. Door track protectors, thresholds, and landing gear pads for semi-truck trailers are examples. If we let variability creep into these, there would be problems with how they fit into parts made by other manufacturers. The closer we keep to the nominal dimensions, the easier they install.
Material handling devices provide another example. By exercising tight control over our cutting processes, we ensure bins and chutes are sized consistently. This way, we and our customers know they will fit with racking and other storage and handling systems.
Looking for Improvements
For many metal fabrication projects, tighter precision isn’t needed; we’re already good enough. What we keep working on though is defining and maintaining the right levels of metal precision. This way, we achieve the fit and appearance needed while minimizing any manual trimming or finishing work.
When we’re researching new machinery, accuracy, and repeatability are among the performance metrics we look for in the specifications. More generally though, our emphasis here is on using GD&T techniques to optimize fabrication design processes, and on training our people so they understand the prints and use best practices.
Consistency is Key for Quality Fabrication Work
We’re focused on maintaining excellent levels of quality in every fabrication that leaves our shop. Precision, accuracy and repeatability are big parts of this, and we work hard to deliver what’s needed. If you have a fabrication project in mind, or you’d like to learn more about our capabilities, contact us, and let us talk.