The words “precision” and “accuracy” are often used as though they’re interchangeable. Engineers and scientists of course know otherwise. We thought we had a good understanding but it seemed prudent to check before writing this, and that lead us to the “Practices of Science: Precision vs. Accuracy” web page maintained by the University of Hawaii. The definition and examples they provide seem bang-on to us, but we can’t help thinking a field trip might be necessary, just to confirm our understanding. Maybe in February.
But back to the title. When we talk about our “High Precision Engineering Team” we’re not saying they’re all very repeatable. What we mean is that we have a team that works on projects requiring high precision. This work starts in the Engineering offices but ends up on the factory floor, because Wiley Metal is after all a fabrication company.
The goal of this TikiTalk post then is to answer some of the questions that come up most often regarding our high precision capabilities.
What is “High Precision” in Fabrication?
Fabrication is the cutting, bending and assembling of metal pieces into a useful object or device. Unlike machining, which operates in the realm of thousandths and even millionths of an inch, fabrication tolerances are traditionally more like eighths and sixteenths.
Clearly, this is not high precision, so let’s discuss why this is so. We see two main reasons for variability:
- Poor process repeatability
- Inconsistent metal behavior
Starting with poor repeatability, many fabrication processes are either wholly manual or have a large manual element. Take bending on a press brake for example. Getting the bend in the right place depends on pushing the metal workpiece up square against the backstop. That’s not so easy to do time after time, especially when someone is impatient for the bent parts.
Welding is another very good example. It’s primarily a manual process that relies on the consistency of the set up and the ability of the welder to manage heat input and distortion. Getting two pieces out of welding that are absolutely identical is almost impossible.
Metal itself introduces some variability to fabrication, especially sheet metal. Hardness for example can vary between batches, and even on where the piece went in the oven, if it was a batch treatment process. Likewise, the coiling process imparts a degree of work hardening, and this is greater towards the center of the coil.
Metal variability can show up in cutting but where it creates the most challenges is in bending, thanks to springback. Springback is that elastic deformation effect where, once bent, a piece of metal wants to go back to its original shape.
Now, returning to the question, high precision in fabrication means being aware of and accounting for these sources of variation at the design stage, and engineering appropriately. By doing this it’s possible to maintain much tighter tolerances than is typically the case. How tight? Well that’s job-dependent but lets think in terms of +/-0.010″ on dimensions and +/-0.2° on angles.
What Machines and Processes are Used in High Precision Fabrication?
Machines using CNC controls generally yield higher repeatability and accuracy than those that depend on manual positioning. Our laser cutters for example can hold accuracies of +/-004″ and maintain repeatability of +/-0.002″. Yes, a skilled operator might be more accurate on a shearing machine when cutting a single piece, but maintaining that performance on a whole batch of parts would be well-neigh impossible.
Turret punches are another very accurate machine, perhaps more precise than the laser because the laser beam can wander a little, especially in corners. CNC press brakes can also provide good repeatability, thanks to automatic back stop positioning and control over downstroke velocity.
Regarding welding, repeatability is best off our Genesis Versa 2 robotic welder. It still relies on manual set up, but once the start button is pressed it follows exactly the same path at the same speed, every time.
What Types of Projects Does the High Precision Team Handle?
It’s application-specific. Generally speaking, batch jobs require higher repeatability than one-offs because they’re either going into an assembly operation or having parts assembled into them. In these cases variation between parts would mean lots of adjustment and modification on the assembly line. These often qualify for High Precision Engineering treatment.
However, a one-off job can sometimes require fabricating to a very high accuracy. For example, that would be the case with an architectural feature that had to line up with other structural components. Very large weldments can be another example of a project needing high accuracy. In cases like these we call in the High Precision Team.
There’s a list of examples on our High Precision Fabrication web page. Two that illustrate the type of work we’re discussing are:
- Self-serve kiosks – need both accuracy and repeatability to ensure easy assembly
- Medical press components – there’s no margin for variation on these!
What is the High Precision Engineering Team?
Achieving high precision in fabrication takes more than just sound engineering skills: it’s important to have a feel for the machines, the processes, and most of all, the metal.
A good engineer designs what the customer wants. A High Precision Engineer designs what the customer wants and for what the processes can deliver. A couple of examples:
- Incorporating tabs and slots to improve repeatability during welding set up
- Considering grain direction when planning how to cut out a blank that will pass through a press brake operation
Our High Precision Engineering Team is a group of specialists that collectively, can engineer and fabricate designs that need abnormally high levels of accuracy and repeatability. They work with exacting specifications to create precisely what our clients request. It is where close is never good enough. It’s a team effort that requires as much feel for metal fabrication as engineering know-how.
Let’s Create Something Precise and Accurate
What’s particularly exciting about this area of custom metal fabrication within Wiley Metal is that it’s where ideas, concepts and dreams become tangible. It’s where technology and fabrication come together in some amazing new ways. It’s where imaginations fuel exciting new products.
If you have ideas about creating, improving or replacing a product, we would love to hear them. Perhaps we can partner and even find additional talents to make your concept become a reality. How can we help you? Contact Wiley Metal today and let’s discuss it.