Engineers who develop complex metal fabrication specifications are highly skilled technical experts. In the pressure to produce accurate results, however, they can sometimes overengineer parts or specify features and tolerances that aren’t necessary.
Not all products require the ultra-tight tolerances that an engineer might include in drawings, adding unnecessary costs and extended lead times. And there are occasions when what looks good on paper or a computer screen doesn’t translate to the manufacturing floor.
Metal fabrication engineers need to consider the following potential complications to help improve metal fabrication drawings and get accurate pricing and shorter lead times for their projects.
Advances in technology have helped to transform the metal fabrication industry, both on the production line and in the engineering room. Many engineers rely on 3D modeling and simulation software like Solidworks, while some still use AutoCAD.
Modeling software is fairly new to some companies, and it’s extremely capable of displaying a part as it will look in its final form. Some advanced software will also have preset tolerances or recommendations that can be implemented with the click of a mouse.
While automated functionality can aid the engineering process, it can also be a hindrance. Automated settings may default to unnecessarily tight tolerances — such as .002” — for a project that may only need .015” tolerance. Relying on computer generated data can easily add unnecessary costs.
Modeling software allows an engineer to design parts in exhausting detail. But that also means they could design pieces in ways that may not translate to the real world. A finished metal fabricated project can’t be designed as though it were molded out of plastic or carved out of a block of steel. Sheet metal has inherent limitations when it comes to corners, bends, angles, seams, and other dimensional aspects. Pieces of sheet metal will need to be formed and manipulated into the shape indicated on the drawing, but there are times when those shapes aren’t physically possible or are extremely difficult to achieve. Design for Manufacturability (DfM) knowledge must be combined with engineering skills to produce the desired results.
As noted, if extremely tight tolerances are included in drawings, the fabricator will use additional processes and labor to adhere to those specifications, even if the customer didn’t really need them to be that precise. For example, an engineer might specify that a wall panel needs to be .500” thick with a flatness of +.005. While it sounds simple enough, it’s important to know that a half-inch thick piece of metal, whether it’s steel, aluminum or stainless steel has minor variances across its surface and could be out of tolerance per the drawing requirement.
To achieve precisely .500” thickness across the entire span, the fabricator will need to machine a thicker piece down to that specification, and price it accordingly. However, if the engineer simply means that they want to use half-inch thick material and aren’t concerned about minor variances, machining won’t be necessary. This small detail can result in a considerable cost difference and needs to be noted in the drawings.
While the differences might seem negligible to the human eye, they are significant to a metal fabricator who will require different machining capabilities and processes to produce each.
Most commercial applications don’t require the tight tolerances that might be required for defense industry projects like complex electrical enclosures used on Naval ships. Examine drawings closely to ensure the tolerances truly match the product’s intended use.
An engineer isn’t just designing parts; they also need to design with the manufacturing process in mind and how parts will flow through a manufacturing facility. Understanding materials and which equipment is used to produce the product can help inform an engineer’s approach to design and potential cost savings.
Different material types react differently in various stages of the fabrication process. For example, aluminum is less dense than steel and is prone to cracking when bent, requiring a large bend radius. Steel is more forgiving and can have a tighter bend radius. Understanding a material’s properties, what it can do, and how it is fabricated are critical to successful design engineering.
Equipment also needs to be considered. Does the bend radius require a roller versus a press brake? Will a component be cut on a laser or does it need to go through a machining center? A machining center produces extremely accurate tolerances to CNC code. A laser, however, can cut sheet metal to the drawing’s dimensions but, when formed into shape, may not be able to hold those tight tolerances. Again, if the engineer specifies extremely precise tolerances, then it will need to be machined, which takes considerably more time and labor than laser cutting.
Knowing the use and intent of a finished product helps to ensure that an engineer doesn’t include specifications that aren’t necessary. For example, the interior of a fabrication that will never be seen by an end user probably doesn’t need the extra step of grinding and polishing that might be required on external seams. Yet, if it’s included in the drawings, extra labor charges will be quoted as part of an RFQ.
Cosmetic finishings are another area with potential savings. Specifying class A finishes on all painted surfaces — like the quality finish found on a new car — comes at a cost and isn’t necessary for many applications.
Finishing work on seams, painting, materials, and tolerancing all have significant costs associated with each. Overengineering these elements could explain why a customer might be surprised at the price tag when they receive a quote.
One of the best ways for metal fabrication engineers to hone their skills and bring more value to their organizations is to tour a precision metal fabrication facility. Doing so allows them to see and hear first-hand how materials flow through a facility and the processes used to achieve precise tolerances. They can also gain a deeper understanding of how to more accurately engineer fabricated products to achieve the greatest cost and time savings.
Even without a tour, it’s helpful to connect with the engineering team at a metal fabrication company to confirm tolerances and talk through a project’s intended use. This type of collaboration can provide valuable insights and cost savings.
Streamlining processes and managing workflows is an important aspect of keeping metal fabrication costs in check and submitting an accurate RFQ. For additional RFQ tips, be sure to download our helpful checklist below, and reach out to our team of experts with questions.