The term "weldment” refers to an assembly created by welding together a range of commonly available metal products, such as sheet metal, plate, tube, and structural sections. The process is often more cost-effective than other manufacturing processes like casting or machining, with less restrictions on size and quantity. Here, we'll describe how best to leverage the benefits of weldment design and how to avoid some of the more common pitfalls.
Why use weldments?
Choosing to incorporate a weldment into your industrial product can be an excellent way to reduce the overall cost and complexity of the product. Weldments excel at reducing the weight of a product while still maintaining sufficient levels of strength and functionality. In addition to this, weldments are cheaper to manufacture because they require no specialized tooling, and fabrication times are shorter compared to other techniques. To leverage these benefits, some basic design principles must be followed. Poorly designed weldments can actually increase costs without any added benefit.
Some of the benefits of using weldments include:
- Rigid and strong frames which can withstand impact loading and maintain alignment.
- High design flexibility.
- The ability to create watertight and airtight products.
- Low investment in equipment and overhead.
- No tooling cost or lead time (custom jigs can be created for high volume production).
- Little to no cleanup or extra finishing required - weldments can be painted soon after they’re welded (and cooled).
- Post weld machining costs can be minimized by combining parts and setups.
- Low per piece cost and small lead times.
The design of weldments is a multi-step process that requires an understanding of the application, material, welding technology, and joint design.
Much like any other design process, it is important to define the purpose of the product before addressing the details. Knowing where the weldment will fit into the larger vision of the product is essential. The product requirements, specifications, budget, and production time frame are critical things to consider as these will guide the designer to produce an efficient product and reduce the risk of over-designing.
In general, weldments are either made from steel or aluminum. Each of these materials has its advantages and disadvantages.
- Steel - Steel is an incredibly versatile material with a wide range of alloys available to fit almost any use case. Mild steel is easily weldable, inexpensive, and available in a variety of shapes and thicknesses. Some alloy steels can be welded to provide a high strength, impact resistant weldment. Welded steel joints, if done correctly, are often stronger than the base metal.
- Aluminum - Aluminum is widely used due to its excellent strength-to-weight ratio and formability. Custom aluminum extrusions can be incorporated for even more flexibility. There are also additional options for finishing cosmetic parts. Aluminium weldments are, however, more expensive, and the joints tend to be weaker than the base material. Aluminum can also be difficult to weld.
Weldment design considerations
Designing a weldment can get complex, but there are a few basic design principles. A few of the more pertinent points are listed below.
To reduce cost, joints should be optimized to use a minimum amount of material while still achieving the required design strength. Choosing the incorrect joint type can significantly increase the welding cost or compromise function.
Joints not only need to be properly designed for the loads they will encounter, but also designed to be easily welded. Overcomplicated assemblies with complex joints make it difficult for a welder to achieve a consistent welded product.
Selecting the correct welding process is an important part of keeping weldment design costs low. Some welding processes are faster than others. For example, TIG welding results in a neater weld but is slower than MIG welding, whereas automatic welding like SAW is both fast and produces a high-quality weld with superior penetration.
Overwelding refers to the practice of over-designing welded joints. This is often seen when a designer specifies continuous welds where intermittent welds will do, or large throat sizes when smaller ones will suffice. Overwelding can result in numerous undesired outcomes, some of which are listed below:
- Distortion - Excessive welding can introduce too much heat into the part and cause it to distort. Some metal alloys, like stainless steel, are more prone to thermal distortion than others. Distortion can be controlled by reducing weld size and length, using intermittent welds, and alternating the sequence of welding to counteract the distortion.
- Increased cost - Adding unnecessary welds to a weldment design will result in additional weld material, higher labour costs, and potentially increased testing costs. Welds should be designed to only be placed where they are needed to achieve the required joint strength.
A welding procedure needs to be set up to both meet code requirements as well as make the welding efficient and economical. For example, specifying the wrong process for a given material will lead to poor weld quality, and excessive weld prep has the knock-on effect of increased welding cost. If you are using a fabrication shop to manufacture your products, they will be able to advise on the best processes for the type of material and desired outcome. It is ideal for the designer and fabrication shop to collaborate on the design and agree on a process before production. Some methods of reducing weld costs through weld procedures are listed below.
- Weld position - Welding downwards is the most economical. Overhead vertical welds are more expensive because they require more experienced welders and additional precautions and checks.
- Preheat - Reduce or eliminate the amount of preheating required by specifying the correct filler material, weld process, or changing materials. Pre-heat slows down the welding process and introduces additional costs due to heating requirements.
- Welding speed - If distortion is not expected and weld appearance is not important, welding speeds can be increased without sacrificing the joint strength. This will reduce welding time and thus save money.
A properly defined welding procedure can cut down on welding defects and ensure that welding results are consistent.
The proper use of weldments in product design can significantly reduce overall costs, lead time, and part complexity. Following the weldment design principles discussed here can help you start making the most of your welded products. And if you need an experienced design team to get the job done right, reach out and see how Riganelli Design can help!