With metal prices steadily rising it’s important to make sure your scrap pile isn’t rising too. You can significantly cut costs by cold forming, which reduces waste and also offers enhanced material properties into the bargain, says Mark Jennings, technical director at Dawson Shanahan
Modern CNC machine tools are highly sophisticated and extremely accurate, capable of producing precision components consistently and in large volumes. Yet, regardless of the skill of the machine operator, conventional machining – cutting, milling or grinding parts from a solid block of metal – creates considerable waste.
For many components this waste can amount to more than 80 per cent of the original material. This mountain of scrap has to be recycled, often at a cost both to the company and the environment, while the need to purchase more metal than is required for the finished component leads to higher part costs to the end user, or lower margins for the producer.
While for some components conventional machining remains the best solution, there are also many more instances where the use of precision cold forming, combined with CNC machining, can reduce the size of the initial blank of metal by 75 per cent and scrap volumes by up to 90 per cent.
Cold forming can now be used to shape a wide range of metals, from copper, brass and aluminium to steel and even stainless steel. Machining a circular, hollow shaped copper part such as might be used in a power generation or distribution unit, with a finished weight of 345g, would typically require a solid section of rod weighing 1,071g, from which around 68 per cent of material is removed as waste. That’s over £3.50 of raw material wasted, of which (at best) a value of maybe £2.50 might be recouped from recycling. In contrast, a section of copper wire weighing 423g can be cold formed and then finished with a minimal amount of conventional machining, reducing waste to just 78g. This represents a considerable saving of 90 per cent raw material and scrap costs.
In addition to the achievable cost savings, precision cold forming can actually enhance the material properties of the metal. Cold forming using oxygen-free copper produces significantly better results than machining in many applications. This is due to its superior electrical and thermal properties, which result in components with optimised mechanical characteristics and highly polished surface finishes. Parts can have highly complex geometries; indeed, complex internal shapes that would be almost impossible using traditional machining can easily be produced using the cold forming process.
In cold forming, a simple blank, which has been sawn or cropped from a round bar or wire, is placed within a cold forming press, where die and punch tooling is used to extrude the metal under extreme pressure; this is typically between 100 and 200 tonnes, but can be far greater in some systems, up to 2,000 tonnes. The metal is stretched beyond its yield strength, so that it takes on and retains the exact shape of the mould, but without adversely affecting its tensile strength. Unlike conventional machining, where the material removal processes cut across the grain structure of each part, cold forming allows the grain structure of the material to follow the contours of the die or mould. As a result, the strength of the part is maximised along its length, in much the same way that a sawn piece of timber is stronger along the length of the grain.
Parts effectively undergo work hardening during the extrusion process. This improves their machinability and durability still further, as it aligns the structure of the metal in such a way that it prevents subsequent rearrangement. This increase in strength is comparable to that achieved by heat treatment, making it more cost effective to cold form a less costly and weaker metal than it is to hot work a more expensive material, especially where a precision finish is required.
Cold forming also delivers significant ecological benefits compared to processes such as hot forging, where the high level of heat, and thus energy, required comes at a price to the environment. Consequently, cold forming can contribute to a lower carbon footprint, as well as enhancing productivity and business performance.
The benefits of precision cold forming described above are consistent with all types of metal, not just copper. Recent developments have even enabled stainless steel to be cold formed, something that has traditionally been extremely difficult to achieve commercially, underlining why cold forming is increasingly recognised as a fast, economical way to produce robust, complex components in a wide range of metal.
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