Reducing metal waste
Mark Jennings looks at innovations in sustainability within manufacturing and engineering that open up a world of new opportunities for the manufacture of precision parts and which also reduce metal waste.
Mark Jennings Dawson Shanahan
HE ENGINEER magazine recently reported that UK manufacturers are losing millions in potential profit through inefficient recycling, quoting a report that claimed
British engineering is losing up to £780 in potential revenue for every tonne of metal waste recycled. However, the report took a positive outlook by highlighting the potential of a new wave of swarf (metalworking waste) processing machines. For manymanufacturers metal is an
essential raw material and so swarf processing represents a powerful cost saving initiative. The problemthat most companies face is
that their critical engineering processes can generate large volumes of waste materials, of which metal in the form of swarf, chips and offcuts accounts for a considerable proportion. For the production of many components
that are cut, milled or ground from solid workpieces, the ratio of metal retained in each finished part to the volume of scrap can be as high as 1:4 which means that 80% or more of the original material is being converted to waste.
Reducing scrap levels The volume of scrap can be minimised through careful part design and the use of precision computer numerical control (CNC) machine tools, operated by experienced engineers. However, by combining this with the recycling of swarf, chips and offcuts, either using dedicated and expensive on-site systems or the services of specialised suppliers, manufacturers can follow two parallel routes to increased efficiency.Me
tal prices have been rising year-on-year and show no sign
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of abating. The price of swarf has doubled then trebled in recent years, but new systems that use vacuum pumps to automatically collect swarf from the machining process show a way forward. Bigger companies can land themselves with
tonnes of valuable metal using this method and if they can conduct recycling operations in-house, without incurring the added cost of sending the material to an outside contractor for processing, companies can give an even bigger boost to their revenue stream. For example, Honda UK Manufacturing
(HUM) is using the new system to process the 1,000 tonnes of swarf waste produced every year, as well as increasing income from recycling coolant. And there are added benefits, as if any were needed, to be gained from this process; removing swarf streamlines production which can minimise the likelihood of downtime.
The process To summarise the process, tangled swarf is shredded into chips that are easier to process by the recycling machines. These are then passed by conveyor to a centrifuge that removes moisture to prevent clogging. The swarf is then passed over a multi-stage
set of magnetic rollers to remove any ferrous particles. Coolant, water and oil are reclaimed throughout the process and recycled where possible, while the final product is reduced to briquettes in order to reduce its size. While swarf recycling is a potentially
powerful way to make savings, there are manufacturing processes that can be adopted to prevent the generation of scrap in the first place. Of these, perhaps the most effective is the use of precision cold forming, sometimes combined with CNC machining for final part finishing. Cold forming can be used to process
a wide range of metals, including copper, brass
and aluminium. Copper is perhaps the most commonly used material and it is here that companies currently machining high volumes of components from tellurium copper (CuTe) rods or bars can derive the greatest benefits. CuTe is ideal for machining, but techniques
such as milling, grinding, turning and drilling all produce large volumes of waste. At current market rates the scrap value is far lower than the initial stock or raw material price. So for a circular, hollow shaped part such as might be used in a power generation or distribution unit, with a finished weight of 345g, you would typically require a solid section of rod weighing 1071g, from which around 68% of material is removed as waste. That’s over £3.50 of raw material wasted. A value of maybe £2.50 can be recouped from recycling, but why not adopt a process that minimises the need for recycling from the outset?
How does it work? Here’s a typical example of how the cold forming process works. A simple blank, sawn or cut from a round bar or wire, is placed into the cold forming press, where die and a 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 conventionalmachining, 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, while internal surfaces take on a highly polished finish. Because cold forming has proved
increasingly popular, engineers have advanced www. r e c y c l i n gwa s t ewo r l d . c o . u k Recycling & WA S T E W O R L D
the process so that now even stainless steel can be cold formed. With growing demands from industry, combined with the need to reduce wastage rates and energy consumption for both economic and environmental reasons, an increasing number of manufacturers are adopting the more efficient and cost- effective method of producing stainless steel components via cold forming. This new development in cold forming
looks set to revolutionise the way stainless steel components are manufactured in the future. Precision cold forming is not necessarily the perfect solution in all cases, but as an engineering process it deserves greater consideration as part of manufacturers’ portfolios of production options. More importantly, at a time of rising raw
material costs precision cold forming can provide a valuable method of protecting profit margins.
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