Energy Efficiency in Die Casting: Where Energy Is Used and Where It Can Be Saved

Where Energy Goes in a Die Casting Cell

A brochure of the US Department of Energy on the metal casting industry attributes 55 % of energy use to melting. The figure is older and covers the whole casting industry, but it confirms what die casters see in their own plants: thermal processes dominate.

First Measure, Then Decide

Without data, saving measures remain guesswork. In many plants, energy is only recorded at the main meter. Sub-meters at furnaces, machines and compressors make the distribution visible.

• Energy per good part or per kilogram of good castings as the central key figure
• Base load during breaks, weekends and die changes
• Comparison of identical machines or shifts
• Recording of scrap and returns in kilograms, not only in pieces

A systematic framework for this is provided by energy management systems according to ISO 50001.

Less Metal in Circulation, Less Heat Loss

Every kilogram of metal that does not end up in a good part has to be melted again. The yield – the ratio of good casting weight to poured metal – is therefore an energy key figure. Optimised gating and overflows, stable processes and low scrap rates reduce the amount of returns.

• Keep furnace lids and doors closed and seals intact
• Check insulation and refractory lining regularly – hot spots on the shell indicate losses
• Do not set holding temperatures higher than the process requires
• Avoid long holding times and unnecessary ladle transport
• Match furnace size and melting capacity to actual demand

Which furnace type fits which task is described in Dosing Furnace, Melting Furnace or Holding Furnace?. Used furnaces are available under furnaces.

Hydraulics: Supply Flow Only When It Is Needed

On older die casting machines, constant-speed motors often drive the pumps permanently, even when the machine is waiting for spraying, part removal or the next shot. Drives with variable speed adapt the flow to actual demand.

Bühler, for example, offers a ServoDrive upgrade for its Carat and Ecoline series – a frequency-controlled motor combined with a multi-stage fixed displacement pump – and states that it can save more than 40 % of the machine’s electrical energy consumption. Such figures are manufacturer statements; the actual saving depends on the machine, cycle and share of waiting times.

Die Temperature Control, Spraying and Cooling

The die has to be kept within a temperature window: heated at the start, cooled during production. Temperature control units, insulated lines and a well-designed die cooling system keep this balance with less energy. Spraying also cools the die – an excessive spray quantity costs release agent, compressed air and often additional heating energy.

Background on these topics can be found in Temperature Control in Die Casting and Die Spraying in Die Casting.

Compressed Air: Expensive and Often Leaking

Compressed air is one of the most expensive forms of energy in a plant. According to the Compressed Air Challenge fact sheet on leaks, leaks can waste 20–30 % of compressor output; a plant that has not been well maintained will likely have a leak rate of around 20 % of total production capacity, while in a well-maintained system it should be less than 10 %.

• Regular leak detection, e.g. with ultrasonic devices, and prompt repair
• Check whether blow-off functions can be shortened or replaced
• Do not set the network pressure higher than the most demanding consumer requires
• Shut off supply to cells that are not in production

Used Machines and Modernisation

Energy efficiency is not only a question of the newest machine. Producing a new machine also consumes energy and raw materials; continuing to use a machine that is in good condition avoids this. With an overhaul, older machines can be upgraded, for example with demand-based drives, where the manufacturer offers this.

More on the role of used machines in sustainable production on the page Sustainable Alternative.

Stable Processes Are the Best Energy Measure

In die casting, energy efficiency starts with the metal: low scrap, good yield and well-insulated furnaces have the greatest effect. Demand-based hydraulics, consistent standby management, good thermal management and a tight compressed air network add to this. Those who measure energy per good part can prioritise measures and verify their effect.

Questions About Energy Efficiency in Die Casting