Mercury castings increases quality, repeatability with shot control system.

To successfully compete in today's diecasting industry, a firm must know its niche and be efficient. Mercury Castings, a division of Mercury Marine, casts more than two million pounds of aluminum a month for outboard engine components and other custom OEM applications. Located in Fond du Lac, Wisconsin. Mercury Castings started casting custom components for OEMs in the mid 1990s. Today, this business has grown to more than 20% of its total aluminum castings production. Using the experience they've gained over the years, the company focuses on making big parts, ranging from 12-60 lb, where their technical expertise and production methods give them an advantage with OEM customers.

Given the size and volume of parts, repeatability and scrap reduction are critical factors for cost effective production. Another major goal is the reduction of microporosity to produce higher quality parts. An important component of the process Mercury Castings uses to achieve these goals is the installation of a Sure-Trak shot control system on 24 of its diecasting machines. The control system is a real time, all digital, closed loop shot control system produced by Visi-Trak Worldwide. L.L.C., Valley View, Ohio.

The first retrofit with the control system at Mercury Castings was made in 1993 when a shot controller, integrated with a new HPM shotend, was installed on a 2500-ton diecasting system. Nine more installations soon followed in the next few years. These were followed by further installations on 900- and 1200-ton diecasting systems. "Retrofitting the shot controllers has allowed us to convert older machines to a full closed loop system at a fraction of the cost of a new shot end," said Mark Potratz, senior process engineer at Mercury. "They enable us to do a number of things, such as reduce air entrapment during the slow shot phase and control constant acceleration."

Production benefits include reducing the scrap rate by up to 2% and decreasing microporosity by as much as 50% for certain parts. Equally important, repeatability of the casting process has improved significantly.

"As castings become more complex, the demand on the machine to be more repeatable increases," explained Potratz. "With the shot control system, we put in the process parameters and the machine monitors the shot. If we fall outside the parameters, we get a light or alarm. We've gotten to the point that if the light comes on, the casting is scrapped or set aside for X-ray evaluation."

While different settings in the control system might be programmed depending on the part, a typical casting might use a closed loop motion block to slow the shot cylinder as the die is nearly full. The shot controller would slow the speed from 200 IPS to 100 IPS over a distance of 3 in. to begin reducing the kinetic force of the shot cylinder as impact approaches. Then, there would be a final open loop closing of the throttling valve at a fixed position to dampen the impact even further.

Mercury Castings uses industry formulas and calculations to determine settings, as well as information that they have learned from their own experience. One example involves the ramping of certain areas in the shot. When this occurs, velocity increases and stepped velocity increases. The shot control velocity profile can be programmed in up to six separate motion blocks, and four electronic limit switch settings are available for initiating vacuum, start of intensification and follow through.

Using the shot profile display, Mercury Castings can rune the deceleration of the shot end to the force that the clamp end can hold closed, allowing flash reduction and leading to more stability in the biscuit size. Reducing flash helps extend tool life and improves productivity because the operator can run one shot after another without extensive clean up.

Potratz noted that very little training is required to use the shot control system. The critical process settings can be password protected to prevent individual operators from changing defined parameters. This can be an important quality control advantage in a multi-shift operation.

Experience in using the control systems also has made it easier to analyze and justify the cost benefits. Initial calculations, based on anticipated savings, have been verified now with historical data.

Installation costs for retrofitting the shot control system also have declined for Mercury Castings because initial engineering costs have been eliminated for repeat applications. Potratz estimated that retrofitting a 900-ton machine initially runs $75,000 hut that subsequent installations averaged $50,000. The easter plans to continue to upgrade its diecasting machines each year, and has recently purchased a 1600-ton machine outfitted with the shot control system.

Select No. 045 at www.moderncasting.com/info

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