Controlling Pouring Through Automation
While still not widely adapted, autopouring can improve process control for higher quality castings and lower energy consumption, and the need for it is growing in high production and job shop facilities.
Shannon Wetzel, Senior Editor
(Click here to see the story as it appears in the February issue of Modern Casting.)
While methods to automate molten metal transfer from the furnace to the mold have been around for decades, the incorporation of automated pouring in job shops lags behind the adoption of automation in other areas of the metalcasting facility for several reasons—alloy changes, cost, low volume, etc. However, the advantages of automated pouring exist for high production and job shop casting facilities alike. It leads to better control of temperature, pouring speed and pouring volume, and eliminates an unpopular and potentially hazardous job from the shop floor.
“I think overall, automation got a black eye in the 80s and 90s because everyone was trying to do it and using in the wrong areas,” said Robert Conrad, vice president foundry sales, Roberts Sinto Corp., Lansing, Mich. “Autogrinding and autopouring takes operators to a safe place, and they give repeatability for part quality.”
Increasing standards demanded by customers are driving all metalcasters to incorporate more control in the process, which could include pouring.
“Simple castings are being made offshore. More sophisticated castings are made here,” said Patrick Brown, vice president, Stotek Inc., Pewaukee, Wis. “That is driving the requirement to autopour.”
Metalcasting facilities have a wide variety of automated molten metal transfer methods to choose from depending on their existing production layout and equipment. These methods are either heated or unheated systems, meaning the molten metal is held either at a set temperature from furnace to the mold or it loses heat in the transfer process.
Casting facilities using unheated vessels in a high production environment often utilize holding furnaces or other types of melting devices that can maintain a constant source of molten metal to provide a high enough volume of metal to feed production.
Heated devices are more flexible in molten metal delivery and often eliminate the need for holding furnaces. Typically associated with batch melting, a heated pouring device can act as the holding furnace.
One of the most basic ways to automate is with a driven ladle, according to Bill Pflug, manager, automated pouring systems, Inductotherm Corp., Rancocas, N.J. Not 100% automated, it allows the operator to maneuver the ladle to pour a mold without physically doing the work. Facilities can take that a step further by incorporating devices that provide feedback to the ladle’s control, either with a camera, laser or sensors. The feedback allows the system to automatically control the pour.
With automatic ladle pouring, you can exchange the ladle with another for more metal or alloy changes, Conrad pointed out.
Beyond a driven ladle, a vessel with a stopper rod nozzle or valve that will control the pouring from the bottom reduces slag compared to an open-air ladle.
These first few options are unheated, so the molten metal is losing temperature as soon as it leaves the furnace. But, capital and operating costs are kept down.
Heated options, although more costly, provide another level of control in the metalcasting facility, and are well suited for producing thin-sectioned castings, such as fittings and manifolds. Pressurized furnaces can be used to fill the mold directly or transfer metal to the mold via a launder before filling the mold using a stopper nozzle or valve similar to an unheated ladle. Capital and operating costs are higher, but the pouring operation can be better controlled.
Permanent mold and diecasting shops often opt for robotic ladling—where pouring profiles are programmed into the robot to pour different weights for each mold—incorporated into cells. This has been a popular choice in North America, according to Brown, although he sees that changing.
“The majority of North American companies are still using ladles,” he said. “But they are moving away from ladles and part of that is that the quality of the metal to make sophisticated castings is driving the control of the process.”
Dosing pumps take molten aluminum from the bottom of the furnace and transfer it to the mold to distribute the prescribed amount of metal. Dosing furnaces that transfer metal directly to the mold with or without a pressure pump also can be incorporated. For instance, in tilt-pour permanent mold lines, with multiple molds on a turntable, a dosing furnace can be positioned so that the molds come around to the furnace, which distributes the programmed amount of metal for that mold.
“You can mix and match sizes and interface with the furnace so that mold 1 gets 5 lbs., mold 2 gets 7 lbs., and so on,” said Dave Kozman, director of sales, Striko Dynarad, Zeeland, Mich. “You are not restricted to one part and one size.”
Dosing pumps and furnaces also can be incorporated into aluminum green sand lines. Dosing pumps can direct metal from the furnace to the mold without exposing the metal to oxygen until the point of pouring. Or, a short run that requires 50 molds, each with a few sprues or pouring holes, can be accommodated with a dosing furnace on an XYZ axis table, moving side to side or up and down to position itself correctly above each sprue. Similarly, a dosing furnace can pour large castings, giving the advantage of an enclosed pour that holds the temperature within 4-6 degrees throughout the whole process.
Dosing pumps can be purchased together with its matching furnace or separately and then used with existing melting equipment. This can be cost effective, but limitations exist.
“Quite often people are looking to use an existing furnace, but frequently the furnace isn’t deep enough to take the pump,” Brown said. “Without modifying the furnace, it may not be possible. Then you have the added cost of a new furnace, which makes it harder
Barriers and Doors
The pouring process does not have to be automated at the same time as the molding line in a casting facility, although it does help.
“Automation is the driving force,” Brown said. “If a foundry is automating the line, it doesn’t make sense to have an automated molding line and then have pouring be the limiting factor.”
If a metalcasting operation is updating its production by adding a new automatic molding machine, it might be a good time to consider automating pouring at the same time while funds are available. Job shops in particular might want to keep autopouring in mind when adding a new molding line, even if it’s not on the agenda yet.
“When you start getting upwards of 130 molds per hour or more, your manual pouring operator would be getting tired,” Conrad said.
For job shops, many automated molding machines are designed specifically for hand ladling, as it has been thought to be hard to economically justify autopouring.
“In some situations, hands are tied in making an economical system based on mold handling,” Pflug said. “Weight and contraptions over the top of the mold don’t lend themselves well to automation.”
Calculating the return on investment will depend on the level of automation used, the value that the added quality gives to the castings, and production rate. Incorporating automation and control in pouring can reduce scrap, labor and energy costs, which will have to be weighed against the cost of the equipment. Kozman said metalcasting facilities should check for local energy grants where utilities offer incentives to save kw usage in return for money to invest in the capital improvements.
“Most people change lights, but energy is the biggest cost a foundry or diecaster has,” he said. “Improving your furnace and pouring can result in huge energy savings.”
Kozman said a lot of variables go into calculating ROI, but many companies see payback on an autoladle and furnace inside of 12 months.
Conrad offers two main aspects of a pouring operation to study when contemplating automation: safety record and overpours.
“The first and foremost thing to consider is you are taking the operator out of a dangerous situation,” Conrad said. “Then I’d tell people to calculate how much metal their best pourer is leaving at the top of the mold at pouring.”
That calculation should help determine the cost feasibility of investing in automating pouring. If the case is made for autopouring, the facility’s best pourer will be integral in programming the automated ladle for a perfect pour every time.
In many cases, autopouring will not be an economic or logistic fit for job shop facilities. But, Pflug noted a few low-cost options do exist for those jobbing facilities who have a need for higher quality castings or the desire to eliminate the hazardous job of manual pouring.
“A job shop may not have high speed or volume production but still wants to increase the accuracy of pouring, reduce costs and remove people from a hazardous area of the foundry,” Pflug said. “If they just are getting into automating, they might incorporate a ladle that is driven, where the operator stands back and interacts with the control. It does not fully automate the process, but it is something a job shop can do with a low impact on cost.”
Green sand molding manufacturers also are starting to work with furnace and pouring system designers to incorporate automation.
“In many cases, it makes sense to change the pouring when the molding line also is changing,” Pflug said. “Moving forward, we see better opportunities for people starting with new molding machines.”
In high production facilities and markets, demand for better control is evident as structural castings become more common. “Suspension parts and subframes are more and more common in aluminum,” Brown said. “Structural castings are difficult to make without tight control, and that is the direction the U.S. metalcasting facilities are going.”
The pace of automation in pouring in competing countries, such as China, is another indicator of a growing demand for higher quality castings.
“It comes down to repeatability, control and scrap,” Conrad said. “We are selling units overseas like crazy, especially because of the need for quality parts.”
While the pouring methods have not changed dramatically over the years, the technology to process information and relay it back to the equipment has improved, leading to better methods for control.
“A manufacturer of safety critical components can use visual cameras to log pours, overpours, short pours and temperature,” Pflug said. “This is something that was more of a lab tool in the past but now can be used in production. We are working with molding manufacturers to put the whole thing into a package to better control the process.”
An influx of international companies purchasing and building new casting facilities in North America has brought with them their own countries’ preferences for running production, as well.
“The way they are approaching this is to do everything they can to eliminate labor, including in the pouring area,” Kozman said. “I’m an advocate of this industry going out and seeing the rest of the world and how they operate. More can be done to cut down labor in order to build the U.S. casting industry.”