Spray Solutions: The Key to Metal Forming
Troy Turnbull, President, Industrial Innovations
Lubricant spraying is a necessary and critical function to ensuring a high quality manufactured part. Understanding the capabilities of the spray solution and tailoring how to adjust the spraying equipment to meet the specific spraying requirements for the casting or forging is therefore paramount. Lubricants provide a film formation and wetting on the mold surface. Primarily, the lubricant serves as a release agent, but furthermore, reduce corrosion, surface pitting, non-fill, porosity and solder in your castings. Finally, when using water soluble lubricants, the dilution ratio is adjusted to maintain the thermal balance of the tooling and the process speeds, input temperatures, and desired surface finish.
Die casting dies and forging dies require spray with release agents not only for release and formability but for cooling purposes as well. Dies must be clean and free of excess lubricant, slag and or flash. Castings must have minimal porosity; excess coating of release/ forming lubricants can leave casting/forging with porosity and can result in blistering as well. While there are many factors that could result in a poor surface finish, this article will discuss how proper spraying solutions can result in the repeatability of clean and defect-free high-quality castings or forgings.
Lubricants help to release the metal part from the mold. If too much lubricant is used – then porosity becomes a problem along with a poor part surface finish. If not enough is used – then the part may not properly release, causing defects and or serious die damage.
Complex parts or high tolerance castings are more sensitive to spray inputs and can be negatively impacted by improper lubricant application. Some surface defects can be immediately obvious where as other defects are only discovered after machining or other secondary finishing processes. Surface porosity often shows in small holes in the surface, a defect that is often caused by humidity or excess die spray release agent on the surface. Another serious problem related to spray is solder. Solder can be caused from excess heat and insufficient lubricant protection. Conversely, if too much lubricant is applied, excess cooling may cause metal to pre-maturely freeze off resulting in improper fill and/or laminations of metal in the casting or forging.
However, spraying evenly across the die area is often easier said than done. Particular parts with irregular shapes and various wall thicknesses, can create a challenge for the spray application. Unfortunately, to address the hot spots or challenge areas, over spraying is a natural instinct that may lead to increases in part problems and surface defects. Proper, precise spraying is critical, along with adjustability – to ensure intense spraying in hot areas versus low temperature areas.
Therefore, how can we determine the right kind of spraying equipment that would work best for your ever-changing part production? We suggest thinking ahead in regard to what parts are currently produced, and potential parts that will be made in the future. The markets for castings and forgings continues to increase, but not always for the simple, low tolerance parts. More than likely, larger, more complex parts, with higher standards, define the broadening markets. If spraying was critical before, proper spray application is crucial now. Improper application will have an even greater impact on these types of parts that may have very strict surface requirements, or internal porosity standards.
Servo control means the highest automation is being deployed to guarantee accuracy that could otherwise not be achieved. When your parts are long and narrow, are thin or thick walled, nothing provides pin point accuracy like a servo sprayer. The Servo Controlled Sprayer is controlled by a brushless, digital servo motor drive system attached directly to the gear reducer for maximum torque efficiency. Because there are no air cylinders, hydraulics, cams or motor brushes, reliability is improved. Continuous positioning accuracy is achieved by a “closed-loop” absolute encoder feedback system. The encoder is directly mounted to the motor shaft. Positioning accuracy of ±.020 inches provides constant repeatability.
Horizontal or Vertical Layout
The ability to design equipment around vertical, horizontal or tilt casting is necessity. The ability to position your machine to spray from the top or side of your dies is a determination based on available space. Ceiling height and or ancillary equipment in or near the parting line using valuable square footage is a determining factor on how to spray your dies with precise control and accuracy
Adjustable Base Height
In spraying, adjustability to reach your parts the way they need to be sprayed is critical in preventing surface defects as too little lubricant or too much or both creates surface finish defects. An adjustable base height allows for centering between dies and is the ideal solution for variable part production. Adjustability can be done either manually or electronically through a teach pendent or HMI (operator interface)
Programmable Spray / Air Blow Positions
A sprayer with independently programmable nozzles ensures repeatability for the highest quality control and guarantees that low temperature versus high temperature areas are treated with the correct amount of lubricant. Servo Controlled Spray allows for pinpoint accuracy at critical predetermined locations of your die. With the ability to stop and spray at multiple positions for a different pre-determined time, this will assist with preventing non-fill, solder and porosity. Air Blow-Off is used for removing excess lube, flash and slag. Blow-off is also capable of being programmed at key programmed positions at different preset times or simply sweeping the die at a desired speed. All these functions can and should be easily set up through the HMI (Operator Interface).
Flow Monitoring Control
Sensors that monitor lubricant flow through the nozzles are becoming a reliable and valuable tool for production. As the tolerance for too much or too little lubricant becomes more stringent, flow monitors will verify proper flow. Should the lubricant flow fall outside of the process requirements, the ability to accurately monitor this flow can shut down the process if the limits are exceeded, preventing overproduction of scrap parts. Furthermore, an accurate total volume can be obtained per cycle, per hour, per shift etc. This totalizer can help track the usage of costly die lubricant and can assist in the future for quoting jobs.
Controls now have a critical diagnostic capability to allow ease of trouble shooting to keep your production running versus waiting for a service technician, sitting on the phone, or the Internet ‘searching for solutions.’
With the advanced and automated equipment on the market today, lubricant spraying is a process that should be part of your overall defect prevention program.