Cleaning injection molds is a time consuming, labor-intensive process that requires patience, attention to detail, and elbow grease. Lots and lots of elbow grease. At PVS plastics in Huber Heights, OH, rags and steel wool pads are being replaced with bubbles, and elbow grease replaced with a simple push of a button— resulting in much cleaner molds in a fraction of the time.
Injection molding is one of the most popular and widely used methods of mass-producing identical objects—and the production mold one of the most valuable parts of the process. Maintaining the tool steel is critical to the accuracy of the final product, as well as the greatest amount of productive uptime. However, for maximized uptime, any injection molding operation needs to minimize downtime for proper preventative maintenance such as cleaning.
Cleaning is not a popular stage of maintenance. It is messy, monotonous, and requires little talent of a highly trained toolmaker. Still, injection molding is a dirty process. Many resins contain stabilizers or release agents that leave residue: grease, waxy film, or dust. Some resins create hydrogen chloride gases, which can build up and corrode many types of mold steels. Color pigments stain steels and cause buildup—not to mention small surface rust that forms over time.
Whether large or small, all molds include cavities and pathways for molten plastic to enter and vent off gases, as well as channels for mold release agents. Production molds are a nightmare to clean by hand. Bigger molds generally feature more vent paths, ejector-pin holes and cooling channels. Any leftover flashing, grease, dirt, oils or virtually any foreign materials inhibiting the injection of resin can result in off spec parts and downtime as the mold is removed and re-cleaned.
Jesse McIntosh, a Mold Maintenance Technician at PVS Plastics, knows that if the mold isn’t maintained properly, the process mass produces rejects.
“The dirtier a tool becomes, it starts to impact the parts being made, a lot of the parts that we run are wheels that need to be balanced. So if the tool becomes too dirty the balance will start to go out and the parts will be rejected. It’s very important to keep all of our tools as clean as possible to keep them running smoothly,” he said.
PVS Plastics manufactures parts used in air conditioning units in cars, in addition to other related products as varied as blower wheels, over molded stators for motors and stone guards that go underneath cars. They work with a range of plastics and resins, including Polyproplene and nylon, in 1,2,3 and 4-cavity molds. With such a variety of parts and processes, PVS has 11 injection molding machines in a range of sizes to adjust for the different sizes of molds—as small as a 20-ton machine and as large as 300 tons.
Manufacturing blower wheels, which make up more than 50% of their molds, is a particularly involved process: laminations are made, overmolded, and then sent to Mexico, where they are wound in copper wire before being sent back for another overmolding. Any delay or off-spec parts sets everything back, complicating an already complex process.
McIntosh was spending 4 hours disassembling and scrubbing each part of each mold with little more than some brillo pads and rags. The result was passable, but not exceptionally clean. It was, however, exceptionally time consuming—until he rented an Ultrasonic LLC ultrasonic cleaner. PVS’ mother company had been using ultrasonic cleaners for some time, so he researched local options and found Ultrasonic LLC. By employing ultrasonic waves and micron sized bubbles rather than elbow grease, the process is more efficient—molds are cleaner and the preventative maintenance is faster than ever before.
Ultrasonic cleaners induce high frequency pressure waves to agitate a liquid in which a dirty mold is suspended. Micron sized bubbles are created by the alternating pressure waves. These work their way into and around all mold-component surfaces, even the hard to reach crevices, blind holes and channels. When the bubbles contact the hard surface of the part being cleaned, they implode into a micro jet, creating a scrubbing action which dislodges contaminants from the surface.
Smaller molds fit right in the tank, without being disassembled. All McIntosh had to do was close the lid, push the start button, and walks away—no scrubbing required. Side-mounted transducers agitate the liquid, creating bubbles which penetrate holes, cracks, and recesses, thoroughly removing all traces of contamination tightly adhered or embedded onto solid surfaces. Take that, material buildups. The resulting parts were so clean and the process so fast, that he purchased an Ultrasonic machine twice as large as the one he rented.
Ultrasonic LLC cleaners, including the 3200FA, are specially designed to speed up the cleaning process with no solvents or extra maintenance. The v-shaped design allows for easy cleaning between batches. Two side-mounted transducers mean there are no “dead spots” so the cleaning is consistent from top to bottom. With 5040 watts of ultrasonic power, dual 2000 watt heaters, and basket capacity of 27”L x 18.5”W x 5” H, the Ultra 3200FA has the power to quickly clean parts such as rubber and plastic parts, bearings, bolts, transmission components, engine parts prior to assembly, plastic injection molds, and more.
The massive size of many of PVS’ molds means not every mold fits in the 55-gallon cleaner. The cleaner’s agitation table capacity of 300 pounds is sufficient for large parts or multiple batches of smaller components. An optional dual-basket configuration is available, allowing baskets (18.5”L x 13.25”W x 5”H) to be processed simultaneously side-by-side— ideal for larger batches of small components or to clean small and large parts together. With a working depth of 14-inches, the Ultra 3200FA includes a 55-gallon main tank and a 10-gallon weir tank.
For the larger 2-ton and soon to be 5-ton molds, McIntosh suspends them into the tank with a crane, first cleaning one half and then rotating the mold to clean the other half. Even running two cycles like this only takes up to 2 hours—half as long as hand cleaning. Not only does the Ultrasonic LLC clean more effectively than hand scrubbing, but McIntosh also doesn’t have to disassemble and then reassemble the molds to clean hard-to-reach channels.
“With smaller tools it would take me about 4 hours to do a full preventative maintenance on some of our smaller tools – this helps me to cut that down to 2 or 2 ½ hours. It cuts the time in half,” McIntosh said.
Spending half as long cleaning means McIntosh can clean twice as many molds as before. Aside from the involvement of a toolmaker or technician to load and unload the cleaner, the ultrasonic cleaning process is hands-free—allowing employees to devote their energies to projects that make better uses of their time and talents than scrubbing. The machine can even be put on a timer, so it heats up and is ready to use when McIntosh is ready to use it. Such an increase in productive time is sure to result in a positive return on investment.
“It helps us tremendously, the Ultrasonic cleaner is like having an extra half-of-a-person, pay wise,” McIntosh said.
Not only does the Ultrasonic LLC clean PVS’ molds more efficiently, it also is less abrasive than other methods of cleaning. Manual scrubbing is detrimental to the tool surface—especially highly finished steel. Friction-based methods, such as scrubbing with rags, brillo pads, or steel wool invades and wears down the surface of the steel. Not so with the ultrasonic bubbles. The process of cleaning injection mold components via ultrasonic bath efficiently removes the residue of burnt polymers, resins, and mold releases from mold surfaces, in a way that ensures the life of the tool for countless hours of production to come.
Mold cleaning is a process often rushed or overlooked because bottlenecks occur when molds are pulled faster than they can be cleaned and made production-ready again. In order to meet production demands, molds get reset dirty, increasing the likelihood of the tooling becoming damaged or the product being off spec. After all, when the mold goes down, production stops, and scrubbing molds can only go so fast.
The tools are on a P.M. schedule according to how many shots are produced. For example, a normal two-cavity blower wheel is set to be cleaned every 100,000 parts ran. If there is something that happens to the tool, like being sprayed with water or being greased, PVS will clean the tool in that case.
Before the addition of the Ultrasonic cleaner, the cleaning process was the same, regardless of mold size: laboriously take the mold apart, clean each bit with a brillo pad, rag and mold cleaner, hose it off, and put the mold back together. It took up to 4 hours. For each mold.
Even for massive 2-ton and 5-ton molds with a maze of channels and odd shapes, the Ultrasonic machine leaves them looking brand new. Perfect molds make perfect products, keeping the manufacturing process running smoothly and eliminating rejects.
Elbow grease still has a place in manufacturing, but not when it comes to cleaning. With the addition of an Ultrasonic cleaner, Jesse McIntosh has cut his cleaning time in half and reduced the rate of rejects and off-spec parts, saving him time, money and plenty of elbow grease.