September 14, 2004
New requirements for clean, dry parts drive the need for efficient, flexible workcell parts cleaning.
Because stamping suppliers increasingly are required to provide clean, oil-free stampings and assemblies, the focus on parts cleaning cost has intensified. Many companies have discovered that the cost of adding a cleaning system to a press line or contracting out to a parts-cleaning supplier is detrimental to profit margins. In many cases, the surface quality, or level of part cleanness, was not stipulated in the original part specification. It's assumed that delivered parts will be clean enough to be welded or assembled without extra cleaning. The need for extra cleaning usually becomes apparent when a stamping supplier must use a heavy stamping lubricant to prevent excessive tool wear and scrap rates, which can leave a residue that interferes with secondary assembly operations.
Recent research has shown that high-velocity air effectively removes high-solid-polymer (HSP) stamping lubricants when accurately directed to the part's contour. (See Stretching metal's forming limits with HSP.) A compact, one-stage conveyor system fitted with high-velocity precision air knives was built and tested on parts as they exited the press. Parts were 100 percent free of the press-applied lubricant and dry to the touch.
Because HSP lubricants do not contain emulsifying soaps and have low surface tension, they can be removed easily with precision-directed air, which eliminates much of the cost and restrictions of traditional parts cleaning systems.
This technology opens the door for significant workcell flexibility and process savings. For example, removing a heavy-oil or even a water-based synthetic lubricant in an aqueous spray washer requires a heated three-stage system. The first stage includes an alkaline soap; the second stage, a rust-inhibited rinse; and the third, a hot-air dryer. Aqueous systems generally run slower than a press line, which can cause bottlenecks and generate additional labor cost for an offline setup.
From an environmental standpoint, aqueous washer lubricants and soap can create the need for a waste treatment strategy.
In addition, HV systems require no added cleaning chemicals, and line speed matches the press's. The system occupies 4.25 feet of line length and uses 12 kW of power. Chemical disposal can be eliminated, because the removed lubricant can be captured and recycled. Because HSPs reject any mill oils that may come off with the lubricant and aren't contaminated with cleaning soap, they maintain their integrity and can be reused at the press.
HV Chemical-free cleaning system properties:
A Tier-one automotive supplier was faced with the dilemma of having to supply clean, dry parts to its assembly customer. Excess lubricant was causing parts to be rejected. The company first explored the option of purchasing incoming steel precoated with a dry-film lubricant. The dry film was approved by the customer as providing a surface clean enough for handling and assembly. Typical dry films (borax or acrylic) cost about $60 per ton of steel. Though this appeared to be a great option because it eliminated the need for washing parts, the total cost was about the same as using conventional synthetic or soluble oil with a three-stage aqueous parts washer. By using high-velocity air to strip away the HSP lubricants, the company realized a $25 per ton savings.