Eight Great Things Automotive Manufacturing Engineers Need to Know about Leak Testing Equipment
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A Major Truck Manufacturer Improves Quality Control without Sacrificing Production Speed
According to a recent "J.D. Power and Associates Heavy-Duty Truck Customer Satisfaction Study," International® brand trucks ranked highest in the reliability of key components such as engines and transmissions among Vocational Class 8 customers. As any automotive manufacturing engineer must acknowledge, much of the credit for such accolades comes about through diligent quality control.
Especially when manufacturing for automotive-industry applications, quality reigns supreme as the consequences for component or assembly-level failures can come back to haunt the manufacturer in the form of reduced sales from a tarnished reputation, or even multi-million dollar liability claims. Every sellable product must be tested.
At the same time, though, few automotive manufacturers enjoy the luxury of sacrificing production volumes for the sake of excessive time-consuming quality tests. However, armed with some advanced knowledge about what to look for in leak detection devices, test engineers can increase the odds that all products will roll off the production line with absolute quality assurance while not acting as an anchor to production schedules. In fact, awareness of the latest improvements in the design of leak detection equipment helps serve both agendas, as the best examples of this testing equipment actually can help speed production.
"We have a crankcase leak test where we seal all the intake ports, exhaust ports, turbo oil-drain, turbo oil supply, and many other ports," says Jim Bowman, senior manufacturing engineer for the International Truck and Engine Advance Manufacturing Engineering group. "If we had to seal all these ports manually with an operator, it would probably take three minutes or longer to perform that test; whereas the automated leak detector performs the leak test in less than a third of the time."
Such impressive gains come from a refocused emphasis on the process of selecting test equipment-one that recognizes the salient differences between devices. What follows are several important pointers that can help any engineer determine which leak testing equipment can quickly recast the quality control department into a strong ally of the production schedule while still upholding the highest standards.
Insist on application specificity
A one-size-fits-all approach only succeeds at being universally mediocre. Leak testing equipment demands especially exacting attention to the quality check at hand, since even very small leaks can mean the difference between product success and loss of market share.
"We primarily do mass-flow, pressure decay, vacuum decay, and pressure rise leak testing on our diesel engines to make sure the components and assemblies don't leak beyond our specs," says International's Bowman. International Truck and Engine Corporation produces International® brand commercial trucks, mid-range diesel engines, school buses, workhorse brand chassis for motor homes and step vans, and is a private label designer and manufacturer of diesel engines for the pickup truck, van, and SUV markets.
"We leak test the engine oil, coolant and fuel cavities, as well as cylinder head cavities, high pressure common rail (HPCR) assemblies, and many individual engine components," continues Bowman. "These various applications and volumes dictate the test processes we set up. We use several different types and brands based on the applications and specifications (cycle time, volume size, cavity type, and ambient conditions).
For particularly challenging applications, the experience of the test equipment vendor accounts for the bulk of successfully channeling a leak tester's capabilities for the benefit of a specific product. An established provider of leak detection and non-destructive testing tools for more than 40 years, Uson L.P. represents one of the more venerable manufacturers. From its Houston, Texas headquarters, the company has pioneered the development of a broad range of testers designed specifically to address a wide variety of test applications, including Tier 2 manufacturers in the automotive industry.
The vendor should consider each unique case, and then maximize the potential of the test equipment to fit that need through a redesign of the tester or by reconfiguring it-with custom designed pneumatic circuits, for example-to integrate within the manufacturer's production system.
Look for equipment that automates the testing process as much as possible
Ideally, test equipment must feature semi-automatic or fully automated leak detection systems that streamline product delivery, sealing, clamping, testing, and marking.
Timesaving features such as "infills" (which reduce volumes and allow for varying container sizes to be tested in the same chamber with minimum changeover time and expense), PLC connectivity, and remote-start input can greatly speed the testing process. Additionally, the latest multi-channel testers, some of which can run up to 10 channels, automatically cycle through all the tests at the push of a button.
"We have some continuous moving zones where the assembly line never stops," Bowman continues. "If it's a station that has, say, ten different ports to seal, then it doesn't make sense to have an operator there; we'd never have enough time in our process allocation to do that. Here's where automated testers are a huge time-saver. The probes advance, seal up the part, the machine performs the test, everything unclamps, the pallet and engine lower and finally move onto the next station."
Examine ease of operation
A leak tester, no matter how capable its performance, is nothing if the human/machine interface lacks ready comprehension. Programming should be simplified by software with pre-formatted test configurations easily modified to each application.
Leak testers that work within the Microsoft Windows® environment also lend themselves toward instant, intuitive operation. Added features to look for include touch screen input, large graphical displays, selectable engineering units, built-in diagnostics, and remote troubleshooting.
"Just last week, we had a limit change on a low-pressure fuel leak test and had to reconfigure some parameters in the way the program ran," recalls Bowman. "The leak testers we use are excellent for setting up these tests since they are menu-driven."
Check for fixturing that fits your product
Partly a product of application specificity, the physical process of affixing the product to the leak tester is extremely important, as failures here can quickly undo all other attempts at accuracy and expediency.
At a minimum, leak detection testers should have attributes like automatic clamping, sealing, and interlocking guards that perfectly match the dimension orifices of the part being tested. When speed counts, "quick connect" or "auto coupling" pneumatic self-sealing devices can be specified.
Some leak testers have the potential-by way of custom sealing devices-to accommodate industrial components ranging from fuel injection orifices all the way up to large intake-valves ports or bigger. When complicated products--such as those with unusual geometry or multiple orifices--require testing, then a vendor who manufactures custom couplings must be located. Find one who will arrange custom CNC work to create fixtures to handle square and other odd-shaped orifices.
Hold out for options in output
When it comes to certifying a manufacturing process, everything is based on data and there's nothing like a good paper trail. A complete leak detection system must include options for documenting the testing process. At a minimum, the tester should be able to input leak rates and other results right into a database such as Access® or spreadsheet such as Excel®, for archival purposes.
Other industry options for data downloading data include RJ-45 Ethernet connectors, RS-232 serial ports, PCMCIA card slots, and tailor-made data collection packages. Also helpful are screens that display results at the control unit, for interrogation by a supervisor as required. Marking capabilities, whether by ink, percussion or laser, also speed and reinforce the documentation process.
"Like most automotive-industry facilities, we have component tracking-all of our run-log data goes into a file that we can retrieve on a daily basis," says Bowman. "We can attach an engine serial number to that file, download it from the leak tester, and put it into our own data base."
As any quality control person will tell you, a test has no meaning unless it can be repeated with the same results.
Unlike reliance on the memory of an operator to initiate a sequence of tests, the automation of leak detection actually improves repeatability because the testing process becomes non-subjective. Innate to some leak detection equipment, the ability to automatically compensate for temperature changes also helps assure consistent product quality.
"Anytime you make changes to the leak test process or parameters, many times the tester needs to be re-calibrated to a zero-leak master part, and then a gauge capability needs to be performed," notes Bowman. "About 30 times is typical, but sometimes we do 50 runs. Once that is done, we feel confident about releasing subsequently-tested parts into production."
Demand good support from the supplier
Like most any other sophisticated piece of equipment, a leak tester is only as good as the support that it gets after it leaves the factory. Here again, the number of years that a supplier has been in business counts for a lot, as this adds to its knowledge base in following up on challenging applications.
Look for a supplier that offers custom system design, installation, and commissioning services. Also, some suppliers provide online tools to help test engineers dial in their testing parameters. As an example, Uson provides online tables that offer quick calculations for hole diameter-to-flow rate calculation; leak correlation for one gas relative to another; the relationship of leak rate to pressure drop; flow rate conversion; conversion for volume; conversion for pressure; and approximation of hole/size/flow rate.
Seek system flexibility for future upgrades
Nothing is constant. Product variations, specification changes, and the introduction of new components all mandate changes in testing parameters. A quality leak tester can accommodate such changes, saving the expense of having to buy a totally new piece of equipment.
A modular design suits future needs especially well, as users can choose only those features that may be needed for initial requirements, but later expand the same unit to add capabilities for more complicated applications easily and economically.
"When it comes to leak testers and the processes they encompass, the finished product has to be good," say Bowman. "No customer wants to end up with an engine that has a fluid leak on their garage floor. I don't care if it's the size of your fingertip."
For more information, visit www.Uson.com.
Windows, Access, and Excel are registered trademarks of Microsoft Corporation.
Edited by Design-2-Part Magazine
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