Shop Solutions: Waterjet Cuts Production Time, Boosts Quality
Most computer users never give a thought to their hard drive. But the devices, which use a recording head hovering a fraction of a micron over an aluminum platter spinning at up to 15,000 rpm, pose special engineering and manufacturing challenges.
The Data Storage Components Division of Magnecomp International designs and fabricates the suspension mechanisms that support disk drive recording heads. In addition to positioning the recording head within microinches of the disk, the suspension conducts the electrical signals that store and retrieve user data.
Magnecomp develops new products, processes, and tooling at its Technology Center in Temecula, CA. "As a design and supply partner to our customers, we are under constant pressure to reduce tolerances, costs, and lead-times," says VP of Engineering Steve Misuta. "We're always looking for new technologies to answer that call."
Case in point: a recently acquired abrasive waterjet machine from Omax Corp. (Kent, WA). In addition to reducing machining time on tools, dies, and fixtures, the machine has also resulted in improved consistency of critical components.
Magnecomp produces many types of parts using the waterjet, and engineers chose a few for in-depth process analysis to determine cost savings and performance improvements.
One of those is a die frame that locates critical forming components in high-precision production tooling. An essential tooling element, the frame forms the foundation to a progressive die. It is one of the more intricate and complicated tooling components Magnecomp produces.
Previously, the company was producing the frame by machining, heat treating, and finish processing. Front-end machining included six processes, and took six hours to complete. The processes were:
- Bandsaw/cut off saw
- Mill square, drill, and tap
- Rough grind
- Rough wire EDM critical cavities and locating features
- Mill critical features
Magnecomp was considering increasing its wire EDM capacity, but after seeing a demonstration of Omax's Tilt-A-Jet waterjet technology at a trade show, engineers decided to explore using the waterjet system instead. After success in several rounds of test cutting and further time studies, they became convinced that buying one waterjet was better than buying additional wire machines.
"In our business, cutting out one operation is a big deal," says tooling manager Rick Koch. "With the waterjet, we have reduced six front-end machining steps to three steps and cut the manufacturing time from six hours to less than two hours."
The waterjet eliminated the cut-off saw, rough wire EDM work, and rough milling operations. The new front-end processes are:
- Waterjet cut perimeter and TBW (to be wire EDMed) features
- Mill critical features, tap
- Grind (before heat treat)
Magnecomp has seen other benefits as well. "We can move material directly into tapping without secondary hole preparation," Koch reports. "As we eliminate operations, we reduce the opportunity for error and improve our ability to get it right the first time."
According to Koch, part quality is "every bit as good and possibly better" than components produced by the six-step process. "There's less stress on the material from the waterjet. It produces flatter parts that are capable of holding better tolerances after heat treat," he says.
Koch says the waterjet also quickly exposed other bottlenecks in Magnecomp's fabrication process, allowing engineers to address them as well. "To get the maximum productivity benefit, be prepared to optimize your downstream operations, because they won't keep up with the speed of the waterjet operation," he concludes.
Aiming for Picture-Perfect Quality
At BMW Mfg. Co. (Greenville, SC), members of the Quality Control team balance their attention between keeping production lines in working order and ensuring they are producing quality parts and products. Where a potential problem lies is where they want to be.
Measuring and recording data "on-demand" from large assemblies and processes is a goal at BMW. However, completing this task in a production environment is not as easy as it sounds. Next to the production line are workers, tools, equipment, cabling channels, and many other obstructions that can impede the line of sight needed for certain types of metrology equipment. This is not "laboratory conditions" by any stretch of the imagination.
Metrology Planning Engineer Bob Clement sees the plant floor as a place where metrology must interact with the production line in numerous ways. QC personnel need to gather critical coordinate data, perform analyses, and make adjustments--all with minimal impact to production workers.
To accomplish that, QC relies on two V-Stars industrial photogrammetry systems supplied by Geodetic Systems Inc. (GSI; Melbourne, FL). Applications inside and outside the plant include tooling inspection and adjustment, test/retest measurement, deformation studies, part inspection, and disassembly/reassembly studies using both single-camera and probing type measurements.
Photogrammetry is a 3-D coordinate measuring technique based on triangulation. By taking photographs from at least two different locations, "lines of sight" or rays can be developed from each camera to points on the object and then mathematically intersected to produce the 3-D coordinates of the points of interest. Accuracy is comparable to that of large-volume portable coordinate measuring machines: 25 - 50 µm on a 3-m object.
The V-Stars system consists of a hand-held digital camera with integrated flash system, a notebook or desktop computer system, interface hardware and software for connecting the camera to the computer, and software for measuring and processing the images. The high-resolution camera can operate independently of the computer (via hand-held operation or remote control) and can store pictures internally for later downloading. The camera can also be connected directly to the computer so each image can be measured immediately after it is taken. The entire system (camera and notebook computer) weighs less than 13 lb (6 kg).
"Industrial measurement based on photogrammetry has delivered several benefits, with the major ones being portability, reliability, and CMM accuracy out on the floor--especially on car length tooling," Clement says. "The system helps us bypass all the roadblocks presented by an automotive manufacturing environment."
One method used for 3-D data collection in industrial photogrammetry is targeting--measuring targets made of a thin, retro-reflective material that are applied at points of interest on the measured object. Once targets are applied, the operator can take the camera to the object or tooling being inspected and quickly capture photographs.
BMW worked with GSI to develop an Automated Repeatability Measurement (ARM) software module for V-Stars, which includes advanced 3D data collection features, automatic data processing, statistical software, and visualization tools. BMW QC personnel can now quickly and accurately study everything from a headlight assembly to the effects of welding on the body structure.
"In the past, we could not do repeatability studies at all, so ARM ushered in a 100% improvement," Clement says. "The test/retest method used by ARM allows us to quickly test a tool or even a hand-applied process for repeatability."
Tests that were not feasible using other types of CMMs are easily conducted with photogrammetry, according to Clement. "Unlike a CMM measurement point, a photogrammetry target stays on the part in the exact same location," he explains. This allows us to track planar movement and not just hard features like holes, edges, and slots, because the points stay on the part when it is removed and replaced."
Clement says another benefit of photogrammetry is the ability to compare and recalibrate measurement data. "This process gives you a backup, a database of information based on the photographs," he says. "You can make adjustments to the data a lot easier.
"To my knowledge, we are the first automotive company to embrace the benefits of photogrammetry and use it extensively in our operations," he continues. "Measuring our tooling and making corrections before it gets bad puts us way ahead of the game. The QC department can now perform dimensional maintenance in a very proactive manner, instead of the conventional reactive way of responding to problems," he concludes.
CNC Retrofit Gives New Life to Old Mills
Stellex Monitor Aerospace Inc. (Amityville, NY) operates 10 Cincinnati Milacron gantry-style milling machines to produce titanium and aluminum alloy aerospace components. A CNC retrofit--completed on five units so far--has given the machines a new lease on life.
Originally equipped with Cincinnati's Acramatic controls, the mills now have new digital servomotors, drives, and CNCs supplied by the Machine Tool business unit of Siemens (Elk Grove Village, IL). The Sinumerik 840D controls run on a Windows XP platform, and provide true 3-D five-axis cutter compensation and kinematic transformation.
According to VP Gary Kahrau, benefits from the retrofit include reduced setup time, improved part surface finishes, fewer secondary finishing operations, and significant improvement in overall productivity.
The oldest mills retrofitted were built in 1978. "They actually perform better now than when they were new, owing to the significant improvements in control technology," Kahrau says. "The Sinumerik CNCs include several features for five-axis aerospace cutting simply not available from other control suppliers."
One such feature of the open-architecture controls is real-time, five-axis kinematic transformation capability called TRAORI, which eliminates postprocessing and the potential loss of part geometry information. By directly accepting part data, the CNCs can reproduce smooth, accurate toolpaths and provide accurate 3-D cutter compensation.
When Stellex runs the same part on different machines, TRAORI compensates for the particular machine kinematics, minimizing the need for part programs for each machine configuration and providing flexibility to move production from one machine type to another. The controls can also accept program data from a postprocessor, allowing Stellex to use previously developed programs if desired.
In addition to the CNC retrofit, Siemens also provided a dynamic machine engineering analysis called Mechatronics. The three-step process involves collecting real-time machine performance data, establishing optimized CNC and servodrive parameters, and verifying the resulting machine performance. Kahrau says the process cut rotary axis error on the five-axis gantry machines in half.
Workholding Key to Productivity
SPX Service Solutions (Owatonna, MN) manufactures tools and equipment for automotive repair shops. Many of the products require turning, milling, drilling, and tapping, and an efficient but flexible workholding setup helps maintain throughput of a variety of parts in relatively small production quantities.
Set up on a DMG DMC 80H machining center that operates 24 hours a day, five days a week, the workholding system combines CarvLock Cluster Towers and vises from Kurt Mfg. Co. (Minneapolis). Four Kurt towers and five dedicated fixtures are mounted on pallets, and part blanks are loaded into the fixtures based on production needs.
"We have over 2000 part configurations programmed into this machining center," explains facilities and manufacturing engineering manager Daniel Sayner. "Parts range from small to large in tool steel, 4140 steel, and aluminum as well as castings and investment castings." Typical tolerances are ±0.005" (0.13 mm), he adds.
According to Sayner, scheduling is complicated by the constantly varying parts and lot sizes. "Quantities needed range from one to several dozen, so it's a real scheduling challenge to keep the machining center in the cut 24 hours a day all week long with efficient setup and minimal system downtime," he says.
The combination of dedicated workholding and flexible, high-density Kurt towers helps keep the machine in the cut, and enables the system to operate with high feed rates and minimal spindle travel between parts. The towers use Double Lock vises in several sizes, as well as CarvLock vises with interchangeable and machinable jaws. "The changeable jaw plate systems give us all of the clamping options we need for our parts," Sayner reports.
All the vise systems employ Kurt's Anglock design, which is said to minimize jaw lift. Each vise has a hardened steel screw that clamps by hand with force up to 5556 lb (25 kN). Jaw changeover is fast; one jaw set snaps out and another snaps in easily in about a minute. The CarvLock vises can use any of four different jaw systems, including machinable aluminum or ductile iron jaws, quick-change jaw plates, and standard hard jaws.
SPX maintains an inventory of more than 200 sets of machinable ductile iron jaws, which are located near the machining center in an enclosed shuttle system that provides automated storage, locating, and delivery as needed.
This article was first published in the December 2004 edition of Manufacturing Engineering magazine.