Automotive assembly most often conjures up images of welding robots and electric nutrunners. But, another technology is just as important for assembling a wide range of automotive components—presses.
Pneumatic, hydropneumatic, electric and manual presses are used to assemble ball joints, control arms, steering knuckles, fuel rails, bus bars, pumps, wheel studs, brake calipers, transmissions, door locks, freeze plugs, hydraulic motor mounts and windshield wipers.
Presses are used for high-force applications, such as inserting ball bearings into castings, as well as for delicate operations, such as installing the needle of a speedometer. They are also used to install parts such as self-clinching fasteners and compliant-pin electrical connectors.
Any process that can be performed by a press—inserting, crimping, clinching, swaging, riveting and staking—is used to assemble automotive components of one form or another. There are also unique applications. Remanufacturers use presses to disassemble and reassemble auto parts. Another automotive manufacturer uses a press to hold parts tightly together during a welding operation. The pressure keeps the assembly from warping.
“There is a plethora of pressing operations in an automobile,” says David J. Zabrosky, North American sales manager at Schmidt Technology. “Our presses are used to insert bearings and bushings into transmission components and steering columns. …One of our presses is used to insert a pin into a powdered metal component, and then stake it to make sure it’s retained. …
“Another press is used in a forming application for a capacitance sensor for an automatic door lock. …The blower wheel for a car’s HVAC system is pressed onto the shaft of a motor.”
Don’t Beat Around the Bush
Inserting bushings into metal castings or stampings is one of the most common automotive applications for assembly presses. Bushings can be installed with any type of press, depending on the material and the production volume, says Charles A. Rupprecht, executive vice president of BalTec Corp. A manual press is sufficient for low-volume applications involving elastomeric bushings. A powered press is necessary to install a large metal bushing in a higher volume application.
Regardless of power source, a C-frame press is most often used for such applications, says Michael T. Brieschke, sales coordinator at Aries Engineering Co. Inc. With its open front, the press can accommodate a range of part sizes, and parts can be loaded and unloaded either manually or robotically.
To facilitate changeovers and prevent undue wear on the ram and cylinder, Brieschke recommends a press setup with two or four guideposts.
“You can change die sets relatively quickly with a guided system,” he says.
That’s important, because the tooling for inserting bushings can be very part-specific. “With a straight bushing, you have a very small area you can push on,” says Brieschke. “With a flanged bushing, you have a relatively larger area. There are a billion different bushings out there.”
Glenn Nausley, president of Promess Inc., says machine builders often underestimate the difficulties of a seemingly simple application such as installing bushings into a control arm. These bushings must be pressed to a specific distance—for example, to a position relative to a datum on the part or to a distance from another bushing. However, these datums are often not available until after the part is fully assembled.
To complicate matters, the stamping or casting for the control arm is not exactly a high-precision part. It can also flex during assembly.
The answer, says Nausley, is to use a servo press in conjunction with a special gauging fixture. “The servo press gives you control and feedback,” he explains. “You’re not pressing to a dead stop.
“You can’t use a traditional fixture that simply holds the parts so you can bang these bushings into place. You need a precision fixture with built-in probes that measure the position of the bushings.
“Now, you can [press the bushings partially in], back off, and let the part relax. Then, you measure where the bushings are at with the probes. That information gets fed back to the controller, so the press can come in a second time and finish the part. You’re making a good part every time. You’re gauging the part as you’re making it.”
Given the production volumes in the automotive industry, bushing insertion is often automated. For example, BalTec recently provided an automated rivetng system to assemble the linkages that raise and lower the roof of a popular convertible. The entire production system consists of two indexing dials with Baltec radial forming machines and custom servo press systems (not supplied by Baltec). The presses automatically insert bushings into the stampings, which are then sent to the riveting systems for final assembly.
The spiderweb framework has multiple pivot points—and thus, requires multiple bushings. And, since each convertible requires two sets of linkages (a right and a left), the volume adds up. Indeed, the system inserts some 15,000 bushings daily, says Rupprecht. Both the pressing and the riveting operations are monitored to ensure the linkage pivots smoothly.
Aries Engineering recently designed a robotic system to install bushings in the control arms for a pickup truck. One robot loads and unloads the control arms, while another loads the bushings. Force-distance monitoring ensures error-proof insertion of the bushings.
“Cycle time is 18 to 23 seconds,” says Brieschke. “To do that process manually would take 30 to 40 seconds.”
Measure as You Make
Servo presses can be used in conjunction with rotating equipment to measure the performance of an automotive component even as it’s being assembled. For example, a servo press can be used to apply a load to a bearing while a servomotor spins the hub to measure the torque value. “You want to make sure there’s no drag,” says Keith Lowery, press system specialist at FEC Inc.
Ball joints are another example. A servo press is used to form material around the ball to hold it in place. A servomotor rotates the bearing stud while the forming operation is being performed. Instead of pressing to a specific distance or force, “we’re pressing to a torque value produced by the parts that are turning inside the assembly,” says Lowery.
Fuel Injector Assembly
Presses are used to assemble the fuel injector itself and to insert the completed injector into the fuel rail.
A fuel injector is an electronically controlled valve that is supplied with pressurized fuel from the fuel pump. When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing pressurized fuel to squirt out through a tiny nozzle. When the injector is de-energized, a spring pushes the plunger down against the nozzle, cutting off the fuel.
For optimal engine performance, the spring must push against the plunger with just the right amount of force, and that force must be consistent from one injector to the next. Unfortunately, even precision springs vary in how much force they exert at a given height.
A press equipped with force-distance monitoring solves the problem. The press pushes down on the spring until it produces a predetermined preload value, explains Nausley. The height of the spring at that point is then recorded. When the injector is assembled, the depth of the pressing operation is automatically adjusted to match that height. Thus, injector springs might be compressed slightly more or slightly less from one unit to another, but the force each delivers will be the same.
Finished injectors are press-fit into the fuel rail.
“Typically, we use pneumatic presses for that,” says Rupprecht. “The upper tooling is critical for that application, because you have to make sure that the injector is inserted to the right depth and that there’s no cracking or distortion. We usually advise press-force monitoring.”
Monitoring can instantly detect problems during assembly. For example, if the force is lower than expected, it could mean the O-ring is missing. If it’s too high, the O-ring might be pinched or rolled, or there could be debris in the joint. If the initial force is very high, it could mean the injector is misaligned with the hole.
A similar application is installing the pistons on brake calipers. “It’s common for the seal on a caliper piston to catch on the hole and tear,” explains Lowery. “To avoid rolling over the seal, we use a servo press that rotates the piston as it is inserted into the hole.”
The days of solid steel bumpers are long gone. Instead, today’s vehicles have large, plastic fascias. For better molding, the fascias are typically produced without holes for things like fog lamps, tow hitches, cameras and sonar systems.
Instead, holes for these devices are punched out using a press equipped with force-distance monitoring. If you think process monitoring is overkill for a simple punching application, think again. Anyone who’s ever been in a fender bender knows just how expensive a front or rear fascia can be.
“Force-distance monitoring lets you know right away if a part has been loaded incorrectly,” says Brieschke. “The press knows that it must be at a certain position when it reaches a certain force. If either of those measurements fall outside the curve, something is wrong: The parts were loaded incorrectly. The slug didn’t eject. The tooling has been damaged.
“The ram returns to the home position, and you don’t make a scrap part.”
Testing Is Key
The best press for an automotive application depends on many factors, including the process; the size, shape and materials of the parts; dimensional tolerances; force requirements; quality requirements; and production volumes.
Although equations exist to calculate the amount of force needed for a pressing operation, they really only provide ballpark estimates.
“There are so many variables,” Zabrosky points out. “The results can be significantly off. It’s much easier to get sample parts and test them on a monitored press.”
Zabrosky typically asks his customers for enough parts to produce at least five assemblies. “Ideally, they should be production-grade parts, because surface finish and dimensional tolerances can influence the results,” he says.
For more information on assembly presses, visit www.assemblymag.com to read these articles: