Hydraulic — and even pneumatic — cylinders are used massively throughout auto manufacturing, providing the power, precision and durability needed.
By Josh Cosford, Contributing Editor
If you’re (un)lucky enough to sell and service hydraulics in the automotive manufacturing industry, you understand life in the belly of the beast. The automotive manufacturing industry is not for the faint of heart. Over 3% of North American GDP is related to vehicle production, which equates to nearly a trillion dollars of production.
However, with so much money on the line, the auto manufacturing industry is wildly competitive, unforgiving, and highly demanding at every stage of the process. Manufacturers obsess over the smallest margin improvements, which stem from continuous improvement, tight bookkeeping and operational efficiency. As well, the numerous suppliers they count on to supply parts such as drivetrain, interior components, and electronics are expected to help manufacturers remain profitable and competitive.
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You might be surprised to know that auto manufacturers make very little of what they sell and, by and large, are engineering, marketing and assembly outfits. There are generally three tiers to the automotive supply chain. Tier 1 suppliers sell their components directly to the manufacturer, such as Bosch, Linamar and ZF, to name a few. Tier 2 suppliers will manufacture sub-components to the Tier 1 suppliers, such as a gear for a transmission or frame rail for a seat. Finally, Tier 3 suppliers will provide raw materials ranging from billets of metal to plastic pellets to all levels of the pyramid.
Cylinders play a huge role
Regardless of who makes what, fluid power plays a major role in the manufacture of passenger vehicles, especially so with cylinders. Nearly every type of material and machine is used at one stage or another of the vehicle manufacturing process. It might help to discuss a few vehicle components and the types of applications and cylinders used to make each part. Although there are 30,000 individual parts of a car, let’s look at a few major families to cover the majority of applications: steel chassis components, plastic panels and drivetrain parts.
What first comes to mind when you think about what constitutes a car is that good old steel likely takes the top spot. Steel and iron make up 65% of a car’s mass, and its strength and shape are what keep you safe in an unfortunate accident. Manufacturing chassis components as large as frames, subframes and cross members require equally large machinery.
Using thousands of tons of force, the hydraulic press, Figure 1, is a mainstay in chassis component manufacturing. Using large dies installed on the bed (lower portion) and slide (upper portion), sheet metal is placed into the press before the massive cylinders extend to push the dies together, forming the metal as easily as Play-Doh. Even high-strength steel is no match for the compressive strength of these presses, which are so large that they may stand a few stories tall.
Figure 1. Hydraulic presses are used predominantly in auto manufacturing, relying on the power and strength of hydraulics for chassis manufacturing.
Depending on the size and strength of the press, it will typically have two or four cylinders. These cylinders will have large bores, but strokes may vary widely. You will rarely see any standard, such as NFPA, used as the primary press cylinders in these applications. Almost entirely custom and with bores up to 20 in. in diameter or larger, these cylinders usually have rods sized to match their overall strength. With so much force potential, you will often find ram cylinders used on hydraulic presses, as well.
A ram is simply a rod that acts as the piston as well, often requiring no seals while it floats within the cylinder bore. It is sealed and supported by the massive bearing or gland at the head side of the cylinder. It matters not the lack of sealing at the “piston” side of the ram since all pressure surrounding the rod is equal and opposite in every direction but the piston area. Pressure on one side of the rod is cancelled by the opposite end, so the only direction for force to work is downward. Typically, these presses will have separate cylinders to lift and lower the slide and only employ the press cylinders to bear the brunt of the heavy lifting.
Critical to press applications (and any automotive application) is the requirement for ease of repair. The effort and time to remove and repair a hydraulic cylinder topping a ton is extensive, so designs to speed up the repair work are mandatory. A bearing and seal package installed on the rod side performs best when it can be removed and serviced while the body of the cylinder remains installed on the machine. A repair that takes only a couple of hours ensures that critical production machinery uptime is prioritized.
Because stamped steel panels rarely achieve their final appearance in a single action, they move through a series of machines and dies to achieve their shape. Using tandem presses for large panels or transfer presses for smaller panels, manufacturers pass the material through a series of dies with progressively finished shapes. A tandem setup uses multiple, large presses where the material is moved to each machine with robots, conveyors or both. Meanwhile, a transfer press uses a series of stations inside a single press to achieve similar results on smaller parts.
More than presses
Plastic panels range from those used on interior surfaces, such as doors, pillars and kick panels and a surprising number of exterior panels may also be plastic, such as bumper covers and side view mirror housings. Injection molding is, by and large, the most popular method for creating plastic parts. Injection molding machines clamp a set of dies shaped like the auto part and then through either thermoplastic (think plastic pellets) or thermoset injection molding (think chemical reactions).
The injection molding machine, Figure 2, comes in a vast range of sizes, depending on the size of the part being made, obviously. Two opposing molds are supported by tie bars and the moving mold attached to the clamping unit employs four hydraulic cylinders to ensure the mold remains closed during the high-pressure injection of plastic. The force required to clamp is a combination of the projected area and the injection pressure, but for parts such as dashboards and bumper covers, you can expect well over a thousand tons.
Figure. 2. Injection molding machines rely on numerous cylinders to clamp and eject parts.
Again, cylinders this large are often custom to the application, especially because of the nature in which the cylinders are integrated into the machine. For smaller machines, NFPA cylinders might be suitable for the clamping function, but it’s more likely that custom cylinders with large rods are used. Large rods provide a strong extend proposition because they provide excellent column strength to prevent buckling, and because the retraction force is low, the annular piston area can remain small.
In addition to the clamping cylinders, part ejection cylinders are placed throughout the mold to pop the completed plastic piece(s) out of the mold. These cylinders may be NFPA or custom but are always small enough to be buried within the confines of the mold. The injection unit may also use a single, large-bore hydraulic cylinder. Plastic pellets are heated and fed into the barrel, which prepares the shot for injection. The injection cylinder is often precisely controlled through proportional or servovalves to offer accurate and quick injection of plastic to prevent waste and non-conforming parts.
Machine tool precision and reliability
By far, the most numerous pieces of a vehicle, excluding fasteners, are the machined bits that make up the drivetrain. Gears, bearings, shafts, cams and pumps constitute hundreds of individual pieces that power and drive your internal combustion vehicle. Mostly from metal, each piece is forged, cast or made from billet, but almost always finish machined to the precise and accurate final component.
It’s hard to think of a more reliable and over-engineered man-made item than vehicle drivetrains. Consider that some manufacturers will offer a warranty spanning a decade, and to offer that confidence, parts must be so finely machined as to be nearly bulletproof. Machine tools are any piece of equipment designed to remove material to create a finished workpiece, such as lathes, mills and grinders, to name a few.
Figure 3. This drilling operation on a CNC lathe machine uses a hydraulic chuck for precision machining of tubes, bars or rods.
Although, admittedly, CNC machines offer a modest hydraulic accoutrement compared to presses and injection molding machines, they provide the power and speed to improve the workflow of every manufacturer providing drivetrain parts. A hydraulic chuck, Figure 3, on a lathe beats using a keyed chuck to clamp work material any day of the week, and a hydraulic clamp beats out manual vices within a vertical milling center.
The hydraulic chuck for a through-bore lathe is a unique beast in the fluid power world, as it uses an annular piston to allow long material to reside within the chuck to prevent excessive overhang. The piston pushes on the wedge plunger (or may be the plunger itself), which opens the chuck slightly to allow removal and reinstallation of the workpiece. A rotary joint passes hydraulic fluid from the valve and into the rotating chuck, which is a requirement for such an application. Although it doesn’t provide infinite range throughout and across the distance the jaws move, it provides a fast and powerful method to hold tubes, bars or rods.
Similar to the hydraulic chuck is the hydraulic clamp used in vertical milling centers or other machines with fixed work pieces. It is much faster and more powerful than manually operated clamps, and foot pedal operation provides operators with free hands to remove and replace the piece or to adjust it for a second operation. The clamp might use a tiny hydraulic cylinder to squeeze a clamp together, or it may use one or more swing clamps to hold material fast.
A swing clamp is a small cylinder that rotates partially to lift up and out of the way to place or remove material. When activated, it swings back down and clamps the workpiece with a clamping arm, keeping it fixed in place while the high-powered tooling sheds chips from the material while it works toward its final shape. They often use a ball detent mechanism that requires the ball on the body to follow the helical groove in the rod, providing partial rotation.
Figure 4. Pneumatic cylinders don’t get the spotlight, but they do the heavy lifting — literally. With steel bodies and air-powered efficiency, they keep automotive automation fast, clean, and cost-effective. Here, NC9 air cylinders from Peninsular Cylinder Co. are built to a Ford standard (Steel Air Cylinders).
Pneumatic cylinders, Figure 4, are also used throughout automotive manufacturing for their consistent and efficient movements. They offer precise control for items like gripping, welding and assembling of components. They are often used in robotics cells as well as assembly lines to position and handle parts.
Cylinders are pivotal to the operation, performance and reliability of machinery used in automobile manufacturing. From standard to custom designs, machine designs prioritize productivity and uptime to keep the automotive realm lean and profitable.
Filed Under: Components, Components Oil Coolers, Cylinders & Actuators, Engineering Basics
