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Growing worldwide demand for natural gas and oil has pushed up prices. Gasoline and diesel fuel are hitting record prices at the local station, much to the chagrin of car and truck drivers. Of course, increased demand and higher prices encourage energy companies to find new sources in the ground. This means more well drilling wherever oil and gas deposits are likely to be reached.

That’s good news for companies that make supplies for the oilfield industry, companies such as EWECO in Magnolia, Texas. EWECO is a major manufacturer of mud pumps and related components. “We’ve seen more growth in this market lately than we’ve seen in 30 years. Our backlog is bigger than it’s ever been,” says Michael Williams, president of the company.

Every oil or gas well drilling site needs at least one mud pump; some sites may have two or three. Mud pumps are large pieces of equipment that force “mud” down a well hole so that small pieces of drilled rock can be carried up with the mud as it is sucked back out of the hole. Successful, economical well drilling can’t happen without a mud pump, and if a mud pump fails, drilling stops. According to Mr. Williams, EWECO pumps have a reputation for durability and long life in the field, so his company’s pumps are in great demand right now. He attributes the quality of these pumps to highly efficient designs, high-quality materials and accurate machining of critical components. Moreover, he likes to say that EWECO wrote the book on mud pumps, but some of the best chapters are still being written.

Keeping up with the current rush of orders while maintaining its manufacturing standards is a challenge for EWECO. “Our customers expect to have their pumps delivered when promised; issues with our machinery can’t be offered as excuses,” Mr. Williams says.

Recently the company underwent an expansion to their manufacturing facilities by adding two new HBMs and 50,000 square feet of floor space. The new expansion is served by a pair of 40-ton cranes to meet the need for newer, larger units. If the necessary capacity to satisfy the market demand could not be found under its own roof, then outsourcing would be the only alternative. However, EWECO is both a pioneer and a leader in the mud pump market, and they would rather keep this technology in-house, if possible. EWECO faces pressures from low-cost regions of the world that seek to copy components. Mr. Williams says that copies are typically not made of the same durable materials that EWECO uses and the life of the components is far lower.

Mud pumps can be many feet long and are designed to be delivered on flatbed trucks. Many units are being packaged for sale to companies in the North Sea and provinces in the former Soviet Union. One key feature of EWECO pumps is the large, rigid rectangular frame that gives an assembled pump its stability and durability in the field. Other large components include valve bodies and manifolds. The size and shape of these workpieces call for horizontal machining. Indeed, EWECO relies on HBMs in its shop. The shop has 14 HBMs, all from Nomura (distributed in the United States by SB Machine Tools, Schaumburg, Illinois).

The newest machine is a Nomura HBA-135. This machine has an extra meter of Z-axis travel compared to other models considered for the application. Not only does this extra travel allow several operations to be combined in one setup, but the accuracy of this travel establishes the foundation for the precise, efficient operation of the pumps when assembled and tested. In fact, the ability to machine large, complex components accurately helped make it possible for the company to introduce its new five-piston series of mud pumps last February. These new pumps achieve much more efficient operation than the company’s popular three-piston models.

Although the five-piston designs have more components and a more complex mechanical operation, they have an uptime record as good as the simpler three-piston versions.

“Without the capability of our horizontal machines, EWECO could not have launched this new product line,” Mr. Williams says. “As it is, the new pumps are expected to add double-digit growth to our sales in 2008. We’ve been able to reach new markets and hit our sales targets because of the efficiency and accuracy of our HBMs,” he says.

Reaching Growth Goals
Mr. Williams’ father, Ellis, gave the company both its name and its spirit. EWECO stands for Ellis Williams Engineering Company. The elder Mr. Williams was a pioneer in the oilfield business who highly valued efficiency and innovation. These are two characteristics that his son says he now pursues with the same drive. The father’s legacy reaches back to the 1940s, when he began his career with Continental-Emsco. At that time, the industry still used steam-powered pumps. However, the demand for more power and greater portability eventually made the steam versions obsolete, ushering in the age of the twin-cylinder pump powered by electric motors. The twin-cylinder model D-175, designed by Mr. Williams, became a mainstay of the industry. The need for still more power brought about models such as the D-225 and the D-550. Eventually, a 1,600-hp version, the D-1600 was developed. In 1967, the elder Mr. Williams’ development efforts prompted a change from the Duplex series to what he called the Triplex series. The Triplex used three cylinders instead of two, thus distributing loads more evenly among components and increasing both pump life and performance. At the time, the idea was considered revolutionary. It was well-received in the market, making the Triplex the industry staple that it is to this day, the younger Mr. Williams says.

Years ago, industry needs encouraged changes to pump design, and today, needs are again testing the limits of current technology. Much of the current oil supply is found under shallow sands, and it is being consumed at record paces. Any newly found deposits of oil are deeper and under more layers of rock. Reaching those deposits would be impossible if it were not for an engineered fluid that drillers simply call “mud.” This slurry of dissolved clay and polymers is aptly named—it has the consistency and density of wet cement.

Mud, according to Mr. Williams, has about a dozen functions in an oil well. Perhaps its most important functions are to carry bits of drilled rock back to the surface and to keep the cutting tip cool. A more advanced drilling method allows drilling mud to act as a hydraulic power supply. Instead of turning the whole drill string (the entire length of pipe down the well hole), the hydraulic energy carried by the mud is used to turn just the cutting tip, making it possible to drill deeper and through more rock than previous technology allowed. Using this technique, drilling can penetrate at an angle (directional drilling), avoid difficult layers of rock and hit deposits previously considered too costly to reach. To perform directional drilling successfully, acoustic data must be retrieved from the mud being pumped into the hole. This data is referred to as MWD (measurement while drilling) and LWD (logging while drilling). Acoustic reflections from the hole and surrounding rock layers indicate the depth and direction of the cutting tip. They also reveal information about rock layers surrounding the tip. However, a major source of interference to this technique is the mud pump itself. As the pistons move in and out, forcing material down the hole, resulting pressure variations cause acoustic pulses that must be filtered from the MWD/LWD systems.

In February 2008, EWECO released the Quintiplex series mud pump. The Quintiplex has five cylinders instead of three. Using five cylinders reduces pressure variations by more than 70 percent, thus reducing mud “noise” on the drill string and, in turn, allowing more accurate MWD/LWD readings. Increasing the number of cylinders decreases the load each component is required to carry by more than 40 percent, compared to Triplex pumps of the same horsepower. Although this new design increases the working life of each component, it multiplies their number. Every component, no matter how well designed or well built, will eventually wear out or need to be replaced, so the complex Quintiplex design heightened the importance of precise manufacturing to extend the useful life on critical components. The company’s HBMs have to support this mandate.

Reaching Between Two Extremes
While many configurations exist for HBMs, EWECO has found a size and arrangement that works well for them. “I’ve had floor models, but I prefer the table type. The accuracy of every machining operation downstream is controlled at the HBM. It took me a long time to understand that,” Mr. Michaels explains. Some HBMs provide Z-axis travel by moving a saddle, which has a rotary table mounted to it, to and from a fixed column. Other HBM configurations have a flexible traveling column. In this design, the table is mounted to a saddle that only moves in the X axis. It cannot move to or away from the spindle. For this type of machine, Z-axis motion is accomplished by moving the column to and from the fixed table. At EWECO, the traveling-column design is critical to the overall mud pump accuracy because it allows both sides of the frame to be machined in the same setup without moving the part. With the traveling column, the Z axis can be fully retracted from the table to allow the large rectangular frame to rotate about B axis. When the rotation is complete, the second side can be milled to complete the part. According to Mr. Williams, the B axis of the Nomura HBA-135 can be positioned accurately within 3 arc seconds, thus making the bore-to-bore alignment of the crank bores very good. While fully retracting the Z axis represents one extreme of travel, being able to reach the table requires another extreme—that of the Z-axis stroke. This why the extra meter of travel in this axis is essential.

Rigid Frames Help EWECO Reach Long Life
The frame of the mud pump influences the overall life of the pump because it holds the crank (also called the eccentric), the input shafts and the idler shafts in alignment. The Quintiplex, according to EWECO, is the first pump to have a balanced eccentric crankshaft. It is important to be able to get close to the crankshaft when doing layout work so components fit as they should during assembly. When asked about the traveling-column feature and how important it is to manufacturing the pump successfully, Mr. Williams replied, “If we couldn’t back the column out of the way and machine the frame in one setup, we’d have to redesign the whole product.”

However, the extra-long Z axis isn’t the only must-have feature of EWECO’s HBMs. The quill design produces and transmits a great deal of torque and thrust for heavy machining.

Spade Drilling Works The Quill
According to Mr. Williams, the balanced crankshaft and rigid, accurate frame allow precise alignment of gears, pinions and shafts. Yet, the real workhorses of the pump are its pistons, cylinders, valves and manifolds. Mud is a thick and abrasive material, so it naturally causes wear on cylinders and pistons. However, these components can be serviced in the field, whereas the valves and manifolds are not designed to be replaced on a regular basis. For this reason, they are made of either 4130 or 4340 steel, which resist wear. Manifolds can be as long as 48 inches and can have drilled holes as wide as 5 inches in diameter.

EWECO uses a spade-drilling process to make holes in these parts. Spade drilling requires substantial torque, and EWECO depends on its HBMs to deliver this high drilling force. For example, the three-speed gearbox on the HBA-135 is capable of generating nearly 3,000 foot pounds of torque. The lowest programmable spindle speed is 5 rpm. Using the higher gears yields a maximum 2,500 rpm. According to builder, the gearbox design allows the spindle to reach maximum torque throughout its speed range. The HBM’s 5.3-inch diameter quill is nitride hardened and ground to a mirror finish. This finish increases the amount of surface area in contact with the quill sleeve for greater rigidity.

The spindle quill can feed with a maximum of 7,000 pounds of force and reach a maximum depth of 27.5 inches. For holes too deep to complete from one side, the hole is drilled on the first side, then rotated and drilled on the second side. At EWECO, a mismatch where the holes meet is unacceptable, so the HBM must be accurate and precisely aligned. Mr. Williams reports that the HBMs meet this requirement, even under heavy machining loads.

The combination of the traveling-column configuration, extra Z-axis travel and high-torque/low-rpm capability makes the HBM a very flexible machine tool for EWECO. The company’s success with its new five-cylinder mud pump product line reflects the importance of this flexibility in today’s market. Flexibility is also the key to thriving in the future if and when market conditions change. As Mr. Williams points out, past experience has been a good teacher.

Being Flexible Helps Reach New Markets
The search for new sources of oil and gas hasn’t always been as intense as it is today. As recently as 10 years ago, the price of a barrel of oil was $11. During that time, no one was paying to explore for new oil because the market seemed to be flooded. When well drilling slowed dramatically as a result, EWECO relied on its flexible approach to manufacturing to reach markets that were not energy-related to support the business. In addition to oil well drilling, mud pumps can be used to dispose of saltwater and to remove flood water. Pumping cement is also a significant market for mud pumps because they are more reliable than equipment in use for this application. Also during this last drilling slump, EWECO expanded into industrial water blasting. Perhaps the most innovative application of the mud pump was in the field of horizontal directional drilling. This method is used to drill under rivers, highways or subways. It helps in laying pipelines and adding to communications networks when excavating the site would be undesirable.

Mr. Williams believes that keeping flexible machinery such as the HBM in his manufacturing base means EWECO can respond to similar opportunities as they emerge in the future, without having to outsource production of components.

Reaching Toward the Future
Markets expand and contract as a part of usual business cycles. The oil market is no exception. In 1979, a shortage of oil hit the pocketbooks of car and truck drivers. In 1999, a surplus of oil hit the pocketbooks of oil producers. No one is sure what lies ahead for oil and gas prices. No one doubts that a supply of oil that is easy to find as well as easy to extract is limited. Mr. Williams’ father, Ellis, predicts that the oil market will undergo a correction as it did after the shortage in 1979, bringing prices back to palatable levels. In whatever direction the oil market swings, it is clear that EWECO mud pumps will be pushing cutting tips deeper and in new directions, and that EWECO will be pushing its product lines deeper into other industries and into new applications.

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In many applications, gundrilling can be performed on standard vertical or horizontal machining centers. It does not always require specialized equipment. To perform gundrilling successfully, a standard VMC or HMC must provide sufficient coolant delivery and have sufficient Z-axis travel.

The relatively recent industry-wide standardization of through-spindle coolant allows standard machine tools to drill deep holes effectively in applications that require accurate placement, precise size and improved wall finish. In fact, gundrilling is worth considering any time the tool list specifies an aircraft length or other long-length drill.

Machining centers can accommodate two types of gundrills. The one-piece design is typically found in small-diameter applications of less than 10 mm and is made from a solid carbide blank. It provides superior strength, stiffness and tool life in machining difficult materials. The three-piece design features a brazed construction from a carbide tip, hollow V-shaped tube and shank. It is the oldest and most popular style of gundrill.

The three-piece gundrill’s popularity stems from the fact that it is easy to assemble from modular components, making nearly any diameter between 0.031 inch and 2 inches attainable. Generally speaking, operators are most familiar with the performance characteristics and torque limitations of this type of gundrill.

The relationships between pressure, flow and drilled diameter are critically important when gundrilling because of the inaccessibility of the tip deep within the part and the inability of flood coolant to help flush away chips. As in other applications, coolant reduces the heat-affected zone in the material, cools the tip of the tool and, removes chips from the hole. As the drilled diameter decreases, the required pressure for successful application increases. Coolant pressures can range from 150 psi to 1000 psi. However, as the drilled diameter increases, pressure becomes less important and flow rate becomes the greater concern. The required force to remove chips from inside the hole is based in part on the amount of area in which the coolant has to act. Typical coolant flows can be as little as 1 gallon per minute to as much as 10 gallons per minute.

Auxiliary coolant units are available to help older machines already fitted with through-spindle coolant meet today’s standards in pressure and flow. The positive-displacement type is among the most popular and durable on the market and it can be easily interfaced to virtually all controls. Located on the back of the spindle is a rotary union such as the one pictured above that is manufactured by Deublin Company (Waukegan, Illinois). The rotary union transmits coolant from the pumping system, through the spindle, to the tool. This coupling can be upgraded if necessary to meet new pressure requirements.

Another area of concern is the Z-axis travel limit. Because the tools can be very long, clearing the tool over the workpiece can cause “Z+ over travel” alarms. A good reference point for maximum length is the longest length that can be changed by the automatic tool changer. However, due to the fragility of the gundrill, using the toolchanger is not recommended. These fragile tools are generally hand loaded to prevent damage.

Another machine feature that can help a machining center perform gundrilling is spindle load or tool monitoring. During drilling, the tool tip will not be visible, and the normal visual cues that alert operators to trouble will be absent. The ability of the CNC to monitor torque and force loads is of great value because removing broken drills from workpieces can be a tedious chore, and the control can stop the tool before breakage occurs.
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The use of tapers has never been more important. Most toolholder designs use tapers because tapers provide good alignment and can be “locked” into position. In the manufacture of toolholders and spindles, the control of taper and size determines how well the machine can perform during its cutting cycle.

The two conditions most important in controlling taper are taper size and angle. Size is controlled by tolerance, and is, therefore, identical to a cylindrical ID or OD. Taper angle, on the other hand, can be controlled by at least three different factors: 1) included angle or angle per side; 2) taper per inch or per foot; 3) two diameters at specified datum locations.

Air gages effectively measure virtually all common types of dimensions and are particularly suited to checking such dimensional relationships. As an inspection tool, air gaging can measure many jobs more quickly, more conveniently and more accurately than other gaging methods. In the measurement of high precision hole conditions, for example, air gaging is unsurpassed for speed and accuracy. Also, when checking dimensional characteristics, air offers sufficient magnification and reliability to measure tolerances well beyond the scope of mechanical gages.

Also, air gaging is easy. Production workers do not require special training to use air gages. To check a hole, for instance, it is not necessary to develop skill in “rocking the gage” to find the true diameter: Merely insert the air plug in the hole, and read the meter. It is as simple as that.

How Air Gaging Works
Air gaging uses the principle of back pressure to determine the size of a measured part. According to the laws of physics, flow and pressure are directly proportional to clearance, and they react inversely to each other. Thus, the relationship between air pressure and the distance of a restriction (workpiece) to the air escape (jets) can be plotted on a graph. See line (a) as shown in Figure 1. As the distance between jets and work surface increases, the pressure decreases and the ratio becomes linear as represented by the straight section (b) in Figure 1. This straight portion of the curve can be accurately calibrated, and it represents the scale of the air gage.

For measuring taper in a production environment, few other methods can match the speed and performance of air, as multiple-circuit air jets can be placed in very small taper gages. Air taper gages are used throughout the process of machining, including:

* The inspection of new toolholders,
* the inspection of new spindles,
* the monitoring of used toolholders to ensure that they mate properly with the machine and
* the monitoring of the spindle to ensure that the toolholder is seating properly in the spindle.

Toolholders And Spindles
There are many types of standard toolholders, but the two most common are the CAT-V and the HSK. The NMTB and CAT-V are very similar and most frequently used. NMTB/CAT-V toolholders are external tapers, typically available in common sizes: 30, 40, 45, 50 and 60 (but others exist), depending on the size and capabilities of the CNC machine. Recently the HSK-style toolholder has also become popular for its high performance in high speed machining applications. Tooling sizes 32, 40, 50, 80 and 100 are commonly specified (but again other sizes exist). These numbers define both the gage line diameter and length. Both NMTB and CAT-V typically use a 7:24 taper while HSK uses a shallow 1:10 taper.

There are many reasons for the popularity of these toolholders. One advantage is that they are not self-locking, but instead, are secured in the spindle by the drawbar—an arrangement that makes tool changes simple and fast. They are also economical, because the taper itself is relatively easy to produce, requiring precision machining of only one dimension—the taper angle.

The toolholders must properly position the cutting tool relative to the spindle and, when secured in place, must rigidly maintain that relationship. The accuracy of the tapered surfaces on both the toolholder and the spindle is, therefore, critical.

If the toolholder’s rate of taper is too great, there will be excessive clearance between the two surfaces at the small end of the taper. If the rate of taper is too small, there will be excessive clearance at the large end. Either situation can reduce the rigidity of the connection and cause tool runout, which may show up on the workpiece as geometry and/or surface finish error. Taper errors may also affect the amount of clearance between the flange on the tooling and the face of the spindle, creating errors of axial positioning.

Three Types Of Air Tools
As the demands for precision machining and high speeds increase, manufacturing tolerances on spindle and toolholder tapers have gotten tighter. Nevertheless, both components are still subject to manufacturing inaccuracies and wear. In response, some companies with very high accuracy, quality and throughput requirements—particularly in the aerospace and medical fields as well as some automotive suppliers—regularly check the accuracy of toolholder tapers and the spindles of the machines using the toolholders. This is usually done with differential air gaging, which combines the necessary high resolution and accuracy with the speed, ease of use and ruggedness required on the shop floor. The most common type of air gage taper tooling has two pairs of jets on opposing air circuits and is designed for a “jam fit” between the part and the tool.

Jam-fit tooling does not measure part diameters, as such. Rather, it displays the diametrical difference at two points on the workpiece, as compared to the same two points on the master (see Figure 2). If the difference in diameter at the large end of the taper is greater than the difference in diameter at the small end, the upper jets will see more back pressure than the lower jets. This will reflect negative taper, or a larger taper angle. If the diameter difference at the small end is greater than the difference at the large end, the gage will read positive taper, or a smaller taper angle.

However, because a differential air meter displays diametrical differences only, it will not display the part’s diameter at either location. So, while this type of air tooling provides a good indication of taper wear and allows us to predict a loss of rigidity in the connection, it does not tell us anything about the tool’s axial positioning accuracy.

For that, we need a “clearance-style” air tool. The tool cavity is sized to accept the entire toolholder taper, while the toolholder’s flange is referenced against the top surface of the tool. This makes it possible to measure diameters at known heights (in addition to the change in clearance, as with the jam-fit type). An additional set of jets may be added, as shown in Figure 3, to inspect for bell-mouth and barrel-shape, two more conditions that reduce the contact area between the toolholder and the spindle.

There is a third type of air taper gage, which is a cross between the styles mentioned above. This is called a “simultaneous fit” taper gage. It is basically a jam-fit tool with an indicator that references on the face of the mating flange of the toolholder. This indicates how far the toolholder reaches into the spindle. So, while the air gage provides a reading of the taper angle, the indicator provides an indication of the size of the diameters. When measuring a tapered toolholder, if the taper diameter is too large, it will not go far enough into the gage. If the diameter is too small, it will drop further into the gage.

Given a basic understanding of how an air gage works, these types of tooling are easy to use. Mastering is simply a matter of inserting the taper master and adjusting the zero. Measuring is even easier: Just insert the part and take the reading. However, care is required, especially when handling heavy toolholders. Although air tooling is sturdy, it can be damaged.

Mastering Taper Gages
Air gages for taper tooling require taper masters. Toolholders are of particular interest, because the accuracy of the taper affects the quality of the parts manufactured with these toolholders. According to ANSI standard B5.10, V-flange toolholders are built with a specified rate of taper of 3 ½ inches per foot, +0.001/-0.000 inch. ISO standard 1947 defines a number of taper grades and establishes different tolerances depending upon both grade and taper length.

Regardless of which standard is followed, it is necessary to master the gage before it can be used to measure parts. The taper master is typically a more precise version of the part, but before it can be used to master the gage, it must be certified. ANSI’s 0.001-inch per foot tolerance seems easy enough to achieve until you look at the complexity of the inspection process. First, most toolholders are much shorter than 1 foot, so most gages actually compare diameters that are just 3 or 4 inches apart. Considering the 3-inch example, the part has to meet a gaged tolerance of 0.00025 inch (that is, 0.001 inch ÷ 4). Using a common 10:1 gaging rule of thumb ratio, the gage master should be accurate to 25 microinches, and the gage should resolve to the same amount.

To certify the master—again using the 10:1 ratio—will require a gaging system that has better performance then 2.5 microinches. This is easy to accomplish. A controlled laboratory environment is essential to achieve that level of accuracy. Certifying the master roughly replicates the production measurement process. The diameter of the master is measured at two known heights, and the slope or angle is calculated from the results.

Essential Considerations
The more you know more about your machining processes the better your tooling and spindles will likely perform. Air gaging can help fulfill that need. When specifying a taper requirement, always consider:

* What is to be measured:
-Taper angle?
-Diameters at certain locations?
-Taper and diameter?
* The length of the taper and possible location for sensing points.
* If the gage should be portable or bench-mounted.
* What the operator needs for a readout.
* Simple jam-fit designs provide measurement of taper angle.
* The addition of an indicator provides indication of taper diameter.
* A shoulder-style gage allows for independent circuits for taper and diameter measurement.
* A third air circuit can help determine if the sides of a taper are straight.

About The Author: George Schuetz, Director, Precision Gages at Mahr Federal Inc., is a regular columnist in Modern Machine Shop.
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Twin Disc, a manufacturer of marine transmissions, grinds shafts of all lengths, weights, shapes and sizes. According to the company, the only thing all these shafts have in common is precision—very close tolerances and unforgiving surface finishes. Flawed shaft production can result in transmission failure. Thus, Twin Disc strives to use the best grinding technology available. So, when a bottleneck arose from a labor-intensive shaft-production process involving multiple setups, the company invested in a new grinder equipped with a full B axis. Since then, it has consolidated the troublesome operation from three machines to one.

Based in Racine, Wisconsin, Twin Disc has been in business for more than 75 years making more than 30 different marine transmissions for pleasure craft, military vessels, tugs, pushboats and more. In fact, Allied forces depended on the company’s transmissions to drive some 40,000 landing craft loaded with troops and supplies onto beaches during the Normandy invasion and throughout the South Pacific during World War II. In addition to marine vessels, the company makes transmissions for mining industry trucks and for various military vehicles, including the Bradley armored personnel carrier.

The two plants in Racine have a combined 551,271 square feet of manufacturing space and about 400 employees. The company uses a total of 21 cells, 14 of which are manufacturing cells for milling, turning, grinding, drilling, finishing and other such operations. The others are used for assembly, process completion and so forth. The company performs all operations except heat treating in-house.

The drive shafts are produced in 10 different diameters with various tapers. The shafts range from 8 to 48 inches long, with diameters ranging between 0.5 and 10 inches. The company holds tolerances between 0.0002 and 0.001 inch and surface finishes from 10 Ra to 40 Ra. Materials include 1144, C1144, 4145, 4140 and 8620 steel alloys as well as some stainless. Order quantities range from a single shaft to 500 pieces.

The company had been looking for a process change in the production of transmission shafts. Two grinders were used to grind the straight ODs, and a third was used for plunge grinding tapers. Terry Andersen, grinding team leader, programmer and machine operator, says this was a slow, operator-intensive process. Shafts had to be refixtured from the OD grinders to the plunge grinder. To improve productivity, the company wanted a grinder with a full B axis to combine the processes in a single machine.

When the company began searching for a flexible grinder to do shaft work in one shot, everyone was “a little leery,” Mr. Anderson says. There weren’t many manufacturers to choose from, and certain shaft dimensions eliminated some right away. At one point, the company actually acquired a grinder with a full B axis. However, the machine wouldn’t hold diameter size or taper tolerance and was not consistent, leading the company to continue with the old method.

“There was another company that was just coming out with a full B-axis machine, and they maintained they could accommodate our specs, tolerances, surface requirements and shaft dimensions, but we decided against it,” Mr. Anderson says. “This was going to be their first machine of this type, and frankly, no one wants to be anyone’s guinea pig—especially when you couple this with our previous experience.”

Eventually, the company settled on the Kellenberger Kel-Varia cylindrical grinding system with the Heidenhain GRINDplusIT control. A key factor in the company’s acquisition of the machine was its ability to hold tight tolerances while grinding tapers. On many shafts, the taper is nothing more than a press fit. Most of the tapers’ surface requirements are 40 Ra, but some have an angle of 30 to 1, which is less than a 1-degree taper.

“We had to have a machine that could handle that kind of range of demand,” Mr. Anderson says. “It had to be flexible, agile, rigid, and above all, repeatably consistent in holding very tight tolerances.”

The machine’s hydrostatic guideways are designed to provide accuracy and avoid friction and stick-slip movement. It features absolute measuring in the B axis, incremental, distance-coded scales in the X and Y axes and a high-resolution C axis. The grinder can also be equipped with a second B axis for more dimensional stability and profile accuracy.

The B axis permits automatic positioning of the wheelhead at any angle. For positioning accuracy, it includes a precision worm gear and distortion-free clamping. A Hirth coupling, which indexes at 2.5 degrees, also contributes to positioning accuracy. The Kel-Set automatic grinding wheel measurement system enables automatic movements to the measuring ball and to the grinding system, and it stores position information to the control system. When swiveling the wheelhead into any angle, the system automatically accounts for the positions of the wheel edges. In addition, the option of interpolating the X and C axes allows grinding of non-round shapes such as polygons, free contours and eccentric forms. For various types of grinding operations, the machine can use universal, diagonal and tandem-type wheelheads.

The grinder’s Heidenhain control features a Windows 2000 operating system, a graphics editor, expanded grinding cycles, intermediate dressing at the push of a button, comprehensive tool management, several reference points for each grinding wheel, remaining-travel display and more.

“The Kellenberger not only met all our requirements, but it was a proven machine, so we didn’t have to worry about working the bugs out of a new design,” Mr. Anderson says. “It’s been very reliable, and most important, it holds tolerances and surface finishes with remarkable repeatability.”

Because the company runs as many as 1,200 different shafts, change-over and setup are very common. However, according to Mr. Anderson, the new grinder makes this easy.

“Depending on what’s involved, we can changeover from shaft to shaft in about 10 minutes, especially if we’re not changing centers, and it’s strictly a matter of moving the tailstock and changing the driver,” Mr. Anderson says. “If you need to change centers and drivers, then you may be up and grinding in 20 minutes or less.”

About a year after purchasing the first Kellenberger, Twin Disc bought a second. With the exception of a hydraulic tailstock to handle even heavier shaft work, the second machine is identical to the first. The two machines reside in a single cell, and one operator runs both.

“We’re able to run twice as much product as before,” says Gary Pope, plant manager. “One operator does two shafts at once, and they come off finished. We run these machines 6 days a week, 24 hours a day, and we’ve already seen improvements in productivity. The accuracy and repeatability couldn’t be better.”
http://www.mmsonline.com/articles/flexible-grinder-streamlines-drive-shaft-production.aspx

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“The thing to understand about machining composites is that you only get one shot,” says Jeffrey LeDuc, general manager of Reno Machine Company in Newington, Connecticut. Unlike a metal part, there is little or no possibility of repairing a part made from a composite material such as CFRP (carbon fiber reinforced plastic) if it is machined incorrectly. Adding to the pressure is the fact that a CFRP structure is considerably more expensive than a comparable metal workpiece by the time the part gets to the machine tool. Any crash or misstep during machining would not only scrap the part, but also would result in considerable lost expense.

Partly because the size of its machines, Reno is in a class apart from other machine shops in its region. The shop has an established history of working closely with area manufacturers relying on large composite parts. Most of this work relates to helicopter manufacturing, and most of that work has involved machining metal to make both the layup tooling and the machining fixtures for composites manufacturing. Recently, however, customers have been turning to Reno for machining of the composite structures as well. Now, of the two five-axis Henri Liné machines with 35 feet of X-axis travel in this shop, one of those machines is booked for a solid year with just composites machining work.

Because of all the activity, a particular part on one of these machines is now likely to get just one shot in another way, as well. That is, all of the machining for a particular part may need to be performed in just one rapid stop at the machine tool, before the tight schedule requires the next part in line to get its turn.

However, many of these parts include demanding machining tolerances that may need to be verified multiple times. Because of the value of the part, a critical milled feature is likely to be machined conservatively, then inspected to see how much stock remains to be removed, then inspected again after the finish pass.

Reno does not have a CMM big enough to perform this inspection for its largest composite parts. Even if it did, the shop would not want to spend time on transporting the large parts to and from the busy Liné machine. Instead, Reno uses the machine tool itself as a CMM, thanks to an “On Machine Verification” version of Delcam’s PowerInspect software.

When this software is coupled to the five-axis machine as it employs a spindle-mounted inspection probe, Mr. LeDuc says the software can generate inspection reports that are every bit as thorough as those of a CMM. To confirm that the machine tool can indeed inspect parts accurately, smaller parts are often verified with a CMM. The inspection software makes the five-axis machine tool dramatically more effective for machining high-value, tight-tolerance parts, Mr. LeDuc says.

One particularly critical part provides an illustration of the close working relationship between the shop and its main composites machining customer. A CFRP cuff that connects a helicopter’s main rotor blade to the center hub is sent to Reno two different times for machining. The shop does initial machining of features including a bore that receives a metal bushing. The customer inserts this bushing. Then, the part goes back to Reno to machine features that have to locate with respect to the bushing’s position. In other words, on this part, there are actually two different moments when the shop gets just one shot.

http://www.mmsonline.com/articles/composites-keep-a-big-machine-busy.aspx

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Vertical grinding machines have been available for some time. These machines typically fixture a workpiece in a chuck located in the base of the machine. A spindle then travels up and down and side to side to allow a wheel to grind various workpiece features. This design uses gravity to its advantage—the weight of the workpiece is directly supported by the machine’s base. Thus, it doesn’t require the large amount of clamping force that horizontal grinding machines need to chuck workpieces. That’s why verticals are commonly used for relatively short, heavy workpieces.

Emag Salach Maschinenfabrik GmbH is applying the vertical grinding concept in a new way for longer, shaft-type workpieces. (Emag’s U.S. headquarters is located in Farmington Hills, Michigan.) Its vertical design uses dual, opposing grinding wheels that cut simultaneously. The prime advantage is that the axial forces created by the wheels are directed toward each other, so they are canceled. According to the company, this vertical machine is an alternative to two- and four-axis horizontal grinding machines for smaller batches of shafts that have many bearing seating surfaces.

Vertical Advantages

The company’s VTC 315DS is said to be the first vertical grinding machine with the dual-opposing-wheel design. The two grinding spindles move in X and Z axes on independent, compound slides. Located vertically between the two spindles, the workpiece is secured from below by a fixed tailstock center and from above by a moveable work-head center. This provides the wheels with ample access to the workpiece to allow simultaneous grinding from both the left and the right.

During a cylindrical grinding operation, the highest cutting forces are the axial forces that are normal to the workpiece centerline. The axial forces can be three to four times greater than the tangential forces. On the dual-wheel machine, the axial forces are canceled because the wheels face each other. This allows shorter cycle times and enables the machine to grind thin, less stable workpieces. In addition, the counter-rotational spinning of the grinding wheels cancels out the grip torque created by the tangential forces (see the drawing on the right). This simplifies changeovers and eliminates the need for workpiece clamping equipment and drivers. Changeover is performed by simply raising the upper work head center and removing the workpiece. This short setup makes the machine particularly effective in grinding smaller batches of workpieces as long as 700 mm.

Because the machine design prohibits the use of an overhead crane for wheel changes, the company developed a fixture that has a receiver with an HSK-like taper. This rigid interface also allows CBN grinding wheels (recommended) to be used for in-feed, plunge-cut and longitudinal grinding in addition to grinding shoulders and radii. The machine’s base is made from Mineralit, a polymer-granite material that damps vibrations during these operations.

http://www.mmsonline.com/articles/a-new-spin-on-vertical-grinding.aspx

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Chinese manufacturing affects the Pittsburgh-area production facility of the FS-Elliott Company. The plant has changed significantly due to the growth of manufacturing overseas—though not in the way you might expect. Business is booming for this manufacturer. Ninety-five percent of FS-Elliott’s production is exported, with 75 percent of that going to China alone.

The company makes industrial air compressors, including the large compressors that feed shop air through plant-wide systems. As new production facilities of all types open in various parts of the world, they often get their air from a newly purchased FS-Elliott compressor.

These compressors are rarely off-the-shelf products. Supplying a sophisticated compressor system generally means guaranteeing just how much air the customer can obtain for a given amount of electrical power. Meeting these commitments calls for customizing the system, and that generally means machining carefully designed custom profiles into the compressors’ impellers.

In the past, these custom impeller profiles would have been machined through turning. Cutting the part in this way, with the tool hitting one impeller blade after another, might seem like the most extreme interrupted cut imaginable. Even so, the programmable movement and large X-Z travels of a CNC lathe provided an effective way to obtain the precise OD forms. To overcome the interrupted cut, impellers were filled with wax, allowing them to be machined as solid cylindrical forms. After machining, the wax would be melted out. The process was messy, but it worked.

This mess was just part of the reason why the plant recently adopted a new process—making a clean break from the old method in more ways than one. Thanks to a grinding machine from Max-Tek Superabrasive Machines that offers travels and programmability comparable to a lathe, the plant is now producing the impeller profiles through grinding instead of turning. No wax is needed. Less time is needed, too. The machining process is now so fast that it is difficult for the plant to keep this new machine busy.

Though the move from turning to grinding represented a fundamental change to the way a core component is made, the production process at FS-Elliott is new for reasons that go well beyond this change. Even the people are new. In 2004, the company let all of its production staff go, and restaffed the plant floor with approximately 110 new employees.

Insourcing, Too

Manufacturing manager William Turek hired all of this staff. The move was the result of FS-Elliott changing ownership. The employees of the plant remained attached to the previous owner because of a labor agreement. For the first year under new ownership, FS-Elliott leased its existing workforce from the previous owners. The arrangement was unsustainable, and the new owners ultimately resolved to make a clean break in this area, too. To Mr. Turek, who oversaw the massive change in staff, this was a challenging time. He watched a lot of experience go out the door. But the fresh start also represented a tremendous opportunity. He was free to implement entirely new processes and procedures without having to retrain existing employees and without having to make the changes gradually. Replacing turning with grinding was just one example. Even bigger changes have involved reconfiguring the layout of the plant and rethinking how to use the company’s various large machining centers. In addition, the plant has begun to take in production that once had to be performed outside—the machining of impeller “blanks.”

These raw impellers are made through casting or five-axis machining, depending on their size. The machined versions used to come from a small number of five-axis machining suppliers in and around the plant’s Export, Pennsylvania, location. Now, that machining mostly comes from the plant itself. One of the newest machine tool purchases here is a Hermle five-axis machining center.

Mr. Turek says having this capability in-house makes the plant even more nimble. Last-minute design changes are now much easier to implement.

Even better, the insourcing makes the plant less vulnerable. “What if a competitor—or even some unrelated company—ended up purchasing our main five-axis machining supplier?” he says. Owning this vital capability means that the capability cannot be taken away.

Wax Free

Machining custom profiles is the work that comes later for these parts. With the work now done through grinding instead of turning, many problems have been eliminated that were the result of the previous process’s wax. The mess was just one of these problems, but it was a major one. Lathes had to be torn down every 4 to 5 weeks for complete cleaning. However, impellers also had to be cleaned thoroughly, because melting alone was not enough to clear the wax away. Any small amount of wax that remained on the part could cause the impeller to fail one of its quality tests—its fluorescent penetrant test—because the wax would show up as a crack. The need for scrupulous cleaning therefore complicated an already time-consuming process.

Grinding overcomes these problems. Because the grinding wheel is big enough that there is no worry about interrupted cutting, no wax is needed to support the blades. In at least one case, the new machine created a new problem, but Mr. Turek was able to turn this into an opportunity as well.

The problem related to inspection. Each impeller has an odd number of blades. That means the impeller has no solid “diameter” along its profile. The wax gave the machined part a smoothly cylindrical form that enabled the shop to measure machined diameters with a micrometer. Now, with the wax taken away, how would the plant measure these parts?

For the sake of continuing to push what this plant can do, Mr. Turek chose to over-address the problem. He bought a portable CMM—a Faro measuring arm—not just because it could accurately gage the part without any need for wax (which it could easily), but also because he wanted to bring a measuring device such as this one in-house. He knew the instrument would be so useful in so many different capacities that it would easily pay for itself. First, however, he had to make it enough of a part of the shop’s standard process that employees would be forced to use it and grow accustomed to it.

Now, machined impellers are inspected in dramatically greater detail with the Faro arm than the micrometers ever would allow. In addition, the same device has been applied to setup—speeding this part of the process as well. Operators now use the arm to quickly determine whether each workpiece has been positioned correctly on the grinder.

Ready And Waiting

Machining an impeller profile is now a significantly faster operation. The speed comes not only from the steps that have been eliminated because wax is no longer used, but also because of the raw improvement in cycle time. Parts that might once have taken as long as 7 or 8 hours to turn can be ground in 25 minutes, Mr. Turek says.

Such a marked speed improvement has led to a sight that this busy plant is not all that accustomed to seeing: an idle machine tool that is waiting for work.

In fact, the grinding machine spends so much time waiting for work that it does not even need a dedicated operator. Matt Fulton, the operator who appears in photographs on these pages, actually spends most of his time tending horizontal machining centers. Operating this particular grinder is enough like operating a lathe that separate training and specialized operators are not required.

That’s good, because the new process churns through impellers so fast that there is rarely enough work to fill a full shift. Therefore, the plant applies a workflow strategy to this machine that is different from the strategy used with other machines. On this machine, it allows work to pile up.

That is, in order to use the grinding machine efficiently, the plant waits for at least three or four different impeller workpieces to accumulate. Then, an operator makes a stop at this machine to quickly process this backlog, before leaving the machine again to return to other work.
http://www.mmsonline.com/articles/replacing-turning-with-grinding.aspx

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