New Gains in Grinding Pinions

In building a machine that completely grinds pump pinions in a single clamping Junker presents a unique production technology, and the ability to replace three machines with a single unit.

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The demand for lower costs and higher flexibility are shaping modern production more than ever before. Mechanical engineering companies are in turn required to develop ever more advanced, flexible and economical machines. Erwin Junker Machinery—headquartered in Germany, with its U.S. location in Elgin, Illinois—attempts to meet these challenges every day. As an example, since 1985 the company has been promoting its QUICKPOINT CNC OD grinding process, which through punctiform contact with the workpiece achieves a far higher chip removal rate than conventional grinding methods. Junker has developed high-speed grinding with CBN into a key area of expertise, which contributes significantly to the company’s high-tech reputation. The grinding technicians at the company’s Technology Center in Nordrach, Germany, continue to employ their expertise to further develop this world-renowned grinding process.

One of the applications they’ve been working to refine is for pump pinions—grinding the entire outer contour, shoulders, radii, and taper to final quality. In building a machine that completely grinds pump pinions in a single clamping, Junker presents the pump manufacturer sector with a unique production technology. Conventional grinding required three different machines in order to fully grind pump pinions. Now all a manufacturer needs is one machine.

Complete Machining
The QUICKPOINT concept involves removing all of the cutting stock at the fastest possible feed rate in a single pass and at extremely low cycle times using a CBN grinding wheel only a few millimeters wide. The most beneficial features of the QUICKPOINT process include its high chip removal rate, extremely precise workpiece geometry, uniform dimensional and surface quality, narrow tolerance ranges—ultimately due to CBN—minimized grinding tool costs, high availability, and significantly shorter production times. Product quality with respect to axial runout, roundness, angularity, parallelism, and cylindricity is optimally improved by the QUICKPOINT method of complete grinding in a single clamping.

This grinding process uses an abrasive wheel just a few millimeters wide to carry out all machining steps in a single clamping. This means that all operations are performed on one machine. The advantage is good concentricity and improved roundness, cylindricity, and angularity. All this is made possible because the grinding process requires no workpiece carriers.

In a recently completed project for a well-known pump manufacturer two plunge-cut grinding machines were replaced by just one QUICKPOINT. The machining task was as follows: external cylindrical grinding, radius grinding, and shoulder grinding to final quality in a single clamping (see Figure 1, positions 1-5) in a completely automatic production process. The following qualities were achieved to the complete satisfaction of the customers:

• Roundness: < 0.0015 mm
• Concentricity on outside diameter:
< 0.0035 mm
• Axial run-out: < 0.005 mm
• Straightness: < 0.003 mm
• Angularity (at pos. 3): < 0.0030°
• Parallelism (pos. 1/3): < 0.004 mm
• Pinion width tolerance: < 0.010 mm
• Surface quality: Rz < 3.0 µm

The project afforded the customer with significant benefits including the first part being a good part, random and flexible production, 25-percent lower unit costs, low manpower operation, and retooling times of less than one minute. The rejection rate is practically reduced to zero since after retooling the workpiece is automatically pre-ground, measured, and finish ground. The workpiece data is stored in the PLC and provides the machine with a reference for further production. Random production within a workpiece family can be performed without retooling thanks to the automatic workpiece recognition function. Add to this a completely automatic loading system connected to a host computer, and the machine practically runs itself.

Here’s how it works: the host computer, which is connected to both the machine and the loader, manages a complete list of workpieces to be machined in sequence. The individual jobs are imported by the scanner, and the information is then transmitted to the loader and machine for processing. All of this happens automatically and with minimal manpower.

Due to the narrow grinding wheel and its point-sized contact area with the workpiece, the QUICKPOINT method also enables highly flexible production of many different workpiece geometries and batch sizes, resulting in retooling times of under a minute. The long service life of the CBN abrasive contributes to minimal secondary processing times. In this way the productive utilization ratio—i.e. the technical availability of the QUICKPOINT grinding machine—amounts to up to 95 percent, as determined according to CDI 3423. All these benefits result in unit costs that are up to 25 percent lower than those of the competition.

The Concept

The grinding process developed by Junker has become particularly well established on the market in the machining of automotive components. One advantage is the low grinding forces; QUICKPOINT means high-speed OD grinding with only punctiform abrasive contact in the finish-grinding area, using a low-wear CBN or diamond wheel only a few millimeters wide. The tilt of the grinding body axis relative to the horizontal workpiece axis creates a relief angle that reduces the contact line to a contact point. This significantly reduces the grinding forces. Due to these extremely small radial and axial grinding forces, work can be performed without special workpiece carriers. This means that the workpiece is only clamped and driven between centers.

The QUICKPOINT allows the operator to completely machine right and left shoulders, cones, chamfers, radii, grooves, faces, and multiple edges at both ends of the workpiece, all in a single clamping and without changing the grinding wheel. Typical workpieces include gearshafts, drive shafts, camshafts, engine valves, and pump shafts. Thanks to the high cutting speed of up to 140 m/s, just about any materials can be machined including steel, aluminium, carbide, and powder metal materials, as well as special materials such as industrial ceramics, glass, plastic, or titanium. Manual, semi-automatic, and completely automatic loading systems can be modularly docked to each model in the series according to individual customer specifications. The QUICKPOINT series is modularly designed, which means that a version can be found for practically any application. The following section lists the individual machines available that utilize these technologies.

The Lineup
QUICKPOINT 1000: The machines in this series—with a center height of 100 mm, a clamping and grinding length of 150 mm, and a grinding wheel diameter of 350 mm—are suitable for the complete grinding of small, rotationally symmetrical parts weighing up to 5 kg. The 1000/10 version with a permanently mounted grinding spindle and an abrasive is designed for productive external cylindrical grinding, single-sided shoulder grinding, and plunge-cut grinding. Using the 1000/20 fitted with a grinding spindle, cones, and partial right and left shoulders can also be ground with the QUICKPOINT method. The third version, with two offset abrasives, also allows the unlimited grinding of right and left shoulders.

QUICKPOINT 3000: Particularly universal, this series features a 150 mm center height, a 500 mm clamping and grinding length, and a grinding wheel diameter of 350 mm, and it can be used for workpieces weighing up to 15 kg. In addition to the versions already mentioned there are also the 3000/40 and 3000/60 versions. The former has a grinding wheel that swivels 180° and 15° at the work level. These machines can therefore grind the complete length of a workpiece up to the ends, and right and left shoulders without any limitation. The 3000/60 version is fitted with three swiveling grinding spindles offset by 120°. Thus, for example, outer diameters, plunge/relief cuts, or threads can be machined on a workpiece in quick succession in a single clamping. It is especially due to this sort of complete grinding that production facilities in the automotive industry, and their suppliers, can significantly minimize production times while increasing product quality.

QUICKPOINT 4S and 4L: The Platform 4 machines are each available in 4S and 4L versions. The 4L is also available with two carriages. Thanks to the wide variety of wheelhead versions, the new Platform 4 enables the realization of complex grinding concepts tailored precisely to the customer’s workpiece. In addition, due to the use of two grinding carriages it is also possible to machine workpieces in parallel in the future, which almost doubles the output quantity. The Platform 4 is intended for workpieces with a maximum clamping length of 750 mm and a maximum workpiece weight of 130 kg. For this reason Platform 4 represents an interesting concept for a multitude of sectors, from the automotive industry and suppliers all the way through to mechanical engineers, the electrical industry, and environmental technology. Platform 4 supplements the already existing Evolution² platforms by Junker, also providing customers with the usual basic benefits such as an identical guide system, a large number of identical parts, and a uniform, round cover shape with the EJ-OP operator panel. Evolution² increases the output by reducing cycle times, which is achieved by means of shorter and superimposed travel within the machine. Another customer benefit is the compact design, as this reduces the footprint.

QUICKPOINT 5000: With this series users can also benefit from the advantages of the QUICKPOINT process for workpieces meansuring up to 1000 mm in length and up to 280 mm in diameter and weighing up to 130 kg. The machines permit fast and flexible adaptation in machining parts from large workpiece families, as well as small and medium batch sizes. This large series is available as a 10, 20, 40, 50, or 60 version.

QUICKPOINT 6: The Platform 6, with its two S and L versions, has grown to include the new 6 XL. This version is intended for large workpieces with a maximum clamping length of 3,000 mm and a maximum workpiece weight of 300 kg. This includes parts used in railways, for example, as well as wind turbines—shafts and axles—or ship drives. All the Platform 6 machines can be provided both as single-carriage as well as two-carriage versions.

Minimizing Costs and Complexity
With all three series, users benefit from the largely similar design of the machines. For instance, all input and information go through the operating platform known as the Erwin Junker Operator Panel EJ-OP. Its benefits are the graphical display, interactive processes for programming and operation, reduced training requirements, and fast retooling and setup. Once trained, employees can operate all QUICKPOINT machines from all five series or platforms. In addition, the same design characteristics of all three series ensure high accuracy and minimal setup times. This includes the patented three-point mounting system for abrasives and for sensors and drivers. These are thus clamped without complex adjustment for an axial runout accuracy of approximately 1 µm. The automatic balancing system integrated in the abrasive holder provides optimal smooth rotation, even at high speeds. For complex grinding tasks, Erwin Junker Machinery produces customized grinding solutions to fit its customers’ needs and criteria.