Double‐Rough Pinch Grinding Cuts Cycle Time in Half

Manufacturing’s “need for speed” is truer today than in the past, as customers demand faster turnaround for products. And if one manufacturer cannot accommodate, the customer will find another company that will. Therefore, many machine shops are inventing processes — or investing in new and more efficient equipment — to enable

The double-rough cylindrical pinch grinding process is shown in both photos. However, the top photo shows the wheel positioned at 10 degrees. Here, the wheel almost moves in line with the part axis. The wheel can grind more efficiently if it advances into the material in such an axial movement. However, at 90 degrees (bottom photo), the wheel can perform movements for back angles and recesses, but more vibration will be introduced compared to the 10-degree position. According to Rollomatic, the 10-degree position should be used if the profile allows. Photo credits: Rollomatic Inc.

faster production.

This is true for tooling manufacturers as well. One process that can help them do so is an alternative pinch grinding process called double-rough pinch cylindrical grinding. Not only does the new grinding process cut cycle time in half compared to traditional pinch grinding but it also generates less heat and is a quieter process, to name some advantages.

This double-rough pinch grinding method was designed by Rollomatic Inc. specifically for blank preparation of carbide cutting tools and T-slot cutters. The process has been integrated into the company’s ShapeSmart NP50 pinch/peel grinding machine, which was originally developed in 1996.

The method differs from traditional pinch grinding that uses a leading roughing wheel to remove most of the material, which is then closely followed by an opposing finishing wheel to provide a fine finish. Both wheels oppose each other during simultaneous grinding, therefore counteracting their pressure on the part. Conversely, during double-rough pinch grinding, both grinding stations are equipped with diamond wheels with a grit size for rough grinding. These two roughing wheels are synchronously run, but the leading wheel does most of the material removal. The other wheel cleans up the material left from the first wheel. The second wheel’s lag distance depends on the position along the profile because the double-roughing process has been specifically developed for the necking of tool blanks.

The grinding spindles play an important part of the process as well. The NP50’s synchronous direct‐drive spindles each have a 19-hp peak with a synchronous motor that provides constant speed during operation. The torque curve is highly efficient as well, according to Rollomatic. The rotational force of the synchronous motor is not reduced with higher rpm.

The efficient synchronous spindles on the machine are also beneficial because they run at only a 35% power draw or less. As a result, they do not release any heat into the machine or into the grinding process. They also are said to operate much quieter, even under load, compared to their induction motor counterpart.

Case in Point

Rollomatic suggests this grinding method is best suited for carbide and hardened steel workpieces. These materials’ hardness and heat resistance are said to make them the best choices for grindability.

For example, on a test production run of 100 pieces of solid carbide blank with a shank diameter of 5/8 inch, 0.400-inch neck diameter and 2.25-inch neck length, double-rough pinch grinding reduced cycle time to 5 minutes and 5 seconds, compared with a cycle time of about 10 minutes with the conventional rough/finish pinch grinding, according to the company.

This solid carbide T-slot blank was ground using double-rough pinch grinding technology. On a test production run in the ShapeSmart NP50 pinch/peel grinding machine using double-rough pinch grinding, cycle time without loading/unloading was 5 min. and 5 sec.

Acceptable Finishes, Improved Repeatability

Double-rough pinch grinding can achieve a surface finish of 12 to 32 microinches compared to 1.2 microinches using a finish diamond wheel.

The repeatable process of this grinding method is another advantage. Rollomatic says an operator can set up a grinding job without having to continuously and meticulously dial in optimal feeds and speeds.

The technology’s repeatability also enables long-batch production without the need to frequently redress grinding wheels. Roughing wheels usually have better corner retention compared to the finer grit finishing wheels, the company says.

With all the efficiency benefits that double-rough pinch grinding offers, there are even more capabilities that are available on the NP50 grinding machine that enhance productivity.

Although the machine offers this double-rough pinch grinding technology, rough and finish pinch grinding can still be performed on the machine. Also, options such as part measurement and automatic loading units are available.

If in-process part measurement is important to an application, Rollomatic offers a Marposs diameter gage as an option on the machine. The unit measures the diameter in one place along the axis of the tool, and the feedback signals the machine to make an automatic wheel position compensation. According to the company, this correction is useful in cases of ambient temperature changes and grinding wheel wear. The gage can also be used to probe flats and preset the circular position of the part according to the flat surface.

The ShapeSmart NP50 pinch/peel grinding machine not only does traditional pinch/peel grinding but also has been upgraded to use the double-rough pinch grinding technology. Double-rough pinch grinding cuts cycle time in half, improves surface finish and also produces less heat and noise.

Automated loading units can also be integrated into the standard NP50 machine. A three-axis, high-speed automatic pick-and-place tool loader has been developed by the company with rapid setup speed in mind. It uses pre-calibrated cassettes and a gripper design that enables holding different diameters without having to reset the gripper positions.

Rollomatic | rollomatic.ch/en