Time To Wipe Off Some Machining Costs
Wiper inserts should be examined: Never overlook any chance to save on machining costs. In 1959, I would have loved to have opened a container and selected a wiper insert, instead of spending a long time on a manual tool grinder.
Standing on the foredeck of the preserved battle cruiser HMS Belfast under the 6-inch barrels of the ship’s forward turrets, I think about a machine shop at an electrical lamination works. Would you believe there is a connection between the two?
The connection is not the electrical laminations in the motors driving the ammunition hoists. But odds are the plant where I spent the first 6 months of my apprenticeship produced the laminations.
The connection was talking with Sandvik Coromant about wiper inserts at the company’s press function in the admiral’s boardroom. During the conference, the Swedish company gave a business and technical overview of the last fiscal year.
How does the lamination works fit in? Once, for an apprentice job, I was asked to produce lamination press tool dowels. After turning them, I could not find spare capacity on a cylindrical grinder.
A toolmaker took me back to the lathe. He picked up a high speed steel tool bit (there were no carbide inserts in that factory in 1959), then he went over to a tool grinder and ground a tool bit with a very shallow nose radius. We came back to the lathe, loaded a turned dowel and produced a mirror finish that was far superior to what could have been achieved on a cylindrical grinder.
Now, more than 40 years later, I find myself back on the subject of wiper tools. If you look in literature from companies such as Kennametal Hertel, Sandvik Coromant, Seco or Walter and, I daresay, some Japanese tooling suppliers, you will find wiper inserts.
Sandvik Coromant describes its wiper inserts as having a modified radius for improving finishing operations. The ongoing development of carbides and coated carbides, plus some fine tuning of the cutter geometries, have produced the added bonus of doubling the feed rates of roughing and semi-finishing operations while achieving the specified surface finishes. For example, the Coromant-WR insert is designed for relatively high feeds and takes a satisfying 6-mm depth of cut. Sandvik Coromant points out that the main influence on any turning operation time is feed rate. The operator can nearly halve cutting time by doubling the feed rate. And, if the material allows it, the wiper insert will eliminate a grinding operation.
Another tack is that the wiper insert, as Walter says about its Wiper PF and PM products, provides a better surface finish, at the same cutting parameters, as a conventional turning insert. Or, as said above, you can double the feed rate while maintaining existing surface finish. Sandvik Coromant also says a wiper insert can last 20 percent longer than a non-wiper type. Naturally, it depends on the machinability of the material being cut.
Another benefit of wiper inserts is reducing chatter, the result of tool or workpiece vibration. Turning thin-walled components often produces this effect. Seco offers its W-MF2 wiper inserts, which have a vibration-damping effect on the turning operation as a result of much more widely distributed cutting forces at the cutting edge.
It is worth asking tooling suppliers about wiper inserts for cutting steels up to 65 Rockwell. Whether or not you try wiper insert technology depends on your own philosophy about cutting tools procurement. Any increase in insert procurement cost has to be balanced against the possible elimination of a grinding operation. Any reduction in machine setup has to be beneficial, when you think about production inventory and setup costs. Perhaps the doubling of feed rates has to be taken into consideration in terms of the overall cost of when the component is sitting in the machine tool. The removal of 1 or 2 seconds from a 5-minute floor-to-floor time might not be worth the extra tool in the turret.
Even so, wiper inserts should be examined: Never overlook any chance to save on machining costs. In 1959, I would have loved to have opened a container and selected a wiper insert, instead of spending a long time on a manual tool grinder.