Durable Tooling Cuts Cycle Times for Tough Turn-Peeling Job

Weingärtner paired a turn-peeling head on its Vario⁺ 700 machine tool with nine roughing inserts and one finishing insert, all using Kennametal’s KCU25B carbide grade. As tool failures or large drops in tool life can damage both the workpiece and the head, machining needed to be completed within a single setup with no tool changes. All images courtesy of Weingärtner.

Turn-peeling almost 60 millimeters of austenitic stainless steel 1.4435 from a part 3,900 mm in length is already a demanding task. Doing so without a tool change is nearly impossible. But a customer of Weingärtner, an Austrian OEM of machine tools for complex, rotating components, recently came to the company with this task.

While Weingärtner was able to consult with the customer and offer one of its Vario⁺ 700 machines to tackle the job, most tooling it tried could not meet the tool life requirements. In the end, the OEM partnered with tooling company Kennametal, whose KCU25B grade tooling proved durable enough to last through the whole machining process — and then pushed the process further.

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The Turn-Peeling Challenge

Daniel Weber, a process researcher in Weingärtner’s software development division, says the company prides itself on complete solutions, with customer consultations, a catalog of modular machines, an in-house CAD/CAM system (WeinCAD) for helical components, service and more. So when the customer who had purchased the Vario⁺ 700 with a turn-peeling head to produce 60 progressing cavity pumps needed to deliver parts before it had finished preparing its facility to house the new machine, Weingärtner stepped in to produce the parts and design the machining process.

Weingärtner’s specialized WeinCAD CAD/CAM software provided a simulation method for helical components like the pump rotors, helping the OEM test its process solution without risking the turn-peeling head.

The parts would be pre-turned from stock to 160 mm in diameter and 3,900 mm in length. The main turn-peeling operation creates an eccentric contour on the pump rotor, with a final diameter of 100.5 mm. Turn-peeling would engage the part in a staggered sequence of several roughing inserts and one finishing insert to promote short, easily broken chips that would not interfere with the tool during the 150-minute cycle time. Creating the eccentric shape also required both interrupted and continuous cuts, as well as an off-center position for the turn-peeling head, a circumstance which made access to the head difficult and would push tool changes to about a half-hour each. Tool changes would also affect surface finish, even under the best circumstances, when a tool failure or large drop in tool life didn’t damage the workpiece and peeling head.

As such, cutting tools and inserts would need to last for the entirety of the cycle time for each part — a challenge made more difficult by the part’s austenitic stainless steel 1.4435 material. This is a tough material with poor thermal conductivity and a tendency to work harden, factors which place strict demands on the cutting tool. Many of the cutting tools Weingärtner tested were unable to meet the tool life requirements of the job, so the machine tool OEM partnered with Kennametal to find tooling that would meet the needs of this high-requirement job.

Each rotor Weingärtner and its customer produce undergoes pre-turning to a 160-millimeter diameter before entering the Vario⁺ 700 for turn-peeling. The process removes almost 60 millimeters of material all along the part’s 3,900-millimeter length.

A Solid (Carbide) Solution

After analyzing cutting data from Weingärtner and adjusting some geometries, the Kennametal team recommended its KCU25B carbide grade. This grade uses the company’s three-layer KENGold PVD coating, which Kennametal says improves resistance to thermal deformation, edge wear and general wear, to improve tool durability.

“The tool life was impressive right from the start, the surface quality was consistent and chip control was reliable,” Weber says, noting the tooling was able to reliably meet the necessary 150-minute tool life. For the application in question, Weingärtner paired its turn-peeling head with nine roughing inserts operating at an axial depth of cut of 5.5 mm and one finishing insert operating at an axial depth of cut of 2.0 mm.

Weingärtner achieved surface finishes of a 2.2-micrometer Ra and a 9.5-micrometer Rz with these tools, a result which the company says reduces the amount of grinding necessary in later manufacturing stages. The tools have also proved durable enough that Weingärtner and its customer can use more aggressive cutting parameters than expected. As Markus Pleyer, Kennametal’s sales engineer for the project, says, “By optimizing the process, we reduced the machining time from 150 to 126 minutes — with consistently excellent results.”