Why You Should Take Another Look at Shrink-Fit Tooling

First, A Brief Overview

Shrink fitting uses heat to clamp the cutting tool into the toolholder.

A machine using an induction heating device or hot air heats the outside diameter of a toolholder, expanding the inside bore, which starts slightly smaller than the cutting tool shank’s outer diameter. An adjustable stop disc ensures the toolholder isn’t overheated. A cooling sleeve containing circulating cold water is then placed over the assembly. As the assembly cools, the toolholder contracts around the entire cutting tool shank.

The result is an extremely tight, 360-degree friction fit with a tremendous amount of gripping torque, up to five times stronger than other friction-fit toolholder options. Total indicator readings (TIR) are around 0.00012-inch at three times the cutting tool diameter. Haimer, for example, guarantees less than 3 microns runout at 3xD with its shrink-fit chucks.

The entire process typically takes less than a minute: 3 seconds to 5 seconds to heat up and 30 seconds to 60 seconds to cool down. Some Haimer machines accommodate multiple toolholders simultaneously, effectively making tool change time 5 seconds per holder.

Shrink fit is considered one of the best toolholding methods for high-performance machining. Metal mold and die makers were the first to adopt the technology because they need a slim nose and long reach. However, today virtually any metal fabrication and metalworking processing facility may use shrink-fit tooling.

Shrink-Fit Cost/Benefit Analysis

Shrink-fit machines start at around $5,000. They also require additional power, adding an ongoing expense. While that may scare off some shops, the technology provides a quick return on investment by increasing overall process efficiency.

“The answer lies in the toolholder assembly’s performance benefits,” says Haimer USA President Brendt Holden. “Setup consistency is the best improvement. Because setup is the same from operator to operator, a shop can confidently predict  tool life. Also, in most cases, removal rates increase because of better balance, lower runouts, and solid gripping torque.”

A shop would have to spend twice as much on high-precision collet, milling, or hydraulic toolholders to get the same benefits. Tooling up two machining centers with a shrink-fit machine and shrink-fit toolholders costs the same as tooling up two machines using traditional toolholding – and, once installed, a shop’s other machines can use the technology to improve other operations. In addition to providing tight tolerances, shrink-fit tooling increases metal removal rates, results in less runout, and speeds up tool changing.

“These three benefits greatly assist any shop’s production,” Holden says. He estimates a high-end shrink-fitting system pays for itself within six months.

Shrink-fit extensions also enhance flexibility. For example, when machining deep cavities, shrink-fit extensions can be placed into standard shrink-fit chucks to increase gage lengths with minimal runout.

A shrink-fit toolholder is a sealed system by design. Therefore, shrink fitting also eliminates the chance that contaminants will compromise runout accuracy by getting into the toolholder’s bore during machining.

Some machinists think shrink-fit tooling complicates setup, but the reality is the opposite. Shrink-fit holders are the fastest and most consistent way to clamp cutting tools. In 5 seconds to 10 seconds, the tool is changed in a process that’s done the exact same way from operator to operator.

“There are no variables in the assembly setup whether you’ve been setting up tools for two weeks or 20 years – the cutting tools go in and out the same every time,” Holden says. This leads to consistent setup, with translates to consistent part production and reliable tool life.