All stages of manufacturing play an important role in producing high-quality components, and tool holders have helped many manufacturers deal with the tough challenges facing the aerospace industry.
Today's aerospace industry is facing several toolholder challenges - difficult material to machine, sub-par metal removal rates, and cumbersome components that require long, awkward prop overhangs. In these cases, toolholders must perform flawlessly and provide strong clamping force, high precision and vibration control, as failure of a single toolholder at any stage can lead to huge losses in time and money in an aerospace factory .

To avoid this outcome, many aerospace factories replace other popular toolholder systems that use thermal or hydraulic system functions with mechanical toolholder systems. The advanced mechanical tool holder system not only provides a high level of clamping force, but also provides the best possible vibration damping for extremely low TIR rates for improved tool life and improved component surface finish.

One of the main reasons aerospace factories choose mechanical systems is straightforward: They experience multiple failures, often due to tool pullout, vibration, or runout. For example, we can imagine that a typical aerospace factory with a JIT distribution environment has converted a week's worth of machining time into a giant aircraft wing spar. Then, at the end of the machining process, the milling cutter is withdrawn from the tool holder, and the aircraft spar has changed by an inconspicuous amount of 0.060".

For example, it's not uncommon to machine a large aerospace component from a $100,000 piece of titanium stock that's already worth $500,000 by the time it's three-quarters finished, so apart from the wasted machining time In addition, if the tool is withdrawn at this point, it will cause huge losses.

For example, it's not uncommon to machine a large aerospace component from a $100,000 piece of titanium stock that's already worth $500,000 by the time it's three-quarters finished, so apart from the wasted machining time In addition, if the tool is withdrawn at this point, it will cause huge losses.

Prevent the tool from pulling out

In an effort to prevent cutting tool pullout, aerospace factories tend to take a do-it-yourself approach. These home-made solutions include EDM machining holes in the tool so that drive pins can be inserted into the holes to hold the tool in place.

While mechanical toolholder systems offer incredible control, moldmakers continue to aggressively develop mechanical systems that provide greater security by locking the tool to prevent it from pulling out.

"With systems that can change the shank of a cutting tool, toolholder manufacturers often develop a patented system and agree to cutting tool companies to modify their cutting tools for a particular toolholder system."

There are also other locking systems that use special ER collets to increase length. This extra solid part will have a nub or pin that will fit into the groove of the cutting tool as the tool will turn to the back of the fixture. The end position of the locking system groove is very reliable.

The disadvantage of this is that the cutting tool flute ends are rarely straight, so there is no secure receptacle when the tool is mated due to the presence of a typical taper at the end of the tool. For maximum holding force, the entire collet must grip the cutter, but since there is a solid part on top of the collet, only the back of the collet needs to be clamped.

A special threaded insert or key is used as opposed to a label on the shank or a special groove pattern that is ground, eliminating the need to change the tool. As long as the shank has a common standard Weldon-type flat, the factory can use any off-the-shelf tool.

To lock the cutter in place, a small insert for the cutter system is placed on the Weldon-type flat surface of the cutter. The bottom profile of the insert mates with Weldon-type flats, and its exposed threads mate with the internal threads of the PG collet. The user holds the insert in place while sliding the tool onto the collet. The collet is spun so that its threads fit the insert, and everything is done to tighten the tool onto the collet. The collet assembly of this cutter is pressed into a powRgrip cutter system, and a special external nut is tightened to the carrier for added safety of extraction.

According to McHenry, the aerospace factory has been working on making tool life longer. When machining special materials for turbine blades, for example, getting a few extra minutes of cutting time, or even using one cutting tool to machine an extra part, may seem like insignificant benefits, but they all mean a cost significant reduction and time savings. Additionally, many tools used in aerospace are expensive and often cannot be resharpened after dulling, so longer tool life in these cases can reduce tool cost.

Maximizing life with today's advanced tools depends largely on the toolholders they attach to the machine tool spindle. As machine tool spindle speeds and feed rates continue to increase in aerospace factories, the ability to dampen toolholders becomes a more important factor. If the shank is better controlled or dampened, the TIR of the shank will be tighter. A tighter TIR on the shank will help increase tool life, as well as improve part accuracy and surface finish.

Mechanical tool clamping systems can provide TIR ratings down to about a few microns. A powRgrip tool, for example, ensures concentricity (TIR) with less than 3µ (0.0001") deviation for tool lengths up to 3xD (diameter), and less than 10µ (0.0004") repeatability before length adjustment.

Greater vibration damping will be achieved due to the functional contact surface between the tool holder and the collet. Such tools have better vibration absorption than non-mechanical systems such as heat shrink tools.

Vibration arises from the cutting tool, or even from the fixture system that takes the machined part - through the cutting tool, into the tool holder system, to the machine tool spindle, and back to finish machining the workpiece surface. Vibration occurs because vibration cannot be absorbed anywhere along the spindle tool post interface.

The tooling system absorbs vibrations by creating what McHenry refers to as material fractures. The process of absorbing vibration starts with a cutting tool, which is mainly made of high-speed steel, carbide and cobalt, and each material has its own vibration frequency or harmonic. The cutting tool is held in a collet, also made of a special type of steel, and the cutting tool is inserted into a tool holder made of a different type of steel.