Hot Air Acutates Shrink Fit Tooling

Shrink fit tooling is an increasingly popular toolholding system for high speed machining and other applications where minimal runout and good balance are required.

Article From: 5/15/1998 Modern Machine Shop

High spindle rotational speeds require better-balanced tools. The faster a spindle rotates, the less tolerant it becomes for out-of-balance conditions.

Shrink fit tooling is an increasingly popular toolholding system for high speed machining and other applications where minimal runout and good balance are required. It's competitive with collets and hydraulic chucks as a very accurate and balanced method of maintaining concentricity between a cutting tool and holder.

There are several shrink fit processes on the market. Each operates using an input of heat to expand the bore on a toolholder.

A size matched cutting tool is then inserted into the bore. As the toolholder cools, the bore contracts securing the cutting tool.

With shrink fit tooling, expansion and contraction of the toolholder bore is uniform. The cutting tool is firmly gripped over the entire area within the toolholder bore. Precision machining of the toolholder bore creates concentricity between the cutting tool and holder hence the use of these tools in high rpm applications.

The underlying principle behind the Marquart shrink fit tooling system is to use a minimum amount of heat to expand the toolholder body. Hot air is used in this process to accomplish controlled heating.

Marquart's shrink fit system is hands-off. Their toolchanger unit mounts on a tabletop. Tools are mounted in a vertical orientation—pointing either up or down—to take advantage of gravity assist for removing or installing cutting tools.

Two 4,000-Watt heaters expand the toolholder bore to sufficient size for cutting tool interchange. Cycle time is dependent on the toolholder size. Generally it is within a few minutes. Total tool change time, including heat-up and cool down, is comparable to other systems because temperatures are held to the minimum necessary to expand the holder.

To install a cutter, the toolholder is placed on the changer unit with the bore pointing up. The cutter is placed on the bore. A guide weight laid on its tip.

Heat is applied to the toolholder bore through a collar that surrounds the bore. Hot air is circulated through the collar transferring heat and expanding the metal. As the metal grows to sufficient size, the weighted cutter automatically slips into the bore. Once the cutter seats in the holder, the unit automatically shuts off.

To unload a cutter, the holder is placed into the changer unit with the tool pointing down. The heating collar is applied to the toolholder. When the temperature is sufficient to expand the holder, the tool simply falls out. Any configuration or style, such as HSK or V-taper tools can be used in the unit.GCK

The Marquart system is available through Production Dynamics (Valparaiso, Indiana).

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