The machining process Reaching difficult pockets: hydraulic or shrink fit?
The ultimate goal is to make every tooling assembly as short as possible, 5-axis machine or not. The shorter the tooling, the less room for error. That said, the unusual angles, sizes and shapes of the parts that require multiple axes don’t always allow for that. We’ve talked about some workholding solutions for this challenge, but you have options in tooling selections too. The choice often comes down to hydraulic chucks and shrink-fit holders. Compared to collet chucks, shrink-fit holders and hydraulic chucks have a smaller nose diameter relative to the tools they hold. This is critical, as these holders allow a further reach into mold cavities or other tricky work envelopes without interference. Let’s quickly explore what to consider when choosing between the two holder types.
Cost – When it comes to the holders themselves, shrink-fit is generally a slightly lower cost. Where the major difference in expense lies is in the equipment needed to heat shrink-fit holders.
Maintenance – Because shrink-fit heating temperatures can approach 600° Fahrenheit, we recommend using dry cutting tools without oil on them. From there, diligent attention must be paid to the holder bores and tool shanks. Any contamination will be baked onto the metal and progressively deteriorate performance. Hydraulic chuck maintenance is straightforward as long as the hydraulic chamber stays sealed. Training, handling and safety – Hydraulic chucks are infinitely simple. A turn of a wrench locks the tool in place. When it comes to shrink-fit systems, there are a few more factors to consider when getting the team up to speed, including safety considerations. Setup – Hydraulic chucks use a simple wrench to lock in the tool, providing the option to swap tools at the machine or offline. Shrink-fit setups must be done exclusively offline where the heating and cooling can be powered. Most heating cycles can be as fast as 15 seconds. Vibration – Potential out-of-balance issues due to a hydraulic holder’s one-sided set screw design are a worry of the past. A good-quality hydraulic chuck has some natural damping characteristics that run every bit as true as a shrink-fit holder, with more consistent clamping tolerances and forces over the life of the holder. That’s not to say shrink-fit holders are ineffective in terms of vibration management. Their runout is five times better than side-lock holders.
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