April 6, 2015: High precision tool holding
Shrinking technology for milling tools had its beginnings in the die and mold industry but by now this technology established itself as the standard for many other application areas of high precision machining. It is worth investing in high quality shrink chucks, because only then will the desired advantages be visible in the long run.
For many years now tool shrinking technology has proven itself to be very popular, not only in the area of die and mold making but also when it comes to high precision machining for the automotive, aerospace and mechanical engineering industry. Especially in the high end range of metal cutting, many users appreciate the excellent radial runout accuracy and the easy and fast tool change. Also, users can benefit from shrink fit chucks due to their wide range of available contours and geometries. During machining they contribute to high precision and surface quality of the workpiece and are usually more economic than conventional tool holders.
However, this wasn’t the case a couple of years ago: machine tool, spindle and cutting tool were considered to be the decisive factors in milling and the tool holder itself remained unnoticed. This is a mistake because high runout on a tool holder has a direct consequence on the cutting results: both accuracy and the surface quality suffer. Tool and spindle wear out much faster and in the end the process reliability decreases. This leads to severe disadvantages which in turn can cause significant costs.
Low investment, great impact
All in all, the expenses for tool holders – even for high quality ones – are low: usually tool holders are purchased together with the original equipment of the machine tool and they remain in the machine for a very long time. Studies have shown that the total expenses for tool holders amount to less than 1% of the entire machining costs. Why try to save money with tool holders when doing so can result in visibly bad quality, low productivity and wear?
Innovative companies have asked themselves this question and hence they have been searching for the best technique in order to clamp their tools. Also, the market has shown a reaction and is currently offering different systems which should match the consistently growing demands of the milling process in regards to precision, surface finish, metal removal rate and process reliability.
Shrinking technology, which was put into the product offerings of most of the big cutting tool producers, has proven to be especially successful. Having a look into German, European and North American production facilities will confirm this. In most high quality machining centers you will see solid (milling) tools that are clamped into shrink fit holders. However, even these shrink fit holders that seem to be very similar at first glance, show some significant differences. HAIMER, the world market leader for high precision shrinking technology from Igenhausen, Germany, emphasizes the following advantages of shrinking in general and explains which important details have to be taken into consideration:
The quality has to be right in all respects
Accuracy: a properly produced shrink fit chuck should reach a runout accuracy of less than 3 µm (at three times the cutting tool diameter). Only if this condition is met, the precision can be conveyed to the cutting edge of the tool.
Balance grade: every shrink fit chuck should be fine balanced. HAIMER balances every tool holder to G2.5 at 25,000 RPMs or < 1 gmm of residual unbalance for smaller tool holders. After each shrinking process, the balance stays the same. As shrink fit chucks don’t feature any moving parts, they offer the best balance grade repeatability among all clamping systems on the market. Other clamping systems with many movable parts, of which the position gets displaced with each clamping process, are not characterized by a repeatable balancing grade.
Clamping force: a shrink fit chuck clamps the cutting tool 360 degrees around the shank. This leads to a very high clamping force and rigidity. This effect can be further increased through a shortened chamfer and an expanded clamping area.
Quick tool change: nothing beats the tool change time of shrink fit chucks, assuming that the shrinking process is operated by a powerful <s>and</s> inductive shrink fit machine. Tools can be changed within 5 to 10 seconds. Furthermore, production facilities don’t require a lot of additional items such as collets, lock nuts, seal disks, etc.
Different standard geometries: depending on the application (roughing, finishing, deep contours etc.) the requirements for the shrink fit chucks can differ. The supplier should match these requirements with a broad range of contours and designs. For example, when it comes to 5-axis machining in the area of mold making, very slim holders with a 3° draft angle are required. Milling Chucks or ER collet chucks could never be designed in such slim geometries.
Extended holders: in order to work on deep cavities you can combine shrink fit chucks with shrink fit extensions. This way, you can create very long tool holders that still show very little runout.
Tool coolant: shrink fit chucks are ideally suited to intelligently guide the coolant or air/oil mist to the cutting edge of the tool. To this effect, some manufacturers offer optional systems.
Cleanliness: this is a fundamental strength of shrink fit chucks. The sealed by design system is protected much better against any form of contamination than other tool holder systems.
Maintenance: compared to roller bearing milling chucks or hydraulic chucks, shrink fit chucks don’t require any expensive or unplanned maintenance. This in turn reduces the costs and creates consistent and predictable working conditions.
The right chuck for each application
Over the years, HAIMER has broadened its range of shrink fit chucks and today the possibilities of using them are limitless. Even the standard shrink fit chucks are fine balanced (G2.5 at 25,000 RPMs or <1 gmm residual unbalance) and produced of high temperature resistant special steel. All functional surfaces are fine machined, grinded and the taper tolerance is verifiably better than AT3.
Based on the standard shrink fit chucks HAIMER was able to develop the Power Shrink Chuck series for high speed or high precision milling applications. The patented design combines low tendency towards vibrations, high rigidity and a slim design at the top. This special design makes it possible to increase the depth of cut and feed rates in order to achieve a better metal removal rate. Every Power Shrink Chuck can optionally be equipped with the patented pull out protection system Safe-Lock™.
HAIMER Heavy Duty Chucks are characterized by a reinforced wall thickness in the clamping area, an extremely rigid outer geometry and patented expansion grooves in the clamping bore. This way, high clamping forces are enabled which can easily be compared to those of a milling chuck.
The range of shrink fit chucks is completed by HAIMER Mini Shrink Chucks. These are one-piece shrink chucks with an extremely slim design and a three degree outer geometry designed for mold making. Also available are the HAIMER Power Mini Shrink Chucks. At the top they are slim like a Mini Shrink Chuck but feature a reinforced base in order to dampen vibrations and achieve a better torque transmission.
The right spindle interface
Since high precision machining also depends on the right connection between the tool holder and the spindle, HAIMER offers premium quality spindle interfaces for all shrink fit chucks: HAIMER grinds all functional surfaces and guarantees a taper tolerance better than AT3. HAIMER also carries HSK-A/E/F tapers which, compared to standard steep tapers, offer many advantages such as a high repetition accuracy, a fixed axial positioning by the flat contact surface and suitability for high speed cutting. Furthermore, HAIMER offers successful spindle connections such as Haimer Capto™ (licensed by Sandvik Coromant) and Kennametal’s KM4X.
Shrinking machines for every requirement
In order to successfully combine the tool and the shrink chuck, you need a suitable shrink fit machine. HAIMER offers a wide range of shrink fit machines and therefore has the right solution for every requirement.
The HAIMER Power Clamp Nano is a horizontal shrinking machine for small spindle interfaces such as HSK-E25 up to HSK-A63 or SK/BT30 up to SK/BT40 and for smaller tools up to diameter 16mm.
The HAIMER Power Clamp Comfort NG is the shrinking machine for high demands. With all HAIMER Power Clamp machines you can shrink in and out HSS and solid carbide tools with a shank tolerance of h6 and Ø3mm up to Ø32mm in record time. The Power Clamp Comfort NG is equipped with the patented and revolutionary double coil technology and the latest contact cooling system. The coil automatically adjusts to the length and diameter of the chuck. Only the clamping area is heated which shortens the cooling time considerably. Exchangeable stop discs or changing the coils is no longer necessary. The power output of the coil is up to 13KW which helps reduce the heating time. The software automatically recognizes the chuck volume and choses the correct shrinking diameters. For Power Clamp Comfort NG an upgrade kit was recently added to the delivery program, which enables the shrinking of Heavy Duty chucks up to diameter 50 mm reliably with a Heavy Duty coil.
The HAIMER Power Clamp Premium series is the high end solution for professional shrinking and cooling. It offers a lot of working space, perfect handling and linear guided cooling bodies with temperature monitoring for maximum security. Presetting the tool length to exactly 0,02mm (e.g. for sister tools) can optionally be integrated to this series with a length presetter.