Shrink technology

When used correctly, shrink chucks offer optimum concentricity and repeatability, maximum torque transmission, long service life, are maintenance-free and easy to use.

Shrink chucks are often used for complex 5-axis machining operations, as they maintain excellent concentricity even with long tools and can be used in confined spaces. In addition, shrink fit chucks can transmit high torques and are therefore suitable for high-performance machining (HPM). Their symmetrical design, without mechanical moving parts, also makes them suitable for high-speed machining.

Designs

Shrink chuck

How shrink fits work
The tool holder bore into which the tool is inserted is slightly smaller than the tool shank. Heating enlarges the bore so that the tool fits into it. As it cools, the bore contracts again, creating concentric pressure on the entire shank. Bore diameter: 3 to 32 mm.

Features of shrink fit holders
- Made of high-quality heat-resistant material (max. 400°C temperature) hardened to 56 HRC +/- 2
- Finely balanced to G2.5-25,000 rpm or ≤1 g.mm as standard
- Strong body for maximum static rigidity
- Sealed as standard, ideal for machining materials that generate dust
- Repeatable concentricity deviation ≤ 3 μm
- Slim design, available in various lengths to avoid collisions with the workpiece
- Use of extensions enables machining in deep cavities
- Axial stop screw included in the scope of delivery of the holder, with bore for cooling lubricant supply

Advantages of shrink-fit chucks
- High concentricity
- Extreme clamping force
- One-piece design
- No moving parts
- Low interference contours thanks to slim design
- High speeds for high-speed milling
- No wear (compared to hydraulic chucks)
- Extremely long service life

Disadvantages of shrink-fit mounts
- Material fatigue: Repeated heating and cooling during each tool change puts strain on the material of the mount and can lead to fatigue, which limits the service life of the mount. You can assume ~ 500 cycles.
- Cost of shrink device: The purchase of a shrink device, which is required for the shrink fit process, represents an additional investment.
- Energy consumption: A shrink device consumes ~10,000 kilowatt hours of electricity per year.
- Tool change: Changing a hydraulic expansion chuck takes ~two minutes. Depending on the size, a shrink fit chuck takes approximately six minutes.
- Occupational safety: A shrink fit device is not only cumbersome to operate, but also poses a potential hazard. With a hydraulic expansion chuck, there is no risk of burns from a tool holder that has not yet cooled down completely.

Thermal expansion
Approx. 11 µm/m/° for steel and HSS
Approx. 6 µm/m/° for carbide and heavy metal
e.g.: Diameter 20 mm, heating from 20°C to 270°C
Steel: 0.020 x 11 x 250 = + 55 µm
Carbide 0.020 x 6 x 250 = + 30 µm

Shanks
Cylindrical DIN 1835-1 Form A/ DIN 6535 Form HA

Shaft tolerance
Diameter 3 to 5 mm maximum h5, tool shaft made of carbide or heavy metal (e.g. Densimet). Diameter 6 to 32 mm maximum h6, tool shaft made of steel, HSS, carbide or heavy metal. Tolerance h5 instead of h6 is recommended for diameters 6 to 32 mm for a secure torque. The minimum shrinkage depth LSC, as specified on the product pages, must be observed when shrinking the tool shank into the holder.

Concentricity deviation
The maximum concentricity deviation is 3 µm at 3 x DCB (DCB = tool holder bore diameter, specified as DCONWS on the product pages). The maximum concentricity deviation of the workpiece-side mounting bore in relation to the machine-side mounting mandrel or shank is 3 µm.

Heat resistance
Shrink mounts are made of heat-resistant steel, which ensures the mounts remain stable even after many shrink cycles. The maximum permissible temperature is 400°C.

Material
Shrink fittings are made from 1.2343 (X38CrMoV5-1) – also known under the commercial designation JIS SKD6. This is a tool steel or hot-work steel used for plastic moulds, construction parts with high strength requirements or tools with high thermal stress, among other things. The material has moderate machinability. The steel has very good toughness and is extremely wear-resistant. The material has moderate weldability and good corrosion resistance. The material has excellent polishability. The hardenability of material 1.2343 is moderate to good. Material 1.2343 or X37CrMoV5-1 / X38CrMoV5-1 has a tensile strength of 790, an elongation at break of ~12 and a yield strength of 423.

Normative references
DIN 69882-8 - Werkzeughalter mit Kegel­Hohlschaft nach DIN 69893­1 - Teil 8: Form G, Schrumpffutter - Maße
DIN 69882-8 - Tool holders with hollow taper shanks according to DIN 69893­1 - Part 8: Type G, shrink chuck - Dimensions
DIN 69882-8 - Porte­outils avec queue creuse conique conforme à DIN 69893­1 - Partie 8: Type G, mandrin de frettage - Dimensions
DIN 69882-8 - 3.1 Shrink chucks for automatic tool change
DIN 69882-8 - 3.2 Shrink chucks for manual tool change