In this article, we will be discussing the knowledge of machining center tool holders.
CNC machine tools are widely used in factories, and these machines and tools come from all over the world with different models and standards.
Do you know what 7:24 means in a machining center BT tool holder? Also, are you familiar with the standards BT, NT, JT, IT, CAT?
The tool holder is the connection between the CNC machine tool and the cutting tool, and it is a crucial link that affects concentricity and dynamic balance. It should never be treated as an ordinary component.
Concentricity is important in determining whether the cutting amount of each cutting edge part of the tool is uniform when the tool rotates one circle. Dynamic imbalance, on the other hand, will produce periodic vibration when the spindle rotates.
Types of tool holders
According to the taper of the tool hole of the machining center spindle, it is usually divided into two categories:
- SK universal tool holder with a taper of 7:24
- HSK vacuum tool holder with a taper of 1:10
SK universal tool holder with a taper of 7:24
7:24 means that the taper of the tool holder is 7:24, which is a single taper surface positioning with a longer taper shank.
The tapered surface serves two important functions at the same time, which are the precise positioning of the tool holder relative to the spindle and the clamping of the tool holder.
The non-self-locking design allows for quick tool loading and unloading. The cost of the tool holder is relatively low since the taper angle can be machined to a high degree of accuracy, ensuring a precise connection.
During high-speed rotation, the tapered hole at the front end of the spindle will expand. The amount of expansion increases with the increase in rotation radius and speed, which decreases the taper connection rigidity. The axial displacement of the tool holder will also change under the action of the drawbar tension. After each tool change, the radial dimension of the to
There are usually five standards and specifications for universal tool holders with a taper of 7:24:
HSK vacuum tool holder with a taper of 1:10
- International Standard: IS0 7388/1 (abbreviated as IV or IT)
- Japanese standard: MAS BT (abbreviated as BT)
- German standard: DIN 2080 type (abbreviated as NT or ST)
- American Standard: ANSI/ASME (abbreviated as CAT)
- DIN 69871 type (abbreviated as JT, DIN, DAT or DV)
Type NT tool holders are tightened by a drawbar on conventional machines, which is also known domestically as ST.
The other four tool holders are tightened on the machining center through a spigot at the end of the tool holder.
(1) At present, the most widely used tool holders in China are DIN 69871 (JT) and Japanese MAS BT.
2) DIN 69871 tool holders can also be mounted on machines with ANSI/ASME spindle taper bores.
(3) The international standard IS0 7388/1 tool holder can also be installed on DIN 69871, ANSI/ASME spindle tapered bore machine tools. So in terms of versatility, the IS0 7388/1 tool holder is the best.
HSK vacuum tool holders with a taper of 1: 10
HSK vacuum tool holders rely on the elastic deformation of the tool holder, not only the tool holder with a taper of 1: 10 in contact with the 1:10 taper of the machine tool spindle bore, but also the flange face of the tool holder is in close contact with the spindle face.
This double-sided contact system is superior to a 7:24 universal tool holder in terms of high-speed machining, connection rigidity and overlap accuracy.
The HSK vacuum tool holder can improve the rigidity, stability, and product accuracy during high-speed machining, and also shorten the time of tool replacement, which is essential for high-speed machining. It is suitable for machine tool spindle speeds of up to 60,000 rpm. The HSK tool system is being widely used in the aerospace, automotive, and precision mold industries, among others.
HSK tool holders are available in types A, B, C, D, E, and F, with types A, E, and F being commonly used on machining centers with an automatic tool change (ATC) process.
The biggest difference between Type A and Type E:
(1) Type A has a transmission groove, but Type E does not. Therefore, Type A has a relatively larger transfer torque, which can handle heavy cutting. The torque transmitted by Type E is relatively small, so it can only handle light cutting.
(2) Type A tool holder has manual fixing holes and direction grooves, in addition to the transmission groove, resulting in relatively poor balance. Type E does not have these features, making it more suitable for high-speed processing.
The mechanisms of Type E and Type F are identical. The difference between them is that for handles with the same name (such as E63 and F63), the taper of the Type F handle is one size smaller. This means that both E63 and F63 have a flange diameter of φ63, but the F63 taper is only the same size as the E50. Therefore, the F63 will rotate faster (with a smaller spindle bearing) compared to the E63.
Tool clamping form of the tool holder
Spring cartridge tool holder
It is mainly used for straight tool holders such as drills, milling cutters and taps, or tool clamping.
The elastic deformation of the circlip is 1mm, and the clamping range is 0.5~32mm in diameter.
- A- Locking screw, which use an Allen key to tighten the locking screw;
- B- Locking piston, which presses the hydraulic medium into the expansion chamber;
- C- Expansion chamber, which pressurized by liquid to generate pressure;
- D-Thin expansion bushing, which enables the center of the tool clamping rod to be positioned and evenly enveloped during the locking process.
- E- Special seals, which ensure ideal sealing and long service life.
Heated tool holder
Sensing heating technology is used to heat the tool clamping part of the tool holder, causing it to expand in diameter. The cold shank is then inserted into the hot tool holder. This results in a high clamping force and good dynamic balance, making it suitable for high-speed machining.
The technology also provides high repeatability accuracy within 2μm and radial runout within 5μm, and has good resistance to stains and interference during machining.
However, only one tool of a specific shank diameter can be installed for each tool holder specification, and a set of heating equipment is also required.
The principle of pyrocondensational tool holder clamping:
Comprehensive evaluation and comparison of tool holders
|Evaluation||Spring clamp type||Hydraulic type||Pyrocondensational type|
|Versatility||be used in all processes; highly versatile||limited for high-speed machining; high maintenance costs||excellent performance in a wide range of high-speed machining applications|
|Toolholder beating||quality spring clip <10µm||>5µm||about 3µm|
|Vibrations||no advantage||can absorb vibrations||no advantage|
|Convenience||accuracy depends on the operator||clamping structure is easily damaged||standardized operation|
|Cost||general||expensive||Cheaper than Hydraulic type|
Other types of tool holders