What does 7:24 in the BT handle mean?
What standards are BT, NT, JT, IT, CAT?
Nowadays, CNC machine tools are widely used in factories. These machine tools and the tools used come from all over the world, with different models and standards. Today I will talk to you about the knowledge of machining center tool holders.
The tool holder is the connecting body of the machine tool and the tool. The tool holder is a key link that affects the concentricity and dynamic balance. It must not be treated as a general component. Concentricity can determine whether the cutting amount of each cutting edge part of the tool is uniform when the tool rotates one circle; dynamic imbalance will produce periodic vibration when the spindle rotates.
01
According to the spindle taper hole is divided into two categories
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 7:24 taper
HSK vacuum tool holder with a taper of 1:10
SK universal tool holder with 7:24 taper
7:24 means that the taper of the tool holder is 7:24, which is a single taper surface positioning, and the taper shank is longer. The surface of the cone plays two important roles at the same time, namely the precise positioning of the tool holder relative to the spindle and the realization of tool holder clamping.
advantage:
It is not self-locking, which can realize quick loading and unloading of the tool; the manufacture of the tool holder only needs to process the taper angle to high precision to ensure the accuracy of the connection, so the cost of the tool holder is relatively low.
Disadvantages:
The taper hole at the front end of the spindle will expand during high-speed rotation. The amount of expansion increases with the increase in the radius of rotation and the speed. The rigidity of the taper connection will decrease. Under the action of the tension of the tie rod, the axial displacement of the tool holder will also be changes happened. The radial dimension of the tool holder will change every time the tool is changed, and there is a problem of unstable repeat positioning accuracy.
There are usually five standards and specifications for universal tool holders with a taper of 7:24:
1. International Standard IS0 7388/1 (referred to as IV or IT)
2. Japanese standard MAS BT (abbreviated as BT)
3. German standard DIN 2080 type (abbreviated as NT or ST)
4. American Standard ANSI/ASME (CAT for short)
5. DIN 69871 type (abbreviated as JT, DIN, DAT or DV)
Tightening method:
The NT type tool holder is tightened by a tie rod on a traditional machine tool, which is also called ST in China; the other four types of tool holders are tightened on the machining center through a pull nail at the rear of the tool holder.
Versatility:
1) At present, the most widely used tool holders in China are DIN 69871 (namely JT) and Japan MAS BT type tool holders;
2) DIN 69871 type tool holder can also be installed on ANSI/ASME spindle taper hole machine;
3) The international standard IS0 7388/1 type tool holder can also be installed on the DIN 69871 type, ANSI/ASME spindle taper hole machine tool, so in terms of versatility, the IS0 7388/1 type tool holder is the best.
HSK vacuum tool holder with a taper of 1:10
HSK vacuum tool holders rely on the elastic deformation of the tool holder, not only the 1:10 taper surface of the tool holder contacts the 1:10 taper surface of the spindle hole of the machine tool, but also the flange surface of the tool holder and the spindle surface are in close contact. The surface contact system is superior to the 7:24 universal tool holder in high-speed machining, connection rigidity and coincidence accuracy.
HSK vacuum tool holder can improve the rigidity and stability of the system and the product accuracy during high-speed machining, and shorten the time of tool replacement. It plays an important role in high-speed machining. It is suitable for machine tool spindle speed up to 60,000 rpm. HSK tool systems are being widely used in manufacturing industries such as aerospace, automobiles, and precision molds.
HSK tool holders are available in A-type, B-type, C-type, D-type, E-type, F-type and other specifications. Among them, A-type, E-type and F-type are commonly used in machining centers (automatic tool change).
The biggest difference between Type A and Type E:
1. Type A has a transmission groove but Type E does not. So relatively speaking, the A-type transfer torque is relatively large, and it can relatively carry out some heavy cutting. The torque transmitted by the E type is relatively small and can only perform some light cutting.
2. In addition to the transmission groove on the A-type tool holder, there are manual fixing holes, direction grooves, etc., so the balance is relatively poor. The E type does not, so the E type is more suitable for high-speed processing. The mechanism of E-type and F-type is exactly the same. The difference between them is that for the same-named E-type and F-type handles (such as E63 and F63), the taper of the F-type handle is one size smaller. That is to say, the flange diameters of E63 and F63 are both φ63, but the size of the cone of F63 is only the same as that of E50. So compared with E63, the speed of F63 will be faster (small spindle bearing).
02
Mounting form of knife handle
Collet chuck
It is mainly used for clamping straight shank knives and tools such as drills, milling cutters, and taps. The elastic deformation of the circlip is 1mm, and the clamping range is 0.5~32mm in diameter.
Hydraulic chuck
A- Locking screw, use an Allen key to tighten the locking screw;
B- Lock the piston and press the hydraulic medium into the expansion chamber;
C- Expansion chamber, pressurized by liquid;
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 ensure ideal sealing and long service life.
Heated knife handle
Application of induction heating technology to heat the tool clamping part on the tool holder, so that its diameter will expand, and then put the cold tool holder into the hot tool holder. The heating tool holder has large clamping force and good dynamic balance, which is suitable for high-speed processing. The repositioning accuracy is high, generally within 2μm, and the radial runout is within 5μm; the anti-fouling ability is good, and the anti-interference ability in the processing is good. However, each type of tool holder is only suitable for installing a tool with one shank diameter, and a set of heating equipment is required.
The principle of heat shrinkable tool holder clamping:
Comprehensive evaluation and comparison of tool holders:
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