CNC machining centers have continued to improve and develop over the past 30 years. The design of these machines is now fully flexible and can be applied to a variety of processing applications from short-term tool manufacturing to long-term product production with minimal structural changes. In the past, aircraft components that had been assembled by welding or riveting can now be machined from hollow aluminum blocks in high-speed, high-power machining centers. Automotive engines used to be manufactured almost exclusively from dedicated conveyor lines, and today they tend to use a machining center for agile manufacturing. These machining centers have a basic feature: they can be automatically replaced without operator intervention.
Toolholders provide a standard connection between the various cutting tools and the machining center spindle. It works in the same way as an adjustable drill chuck, just as a home maintenance worker can change the drill bit of a jackhammer. The spindle hole of the machining center and the shank and flange of the tool holder are all manufactured according to standards. These standards have been developed worldwide over the past 25 years. In general, the development of these standards is relatively complete, as long as the spindle and tool holders are in compliance with the standards, they can ensure that the connection between them is both strong and high concentricity.
Due to the standard structure of the tool holder and its relatively slow innovation relative to the machine tool body, a lingering impression has been formed among users of some machining centers: the tool holder seems to be a kind of “commodity”. (standardized products). Judging from the number of tool chuck manufacturers that have succeeded in market competition today, it is easy to draw this conclusion. However, some end users do not agree with the concept of "goods." Indeed, all the tool chucks of a certain type seem to be similar, but certainly not exactly the same.
Tool chuck quality difference
What makes one product better than another? In most metal cutting operations, the difference between a qualified part and a scrap product is often a very small difference in critical dimensions. Similarly, the difference in a high-precision tool holder also depends on the manufacturing tolerances used.
Evaluation index 1: Concentricity
The axis of rotation of the cutting tool must exactly match the axis of rotation of the machine tool spindle. The method of achieving near-perfect concentricity is clear but complex.
First, when the taper shank of the tool holder is installed in the corresponding spindle taper, each time must be very accurate. For this reason, the tolerance of the taper angle of the mating surface must be small. These tolerances are formulated and promulgated by national or international standards committees and are generally available to anyone. The manufactured tool chucks are to be tested for their roundness and taper angle using a gauge, and these rules are calibrated by a physical reference gauge. Measurement methods used at the production site vary from physical contact mechanical measurements, physical contact/electronic analog measurements, to non-contact analog measurements (eg, pneumatic gauges). All of these proven methods have one thing in common: they must all be calibrated using physical reference gauges.
There are significant differences between the gauges of different toolholder manufacturers. This positive judgment is based on the results of hundreds of measurements performed on tool holder products from different manufacturers over the years. In short, they are different. Even assuming that all the tool chucks sold in the market match the specifications of their respective manufacturers, the benchmarks used by different manufacturers are not the same. This created a problem: The adaptability of the tool chucks of different manufacturers and the spindles of the machine tool is not the same. The reason for this is simple: There is no "mother gauge" that marks the standard taper. Although the National Institute of Standards and Technology (NIST) in Maryland and some high-level metrology laboratories (such as the Timken company's laboratory in Ohio) have been equipped with rotary table measurements with matching accuracy under certain environmental conditions. Taper capability, but no single reference physical gauge can easily characterize other physical gauges with the same size and taper. It can be understood that, in the absence of a single reference source or a reference gauge that can be traced by all gauges, there is a difference in the degree of conformity of the products of different manufacturers on the market with the standards, and these differences will affect the quality of cooperation with the spindle. Below for further analysis.
What is still discussed now is the problem of concentricity between the tool and the spindle centerline. Even if the problem of chaotic spindle adaptability is solved quickly, the problem will turn to the business terminal of the tool holder: because there is no national standard or international standard for taper reference, the end user of the tool holder has more reasons to lose the product. confidence. International or national standards organizations (such as ISO, ANSI, JIS, DIN, etc.) have provided corresponding provisions for the taper adaptability of the spindle and the tool holder and the tool replacement function. On the other hand, the suitability of cutting tools and tool chucks depends on the tool chuck manufacturer. They set the internal diameter tolerance of the end mill chuck, the taper angle tolerance of the collet chuck and the sleeve milling cutter. The verticality of the end face of the shaft, etc., they also set the concentricity of the clamping part of the tool holder and the taper shank connecting the spindle of the machine tool. In this way, only toolholder manufacturers can equip their own machine tools with special fixtures, and use the interface surface of the machine tool spindle as a reference surface to machine an adapted taper shank work surface.
Before concluding the discussion on concentricity, it is also necessary to consider a more general variable—whether manufacturers have the ability to not only produce high-quality products, but also consistently produce high-quality products for a long period of time. In any manufacturing industry, the ability of different manufacturers to manufacture high-quality products long-term day after day is not the same. In your own business, you can always list the names of good and bad competitors and suppliers. There is always a leading company in each market, and good manufacturers will strive to gain this status.
In short, for the primary quality index of the toolholder, concentricity, it is entirely reasonable to believe that toolholders produced by different manufacturers may have quality differences due to different metrology tests, product standards, tolerances, and manufacturing capabilities.
Evaluation Index 2: Clamping Strength
Most tool chucks are manufactured to standard and have a very similar appearance. CAT, BT, or HSK systems are side-locking end mill chucks that use a single set screw to tighten a flat surface on the tool to prevent loosening of the tool. They can use standard jackets to make the collet better suited for gripping tools of different diameters. They can also be used exclusively to hold threaded tools or Morse taper shank drills, among other functions. In fact, every CNC tool holder manufacturer is struggling to provide a solution that is suitable for most cutting tools and machine tool spindles.
