Guide

English Translation:Chiron Werke GmbH & Co. KGChiron Werke GmbH & Co. KG is a globally operating manufacturer of high-precision and high-performance CNC machining centers. The company is headquartered in Tuttlingen, Germany, and boasts a corporate history spanning over 90 years. It is one of the leading providers in manufacturing technology, offering innovative solutions for industrial machining.Company ProfileChiron specializes in the development and production of machining centers that can be used in both single-part production and series production. …

Encoders convert mechanical movement into electrical signals.  This conversion is carried out optically, magnetically or mechanically. Encoders are subdivided into rotary and linear depending on the movement involved. Rotary encoders are used in the field of tool spindles to measure the rotational speed.Encoders work with very small (incremental), counting or absolute material measures as line patterns, magnetisation or contacts.Absolute encoders directly assign a position to each measured value. …

With the fixed-floating bearing arrangement of the roller bearings, most often the tool interface side bearing on the outer and inner ring is set, so that there can be no movements. At the other end of the shaft another roller bearing is set on the spindle shaft, whereby the outer ring is designed to be free to slide within the housing. This type of mounting is suitable for spindle mounting, although to a very limited degree because it is not possible to apply the essential pre-tensioning force to the spindle bearing. 

With bearings lubricated with grease, correct commissioning primarily determines the durability, service life and the performance of the spindle bearing. An optimum grease distribution run will optimise the characteristic value of the rotational speed, reduce the operating temperature in the bearing, achieve a long service life and ensure high operational reliability. During the grease distribution run, the grease is displaced from the running track and the base oil which is continuously added can build up the separating oil film between the balls and the running tracks required for lubrication.The grease distribution run can be split into short intervals and continuous operation.  Initially, the system is run at various speeds for ½ – 1 min. …

The HSK mount is used for clamping tools (milling, drilling). Due to its positive characteristics with regard to accuracy and stiffness, the HSK interface per DIN 69893 has found widespread use in the area of machining. In addition, its suitability for high rotational speeds and the possibilities for rapid tool change have lead to supremacy over the SK interface. …

With most repair work, the vertically or horizontally positioned spindle must be removed from the machine tool. In doing so, it is critical that installation or removal work is only carried out once the machine has been released for this and that safety measures are complied with.  The oil and coolant lines are disconnected first and reconnected last.If it is necessary to ship the spindle, ensure that all open connections for lubrication and sealing air are sealed by suitable means. This prevents the ingress of foreign objects and moisture, which could damage the sensitive precision bearing. Shipping should be carried out only in closed crates in which the spindles are firmly chocked as a matter of principle.  A spindle is a high-precision and sensitive key component of a machine tool. It should therefore always be handled with the greatest care.Written commissioning guidelines are provided with the spindle by the spindle manufacturer. …

In machine tools, the main spindle realises the rotational cutting movement. In doing so, the cutting movement can be carried out both by a rotation of the workpiece (lathes) as well as by a rotation of the tool (drilling or milling machines).   The design of the spindles differs depending on the application, the speed range and the development stage. As a result, from machine to machine, differentiation is made between a directly driven and indirectly driven spindle. In the case of directly driven spindles, the motor is integrated on or at the spindle shaft (motor spindle) with the tool interface.  This has the advantage that the structure is extremely torsionally stiff. …

A motor spindle is a directly driven spindle, where the motor, which is normally a three-phase asynchronous motor, is located directly on the main spindle between the spindle mounts.  Here, the rotor is shrink-fitted directly onto the spindle shaft. The heat arising from the high power losses is partially dissipated via liquid cooling, or occasionally via air cooling over the stator. Compared to conventional drives, motor spindles are characterised by a high degree of torsional stiffness and most commonly belt-driven or gear-driven designs. Further advantages of the motor spindle are the compact construction of the motor, the quiet and precise running of the spindle even at very low rotational speeds, as well as the detection of the motor speed and the spindle position via a rotary encoder. …

A rotary feedthrough provides gases and liquids with a sealed transition from a fixed object to a rotating object or between two rotating objects.In the machine tool spindle, the rotary feedthrough is attached above the floating bearing and feeds the coolant for the tool into the shaft. In wet processing, this is oil or water-based coolant and in dry processing it is air.  With minimum quantity lubrication, where the coolant is precisely metered to suit the machining and the workpiece, an oil-air mix is used as coolant.As a result, the rotary feedthrough is exposed to high rotational speeds and variable coolant quantities because it transfers media from the stationary housing to the rotating shaft. …

Rotor and Stator of Motor Spindles: Fundamentals and SignificanceMotor spindles are crucial components in machine tools used for precision machining tasks such as milling, drilling, or grinding. A fundamental physical aspect that governs the functioning of these spindles lies in the interaction between the rotor and stator. This essay illuminates the functions, structure, and importance of these two key elements.1. The Rotor: The rotor constitutes the rotating part of the motor spindle and bears the tool. Typically made from high-strength materials like alloyed steel or ceramics, the rotor withstands the stresses encountered during machining operations. Its rotation generates the necessary kinetic energy for the precise machining of workpieces.2. The Stator: Surrounding the rotor, the stator is the stationary part of the motor spindle. …

Single-row angular contact ball bearings with a contact angle between 12° and 25° are termed spindle bearings. They comprise solid inner and outer rings as well as solid window cages and cannot be dismantled. In comparison to other bearings, they can be better lubricated thanks to their smaller contact surfaces. For this reason, spindle bearings are used for mounting high-speed main spindles in machine tools, and are distinguished from conventional angular contact bearings by their accuracy and the smaller contact surfaces for the balls.  In order to guarantee a defined rolling behaviour of the balls, spindle bearings always require pre-tensioning in axial direction.As a result of the increasing requirements, particularly for the maximum rotational speed, high-speed bearings (HS bearings) and hybrid bearings (HC bearings) have been developed. Hybrid bearings use ceramic balls, which have lower density and a higher modulus of elasticity than conventional roller bearing steel. …

Tool spindles are cooled by water (with corrosion inhibitor), air or oil in order to protect the spindle components from overheating and to maintain temperature-dependent material characteristics.The coolant is fed through the cooling coil, a wide milled "internal thread" in the housing around the motor spindle. The coolant heated by the waste heat from the spindle is cooled in suitable cooling units so that it can be fed back through the cooling coil again. In doing so, the correct composition of the coolant must be observed because the cooling coil could be destroyed or blocked through the effects of corrosion. 

The main spindles in machine tools are predominantly driven by electrical motors.As an alternative, there is also the option to use a hydromotor for the drive.Conventional machines with older construction styles are often driven by an unregulated electrical motor, which is tied to a speed as a result of the physical principle of operation, with the mains frequency and the number of pole pairsIf the spindle is to have several speed settings, a transmission is required between the motor and the spindle. Different types of transmission can be used depending on the requirements for the speed range and the accuracy of the speed of the spindle. Large transmission ratios, both upwards and downwards, can be realised through belt drives, planet gears or worn gear systems. Smaller speed ranges can be covered through gear wheel transmissions.If it is necessary to cover a speed range without steps, this is done through a variable-speed electrical motor or with a continuously variable transmission, or through a combination of the latter with an additional transmission.The regulated three-phase motor requires a drive inverter system. …

DIN 31051 defines improvement as a "combination of all technical and administrative measures as well as the management measures required to increase functional reliability of the unit under consideration, without changing its required function".Similarly to the repair procedure, the improvement procedure encompasses "calculations, schedule planning, customising, provision of personnel, equipment and materials, creation of work plans" and the implementation of the improvement.   After the improvement measures have been implemented, a renewed functional check is essential to assure the correct functionality.The area of spindle improvement encompasses, for example, the conversion from steel balls to ceramic balls in spindle bearings in order to increase the rotational speed or the conversion to minimum quantity lubrication. 

DIN 31051 defines inspection as "measures for determining and assessing the current condition of the object being considered, including determining the causes of wear and deriving the necessary steps for future use".The inspection procedure encompasses the creation of "a plan for determining the current condition" and the implementation of this plan. Furthermore, the results of the determination of the current condition are assessed and a fault analysis created.  A decision is made about further measures on the basis of this assessment.   This includes maintenance, improvements or further measures.The scope of spindle inspection includes the adoption of measurement data such as spindle run-time, spindle and bearing temperature or spindle noise, and their analysis with regard to a need for repair or improvements. 

According to DIN  31051 maintenance is defined as "combination of all technical and administrative measures as well as the management measures during the life-cycle of the object being considered, required to maintain its fully functional condition or to return it to this condition so that it can perform the required function".Spindle maintenance includes servicing, inspection, repair and improvement.   When devising maintenance, consideration is given to the internal and external requirements of the company, as well as the repair strategies, and repair objectives are tailored to the objectives of the company.BILDSpindle maintenance is often offered under spindle servicing as a service. This encompasses, for example, the removal and installation of the spindle, checking and optimisation of the bearings, repair of the spindles or balancing of the spindle unit.Detailed steps of the procedure are outlined in an overview of the repair services provided by Spindeldoctor:1. …

Electrical motors are most commonly used as spindle drives.  Depending on the requirements on the machine tool, 3 different types of rotational electrical motors can be employed here:  The DC motor, the synchronous motor and the asynchronous motor. Externally excited DC motors have high torsional stiffness under load when regulated and can vary their speed significantly. For this reason they have long been employed as the main drives in machine tools. The stationary exciter field is generated in the motor stators in separately excited DC motors. The conductor windings are located on the rotor of the motor and must therefore be supplied through brushes as a sliding contacts, which means that motor maintenance is required. Synchronous and asynchronous motors are three-phase electrical motors.   Asynchronous motors are normally used in machine tools in conjunction with stepped-gear transmission systems.  There is a trend towards using regulated synchronous motors and regulated asynchronous motors as main drives. …

Alongside the mounting of the feed spindle and the rotary table, as well as the guides on the work table, the mounting of the main spindle is one of the most important components in the machine tool and is responsible for accepting and transferring the forces.The spindle mounting must fulfil the requirements for machine tools. These can be expressed as high working accuracy and high performance over an extended period of time, with low manufacturing and operating costs.In order to fulfil these requirements, spindle mountings have the following features:Exact positioning with low feed forces through low friction and low stick-slipCompliance with the accuracy over an extended period of time through low wear and resistance to being abradedLow positional changes of the components being fed, due to a high degree of stiffness and lack of playAvoidance of the machine tool chattering through good damping in supporting and movement directionsBased on their physical principle or the type of lubrication, the build-up of the lubricating film or the build-up of force, spindle mountings are subdivided as follows:Hydrodynamic,HydrostaticAerostaticElectromagneticRoller bearingRoller bearings represent the most commonly used bearing system for spindle mountings.  The multitude of positive characteristics of the bearing, particularly the international standardisation, the relatively simple calculation and the simple selection by means of catalogues, are responsible for this development. …

The spindle run-time defines the operating time of the working spindle in the machine tool. The run-time is the number of hours for which the spindle has rotated within the course of processing, similar to the mileage of a car. This determines the value of the spindle when sold.The servicing intervals are based on the run-time as this provides the time for which the spindle has actually been stressed, in contrast to the switch-on time. In modern machines the run-time is automatically logged and recorded for evaluation. …

The service life of the tool spindle is largely dependent on the service life of the spindle bearings, the components most affected by wear. The nominal service life calculation for roller bearings is based on fatigue theory. During operating times the roller surfaces of the bearing are subjected to cyclical compressive stresses, which result in the failure of the bearing after a foreseeable period due to fatigue. Moisture, inadequate lubrication or contamination, which result in wear and rust formation, are largely disregarded by this theory.  For this reason, the calculated service life does not generally apply reliably to practical situations.Alongside the pure fatigue period, the calculation of the period of use, which takes account of the external factors, is more relevant. …

DIN  31051 defines servicing as "measures to delay the reduction of the remaining wear stock".The servicing procedure encompasses the creation of "a servicing plan based on the specific requirements of the respective company or the unit being considered, and that is considered mandatory for this" along with the implementation and compliance with this plan.The area of spindle servicing includes tasks such as the topping up of the oil or regular cleaning of the tool spindle to remove chippings or coolant. 

The spindle temperature provides the temperature of the spindle at different locations. Exact measurement, particularly on the inner ring of the spindle bearing, presents a difficult technical challenge due to the high rotational speeds of the spindle.  In most cases the temperature sensors measure in the interior or exterior of the spindle housing, and from this the temperatures of the shaft and the inner ring of the bearings are estimated.    The limit temperatures for the roller bearings depend on the measurement point, the type of lubrication and the cage used. The maximum motor temperature must not be too high in order to prevent the galvanic isolating layer between the copper windings being destroyed. As a guide value, the temperature should not be higher than 110°C.The manufacturing quality of a machine tool is significantly impaired through thermoelastic deformation of the machine components as a result of the various heat sources. …

Similarly to the fixed-floating bearing arrangement, the sprung mounting arrangement can be subdivided into a fixed bearing on the tool mount and a floating bearing on the rear end of the spindle. However, the fixed bearing cannot be moved without force, in fact it is generally definitively pre-tensioned by means of a spring arrangement on the outer ring.  This allows changes in length due to the shaft heating up and the kinematic relative displacement to largely take place without any loss in the pre-tensioning force. The moveable outer ring of the floating bearing is mounted using a so-called floating bearing bushing. …

The steep taper mount per DIN 69871 is a suitable interface for automatic and manual tool changing. Three different forms (A, B, C) of steep taper design are covered in the standard. The most widely used form of steep taper mount is form A per DIN 69871, with trapezoidal fluting and orientation groove. Tool steep tapers that do not have a self-locking effect must be clamped in the machine spindle through additional clamping devices. The frictional connection arising on the taper provides the torque transfer with small loads.   In the case of form B, with greater loads, the key block takes the majority of the torque to be transferred.    The corresponding pull studs per DIN 69872 belong to tools per DIN 69871. …

There are various standard designs for drilling and milling tools that have different interfaces depending on their function.   The standard tools are clamped in basic mounts, which most often take the form of steep tapers or hollow shank tapers on the machine side and which work as an adapter sleeve in principle. The drilling tools are mounted via a Morse taper or via cylindrical shafts in collets, which are also suitable for mounting end mills. …