High Speed Spindle Design 陳冠文 1
Outline a).the components of spindle b).drive System c).bearing System d).tool shank System e).lubrication System 2
The Components of Spindle Tool shank Bearing Drive Sys. Lubrication Cooling 3
Bearing Lubrication Cooling Running Condition The Components of Spindle Type External Force Ball Material Retainer Material Grease Oil Jet Oil Mist Oil Air Outside Cooling Temperature Inside Cooling Duty Cycle High Speed Spindle Gear Belt Part Accuracy Direct Couple Fitting Match of Bearing and Spindle Built-in Motor Dynamic Balance Bearing Clearance Vibration Assembly Preload 4
Normal Spindle Drive System Spindle High Speed Spindle Gear drive spindle (less then 6000 rpm.) Belt drive spindle (less then 12000 rpm.) Direct-Drive spindle (less then15000rpm) Built-in Motor spindle (0 to?? rpm) 5
Advantage Drive System Gear drive Large torque transmission Stable mechanism Disadvantage High inertia, adverse for high speed Large noise Need experienced technical personnel Gear 6
Advantage Lower cost Easy to maintain Disadvantage Drive System Belt drive Lower torque transmission Large noise at high speed Belt tension will influence cutting motor Belt 7
Drive System Belt drive Timing Belt High torque Transmission No slip High noise at high speed V-Belt Higher speed Belt will slip at low belt tension Lower noise at high speed 8
Advantage Drive System Direct drive Structure is simple Easy to maintain Easy for high speed Coupling Disadvantage High cost for coupling Need high coaxiality Complex mechanism for tool release 9
Advantage Drive System Built-in motor Easy to high speed Lower vibration and noise Easy to install to machine Disadvantage Heat from motor Very high cost Need experienced technical personnel 10
Summary Cost Drive System Built-in Motor > Direct Drive > Gear Drive > Belt Drive Torque Gear Drive > Built-in Motor=Direct Drive > Belt Drive Speed Built-in Motor > Direct Drive > Belt Drive > Gear Drive 11
Bearing for Spindle Bearing Roller Bearing -High radial rigidity -Very heavy loading -Low speed Angular contact ball bearing -High radial and low axial rigidity -Medium loading -High speed Double direction angular ball bearing -High radial and axial rigidity -High loading -Medium speed 12
Bearing contact angle Bearing Contact angle refers to the nominal angle between the ball-torace contact line and a plane through the ball centers, perpendicular to the bearing axis Typically, contact angles of 12º, 15º, 18º and 25º are available 13
Bearing Bearing contact angle Characteristics Support of axial load in one direction only Adjustment against a second bearing is necessary High rigidity and loading capacity Suitable for high speeds The forces are transmitted from one raceway to the other under a specific contact angle. 14
Bearing Bearing Arrangement of Spindle Fixed Free Fixed Free Fixed Free Fixed Free 15
Bearing FACE TO FACE - DF Mounting This is referred to as "Face-to Face" or "X" configuration 16
Bearing The contact lines converge towards the bearing center line: The spread H and the rigidity to resist tilting moments are smaller This arrangement is less sensitive to angular misalignment 17
Bearing BACK TO BACK - DB Mounting The most common technique used is back to back, "O", or "DB " mounting This configuration is suited for most applications and provides good accuracy and rigidity 18
Bearing The contact lines diverge towards the bearing center line: Large distance H and thus a high rigidity to resist tilting moments Takes up axial loads in both directions 19
Specialized Configuration Bearing Sets of three or more bearings are sometimes used in special cases having requirements for increased stiffness or capacity, where the shaft or housing size cannot be changed to accommodate larger bearings To increase moment loading capacity and spindle performance, spacers are used to separate the bearing sets 20
By fitting spacers with matched bearings the following is achieved: The spread H (with DF and DB arrangement) is increased Frictional heat is dissipated more effectively increase moment rigidity Bearing Lubrication of the bearing (oil lubrication) is improved as a result of better oil flow 21
To achieve the best possible rigidity: minimize the distance between the front support position and the spindle nose. bearing spacing (between rear and front supports) should be fairly short. As a guideline, a ratio L/d = 2.5-3 provides the best compromise, where are: L = distance between the rearmost bearing row and the first front side bearing row d = bore diameter of the first Bearing 22
Newer bearing technologies using ceramic balls. The ceramic balls, when used in an angular contact ball bearing, offer distinct advantages over typical bearing steel balls. Bearing The ceramic balls have 60% less mass than steel balls Ceramic balls do not react with the steel raceways Ceramic ball bearings operate at lower temperatures Ceramic bearings operate at much lower vibration levels 23
Preload Bearing-Preload Preloading is the removal of internal clearance in a bearing by applying a permanent thrust load to it. Preloading: Remove radial and axial clearance. Increases system rigidity. Reduces non-repetitive run-out. Reduces the vibration and noise. Lower the difference in contact angles between the balls and both inner and outer rings at very high speeds Prevents ball skidding under very high acceleration. 24
Bearing-Preload Angular contact ball bearings are available with a choice of pre-loading magnitude, typically designated as light, medium and heavy. Light pre-loaded bearings are designed to allow maximum speed and less stiffness. Light pre-loaded bearings are often used for very high speed applications, where cutting loads are also light, and top RPM is needed. Heavy pre-loading allows less speed, but higher stiffness. 25
Bearing-Preload Bearings should be preloaded as lightly as is necessary to achieve the desired results. This avoids excessive heat generation, which reduces speed capability and bearing life. There are two basic methods of preloading: Constant force preloading(spring preload) Constant position preloading 26
Bearing-Constant force preload Characteristics Insensitive to different thermal expansion of shaft and housing Suitable for very high speeds 27
Constant pre-loading Bearing-Preload 28
Bearing-Constant position preload Characteristics Higher rigidity at radial loads Lower speed compared with spring preloading Because of the temperature differences between shaft and housing, the preloading will be changed. Distinct higher axial rigidity than with spring preload 29
Bearing-Constant position preload Advantages Increase radial and axial rigidity. Withstand bi-directional thrust loads (DB and DF mounting) Withstand heavy uni-directional thrust loads (DT mounting) Other advantages include their ease of assembly and minimum run-out Disadvantage Increased start torque Sensitivity to differential thermal expansion Reduced speed capacity 30
1/10 Taper High speed Tool shank Tool shank KM NC5 HSK (ISO 12164) DIN (DIN 69871) ISO (ISO 7338) 7/24 Taper Normal CAT (ANSI B.5.50) BT (MAS 403-1982) 31
force force Gripper Tool shank shank 7/24 Taper Low speed 1/10 Taper High speed 32
Tool shank 7/24 Taper a e b d c 33
Tool shank 1/10 Taper a d c b 34
Tool shank - HSK The HSK-interface shows significant advantages in precision and stiffness compared to the steep taper interface. Higher positional accuracy of the tool due to axial face and taper positions Ideal for high speed machining. Easy tool handling due to low weight and dimensions of the short tapers. Heavy duty chip removal can be achieved through total stiffness of the interface, high pull forces and the resulting transmittable torque. 35
Tool shank - HSK 36
Tool shank - HSK 37
Tool shank - HSK 38
Tool shank - HSK 39
The types of HSK shank Tool shank - HSK 40
Tool shank - HSK HSK shanks cover three different application categories. Types A and C serve applications requiring moderate torque and moderate-to-high spindle speeds. (Type A is for automatic tool changing, and Type C is for manual changing.) Types B and D are designed for high torque applications with moderate-to-high spindle speeds. (Type B is for automatic changing and Type D is for manual changing.) Types E and F are designed for low torque and very high spindle speeds on machines that incorporate ATCs. 41
Tool shank - HSK Features central, axial coolant supply with KSM-tube keyways at the taper end Application machining centers,milling machines Features decentralized coolant supply over the flange or central coolant supply through coolant tube enlarged flange keyways at the flange Application machining centers, heavy milling machines 42
Tool shank - HSK Features rotational symmetry without keyways Application HSC- spindles Features enlarged flange Application HSC-spindles e.g. machining of wood and plastic 43
Tool shank Draw bar The preloaded spring stack will provide pull-in force to gripper. Gripper will clamp pull stud of BT shank, or clamp inside of HSK shank. Pull-in force will pull cutting tool into spindle. 44
Tool shank Gripper For 7/24 taper tool shank For 1/10 taper tool shank 45
Tool shank Gripper 46
Grease Lubrication Lubrication Oil Oil bath Oil splash Oil jet Without Air Oil drop Oil circulation Oil mist With Air Oil air 47
Lubrication The correct choice of lubricant and method of lubrication is as important for the proper operation of the bearing as the selection of the bearing and the design of the associated components. Reduce friction by providing a viscous hydrodynamic film of sufficient strength to support the load and separate the balls from the raceways, preventing metal-to-metal contact Minimize cage wear by reducing sliding friction in cage pockets and land surfaces Prevent oxidation/corrosion of rolling elements Act as a barrier to contaminants Serve as a heat transfer agent in some cases, conducting heat away from the bearing 48
Advantages Lubrication Friction and wear reduction Friction heat dissipation Prolonged bearing life Prevention of rust Protection against harmful elements 49
t : temperature rise NR : power lose Lubrication grease lub. oil mist lub. oil air lub. Oil jet 50
Lubrication The most widely used lubricating methods are Oil bath Oil spray Drip lubrication Circulating lubrication Oil mist lubrication Oil-air lubrication (throwaway lubrication) Oil-jet lubrication (cooling lubrication) high speed 51
Lubrication Speed limit of lubrication system Grease Lubrication 0 50 100 150 200 250 300 350 DmN 值 = value *10000 Jet Lubrication Oil-Air Lubrication Ceramic ball Steel ball 52
Lubrication Oil jet This is the most reliable lubricating system for severe (high temperature, high speed, etc.) operating conditions. 53
Lubrication Oil mist Mist Generator Systems Oil Mist is a centralized system in which the energy of compressed gas, usually air taken from the plant supply, is used to atomize oil. Oil is then conveyed by the air in a low pressure distribution system to multiple points of lubricant application. 54
Lubrication Oil mist Using pressurized air, the lubrication oil is atomized before it passes through the bearing. This method is especially suited for high speed lubrication due to the very low lubricant resistance. One lubricating device can lubricate several bearings at one time. Also, oil consumption is very low. But oil mist will pollute environment if there is not any mist recycling. 55
Lubrication Oil air 56
Lubrication Oil air With the air-oil lubrication system, an exact measured minimum required amount of lubricating oil is fed to each bearing at correct intervals. This measured amount of oil is continuously sent under pressure to the nozzle. A fresh lubricating oil is constantly being sent to the bearing, there is no oil deterioration, and with the cooling effect of the compressed air, bearing temperature rise can be kept to a minimum. The quantity of oil required to lubricate the bearing is very small, and this infinitesimal amount of oil fed to the bearing does not pollute the surrounding environment. 57
Lubrication Oil air The air used must be clean (5micron filter) and dry (40 dew point). The oil must be of high quality with a viscosity of 150 SUS at 38 C. Q= w d B in which Q = quantity in mm3/h w = coefficient = 0.01 mm/h d = internal bearing diameter in mm B = bearing width in mm 58
Lubrication Oil air 軸承潤滑檢知 59
Lubrication Oil air The diameter of the nozzle ranges from 0.5 to 1 mm. Feeding of oil-air to the rolling elements 60
Lubrication Oil air Direct oil injection through the outer bearing ring This type of lubrication is a newly developed system, typical for high speed applications. The holes allow the lubricant to directly reach the ball raceway contact and ensure the presence of an oil film even at high speed. (The diameter of this drainage hole must amount to at least 0.5 mm.) 61
Under race (NSK system) Lubrication Oil air 62
Heat 主軸熱源分佈 63
Heat 主軸溫度分佈 64
Heat 冷卻迴路設計 65
Final Test 主軸頻譜量測 66
Final Test 主軸精度檢驗 67
Feature 1. 智慧化 主軸加裝溫度感應器 加速規 與位移計, 達到高精度加工 2. 高速化 選擇較小刀具系統與小軸徑發 展, 達到高速加工 3. 輕量化 開發重量輕的短小型主軸, 達 到複合加工 68
69 THE END