How to reduce vibration in metal cutting
Turning - Rotating Introduction Vibration in metal cutting is familiar to every machine tool operator. This phenomena is recognised in operations such as internal turning, threading, grooving, milling, boring and drilling, to which there are several reasons why this problem occurs. Some are related to the machine tool itself, to the clamping of the tool, the length and diameter of the tool holder and the cutting data to be used. More of this will be discussed later.
Sandvik Coromant – How to reduce vibration in metal cutting
Contents Turning Practical tips and hints on how to reduce vibrations ................ 02 Select your tool system ................................................................. 04 Turning: hands on information ....................................................07 Threading: hands on information ................................................12 Grooving: hands on information .................................................14 Holding the bar ..............................................................
Milling Practical tips and hints on how to reduce vibrations ................ 28 Select your tool system ..................................................................32 Main applications and milling concepts ......................................32 Operations – tool recommendations ...........................................37 Clamping ....................................................................................... 40 Hands on info ................................................................
Turning Practical tips and hints on how to reduce vibrations Dimension and tolerance problems: 1. Choose a smaller nose radius. 2. Choose a more wear resistant grade. 3. If there is between 4 x D to 6 x D overhang choose a carbide bar. 4. If there is over 6 x D overhang, choose a Silent Tool. Chip jamming: 1. Increase the coolant flow. 2. Change the insert geometry. 3. Reduce the cutting speed.
Bad surface finish: 1. Increase the coolant flow. 2. Choose an insert with a sharp cutting edge. 3. Check that all chips have been evacuated. 4. Choose a smaller nose radius than the depth of cut. 5. If there is between 4 x D to 6 x D overhang, choose a carbide bar. 6. If there is over 6 x D overhang, choose a Silent Tool. Vibration: 1. Choose a smaller nose radius than the depth of cut 2. Choose a positive insert with open chip breaker. 3. Increase the feed. 4.
Select your tool system One application within metal cutting that is very sensitive to vibration is internal turning. The different tools for the applications have various parameters that can be adjusted to suit the machine, the component and the material. In this chapter we will talk about the choice of tooling, various applications, how to minimise the risk of vibration and how to improve productivity.
The boring bar families above include insert geometries that are designed for specific applications, such as finish turning of steel materials, roughing in stainless steel machining etc. This is needed to become more productive at every application. Solid steel bars Recommended for overhangs up to 4 x bar diameter. Carbide reinforced bars Recommended for overhangs up to 6 x bar diameter. Carbide reinforced and damped bars Recommended for overhangs up to 10 x bar diameter.
CoroTurn SL (type 570) Modular system for various operations – turning, grooving and threading and holders, including solid steel and Silent Tool holders. Also available are cylindrical bars and Coromant Capto bars. This CoroTurn SL system of boring bars ranges from 16 mm to 100 mm diameter, and all having the benefit of a quick change system. CoroTurn, CoroCut and U-lock solid bars Boring bar programme including Coromant Capto steel bars and cylindrical bars with both steel and carbide bar material.
Turning Choice of insert Choosing the right insert can be enough to eliminate vibration and also improve your manufacturing productivity. Nose radius: It is important to choose a nose radius that is smaller than the cutting depth as this has the same effect as choosing the correct entering angle. If the nose radius is too large it will push the tool in the radial direction and affect the dimensions of the component.
Insert size: It is important to choose an insert strong enough to withstand the cutting forces but at the same time it must suit the component and its application. Too large a cutting depth will lead to excessive cutting forces and too small cutting depth will lead to increased friction between the insert and component causing component dimension problems. Cutting force is extremely important when using long overhangs.
Examples of geometry: - PF: Finshing of steel materials - PM: Medium machining of steel materials - PR: Roughing of steel materials Practical hints: • Choose an open chip breaker, medium chip breaker (PM), instead of a finishing geometry as the finishing geometry can break the chips too hard and lead to excessive cutting forces resulting in bad surface finish. Insert style: Depending on the operation – longitudinal turning or copying – the choice of insert style affects the result of the machining process.
Tool overhangs: Depending on the depth of the hole that needs to be turned, it is important to choose the correct type of tool holder and tool holder material. Boring bar materials: As seen on the diagram the following boring bar materials can be selected to suit the length to diameter ratio overhangs.
Chip evacuation: Chip evacuation during boring is critical to performance and the security of the operation. Relatively short, spiral-shaped chips should be aimed for with internal turning. These are easy to evacuate and do not place such large stresses on the cutting edge when chipbreaking occurs. Hard breaking of the chips, when very short chips are obtained, uses more power and increases vibration. On the other hand, long chips make chip evacuation more difficult and present a risk of swarf-clogging.
Threading Choosing the correct tool for the application Choice of tooling family: T-MAX U-Lock for threading hole diameters from 12 mm CoroCut MB for threading hole diameters from 10 mm CoroCut XS for threading hole diameters from 4 mm Chip evacuation: Chip evacuation is also very important when internal threading, particularly the feed direction which should be from inside out giving better chip control.
Rounded (ER treated) cutting edge First choice in most operations and materials Example: R166.0G-16MM01–150 Geometry F Sharp cutting edge Reduced cutting forces and good surface finishes Example: R166.0G-16MM01F150 Geometry C Chip breaking geometry For maximum chip control and minimum supervision Example: R166.0G-16MM01C150 Inserts: First choice is the all round geometry the GC 1020 for the ISO P, M and K areas.
Grooving Choosing the correct tool for the application Choice of tooling family: CoroCut for grooving hole diameter from 25 mm T-MAX Q-Cut for grooving hole diameter from 20 mm CoroCut MB for grooving hole diameter from 10 mm CoroTurn XS for grooving hole diameter from 4.2 mm Chip evacuation: To avoid chip jamming within grooving operations it is important to direct the coolant into the groove and evacuate the chips.
Inserts: We recommend you use sharp, light cutting inserts with a positive chip breaker such as the CoroCut – CM or GF geometry or the T-Max Q-Cut 5F or 4G geometry. Also it is beneficial to use thin coated inserts which will enable a smooth cutting action and produce a minimal radial force. Grooving applications: When grooving it is possible to change the application to minimise the risk of vibration by selecting a smaller insert width and making several cuts instead of one.
Problem solving Chip jamming: • Use the largest possible amount of coolant as this will help to evacuate the chips from the groove. • Choose a different geometry to reduce the risk of chip jamming. Dimension problems (tolerances): • Choose a Silent tool holder which will reduce the vibration – max overhang is 5 x D. • Choose sharp and positive insert geometry, CoroCut – CM or ground – GF as it enables a smooth cutting action and minimum deflection from the workpiece.
Holding the bar After choosing the boring bar material select the most suitable clamping method for the machine in question. Stability is the keyword to turn bores to the appropriate criteria such as dimension tolerances and surface finish. It is essential, for retaining satisfactory results, to clamp the cylindrical boring bar in a split sleeve, as this will have maximum contact area. With EasyFix sleeves the best possible clamping is achieved together with exact centre height positioning.
operations in order to achieve the best results. It is particularly important when working with overhangs stretching beyond 4 times the L/D ratio. Sandvik Coromant also offers a full programme of conventional tool holders. Clamping with EasyFix sleeves for cylindrical bars: EasyFix gives a fast and simple way to achieve correct indexing of centre height when mounting cylindrical bars into the machine, due to its spring loaded plunger design.
Internal machining theory Internal turning Many external turning operations are also found in boring, as performed with stationary turning tools, (as opposed to boring operations with rotating tools, such as in machining centres). With external turning, the tool overhang is not affected by the length of the workpiece and the size of the tool holder can be chosen so that it withstands the forces and stresses which arise during the operation.
Cutting forces in boring operations: When the tool is in cut, the tangential and radial cutting forces will endeavour to deflect the tool away from the workpiece. The tangential force will try to force the tool downwards and away from the centre line, and in doing so will also reduce the tool clearance angle. When boring small diameter holes, it is particularly important that the clearance angle of the insert is sufficient in order to avoid contact between tool and wall of hole.
Boring very deep holes The internal machining of large diameter holes, deep holes and a combination of both usually needs tool solutions where stability during machining is maximized through combinations of tool solutions.
When discussing tool overhangs of 10 times the diameter or more, damped boring bars and carbide re-inforcement should be considered or a combination of both. The cutting unit coupling is a critical link and needs to be beyond any risk of instability. The front end should also be characterized by low weight. This means that if there is scope for diameter reduction of the cutting unit or the last part of the bar, this is worth considering.
Eliminating vibration with damped boring bars The usual cause of vibrations during machining is the dynamic interaction between the cutting process and the machine tool structure. The source is the variation of cutting force generated between the tool and workpiece. This force strains the structure elastically and can cause a deflection of the tool and workpiece, which alters the tool-work engagement.
or the diameter at the front end of the bar will contribute towards minimizing the vibration tendency. Damped boring bars – Silent Tools - include tools that are pre-tuned to the correct frequency in relation to the tool length. This basically means setting up the damped boring bar and the machine to be set up the same as a conventional, solid boring bar.
Silent Tools Productivity with slender tools When machining deep cavities or with long overhangs you can be faced with vibration problems. One way to overcome this is to reduce the depth of cut, the speed or the feed. Losing productivity in favour of keeping the process running is not beneficial. Productivity is the number one important issue in being competitive. The use of a Silent Tool when going deeper into a bore, will retain, or in many cases improve your productivity.
Which products have Silent Tools Bar dia. 10 - 12 mm CoroTurn 107 and CoroTurn 111 Boring bars Pre-tuned and easy to use cylindrical boring bars with carbide shaft. Optimum performance in a split sleeve holder. Do not use screws directly onto the bar. Shank diameter 10/12 mm and min. hole Ø 13 / Ø 16 mm. Recommended tool overhang from 6-10 x bar diameter. Integrated tip-seat pocket designed for T or D style inserts. Bar dia.
Bar dia. 80-300 mm 580 Carbide Reinforced Boring bars Tunable carbide reinforced cylindrical boring bars. Coolant through the centre and 580 coupling in front. Shank diameter Ø 80 - Ø 300 mm. Carbide reinforced for increased static stiffness. Do not use screws directly onto the bar. Recommended tool overhang from 10-14 x bar diameter. Designed for flat bed machines. Special tools available for slant bed machines. Reduction adaptor in front makes it possible to use a wide range of cutting units.
Milling Practical tips and hints on how to reduce vibrations Adaptor Type and Size 1. Choose the shortest possible adaptor. Every millimetre is important. 2. Choose the largest possible diameter/size of the adaptor 3. For small milling cutters use if possible a tapered adaptor. 4. If possible use Coromant Capto instead of a weaker coupling type. 5. For shank couplings and short overhang use a high clamping force adaptor, e.g CoroGrip. 6.
Positioning, radial and axial depth of cut 1. Choose a milling cutter with correct ratio between the milling cutter diameter and the width of the workpiece. 2. The width of cut should be approximately 75% of the milling cutter diameter. 3. Positioning the milling cutter off-centre in relation to the workpiece surface. 4. Reduce the radial and axial depth of cut. Insert 1. Choose a light cutting geometry (L-geometry) with a sharp cutting edge. 2.
Down Milling / Up Milling Generally Down Milling is recommended in almost every milling operation wherever the machine, fixturing and workpiece allows it. But in some cases it can be favourable to use Up Milling to reduce vibration tendencies. Especially when fixturing and/or workpiece is weak in a specific direction. Cutting Data 1. If possible try to decrease (or in some cases increase) the cutting speed to move away from the vibration frequency range. 2. Normally increase the feed/tooth.
Workpiece 1. Affix the workpiece in the most favourable way to support the cutting forces which arise during the machining process. 2. Use milling concepts with design and entering angle which generate cutting forces in the most stable direction of the workpiece. 3. Optimize the machining strategy and direction to obtain the most stable cutting conditions as possible. Machine 1. Choose machining strategy and cutting force directions to take full advantage of the machine stability. 2.
Select your tool system In some specific milling operations vibration tendencies will more or less always occur. Sandvik Coromant offers a lot of different milling concepts for a number of different applications. Each concept has its own specific properties and advantages considering machines, fixturing, components, materials, etc. Below you will find a short description of each milling concept and a guide to what tool to choose for highest productivity and output.
CoroMill 290 - A good 90-degree shoulder milling concept with four cutting edges per insert for best economy. It´s the first choice for a square shoulder facemill in short chipping materials (ISO-K) and hardened steel (ISO-H). CoroMill 790 - A highly productive 90-degree shoulder milling cutter for a number of different operations from roughing to finishing. The first choice for ISO-N materials. Very good performance in helical interpolations and boring.
CoroMill Century - A lightweight milling cutter concept for face and shoulder milling in ISO-N, ISO-H and ISO-K materials. It is perfect for high speed machining in non-ferrous materials. Balanced cutter body and axial adjustability of the insert contributes to a smooth, stable and vibration-free cutting action. - A versatile and light cutting round insert concept for face milling, profiling, ramping and helical interpolation. High and vibration-free metal removal with both short and long tools.
Profile Milling CoroMill 216 CoroMill 216 - A robust ball endmill concept for roughing operations. Primarily general contouring and profiling. Also suitable for pocketing by ramping or helical interpolation. Insert grades and geometries for ISO-P, ISO-M and ISO-K applications. CoroMill 216F - A ball nose concept for high speed finishing to super finishing of profiles. Possible to achieve a workpiece surface finish equal to what´s possible with a solid carbide tool.
Slot Milling CoroMill 331 CoroMill 331 - A multi-purpose side and face milling cutter concept with high precision capability for numerous operations. A large standard programme and Tailor Made range make it possible to select and optimize for highest precision or productivity. The design makes the setting easy. Insert grades and geometries for all workpiece materials. T-Max Q-cutter - A versatile slitting and cutting off concept.
Operations – tool recommendations some examples and alternative applications General Shoulder and Face Milling Slot Milling - CoroMill 331 Face Milling - CoroMill 200 Face Milling - CoroMill 245 Profile Milling - CoroMill 390 Shoulder Milling (long edge) CoroMill 390 Shoulder Milling - CoroMill 390 Face Milling - CoroMill 300 High feed Face Milling - CoroMill 210 Shoulder Milling, full slot - CoroMill Plura Sandvik Coromant – How to reduce vibration in metal cutting 37
General Profile Milling High feed Face Milling - CoroMill 210 Profile Milling, helical interpolation - CoroMill 216 Profile Milling, ramping - CoroMill 390 Profile Milling, finishing - CoroMill 216F Plunge Milling - CoroMill 210 Shoulder Milling, slot - CoroMill Plura Face Milling - CoroMill 200 Profile Milling - CoroMill 300 38 Profile Milling, helical interpolation - CoroMill 300 Sandvik Coromant – How to reduce vibration in metal cutting
Aluminium machining, different operations Profile Milling, pocketing - CoroMill 790 Face Milling - CoroMill Century Slot Milling - CoroMill 331 Profile Milling, pocketing - CoroMill 390 Shoulder Milling, slot - CoroMill Plura Sandvik Coromant – How to reduce vibration in metal cutting 39
Clamping One application within metal cutting that is very sensitive to vibration problems is milling with long overhang. The different tools for the application have various parameters that can be adjusted to suit the machine, the component and the material. In this chapter we will show some comparison between different holding systems.
Choice of holding tools • Use stiff modular tools with good run-out accuracy • Modular tools increase the flexibility and the possible number of combinations – use largest possible diameter on holding tools (extensions, adaptors) relative to cutter diameter • For spindle speeds over 20,000 rpm use balanced cutting and holding tools Long overhangs The Coromant Capto® modular holding tool system allows combinations of long or short basic holders, extensions and reductions to an assembly of required length, wi
CoroMill® cutters and holding tools with threaded coupling Coromant Capto® Coromant Capto® ISO/MAS HSK HSK Basic holders Solid carbide extension Intermediate adaptors CoroMill cutters 210 42 390 300 216 Sandvik Coromant – How to reduce vibration in metal cutting
Hands on information Insert grade: Choose a small edge rounding (ER). Go from a thick coating to a thin one, if necessary use uncoated inserts. Insert geometry: Use sharp and positive inserts with a chip forming capacity. Entering angle: The smaller the entering angle, the thinner the chip will be and the further it will spread along the cutting edge. This will allow a higher feed per tooth.
Tooth pitch: When machining with long tool overhangs or unstable conditions, it will have a positive effect using a coarse pitch (L) cutter. Sometimes it can be a good idea to remove some of the inserts (e.g remove two inserts from a four inserts cutter). Milling direction: Down milling is the first choice for most machining operations.
Entry/exit: Avoid a situation where the centre-line or the cutter is in line with the workpiece edge. In this situation the insert is leaving cut when the chip thickness is at its maximum, with very high shock-loads at entry and exit. Chip evacuation: Use compressed air to prevent recutting of the chips. In deep cavity milling, this is especially important. Notice that a coarse pitch (L) cutter will have more space to evacuate the chips.
Milling strategy for opening a cavity There are several ways to open a cavity. Three common methods can be the following: Two axis ramping: One of the best methods to reach a full axial depth of cut is linear ramping in the X/Y and the Z axis. If the correct starting point is chosen, there is no need for milling away stock from the ramping section. Use compressed air to get the chips out of the cavity. Three axis ramping: Feeding the tool in a helical shaped path in the axial direction.
Drilling/plunging: Pre-drilling followed by a plunge milling operation is a third option to open a cavity. This option requires an extra tool, more time for positioning and an extra position in the tool magazine. The positive advantage is that it is possible to machine with high axial feed. Use compressed air to get the chips out of the cavity. Milling in corners: Ensure that all programmed radii are 15% larger than the cutter diameter. Keep the same feed and speed in the corners.
Boring Practical tips and hints on how to reduce vibrations Adaptor Type and Size 1. Choose the shortest possible adaptor. Every millimetre is important. 2. Choose the largest possible diameter/size of the adaptor. 3. For long overhang (>4xD) use damped adaptors, Silent Tools. 4. If possible, use a tapered adaptor to increase the static stiffness and to reduce the deflection. 5. For long overhang, make sure to have a rigid clamping with flange contact in the spindle.
Insert 1. Choose a light cutting insert with a positive cutting geometry. Knifeedge inserts are first choice. 2. Choose a small nose radius. For finish boring recommended nose radius is 0.2 mm. Do not use larger nose radius than 0.4 mm. Try to choose a nose radius which is smaller than the depth of cut. 3. Use sharp inserts with relatively thin coatings. Try an uncoated insert. They will have a sharper cutting edge. 4. T-style inserts are first choice for boring operations. Entering angle 1.
Depth of cut 1. Do not exceed half the cutting edge length when rough boring as this will result in too high cutting forces on the cutting edge. When finish boring the maximum cutting depth is small. Typically less than 0.5 mm. Tolerance of hole diameter 1. For finishing with one insert, a tolerance of IT7 can be achieved under good conditions. 2. Tolerances will be influenced by the clamping of the tool holder, the fixture of the component, wear of the inserts etc. 3.
Select your tool system For roughing and finishing in boring operations there are several options. Boring tools for roughing: For roughing operations use Duobore with two inserts or CoroBore 820 with three inserts. For long overhang, beyond 4 x bar diameter, a damped Duobore adaptor is recommended.
Boring tools for finishing: For finishing operations use a single edge fine boring tool or CoroBore 825 with one insert.
Hands on information Nose radius: Use a small nose radius, 0.2 mm is recommended for finishing. A bigger nose radius will give larger radial forces. Insert size: Do not use a a bigger insert size than necessary. Geometry: Use a sharp and positive geometry. A knife edge insert is a good alternative. Insert style: Use a T-style insert and a 90 deg. entering angle. Tool overhang: Always use as short as possible overhang.
Off centre boring In some spindles it is possible to do off centre boring. It is important to remember that the centripetal force will increase and that too high spindle speed may give unstable conditions. Machining at long overhangs with damped tools the damping system can be taken out of function due to too high centripetal force. At Teeness.com it is possible to calculate the maximum spindle speed at a certain eccentric radius.
Silent Tools Silent tools within milling Coromant Capto: HSK: Shank with metric and inch pilot Shank with threaded coupling Shank with metric and inch pilot Shank with threaded coupling - For rough and fine boring operations beyond 4 x dia. tool overhang, it will be a big advantage to use Silent Tools. - In milling applications, it is more difficult to give an exact overhang ratio when to change from solid tools to Silent Tools. For example will a 390 milling cutter (90 deg.
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