User’s Guide Silent Tools® turning products
Introduction This guide will help you to use dampened boring bars (Silent Tools) to achieve the best possible results in internal turning. Silent Tools dampened boring bars and adaptors make it possible to maintain good productivity and close tolerances in long tool overhangs. With Silent Tools it is possible to successfully perform turning operations in overhangs beyond 4 x bar diameter (dmm).
Contents Introduction 2 Symbols used in this guide 2 1. Product overview 4 2. Choice of tools 6 Dampened bars for higher productivity 7 Calculation of boring bar parameters 8 3. Silent Tools in different machine types 9 Turret and multi-task machines 10 Tool post 11 Cutting forces and directions 12 4. Set-up Tool post clamping 14 14 Clamping of Silent Tools bars 17 Centre height setting tool 18 Set-up recommendations 19 5. Coolant requirements 20 6.
1. Product overview The selection of boring bar material has a big impact on achieving the best production economy: • Overhangs up to 10 x dmm are usually solved by applying a steel dampened boring bar to accomplish a sufficient process. • Overhangs over 10 x dmm require a carbide reinforced dampened boring bar in order to reduce radial deflection and vibration.
Maximum recommended overhang Internal turning is very sensitive to vibration. Minimize the tool overhang and select the largest possible tool size in order to obtain the best possible stability and accuracy. • For internal turning with steel dampened boring bars, the first choice is bars of type 570-3C. • For grooving and threading where the radial forces is higher than in turning, the recommended bar type is 570-4C. The table below shows the maximum recommended overhang for different bar types.
2. Choice of tools The design and dimensions of the component decide the diameter and length of the boring bar. • First choice for best clamping rigidity is the Coromant Capto® coupling or split sleeves. • Select the largest possible bar diameter for the application to achieve the best possible stability. • The diameter of the bore and the length needed to reach the bottom will indicate what type of boring bar should be used.
Dampened bars for higher productivity Use a dampened steel bar or a dampened carbide bar to: • Achieve higher productivity at less than maximum bar overhangs. • Improve the hole tolerance and surface finish. • Reduce the number of passes. Example The table below shows an example of how the higher static stiffness of a carbide boring bar makes it possible to: • Take larger depth of cut. • Increase the feed. • Reduce the number of passes. • Reduce the cutting time.
Calculation of boring bar load The load on a boring bar is mainly dependent on the depth of cut, the feed and the workpiece material. Maximum load for each boring bar is listed on page 26-28 and marked on each tool. In turning, the tangential force Ft can be calculated with formula 1. 1)) Ft = kc0.4 u 0.4 fn u sin Nr mc u fn u ap kc0.4; Specific cutting force at feed 0.4 mm/r. See Main catalogue for kc0.4 value. mc; Constant, depending on the material. Use 0.29 as general value.
3. Silent Tools in different machine types For all types of machines it is very important that the component and set-up are stable and rigid since vibration can be transferred to the boring bar. On larger bars, the weight of the bar itself can cause the tool post and set-up to become unstable. • Consider boring bar diameter and length. • Decide machine type and size.
Turret and multi-task machines Due to the design of the turret in a CNC lathe or the flexibility of a multi-task machine, the rigidity is usually reduced. • Small turret widths reduce the ratio between the clamping length and the bar diameter on larger cylindrical boring bars and consequently reduce the set-up stability. • Improve the stability by applying a long design tool holder and sleeve to increase the clamping length. Recommended clamping length minimum 4 x dmm.
Tool post Compared to turret lathes, a flat-bed lathe with a tool post can often be more rigid and stable. This results in the capability of holding larger and longer boring bars. The limitation of the machine in this case can be the tool post, the size of the machine and the rigidity in its design. The stability of the machine slides and gibs is an important factor for achieving good results when holding large Silent Tools boring bars with long overhangs.
Cutting forces and directions Conventional set-ups will risk overloading the boring bar and the tool post because the bar weight and the cutting force will act in the same direction. The result is instability and vibration tendencies because the tool post binds to the gibs. By adding a counterweight, the downward force through the tool post is balanced over the gibs resulting in a smoother machining process.
If the bar is placed upside down the cutting forces will be directed in the opposite direction to the gravity force. The counterweight may not be needed, depending on cutting data. Common set-up Running the bar conventionally generates cutting forces that push the insert downwards. Alternative set-up Running the bar upside down changes the direction of the cutting forces which improves the stablity. This can also improve chip evacuation.
4. Set-up Clamping in the machine is most important for successful machining with Silent Tools boring bars. Both when it comes to clamping of the tool post in the machine and to clamping the bar. Tool post clamping For best results, the tool post clamping should be with large gibs designed with the cross gibs wide apart, equal or wider than the clamping length, 4 x dmm.
The best tool post design is an A-frame where the bar is mounted directly over and in between the slides of the machine. Recommended A-frame mounting A less stable set-up is where the bar is hanging out and away from the most stable part of the machine. This set-up could cause instability and vibration when using large boring bars.
CoroTurn SL customer case story Total application solution for a long overhang. Bar design: • Steel dampened boring bar • 125 mm (5”) bar diameter • Overhang 10 x dmm • Boring bar and clamp holder for the tool post designed by Sandvik Coromant. • Existing flat bed lathe retrofitted according to an A-frame tool post designed to hold the bar. Result Unique clamping design provides a stable set-up and vibration free machining.
Clamping of Silent Tools bars • Ensure maximum contact around the entire circumference by using a split sleeve holder. Recommended clamping tolerance is ISO H7. • Split bushing material minimum 45HRC to avoid permanent deformation. • Never use screws in direct contact with the bar shank.
Centre height setting tool • Quick and simple method to accurately ensure correct centre height setting of the cutting edge. • For all cylindrical CoroTurn SL bars. 1. Attach the setting tool to the serrated edge of the cylindrical boring bar. 2. Twist the boring bar to the right position. 3. The bar is parallel when the bubble is in centre position.
Set-up recommendations, summary Clamping of bar: • Use a clamping length of minimum 4 x dmm. • Use split sleeve mounting for maximum clamping contact. • Use the most suitable boring bar for the operation. Centre height: • Double-check the centre height to ensure the correct cutting angle. Use a centre height setting tool.
5. Coolant requirements Pressure and direction Insert cutting zone: • Use coolant on the cutting edge to ensure low cutting temperature and improve the tool life. • For tools equipped with SL quick change heads, adjustment of the coolant nozzles needs to be done manually, to ensure coolant hits the cutting edge. Adjustment of nozzles: • Use a hexagon key to turn the coolant flow on or off. • Use the same hexagon key to adjust the direction of the nozzle.
The flow and volume of coolant becomes important to evacuate chips out of deep bores when machining long overhangs. Several nozzles increase the volume of the coolant Coolant can be applied through the rear of the boring bar using common size connectors with British Standard Pipe (BSP) threaded fittings. Sandvik Coromant dampened boring bars are equipped with a pre-threaded coolant intake hole D th, see tables on page 26-28.
6. Use of the product 3-pass method Method for achieving high accuracy in internal turning with slender boring bars where the deflection of the bar affects the obtained diameter. Example: 1: Enter the desired finished dia 40.000 2: Measure the dia before the first pass 37.000 3: Run the first pass. The programmed dia is: 4: Measure the dia before second pass: 5: Run the second pass. The programmed dia is: 6: Measure the dia before third pass: 7: Run the third pass.
Template for 3-pass method Copy this template and fill in your own values to make a 3-pass calculation. Template: 1: Enter the desired finished dia 2: Measure the dia before the first pass 3: Run the first pass. The programmed dia is: 4: Measure the dia before second pass: 5: Run the second pass. The programmed dia is: 6: Measure the dia before third pass: 7: Run the third pass.
Cut off boring bar length The most simple example of a special adaption is shortening a standard bar. In a Silent Tools boring bar the built in dampening mechanism is limiting the minimum length after cut-off.
Moment calculation When using Silent Tools bars in machines with automatic tool change (ATC) it is important to control that the moment given by the tool is within the specification that can be found on the machine or in the machine documentation.
G3/4” G3/4” G3/4” G3/4” G3/4” G1” G1” 0-700* 0-1000* 840-1200 570-3C 100 1100 570-3C 100 1500 570-3C 120 1900-80R/L 570-3C 150 2400-80R/L 1050-1500 570-3C 200 3200-80R/L 1400-2000 570-3C 250 4000-80R/L 1750-2500 1000 800 600 480 400 400 320 320 Min rec.
G3/4” G3/4” G3/4” G3/4” G3/4” G1” G1” 0-31.5 (0-800) 0-27.6 (0-700) 0-39.4 (0-1000) 35.0-47.2 (890-1200) 41.9-59.1 (1065-1500) 55.9-78.7 (1420-2000) 70.1-98.4 (1780-2500) A570-3C D48 45 A570-3C D64 44 A570-3C D64 60 A570-3C D80 75R/L A570-3C D96 95R/L A570-3C D128 126R/L A570-3C D160 157R/L Values in parentheses concerns Metric values. *) Contact your Sandvik Coromant representative. G3/4” D th 0-22.1* (0-560) Rec. overhang, inch A570-3C D48 33 Article Inch steel bars, product data 63.
- - - 384 480 300 384 480 600 720 C6-SL3C32352CR C6-SL3C40448CR C8-SL3C25280CR C8-SL3C32352CR C8-SL3C40448CR C8-SL3C50568CR-40R C8-SL3C60688CR-40R - 240 G3/4” 570-3C 60 1040-40 CR 240 300 G3/4” 380-720 570-3C 60 920-40 CR 200 380-840 G1/2” 623-701 570-3C 50 861-40 CR 200 160 160 128 128 100 100 Min rec.
7. Tips and hints General • If the oil in the dampened bar has become too viscose due to long storage or tranportation in low temperatures, knock gently on the bar with a rubber hammer. • For best performance, clean all male and female parts and lubricate with oil at least once a year. Lubricant should also be applied to the screws when needed. • Replace worn or exhausted screws and washers. • Dampened bars can become deformed due to the thin wall thickness.
Internal turning Reduce the risk of vibration: • Choose the largest possible bar diameter with the smallest possible overhang. • Use recommended clamping length, minimum 4 x dmm. Recommended clamping length • Use an entering angle close to 90° to direct the cutting forces axially. • Use an insert nose radius smaller than the cutting depth. Entering angle close to 90° • Ensure sufficient ap and fn to avoid vibration due to friction during cutting.
Internal turning Insert point angle: • Choose insert shape dependent on the entering angle and accessibility requirements of the tool. • In general, the largest possible point angle should be used to maximize insert strength and reliability. However, a large point angle needs more machining power and has a higher tendency to vibrate due to a large cutting edge engaged in the cut.
Internal turning Chip evacuation: • Use a tool holder with integrated coolant. • Insert geometries that give short and spiral formed chips are recommended. Recommended chip form • Consider alternative tool paths if chip formation needs to be improved. • Up side-down cutting units permit improved chip evacuation. • Increase coolant flow, redirect nozzles or utilize high pressure coolant (HPC) to minimize re-cutting of the chips. • Ensure that there is enough room for the chips between bar and hole.
Internal grooving and profiling Reduce risk of vibration: • Set-up should have the shortest possible overhang with the lightest cutting geometry possible. • Use a smaller insert and make several cuts instead of one. • Start from outside and make overlapping cuts inwards for best chip evacuation. • A finishing operation can be a side turning motion. Start from inside and turn outwards. • Ramping/turning can be used for improved chip control and may reduce vibration.
Internal threading Reduce risk of vibration: • Use modified flank infeed. • Infeed per pass should not exceed 0.2 mm and never be less than 0.06 mm. • Final pass always with infeed. • Use a sharp geometry for lowest cutting forces. Chip evacuation: • Use modified flank infeed to lead the spiral chips towards the opening of the hole. • Use inside out feed direction for best chip control. • Use coolant for best chip evacuation. • Use a chip-breaking geometry.
8. Extended offer Sandvik Coromant´s standard boring bars represent a good platform for optimized solutions and high productivity. However, sometimes a engineered solution is desirable. Special versions of dampened boring bars are often tapered, elliptical and/or curved, with the mounting adapted to the machine, or bars with overhang of up to 14 x dmm. For more information about our extended offer, contact your Sandvik Coromant representative.
Head office: AB Sandvik Coromant SE-811 81 Sandviken, Sweden www.coromant.sweden.com E-mail: info.coromant@sandvik.com C-2920:32 ENG/01 Printed on recycleable paper Printed in sweden, AB Sandviken Tryckeri © AB Sandvik Coromant 2010.
