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NCDMM High Performance Machining Theory and Best Practice: Part A “Are you Running at your Speed Limit?”

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Presentation on theme: "NCDMM High Performance Machining Theory and Best Practice: Part A “Are you Running at your Speed Limit?”"— Presentation transcript:

1 NCDMM High Performance Machining Theory and Best Practice: Part A “Are you Running at your Speed Limit?”

2 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 2 Who we are: Research & Development company serving the metalworking industry. Now a member of the Kennametal Complete® Metalcutting Solutions Suite. Our services are available when you purchase a new machine tool.

3 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 3 Toolholder System Comparison Side Lock Endmill Holder Collet Chuck Power Chuck Hydraulic Chuck Shrink Fit Type of Use Heavy Milling Roughing to Semi- Finishing Heavy Rough to Finishing Finishing Heavy Roughing to Finishing Torque Transmission HighMediumHighestLowHighest TIR at 3x D Suitability for HSMNo Small Sizes Only Yes MaintenanceNone Cleaning and Changing Collets Cleaning and Changing Parts None Additional Equipment No Yes Possible to use Collets NoYes No

4 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 4 Collet Chuck TG or ER Runout ” TIR Shrink-Fit Toolholder Runout ” TIR Weldon Side Lock Adapter Runout ” TIR Hydraulic Precision Chuck Runout ” TIR Runout at 3x Tool Diameter

5 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 5  Screw type holders  General purpose tool  Limit clamping area, typically less than 10-15%  High TIR, typically up 3x D.  Cause vibration problems  Low cost solution for holding tools  h6 or h7 tolerance shanks can be used, but h6 is preferred for better consistency. h6/h7 shank H6 = ”/+.0000” H7 = -.001”/+.000” Endmill Holder

6 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 6 Side Lock Endmill Holders

7 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 7 MYTH: Endmill Holder with.0002” TIR  Tool shank would have to be EXACTLY on-size (tolerance ”).  Hole would have to be ”/-.0000”.  Circularity would have to be near perfect.

8 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 8  Large Collapsing Range ER:.020,.040,.080  h6 or h7 tolerance shanks can be used to due large collapsibility  Low to medium clamping pressure - 10K PSI  General purpose clamping system  Large assortment of collets  Industry standard  Clamping around the circumference of the shank  Centering capability h6/h7 shank Collet Chucks

9 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 9 TIP: Use on-size collets or near the top of its range  For maximize gripping force and accuracy.  For example: For a ¼” shank tool use a ¼” (.2500”) collet rather than a 6-7mm (.2362” to.2756”)  Inside of collet flattens to square shape at the low range of capacity.  Reduces contact points.

10 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 10 Over-Torqued Collet Nuts  At a certain point when tightening the nut, the collet stops rotating* in the toolholder and the nut exerts pressure on one side.  In this exaggerated diagram, the collet nut is over-torqued causing the tool shank to pitch toward the engagement point. ER16 = 45 ft/lbs. ER25 = 100 ft/lbs. ER32 = 125 ft/lbs. *Better quality collets will bind less.

11 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 11 MYTH: Stub Collet Chucks are more stable and transfer power  Collet taper is steeper than toolholder shank.  Tightening collet with a tool distorts toolholder shank taper.  High-spotting taper causes vibration and reduces power transfer.

12 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 12 MYTH: Coated Collet Nuts grip better.  Coating causes nut to “stick” to the threads.  No increase in gripping force.  Similar effect as Loctite® on threads (false torque readings)

13 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 13 TIP: Through the Spindle Coolant wo/Thru-Hole Tools  Use larger size coolant discs than tool shank diameter.  Coolant will spray thru gap and toward cutting zone.

14 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 14  Small collapsibility on diameter (.001”)  h6 shanks, or better, should be used  High clamping forces - 30K PSI  Large assortment of collets common shanks  High accuracy  Large assortment of tools  For drilling, reaming & finish milling h6 shank Hydraulic Chuck

15 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 15 Hydraulic Toolholders Very thin membrane will distort under moderate to heavy milling.

16 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 16  Small collapsibility (h6 shanks)  High clamping forces - 60K PSI  Large assortment of collets - common shanks  Any shank type can be used  Must force collet nut on to increase the clamping pressure.  Bearings in chuck wear quickly, therefore reducing clamping pressure after repeated use. h6 shank Milling Chucks

17 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 17 T1 much higher than T2 - The clamping force generated on 20 mm is greater than on 12 mm (Increased surface pressure / greater surface contact on shank) 12 mm 20 mm Collet TIP: Increase gripping force by using collet

18 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 18  Small collapsibility (H6 shanks)  High clamping forces (50k PSI)  No collets  Tools can be made slender & narrow, but NOT short.  Expensive heating systems short tool change  Inexpensive heating systems long tool changing time  Heavy investment in tools & machinery h6 shank Shrink-Fit degrees

19 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 19 Cutting Tools that are not mounted on center cut oversize and one edge does all the work ” MYTH: The effect of runout DOES NOT diminish with a larger tool diameter.

20 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 20 Tapers that do not meet AT3 Tolerance also create forced vibration… 100% Contact Over-torquing or bad screw threads UndersizeOversize Pull Stud Off-Center Only 10 ft./lbs. Can distort taper.001”

21 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 21 …and they rob power. Insufficient taper contact cost you half of your available horsepower Example: Haas VF RPM

22 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 22 TIP: Dedicate toolholders to the machine.  Toolholders are softer than the spindle.  They will conform to the shape of the spindle.  Moving the toolholder to another spindle will create pressure points that cause fretting and damage.

23 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 23 RED = High TIR BLUE = Low TIR TIR directly affects surface finish. TIR also directly affects tool wear. Runout Effect on Surface Finish

24 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 24 Runout Effect on Tool Life

25 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 25 There is no such thing as a Pre-Balanced Tool Assembly  Pre-Balanced Toolholder + Unbalanced Pull Stud + Unbalanced Cutting Tool does not equal a Balanced Tool Assembly.  “Pre-Balancing” without the cutting tool can actually make things worse than doing nothing at all.

26 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 26 Assemblies MUST be balanced with the cutting tool installed  3/4” Endmill in Hydraulic HSK63A Chuck  Toolholder pre-balanced to RPM  Endmill alone had 22 gram-mm of unbalance.  If the endmill is not oriented in the exact same place every time, balance will change dramatically.

27 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 27 Imbalance and runout can cause vibration and chatter at all speeds  Imbalance and runout can create an once per revolution frequency that is different than the tooth pass frequency.

28 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 28 Balanced Tool Effect on Spindle Life  In our test example, every ONE HOUR of use of an UNBALANCED tool assembly (G20 vs. G5) reduces the life of the spindle by FOUR HOURS.  In other words, use unbalanced tools for three months and you will have to change or rebuild your spindle, the most expensive component on the machine, one year sooner. Plus, days or weeks of downtime.

29 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 29 TIP: Keep Tool Stack-Ups Consistent  “Random processes produce random results”  If you have a process that works, keep the tool lengths consistent.  Any change in tool projection may change the dynamics and create instability.  Don’t “cut then measure”.

30 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 30 Toolholder Back-Up Screws are insufficient  Overall length is a loose tolerance +/- 1/32” in ANSI +/- 1mm in ISO Too wide to maintain dynamic repeatability

31 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 31 Heat Shrink Pullback  Tool pulls back into toolholder.020” to.040” during the cooling cycle.  This pullback creates over 400 PSI of force, enough to fracture tool against back-up screw.

32 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 32 Retention Knobs: The Biggest Culprit  Improper retention knobs can cause run- out, taper distortion and resulting vibration.  High quality knob will have ground mating & gripping surfaces, ground qualified diameter pilot and 2A thread tolerance.

33 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 33 Retention Knobs: Effects on Balance Holder Balanced with Knob #1 G0.95 Same Holder with Knob Removed G11.4 Same Holder with Knob #2 G4.4 Same Holder with Knob #3 G12.8 Same Holder with Knob #4 G5.6 Same Holder with Knob #1 Reinstalled G3.3

34 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 34 TIP: Do not over-torque Retention Knobs  30 Taper: ft/lbs.  40 Taper: ft/lbs.  50 Taper: ft/lbs. Use Retention Knob Socket and Torque Wrench. Do not use Loctite®.

35 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 35 TIP: Keep it Clean  Treat toolholders like precision tools.  Do not handle shanks with bare hands.  Do not use Scotch-Brite or abrasives on shank.  Replace if damaged or worn (toolholders DO wear out)  Clean with degreaser, spray with WD-40 and wrap in VOC paper when not in use.  Plastic containers they come in are incubators for corrosion. Always wrap tools first.  Keep collets and nuts clean. Use ultrasonic jewelry cleaner.  Use taper cleaners for spindle and collet holders.

36 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 36 Customer 1 Customer 2 Customer 3 Customer 4 Customer 5 Customer 6 Customer 7 Manufacturer A Manufacturer B Manufacturer C Fragmented Supply Chain

37 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 37 Error Prone Supply Chain (3%+3%+3%)*5 = 45% Error Probability  The average tool assembly has FIVE components from THREE different suppliers.  If each supplier had a 97% shipment accuracy rate, the chance of receiving the correct assembly is only 55%

38 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 38 Error Prone Supply Chain  The average tool assembly has FIVE components from THREE different suppliers.  If each supplier had a 97% shipment accuracy rate, the chance of receiving the correct assembly is only 55% (3%+3%+3%)*5 = 45% Error Probability

39 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 39 Purchasing Through Catalogs 1964 Catalog 2004 Catalog

40 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 40 Online Expert System Online Tool Card® Purchasing and Redemption Online Bill of Materials Creation Online Expert Tool Configuration

41 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 41 Tool Evaluation Results Average Unbalance:86 g/mm Average Runout:.0035” TIR Fail AT3 Spindle Taper Test:78% Overtorqued Pull Studs:91% SOURCE: 1500 tool assembles tested or processed at BlueSwarf Labs between 2002 to 2005

42 Machine Tool Dynamics A Review From Part A

43 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 43 3 Types of Vibration (Frequency Behavior)  Free Vibration  characteristic, natural vibration.  drum, guitar string, transient motion at the start and end of a machine motion.  Not usually problematic in machining.  Forced Vibration (high displacement, normal forces)  deterministic, steady vibration (higher than normal).  unbalanced shaft or rotor is the cause, eccentricity, cutting forces second cause.  Can be a problem, resonance, but limited, due to high stiffness of machine setups and cutting forces are no higher than normal.  Self-Excited Vibration (excessive displacement, excessive forces)  steady input of energy in some way modulated into vibration.  whistle, violin, clock, chatter.  When it occurs in machining (inevitable as speeds and power increase) it is very violent, destructive and very difficult to eliminate.

44 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 44 Types of Vibration (Illustrated) Free Vibration, no external force, frequency natural, amplitude decays. Forced vibration, frequency that of force, amplitude steady, dependent on ratio of force frequency to natural frequency. Self-excited vibration: no external periodic force, frequency close to natural, amplitude increases to saturation. ~

45 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 45 Dynamic Relationship in Cutting (simple visual)

46 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 46 Tool/Spindle/Machine Signature (at tool tip) Frequency Response Function (FRF) (20 mm 3-fluted Tool in 30 kW 24 krpm Spindle) Flexibility Dynamic Static Flexibility Defines deflection of cutter as a function of force and frequency.

47 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 47 Vibration from Cut Results from:  Stability/Chatter Power: cut depth, engagement, feed. Number of cutting edges. Cutter diameter. Machineability of material.  Forced/Resonance Unbalance. Eccentricity of cutter. Chip load.  Both are strictly dependent and controlled by the frequency signature of the cutter and part (frequency, stiffness and damping).

48 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 48 Basis for Analysis: The Stability Lobe Diagram Process Damping

49 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 49 Effects of Stiffness and Mass  Dominant frequency of the cutter will dictate the optimal spindle speed.  The frequency is determined by the following relationship. Frequency (of the stack up) ~ stiffness/mass  Therefore increase the frequency, then increase the speed you can run at.

50 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 50 MYTHS: Dynamics of Machining  Lowering spindle speed is not always the solution.  Feed only affects unstable machining. It has no or very little effect on stable machining.  Shorter/Stiffer is not always the best approach.

51 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 51 TIPS: Dynamic Relationships  For a particular family or class of tooling (e.g. 4-7 L/D end mills or say 2-4” diameter indexables…) Increasing stiffness increases frequency and increases the speed that should be cut at, and vice versa. Increasing mass (e.g. bigger more massive holders) reduces frequency and reduces the speed to cut at. The exact amount of the change is not readily determined unless you make a measurement of the stack-up or use trial and error. M Frequency/Speed

52 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 52 TIPS: Other Dynamic Guidelines  Fewer teeth cause: Depth of cut increases proportionally (MRR remains the same due to lower feed rate). Spindle speed increases by a proportional amount. As an example, using a 2 fluted cutter instead of a 4 fluted cutter allows you to run at least twice as deep at twice the speed. Possibly an “Optimal speed” at the machine and tools’ “speed-limit”.

53 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 53 Application 1: Eliminating Chatter (existing setup)  OFF-LINE (new cutter or new program): Stability diagram points to “premium spindle speeds”.  In-Process (current chatter condition with pre-existing NC program). Use microphone to monitor cut. Chatter or resonant can be detected and compared to prediction.  Periodically monitor high volume jobs to insure chatter or resonance is not present. Unstable Torque Limit Stable Speeds Chatter TXF Harmonizer

54 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 54 Audio Chatter Signal

55 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 55 Application 2: Maximizing Machine and Cutter Performance  Identify 20% of tooling that performs 80% of metal removal or consumes 80% of machining time.  Produce MRR stability maps to identify maximum productivity location.  Record in database.  Make information accessible to NC programmers.  Have machinists monitor and provide feedback periodically regarding performance. Fine tune when necessary, update database and re-measure as needed (generally not required). Highest Power Stable Region with little chance to chatter. 20 krpm max speed

56 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 56 Application 3: Matching tooling to machine.  Identify possibly redundant tooling systems, e.g. multiple length cutter configurations, multiple flute, cutters used across machine platforms, etc.  Measure tooling systems across machine tools.  Review “stability chart” results.  Identify those cutters with superior cutting performance in a given machine and machine- cutting tool combinations.  Look for stability that will result in dramatic reduction in required setups and provide preferred machine-tooling configurations (e.g. better identify roughers, finishers, face millers, end millers, 2 flute machines, 3 flute machines, etc.)  Likely, multiple length cutters of a given size or multiple tooling systems can be eliminated if designated as machine specific.) Shorter Cutter Longer Cutter Larger deeper Stable pocket, (shorter cutter not needed).

57 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 57 Application 4: Tool Tuning (also for new MT purchases)  Similar to matching machine to tooling (application 3) except looking for specific alterations/modifications that will maximize performance for given machine.  Measure original cutter.  Look for cutters where strong stability lobes can be “shifted” to improve performance at higher speeds.  Simply shortening a cutter may improve stability some but shortening it to an ideal length can produce step changes in performance. Original cutter Altered Stack-up (shortened) Performance at least 10X better at maximum speed

58 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 58 Downstream Benefits  Proper implementation of “speed-limit” techniques will lead to:  Elimination/minimization of adverse vibrations  Elimination of catastrophic breakage improved wear on machine and tools thereby lowering maintenance costs and consumables  Expanded flexibility in types of parts and manufacturing processes.  Increased through-put and productivity per machine for any tooling system utilized.  Improved quality and more predictable processes leading to better cost estimation.

59 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 59 Demo Videos  Straight Cut  Corner Cut  Low Speed

60 April 19, 2015©Copyright 2007 BlueSwarf Manufacturing Laboratories 60 Demo’s  Demo 1: 3 Flute carbide tool in PowerGrip holder. Start at 9,000 rpm at low-depth. Finish at ~7,450 rpm at high-depth Will compute improvement in stable MRR.  Demo 2: 5 insert indexable 2” cutter Start at 6,675 rpm Change speed to 6,550 rpm Will observe change in surface and frequency content  Demo 3 (if time permits) 2 Flute carbide tool in Hydraulic holder. ~2” shorter gage length No optimal speed (start at 9,000 rpm). MRR no better than properly selected speed for Demo 1 tool.


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