Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Frictional Coefficients Between Plug and Sheet
Document related concepts
no text concepts found
Transcript
Frictional Coefficients Between Plug and Sheet [Problems with Theories, Experiments in Plug Assist] James L. Throne Sherwood Technologies, Inc. Dunedin Florida 34698-3347 Paper presented at 2004 Thermoforming Conference Indianapolis IN TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Objective To better understand the problems with theories and experiments in plug assist thermoforming TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Caveat It is my intent to raise concerns about the ways in which we view the interaction between the plug and the sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Caveat It is my intent to raise concerns about the ways in which we view the interaction between the plug and the sheet It is NOT my intent to provide answers to the questions about the interfacial conditions between the plug and the sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Think about this Question! In plug-assist thermoforming, what is sliding against what? TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Outline I. A discussion of the coefficient of friction issue II. A sliding experiment III.Some prototypical plug experiments IV. Conclusions TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet I. Some thoughts on the coefficient of friction TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Coefficient of Friction • Frictional characteristics considered part of tribology • Tribology is study of friction, lubrication and wear • Traditional view is that all three are extant in thermoforming TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Historical views of coefficient of friction-I “The relation that the power required to move a body bears to the weight or pressure on the body is known as the coefficient of friction.” W.M. Davis, Friction and Lubrication, A Handbook For Engineers, Mechanics, Superintendents and Managers, The Lubrication Publishing Co., Pittsburgh PA, 1903. TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Historical Views of coefficient of friction-II “The coefficient of friction is the ratio between the resistance to motion and the perpendicular pressure.” W.M. Davis, Friction and Lubrication, A Handbook For Engineers, Mechanics, Superintendents and Managers, The Lubrication Publishing Co., Pittsburgh PA, 1903. TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Historical Views of coefficient of friction-III “There is no other element in connection with… lubrication… that has received so much consideration as that of the coefficient of friction, and yet there is no other that is in so indeterminable a state…” Mr. Hall, Car Lubrication, ca. 1900 - cited in W.M. Davis,Friction and Lubrication, A Handbook For Engineers, Mechanics, Superintendents and Managers, The Lubrication Publishing Co., Pittsburgh PA, 1903. TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Historical views of coefficient of friction-IV “While the coefficient of friction must always be taken into consideration when designing and constructing machinery, it is not always practicable to calculate it with any degree of accuracy, [and] in fact it can only be determined absolutely by experiment.” W.M. Davis,Friction and Lubrication, A Handbook For Engineers, Mechanics, Superintendents and Managers, The Lubrication Publishing Co., Pittsburgh PA, 1903. TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Coefficient of Friction Following discussion assumes that frictional effects are extant in plug-assisted thermoforming TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Blunt-nose plug moving into sheet Contact may involve some sheet sliding TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • • • • Frictional Conditions Between Plug* And Sheet Static CoF, no sliding (coefficient max) Sliding CoF, no static (coefficient zero) Some static, some sliding Slip-stick behavior *or mold wall TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Frictional Conditions Between Plug* And Sheet • Static CoF, no sliding (coefficient max) • Sliding CoF, no static (coefficient zero) • Some static, some sliding • Slip-stick behavior *or mold wall Which of these are relevant when plastic stretches against plug surface? TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Coefficient of Friction • Static CoF - Initiation of sliding between plug (and mold wall) and sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Coefficient of Friction • Static CoF - Initiation of sliding between plug (and mold wall) and sheet • Sliding CoF- Continuation of sliding between plug (and mold wall) and sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Coefficient of Friction • Static CoF - Initiation of sliding between plug (and mold wall) and sheet • Sliding CoF - Continuation of sliding between plug (and mold wall) and sheet • Static friction value usually 100s to 1000s greater than sliding friction value, but not always! TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Sliding Coefficient of Friction • Contact area increases with increasing load Plastic sheet Plug TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Sliding Coefficient of Friction • Contact area increases with increasing load • Ergo, coefficient independent of load Plastic sheet Plug TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • Are there other factors influencing the interaction between the plug and the sheet? TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • Are there other factors influencing the interaction between the plug and the sheet? • Wear TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Sliding Coefficient of Friction Wear v. sliding friction Friction maximum in polymer transition region Wear minimum in polymer transition region TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Sliding Coefficient of Friction Friction maximum, wear minimum in polymer transition region Glass Transition Region TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • Are there other factors influencing the interaction between the plug and the sheet? • Wear • Dry v. wet sliding TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Dry v. “wet” sliding • Dry sliding assumes no lube between surfaces TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Dry v. “wet” sliding • Dry sliding assumes no lube between surfaces • Plastics exude small molecules (low MW polymers, additives, processing aids) TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Dry v. “wet” sliding • Dry sliding assumes no lube between surfaces • Plastics exude small molecules (low MW polymers, additives, processing aids) • Small molecules reside between plug and sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • • • • Dry v. “wet” sliding Dry sliding assumes no lube between surfaces Plastics exude small molecules (low MW polymers, additives, processing aids) Small molecules reside between plug and sheet Small molecules transfer from sheet to plug TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • • • • • Dry v. “wet” sliding Dry sliding assumes no lube between surfaces Plastics exude small molecules (low MW polymers, additives, processing aids) Small molecules reside between plug and sheet Small molecules transfer from sheet to plug Interface may go from dry to wet (or wet to dry!) as plug advances into sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • Are there other factors influencing the interaction between the plug and the sheet? • Wear • Dry v. wet sliding – More than one type of wet sliding TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Two types of wet sliding • Boundary lubrication – low sliding velocity, low interfacial viscosity, high loading TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Two types of wet sliding • Boundary lubrication – low sliding velocity, low interfacial viscosity, high loading • Hydraulic or hydrodynamic lubrication – high sliding velocity, high viscosity, low loading TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Two types of wet sliding • Boundary lubrication – low sliding velocity, low interfacial viscosity, high loading • Hydraulic or hydrodynamic lubrication – high sliding velocity, high viscosity, low loading • Boundary lubrication occurs during start/top activities [as might be the case with plugs in contact with sheet] TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • • • • Two types of wet sliding Boundary lubrication – low sliding velocity, low interfacial viscosity, high loading Hydraulic or hydrodynamic lubrication – high sliding velocity, high viscosity, low loading Boundary lubrication occurs during start/top activities [as might be the case with plugs in contact with sheet] Boundary lube friction 100s greater than hydraulic lube friction TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Two types of wet sliding Sheet does not move far under plug force TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Measuring Frictional Coefficients TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Traditional methods of measuring coefficient of friction • Weight sliding on inclined surface TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Traditional methods of measuring coefficient of friction • Tabor “Abrasor” – stylus rubbing on rotating disk TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Traditional… • Other methods • No methods entirely applicable to measuring plugsheet friction… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Observations • Frictional resistance is a complex issue: o o o o Static v. sliding Dry v. wet The extent of sliding Boundary v. hydrodynamic effects TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Observations • Frictional resistance is a complex issue: o o o o Static v. sliding Dry v. wet The extent of sliding Boundary v. hydrodynamic effects • Standard frictional devices may not give reliable results TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Are We Answering the Question? In plug-assist thermoforming, what is sliding against what? TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet II. A sliding experiment TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Traditional… • Other methods • No methods entirely applicable to measuring plugsheet friction (except g but modified) TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug-sheet friction – experiment • Consider figure below… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug-sheet friction – experiment • Consider figure below… – A is plug material, B is plastic sheet, p is applied load – Plug material moved against sheet… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug-sheet friction – experiment • Consider figure below… – First, plug, sheet surfaces examined optically (100X or SEM) – Plug mounted in fixture, load similar to applied plug force applied… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug-sheet friction – experiment • Consider figure below… – Sheet placed on hot plate, heated to forming temperature – Plug heated to 20C of the sheet temperature… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug-sheet friction – experiment • Consider figure below… – Plug pressed against sheet – Moved at slow rate (~ 1 mm/sec, say) against sheet, then stopped… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug-sheet friction – experiment • Consider figure below… – Plug then lifted and indexed to new place on sheet – Plug held away from sheet for period of time (10 sec, say)… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug-sheet friction – experiment • Consider figure below… – Plug then placed against sheet and moved other direction at (~ 1 mm/sec, say) – After 10 (say) to-and-fro motions, plug removed from fixture and examined… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug-sheet friction – experiment • Consider figure below… – Plug surface examined optically (100X or SEM) – Scrapings from plug surface chemically analyzed (FTIR) to determine mat’l transfer… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug-sheet friction – experiment • Consider figure below… – New plug examined, then heated and brought in contact with fresh sheet surface – Plug moved to-and-fro 100 times, then examined optically and chemically… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug-sheet friction – experiment • Consider figure below… – Only after material transfer level reaches constant value… – is resistance to sliding measured, using strain gauge or load cell… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • • • • • • • Experiment #1 E&C Syntactic Foam, sanded w/180 grit, blown with oil-free air Normal stress= 3 lb/in2 Hot plate temp setting = 162+/-2oF 0.120 inch black GP-PS sheet Block held on sheet 10 s, moved 10 cm in 10 sec, then removed and cooled 15 s Force measured once block moved Concluded after 10 contacts TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • • • • • • • Experiment #2 E&C Syntactic Foam, sanded w/180 grit, blown with oil-free air Normal stress= 3 lb/in2 Hot plate temp setting = 162+/-2oF 0.120 inch black GP-PS sheet Block immediately moved 10 cm in 10 s, then removed and cooled 15 s Force measured once block moved Concluded after 40 contacts TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Parameters Fixed Sheet, heater temperature Sliding length, times Measured Force Block surface temperature TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Visual Observations • After 10 contacts in Expt #1, plug surface is smoother and grayer TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Visual Observations • After 10 contacts in Expt #1, plug surface is smoother and grayer • After 40 contacts in Expt #2, plug surface is gray, with small <1 micron specks in surface TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Mea Culpa • Syntactic foam blocks were sent to local university for FTIR reflectance and ESCA measurements in August 2001 • Blocks mysteriously disappeared (!) • Retesting to obtain new samples has not yet begun TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Observations • Hot plate experiments yield timedependent force TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Observations • Hot plate experiments yield timedependent force • Force is dependent on plug surface temperature TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet III. Some prototypical plug experiments [Focus on ball or spherical plugs] TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug design characteristics Plug types Tapered, bulletor bull-nosed TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plug design characteristics - Plug types Tapered, bullet- or bull-nosed Applications Very deep draws Where thinning of sidewall is critical Where wall thickness is critical Where polymer chills rapidly TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Blunt-nose plug moving into sheet Contact may involve some sheet sliding TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Load Creep • Rough acrylic under load – increasing time or increasing temperature TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Load Creep • Rough acrylic under load • Red – low temp TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Load Creep • Rough acrylic under load • Red – low temp • Yellow – medium temp TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • • • • Load Creep Rough acrylic under load Red – low temp Yellow – medium temp Blue – high temp TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • • • • • Load Creep Rough acrylic under load Red – low temp Yellow – medium temp Blue – high temp Note increasing contact area with increasing temperature TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Sheet stretching characteristics • Sheet stretched in uniaxial, biaxial, equibiaxial and plane strain modes • Mathematical models include Ogden doubly-infinite power-law Mooney form of Rivlin strain energy function Plane strain linear law K-BKZ viscoelastic model TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Sheet stretching characteristics • Sheet stretched in uniaxial, biaxial, equibiaxial and plane strain modes • Mathematical models include Ogden doubly-infinite power-law Mooney form of Rivlin strain energy function Plane strain linear law K-BKZ viscoelastic model • Plugs stretch sheet in plane strain TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plane strain stretching, cont. Top and side view of plug-assisted stretching [Circles appear as circles from top…] TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plane strain stretching, cont. Top and side view of plug-assisted stretching [Circles appear as circles from top, are actually distorted] TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plane strain stretching, cont. Mooney-Rivlin equation: sl = (l2-1/l)(2C1+2C2/l) For plane strain: (ll2-1)1/2(1-1/ll2)=(F/2pr)(2C1-2C2)/to Where 1/l l= lh = t/to TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plane strain stretching Force F required to stretch sheet to a depth d with a flat plug: F = 2pdE(T)to/ln (a/b) Where E(T) is temperature-dependent modulus, to is initial sheet thickness, a is plug diameter, b is sheet diameter TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Plane strain stretching, cont. Comparison of theories and flat plug experimental data – JLT, 1986 TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet 2004 Experiments on Spherical Plugs Into Circular Sheets • 0.015-inch natural rubber sheet, 6.75inch diameter • Two wooden sphere diameters Small ball diameter = 0.75 inch Large ball diameter = 3 inch • Force and penetration measured with scales TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Schematic of Plug Experiment Left HalfInitial Plug Position TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Schematic of Plug Experiment Right HalfPlug Position During Sheet Stretching TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet 1. 2. 3. 4. 5. 6. Large Sphere Surface Treatment As-is [rough-grained exterior pine] Sanded w/200 grit paper Wood-putty-filled, sanded w/320 grit paper Filled, sanded, and polished Filled, sanded, polished and talc-coated Filled, sanded, polished and coated with lube TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet • • • • • • Measurements Height of plug into sheet Force Diameter of spherical cap Calculations Area of spherical cap Area of truncated cone Thickness of sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Thickness of free portion of membrane Two extremes shown in next figure TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Thickness of free portion of membrane Two extremes shown in next figure • If sheet slides on surface (friction coeff=0), thickness is uniform everywhere TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Thickness of free portion of membrane Two extremes shown in next figure • If sheet slides on surface (friction coeff=0), thickness is uniform everywhere • If sheet sticks to surface (friction coeff=1), sheet on cap is original thickness TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Experiment Draw a circle on the free portion of the sheet… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Experiment Draw a circle on the free portion of the sheet… Press the plug into the sheet to a given depth… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Experiment Draw a circle on the free portion of the sheet… Press the plug into the sheet to a given depth… Measure the major and minor axes of the ellipse (a and b)… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Experiment Draw a circle on the free portion of the sheet… Press the plug into the sheet to a given depth… Measure the major and minor axes of the ellipse (a and b)… Use the relative areal draw ratio equation Rarel = r2/ab to calculate reduced thickness, 1/ Rarel TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Comparison Penetration 2.0 in 2.4 in of Theory No Frict 0.832 0.778 and Experiment Max Frict Exptl* 0.813 0.805 0.738 0.744 * Average of 9-10 experiments TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Solid Circles – Measured Red Tk TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Sheet Thickness What about the relationship between stretching force and sheet thickness? TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Sheet Thickness What about the relationship between stretching force and sheet thickness? According to plane strain theory, the force increases in proportion to the thickness. Does this hold true for this experiment? TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Observations The nature of the dry plug surface does not substantially affect the amount of force needed to stretch the membrane TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Observations The nature of the dry plug surface does not substantially affect the amount of force needed to stretch the membrane It appears that from simple measurements, the sheet adheres to rather than slides on the dry plug TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Lubed Interface So far, all experiments have been with a presumed dry interface… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Lubed Interface So far, all experiments have been with a presumed dry interface… Remember the discussion on wet v. dry sliding? TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Lubed Interface So far, all experiments have been with a presumed dry interface… Remember the discussion on wet v. dry sliding? What happens if the interface is lubricated? TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Lubed Interface Large plug coated with… • Heavy grease [oil-based] • Glycerin [water-based] TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Observations So, what happened when the interface is lubricated? TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Observations So, what happened when the interface is lubricated? If it’s oil-lubed, essentially nothing.. TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Observations So, what happened when the interface is lubricated? If it’s oil-lubed, essentially nothing.. But if it’s water-lubed, stretching force is reduced… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Observations So, what happened when the interface is lubricated? If it’s oil-lubed, essentially nothing.. But if it’s water-lubed, stretching force is reduced… [This obviously needs more study!] TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet IV. Conclusions TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Conclusions From simple plug experiments, it is apparent (at least to me) that the interaction between the plug and the sheet is not clearly defined TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Conclusions From simple plug experiments, it is apparent (at least to me) that the interaction between the plug and the sheet is not clearly defined It is not apparent (again, at least to me) that coefficient of friction is an appropriate measure of this interaction TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Conclusions Simple measurements show applied force increases with increasing sheet thickness TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Conclusions Simple measurements show applied force increases with increasing sheet thickness Something is going on when the interface is lubricated. But why is the force reduced only when the lube is waterbased? TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Conclusions Furthermore, one might anticipate that with thick-gauge sheet, compression and shear might also be important - in addition to (or instead of) sliding. TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet Conclusions Furthermore, one might anticipate that with thick-gauge sheet, compression and shear might also be important - in addition to (or instead of) sliding. But the question remains… TF Conference 2004 – Throne Frictional Coefficients Between Plug and Sheet In plug-assist thermoforming, what is sliding against what? Questions? THANK YOU FOR YOUR ATTENTION!
Related documents