Cavitation in die casting Casting Expo Orlando Florida

New Research First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev

Caterpillar Research v High Speed Photography v Special pressure transducers First Slide Copyright ©

Failure from cavitation Ø Previously mistaken for: Bad steel Erosion Heat Treatment Ø None

Cavitation explained Ø Fatigue by Fluid entrained low pressure void bubbles that collapse at

How a bubble collapses Stages 1 -3 spherical Stage 4 small depression Vapor bubble

High speed photography 1 -18 shows a bubble collapsing with high speed photography At

Collapsing bubble video Click on steel bar to see movie First Slide Copyright ©

150, 000 rpm vortex tornado Pressure Slowly Decreasing Slow Motion, 4500 fps Click on

Also sheet cavitation Cavitation pattern during flow Low Pressure void bubbles formed at left

Just water can do this First Slide Copyright © 2008 -2010 Badger Metal Tech,

Cavitation Propeller Damage Ø Propellers, Pumps, Cylinders, & High pressure die casting dies First

Bubbles and Breakout Ø Each operational cycle: local pressures fall below the vapor pressure

Bubble in molten metal Ø Low pressure bubbles created in molten metal: collapse on

Historical Evidence Ø Castings show vividly cavitation effect breakout prevalent at low pressure areas

Breakout from Cavitation in HPDC FLOW Pitting, breakout, erosion, and washout commonly occur in

Chicken and the Egg l Does thermal fatigue cause breakout or does breakout lead

Cavitation & Heat check Pressure drop location Heat check breakout? Cavitation Effect FLOW Cavitation

Diesel Engine - Texturing l Patent 7146939 – Dec 2006 Drawing of the diesel

Flow Effect v/s Cavitation When metal rushes over a flat surface, the metal cools

Buffer by compressive texture? typical compressive finish for 47 -48 Rc macro photo of

100, 000 dies experience it 95% of the used tooling exhibits some form of

Cavitation not heat check? Was investigated & proved in 1964 at SDCE Casting Congress

Application to HPDC l Cavitation – controlled but not eliminated l Factors to control

Reduce it with Ø Buffers the cavitation effect Ø Compressive stress to counter fatigue

$Compressive Curves T-41 H High Surface Compression Shallow Knee Maximized Depth X-Ray Diffraction Curves$

What is it about? Mechanically Induced Micro Precision Compression Texturing to improve Flow Thermally

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Cavitation in die casting Casting Expo - Orlando Florida Mar 2010 Intro to Cavitation How it does damage breakout areas show on casting as risers First Slide Historical Evidence How to counter it’s effect Die with breakout areas shown as pitting Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Failure from cavitation Ø Previously mistaken for: Bad steel Erosion Heat Treatment Ø None of the Above Similar to die casting dies? First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Cavitation explained Ø Fatigue by Fluid entrained low pressure void bubbles that collapse at low pressure locations Ø Tiny bubbles imploding on surface of the member on which or over which the fluid is flowing Ø Resulting in high cycle fatigue failure First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Image source: Dr. Joe Evans Ph. D www. pumped 101. com www. caltech. edu Return to Home

How a bubble collapses Stages 1 -3 spherical Stage 4 small depression Vapor bubble in various stages of collapse. Depression more toroidal in its 3 D shape. Solid lines predicted by model. Dotted lines obtained through experiment. Upon implosion, the re-entrant micro jet would form at the bottom of the bubble with its energy directed towards the nucleation point or solid surface. Image source: Dr. Joe Evans Ph. D www. pumped 101. com www. caltech. edu First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

High speed photography 1 -18 shows a bubble collapsing with high speed photography At stage 8, small dot at bottom of bubble Grows in size in following stages then appears to penetrate the upper boundary in Stage 14. Stage 18 is just prior to total collapse and shock wave generation. Image source: Dr. Joe Evans Ph. D www. pumped 101. com www. caltech. edu First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Also sheet cavitation Cavitation pattern during flow Low Pressure void bubbles formed at left result in damage at right Source: Dr. Joe Evans Ph. D www. pumped 101. com www. caltech. edu First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Bubbles and Breakout Ø Each operational cycle: local pressures fall below the vapor pressure of the liquid. Incipient cavitation effect Ø Billions of cycles extreme high continuous cycle fatigue from the violent collapse of the vacuum bubbles on the die surface First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Bubble in molten metal Ø Low pressure bubbles created in molten metal: collapse on the surface of the die continuously causing a loss of fatigue strength of the die steel as metal and initially microscopic breakout or pitting occur. Ø Jack hammer effect small microscopic particles grow in size until visible chucks of metal from die are noted. Previously attributed to thermal fatigue First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Historical Evidence Ø Castings show vividly cavitation effect breakout prevalent at low pressure areas gate, rebound, and flow direction changes Ø We see daily examples of this damage that use to be attributed to bad steel, heat treat, erosion Ø Look at your tooling to see if your breakout issues correlate to cavitation effect. Then buffer them First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Breakout from Cavitation in HPDC FLOW Pitting, breakout, erosion, and washout commonly occur in the opposite locations of where they would be expected - on the low pressure side of the flowing liquid First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Chicken and the Egg l Does thermal fatigue cause breakout or does breakout lead to heat checking of the die’s surface? l Can heat check cracking lead to breakout without incipient inertial cavitation? l. YES First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Cavitation & Heat check Pressure drop location Heat check breakout? Cavitation Effect FLOW Cavitation effect exacerbates itself when more low vapor pressure develops from the disrupted flow patterns First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Diesel Engine - Texturing l Patent 7146939 – Dec 2006 Drawing of the diesel cylinder liner with textured manganese phosphate coating and resultant textured surface. Coating retains coolant which absorbs the cavitation impact energy of the collapsing cavities that damage the liner. First Slide It is feasible that this same buffering action takes place in compressive stress textured die surfaces with the cooling molten metal absorbing the cavitation shock along with the induced fatigue resistant substrate. Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Flow Effect v/s Cavitation When metal rushes over a flat surface, the metal cools unevenly, impacts flow effect and does nothing to buffer collapsing void bubbles. Flat Surface 1. Fast flow 2. Uneven solidification 3. Erosion prone 4. Cavitation effect First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Buffer by compressive texture? typical compressive finish for 47 -48 Rc macro photo of casting surface shown below After 50, 000 shots, there is no evidence of cavitation damage in the form of breakout, pitting, or erosion. Did the compressive texturing buffer cavitation? First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Cavitation not heat check? Was investigated & proved in 1964 at SDCE Casting Congress – Detroit, MI click here to see white paper First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Application to HPDC l Cavitation – controlled but not eliminated l Factors to control or consider l l l Velocity of metal (dam spillway) Extreme pressure variations (all) Buffering the cavitation effect (diesel) Fatigue resistance (compressive) Design & Operation parameters (pumps) First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

Reduce it with Ø Buffers the cavitation effect Ø Compressive stress to counter fatigue Ø Micro-texture to improve flow First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

$Compressive Curves T-41 H High Surface Compression Shallow Knee Maximized Depth X-Ray Diffraction Curves$

Compressive Curves T-41 H High Surface Compression Shallow Knee Maximized Depth X-Ray Diffraction Curves High Compressive Values help counter tensile metal fatigue failure First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home

What is it about? Mechanically Induced Micro Precision Compression Texturing to improve Flow Thermally Induced Ferritic Nitro Carburizing Tool Steel Recipes (FNC) Click here to find out more First Slide Copyright © 2008 -2010 Badger Metal Tech, Inc – Rev 06 -2010 Return to Home