Lube Free Die Casting

Lube Free Die Casting
Steve Midson - Colorado School of Mines
David Schwam – Case Western Reserve University
Al Miller – Ohio State University
Castings Solutions for Readiness
AMC Technology Review
June 16-17, 2016
Chicago, IL
Die Castings for Military
Applications
•
•
•
•
•
High volume manufacturing
Lightweight and thin wall
Low cost
Excellent surface finish
Close dimensional tolerances
Die casters supply customers who sell to:
• United States Army
• United States Navy
• United States Air Force
• Defense Logistics Agency
• United States Transportation Command
• Missile Defense Agency
• Defense Finance and Accounting Service
• Defense Commissary Agency
www.kineticdiecasting.com/military_parts.html 2
Problem
• Die casting requires that a liquid organic-based lubricant be
applied to the die cast die before each shot
– Otherwise liquid metal will stick to steel die
• Reduces quality of castings
– Die lubricants are a major source of defects (porosity)
• Adds cost to process
– Purchase price of lubricants is high (up to 2.5% of the casting cost)
– Life of die casting dies is compromised by thermal fluctuations caused by
use of die lubricants (die life can be doubled without spray)
• Creates expensive housekeeping issues
– Effluents in air, on machine and on floor must continuously be cleaned
3
Spraying Die Lubricant
4
Needs and Benefits
• DoD/DLA
– Cost savings: reduced cycle time, increased die life, reduced
costs from purchasing lubricants, and enhanced energy efficiency
– Higher quality / performing parts: reduced porosity, increased
production reliability
– Sustainment: increased die life and durability
• Foundry / Casting Supplier / Industry
– Cost savings: reduced cycle time, increased die life, eliminate
the costs associated with buying lubricants
– Improved quality / performance: reduced porosity, better
surface finish of the products, improved production reliability
– Energy savings: reduced cycle time and energy consumption
– Reliability: increased die life and durability
– Environmental improvement: minimize effluents
5
Objectives
• Without lubricant: The molten
aluminum will solder to uncoated dies
• With a suitable coating: Soldering of
the aluminum can be minimized/avoided
Soldering on uncoated core pin
Project Objectives
• Identify and apply permanent and semi-permanent coatings to steel dies
so they do not require lubrication
• Maintain high production rates without lubrication
• Improve casting quality, reduce cycle times, decrease process costs and
extend die life
6
Technical Approach
Colorado School of Mines:
• Utilize advanced physical vapor deposition (PVD) methods to develop
non-sticking and self-lubricating coatings for metal molds
• Develop coating architecture to ensure coating adheres to steel dies
Case Western Reserve University
• Design and benchmark an improved pull-out test for die lube release
load testing
• Use the pull-out test to evaluate Boron Nitride-based dry / semipermanent lubricants
Ohio State University
• Heat transfer modelling to assess the relative importance of spray for
die cooling
• Quantify heat balance, cycle time, and die temperature relationship
7
Previous Work in this
Project
• Developed a simple laboratory test that is representative of the die
casting process
• Evaluated both in-house and commercial coatings
• Generated a quantitative measurement of the “sticking” behavior of
molten aluminum on substrates and coatings
Ceramic tube
Molten A380 aluminum alloy
Tensile test
Procedures
1.
2.
3.
4.
Heat substrate & tube in a furnace and pour the liquid A380 alloy into tube
Keep the filled tube at temperature for 15 minutes
Cool the assembly in furnace, to allow the A380 aluminum alloy to solidify
Test the strength of the interface
8
Results –
Adhesion Strength
Material
Supplier
Method
Adhesive Strength [MPa]
AlCrN
Supplier 1
Cathodic arc
0
AlTiN
Supplier 1
Cathodic arc
0
CrWN
Supplier 2
Thermal diffusion
0
AlTiN
Supplier 3
Cathodic arc
0*
TiAlN
Supplier 3
Cathodic arc
0.01
CrN
Supplier 4
Cathodic arc
0.07
Cr
CSM
Sputtering
0.12
CrN/AlN
CSM
Sputtering
0.19
CrWN
Supplier 4
Cathodic arc
0.26
CrN
Supplier 5
Cathodic arc
0.78
TiN
CSM
Sputtering
0.84
AlCrN
TiB2
Supplier 5
Supplier 6
Cathodic arc
Sputtering
1.30
2.54
*Stuck, but no load required to separate cast aluminum from coating
9
Results –
Adhesion Strength
Material
Supplier
Method
Adhesive Strength [MPa]
AlCrN
Supplier 1
Cathodic arc
0
AlTiN
Supplier 1
Cathodic arc
0
CrWN
Supplier 2
Thermal diffusion
0
AlTiN
Supplier 3
Cathodic arc
0*
TiAlN
Supplier 3
Cathodic arc
0.01
CrN
Supplier 4
Cathodic arc
0.07
Cr
CSM
Sputtering
0.12
CrN/AlN
CSM
Sputtering
0.19
CrWN
Supplier 4
Cathodic arc
0.26
CrN
Supplier 5
Cathodic arc
0.78
TiN
CSM
Sputtering
0.84
AlCrN
TiB2
Supplier 5
Supplier 6
Cathodic arc
Sputtering
1.30
2.54
*Stuck, but no load required to separate cast aluminum from coating
Exceeded
project target
of 0.05 MPa
adhesive
strength
10
Results –
Adhesion Strength
Material
Supplier
Method
Adhesive Strength [MPa]
AlCrN
Supplier 1
Cathodic arc
0
AlTiN
Supplier 1
Cathodic arc
0
CrWN
Supplier 2
Thermal diffusion
0
AlTiN
Supplier 3
Cathodic arc
0*
TiAlN
Supplier 3
Cathodic arc
0.01
CrN
Supplier 4
Cathodic arc
0.07
Cr
CSM
Sputtering
0.12
CrN/AlN
CSM
Sputtering
0.19
CrWN
Supplier 4
Cathodic arc
0.26
CrN
Supplier 5
Cathodic arc
0.78
TiN
CSM
Sputtering
0.84
AlCrN
TiB2
Supplier 5
Supplier 6
Cathodic arc
Sputtering
1.30
2.54
*Stuck, but no load required to separate cast aluminum from coating
AlCrN has
best high
temperature
oxidation
resistance –
so research
has focused
on this
coating
11
In-Plant Trials
Colorado School of Mines
12
In-Plant Trials
• Two plants trials of the AlCrN coating from
Supplier 1 have been performed
– Mercury Castings, Fond-du-Lac, WI
• First trial
– Coated single steel cavity insert in a larger die
• Mercury Castings wanted to:
– Test the durability of the coatings
– Ensure that the coating would not cause problems
• Second trial
– Coated a complete die
13
1st Plant Trial
14
1st Plant Trial
• Casting is a 350 HP Verado Gearcase
• Coated insert is shown in red
• Fabricated from H13 tool steel (46-48 RC)
15
1st Plant Trial
• Trial was performed at Mercury Castings
– December, 2015
• Alex Monroe (Mercury) & Jie Song (CSM)
• Casting is produced with two loose steel inserts
• Inserts are ejected from die
with the casting
• Several loose inserts are
used in rotation
• Inserts are normally
lubricated
16
1st Plant Trial
• Loose piece
coated with
AlCrN
17
1st Plant Trial
Day 1
• First 5 shots with lube
• Sprayed onto insert
• Next 20 shots made with no lube
• No evidence of sticking or soldering
Day 2
• Another 20 shots produced with no lube
• Again no evidence of sticking or soldering
• Mercury personnel indicated that the uncoated
loose piece sticks after 3 shots
18
1st Plant Trial
• Photographs of inserts after trial
No evidence of sticking was observed on the insert
19
1st Plant Trial
Summary
1. This first plant trial appeared to be very successful
2. Castings would be expected to stick to a nonlubricated insert after 3 shots or so
3. AlCrN coated insert ran 40 shots without lubricant
4. No apparent sticking/soldering of aluminum to the
coating’s surface
5. Based on the success of this initial trial
•
A decision was made to run a second plant trial
•
Coating a complete die casting die
20
2nd Plant Trial
21
2nd Plant Trial
• Casting is a
balance shaft
housing
6.64 in
• Weighs 1.75-lbs
• Produced in a
single cavity die
– Using a 700-ton
die casting
machine
22
2nd Plant Trial
• Trial again performed at Mercury Castings
– May 2016
– PPAP (Pre-Production Approval Process) run
• Prove to customer that castings meet requirements
• Alex Monroe (Mercury) and Bo Wang (CSM)
• Uncoated version of die had
been run previously at Mercury
– About 90,000 shots
• Necessary to spray lube on
uncoated die for 12 secs
23
2nd Plant Trial
• Entire die coated with
AlCrN by Supplier 1
Moving side of die
– Moving side
• Cavity, runner block, vent block
and core pins
– Fixed side
• Cavity and vent block
Fixed side
of die
24
2nd Plant Trial
Day 1
• 70 castings produced using 2 seconds lube
spray
– 83% reduction in spray
– No evidence of sticking
• 30 castings produced using 1 second lube
spray
– 92% reduction in spray
– No evidence of sticking
• One casting attempted with no spray
– Stuck
25
2nd Plant Trial
• Stuck casting bent on ejection
Stuck casting bent on ejection
– Red area of casting stuck
• Heavy section near gate
• During removal of stuck casting
– Core pin was bent
• Had to remove die
– Replace all core pins
– With new, coated core pins
Bent core
pin
Area shaded
in red stuck
26
2nd Plant Trial
Day 2
• Die was replaced on machine
• 96 castings were produced using 1
second lube spray
– 92% reduction in spray
– No evidence of sticking
27
2nd Plant Trial
28
2nd Plant Trial
Summary
1. Second plant trial was also very
successful
Lube Free
2. Entire die was coated with AlCrN
•
From Supplier 1
3. Coating allowed a reduction in
spray time from 12 seconds to 1
second
•
Spray zone
92% reduction in spray
4. Casting produced with no lube did
stick in the die
29
Mechanism Controlling
Sticking / Non-Sticking
Behavior
30
Sticking /
Non-Sticking Mechanism
• Continuing to perform laboratory research to
determine the mechanisms that control the
observed sticking and non-sticking behaviors
• Possible cause of the different behavior for AlCrN
1. Differences in chemical composition of the coating
(Al:Cr ratio)
2. Roughness of the coating
3. Presence of an oxide layer on the surface of the AlCrN
coating
31
Summary and
Conclusions
Colorado School of Mines
32
Summary and
Conclusions
1. Based on a simple aluminum adhesion test developed at
CSM
•
An AlCrN permanent die coating has been identified
that exhibits non-sticking behavior with aluminum
A380 die casting alloy
2. Plant trials using the AlCrN coating have demonstrated
excellent results
•
Successfully ran lube free with a single cavity insert
•
Reduced lubricant spraying by 92% on a fully coated
die
3. Still working to understand the mechanism controlling
the observed sticking/non-sticking behavior
33
Future Work
1. Perform laboratory studies to determine the mechanism
controlling the sticking/non-sticking behavior of aluminum
alloy against various coatings
2. Continue the plant trial of both the insert and the fully
coated die
i.
Run the insert until the coating fails
•
Determine the mechanism of failure
ii. Continue to run the fully coated die
•
Determine if the 1 second spray time can be
maintained
34
Case Western Reserve
University
35
Technical Progress
Case Western Reserve
• Design and benchmarking of a new pullout test for die lube testing
• Laboratory testing of BN-based die lubes
in collaboration with Momentive, a
producer of BN
• Evaluation of BN-based die lubricants in
production at Mercury Castings and PHB
Inc. (planned)
• Use of the release tester to develop and
implement a high performance dry
lubricant system
36
Technical Progress
Case Western Reserve
Schematic of the Pull-out Experimental Set-up
37
Technical Progress
Case Western Reserve
Experimental set-up for Pull-out Test
38
Technical Progress
Case Western Reserve
Experimental set-up for Pull-out Test
39
Technical Progress
Case Western Reserve
Evaluated BN Coating
Before
Before
BN FPC 50:50
BN LPC 50:50
After
After
40
Technical Progress
Case Western Reserve
Typical BN Coatings
Before
BN GPC 50:50
After
Before
BN ZYP 50:50
After
41
Technical Progress
Case Western Reserve
42
Technical Progress
Case Western Reserve
3000
Release Load (lbs) - Commercial Die
Lubes
2500
2000
1500
1000
500
0
HMA
1:40
HMA
1:80
Moresco Moresco SL 1:40 SL 1:80
1: 40
1:80
HNA
1:40
HNA
1:80
43
Technical Progress
Case Western Reserve
Summary
• The test provides good sensitivity to measure
release load, differentiate among die lubricants
and determine the effect of dilution ratios.
• BN formulations released at very low loads.
• Commercial die lubricants evaluated at higher
dilution ratios (1:40, 1:80) required much higher
release loads.
44
Project Plans
Case Western Reserve
• Next 12 months
– Benchmark more commercial die lubricants
– Compare release load of die lubricants with
in-plant performance at PHB Inc.
– Measure increase in release load when the
BN-based die lubricant is applied once every
10, 25, 50 pull-out cycles
– Evaluate and implement BN-based dry
lubricants (with Momentive) in production
45
Ohio State University
46
Technical Progress
Modeling
• Impact of elimination of spray on
thermal control
• Post injection heat transfer
modeling issues
• Cooling design tradeoffs
47
Addressed Today
Modeling
• Compensating for lack of spray by
– Letting the die run hot
– Adjusting the internal cooling
• Sensitivity of the die thermal balance
• Do we understand thermal quasiequilibrium?
48
Model
Modeling
To cooling line
Casting
Closed Open
• Cycle:
• Assumptions:
–
–
–
–
Die
Spray
Open
Conduction from casting to die when closed (post fill)
Conduction to platen at face opposite casting
Convection to air at cavity side when open
Spray approximated by convection
• Simple enough for easy sensitivity analysis
• Complete enough for understanding trends
49
Questions
Modeling
• Spray, or lack of spray, affects die
heat load and thermal balance
– How much?
• Spray is intermittent, internal cooling
is continuous (usually).
– Does that matter?
• Spray is at the surface. Cooling
lines are internal.
– Does that matter?
50
Basic Cycle with Spray
Modeling
• Die temperature over one cycle
– Part rapidly dumps heat then heat transfer
slows
– How much heat depends on both part and die
Why not shorten
cycle by 10 or 15
seconds?
Is this die
thermally stable?
51
Equilibrium
Modeling
• With or without spray, die temperature
equilibrium depends on
– How rapidly die temperature can change
when temp difference exists
– Heat fluxes in and out
• Fluxes depend on both die and sink or source
temperatures
• Die temperature transient has to play out
– Depends on how far to go and how fast you
can go
52
Is This Die Stable?
Modeling
Temperature still rising,
and not slowing, after 200
cycles without spray
Same Curve
53
Die and Part Surface
Modeling
1.5oC (0.5%) ∆ at cycle 20
0.3oC (0.07%) ∆ at cycle 100
Eject Temp: 370oC cycle 20
465oC cycle 100
475oC cycle 200
Acceptable?
54
Improved Internal Cooling
Modeling
• Locked in by cycle 20
• 250oC initial condition close to long
term average
Ejection Temp @ cycle 20: 318oC
55
Both Dynamics and Die
Heat Content Matter
Modeling
• Blue curve - initial
surface temp history
from previous slides
• Orange curve has
exact same cooling
• No equilibrium until
enough heat to
balance flux in and
out
56
Summary
Modeling
• Letting a die run hotter, i.e. no change
in internal cooling or cycle time, may or
may not work
– How much heat did spray remove?
– Will affect other variables, e.g. part
ejection temp
– Initial conditions matter
– How long do you run before interruptions
57
Project Plans
Modeling
• Compete and use 2-D version of model
for more complete internal cooling
pattern studies
• Review practices used in Mercury
Castings experiments
• Guidelines / recommendations for
NADCA
58
Project Metrics
Description
Baseline
Threshold
Objective
Non-wetting/ Nonsticking (Sticking
strength)
0.5 MPa
0.1 MPa
0.05 MPa
Thermal stability
675oC
800oC
1,000oC
Mechanical
properties
(Hardness)
25 GPa
30 GPA
35 GPa
Wear resistance
(Wear rate)
5x10-5 mm3N-1m-1
1x10-5 mm3N-m-1
2x10-6 mm3N-1m-1
In-plant testing of
coatings (Die life)
5,000 shots
10,000 shots
30,000 shots
59
JDMTP Criteria - Summary
Jointness
B – Benefit to more than one service, but not jointly funded
Needs: Non-sticking and self-lubricating coatings for metal molds to reduce
cycle time / production costs, and improve die life and part quality
Needs and
Benefits
Transition
Leveraging
MRL
Benefits:
–Cost savings: reduced cycle time, increased die life, and energy savings
–Higher quality / performing parts: production reliability improves quality
–Sustainment: increased die life and durability
–Environmental improvement: lubricant-free process
• Commercial suppliers such as Tribologix, Dayton & Phygen will reproduce the
optimized self-lubricating coatings on die components in their industrial sized
coaters.
• In-plant trial testing at Mercury Castings and others
• Computer Modeling Guidelines for lube free die casting through NADCA
• Presentations at committee & chapter meetings and annual NADCA Congress
• Webinars, Die Casting Engineer articles
• DOE E-SMARRT “Smart Die Coatings”
• CSM’s ACSEL and CANSFA consortia
• NADCA-funded project on ultra-sonic coatings evaluation
4 – Manufacturing capability to produce the system in a laboratory environment
60
Lube Free Die Casting
DLA - POC: Dean Hutchins ([email protected], 804-279-5033)
Problem
– Applying die lubricant:
–
–
–
–
Partners:
• Colorado School of Mines, Case Western
Reserve, Ohio State University, NADCA,
Phygen, Mercury Marine, Twin City Die
Casting, Premier Tool and Die
Source of porosity
Reduces die life
Adds time to the casting cycle, increases costs
Produces effluent with associated waste issues
Objective
– Develop non-sticking and self-lubricating
coatings for metal molds to improve part quality,
decrease cycle time and reduce process costs.
Benefits
– Higher quality / performing parts
– Cost savings from reduced cycle times and
increased die life
– Supply chain reliability from increased die life
– Environmental improvement (lubricant-free
process)
Milestones / Deliverables
– Coating properties measured and characterized
– Computer modeling method for die and process design
– In-plant trails on coating system
61