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Dome PistonDesign and Manufacture of a Dome
Shaped Piston Head
April 10, 2015
List of all Slides and their Related Information Presented
Slide Information Presented
1 Group number, members, and project title
3 Overview of dome shaped piston head
4 Design focus for manufacturing process and final product
5 Detailed list of piston components
6 Detailed explanation of the expansion of the piston shape during operation
7 Piston rings and there functional purpose
8 List of all steps performed during the manufacturing process
9 Detailed description of casting and its related characteristics
10 Detailed description of forging and its related characteristics
11 Description of the heat treatment process and purpose
12 CNC Turning list of operation performed and characteristics of the CNC lathes
13 Drilling and grinding applications listed and described
14 Explanation of deburring and coating processes and their effects on the piston
15 Description of reaming and finish boring processes and matrices relating their individual pros and cons
16 Final inspection description
17 Performance and cost matrix related to the forging process
18 Performance and cost matrix related to two casting types
19 Performance and cost matrix related to coatings used on the piston head and skirt
20 -21 Manufacturing improvements and recommendations related to casting and forging
22 Cost and performance assessment matrix addressing each manufacturing process
23 Identifying the best technique and supporting information
24 Member contributions related to subject matter and percentage
25-26 List of all reference cited throughout the power point
• Increase in volume from the dome shape increases compression ratio. [15]
CR= (.25πb2 s+Vc )/Vc
Where: b=cylinder bore, s= piston stroke, Vc =clearance volume
• Dome shape deflects the inlet charge up toward the spark plug. [15]
• Flat portion decreases quenching effects. [15]
Dome Piston with Flat Portion
FOCUS REVIEW
• Improving the manufacturing process of the dome piston.
• Maximize life span based on manufacturing techniques (i.e. Forging and Casting).
• Identify cost benefits between casting and forging.
• Limit failure modes through the manufacturing process.
Crown Top of piston Combustion gases exert pressure on the
piston crown
Ring Land Sealing surface and support piston rings [8]
Relief cut into side profile where thepiston rings sit [8]
Ring Grooves Grooves used to retain piston rings [8]
Recessed area located around perimeter of the piston [8]
Skirt Portion of the piston closest to the crankshaft that
helps align the piston as it moves inside cylinder bore [8]
Wrist Pin boss Connects the small end of the connecting rod to the
piston by a wrist pin [10]
Aluminum expands so there must be an allowance between the piston diameter and the cylinder to account for the expansion, allowing the piston to move freely [13]
Top of piston (crown) experiences more heat than the bottom (skirt) so the crown will expand more[13]
Top diameter needs to be smaller than diameter of bottom of skirt, providing tapered shape[13]
The partial skirt lightens piston, thus increases the speed range of the engine and reduces the contact area between the cylinder wall, which decreases friction [14]
The skirt is also elliptical shape at room temperature
As the piston heats up, the pin bore area expands more than thinner areas of the piston making the piston shape become circular[ 13]
This circular shape matches the cylinder bore and improves sealing and efficiency[13]
Compression ring
Piston ring located in ring groove closest to the piston head [8]
Prevents oil from reaching combustion chamber[10]
Seals the combustion chamber from any leakage [10]
Wiper ring
Middle ring
Provides a consistent film of oil to lubricate the running of the compression ring [8]
Wipes away excess oil from cylinder wall
Combustion gasses which pass the compression ring are stopped by the wiper ring [8]
Oil ring
Piston ring located in the ring groove closest to the crankshaft [8]
Thin slots cut in ring to allow flow of excess oil back to oil basin [8]
Casting or Forging
Heat Treatment
Machining process
CNC turning
Drilling, slotting, and grinding
Deburring and Coating
Reaming or Finish boring
Cast pistons are made from an aluminum/silicon alloy (Hypereutectic ) Hypereutectic pistons have a lower coefficient
of thermal expansion than pure aluminum, so tighter tolerances can be set.[2]
Hypereutectic pistons are more brittle than pure aluminum.
Alloy is heated to 700°C , collected with a ladle and poured into mold, and cooled.[5]
Permanent molds are used and are typically made of cast iron.
The mold itself is expensive, but it is very durable so it can be reused for a long period of time.
Once the mold is made the cost per piston is very low.
High production rate
Forged pistons are mechanically shaped.[3]
A aluminum bar stock is cut into slugs that are then heated in an oven to about 425 °C
A mechanical or hydraulic press and die are preheated to the same temperature.[9]
The press applies 2,000 lbs of force to the heated slug shaping it to the desired shape.[9]
The forged piston then air cools slowly for roughly an hour.[9]
Forged pistons are more ductile and dense than cast pistons. [2]
Forging eliminates porosity. Tools used are expensive, develop wear more quickly, and are
slower compared to casting tools. More expensive final product Tend to go into plastic deformation when overloaded Engines > 500 hp will always have forged pistons
Diesel engines and race cars
Piston is placed into an oven twice
First time is at a higher temperature to strengthen the material [10]
Second is at a lower temperature to stabilize the material [10]
Controlled heating and cooling to change physical and mechanical properties of the piston, but maintain the same shape.
Increases strength and hardness
Simplifies machining processes
For the heated treated piston, CNC will perform the following: Facing Piston is cut down to desired bore diameter Oil ring grooves are cut Boring
CNC lathes are very accurate and are capable of holding tight tolerances.
The cycle is programmed in G-Code which tells the lathe to move to certain (X, Y, Z coordinates) at specific spindle speeds and feed rates.
CNC lathes are expensive and the computer training to operate them is intensive.
CNC lathes are easily programmable and processes can be repeated.
Drilling Drill Press
All oil holes (i.e. gudgeon pin, bosses, and oil rings)
Slotting Milling machine
Piston skirt or in oil ring groove
Grinding Only the skirt of the piston is grinded.
The skirt is usually cam grinded, ensures the expansion of the piston will be uniform in the bore of the engine.
Deburring tool is used to remove any unwanted material on piston surface
Piston is cleaned to remove oil, dirt, residue, etc.
Coating is typically sprayed on Dry film lubricants
Reduce friction, reduces scuffing, extends bore life[4]
Good safety margin[4]
Applied to piston skirts[4]
Thermal barriers Transfer heat and prevent hot spots on piston
face[4]
Results in less fuel needed for desired power[4]
Applied to piston crowns[4]
Oil shedding Increase cooling efficiency by not allowing oil
to coat certain surfaces[4]
Applied to piston bottoms[4]
Final process
Reaming or finish boring makes existing holes dimensionally more accurate and improves surface finish. [5]
Piston is placed in bath of oil and reamed at different size to reach desired size. [5]
A typical tolerance is about 0.4Ra. [5]
Pros Cons
Multiple cutting edges, so tool life is longer
Requires coolant
Can hold tighter tolerances
Time consuming
Pros Cons
More flexible and forgiving
Can’t hold tight tolerances
Precise hole location is less critical
One cutting tooth, so tool life is lower
Piston is cleaned of any residues left over from the manufacturing process [5]
Fitted with appropriate wrist pin [5]
Stamped with the piston’s overall size and any other manufacturer’s markings [5]
Manufacturing Process
Pros Cons CostAverage Lifespan
Forging
•Stronger than cast pistons [3]
•Less porosity and closer alloy
grains due to not using a cast.[3]
•Greater dimension stability [3]
•Dissipates heat better and can
with stand greater operating
temperatures [3]
•The dense, stretched, and strained material makeup of a forged
piston doesn't heat up to the operating
temperature as quickly as a cast piston. [2]
•They are more likely to cold seize.
•The high pressures required for the
operation increase wear on the dies per
run, which are costly to replace.
Higher than cast
pistons.
2X Lifespan of Cast Pistons
Manufacturing
ProcessPros Cons Cost
Average
Lifespan
Casting Types
Cast Aluminum
Piston with
Steel Struts
•Help control flow of heat
from combustion process
•Lightweight reduces
force required to initiate
and maintain
acceleration. [9]
•Can be embedded into
the piston assembly to
help control piston
expansion
•Lower strength than forged
pistons
•Contains neither grain flow
or directional strength[10]
•Fractures easier under
detonation and has few
options for compression and
rod length [2]
Less costly
than forged
pistons.[3]
1/2 Lifespan of
Forged Pistons
Hypereutectic
Piston
•Stronger than 100%
aluminum piston [3]
•Hypereutectic pistons
expand less than ordinary
cast aluminum alloys, and
CNC machining of the
piston profile allows
piston-to-bore clearances
to be reduced. [3]
•Reduces heat transfer. [3]
•Require close control of
melting and cooling process
because alloy separation may
occur. [1]
•Not easily modified.
Less costly
than forged
pistons.
1/2 Lifespan of
Forged Pistons.
Greater lifespan
than cast
aluminum with
struts.
Coatings Pros Cons Life-span
0.002" Ceramic Thermal Barrier
Coating
•Holds heat inside combustion
chamber reducing dissipation
through the piston that can weaken or
burn the metal.• Thin coating does not effect
clearance. [6]
Increases the cost
Increases
0.008" Tungsten-Molybdenum
Disulfide Polymer Matrix
•Reduces friction between piston
skirt and cylinder wall.[6]
Increases the cost
Increases
Forging■ Increase material resistance to
cracking by properly aligning the grain flow with the crack propagation direction during the extrusion process. [12]
■ Heat the press and die to the same temperature as the slug (425 C) so the slug is not cooled when put into the press.[9]
■ Allow roughly formed piston to air cool after it has been heat treated in an oven after pressed. This will allow for the molecular structure of the piston to reach a lower energy state and be therefore more uniform molecular.[11]
Result: Increases the strength of the forged piston
Casting
■ As the ratio of silicon to aluminum is increased the more brittle they become, as well as the coefficient of thermal expansion reduces and the piston expands less. A ratio of 16%- 19% is recommended.[3]
• Less than 12% Piston will expand too much.
• 25% and on Piston will be excessively brittle and loose strength. [ 3]
Result: Reduces piston expansion under during operation and increased strength without sacrificing too much ductility.
Forging
■ Apply adequate force (2000 tons) to the heated slug of aluminum in the press
Result: Decrease porosity, and compact grain flows.
■ Heat treat the pressed piston twice.
• First time at higher temperature to ensure the entire volume is heated to the same temperature.
• Second time to a lower temperature to allow for the molecular structure to stabilize. [11]
Casting
■ Repeatedly measure the dimensions of the cast for accuracy after a specific number of casting cycles.
Results: Dimensionally consistent casts
■ Reduce the amount of hydrogen gas in the molten aluminum prior to injecting the cast. Use high quality aluminum.
■ Use a vacuum while pouring the molten Al alloy to limit the porosity of the cast due to gas bubbles. [10]
Result: Decreases the porosity of the casted piston, thus increasing strength.
Manufacturing Processes for Dome Shaped Piston Head
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il H
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Manufacturing Process Influence on Piston
Quality and Cost Correlations
Cost 1 3 1 2 1 1 2 2 1 2 1 1 2 2 2
Equipment Cost 3 3 3 3 3 1 2 2 2 2 3 3 3 3 3
Manufacturing time 1 2 3 2 2 1 2 2 1 2 2 2 2 2 3
Strength 2 3 1 1 3 1 1 1 1 1 1 1 1 1 1
Thermal Expansion 3 2 1 1 2 1 2 3 2 2 1 1 3 2 1
Ductility 1 3 1 1 3 1 1 1 1 1 1 1 1 1 1
Friction 1 2 1 1 1 1 3 1 2 1 1 1 1 3 1
Porosity 3 1 1 1 1 1 1 1 1 1 1 1 1 1 1
Density 2 3 1 1 2 1 1 1 1 1 1 1 1 1 1
Precision of Piston
Dimensions 2 3 3 1 1 1 2 2 1 3 2 1 2 2 3
Lifespan of Piston 2 3 1 1 3 1 3 3 3 3 3 3 3 3 2
Ranking: 8% 10% 7% 6% 7% 4% 7% 6% 5% 7% 6% 6% 7% 7% 7%
Forging is the Best Technique of the Manufacturing Process.
• Largest influence on ductility of the piston head.
• Greater dimensional stability effectively decreasing machining time
• Produces the greatest strength resulting from the grain flow in the extruded material
• Eliminates porosity in the material
• Extruded product dissipates heat better than casting and can withstand greater operating temperatures
• Forged pistons have a greater life span
[1] “Aluminum Piston Manufacturing Process.” Cast and Alloys. 05 May 2015 <http://www.cast-alloys.com/products/aluminium_piston_manu_process.htm>
[2] “Cast and Forged Pistons.” Tech Speak. 05 May 2015 http://www.hoon.tk/tech_tips/pistons.html
[3] “Cast, Hypereutectic or Forged Pistons.” Probe Industries. 05 May 2015 <http://www.probeindustries.com/Articles.asp?ID=144>
[4] “Coating Pistons.” Tech Line Coatings, Inc. 05 May 2015 <http://techlinecoatings.com/articles/Coating_Pistons_Article.htm>
[5] “How Pistons are Made” JP Pistons. 05 May 2015 http://www.jp.com.au/Made.html[6] “Piston Selection Guidelines.” Federal Mogul Technical Education Center. 05 May 2015
<http://fme-cat.com/docs/1104.pdf>[7] “Ultimate Ford FE Engine Piston Guide.” DIY Ford. 05 May 2015
<http://diyford.com/ultimate-ford-fe-engine-piston-guide/>[8] “Piston and Piston Rings.” Univsersity of Windsor. 03 May 2015
<http://courses.washington.edu/engr100/Section_Wei/engine/UofWindsorManual/Piston%20and%20Piston%20Rings.htm>
[9] “Piston Manufacturing Process.” Thomas McNish. 03 May 2015 <http://www.ehow.com/how-does_5502005_piston-manufacturing-process.html>
[10] “Casting Defects and Design Issures.” Prof. J.S. Colton. 03 May 2015 <http://www-old.me.gatech.edu/jonathan.colton/me4210/castdefect.pdf>
[11] “Heat Treatment of Ferrous Metals.” 03 May 2015 <http://avstop.com/ac/apgeneral/heattreatmentofferrousmetals.html>
[12] “Failures Related to Metal Working.” Fudan University. 04 May 2015<http://jpkc.fudan.edu.cn/picture/article/348/1b/ee/6dce0ae740cf8673b53e4e96abb8/7aa78636-dda1-46b9-859b-95db3cb616f8.pdf>
[13] “Piston Design.” University of Windsor. 05 May 2015 <http://courses.washington.edu/engr100/Section_Wei/engine/UofWindsorManual/Piston%20Design.htm>
[14] “Piston Assembly” SweetHaven Publishing Services. 05 May 2015 <http://www.waybuilder.net/sweethaven/MechTech/Automotive01/?unNum=2&lesNum=3&modNum=1>
[15] “Piston Dome.”Performance Trends Inc. 02 May 2015 <http://performancetrends.com/Definitions/Piston-Dome.htm>