plugin-04 - Materials and Intro to Mechanical Elements

plugin-04 - Materials and Intro to Mechanical Elements -...

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ME250 PUZZLE Imagine you are designing a stapler. What factors would you consider when choosing the materials for the different parts of the stapler?
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Materials, Intro to Mechanical Elements ME 250 Lecture #04 9/21/10 Mike Umbriac
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Reminders Machine Shop Training: Last day is this Friday! Milestone #2 (MS2) is due tomorrow. Same procedure as Milestone #1.
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Possible Factors to Consider when Choosing a Material (a partial list) Strength Stiffness Weight Hardness Cost Ductility Corrosion Resistance Coefficient of Thermal Expansion Manufacturing Process and/or Machinability Function of the Part Desired Properties and Service Attributes Material Selection
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Project Kit is on CTools
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Materials in the Kit (Refer to the latest update on CTools.)
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Steel Steel is composed of iron, carbon, and sometimes other elements like chromium, manganese, vanadium, and tungsten. Images: topsteel.com.my, shsailer.com Advantages High strength High stiffness (elastic modulus) Relatively ductile instead of brittle Some steels can be heat treated to improve the hardness or change other properties Disadvantages Heavy (high density) compared to most other materials Carbon steel tends to rust unless it is protected Painting Galvanization (zinc coating) Black Oxide
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Steel Processing Hot-rolling (for bar stock) The steel is heated, then fed through rollers to form it into a flat shape. Cold-rolling (for bar stock) The previously hot-rolled bars are fed through rollers while at room temperature. Improves precision and surface finish Cold-drawing (for bar stock or round stock) The previously hot-rolled bars are pulled through a die which reduces the thickness or diameter and increases the length. Improves precision and surface finish Images: Kamal Narang, arcabrasives.com, clarkprecision.com
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Most Commonly Used Types of Steels Carbon Steels Low- carbon or “mild” steel: 0.05 - 0.30% carbon Mild steel has a relatively low tensile strength, but it is cheap and malleable. Includes most structural steel. Can be case hardened (“carburized and hardened”) to improve the surface hardness. ANSI Designations: 1018, 1020 etc. (last two digits indicate carbon content) High-carbon steels: 0.30-2.0% carbon Harder and stronger, but more brittle. Can be heat treated after machining, to improve the through-hardness. Can be flame-hardened (locally on a section of the part) HARDEN the sections that tend to WEAR. Keep the rest soft so it can withstand bending loads, etc. ANSI Designations: 1045, 1060, etc. Images: www.centuryae.com
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Most Commonly Used Types of Steels Alloy Steels: The iron is alloyed with other elements to improve mechanical properties. Examples:
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This note was uploaded on 01/26/2011 for the course ME 250 taught by Professor Dutta during the Fall '07 term at University of Michigan.

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plugin-04 - Materials and Intro to Mechanical Elements -...

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