4/19/06: Group 8 – Chapters 34 and 35

transcript

4/19/06: Group 8 – Chapters 34 and 35•Jason Becker

•Andrew Nawrocki

•Ryan Niehaus

•Jonathan Ogaldez

•Stephen Wakeland

Chapter 34

Surface Treatments, Coatings, and Cleaning

Introduction

• Performing surface treatments can:– Improve resistance to wear

– Control friction

– Reduce adhesion

– Improve lubrication

– Improve resistance to corrosion

– Improve fatigue resistance

– Rebuild surfaces

– Modify surface texture

– Impart decorative features

Mechanical Surface Treatments

• Shot peening– Uses a large number of cast steel,

glass, or ceramic shot (small balls)

– Causes compressive residual stresses, improving fatigue life

– Used on shafts, gears, springs and jet-engine parts

• Laser shot peening– Uses short laser pulses to produce

compressive stress on the surface

– Very effective

– Lasers are expensive and require a lot of power

• Water-jet peening– Uses up to 60,000 psi water blasts to

produce compressive stresses

– Process variables must be controlled•Pressure

•Velocity

•Nozzle design

•Distance from surface

• Ultrasonic peening– Piezoelectric transducer

• Roller burnishing– Uses a roller to "cold-work" a

component's surface

– Induces compressive surface residual stresses

• Roller burnishing (cont'd)– Internal surfaces can be treated by

ballizing or ball burnishing

– A smooth ball that is slightly larger than the bore diameter is pushed through the length of the hole

• Explosive hardening– Detonation of a layer of an explosive

sheet directly on the workpiece

Mechanical Plating and Cladding

• Mechanical plating– Fine metal particles are compacted

over the work piece surface by glass, ceramic, or porcelain beads

– Beads are propelled by rotary means (like a dryer!)

Mechanical Plating and Cladding

• Cladding– Metal is bonded with a layer of

corrosion-resistant metal

– Can be applied by rolls, dies, explosives, or lasers

– Aluminum (Alclad) is a typical application

Case Hardening and Hard Facing

• Case hardening– Discussed in chapter 4

– Heat surface treatment

• Hard facing– A piece of wear-resistant hard metal

is deposited on the work piece using fusion-welding

– Can be used to repair worn parts

– Enhances wear resistance

– Used for tools, dies, and other industrial components

• Spark hardening– Hard coating of tungsten, chromium,

or molybdenum carbides are deposited using an electric arc

– Used for valve seats, oil-well drilling tools, and dies for hot metalwork

Thermal Spraying

• A coating of various metals, alloys, carbides, ceramics, and polymers are applied to metal surfaces by a spray gun

• Surfaces must be clean, oil-free and roughened

Thermal Spraying

• Combustion spraying– Thermal wire spraying

• Oxyfuel flame melts wire

– Thermal metal-powder spraying• Uses metal powder instead of wire

– Detonation gun• Controlled and repeated explosions

• Performance similar to plasma

– High-velocity oxyfuel-gas (HVOF)• High performance

• Lower cost

Thermal Spraying

• Electrical spraying– Twin-wire arc

•An arc is formed between two wire electrodes

•Good strength, lowest cost

– Plasma•Produces temperatures of around

15,000oF

•Good bond strength

•Very low oxide content

•Very low levels of porosity

Thermal Spraying

• Cold spraying– Particles are at a lower temperature

– Oxidation is minimal

– High impact velocities

Thermal Spraying

Vapor Deposition

• Process of coating the surface of a work piece (substrate) using chemicals in gaseous form

• Deposited materials: metals, alloys, carbides, nitrides, borides, ceramics or oxides

• Typical applications include coating of cutting tools, drills, reamers, milling cutters, punches and dies

• Two distinct processes: Physical vapor deposition and Chemical vapor deposition

Physical Vapor Deposition

• Three basic types: 1) Vacuum deposition 2)sputtering 3)ion plating

• Carried out at temperatures between 200 and 500 degrees Celsius

• Processes carried out in high vacuum

Vacuum Deposition

• Metal is evaporated at a high temperatures and deposited onto the substrate which is usually at room temperature

• Provides coatings of uniform thickness even of complex shapes

• Similar to arc deposition (cathode is to a plasma state evaporated using electric arc evaporators)

• Arc deposition provides both functional and decorative applications

• Pulsed laser is the latest development in vacuum deposition

Sputtering

• Electric field ionizes an inert gas which then bombards the cathode causing the ejected atoms to coat the substrate

• Substrate is heated to improve bonding

• Reactive sputtering uses a reactive gas like oxygen. This deposits oxides onto the surface of the

• Radio-frequency sputtering is used for nonconductive materials (electrical insulators and semiconductors)

Ion Plating

• Generic term used for various combined processes of sputtering and vacuum evaporation

• Ion-beam enhanced deposition is capable of producing thin films as coatings for semiconductors and optical applications

• Large bulky parts can be coated in large cambers but require high-current power supplies

• Dual-Ion beam deposition combines physical vapor deposition with simultaneous ion-beam bombardment

• Provides good adhesion for metalsm ceramics and polymers. Used to make ceramic bearings and dental instruments

Chemical Vapor Depositon

• Aka CVD• Thermochemical process. Induced gas reacts with the

heated substrate to coat the substrate through a chemical reaction

• Used for coating cutting tools with titanium nitride and titanium carbide

• Coatings usually are thicker that those obtained using PVD and CVD cycle is longer, however the types of coatings and work piece materials are fairly unrestricted

• CVD process is used to produce diamond coatings without using binders

• Latest development is medium-temperature CVD which provides a higher resistance to crack propogation

Ion Implantation

• Ions are accelerated in a vacuum and penitrate the surface of the substrate a few μm

• Process actually alters the surface properties (can increase surface hardness and improve resistance to friction, wear and corrosion)

• Can mask the surface of the substrate to accurately control surface properties in certain locations

• Typically used on cutting and forming tools, semiconductors, dies, molds and metal prostheses

Electroplating

• The workpiece (cathode) is coated with a different metal (anode) through a water-based electrolytic solution.

• Process is long because the deposition rate is low (75μm/hour)

• Thin plate layers are typically 1μm thick layers are generally 500μm

• Rinse tanks are a necessity because of environmental hazards and recycling of unused material

• Common coating materials include chromium, nickel, cadmium, copper, tin and zinc.

• Process used for wire, printed circuits, chrome-plated hardware, galvanizing sheet metal and metalworking dies

Electroplating

Electroless Plating

• Process carried out by a chemical reaction rather than with an external source of electricity

• Used for nonconductive materials like plastics and ceramics

• More expensive than electroplating but coating surface is always uniform

• Common metals used for coating include copper and nickel

Electroforming

• Variation of electroplating but is actually a metal fabrication process

• Metal is electrodeposited onto a mandrel or matrix then removed (the coating itself is the product

• Mandrels can be made of conducting materials, non-conducting materials coated with a conducting material or have a low melting point and are melted away or dissolved with chemicals

• Process only suitable for low production quantities, aerospace parts or intricate parts like molds, dies and nozzles

Anodizing

• Conversion coating process• Oxidation process in which the work piece surface is

converted to a hard and porous oxide layer that provides corrosion resistance and decorative finish

• The work piece absorbs oxygen into its surface by a chemical reaction between it and an acid bath

• Organic dyes can be used to produce a stable and durable surface finish

• Anodized surfaces also provide a good surface to paint otherwise difficult materials like aluminum

Coloring

• Process that alters the surface color of metals, alloys and ceramics.

• Caused by the conversion of the surface into chemical compounds like oxides, chromates and phosphates.

• Coloring can be a chemical, electrochemical or thermal process

• Example: blackening of iron cookware

Hot Dipping

• Hot dipping is the process where a continuous thin sheet is run through a liquid metal.

• Used in making galvanized sheets and food cans• Protects against corrosion.

Porcelain Enameling

• Porcelains– Porcelains are applied by heating both the workpiece and

coating meterail to 425 to 1000 C– Can be applied by dipping spraying or electrodeposition.– Good corrosion resistance

Ceramic Coatings

• Ceramic coatings consist of hard metals, aluminum oxide, or zirconium oxide applied to the workpiece with the use of binders.

• Used for thermal barriers such as hot extrusion dies and in plasma arcs.

Organic Coatings

• Consist of coatings, films, and laminates that provide corrosion resistance and improve appearance.

• Uses in cabinets, paneling and aircrafts.

Diamond Coating

• Diamond coatings are produced by the various vapor deposition.• Used for such things as scratchproof windows, sunglasses, drills,

cutting tools, and missile sensors.

Surface Texturing

• Uses Etching, arcs, lasers, and atomic oxygen to modify the surface texture of the workpiece for appearance and function.

Painting

• Paints serve 2 main purposes, appearance and a protective covering.

• Paints are relatively cheap easy to apply.• Paints are available with good resistance to abrasion, temperature

extremes, and fading also resistant environmental attack.

Cleaning

• Cleaning is the removal of contaminates from the suface.• Cleaning can be done in many different ways, mechanically,

electrolytically, and chemically with a variety of cleaning fluids.• When designing always making sure that the part to be made can

be cleaned. Avoid deep blind holes, large parts, and incorporate drainage holes.

Engineering Metrology and Instrumentation

Engineering Metrology

• Defined as the measurement of dimensions such as length, thickness, diameter, taper, angle, flatness, profile, and others.

• Post-process inspection; measuring the dimensions after the part is created

• In-process, on-ling, or real-time inspection; measuring the dimensions while the part is being created

• Dimensional Tolerance is an important aspect of metrology because it influences the functionality of the part, interchangeability, and manufacturing cost.

Analog and Digital Measurements

• Resolution– The smallest difference in dimension that an instrument can

detect or distinguish.• Precision

– The degree to which the instrument gives a repeated measurement of the same standard.

•Accuracy–How close the dimensional tolerances are to the required value/measurement.

Analog and Digital Measurements (cont.)

• Common geometric features typically measured in engineering practice and manufacturing.

– Length: all linear dimensions of parts– Diameter: outside and inside dimensions– Roundness: out-of-roundness, concentricity, and eccentricity– Depth: such as drilled or bored holes and cavities– Straightness: such as shafts bars and tubing– Flatness: machined and ground surfaces– Parallelism: such as two shafts or sideways in machines– Perpendicularity: such as a threaded bar inserted in a flat plate– Angles– Profiles: such as curvatures in casings, forgings, and on car

bodies

•Major advantage of Digital instruments: They do not require any particular skill to operate, like with the analog instruments

Traditional Measuring Methods and Instruments

• Linear Measurement: Direct Reading– Rules: Simplest and most commonly used instrument for

making linear measurements.– Calipers: Used to measure inside and outside lengths.– Micrometers: Commonly used to measure the thickness and

inside or outside dimensions of parts.

Traditional Measuring Methods and Instruments (cont.)

• Linear Measurement: Indirect reading– Bevel Protractor: Made with 2 blades joined

at a central point and both blades come in contact with the part and the angle is read directly on the scale

– Sine Bar: Involves placing the part on an inclined bar or plate and adjusting the angle until the top surface it parallel to the surface plate and the angle is calculated using trigonometric identities.

– Surface Plates: Extensively used in Metrology and are typically made from cast iron or natural stone. Granite is the most common due to its low thermal expansion, nonmagnetic, and corrosion resistance. Parts and the measuring instruments are placed on these plates.

Measuring Geometric Features

• Straightness: Commonly checked with a straightedge or a dial indicator. Autocollimators are used to accurately detect the slightest imperfections in the surfaces of the part. Lasers are used for aligning machine components.

• Flatness: Flatness can be measured using surface plate and dial indicator (mechanical), or Interferometer, which uses an optical flat. This device is a flat disk of glass or fused quartz with parallel flat surfaces and placed on the surface of the work piece. When a monochromatic light is aimed at the surface, the optical flat splits the light into two beams appearing as light and dark bands to the naked eye. The number of fringes that appear is directly related to the bottom surface of the flat and the work piece. When the work piece is truly flat, the light beams are not split and fringes will not appear. When a work piece is not flat, the fringes are curved. With modern equipment, the resolution can achieve 2.5µm (0.00001 in) and having 1000 lines/in.

Measuring Geometric Features (cont.)

• Roundness: Described as a deviation from true roundness. True roundness is essential for bearings, rotating shafts, pistons, and cylinders to be functional.

•Screw Threads and Gear teeth: Measured with thread gages; common types are threaded plug gages, screw pitch gages, and snap gages.

Dial indicator where the part rotates and the dial displays the deviation in the roundness

Screw pitch gage which can measure inside or outside threads.

Measuring Geometric Features (cont.)

• Optical contour projectors

– Developed in the 1940’s

– Used to check the geometry of cutting tools and machinery profiles

– Now used to measure all profiles

– Object is magnified x100 and measurements can me made directly on the screen.

Gages (non instruments)

• Fixed gages: only determine if a part is too small or too large compared to a standard– Plug gages: GO gage/NO

GO gage; the GO gage fits into the hole but NO GO gage is to large to fit into a hole.

– Ring gages: used to measure shafts and round parts

– Snap gage: used to measure external dimensions

Gages (cont.) (non instruments)

• Air Gages: – Also called Pneumatic

Gages– Resolution can be as low

as .125µm (5µin.)– Uses pressurized air to

measure out-of-roundness.

– Gages measure the back pressure and are calibrated to measure the dimensional variations.

CH 35.5 Modern Measuring Instruments and Machines

•Electronic Gages•Laser Micrometer•Laser Interferometer•Photoelectric Digital Length Measurement

Electronic Gages

Figure 35.7 An electronic gage for measuring bore diameters. The measuring head is equipped with three carbide-tipped steel pins for wear resistance. The LED display reds 29.158 mm. Courtesy of TESA SA.

Figure 35.8 An electronic vertical length mesauring instrument, with a sensitivity of 1 m (40 in.). Courtesy of TESA SA.

CH 35.5.1 (CMM)

• Coordinate-measuring machines

A (CMM) basically consists of a platform on which the workpiece being measured is placed then is moved linearly or rotated.

CH 35.6 Automated Measurement

• Automated measurement and inspection is based on various on-line sensor systems that monitor the dimensions of parts and while they are being made and, if necessary, use these measurements as input to make corrections.

• Factors static and dynamic deflections, distortion of the machine, wear of tools, human errors, are all factors that make continuous monitoring necessary.

CH 35.7 General Characteristics and Selection of Measuring Instruments

• Accuracy: The degree of agreement of the measured dimension.• Amplification: see magnification; increase in number• Calibration: Adjusting or setting instrument to give readings that

are accurate. • Drift: stable, see Stability .• Linearity: The accuracy of the reading of an instrument over its full

working range.• Magnification: The ratio of instrument out put to the input

dimensions.• Precision: Degree of to which an instrument gives repeated

measurement of the same standard.• Repeat accuracy: The same as accuracy, but repeated many times.• Rule of 10: An instrument or gage should be 10 times more

accurate than the dimensional tolerances of the part being measured.

• Sensitivity: Smallest difference in dimensions that an instrument can distinguish or detect.

• Speed of response: How rapidly an instrument indicates the measurement, particularly when a number of parts are measured in rapid succession.

• Stability: An instrument’s capability to maintain its calibration over a period of time.

CH 35.8 Geometric Dimensioning and Tolerancing

• Dimensional Tolerance: The permissible or acceptable variation in the dimensions of a part.

• Importance of tolerance control: Only when a part is to be assembled or mated with another part.

• Definitions: Could be looked up ANSI B4.2, ANSI Y14.5, AND ISO/SC5 standards.

Tolerance Control

Figure 35.20 Basic size, deviation, and tolerance on a shaft, according to the ISO system.

Figure 35.21 Various methods of assigning tolerances on a shaft. Source: L. E. Doyle.

Con’td CH 35.8Commonly used terms for geometric

characteristics• Allowance• Basic size• Bilateral tolerances• Clearance• Clearance fit• Datum• Feature• Fit• Geometric tolerancing• Hole-basis system• Interference fit• International tolerance grade• Limit dimensions• Maximum material condition• Nominal size• Positional toleranceing• Shaft-basis system• Standard size• Transition fit • Unilateral tolerancing• Zero line

Engineering Symbols

Figure 35.24 Geometric characteristic symbols to be indicated on engineering drawings of parts to be manufactured. Source: The American Society of Mechanical Engineers.

References

• http://www.sbi-foundry.com/hstc4.jpg

• http://www.allproducts.com/metal/worldclean/aluminum-anodizing.jpg

• http://www.vecom.nl/images/other/Ker_par.jpg

• http://www.bucorp.net/images/shotpeen_cs.jpg

• http://www.uidsupport.com/system_installation/images/laser_shot2.jpg

• http://www.radgraphics.net/images/main/atomic%20explosion%20-%204.jpg

• http://www.akaida.org/images/dryer.jpg

• http://www.coiningllc.com/images/cladding.jpg

• http://www.towndock.net/salty/img/knight.jpg

• http://webpages.charter.net/zimphire/forums/redundant.png

• http://home.flash.net/~kreld/two%20sided%20spark.jpg

• http://www.precisionrolls.com/graphics/photos/spraying%20lg.jpg

• http://pingus.seul.org/~grumbel/tmp/ice.jpg• http://www.blum-novotest.com/. ../micrometer2.jpg• http://www.n4mw.com/ hp5526/hp10550b.jpg• http://www.leitz-metrology.com/ pics/fotos/reference.jpg• http://www.mathworks.com/.../ toolbox/daq/c1_int16.html

• Manufacturing Engineering and Technology Serope Kalpakjian and Steven R. Schmid

4/19/06: Group 8 – Chapters 34 and 35

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