group 4 11/16/05 david reis jeremy huckins alberto barraza nick mellady

Group 411/16/05

David ReisJeremy HuckinsAlberto Barraza

Nick Mellady

The Process of grinding Grinding – a chip

removal process that uses an individual abrasive grain as the cutting tool.

Work pieces

Cylindrical, conical, fillets, helical, concave, slotting, internal grinding

Naturally Occurring Abrasives

Emery, corundum, quartz, garnet, diamond

Grinding Wheels

Structure, wear, and fracture patterns

Grinding Wheels

•The surface of grinding wheels are made up of these grains.

•Grains have random irregular shapes that are located at the edge of the grinding wheels.

Common Grinding Wheels

Colored surfaces indicate grinding faces

Superabrasive wheels

Colored surfaces indicate grinding faces

Types of Bonds Vitrified (ceramic bond) – most common

type of bond. Resistant to water, oil, and acids. Sometimes made with steel backing plates to improve physical strength.

Resinold (thermosetting resins) – Also known as organic wheels. Resistant to extremely high temperatures

Reinforced Wheels – Made with layers of fiberglass. If it did break it would not disintegrate, it would just crack.

Types of Bonds

Thermoplastic – sol-gel abrasives bonded with thermo plastics

Rubber – the most flexible bond. Metal – lowest cost. Used mainly

in small quantity production

Grinding FormulaL = (Dd)

Undeformed length = (Diameter)(depth)

Chip Formation

•When a chip forms ridges are formed where the chip left the material. This is known as plowing.

Considerations while grinding

Temperature If it gets too high it can:

Affect surface properties, including metallurgical change

Cause residual stress on the work piece Cause distortions in the work piece,

therefore accuracy goes down

Wheel wear

Once a wheel starts wearing it becomes less accurate

Grain wear – grains become flat and dull

Bond fracture – the bond breaks and the grains come off the wheel

Grinding Ratio

G = Volume of material removed

These vary widely, ranging from 2 to 200+ Using grinding fluids can increase the life

of a grinding wheel 10 fold.

Volume of wheel wear

Shaping grinding wheels

•The edges of grinding wheels are shaped with diamond dressing tools controlled by computers.

•Shaping the wheel sharpens it and restores its accuracy.

Grinding

Almost any material can be ground - aluminum, steel, ceramics, even diamond or glass.

Grinding is used whenever something needs to be smoothed or shaped.

Grinding is used to form countless types of products such as automobile engines, sharp edges on knives, ball bearings and drills. The smooth, accurate surface of the Hubble Telescope lens was formed by a process of grinding and polishing.

How Grinding Is Used

Types of grinding Machines Surface grinder

Cylindrical grinder

Universal Tool and Cutter Grinder

Lapping and Polishing

• Cylindrical grinding

center

cylindrical grinding centerless.

The bench grinder

Chemical Milling

• chemical milling/blanking is a chemical process that dissolves material from unmasked (unprotected) areas of metallic parts immersed in a tank of heated and agitated chemical reagents.  The term "blanking" denotes small, thin workpieces, and "milling" indicates relatively large workpieces.

              (a) Schematic illustration of the chemical machining process. Note that no forces or machine tools are involved in this process.

(b) Stages in producing a profiled cavity by chemical machining; note the undercut.

• considerable advantages compared to punching, laser-cutting and wire-erosion

(left) Missile skin-panel section contoured by chemical milling to improve the stiffness to-weight ratio of the part.

(top) Weight reduction of space launch vehicles by chemical milling

aluminum-alloy plates. These panels are chemically milled after the plates have first been formed

into shape by processes such as roll forming or stretch forming.

Chemical milling is used to reduce the overall weight and other non desirable factors of a workpiece

Process of Chem. Milling1. Artwork and Negative Preparation

An image is printed by a program with a laser plotter directly to the film at any size needed

2. Photoresist Application / Exposure / Develop

Apply Photoresist coating to make the metal sensitive to light.Expose coated metal to UV light source which applies the image from the art work to the metal part.Treat exposed metal part with a developing solution which removes the soft portion of the Photoresist.

3. Etching / Resist Removal

Process the metal through chemical etcher which dissolves all metal not protected by the hardened photoresist coating. 

Electrochemical Machining (ECM)

uses an electrolyte at a high rate from the tool piece to wash away the metal ions from the workpiece

the tool is usually solid or tubular form

Material removal rate is 1.5 – 4mm³

ECM was developed in 1929 Not as widely used as other processes Generally used to make complex

cavities and shapes Finishes parts burr-free and bright

surfaces Never has any thermal damage to

part or wear on the tools

Parts From Electrochemical Mill

Replacement Knees

Design Considerations for ECM

ECM is not suitable for producing sharp edges or flat sufaces

Flow of electrolyte can become difficult

Designs should make provision for a small taper for holes to be machined

Electrochemical Grinding (ECG)

• Process that combines electrochemical machining with conventional grinding

• Grinder wheel is embeded with abrasive particles of dimond or aluminum oxide

Abrassives on the spindle have two functions

To act as insulators between the wheel and workpiece

To remove electrolytic products from the work area

• Majority of material is removed by the electrolytic action, less than 5% is removed by the wheel

The ECG process is similar to that of milling, and grinding

Much better than traditional grinding where wheel wear is high

Electrical discharge machining Erosion of metals

by spark discharge Capacitor

discharge is between 50 and 380 V

EDM can be used on any material that is an electrical conductor

• Uses an electrode that sends out the sparks which erodes the metal

• Uses dielectric fluids for cooling and flushing of the material

• EDM wire • Wire is brass,

copper or tungsten• With wire edm you

can basically cut out any design

Laser-Beam Machining

Focuses optical energy on the work piece The high focus high density energy melts

the material Rough surface and has heat affected

areas Oxygen maybe added to the laser for increase

of energy, doing this leave a oxide free edge which improves welding

Lasers are also used for etching

Design consideration with LBM

Sharp corners should be avoided Deep holes will have tapered walls Don’t use highly reflective material

Electron-Beam Machining

The energy source in EBM is high-velocity electrons that move from 50% to 80% the speed of light!

It is a lot like Laser beam Machining but needs a vacuum because it puts of harmful x-rays, so is only used by trained personnel

Electron Beam Machine

• Plasma arc cutting is a type of EBM its temp. gets from 9400 C to 17,000 C

Which makes the process much faster the LBM and EDM with better products

• EBM have limited machining because of the vacuum capacity

Water Jet Machining• Cut a variety of metal and nonmetal

material up to 6-ft. x 12-ft. x 12-in. thick • Reduce machining time by as much as

70% • Provide a burr-free finished edge • Leave no heat-affected zone (HAZ) • Reduce waste material • Eliminate costly set-up time

Water jet cutters have no start holes

The jets have an extremely high velocity

No heat during cutting

Very intricate designs

The water jet is the most versatile machine on the market today

The water leaving the nozzle is from 400 MPa to 1400 MPa

The diameter of the spray is .05mm - 1mm

It is used in lots of industries from wood, to food processing, metal working

The material is wet very little It is environmentally safe process

Abrasive water jet machining

The same thing is water jet but with added abrasive particle, such as silicon carbide or aluminum oxide

This increases the material rate removal of the product

The machine is a little more complicated cause it needs to mix the contents

References

www.nd.edu/~manufact/pdfs/Ch26.pdf - Supplemental Result

Kalpakjian • Schmid Manufacturing Engineering and Technology © 2006

www.storkvecousa.com/ technology/2_etch.htm