7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 1/24

ENMF417

SP

Lect. 9: Abrasive MaterialRemoval

Dr. Simon Park

simon.park@ucalgary.ca 

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 2/24

ENMF417

SP

Announcements

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 3/24

ENMF417

SP

Learning Objectives• Fundamental Cutting Operations

– Machinability

– Tool Materials

– Chatter

– Abrasive Methods - Grinding

• Video: SME – Tool Material, PM,Grinding (if time permitted)

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 4/24

ENMF417

SP

Machinability• a measure of relative ease of

machining operations

• longer tool life, lower force, bettersurface finish, easier chip disposal,higher MRR means Good Machinability

• Ex.AISI 1112 steel: MR (Machinability rating) = 1

Titanium: MR=0.2 (poor machinability)

Aluminum: MR = 2 (good machinability)

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 5/24

ENMF417

SP

Tool MaterialsImportant properties

• Toughness – avoid fracture

• Hot (high temp) hardness – resistabrasion

• Wear resistance

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 6/24

ENMF417

SP

• High Speed Steel (HSS)

• Carbides (the most common)

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 7/24

ENMF417

SP

• Ceramics/Cermets (Ceramic and metal)

• Diamond (Polycrystalline Diamond – PCD)

• Cubic Boron Nitride (CBN)

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 8/24

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 9/24

ENMF417

SP

Chatter (self-excited vibration)

E

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 10/24

ENMF417

SP

How to Avoid Chatter?  

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 11/24

ENMF417

SP

Chatter Simulation

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 12/24

ENMF417

SPStability Lobes

Example (Modern Chatter Theory) in milling

 – Controlling spindle speed so that it matches with chatter frequency (~wn)

• Wn = 2000 Hz

• 2 Fluted Cutter

• Chatter free speed: 2000 Hz / 2 flute x 60 sec/min = 60,000 rpm

• RUN the machine at 60,000 rpm, 30,000 rpm, 20,000 rpm, …. 

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 13/24

ENMF417

SP

Selection of Cutting Conditions• Cutting Conditions:

– Speed, feed, depth of cut, and cutting fluids– Machining Handbook or Tool Catalogs’Recommendations

• Limitations:– Horsepower and torque

– Machine tool and rigidity– Strength of cutting tool– Chatter– Tolerances 

• Selection of Feed and Speed  – Select Cutting the Depth and Speed – minimize

chatter vibration– Select Feed – roughing or finishing– While maintain good MRR

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 14/24

ENMF417

SP

Surface Integrity1. Strain hardening of a surface

2. Cracks formed in low speed cutting

3. Phase transition due to high temp.

4. Residual stress

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 15/24

ENMF417

SP

Abrasive Machining

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 16/24

ENMF417

SP

Abrasive Machining • Material removal by abrasive particles

– Grinding is the most common abrasivemachining– (others ex: honing, lapping, buffing)

• Reasons for grinding are:1. The material is too hard to be machined

economically. (The material may have beenhardened in order to produce a low-wear finish,such as that in a bearing raceway.)

2. Tolerances required preclude machining.Grinding can produce flatness tolerances ofless than±0.0025 mm (±0.0001 in)

3. Machining removes excessive material.

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 17/24

ENMF417

SP

Abrasive Machining (Different thanMilling)

• Cutting speeds are higher

• Higher negative rake angle

• Self-sharpening as each abrasive fallsoff

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 18/24

ENMF417

SP

Grinding MechanismSpecific Energy is greater

than machining

• Size effects (small chipsize causes energy toremove each unit volume)

• Extremely negative rakeangles (low shear plane

angles and high shearstrains)• Part of grits is engaged in

cutting• Shearing (knife), plowing

(plastic and elastic

deformation), and rubbing(friction)

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 19/24

ENMF417

SP

Honing

• For internal holes or bores

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 20/24

ENMF417

SP

Lapping• Lapping is a loose abrasive machining

process to form a slurry to form anabrasive film between the plate and theparts to be lapped.

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 21/24

ENMF417

SP

Polishing/Buffing

Before After

Toyota MR2 Intake Manifold

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 22/24

ENMF417

SP

Abrasive types• Aluminum oxide

• Silicon Carbide

• CBN

• Diamond

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 23/24

ENMF417

SP

Dressing• Dressing is… 

– Conditioning worn grains by producing sharpnew edges

– Truing – producing a true circle on a wheel

– Usually uses a diamond point tool

ENMF417

7/27/2019 Grinding and Other

http://slidepdf.com/reader/full/grinding-and-other 24/24

ENMF 7