A Study of Fixture Layout and Clamping Force for a Ti-6Al-4V Disk in a Vertical Turning Lathe Numerically Controlled Machine

Maureen Fang Sept 17, 2009

Overview

Vertical Turning Lathe (VTL) Machine

Fixture-Disk Assembly Cutting Forces Finite Element Models in ANSYS Initial Fixture Layout Deflections within Disk Questions

Vertical Turning Lathe (VTL) Machine

Machine Table/

Worktable

Numerically Controlled Unit

Tool Head

Fixture-Disk Assembly

Clamp

Plate

DiskInner Diameter=0.457m (18 in)Outer Diameter=0.508m (20 in)Height=0.0508m (2 in)

Locator

Machining an Outer Diameter

Cutting Tool

Cutting Forces Orientations

Cutting Forces Calculation Flow Diagram

Tool Geometries

Machining Parameters

Input Variables

Normal Shear Angle

Chip Compression Ratio=1.2

Cutting Constants

Cutting Forces Formulas

Cutting Forces (Fr, Ft, Ff)

Formulas and assumptions from

Manufacturing Automation By Y.

Altintas

Normal rake angle

Matlab Codes

Input Variables Tool Geometry Machining

Parameters

Cutting Forces Results are

generated by Matlab codes for both oblique and orthogonal cutting

Orthogonal cutting has only two cutting forces components

Tangential force is the dominate component.

Cutting Forces using Feedrate=0.178mm/rev or 0.007 in/rev

0.0

50.0

100.0

150.0

200.0

250.0

300.0

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700

Depth of cut (mm)

Cu

ttin

g F

orc

es (

N)

Ft, Tangential Ff, feed Fr, radial Ft. Tangential_Orthogonal Ff, feed_Orthogonal

Tangential Force

Orthogonal Cutting

Finite Element Model in ANSYS

Number of elements 32000

Number of Nodes 38720

Degree of Freedom per Node 6

Type of Elements Brick

Material of Workpiece

Ti-6Al-4V

Modulus of Elasticity 110 GPa

Poisson Ratio 0.34

Clamps, Locators, and Cutting Forces applied to Initial Fixture Layout

Cutting Forces Orientations Magnitude(N)Fr, radial -x 10Ft, Tangential -y 736Ff, feed -z 275

Cutting Speed

Feed Rate,

h

Depth of Cut,

bm/min mm/rev mm

Finish 60 0.178 0.635

Type of Cut

• Locators are constraint in 3 axis

• Clamping Force = 1500N

Deflections within a Finish Cut

Top

Bottom

Middle

1.40E-05

1.45E-05

1.50E-05

1.55E-05

1.60E-05

1.65E-05

1.70E-05

1.75E-05

1.80E-05

1.85E-05

1.90E-05

Location of cutting forces (node position)

Dis

pla

ce

me

nt

ve

cto

r s

um

(m

)

The “U” shape curve presents the magnitude of deflection changes as the cutting tool travels from the top to the bottom surface of the disk.

The displacement vector sum is largest at the top.

The subsequent models will have the cutting forces applied at the top surface.

Key Locations to Represent a Dynamic Machining Process

ANSYS model is static analysis of a dynamic process. Therefore, selected cases are used to represent snap shots of the overall machining process.

Point A, B, and C are key locations of disk where cutting forces have been applied, as disk rotates.

Displacement vector sum

6.00E-06

8.00E-06

1.00E-05

1.20E-05

1.40E-05

-50 -40 -30 -20 -10 0 10 20 30 40 50

Circumferential location of one clamp and locator w ith respect to cutting forces (degree)

Disp

lace

men

t (m

)

Displacement Vector Sum

A

B

C

Displacement components

0.00E+00

1.00E-06

2.00E-06

3.00E-06

4.00E-06

5.00E-06

6.00E-06

7.00E-06

8.00E-06

9.00E-06

1.00E-05

-50 -40 -30 -20 -10 0 10 20 30 40 50

Circumferential location of one clamp and locator w ith respect to cutting forces (degree)

Dis

plac

emen

t (m

)

maximum x-component Displacement Absolute minimum y-component Displacement Absolute minimum z-component Displacement

Displacement Components Z-component = axial direction

Y-component = circumferential direction

Clamp and locator is aligned with cutting forces at Key Location “B”

X-component = radial direction

Contour Plots from ANSYS

Questions