Fine Machining: Lean ApproachShareef M Syed

sshareef@sigmaelectric.com

The need for high precision manufacturing was felt by manufacturers worldwide to enhance Interchangeability still

maintaining the same product performance to that of selective assembly. In this era of Global village it has further fueled

the need of interchangeability, as the components are sourced from low cost countries and assembled at the location where

the deliveries to be made so as to make the supply chain more competitive. This necessitated the need for Fine Machining.

Fine machining is all

about achieving stringent

manufacturing tolerances

to meet high performance

standards. Variation reduction

is a subset along with

achieving desired surface

roughness (Ra / Rz) values.

Global competition demands

high performance combined

with low cost manufacturing.

This compelling challenge

can be de-puzzled once we

understand the components

of machining cost and there

by counter challenging

technically to arrive at the best

manufacturing process which is

highly reliable still competitive.

Value addition thru Machining,

the cost elements basically

consists of

1. Cycle times

2. Cost of consumables

3. Energy consumption

4. Rejections / rework

s·Space

6. Work in Process ( WI P)

7. Labor cost.

8. Asset depreciation

The task of manufacturing

engineers is to come out

with alternate concepts of

optimizing each and every

element. This way, not only

we have a tab on total cost

of machining but it gives the

right direction. Here Deming's

PDCA cycle (1. Plan 2. Do 3.Check 4. Act) can be applied

to carry out experiments

systematically.

Thru Coolant Spindles

22 www.martonline.in

Now let us dwell on concepts

of fine machining and

reliability with a focus on

competitiveness.

1. Cycle times:

. Right selection of Machine

size, Spindle speeds, Rapid

movements of X, Y, Z axes,

Tool change Time / Cut to Cut

time helps in optimizing cycle

Each component is unique and

selection of Machine tool is to

be based on

a) Takt time / Cycle time

calculations

b) Component material and

Material removal rate and

features

c) Sequence of operations and

number of setups

d) GD & T to be achieved WRT

Datum features.

e) Critical Ra value

requirements.

times. High speed spindles are

suitable for Non ferrous metals

whereas, High torque spindles

are for heavy metal removal

rate of ferrous components.

- Where the requirement

of Ra values in the range of

0.2 to 004 microns integral

spindle with high spindle RPMs

Integrated Spindel

May 2014

over Belt driven machines

are recommended. Spindle

housings are provided with

chiller option to maintain

thermal equilibrium even at

prolonged working hours. This

helps bearing life enhancement

and avoids possible bearing

seizure.

Combination Drill & Tap

for achieving desired positional

accuracy.

- Deep holes where LID ratio is

more than 3, it is recommended

to have thru coolant spindles.

This helps in better Ra values of

fine bored holes and reduced

Cycle times.

they work on higher cutting

parameters (Vc)

- Combination tooling helps in

reducing cycle times. No doubt

is calls for a specially designed

tailor made tools and tool

holders, the savings are very

attractive.

- Chucking systems and

Fixturing plays a vital role but

generally it is neglected. Simple

wedge type chucks are suitable

for rough I proof machining

of components. Depending

upon the component features

and accuracies involved the

1. UBL Chuck 2. Collet Chuck

- For fine machining, table

positioning accuracy is very

critical. Machines with linear

scales gives better response

(sub micron level) over Encoder

feed-back type machines.

Some Ball screw machines with

Encoder feed-back have cooling

mechanism for maintaining

thermal equilibrium and in

some machines temperature

sensors senses the expansion Icontraction of ball screws and

accordingly system is corrected

3. Diaphragm Chuck 4. Compensated Chuck 5. Face Clamp Chuck

- Cutting tool material and

Geometry plays a vital role.

Selection of positive and

negative rake angles depending

upon the material to be

cut along with chip breaker

geometry helps in better Ra

values and cycle times. Many

carbide grades are available for

steel and cast iron components

where as CBN inserts best

suited for hard part and PCD

inserts for Aluminum machining

saves lot on cyde times as

component chucking systems

could be For Machining centers

the fixturing I component

clamping devices depending

upon component features Iprofiles could be

- Precision hydraulic vices

- Magnetic chucks

- Vacuum chucks

- Special fixtures with hydraulic

clamps.

Fixture design should be such,

cutting forces are directed

towards rigid fixture elements,

not to distort component

profiles while clamping, able

to reproduce dimensional

accuracies and the desired

GD & T with ease of loading Iunloading, Poka-Yoke ( Mistake

Proofing) concepts.

Rigid fixture concepts enables

higher cutting parameters,

doesn't distort components

upon clamping thus saves on

Cycle times and rejections.

2. Cost of consumables :

Critical component machining

always attracts expensive

cutting tools and thus cost. By

following some ground rules

one can exercise better control

over tooling cost.

Reduce number of cutting tools

by combining and standardizing

where ever possible. For e.g.,

2 features combined in one

drill as a combination tool.

The savings are two-fold, one

reduction in cutting tool cost,

second, savings in non cut time

i.e., reduced machining cycle

time.

Experiments for right geometry

insert and carbide grade.

Make sure that total cost of

machining comes down during

this exercise even it calls for

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Illustration Of Lean Layout

www.martonline.in 23

TaktT.

high initial investment towards

insert. The whole idea is even

capture reduction in machining

cycle times and capture total

cost of production.

Pre decide tool life and re-

6050

Time 40302010

5.4<:; Takt TIme = 50 see':II:::

30I--

.... .2 3 - 4 . 5 . 6 - 7 8 9 10 -11 12

Opemtor#

production volumes support,

these small specific machines

not only saves Energy, Cycle

times but on shop space

requirements.

4. Rejections I Rework

7. Labor cost:

8. Asset depreciation :

One best way of optimizing the

above cost elements is thru

following Lean Manufacturing

~i ~~

grinding frequency to enhance

tool life. This saves lot on

cutting tool cost and thus cost

per piece.

3. Energy Consumption:

On a production shop-floor,

machines have to be specific

to a product line rather than

using general machines which

have high KVA ratings. If the

~J

Concept of Flow Production

Rejections are true replica of

process performance. COPQ

(Cost of poor Quality) needs to

be assessed and can be tackled

systematically using QC tools

and 6~methodology depending

on the nature of the quality

problem.

5. Space:

6. Work in Process (WIP) :

24 www.martonline.in

techniques.

LEAN cell is all about

Small dedicated machines

arranged in process sequence -

Small machines are robust and

easy to maintain and reduces

Capex burden.

- Takt time and Cycle time

balancing - Machining cycle

times are balanced to Takt

times (Takt time = Total

available time I Number of

units to be produced). As the

lines are balanced to Takt time,

there is no waiting time and

thus reduction in WIP.

- Load I Load cells - Operator

has to only load the

components into machining

fixtures, unloading is automatic

thus saves upon OCT

( Operator Cycle Time) and

hence reduction in total

machining cycle time.

- Autonomation - Man-Machine

optimization - Perfect balance

between Machine operations

and Manual operations to bring

harmony in the manufacturing

process helps in quick response

to abnormalities.

- One piece flow - Focus is

on Single piece flow in Anti-

clockwise direction to ease

Load I Unload.

The whole concept LEAN is

based upon optimization,

identification and elimination

of waste.

Conclusion:

If we have to be competitive

in this global environment,

the process has to be highly

reliable and optimized to

meet customer demands.

Fine machining techniques

together with LEAN

manufacturing methodology

helps in implementing

cutting edge technology and

identification and elimination

of waste systematically in a

manufacturing process. This

process has to be dynamic and

proactive in nature to reap the

benefits on a continuous basis.

The author Shareef M Syed, a

Mechanical engineer with MBS

qualification, ,having around

25 years of industrial experience

in Design and Development

of Metal cutting machines,

Assembly Automation systems

and component manufacturing

companies. He is certified

by ASQ (American Society

for Quality) or Black Belt

programme. Developed more

than 500 SPMs in Metal cutting

area as a part of Productivity

improvement programme.

Presently he is the Vice

President - Manufacturing

Engineering with Sigma Electric

Manufacturing Corporation

Private Limited, Pune.

May 2014