A case of shape control by a temperature gradient

A case of shape control by a temperature gradient

Citation for published version (APA):

Koning, J., Schellekens, P. H. J., & Kroot, J. P. (1970). A case of shape control by a temperature gradient. (TH Eindhoven. Afd. Werktuigbouwkunde, Laboratorium voor mechanische technologie en werkplaatstechniek : WT rapporten; Vol. WT0251). Technische Hogeschool Eindhoven.

Document status and date: Published: 01/01/1970

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'"

-~

technische .hogeschooleindhoven ' '

laboratoriwm

voo~

mechanische technologie' en werkploatstechniek

rapport van de sectie: Lengtemeting -. _,

titel: auteur(s): sectieleider: hoogleraar: samenvatting prognose

A case of shape'control by a temperature

gra.dient. ,

-

~

J. Kom.ng

P.H.J. Schellekens

J.P. Kroot

(GTD)

Tijd~ns

het betverken van een groat bed vOOr een ..

me,etmachine werd. de .invloed van de temperatuur

op de resullj:erende vorm bestudeerd. _,

Het blijkt mogelijk de vorm g~nstig te beinvloeden

doorhet aanbrengen van een verticale temperatuurs-gradient van be-paalde -grqotte .

.

.

--

..

..

..

,

.

Hoewel het onderwerponie interesse heeft en zeker

niet zonder bEilang -' moet voortz,etting Van het

.-, onderzoek uitgesloten gea.cht worden op grond van de

ontoereikende personeels,formatie van het laborator.ium voor lengtemeting ..

blz.O van 6 biz.

rapport nr. 0251 codering: . M-9-a trefwoord: teinperatuurs-invloed

.

datum:

26

augustus 1970

,

aantal biz. 6 geschikt voor pubHcatie in:

CIRP

.

I

L

A case of snape 'control

by

ai _{:temperature',gra4ient}

• I -~

J. Koning. P.H.J. Schellekens.and J.P. KrOot.

,

. '

The following note describes sOme incomplete experiments' on the . influence of fempe.ratute on' the shape of a long workpiece. Shape can be controlled to some extent .b,y

a

,vertica.1 temperature gradient, applied during .the machining ope~ation.

Some time ago two large.instrumentbeas were needed in the metrology ,

, "

department of Eindhoven University, respectively for a dividing machine

"

arid for an interferometer. (length 4m, width 0,3

_.

tn, mass ca. I tOll) .

'

As can be seen from the sketch, ther\'! al:~ 5.plane sur.faces whicli determine the position of cariages, etc.·Both instruments were designed following Abbe's principle, so tolerances were not too severe. As, however, th~ beds might well be used for, different purposes at a later time, it was decided to make them as good as possibl: with' areasonable'expe~diture of time. The machine tool available is a plan~rQf 4 meter' travel, which can be used with an auxiliary., grinding head.: There are no' facilities for cooling. The shop has no temperature control, the daily .temperature cycle' covers . a range. of SoC.

The first bed was planed, and groun,d in

a

no,rmat' way : Next the ways were

, > > i , ~. ~

fine-ground. After'some experimenting, best results were obtaine? if the

, '

grinding w.as done with a very ~ight cut;, such that the surface was. finished around 160' clock. Next morning the shape was· measured by an autocollimato,r .

.

Only one surface was ground each day. The finished bed was trimsferred to

.

. ,

.a- temperature control~ed room and measured. If the ends of the bedCj.re . disre.garded, the ways are straight within.:. 5 jJm over 3 meter length, that

7S% of the total length.

The second 'bedwas machined ~n the same way. However, ,during the last stage

some foxperiments were perf9rmed.

i

1 ) a provisional c~oling system was installed. This resulted in a

some-~h~t better ~urfBce quality~

i)

~'few surfaces .were'machined, in the ea?-,ly morning hours (5-7 0 t clock);

'so the surfaces we're finislied befo're no::tmal work in the shop, started • ...

Results; altpough good~ w~,l;"e' certainly not bettertha:n had be.en' obtained

.,'

-2-3) temperature of the workp~ece :was measulied at ,tw?, positions, ,

respectively at, the' .topand r bottom, by means of a quartz thermometer ,

(Hewlett-Packard model 280 I-'A) .' This' ins't-rument

~as

a facility

fo~

di-rect reading of

·te~pe17a·ture,

differen<;e.

Fur~h~?\

,a

the~~s~.at

was'

included irt the cooling system. By these means a vertical 'temperature

. , , ' " ' . I f

gradient can be introduced ~s required. 'The thermomete-r probes were considered too deli.cate to. measure temp' erature during' the actual

" :r machining.

. ..

~ ,

In graph II some results are represented. Curve A gives the shape of the workpiece, -ground 'and.irieasuredat' zero temperature difference (zero

• - ' , : 't ' ; " ,

to be understood as < 0,01 K '" 0,01

~C).

Thus, the shap,e is determined by the shape of the machine tool. Curve Bgives the. shape 'of the same,

.' " .( ,Y .

. ,', I ' ~ ~ 1 .

surface, measured at a temper,ature. difference of 0,9 K.' As can be expected,

~

. .

the surface is more etme;;r:ve~ I f the workpiece is ground ·1'n this condition,

• w '.~.

metal ,is removed in the middle, 'so i t will'be less ·ee!!:@8$e aft·er . cooling

down. As the temperature<itir~ng mach~ning is not the same as measIfred

before the maChining., operation, s~m~ experimenting is necessflry. Curve C gtves the shape of the surface', when a ,temperature difference of 0,5 K was

I

introduced during grinding;~themeasu'reinentwas done, at zero temperature difference. It is ~eenthat;the surface is straight within + 3 ~~ over 90%

of its length. '1'> i..

( .

It .is now clear what has happened during the' machining of thefirs't bed. It is well known ,that in a "uncontrolled" shop the

temperattireri~es

during the day, causing a vertical temperature gradient in metal structures. Evidently; the operator's have selected such machining condi tions . that a temperature differertceo!·ca. 0,5 K .was present during the finishing cuts.

~c t, . ' . •

I t is' a good example cfa procedural solution (Mc Clure, p. 9). It must '

be emphasi~ed again, that the systematic solution described above is very

"

incomplete, e. g. no attempt. has been ,made to measur'e temperature gradient,S in the machine to"l structure.

Th:e . tempe'rature measuring instrument was replaced later by a diffe:r;ent setup. It uses ,two, platimitn resistance thermOmeters in a bridge circuit.

, ' , . . ' . -~. .

" Itthetheimometers are.reasonable equal, such a bridge circuit responds

. .

. ,only to temi'erature differenqe; ,'fhe 'properties of' the cir'cui t can be predicted from the properties of t;hethermometers. In our case the

' - , . , .

thermometers (specified according to DIN 43760) have R = 100 Ohm. I f the

~ .. .. ,,~ " . ~:, . ' . .' . . ' 0

~urrertt

of the

thermom~.ters b

5,13

rnA,

a:

temperature difference of lK'

-3-o .

(= I. C). results J.n a p<?~ential o'f 1 ,mV, giving full scale deflection of a conventional potentiometric recorder. ;Tolerances of the thermoineters are

.

. '

. .

such, that no calibration is

_,

necessary rorO ,~O

rK

accuracy. i f the ~ri~ge

i~

balanced for

~t

=

O.

_."

~

The was

pla!=inum wi're is sealed in glass

.b;i

the manufacturer;

th~

mou~ted

in a brass block of.'dimensions. 60 x 8 x 10 mm3 •.

~ '"' - f ..

glass tube

The brass block is fixed ,to, thee' workpiece with a classical wax-and-rosin'

• i

mixture. Although only limited experience has beengatl:lered at .themoment, the circuit 'performs well and cBn be used duririg machining without trouble.

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