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Design, manufacture and testing of precision machines with essential polymer concrete components
Design, manufacture and testing of precision machines with essential polymer concrete components M. Weck and R. Hartel* High accuracy in precision machinery can be achieved by using new materials such as polymer concrete. The possibifity of using these materials in service depends mainly on the physical features of the materials and on the material dependency of the machine-parts. The construction, manufacturing and testing of the precision machines mentioned in this article have led to a better understanding of the materials and to the development o f expressions relating to their use.
Keywords: machines, polymer concrete, accuracy
In the machine tool industry 'precision' is the term used to describe machinery and function-elements that, compared to conventional production systems, meet the highest specifications of manufacturing accuracy identified by size consistency, angular accuracy, parallelism and surface finish. The general trend is towards achieving smaller tolerances for production machinery (Fig 1). Standard machinery now achieves precision of the order of 1 #m; precision and ultraprecision machines are capable of accuracy two to three decimal places better than this 1. To achieve the accuracy now required of precision cutting machines the use of compound materials for structural components is assuming greater importance, as machine characteristics can be influenced by dynamic and thermal factors.
Precision limits due to w e a k points of sub-assemblies In an extensive series of tests dealing with the static and dynamic behaviour of precision machines, weak points which influence quality have been analysed. 2 By recording machine-part movements it is possible to find the cause of the off-size condition and to describe the behaviour of these elastic parts. The maximum elasticity Gg(j(o) at the cutting point is used as a criterion for recording and assessing the weak points of a machine structu re under process-dependent forces. One reason for reduction in manufacturing quality is the existence of weak points in the machine bed and the supports as shown in Fig 2. Fig 2(a) shows the frequency of occurrence of the dominant weak points of 25 precision turning machines and Fig 2(b) those of 11 precision milling machines. The instances of some machine-part vibrations could be reduced in number by using polymer concrete in building precision machines (see shaded area of figure). * RWTHAachen, Fraunhofer-lnstitutf(JrProduktionstechnologie (IPT),Aachen, FRG
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ultra precision
1c Fig 1 Historical development o f achievable machining accuracy Apart from the vibration modes of the spindlebearing system, torsional and bending vibrations of the machine structure (eg in the machine bed and machine support), can lead to large deformations at the cutting point. The adverse effects of vibration of machine sub-assemblies of precision machines can also be significantly reduced by a well-aimed selection and use of materials like polymer concrete.
Material comparisons The physical characteristics of metallic and composite materials are largely known 3. Substitute materials can be produced and optimized according to their material characteristics to perform the same function and possess the same strength as other materials. The cross-sections of these materials must be adapted according to their specific strengths so that the machine function is not affected. As a comparison of the features of the compound material, polymer concrete, with those of steel or cast iron, Fig 3 shows the characteristic static, dynamic and thermal curves for the three materials. The low tensile strength of polymer concrete shown in the stress-strain diagram must be
0141--6359/85/030165--06 $03.00 © 1985 Butterworth & Co (Publishers) Ltd JULY 1985 VOL 7 NO 3
165
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Fig 2 Significant weak elements of (a) chuck lathes; (b) precision drilling and milling machines offset by adequate dimensioning of the actual machine-elements. The vibration amplitudes of polymer concrete parts caused by dynamic excitation (eg due to cutting process) are smaller than the amplitudes of metallic materials, and the composite also has higher damping. Differences of the heat-conduction and expansion coefficients of the various materials are the cause of the thermoelastic relative movement measured at the cutting point. Metallic materials are quick to react to changes in temperature with large shifts, and they reach their final state in a short time, whereas polymer concrete parts change their size much more slowly.
166
This knowledge is of great importance in the design of structures so that deformations due to bi-metallic effects are avoided, such as between polymer concrete machine bed and metallic guideways fixed to the bed. M a t e r i a l - d e p e n d e n t design and construction Detailed knowledge of material-dependent construction and calculation is necessary if one is to profit from the material-specific features of compound materials when building precision machinery. This experience has tended to be gathered empirically". Detailed understanding o:f manufac-
PRECISION ENGINEERING
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turing and asembly, as well as knowledge from the measuring tests has led to continuous improvements of these parts (Fig 4). The constructional design ofa guideway main body was adapted according to its surface shape to achieve a smooth tension distribution in the joint. During design and construction of these machine-parts it became obvious that there was no quantitative data available on which to base calculations for elements connecting metallic and compound materials. Optimized shapes have to be found for the machine-parts to achieve an assembly with adequate strength taking the material characteristics into consideration s. Characteristic values for static and dynamic features of the connecting elements are therefore required as input to finite element method calculations (FEM), Having obtained expressions for connections between materials approximated for the calculations, the improved solutions for the tension and deformation analyses can be determined for a complete machine structure.
Production of structural components made of compound materials Machine elements made of compound materials like polymer concrete are manufactured using a cold moulding procedure. Apart from shaping the single machine elements the moulded shapes have
PRECISION ENGINEERING
to fulfil additional tasks: they have to locate the metallic function elements such as guideways. Fig 5 shows the open-welded steel mould for the machine bed of a precision turning machine with hard-foam cores inside. The finished demoulded structure of the machine bed is also shown; the guideways are easily visible. A precision milling machine has also been built and is shown in Fig 6 together with a machine bed and machine column made of polymer concrete. The moulding technique chosen for this machine allows supplementary bonding of the guideways. A cross-section of part of the figure shows the adhering joint between the guideway main body and the machine bed. The positioning and fixing of the guideways, using a holding device during the bonding process, saves expensive finishing of the high-precision guideways. The achievable size consistency of the holding devices is the essential function in determining the manufactured precision of the machine.
Results of measuring tests Modal analysis has been used to assess the load deformation of precision machinery 8. In this work the static and dynamic elastic behaviour was determined by using an electrohydraulic relative exciter that produces stochastic alternating forces in the frequency range 0-1000 Hz at the cutting point
167
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Fig 6 Milling machine with a frame made o f polymer concrete
PRECISION ENGINEERING
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between tool and workpiece. These forces and the resulting deformations between tool and workpiece were measured by suitable pick-ups and were registered and analysed by a fast Fourier analyser system. Two precision machines of the same construction, one conventional and the other using compound materials, were tested to achieve comparisons between the use of compound and metallic materials. The conventional machine bed was made of cast iron and the new machine bed, of the same outer dimensions, was manufactured in polymer concrete. The results of the static and dynamic examinations are shown in Fig 7. The elasticity (the relation between the resulting deformation amplitude and the exciting force) in all three machine directions, X, Yand Zat various frequencies is shown for a conventional turning machine and for one with a polymer concrete machine bed. The phase-lag between the deformation and the exciting force was measured too. The elasticity amplitude distinguishes the size of the vibration amplitude at certain frequencies. The phase relation is important as it influences any tendency to chatter during the cutting process. If the phase-angle between force and displacement reaches - 9 0 ° the cutting procedure tends to become unstable at the corresponding frequency. The static machine elasticity can be seen at zero frequency.
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The elasticity characteristics of all three axes show that the machine with a polymer concrete bed has lower static and dynamic elasticity, which means it is stiffer (the static elasticity in the X-direction is an exception). Also, the resonance frequencies are higher for the polymer concrete machine. In X- and Z-directions the frequency ranges for which the phase is greater are much narrower than - 9 0 °. Phase angles of more than - 9 0 ° do not occur in the Y-direction in the illustrated frequency range for the polymer concrete machine. In the highfrequency range the two machine-types differ only slightly from each other. Thermal deformation, caused by internal heat sources (for example, a driving motor) can be up to 20% less in a machine with polymer concrete machine bed when compared to a conventional machine 4.
Conclusions
The advantages and disadvantages of using polymer concrete in essential structural components of precision machines are determined by the physical material features and the materialdependent construction of the machine modes. The high material damping of polymer concrete is a big advantage during dynamic loading of the machine stuctures. In addition the small heat-
169
t r a n s f e r coefficients of c o m p o u n d m a t e r i a l s result in s m a l l e r d e f o r m a t i o n at t h e c u t t i n g - p o i n t . The l o w y i e l d strength and t h e v e r y m u c h l o w e r t e n s i l e strength of p o l y m e r concrete are i m p o r t a n t d i s a d v a n t a g e s . These l o w s t r e n g t h values make p o l y m e r concrete u n s u i t a b l e f o r service in h i g h l y - l o a d e d m a c h i n e parts so that it is n o w m a i n l y m a s s i v e m a c h i n e structures such as c o l u m n s and beds w h i c h are m a n u f a c t u r e d f r o m this m a t e r i a l . E c o n o m i c aspects are n o w b e c o m i n g m o r e i m p o r t a n t f o r the service of p o l y m e r concrete in m a c h i n e structures.
References 1 Taniguchi N. Current status in, and future trends of, ultraprecision machine and ultrafine materials processing. Annals ClRP, 198332 (2) 2 Weck M. and Petuelli G. Experimentell-rechnerische Ermittlung des statischen und dynamischen Verhaltens spanender Werkzeugmaschinen. VDI-Berichte, 1982, Nr. 456 3 Cranfield Research & Developments Ltd; Report: Synthetic Granite-Granitan $100. A new improved structural material for production machinery 4 Week M. and Sahm D. Gestaltfestigkeit und Schwingungsverhalten gegossener Maschinenteile. VDG-Bericht, 1985 5 Koller R. Entwicklung einer Systematik fLir Verbindungen - ein Vortrag zur Konstruktionsmethodik. Konstruktion, 1984, 36 6 WeckM. Werkzeugrnaschinen Band4: Mel3technische Untersuchungen und Beurteilung. VDI-Verlag, ISBN 3-18-40 0485-6
|,
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the model during development stages • Surface to surface intersection capabilities make developing complex surtaces a simple task • With the selection of a single menu, any element type can be projected onto a defined surface • Complex surfaces can be stored as one entity, even if created through a combination of many surfaces • Distances and vectors can be obtained from any elements The results of the design stage can be down loaded to the shop floor as NC/CNCprograms using MDSI's DNC package. MDSl Schlumberger, Radcliffe House, Blenheim Court, Solihull, West Midlands B91 2AA, UK
Stimulating standards for design and performance To stimulate new interest in robot standards development and to establish priority areas for its own work, the Robotic Industries Associa-
tion (RIA) has issued a questionnaire to robot users, builders, educators, researchers, accessory suppliers and other groups in the USA with an interest in robotics. According to Samuel Korin, Chair of RIA's R15 Committee on Robotic Standards and Director of IBM's Manufacturing Technology Institute in New York, standards development in the robot industry will be a slowly-evolving process: 'The industry is still developing new equipment features and functions, making it more difficult to develop broad standards'. The work of the RtA parallels the work of the International Standards Organization (ISO). Currently, the ISO is working toward developing robot standards in the areas of terminology and graphic representation; performance criteria and related testing methods; safety; requirements for programming methods and data; and mechanical interface. Robotic Industries Association, Manager of Standards, PO Box 1366 Dearborn, M148121, USA.
PRECISION
ENGINEERING
Keywords: machines, polymer concrete, accuracy
In the machine tool industry 'precision' is the term used to describe machinery and function-elements that, compared to conventional production systems, meet the highest specifications of manufacturing accuracy identified by size consistency, angular accuracy, parallelism and surface finish. The general trend is towards achieving smaller tolerances for production machinery (Fig 1). Standard machinery now achieves precision of the order of 1 #m; precision and ultraprecision machines are capable of accuracy two to three decimal places better than this 1. To achieve the accuracy now required of precision cutting machines the use of compound materials for structural components is assuming greater importance, as machine characteristics can be influenced by dynamic and thermal factors.
Precision limits due to w e a k points of sub-assemblies In an extensive series of tests dealing with the static and dynamic behaviour of precision machines, weak points which influence quality have been analysed. 2 By recording machine-part movements it is possible to find the cause of the off-size condition and to describe the behaviour of these elastic parts. The maximum elasticity Gg(j(o) at the cutting point is used as a criterion for recording and assessing the weak points of a machine structu re under process-dependent forces. One reason for reduction in manufacturing quality is the existence of weak points in the machine bed and the supports as shown in Fig 2. Fig 2(a) shows the frequency of occurrence of the dominant weak points of 25 precision turning machines and Fig 2(b) those of 11 precision milling machines. The instances of some machine-part vibrations could be reduced in number by using polymer concrete in building precision machines (see shaded area of figure). * RWTHAachen, Fraunhofer-lnstitutf(JrProduktionstechnologie (IPT),Aachen, FRG
102 Processing machines
~' ]0
lathes
i~
~ 10 ~=10 _~10 1c
millingmachines grindingmachines boringmachines machiningcenters precisionjig borers precision diamond lathes superfinishing machines precision grinding m3chines precision lapping machines -diam, grinding roach. lapping m3chines polishing machines chemicalfmechanical re]chining electron beam machining
ultra precision
1c Fig 1 Historical development o f achievable machining accuracy Apart from the vibration modes of the spindlebearing system, torsional and bending vibrations of the machine structure (eg in the machine bed and machine support), can lead to large deformations at the cutting point. The adverse effects of vibration of machine sub-assemblies of precision machines can also be significantly reduced by a well-aimed selection and use of materials like polymer concrete.
Material comparisons The physical characteristics of metallic and composite materials are largely known 3. Substitute materials can be produced and optimized according to their material characteristics to perform the same function and possess the same strength as other materials. The cross-sections of these materials must be adapted according to their specific strengths so that the machine function is not affected. As a comparison of the features of the compound material, polymer concrete, with those of steel or cast iron, Fig 3 shows the characteristic static, dynamic and thermal curves for the three materials. The low tensile strength of polymer concrete shown in the stress-strain diagram must be
0141--6359/85/030165--06 $03.00 © 1985 Butterworth & Co (Publishers) Ltd JULY 1985 VOL 7 NO 3
165
Weck and Hartel - - machines with p o l y m e r concrete components
Frequencyof causes o, v, ration for
significant resonances
]'~o~.1~ ,0 --4 J~ k \
1 I I I I
I I I I I
Pre~i2S5°mn aCchh~C:sl:the
~
I~11"t~1 ] /I
x
Cr,t r,on
z Y
Cuttingconditions xM = 90° ~o~th : 76° X =0 °
Improvement
by using polymer concrete
No significance 111
1
11
111
Significance of resonances
a
Precision drilling and milling machines Frequency of causes of vibration for significant resonances Criterion : I Gg(]'W ) Imax
n° n"dlSll, amCeacbl:sP)i ien ndle I~ I r~
k ~ ~ ~ /
m Cutting conditions
.~. ~ ~.~ i ~ Normal tangential movement in ways of table unit ~.~ ~ ~ Ii~!i!!ii~ T°rsiOnalvibrati°ns°fc°lurnnwithmOvementinways ~ i ~ ~ ~ ~ I~il ~N°rmaltangentialrel'm°vementinways°fc°lumn'bed ~ ~--~ ~ ._~Vibration of spindle-bearing system
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Fig 2 Significant weak elements of (a) chuck lathes; (b) precision drilling and milling machines offset by adequate dimensioning of the actual machine-elements. The vibration amplitudes of polymer concrete parts caused by dynamic excitation (eg due to cutting process) are smaller than the amplitudes of metallic materials, and the composite also has higher damping. Differences of the heat-conduction and expansion coefficients of the various materials are the cause of the thermoelastic relative movement measured at the cutting point. Metallic materials are quick to react to changes in temperature with large shifts, and they reach their final state in a short time, whereas polymer concrete parts change their size much more slowly.
166
This knowledge is of great importance in the design of structures so that deformations due to bi-metallic effects are avoided, such as between polymer concrete machine bed and metallic guideways fixed to the bed. M a t e r i a l - d e p e n d e n t design and construction Detailed knowledge of material-dependent construction and calculation is necessary if one is to profit from the material-specific features of compound materials when building precision machinery. This experience has tended to be gathered empirically". Detailed understanding o:f manufac-
PRECISION ENGINEERING
Weck and Hartel - - machines with p o l y m e r concrete components
4oot St
7.8
240
400
CI
7.2
120
200
PC
2.4
20
20
~
200 0.02
Cl
;
SteeHSt)
f=const.
-hstr
0.02
A
0,2
2
20
St = ~ Cast iron(Cl) f=const.
hcl ~
T-
j~
Polymer concrete(PC)
95 gB
St
210
0.002
0.11
80
11
CI
105
0.03
0.14
75
10
PC
35
0.02
0.21
10
10-20
go Temperature
Fig 3 Comparison o f material characteristics
turing and asembly, as well as knowledge from the measuring tests has led to continuous improvements of these parts (Fig 4). The constructional design ofa guideway main body was adapted according to its surface shape to achieve a smooth tension distribution in the joint. During design and construction of these machine-parts it became obvious that there was no quantitative data available on which to base calculations for elements connecting metallic and compound materials. Optimized shapes have to be found for the machine-parts to achieve an assembly with adequate strength taking the material characteristics into consideration s. Characteristic values for static and dynamic features of the connecting elements are therefore required as input to finite element method calculations (FEM), Having obtained expressions for connections between materials approximated for the calculations, the improved solutions for the tension and deformation analyses can be determined for a complete machine structure.
Production of structural components made of compound materials Machine elements made of compound materials like polymer concrete are manufactured using a cold moulding procedure. Apart from shaping the single machine elements the moulded shapes have
PRECISION ENGINEERING
to fulfil additional tasks: they have to locate the metallic function elements such as guideways. Fig 5 shows the open-welded steel mould for the machine bed of a precision turning machine with hard-foam cores inside. The finished demoulded structure of the machine bed is also shown; the guideways are easily visible. A precision milling machine has also been built and is shown in Fig 6 together with a machine bed and machine column made of polymer concrete. The moulding technique chosen for this machine allows supplementary bonding of the guideways. A cross-section of part of the figure shows the adhering joint between the guideway main body and the machine bed. The positioning and fixing of the guideways, using a holding device during the bonding process, saves expensive finishing of the high-precision guideways. The achievable size consistency of the holding devices is the essential function in determining the manufactured precision of the machine.
Results of measuring tests Modal analysis has been used to assess the load deformation of precision machinery 8. In this work the static and dynamic elastic behaviour was determined by using an electrohydraulic relative exciter that produces stochastic alternating forces in the frequency range 0-1000 Hz at the cutting point
167
Weck and Hartel - - machines with polymer concrete components
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Fig 4 Optimization in construction o f a precision machine
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Fig 5 Manufacture of a precision lathe
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Fig 6 Milling machine with a frame made o f polymer concrete
PRECISION ENGINEERING
Weck and Hartel ~ machines with polymer concrete components Tool changingsystem / C
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between tool and workpiece. These forces and the resulting deformations between tool and workpiece were measured by suitable pick-ups and were registered and analysed by a fast Fourier analyser system. Two precision machines of the same construction, one conventional and the other using compound materials, were tested to achieve comparisons between the use of compound and metallic materials. The conventional machine bed was made of cast iron and the new machine bed, of the same outer dimensions, was manufactured in polymer concrete. The results of the static and dynamic examinations are shown in Fig 7. The elasticity (the relation between the resulting deformation amplitude and the exciting force) in all three machine directions, X, Yand Zat various frequencies is shown for a conventional turning machine and for one with a polymer concrete machine bed. The phase-lag between the deformation and the exciting force was measured too. The elasticity amplitude distinguishes the size of the vibration amplitude at certain frequencies. The phase relation is important as it influences any tendency to chatter during the cutting process. If the phase-angle between force and displacement reaches - 9 0 ° the cutting procedure tends to become unstable at the corresponding frequency. The static machine elasticity can be seen at zero frequency.
PRECISION ENGINEERING
The elasticity characteristics of all three axes show that the machine with a polymer concrete bed has lower static and dynamic elasticity, which means it is stiffer (the static elasticity in the X-direction is an exception). Also, the resonance frequencies are higher for the polymer concrete machine. In X- and Z-directions the frequency ranges for which the phase is greater are much narrower than - 9 0 °. Phase angles of more than - 9 0 ° do not occur in the Y-direction in the illustrated frequency range for the polymer concrete machine. In the highfrequency range the two machine-types differ only slightly from each other. Thermal deformation, caused by internal heat sources (for example, a driving motor) can be up to 20% less in a machine with polymer concrete machine bed when compared to a conventional machine 4.
Conclusions
The advantages and disadvantages of using polymer concrete in essential structural components of precision machines are determined by the physical material features and the materialdependent construction of the machine modes. The high material damping of polymer concrete is a big advantage during dynamic loading of the machine stuctures. In addition the small heat-
169
t r a n s f e r coefficients of c o m p o u n d m a t e r i a l s result in s m a l l e r d e f o r m a t i o n at t h e c u t t i n g - p o i n t . The l o w y i e l d strength and t h e v e r y m u c h l o w e r t e n s i l e strength of p o l y m e r concrete are i m p o r t a n t d i s a d v a n t a g e s . These l o w s t r e n g t h values make p o l y m e r concrete u n s u i t a b l e f o r service in h i g h l y - l o a d e d m a c h i n e parts so that it is n o w m a i n l y m a s s i v e m a c h i n e structures such as c o l u m n s and beds w h i c h are m a n u f a c t u r e d f r o m this m a t e r i a l . E c o n o m i c aspects are n o w b e c o m i n g m o r e i m p o r t a n t f o r the service of p o l y m e r concrete in m a c h i n e structures.
References 1 Taniguchi N. Current status in, and future trends of, ultraprecision machine and ultrafine materials processing. Annals ClRP, 198332 (2) 2 Weck M. and Petuelli G. Experimentell-rechnerische Ermittlung des statischen und dynamischen Verhaltens spanender Werkzeugmaschinen. VDI-Berichte, 1982, Nr. 456 3 Cranfield Research & Developments Ltd; Report: Synthetic Granite-Granitan $100. A new improved structural material for production machinery 4 Week M. and Sahm D. Gestaltfestigkeit und Schwingungsverhalten gegossener Maschinenteile. VDG-Bericht, 1985 5 Koller R. Entwicklung einer Systematik fLir Verbindungen - ein Vortrag zur Konstruktionsmethodik. Konstruktion, 1984, 36 6 WeckM. Werkzeugrnaschinen Band4: Mel3technische Untersuchungen und Beurteilung. VDI-Verlag, ISBN 3-18-40 0485-6
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Harnessing CADCAMexpertise An expert system with a CADCAM application, claimed to be the first in the world, has been launched by MDSI Schlumberger. Based on MDSI's EQINOXsoftware, the fabrication and geometric modelling packages allow the user, regardless of level of knowledge, immediate access to the expertise of experienced engineers. Features of the 'fabrication CADCAM' software, developed for the sheet metal design and fabrication process, are that: • Fabrication designs are created with natural three-dimensional visualization • Three-dimensional component representations are automatically unfolded for flat pattern development and manufacturing instructions • Fabrication processes are automatically generated based on part features, machine selection, tooling libraries, and material libraries • Development of press brake instructions is simplified • The user can apply his own company's methods at any time in the process The EQINOXgeometric modeller contains several powerful features for 3D design: • A complete list of standard primitives and geometric building blocks allows users to define easily threedimensional surfaces such as ruled, warped, and fillet surfaces, as well as surfaces of revolution • Automaticwireframe development permits quick visualization of
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7-10April
1986, B r i g h t o n , U K
Low energy ion beams The aim of the conference is to bring together specialists in the fields of ion source development, beam transport, ion beam machines and the application of ion beams for the modification and analysis of solid surfaces. The conference programme will include coverage of the following areas: ion implantation, ion assisted deposition and annealing, sputter profiling, microbeams, low energy ion beams for surface studies, ion and plasma etching, effects on ion bombarded surfaces and interfaces, ion and atom beam source technology, excitation, ionization, charge transfer, ion accelerators. The Institute of Physics, 47 Belgrave Square, London SWIX 8QX, UK
the model during development stages • Surface to surface intersection capabilities make developing complex surtaces a simple task • With the selection of a single menu, any element type can be projected onto a defined surface • Complex surfaces can be stored as one entity, even if created through a combination of many surfaces • Distances and vectors can be obtained from any elements The results of the design stage can be down loaded to the shop floor as NC/CNCprograms using MDSI's DNC package. MDSl Schlumberger, Radcliffe House, Blenheim Court, Solihull, West Midlands B91 2AA, UK
Stimulating standards for design and performance To stimulate new interest in robot standards development and to establish priority areas for its own work, the Robotic Industries Associa-
tion (RIA) has issued a questionnaire to robot users, builders, educators, researchers, accessory suppliers and other groups in the USA with an interest in robotics. According to Samuel Korin, Chair of RIA's R15 Committee on Robotic Standards and Director of IBM's Manufacturing Technology Institute in New York, standards development in the robot industry will be a slowly-evolving process: 'The industry is still developing new equipment features and functions, making it more difficult to develop broad standards'. The work of the RtA parallels the work of the International Standards Organization (ISO). Currently, the ISO is working toward developing robot standards in the areas of terminology and graphic representation; performance criteria and related testing methods; safety; requirements for programming methods and data; and mechanical interface. Robotic Industries Association, Manager of Standards, PO Box 1366 Dearborn, M148121, USA.
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ENGINEERING