O IDDRG, International Deep Drawing Research Group (Grupo Internacional de Pesquisas em Conformação de Chapas) é uma organização formada por grupos nacionais devotados ao estudo da conformação de chapas, incluindo processos de conformação, materiais, plasticidade, ferramentaria, tribologia e outros aspectos de interesse para a pesquisa e aplicações industriais. O IDDRG iniciou-se em 1950 e desde então formou vários grupos fortes. Por exemplo, na Alemanha, EUA e Japão. A missão do IDDRG é coordenar pesquisa e desenvolvimento em conformação de chapas, reunindo cientistas, pesquisadores e industriais que trabalhem nessas áreas no mundo inteiro, oferecendo um canal aberto e de alto nível técnico para seus membros apresentarem suas pesquisas e desenvolvimentos.
Fomentar no Brasil o desenvolvimento e o estudo de técnicas e fenômenos envolvidos nas atividades de estamparia e conformação de chapas, incluindo processos de conformação, materiais, plasticidade, técnicas de ferramentaria, fenômenos tribológicos e outros aspectos de interesse para a pesquisa e aplicações industriais. Orientar atividades de pesquisa e desenvolvimento em conformação de chapas, reunindo especialistas acadêmicos e da indústria dedicados ao tema, oferecendo um canal aberto e de alto nível técnico para seus membros apresentarem suas pesquisas e definirem temas de interesse comum.
This text examines the first years of the well known “International Deep Drawing Research Group” launched in 1957, the justification of its name and the organisation of the first international conference that was held in 1960 in Paris.
Details are first given on the state of the art existing at the time and what were the main problems still remaining that justified this group. Some information also appears about the actors of this birth and the long adventure they started.
Key words: IDDRG, deep drawing, forming, history.
This 2010 year is very important for us because we celebrate the fiftieth anniversary of the first international conference held by the IDDRG.
After such a long time of existence, it is not surprising that many of you completely ignore the exact origin of our organisation and even the reason of its name:
International Deep Drawing Research Group.
This is to fill this lacuna that I have collected and gathered information on the IDDRG birth at the end of the fifties. I will present them now.
To replace this event in its context, we must first quickly define the state of the art when it happened.
1. State of the art concerning metallic materials properties
Around 1950, the material properties at the origin of formability were not precisely identified and engineers were surprised to observe that all metals having a certain level of ductility were able to make the same parts. As an example, a sauce pan could be made either of mild steel, copper, tin, brass, aluminium, silver, gold, etc.
As today, fundamental knowledge of material properties was mainly based on the tensile test and the four basic characteristics that were issued of: yield strength,
ultimate tensile strength, uniform and total elongations.
The tensile test was known since a long time. Here is a sketch of a machine invented by Leonardo da Vinci around 1500, designed to measure the resistance of wires (see Figure 1). It does not seem it was ever realised.
Some pretend that the first tensile test was performed by Galilei Galileo around 1590 from the Pisa tower: he progressively made a copper wire hanging and just had to weigh the fallen part after it had broken to know its resistance. But the reality of all Galileo’s experiences is discussed…
However, more astonishing, given the experimental possibilities of the times, is the first strain hardening law proposed by Bullfingeri as soon as 1729:
E = S^n
We know today that it is not the best formula , but it is always easy to criticize later…
In 1885, Considère published a famous paper of about 200 pages, of which three or four only are dedicated to the explanation of the load instability, just believed at this moment to be the result of local scatter in metal properties. He demonstrated that this instability was not at all the result of hazard but that it appeared when strain hardening was no longer sufficient to compensate reduction of cross section.
He thus introduced what we now call “true stress” and showed that the tangent modulus was equal to this stress at the load instability (Figure 2).
Contrarily to what is often said, he never posed that true strain at instability was equal to the strain hardening exponent “n” of the power law:
Einst = n
This for two simple reasons:
- the notion of true strain was not known (later introduced by Ludwik),
- the n-value of the power law did not exist yet (this was only shown by Hollomon in 1945).
It was not before 1909 that Ludwik proposed his famous law and, in the same paper, the use of logarithmic strains , also called true or natural strains.
S = So + k^n
2. Knowledge of the stamping process
Stamping was a technique, not a science. We can say that it is still true, despite our efforts and even if large progress has been made.
Scientific researchers were not so much interested in exploring sheet metal forming because it was obviously too much dependent of many process variables , the influence of which was uncertain: tooling shape, tooling roughness, lubrication, speed, temperature, blankholder pressure, etc. In fact, press forming was more an art, sometimes mysterious, than a technique and it was more useful to be observant and intuitive than having a scientific knowledge. Stamping was essentially studied through the so-called “simulative ” tests, that is to say, small tests reproducing typical forming operations.
Such studies existed in Germany, England, Sweden, North America, Japan and France. In Germany, a lot of work had already been dedicated by researchers to sheet metal forming issues and many tests were defined:
· a theoretical study of wrinkling under the blankholder was published in 1924 by Geckeler,
· the KWI test was set up by Siebel and Pomp from the Kaiser Wilhelm Institut, in 1929,
· the shrink drawing test of a wedge-shaped test piece was imagined by Sachs in 1930,
· the Erichsen test, invented in 1912, was already defined by the standard DIN 50101 in 1947…
In England, the automotive industry, when passing from hand-made parts to stamped parts, faced many problems of process robustness due to the very irregular quality of the steels then available. Managers of this industry were thinking that a better understanding of the stamping process was necessary or, at least, that universally accepted tests able to evaluate the level of formability of material deliveries were mandatory.
As early as 1930, they asked Professor Swift from Sheffield University to study sheet metal stamping. It was, at the time, considered in Great Britain as a first and unique example of cooperation between industry and academy! Cups with flat or hemispherical bottom were intensively studied. It’s in the course of this research that Swift also studied in depth bending under tension (1948), thought to be one of the important items of deep drawing because it was one source of the metal resistance to flow into the die cavity. It seems that he was also the first one to design an instrumented press for stamping study. In North America also, many studies were developed concerning sheet metal formability. There were some reputed researchers such as Gensamer, Lankford, Backofen… The discovery of the plastic anisotropy influence is a symptomatic example: the first observations were made by Baldwin on copper in 1946, followed by Howald, then Lankford, but without clearly understanding its interest.
A detailed research was started in cooperation between Carnegie-Illinois Steel Co and the Pennsylvania State College at the end of which was published the famous paper by Lankford, Snyder and Bauscher (1950) clearly demonstrating the usefulness of a high R-value (the symbol R used for plastic anisotropy - then called normal anisotropy - was given by Lankford) for the stamping of automobile front fenders. For circular parts (cups) however, it was still thought that a high planar isotropy was necessary because ears were considered as the source of failure. Only in 1959 did Witheley show that a high R-value was also beneficial for forming round parts.
By the way, Lankford also discovered the concept of Forming Limit Curves (that he called “Analysis of forming limits”) in 1945. However, Lankford was more interested in studying anisotropy and abandoned this although promising clue. This discovery was then forgotten and re-discovered by Keeler in 1963 during its PhD thesis at MIT.
It must be emphasized that all the merit of the diffusion of this invaluable tool must be attributed to Stuart Keeler only. We must objectively recognize that he worked hard during his entire career to perfect and diffuse the use of FLCs.
In Sweden, the Research Organization of the Jerkontoret had been working on the problem of press forming since 1945. They had clearly differentiated, in 1954, the pure stretch forming from the shrink drawing mode. They were strongly interested by the Swift cup test.
In Japan, many studies were driven by Professor Yoshida from RIKEN, who had a large influence by gathering researchers and industrial peoples. They set up a classification of forming operations. A working group was studying the Fukui’s
test at the end of the fifties.
In France, Jovignot had published the definition of his hydraulic bulging test in 1930, Guyot modified and improved the wedge test, etc.
It must be remembered that international communication was, before and just after the war, far from being as easy as today and exchanges were mainly the result of “missions” in which researchers or industrialists met their peers from other countries. There was thus a strong need of cooperation.
3. IDDRG’s birth
Around 1955, the superiority of aluminium killed steels over rimmed steels was fully recognized for the fabrication of deep drawn parts but the reason for this superiority was not understood, as already mentioned. Many considered that studying cups deep drawing was an absolute priority. As a consequence, the cup test was standardized in England in 1956. The name “Swift test” was attributed to it after retirement of Pr Swift, whose modesty was shocked. He did not approve this name.
F. Wistreich from the BISRA (British Iron and Steel Research Association), Pr O. Svahn from Sweden and Dutch researchers simultaneously thought, in 1957, that an international cooperation on this difficult topic would be useful and would help to spread the use of this standard ised test. They met in Amsterdam, 19th & 20th of March 1957, with representatives from Germany, Belgium, France and Chile (Some months before, there had been a conference on steelmaking in South America where the interest of Chile was probably aroused. No Chilean representative ever attended the subsequent IDDRG conferences.). At the end of technical discussions, they decided to found a permanent research group strictly dedicated to deep drawing, to which they already gave the name of “International Deep Drawing Research Group”: IDDRG was born. The two goals were to study the Swift test and explore the interest of the so-called “Limiting Drawing Ratio”.
We have no traces of the following meetings (if any) before 1960. One of the taken decisions was not to accept individuals but only national delegations at the meetings.
It is to fulfil this requirement that in 1959, the “Société Française de Métallurgie” (SFM) decided to create the “Commission Française d’Emboutissage” dedicated to deep drawing. Charles Crussard was named president, Gilles Pomey being secretary.
It was apparently the largest national group concerned by sheet metal forming, so it was decided that it will be in charge of organizing the next meeting of IDDRG as well as its first international conference, open to everybody. Maybe was also playing a role in this choice the fact that it could be organized in Paris. In one issue, “Sheet Metal Industry” sang the praises of “these delightful attributes which have so justly earned for Paris its reputation as the gay city… ”
4. The first international conference
This first conference of IDDRG was held from 23rd to 25th of May 1960 (exactly fifty years and one week from today) in the Conference Room of the Association of Automobile Builders, situated in the Etoile district. It was entitled “Sheet Metal Forming and Methods of Testing”. The fees were of 60 new francs. Like for all international organisms at the same time, official languages were: English, French, Russian a nd Chinese.
The event had a considerable success since there were 212 attendees from 15 nations, clearly confirming the need of an international cooperation.
Thirty papers were presented and discussed (Figure 3).
The introductory lecture was by Dr de Witte, current president, about tests, in which he made a distinction between “specific formability” (related to a given job in the press shop) and “general formability” (judging properties of a metal).
A great concern in the forties and fifties was the origin of ears in cups and its relationship with anisotropy. There was some confusion between what we now call plastic and planar anisotropy. This topic was studied by C. Crussard in the first paper of the conference.
R.L. Witheley then explained his revolutionary views about the influence of plastic anisotropy upon deep drawing of cups.
A classification of the different types of press forming processes was presented by K. Yoshida.
One complete day was dedicated to testing methods: Swift and Erichsen tests were lengthy discussed and a new test proposed by Fukui.
Concluding remarks were done by Pr O. Svahn.
Nothing was said, as you can see, of topics that are now current:
- FLCs, to be put on the front of the scene only in 1965,
- Springback, which mainly became a problem since the introduction of HSLA steels in the seventies,
- High Strength steels,
- Tailored blanks, although they were already used since 1928,
- Influence of sheet roughness,
- Plasticity criteria,
- and of course, Finite Element calculation, due to appear at IDDRG in the 1984 conference in Melbourne…
5. The technical meeting of IDDRG
After the conference itself was a closed meeting of the IDDRG delegates in the laboratories of IRSID, in Saint Germain en Laye (close to Paris). There were 25 attendants from 8 nations: England, Sweden, The Netherlands, Belgium, Germany, Italy, Japan and France (Figure 4).
One of the traditions to be long respected by IDDRG was then established: the president of the receiving delegation was set up as the president of IDDRG until next international conference, normally held two years later. This is how C. Crussard became IDDRG’s president in 1960. Exceptionally, he kept the function until 1964.
John Hooper was elected General Secretary and Gilles Pomey Technical Secretary. They worked together during about twenty years (figure 5).
C. Crussard used his influence to convince the other delegates that the initial goal of IDDRG, the study of cup forming tests only (as indicated by the name), was not large enough and that many other questions justified interest: other tests, materials, processes. This was the origin of the three Working Groups that were maintained until 2000.
We are gathered here, in the twenty first century, to discuss and study the technical aspects of sheet metal forming. Many problems are not solved, many new ideas are proposed, and we can reasonably think that this will still be true in fifty years…
But, is it not fantastic that the “International Deep Drawing Research Group”, founded in 1957, be still active more than fifty years later and organizing a yearly conference? I believe we can be satisfied and proud of it.