Impress Project summary
IMPRESS - Improvement of Precision in Forming by Simultaneous Modelling of Deflections in Workpiece-Die-Press System.
Research Project developed in collaboration with UNIVERSITA' DEGLI STUDI DI PADOVA - DIMEG - Dipartimento di Innovazione Meccanica e Gestionale.

Project director: Prof. Paolo Bariani

PROBLEM DESCRIPTION

The achievement of narrow tolerances and a long service life of tooling systems are among the main aims in the forging industry. In particular, deviations from symmetric conditions generate eccentric loads on the press resulting deformation of the machine and consequently loss of tolerances and accuracy. The press frame deflections are the result of the combined stiffness of the press-die-workpiece system, which is changing during the process because of the changing geometry of the workpiece. A system able to predict the optimal tool shape, the position of the tool and the angles of the main planes in the tool cavity in relation to the press, the workpiece material and the required tolerances must therefore be available.


Deflection caused by complex geometries

In this contest IMPRESS project was born aimed at improving quality of products, reducing production costs, mainly in the forging sector, and overcoming the difficulties to predict the effect of a technological change on the overall interplay during forming operations. Several partners are involved in the project as it can be seen in the following table.

Partner	Nation
Association pour la recherché et le Developpement des Methods et Processus Industriels	F
Dipartimento di Innovazione Meccanica e Gestionale – Università di Padova	I
Centre for Computational Continuum Mechanics d.o.o	SI
Instytut Podstawowych Problemòw Techniki	PL
Smetek ApS	DK
Istituttet for Produktudvikling	DK
Buurskov & Lassen Maskinfabrik I/S	DK
Vaccari S.P.A.	I
Iskra Avtoelektrika d.d.	SI
Transvalor	F

SCIENTIFIC AND TECHNICAL APPROACH

The approach proposed is to develop a model of deflections in forming systems by studying the following aspects:

measurement and characterisation of press stiffness under complex loading conditions: an advanced press-stiffness system is developed where a cardanic calotte is combined with a separate loading unit for horizontal loads. This allows measurements of press-stiffness in 12 possible testing constellation and its characterisation under complex loading conditions encountered in industrial production.
computation of deflections that simultaneously interact in a combined workpiece-die-press system and optimisation of precision of components and service life of tooling systems by taking into account press stiffness. The influence of press stiffness on precision of parts and scatter of product dimensions is considered in contrast with fatigue damage and wear of tools. Research efforts are dedicated to introduce software architecture in such a way that parallel solution of coupled workpiece-die-press problems is possible.

INDUSTRIAL TASK

Vaccari task during the project is mainly concerning press qualification, providing presses for stiffness measurements and expert knowledge in designing. In order to characterize press stiffness it is necessary to generate and measure loads and simultaneously deflections of the frame and for this purpose an experimental equipment has been designed. Two loading devices , respectively for horizontal and vertical loads, have been designed by DIMEG (University of Padova) in collaboration with Vaccari in order to apply and measure eccentric loads on a screw press. The load cells are equipped with a piezoelectric sensor, which permits the measurement of force. Furthermore, a non-contact measuring system has been developed to measure the elastic press deflections.


(a)	(b)
(a) The developed loading devices and the deflection measurement system (b)

MAIN RESULTS

This equipment has been used to evaluate the stiffness of a Vaccari 2300kN screw press. The proportional stiffness matrix and the graphical stiffness matrix have been determined for the screw press. Experimental validation trial with the forging of a hammerhead primitive have been carried out measuring deflections of the press and the results have been compared with the deflections predicted using the stiffness matrix. Furthermore two industrial components, a T-joint and a turbine blade, have been forged on the screw press monitoring loads and deflections and results have been compared with the numerical ones obtained using the stiffness matrix.



The T-joint industrial case


The turbine blade industrial case - displacements


The turbine blade industrial case - loads