Elsevier

CIRP Annals

Volume 59, Issue 1, 2010, Pages 267-270
CIRP Annals

Increased total flexibility by 3D Servo Presses

https://doi.org/10.1016/j.cirp.2010.03.013Get rights and content

Abstract

It is widely accepted that uncertainties influencing product costs and quality can be overcome by an increased manufacturing flexibility. Several approaches for flexible manufacturing machines and processes are known from literature. So far forming machines which enable high process flexibility have not been discussed thoroughly. In this paper, recent developments in the field of servo press technology are described and discussed under this aspect. Special attention is paid to the recent development of a 3D Servo Press concept which opens new horizons for flexible forming machines.

Introduction

Planning and selection of manufacturing systems are accompanied by uncertainties. This is caused by the limited validity of assumptions concerning future events which are made during the development and selection of manufacturing technologies and equipment. Uncertainties can occur either if the relevance of a future event for the manufacturing system under consideration is unknown or the occurrence of a relevant future event is probabilistic.

According to Gerwin [1], manufacturers have to deal with four main uncertainties: market acceptance of kinds of products, length of product life cycles, specific product characteristics and aggregate product demand.

One approach to encounter unavoidable uncertainties in the field of manufacturing is an increased flexibility of the applied systems and processes. Flexibility is classified, according to Slack [2], into two aspects: time and range. One solution to handle the uncertainties is called “bank” flexibility, i.e., a financial cushion is built to handle future needs. This investment opens up the possibility for several options, for example a dramatic change in market conditions can be intercepted rapidly. The second solution to deal with uncertainties is to work with flexible manufacturing systems. One manufacturing system is more flexible than another, if it can handle a wider range of possibilities [1]. Wiendahl and Heger [3] show the differentiation of production systems among each other according to their flexibility.

According to Son and Park [4], total flexibility consists of four different kinds of flexibility:

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    Equipment flexibility

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    Product flexibility

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    Process flexibility

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    Demand flexibility.

Equipment flexibility is the capability of a system to integrate new products and variants of existing products. Product flexibility is determined as the adaptability of a production system to variances in the product mix. Process flexibility is defined as the adaptability of the system to changes in part processing, for example caused by changes of technology. Last, demand flexibility, describes the ability of a manufacturing system to respond to changes in market demand. Flexible manufacturing systems anticipate variations and built-in flexibility a priori [5].

Different concepts for flexible assembly and cutting machines have been investigated intensively in the past. Uncertainties can also heavily affect the future value of a selected forming machine. But so far, forming machines are either designed for large batch productions with fixed selected forming methods or for small batch productions with predetermined specialised tool movements. Consequently, their flexibility in terms of adaptation to changing market conditions is very limited [6]. The development of servo technologies for forming presses creates new possibilities for flexible forming machines [7]. This paper shows basic design principles for forming presses capable of fulfilling requirements resulting from large batch and specialised small batch forming processes simultaneously.

Section snippets

Measure of flexibility

Forming processes and associated machines vary in their number and types of driven degrees of freedom (DoF) necessary for the relative movement of tool and workpiece. Equipment, product and process flexibility can be increased by additional driven DoFs. Therefore the various processes and machines are analysed in Fig. 1 regarding the number of driven DoFs. On the other hand, demand flexibility is becoming poorer if the number of driven DoFs is increased. Especially high volume production is

Transformation of degrees of freedom

Conventional presses drive a translational relative movement of tool and workpiece. The analysis of forming processes shows that flexible forming machines should enable driven tool movements with several DoFs. Nevertheless, in order to reach a high productivity the drive system of a press should also be usable for simple linear motions without any reduction of production rate compared to conventional presses. Investments could be kept low, if all implemented drive systems are used for all kinds

3D Servo Press

Servo presses are presses, in which servo drives control the motion of the ram. Servo motors are electrical actuators that operate with servo controllers in closed loops. The actuation can be torque-, velocity- or position controlled [10], [11]. These presses allow flexible punch motions and a high accuracy.

The afore mentioned considerations have been transferred to a new type of servo press, called 3D Servo Press, which provides a flexible ram motion with various numbers of DoFs. A sketch of

Application

To show the flexibility of the press system, a combined flexible blanking and rolling process for internal geared wheels is examined. The used tool, as shown in Fig. 4, is subdivided into three sections. During the different manufacturing processes, each of the tool sections are in use subsequently. The orbital motion of the ram, a rotation around the x- and y-axes like shown in Fig. 2 on the right side, is transferred by a gear into a translation in the xy-plane. The ram motion in z-direction

Summary

In this paper flexibility requirements for forming machines in the manufacturing sector are described. Flexibility is especially needed to handle different uncertainties in manufacturing. A classification of flexibility in forming systems is presented. Based on the definitions of flexibility, a scheme is developed which shows that the more degrees of freedom a system offers, the more flexible it is. Servo presses already provide a high flexibility in one degree of freedom. Therefore they build

Acknowledgements

The investigations presented in this paper were carried out within the research project B2: “Forming–Production Families with Uniform Quality” of the Collaborative Research Centre 805 “Control of Uncertainties in Load-Bearing Mechanical Engineering Structures” (CRC 805). The authors wish to thank the German Research Foundation (DFG) for founding and supporting the CRC 805.

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