Dieless forming of sheet metals

ISF forms sheet metal into complicated shapes without the use of conventional punch and die
Local micro-deformations incrementally occur on the blank through a rotating and translating single point tool

Deformation of the sheet is achieved with or without a supporting, fixed tool about which the single point forming tool moves (see Figure 1)

Being investigated by researchers in the UK [1, 2], Japan [3], China [4, 5, 6], South Korea [7, 8], Italy [9, 10] and Germany [11]

Mechanics of ISF

The mechanics of ISF is similar to that of conventional spinning, shear forming and flow forming in that the deformation mechanism is localized to a small region under the forming tool

Deformation occurring in forming products is due to local stretching and bending occurs at clamping position

Strain conditions ranges from pure uni-axial stretching to bi-axial stretching and dominant mode of failure is due to excessive thinning of the sheet in areas overstretched

Researchers such as Kim, Yoon, and Yang [7, 8], Filice et al [9], Fratini et al [10] and Hirt et al [11] have made contributions to the understanding of the mechanics of incremental sheet forming and overcoming existing limitations

Equipment and software for ISF

The equipment required for ISF can be standard CNC milling machines, though specialized machines have also been developed [12]

Minimal toolings are required to offer non-specialised support and clamping to the sheet metal during the forming process. A simple cylindrical forming tool is also required. (eg is shown in Figure 2)

Standard CAM systems for generating toolpath for machining are employed and the toolpath strategy is the contour parallel type

Accuracy of incremental ISF

The accuracy is affected by spring back, the shape of the formed part, the shape and size of the tool, the forming toolpath, material and thickness of the blank

Accuracies of between 1.5mm and 2 mm have been achieved [13]

Researchers are investigating ways of improving the accuracy

A methodology proposed [15] modifies the ideal path of the forming tool using the ideal and actual positions of points formed in an earlier increment obtained by using a 3D digitizing system, allowing the error to be reduced by approximately 70%

Another method [11] inverts deviation from measurement made in a first component and applies it to the required shape to obtain a modified shape which gives an improvement in the accuracy

Economics of ISF

Though the process can form almost as intricate shapes, compared to the conventional sheet metal forming process, the tooling costs can be as low as 5-10%

Shorter lead-time for prototyping obtains

Forming forces are considerably lower

A standard CNC machine which is quieter, occupies less floor space and cheaper than conventional forming presses can be employed

Research issues in ISF

Systematic investigation of the mechanics of incremental sheet metal forming considering the process variables such as shape, tool shape and size, blank material and toolpath strategy/parameters is required

A validated finite element analysis of the process

Issues involved in designing products for incremental sheet metal forming

Software dedicated to incremental sheet metal forming needs to be developed

Use of 4 and 5 axes CNC machines need to be investigated

Forming Of Sheetmetal using Reconfigurable Tool

Conventional sheetmetal forming use of tools which have to be fabricated each time a new shape is required results in long lead time, high tooling cost and waste of material.

The replacement of such conventional tools with ones that can be reconfigured each time a new product is required offers considerable advantage

There are ongoing contributions to the understanding of this technology

Mechanics & Equipment for sheetmetal forming using reconfigurable tooling

The mechanism of forming is similar to that of conventional dies since the ends of discrete elements are usually smoothened

Conventional sheet metal press is used and main difference is in toolings

As for conventional sheet metal forming, only one tool is required for operations such as stretch forming. The use of reconfigurable punch and die have also been investigated by researchers [16, 17] as illustrated in figure 3

There is a similarity in the technology of reconfigurable tool proposed by various researchers. Differences arise in the method of positioning and clamping the discrete elements and the method of smoothening the discontinuous surface of the tool

Contributions have been made by Nakajima [18] Pinson [19], Walczyk and Hardt [16], Papazian [20] (figure 4) and owodunni et al [17]

CAD/CAM system for sheetmetal forming using reconfigurable tooling

To reconfigure the tool, software to determine the position of the discrete elements and the control instruction for the actuator device or CNC machine used for positioning the discrete element is required (Fig. 5)

The positions of the discrete elements are determined by intersecting the surface model of the die/punch with a line which represents the centre line of the discrete element

The positions of the tip of the discrete elements are used as an input to the program which generates the instructions for the actuator device or CNC machine

It is possible to generate efficient toolpath by minimizing idle time of the positioning tool [17]

Accuracy & Economics of sheetmetal forming using reconfigurable tooling

The accuracy of the sheetmetal formed depends the accuracy with which the discrete elements are positioned, the smoothening of surface of the discrete elements and springback (Fig. 6)

It is possible to compensate for spring back and other size variations using techniques such as experimental determination of the deformation transfer function and FEA method [20]

Papazian et al [20] reports that a reduction to 1/8th and 1/3rd of the current tool fabrication cycle time and labour hour respectively is obtained

Owodunni et al [17], showed that it is possible to achieve great savings in the capital investment to the extent that the cost of a reconfigurable tool can be comparable to that of a conventional die

Research issues in sheetmetal forming using reconfigurable tooling

More investigations are needed to achieve low-cost positioning mechanism that are faster and for large scale tools

The limit on the size of small features that can be captured need to be considered

Efficient CAM system that will give more consideration to optimal planning is an important research issue

Experimental and numerical analysis of the mechanics of sheet metal forming using discrete elements also need to be investigated

Conclusions

Contributions in the research which have great potential for rapid manufacturing of sheetmetal parts have been reviewed

Reduction in cycle time and labour is possible for the reviewed technology

The possibility of having a capital cost for the technology comparable to conventional tooling has been demonstrated for prototypes.

Several research issues that will address the mechanics, the equipment, software, accuracy and economics of rapid sheetmetal forming were identified and discussed

Acknowledgement

The University of Manchester is a partner of the EU-funded FP6 Innovative Production Machines and Systems (I*PROMS) Network of Excellence