Applying TRIZ for systematic manufacturing process innovatio(2)

In Fig. 4 the equivalent FR-DP mapping is depicted for the TPIF process variant. The relations between both spaces illustrate that the independence axiom [7] is not fulfilled by the TPIF design parameter choice. Included in this figure are also the additional relations with the functional requirements when a heating system for the complete workpiece would be added to the process setup. It is clear that the degree of coupling is further increased.

The compliance check with the independence requirement as formulated in the Axiomatic Design theory thus indicates that, even if one would be willing to reduce the flexibility of the incremental forming process by reintroducing a partial or full die as a counter pressure system, this does not result in a favourable process design. An alternative enhancement of the process setup is thus required.

Joost R. Du ou and Joris D’hondt / Procedia Engineering 9 (2011) 528–537531

Functional Requirements Design Parameters

3.2. Su-Field analysis

A Su-Field analysis provides deeper insight in the system conflicts to be resolved. A summary of such an analysis is provided in Fig. 5.

Figure 5: Substance-Field analysis overview for the subsystems in a basic SPIF setup.

Conflicting relations can be detected in the interaction between the workpiece and the tool. While a local, controlled plastic forming effect in the tool contact zone is the target of the process, unwanted deformations are often simultaneously introduced in workpiece areas not in contact with the tool. These deformations are the result of excessive stress levels linked to process force transmittance to the clamping system (or backing plate support system).

4. Physical conflict resolving

532 Joost R. Du ou and Joris D’hondt / Procedia Engineering 9 (2011) 528–537

The problem to be solved can thus be formulated as follows: “Identify a system enhancement that allows to

locally form the workpiece sheet material without introducing unwanted plastic deformations in the area not in contact with the tool”.

In order to achieve this without the reintroduction of a die set (TPIF), the following strategies could be applied:

1. Lower the yield strength of the workpiece material in the processed area (in order to lower the process

force level).

2. Limit the hardening behaviour of the workpiece material in the processed area (for the same reason). 3. Increase the yield strength of the workpiece material in the non-processed area (in order to avoid plastic

deformation)

4. Maximise the hardening behaviour of the material in this non-processed area (for the same reason).

It is obvious that strategies 1 and 2 are not compatible with measures 3 and 4, leading to the identification of a clear physical conflict: how can the material be chosen to be ductile on the one hand and stiff and hard to deform on the other hand?

Calling upon the often used technique of preheating the material in order to improve the formability and to lower the process forces (see Figure 6) does not provide a solution here. Indeed, while this would form an implementation method for strategies 1 and 2, it would simultaneously result in a weakening of the material in the zones where unwanted plastic deformation is to be avoided (in conflict with strategies 3 and 4).

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Figure 6: Influence of temperature on constitutive law for DIN65Cr2 and Al 5182

TRIZ provides an answer through the principles of separation:

1. Separation in space 2. Separation in time

3. Separation between the whole system and its parts 4. Separation based on different (external) conditions

Combining the contradicting requirements of the four strategies can indeed not be achieved for the complete workpiece simultaneously. However, through the principles of separation in space and time, it can be envisaged to differentiate the material properties between the different zones of the workpiece. Since the contact zone is constantly changing, this localisation has to be applied dynamically. Applying heating of the sheet material in a localised (principle 1) and dynamic (principle 2) fashion was therefor considered as a promising process enhancement strategy. This would require local heat supply during the process, rather than a uniform preheating of the sheet metal blank. Furthermore, in order to assure a local heated spot in the processing zone only, active cooling of the surrounding area is also required, resulting in a clear temperature gradient between the tool contact zone and the workpiece area where uncontrolled deformation is not desirable.

Joost R. Du ou and Joris D’hondt / Procedia Engineering 9 (2011) 528–537533

Figure 7: Mapping of functional requirements and design parameters for the modified SPIF process, with indication of the effects of the

added design parameters associated with local dynamic heating and active cooling (dashed arrows).

By localising the heat input according to separation principles 1 and 2, automatically distinction is made between the whole workpiece (which is kept at near ambient temperature), and the tool contact zone (where the temperature can be significantly increased depending on the applied material and required differentiation), as suggested by separation principle 3. Furthermore, the heat supply can be decided upon taking the workpiece geometry into account. For example, in the vicinity of strong slope changes, maximal use can be made of the heating effect and the resulting temperature gradient, while in areas where a flat bottom surface needs to be formed, the heating could be switched off all together (separation principle 4). The effects of introducing localised, dynami …… 此处隐藏：5891字，全部文档内容请下载后查看。喜欢就下载吧 ……