Advanced design of high pressure die casting moulds.

Baltes, Liana ; Tierean, Mircea ; Eftimie, Lucian 等

1. INTRODUCTION

The fast going changes in the economy of the last years has determined several strategic changes in the industrial manufacturing. Aspects as:

* decreasing the designing time of the products due to the development without precedent of software and computers; in automotive industry for example, which is one of main factors in the development of casting industry, the design time for a new car decreased to six months;

* the decreasing of replacement period of parts with a new one due to the same development of IT industry and market demands;

* the increasing pressure on manufacturing price, effect due greatly to the globalization of world economy;

* the demands to obtained the final parts without other further machining, which means time and money;

* the necessity to modulate the tools due to the decreasing of manufacturing cycle, the design and processing costs; asses the necessity to rethink the strategies in high pressure die casting execution (Bralla, 1999).

2. ACTIVE PARTS DESIGN

The classical design system is based, for the most parts, on massive constructions, strategy due in the main part to the large-scale series production with quite rarely changes of manufacturing type, in which the massively mould (single casting construction) was the guarantee of a high number of casting pieces (Madan et al., 2007).

[FIGURE 1 OMITTED]

The reduction of the manufacturing exchanging rate, the decreasing of mould casting number of pieces until the product replacement in addition with the new equipments and manufacturing techniques, warrants the new directions in designing.

It is possible to see in figure 1 the simply positioning system of the sliders (1) in relation to the mould body (2) inclusive one face to other, that allow their changing with other sliders, having only the overall size and sealing system identically, but other active parts, so pieces with different profile.

Assembling, disassembling, maintenance and correction working are very simple through the replacement or maintenance of part symbols 3 and 4.

As well it is possible to remark in figure 2 how the active part was divided in critical surfaces end/or interchangeable.

Thus, central part (2) for reason of ventilation, to prevent the complete filling of the shape, has a simple positioning due only to the constructive shape which prevent the wrong positioning (rotation, translation without iteration) not only plane but also in elevation. The same principles are applied to the fixed part of the mould, figure 3.

Positions 3, 4, 5 and 6 (fig. 2) are interchangeable inserts which assure good ventilation, easier manufacturing as component parts, facile displacement without high qualified personnel, directly in the casting house. Their replacement could allow the execution of other profiles of cast moulding.

The total costs of a mould obtained through this designed system, for a family composed by different three-pieces, are appreciatively with 45% lower than the execution of tree different moulds. The maintenance costs decrease with 20-25%. Statistically, the down-time, the maintenance work, and reconditioning of the mould due to the accidental lock-out, decrease with 20-30% depending on the mould complexity, dimensions, cavity number, etc (Driscoll, 2002).

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

High reliability and the decreasing of the maintenance time are assured by sliding guides with high hardness, rigorous unstrained as position, only as thickness, in order to assure the free distance gliding of sliders. It is also considered the specific heat expansion which appears for different type of materials, dimensions and shapes. These, together with gliding slides for sliders displacement in the work direction, are spare parts easier to dismantling, to replace and to repair.

In this way it is possible to realise gliding systems for sliders, considering only the keeping of geometry in the guiding area, inclusive the strict bordering in tolerance zone provided for all interchangeable sliders.

The interchangeable inserts which can be delivered in assemblage sets, allow the different shapes parts execution. Thus from design we realised different mould shapes within the same project through the activation/visualisation of a certain configuration of the project (Zhao et al., 2005).

These insertion pieces can be assemble either through the positioning of pins and screws compression, or through the direct positioning on "key" type profiles, which lock up at assemblage the wrong assembling or the assembling of other interchangeable component instead of the correct one.

Such a mould exceed the tools cost and the time for completion in comparison with a simple mould for one part realising. The design time and costs increase but, in opposition, the overall cost with the casting tools decreases dramatically, due to incorporation of several moulds in one.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

3. ADVANTAGES OF THE NEW DESIGN

The advantage of this design and manufacture type consist in a better controlling of the uncertain collisions and interferences on each mould shape, the whole project having different profiles attached to each casting part.

Other real advantage of this type of design consist in fact that designer being forced to use insertion pieces due to the multiple shapes of the pieces rank from the demand pieces family, the active tools instead of the manufacturing from the massively ingot are realised from insertion pieces, configuring in this way the piece geometry. This fact increase the lifetime of the mould and the down-time of the tools, witch is very costly. At each accidentally damage or due to the wear, the mould is get out from the pressing machine table and with nonqualified personnel the defective parts are replaced with new ones.

As it is observed in figure 4, the different shapes of the mould are grouped almost in totality in the centre of the mould, in the active part.

4. CONCLUSION

Last years changes concerning the demand of casting aluminum alloys parts forced major changes in design and manufacturing strategies of this type of moulds. The present paper joins the new trend of the market.

5. ACKNOWLEDGMENTS

The authors thank to Aeromold Ltd. Brasov, Romania for credit and support in the design and experimental research.

6. REFERENCES

Bralla, J.G. (1999) Design for Manufacturability Handbook, McGraw Hill, New York

Driscoll, M. O. (2002) Design for manufacture, Journal of Materials Processing Technology, 22, pag. 318-321

Madan, J.; Rao, P. V. M. & Kundra, T. K. (2007) Computer Aided Manufacturability Analysis of Die-cast Parts, Computer-Aided Design & Applications, Vol. 4, No. 1-4, pag. 147-158

Zhao, Z. & Shah, J. J. (2005) Domain independent shell for DfM and its application to sheet metal forming and injection molding, Computer-Aided Design, 37, pag. 881-898

SolidWorks Co. (2007) Solid Works documentation