Modern machining of die and mold tools

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Abstract

Modern production of die and mold tools is quite different in comparison with conventional machining. The basic theory of cutting process and cutting geometry is similar, but the techniques and technology is quite different. High-speed cutting (HSC) principles are not applicable with conventional machine-tools. Difference between conventional and high-speed cutting velocity is analysed on chip formation. The comparison between EDM and HSM has been made and shows great HSC benefits. Usage of modern software (CAM) optimises tool production and helps us to save unnecessary additional machining time and costs.

Introduction

High-speed machining (thereinafter HSM) is a relatively new production technology that allows a higher productivity, an excellent surface finish and a good dimensional accuracy in the manufacturing process. Slovenian die tools production mainly contains: plastic molds, die casting molds, vacuum molds and forging dies. High-speed milling is one of the most important of all high-speed cutting (HSC) methods [1], [2], [3]. Thanks to the advances in machine-tool performance as a result of improvements to the main spindle, feed drives, etc., high-speed milling has become a cost-effective manufacturing process that produces products with a high surface quality, low variations in the machined surface and dimensional accuracy. High-speed milling was first used successfully in the aircraft and automotive industries for machining complex machine parts made of aluminium and its alloys. Recently, with the advances in cutting-tool materials and technologies, high-speed milling has also been used in the machining of alloy steels in their hardened state (above 30 HRC up to 60–65 HRC) [4], [5].

Customer expectations are striving to: high-quality products, short machining times and low machining costs. European machine-tool market is getting stronger and stronger in favor of HSC machine-tools in comparison with EDM machines.

Section snippets

HSM in tool-making industry

High-speed machining assures two times more efficient productivity, which is achieved at first with the cutting speed and secondly with feed-rate. Conventional feed-rate is increased with software solutions and modern machine-tool design up to 1600 mm/min.

Fig. 1 shows water bottle mold machined with HSC by using modern CAM programs. By deep cavity the machined surface quality is very uncertain, especially the second part where polishing is used as a finish operation.

More exacting machining of 3D

Finish machining of heat-treated tool steels

Modern cutting materials, tools shaped as a ‘pencil-tools’, enable small metal removal rate but also much faster machining. It is very important to use right technological parameters for successful machining (Fig. 3).

Fundamental parameter of heat-treated tool steels high-speed finish machining is small cutting depth.

The cutting depth should not exceed 0.2/0.2 mm (ap/ae) value. In this way we prevent tool deflexion/deviation and preserve high level of accuracy (tolerance and geometry).

Cutting

Some theoretical backgrounds

There are several criteria used for defining high-speed machining, i.e. the criteria for determining the boundary between conventional and high-speed machining.

These include [7], the magnitude of the cutting speed, the revolutions of the spindle or the rotating tool (the spindle speed), the DN number (DN is the spindle diameter in mm multiplied by the spindle speed in rev/min), the dynamic behaviour, and the workpiece material. The most appropriate definition of high-speed machining is based on

CAM concept by manufacturing approach

Successful HSM is always related with appropriate CAM software. We should use the same CAD–CAM system for development (modeling of a product), design (tool design) and process planning (using CAM program). In this way data transference is not complicated since their formats are not different. It is important that CAM module includes milling simulation, which enables virtual check before actual machining. Simulation usually shows metal removing dynamics and tool path. A CAM role in manufacturing

CAD–CAM system

Today's PC-based CAD–CAM software grows more sophisticated. The prospective CAD–CAM users are presented with dozens of options through trade shows. It becomes difficult for a shop to decide exactly what they need. Due to a rapid development of information technologies, CAD–CAM packages can perform NC programming tasks that would have been impossible a few years ago without an expensive workstation-based system. In general, mould shops should not purchase a system for their far future plans,

G-optim software for optimization of machining process

In order to improve a machining process at low performance machine tools, we developed an optimization software G-optim. It eliminates the bottleneck of insufficient Look-ahead function, problem of long cycle time of CNC controller and the problem of weak data connection between computer and machine tool. The program works as off-line optimizing software which adjusts the feed rate function to pre-generated standard G-code—Fig. 15.

Conclusions

Entrance to the European/Western market of technology and manufacturing requires introductions into modern methods of cutting technologies.

HSM assures competitive position in the field of mass production in automotive manufacturing. Mass production in quality tool-making, which demands short time for (die/mold/forging) tool preparation, represents key element of profit.

Furthermore we can list the following HSC benefits:

  • shortening of the whole machining process,

  • surface quality improvements–less

Acknowledgements

I would like to thanks to the Authorities of the Materials Science Committee of the Polish Academy of Science and Chapter of the AMME 2002 conference, accepted me for Honorary Award in the name of Fryderyk Staub “Golden Owl” and specially to Prof. Leszek A. Dobrzański.

References (7)

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