Of maximum security and predictability!

By Niraj M Wanikar, Chief Editor, CNCTimes.com, 2014-02-20 07:22:08

By Patrick De Vos

The target for every machining process should be maximum security and predictability while maintaining high productivity and low production costs. To achieve this, several elements need to be considered – the material, geometry and dimensions of the work piece, the machine tool, CAM systems, clamping of the work piece and tools, the cutting tools and how they are to be used.

The variables that can lead to problems when machining are:

• Chip forming and evacuation: This needs to be fully under control. If not, long chips can cause production stoppages and damage to work pieces, machine tools and cutting tools – as well as op- erators. Cutting forces acting on the tool need to be completely understood. If control is lost, there is a risk of broken tools, broken cutting edges and vibrations during the operation. All of these will cause production stoppages and wrongly finished work pieces.
• Tool wear: This needs to be continuous i.e. flank wear or crater wear. Tool wear that occurs suddenly (breaking or chipping) needs to be avoided.
•  Heat: Machining metal generates a lot of heat. If not evacuated by the chips, this heat will concentrate in the cutting tool or in the work piece surface, jeopardising the quality of the finished work piece. The high temperature in the cutting tool will cause changes in the cutting properties of the cutting material with loss of tool life as a logical consequence.

All of these factors can make it difficult to finish work pieces with the correct quality in terms of dimensions, shape, surface roughness and surface structure etc. To avoid these problems, the cutting process and the interaction between the different elements need to be carefully considered. A key element is the cutting method. We can choose between traditional machining, high speed machining, high feed machining or high volume machining. Each offers advantages as well as constraints. This means that not every method – in a given situation – offers the same operating security.

A well selected cutting edge – in terms of cutting material and geometry – in relation to the selected cutting method is of the highest importance in making the cutting process reliable. The cutting material needs to be adapted to the work piece material with cutting speed as the linking element. The cutting edge geometry has to be well selected to serve the purpose of the operation e.g. roughing or finishing. The linking elements here are the feed(s) and the depth(s) of cut.

Then there is the correct selection of the cutting data combination to consider high cutting speeds combined with low feed or high feeds with moderate cutting speeds. Each cutting condition needs to be selected correctly. Cutting speed needs to be high enough to avoid built-up edge wear. But, the cutting speed should not be so high that the wear process is mainly governed by thermo-chemical wear patterns. The depth of cut and feed have to be selected so that chip formation and mechanical impacts on the cutting edge (cutting forces) are under control.

When security is important during the metal cutting process (while maintaining the highest possible productivity), the preference should be for high depths of cut and feeds coupled with moderate cutting speeds (economical cutting). Cutting speeds can be further increased if circumstances allow and if productivity weighs more than production costs in the total picture. But higher cutting speeds will also involve more “risk for the un foreseen” during the process.

TOOLING EXAMPLES

Seco has a long history of looking for more reliable solutions for metal cutting processes that keep productivity high and costs. One example of increasing security during the process, especially in risky machining scenarios, is Seco's Jetstream Tooling (a high pressure directed coolant concept and system). This concept has demonstrated major advantages, such as increased tool life, better chip control, higher productivity, lower costs, lower residual stresses in the work piece surface, better machining tolerances and improved surface finish to name just a few.

Another example is turning, using Seco Tools wiper geometries on the cutting point (high feed turning concept). This allows significantly higher feeds to be used, making it easier to achieve good surface finish faster (productivity), over a longer period of time (more work pieces) and last but not least in a very controllable way (security).

And there is of course high feed milling based on the classic compensation principles in milling. In this approach, the basic concept of high feeds to look for problem-free metal cutting is truly outstanding.

SUMMARY

An economical metal cutting process demands maximum security and predictability, while maintaining the highest productivity and lowest production costs. Different approaches to reach this objective are possible. For general engineering scenarios, the “increase your feeds” concept offers the best possible results in the majority of situations.

Seco has a long history of providing effective tooling innovations (Seco Wiper geometries, Seco HFM tools, Seco Jet- stream Tooling). When correctly applied, predictability in metal cutting processes can be lifted to a considerably higher level.

Patrick De Vos is Seco’s Chief Technical Education Manager. Born in Belgium in 1959, he has a Masters degree in Mechanical and Electrical Engineering (specialised in Production Technology). From 1981 to 1983, he was post graduate lecturer and researcher (research subject optimizing strategies for metal cutting processes and production economics) at the university. From 1983 till 2006, he was employed by Seco Tools Benelux in several technical, commercial, marketing and management positions and was member of several international council groups in the company. Since 2006, he is Corporate Technical Education Manager for Seco Tools AB. In the last 30 years, he has trained more than 50,000 people in more than 55 countries worldwide. He has also authored a book, “Metal Cutting, theories in practice”. He can be reached on patrick.de.vos@secotools.com

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