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Hard Turning

Project Title

Investigations into machining of Ceramics using ultra precision hard turning machine.

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Overview

Introduction to hard turning process Characteristics Requirements Hard Turning v/s Grinding Advantages & Limitations Case Study Conclusion

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Definition

Hard turning is defined as the process of single point cutting of part pieces that have hardness values over 45 Rc.

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Introduction

Producers of machined components and manufactured goods are continually challenged to reduce cost, improve quality and minimize setup times in order to remain competitive.

Frequently the answer is found with new technology solutions.

Such is the case with grinding where the traditional operations involve expensive machinery and generally have long manufacturing cycles, costly support equipment, and lengthy setup times.

The newer solution is a hard turning process, which is best performed with appropriately configured turning centers or lathes.

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Introduction Turning of hardened metals (hard turning), has been

popular in recent years as an economic way of generating a high quality finish.

Hard turning can machine complex workpieces in one step.

Hard turning produces finishes approaching grinding quality.

It is less time consuming, more flexible, and economical.

Although grinding is the typical finishing process employed in industry, in many cases hard turning is a better option for internal and external finishing.

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Machine Rigidity To deliver the cutting performance required (accuracy, finish,

extended tool life etc) turning centers need to be of a rigid construction and good design.

A polymer composite base combined with wide-spaced, heavy-duty linear guides; super-finished tracks and centrally-located, short-pitch ball screws help reduce vibration and minimize stick/slip movement.

- Slides mounted on preloaded roll bearings guide ways - Rigid tool holders system - Specific chucking device designed to minimize the

deformation on the part

Part Rigidity

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There is little point attempting to hard turn a part that does not have sufficient inherent rigidity to withstand the cutting forces generated by the process.

To understand whether parts are literally up to the job – it is recommended that we must consider the length (L): diameter (D) ratio of the part.

As a rule of thumb a L:D ratio of 4:1 for unsupported components and 8:1 for supported ones - produce optimum results.

If the ratio is exceeded (for longer parts supported with a tailstock), it is likely that chatter will result.

Kind of tools required High quality hard turning applications do require a

properly configured machine tool and the appropriate tooling.

For many applications, CBN tooling will be the most dominant choice.

CBN tools are widely used for both continuous and interrupted hard turning applications as they deliver exceptional cutting performance with low wear.

However, because of CBN's high cost - alternative cutting tools or inserts can be used - i e, Cermet and Ceramic.

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11Graphical Rep.

Coolant • Coolant—The biggest question with respect to coolant is whether or

not to use it. For parts, such as gears, that have interrupted cuts, it is best to run dry. That is because the thermal shock the insert would experience exiting

and entering cuts would likely cause breakage. Cutting without coolant provides obvious cost benefits as well. Coolant can be helpful for continuous cutting applications in terms of

providing longer tool life and better surface finishes. The key is to get the coolant to the tool tip.

High-pressure coolant is the best bet for reaching the tool tip, and it is not likely to vaporize because of the high temperatures

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V/SHard

Turning Grinding

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Can start with solid blank operations and produces a finished component in one machine.In hard turning you can start with pre hardened material and machine it. You can skip several steps and actually cut days of process.

Choosing between these two process is purely application driven.

Grinding is better suited is it against thin walled or delicate from crushing perspective.

Hard turning is very well suited when you have complex figures. Complex contours, difficult radii, angles and diameters all in one part. Hard turning can do it with one setting

Grind = Lot of fine particles= special filtration unit= clean regularly.

Hard Turning = producing steel chips= much easier to dispose or recycle

It is becoming more popular than grinding as it usually less expensive, faster, machines cost less and operator learning curve is less. Operator has to learn one machine and that machine does it all.

Speed – 91 – 150 m/min.Feed- 0.13 mm/min.Depth- 0.08 mm– 0.5mm.Surface finish- 0.003mm.Roundness value -0.00025mm.Size control – 0.005mm.

To the naked eye, ground surfaces appear to be smooth and free from defects. The photomicrographs to the left show the surface of ground tungsten carbide compared to Hard Turning on right show.

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Hard Turning Limitations

Tooling White layer formation Machine process capability

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Tooling

When considering the tooling material, it's important to understand the application and critical attributes such as size and finish requirements.

The typical brazed tip CBN insert has a cost structure 3-4 times that of carbide.

Ceramic, on the other hand, has a cost structure more similar to carbide but would not be used for applications which had a tolerance range smaller then , Parts requiring a greater accuracy would logically use CBN.

Ceramic does not perform well in the presence of high thermal shocks, so it is not generally a good candidate for coolant cutting.

Tool rigidity, tool placement, cutting tool geometry….

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White layer formation

The infamous "white layer" can rear its ugly head in both hard turning and grinding operations

Hard turned surfaces frequently experience "white layer" formation, which appears as a white layer at the surface of the material under metallographic examination.

This layer depth can vary greatly but for general discussions it is in the area of 1 micro-meter thick.

The white layer cannot be seen visually but requires a metallographic examination to detect its presence

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white layer can be caused by either 1) severe plastic deformation that causes rapid

grain refinement or 2) phase transformations as a result of rapid

heating and quenching. White layer formation is not limited to hard

turning operations but is also routinely found in grinding applications.

White layer is not desirable in products which have high contact stresses and where fatigue failures can occur.

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Machine process capability

Rigidity is critical for successful hard turning: the rigidity of tooling, workholding, and the machine tool itself are all crucial elements that will affect your ability to successfully hard turn.

Hard turning is a technology-driven process, dependent upon:

Machine technology Process technology Materials and tooling technology Work holding technology

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Applications..

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Case Study

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Case Study About??

How did Hard Turning provide the winning methodology for meeting critical deadlines in Turner Powertrains Systems (TPS) Engine Development Program.

Located at Wolverhampton, United Kingdom.

Turner Powertrain Systems is the world market leader in the design, development, manufacture, sales and support of off-highway transmissions (50 kW / 67 hp to 135 kW / 181 hp) for Backhoe Loaders, Telescopic Material Handlers and 4 - 9 tonne Site Dumpers

Company Profile…

Meeting new challenges TPS needs revolutionary technology that catapults them into highly competitive market at faster rate.

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The Challenge

TPS produced High precision shafts by cycles of grinding and machining process, which they realized that this was taking their precious time; more Non value added activities were hampering their progress to market at faster rate.

For a standard size of shaft ASA took nearly 20 (only grinding hours) working hours and cost $ 210 prior to adoption of hard turning operations. This also includes additional cost of heat treatment, coolant and frequently changeable grinding wheels.

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The process adopted

The company's move to integrate hard turning into its spindle shaft manufacturing process was spurred by the surface, work, machine distortion problem, right kind of tool, coolant, machine adopted etc.

4320 steel (60-62 Rc) - Shaft material used. CBN (PCBN) – Tool inserts. FUJI –ANS 3100 – Hard turning lathe. Dry turning operations carried out. Composite material dampness System Adopted 29

The results

The results were astounding and positive. By adoption the above process ASA took

nearly 9 working hours and cost reduced to $ 112.

This took only 3 days for shaft to fit in engine development process compared to 6 days or above prior adoption of hard turning.

11 grinding machines were reduced to 5 hard turning lathes.

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References

thefreelibrary.com azom.com manufacturingtalk.com hardingeus.com mit.edu/~cforest/projects soe.rutgers.edu journals.iucr.org

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Thank You……

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