Abstract

of thesis master's degree work

Ivan Zhulin

Theme of master's work:

Internal grinding of hard-to-machine materials cutting modes determination taking into account changes in tool grinding ability

Supervisor: an associated professor Poltavets Valeriy Vasil’evich

Introduction

Modern machine-building development causes using more tough and reliable materials for responsible details  production with high demands in accuracy, toughness and reliability. All that range of properties is provided by high-strength materials: heatproof and corrosion-proof steels and alloys, high-hardness construction steels, hard alloys. However, such materials machining is difficult because of their mechanical properties. That is why such materials grinding is most effective by diamond tools.

That is why a task to optimize such materials grinding process as much as possible in order to improve machining quality and save cost is assigned.

Topicality

Machine-building development is speeding up and demands to use high-strength materials in most responsible details to obtain high machines reliability.

The basic way to improve details reliability is making them from high-strength materials. It is expensive because of high material price and high machining price.

For demanded surface quality reaching earlier was necessary to designate cutting modes reasoning from tool average cutting ability.

A new generation  of grinding machines with digital control helps us to solve this problem by each turn grinding depth designation. It is necessary to explore tool cutting ability for that .

Each turn grinding depth designation lets to get needed surface quality and to fully use tool grinding ability, which brings economy in time and cost.

Aims

Aim of this work is to get the method of most effective internal grinding cutting modes designation looking on two main factors: minimum machining cost and maximum blank surface quality.

It is needed for that:

1 To develop internal grinding by elastic setup device.

2 To develop a way to designate necessary blank-tool tightening force

3 To designate required electrospark effect on tool working surface.

Scientific novelty

Scientific novelty of this work is in developing of method to designate internal grinding cutting modes reasoning from surface quality and taking into account tool grinding ability change.

Practical value

Problem of high quality machining by diamond tools with metal bond is not solved. It is because of diamond tool with metal bond low durability in high-productive grinding process. Low durability is connected with fast tool dressing, glazing and as a result, tool effectiveness reducing.

Knowing the law of tool grinding ability change lets to designate cutting modes that are corresponding to grinding tool cutting ability and besides, to correct tool grinding ability with electrospark effect on tool working surface.

This lets to optimize internal grinding process in order to reduce the waste part, which is connected with not quality blank surface (grinding burn, thermal stress)  and to fully use tool grinding ability.

The content of problem

The basic area of application of diamond grinding tools is machining of high-strength and hard-to –machine materials: high-speed steels and hard metals and also heat-proof and corrosion-proof steels and alloys, high-hardness construction steels.

For blanks  made from this materials grinding diamond grinding tools with metal bond are widely used, which provides expensive diamonds consumption reduce and high productivity.

internal grinding. (47,3 KB; 19 frames; 10 cycles)

But metal bond diamond tools are worn and glazing because they are almost not self-sharpening. Grit wear and pore glazing causes grinding forces increasing and as a result, increasing a temperature while grinding process.

As a result of high temperature in blank thin surface layers is possible defects precipitation, which called a grinding burn. Grinding burns are  areas looking like spots or traits with changed metal structure.

Grinding burns alike traits are the result of high local temperature on working contact areas of blank and grit. Grinding burns alike spots are the result of high temperature on all tool and blank contact surface.

Local  temperatures reduction is necessary, because grinding burns greatly reduce reliability and longevity of machine blanks. Grinding burns on a flank sides of cogs reduce longevity of cog-wheel in 5-8 times, and grinding burns on a bearing race paths reduce their longevity in 3 times.

Intolerable defect is interstice gauze on grinded surfaces. This interstice appear in blank machining process or while blank is cooling down. They are a result of grinding stresses or tempers in blank surface layer.

Reduce temperature of grinding is possible by following ways:

1-  making cutting edges of optimal form while the all geometrical parameters dispersal is minimum.

2-  Maximum time tool grinding ability maintenance.

3-  Leading an additional energy into cutting zone to reduce material strength.

As an analysis of tendencies of technology of mechanical machining development for the nearest 15-20 years has shown, one of directions of tooling of hard –to-machine materials perfection is the usage of electrophysical methods of treatment and usage of additional types of energy in the area of the treatment carried out by a traditional method.

Grinding tool effectiveness at this time is described by G-ratio or by cutting ability ratio. But they do not let to define machining conditions, which would provide needed quality and maximum process productivity. Because of that they are oblique indexes that describe tool cutting properties for one totality of grinding process factors.

Because of that now the search is guided to find the index that would directly characterize diamond-abrasive tool cutting ability taking into account its change dynamics.

It is proposed to describe hard-to-machine materials diamond grinding process using new term “the flowing limited wheel cutting ability”.

The flowing limited diamond wheel cutting ability is machined material volume, which is deleting by tool working surface in time unit in condition that all demands layed on machining modes by technical reasons, are kept.

The flowing limited wheel cutting ability change is visible in machining process by elastic setup as a grinding depth change while the rest cutting modes are the same during process.

That is why for that term exploration in internal grinding development of internal grinding by elastic setup device is necessary.

The needed quality of blank surface after grinding by elastic setup can be achieved by observance of few parameters:

1.  The radial force Py

2.  The tangential force Pz

3.  Blank surface layer temperature T.

As the blank surface layer temperature depends a force factors that appear during grinding, it would be logical to find out grinding forces, which provide necessary blank quality from temperature in machining zone.

Grinding by elastic setup describes grinding depth change with tool cutting ability change. Using that it is possible to find out the grinding depth, which is corresponding the tool cutting ability in each moment while the grinding forces, and it means the blank quality are constant.

Conclusion

Using the flowing limited wheel cutting ability it is possible to designate cutting modes reasoning from blank surface quality and to know the moment for correcting the tool is necessary.

All that will let to improve diamond tool using effectiveness and to economy on machining time and on tool.

Literature

1. Матюха П.Г., Стрелков В.Б., Полтавец В.В. Определение режимов плоского шлифования твердых сплавов с использованием нового критерия о текущей лимитированной режущей способности круга/ Сверхтвердые материалы. Научно-теоретич. журнал. – Киев: 2004. – № 3. – С. 67-73.

2. Резников А.Н., Резников Л.А. Тепловые процессы в технологических системах: Учебник для вузов по специальности "Технология машиностроения" и "Металлорежущие станки и инструменты". М.: Машиностроение, 1990. - 288 с.: ил.

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