Casting Process of Improving Cutting Machining Properties of

Vermicular Graphite Cast Iron

Yongchuan LIN

College of Mechanical Engineering, Guangxi University, Nanning, Guangxi, 530004, China

Keywords: Vermicular Graphite Cast Iron, Origin and Development, Casting Process, Cutting Machining, Tool-break

and Problem Treatment.

Abstract: Based on casting process of vermicular graphite cast iron, we can improve cutting properties, stability and

machining efficiency for decrease of casting scrap and application in other fields. Combined with

development and casting process of vermicular graphite cast iron, the work analyzed problems such as tool-

break in cutting machining. After that, the work proposed suggestions to improve machining efficiency and

casting process in vermicularizing, inoculating and heat treating for promotion of cutting properties and

production efficiency.

1 INTRODUCTION

With good thermal conductivity, toughness and anti-

fatigue, vermicular graphite cast iron has been

widely used in industrial society. Casting process of

vermicular graphite cast iron has made great

progress in application and research for half a

century. However, unstable factors in production

caused high scrap as well as poor production

deficiency and cutting machining properties, thus

affecting development of casting industry.

Optimization of casting process, as well as

improvement of vermicular graphite rate and

inoculant effect, is the key of developing cutting

machining of vermicular graphite cast iron.

2 DEVELOPMENT AND

CASTING PROCESS OF

VERMICULAR GRAPHITE

CAST IRON

2.1 Origin of Vermicular Graphite

Cast Iron

In 1947, H.Morrogh found that an element—cerium

could be added to improve iron properties. Spherical

graphite also makes significance in casting process.

In 1948, thick lamellar graphite was considered as a

bad spheroidization product by adding magnesium

in casting. Research showed that the smelting

technology had an active significance in developing

strength and fatigue resistance of cast iron. After

that, the concept of vermicular graphite cast iron was

proposed. In 1960, vermicular graphite cast iron was

developed in USA, Japan, Germany, etc. J.W.Estcs

firstly applied vermicular iron to casting for

systematization of vermicular graphite cast iron

theory in 1965. Vermicular graphite cast iron has

advantages including good strength, thermal

conductivity, heat resistance and anti-fatigue. After

that, vermicular graphite cast iron was greatly

developed.

2.2 Development of Vermicular

Graphite Cast Iron

Vermicular graphite cast iron was in production in

1948. With a production of 50,000 tons, its

application was not mature. After that, vermicular

graphite cast iron was developed. The productions

were 53.5, 500 and 915 tons in 1960, 1970 and

2000, respectively. Vermicular graphite cast iron has

advantages of high tensile strength, anti-friction,

elongation and impact toughness. With properties

between gray and ductile iron, it was used for part

casting. Production technology of vermicular

graphite cast iron has reached a high level by

experiments and research in many countries. At

present, vermicular graphite cast iron, with great

potential, is widely used in car engine, cylinder

cover of internal combustion engine in train, etc.

236

Lin Y.

Casting Process of Improving Cutting Machining Properties of Vermicular Graphite Cast Iron.

DOI: 10.5220/0006023102360239

In Proceedings of the Information Science and Management Engineering III (ISME 2015), pages 236-239

ISBN: 978-989-758-163-2

2.3 Development of Vermicular

Graphite Cast Iron in China

As one of leading countries of vermicular graphite

cast iron research, China successfully developed this

technology for production in 1950. The production

of vermicular graphite cast iron in China is less than

USA and Japan at present. Vermicular graphite cast

iron technology was applied to improve life of

ductile iron ingot mold in Baotou Steel Factory in

1960s. In 1966, Shandong Machinery Design and

Research Institute published the thesis about

vermicular graphite cast iron technology. Then

research on vermicular graphite cast iron went into

an active period. Using magnesium and rare earth as

the vermiculizer, the production process is unstable.

However, research of vermicular graphite cast iron

was selected as one of 7th and 8th five-year

communication projects by government. The

application was not developed until 1990s. There is

certain deficiency in research and development of

application. E.g., research on tensile strength in

China was lower than advanced level in the world.

The tensile strength of vermicular graphite cast iron

is about 450MPa. In common application, the key of

research is processing technology rather than tensile

strength.

2.4 Casting Process of Vermicular

Graphite Cast Iron

Casting process of vermicular graphite cast iron

consisted of material selection, vermicularizing and

inoculating. Material selection was the basis of

vermicular graphite cast iron. Firstly, cast iron with

less S, P and Si was selected for stability of casting.

Secondly, gray cast iron had a high sulfur content

and bad stability. Therefore, vermicular and ductile

iron, rather than gray cast iron, was selected as scrap

returns, thus improving casting and cutting quality.

Thirdly, steel scrap with low carbon content was

selected for machining. Fourthly, in special

vermicular graphite cast iron, materials with better

performance were used to ensure quality of

vermicular iron. E.g., carbon content can affect

casting performance instead of strength. Therefore,

this property should be considered to change carbon

content. Pig iron content was more than 50%, and

scrap return less than 40%. Other elements were

determined as required. Experiments were

conducted to ensure scientific addition of elements

and production quality of vermicular iron.

Vermicularizing was the key of vermicular graphite

cast iron. Traditional vermiculizers were mainly

magnesium and rare earth. The former included

magnesium titanium alloy, magnesium titanium

aluminum, etc. The latter consisted of rare earth #1,

rare earth calcium, rare earth magnesium, etc. With

the development of vermicular graphite cast iron

process, rare earth vermiculizer was widely used.

Moreover, rare earth #1 had widest application.

Inoculating aimed at chill elimination and

microstructure refinement. The common inoculant

was silicon iron. In addition, Ca, Ba and Sr

inoculants were also used. In inoculant selection,

thickness of casting was considered. E.g., Ca, Ba

and Sr inoculants were suitable to thick casting.

Complicated vermicular graphite cast iron process

had great influence on performance. E.g., bad

control of vermicularizing process will cause cast

iron defects, cutting difficulty and tool break. In raw

material smelting, temperature of melted iron

reaches 1400-1480 . Raw materials with low S

content were selected to decrease consumption, thus

ensuring high temperature, homogeneous

composition, little impurity and pollution.

Meanwhile, C, Si, P and S in melted iron should be

stable to ensure the final component of cast iron.

With suitable furnace pretreatment, vermicular

graphite cast iron process can be improved to satisfy

cutting quality.

3 ANALYSIS OF VERMICULAR

GRAPHITE CAST IRON

CUTTING

3.1 Research Situation of Cutting

Process of Vermicular Graphite

Cast Iron

In vermicular graphite cast iron, vermicular graphite

structure exists in a state between spheroidal and

flake graphite. The unstable structure results in the

instability of vermicular graphite cast iron

production. Cast structure is designed to increase

iron content in cast iron. Vermicularizing and

inoculating are applied to improve strength,

toughness and abrasion performance of cast iron for

a better quality and longer life. At present, the main

problems of vermicular graphite cast iron process

are machining efficiency, waste product and tool

life. In cutting process, the broken parts of the tool

are examined to derive reasons of tool break by

experiences. Firstly, tool break is caused by

unreasonable cutting parameters as well as overlarge

speed of cutting tool and feed. Secondly, bad

Casting Process of Improving Cutting Machining Properties of Vermicular Graphite Cast Iron

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Casting Process of Improving Cutting Machining Properties of Vermicular Graphite Cast Iron

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process control results in defects including

blowhole, cast deficiency and hard spot. These

defects will cause sudden increase of cutting force

and tool break. Thirdly, the reasons of tool break

involve the screw tap break caused by broken bit, as

well as unfree chip removal and tool abrasion by

broken tool in the bottom hole. Fourthly, overlarge

unbalanced radial force at the exit will result in

uneven cutting force of tool break. In addition, the

port crack of broken tool should be conducted with

careful examination and scientific analysis. The

possible reasons are analyzed according to crack

situation and fracture materials. The quality

problems of cutter are eliminated at first. Then,

cutting process of vermicular graphite cast iron is

optimized.

3.2 Thinking of Improving Cutting

Process of Vermicular Graphite

Cast Iron

Vermicular graphite cast iron has a good thermal

conductivity. Its expansion coefficient is higher than

gray cast iron, and lower than high strength gray

iron. With stable casting process and good

castability, it can form compact and sound castings.

However, some problems of cutting process result in

the poor machining efficiency and high scrap rate.

These problems are researched to optimize

vermicular graphite cast iron process. Scientific

experiments are performed to select reasonable

cutting parameters. The cutting process is monitored

to ensure complete bit, little tool wear, fluent chip

removal and high cutting efficiency. Casting defects

should be controlled. It is the key of vermicular

graphite cast iron process. Firstly, vermicular

graphite rate should be increased to prevent casting

defects. Titanium is added to increase vermicular

graphite rate in traditional vermicular graphite cast

iron. However, the titanium carbide produced will

weaken cutting performance. Certain Fe-Si-Mg alloy

and residual Mg in melted iron contribute to increase

of vermicular graphite rate and cutting performance.

After performance estimation by total Mg content

calculation, Mg addition in inoculant is determined

to ensure performance of casting iron. Besides,

vermicularizing effect can be improved by applying

discontinuous reversed traveling wave magnetic

field. Secondly, inoculation process should be

controlled. Mg alloy and inoculant are added to

eliminate chilling for microstructure refinement and

performance improvement. There are many types of

inoculation process. Thereinto, metal-stream and

ladle inoculations are most widely used. In

inoculation process, melted iron is sampled to

determine amount of inoculant we use. Fracture

should be examined to determine components.

Thirdly, in thermal treatment, cutting performance

of cast iron can be improved by eliminating casting

stress and free cementite of thin wall. E.g.,

ferritizing annealing can be applied to improve

plastic toughness and thermal conductivity, and

eliminate free cementite of thin wall, thus increasing

homogeneity, stability and processability. In

addition, normalizing benefits the increase of

pearlite content, cast iron strenght and abrasion

resistance. However, the process is difficult to

control. In a word, vermicular graphite cast iron

process has characteristics such as complexity and

changeability. The whole sections of casting process

interrelate. E.g., vermicular graphite rate is

determined by type and addition of vermiculizer.

The production standard control of vermiculizer

directly affects vermicularizing operation. Besides,

inoculation is affected by vermicularizing.

Consequently, careful research and experiments are

required in each section of vermicular graphite cast

iron process. The casting process should be

emphsized to improve cutting performance,

production efficiency and quality.

4 CONCLUSIONS

To improve cutting performance of vermicular

graphite cast iron, we should focus on research of

casting process and vermiculizer production

standard. Vermicular graphite rate and inoculation

quality are increased to ensure production stability

and quality. Meanwhile, vermicular iron should be

developed for a larger manufacturing application

range and better cutting performance.

ACKNOWLEDGEMENT

The work was supported by Guangxi Natural

Science Foundation Project

(2014GXNSFAA118347); Science and Technology

Cooperation Project of Yulin City and Guangxi

University (201402801); Guangxi Key Laboratory

of Manufacturing System & Advanced

Manufacturing Technology Project (12-071-11S08).

ISME 2015 - Information Science and Management Engineering III

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ISME 2015 - International Conference on Information System and Management Engineering

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