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Metal cutting process

Chapter 1: Introduction

1. 1 Background

Manufacturing of products has been done throughout background by the process of metal clipping. Through the advancement in technology over the years, significant improvements have been manufactured in the metal cutting process. Currently, the primary method employed in the metal trimming operation is the work-piece is worked on by the cutting tool on a machine. [1 the book]

During the process of machining, the trimming tool wears out noticeably. The wearing out of the slicing tool can be an important aspect to the manufacturers as it offers major financial and production implications. Therefore, the prediction of chopping tool life is greatly researched.

Cutting tool models are developed to assist in the prediction of the cutting tool life. This process allows better design and reducing tool variables to be executed to ensure efficient use to increase the reducing tool life up to possible.

Cutting push coefficients play an important role in determining the cutting causes which are main in identifying the reducing tool life. However, chopping force coefficients change during the milling process. Therefore, chopping force coefficients are significant factors that require to be looked at accurately through the reducing tool modelling.

1. 2 Procedure for Milling

Milling is a process of lowering away materials by nourishing a work-piece past a revolving multiple teeth cutter. The chopping action of one's teeth across the milling cutter offers a fast approach to machining. The surface produced may be milled to any combinations of condition while the surface may also be angular, curved or chiseled. [2 website http://www. mfg. mtu. edu/marc/primers/milling/index. html]

There are three main types of milling that is used in practice, namely, face-milling operation, up-milling operation and down-milling operation. In face milling, the entry and exit perspectives of the cutter relative to the work-piece are non-zero whereas in up-milling and down-milling the admittance and exit angles are zero respectively. Both up and down-milling procedures are also called peripheral or end-milling operations. [1]

1. 3 Ball Nasal Milling

An end mill is a type of a milling cutter that is utilized in commercial milling applications. A wide variety of materials are being used to produce the reducing tools. Carbide inserts are incredibly common because they are best for high creation milling. Broadband steel is utilized when a special tool condition is needed nonetheless it is not usually used for high development procedures. Ceramic inserts are typically used in high speed machining with high creation. Diamond inserts are typically applied to products that require high tolerances, typically comprising high surface attributes, such as non ferrous or non-metallic materials. [3 http://en. wikipedia. org/wiki/Endmill]

A ball nose area end mill cutter is a kind of cutter that can be used on the market. Below shown in 4 are the several types of end mill cutters available.

A ball-nose end mill is well suited for milling numerous kinds of materials from plastics to metal alloys. The rounded edge design provides ball nose an advantage over the other cutters since it is more rough and durable. Another advantage is the fact it are designed for high feed rates supplying it greater output for current commercial applications. The round hint of the cutter allows for lesser impact pushes during cutting ensuring that the trend to fail under pressure is reduced. This results in cost benefits as enough time taken for the cutter to fail is longer therefore making it more appealing to consumers. [4 http://www. wisegeek. com/what-is-a-ball-end-mill. htm]

Ball end mills are mainly made of tungsten carbide with a protecting covering. The coatings are applied to reduce wear and friction and can also prevent significant harm to the chopping surface. [4] However, after extended use, the ball end mill will eventually wear and can need to be replaced.

1. 4 Scope of Research

This research is conducted to accomplish certain aims:

˜ Understanding the use of mechanistic lowering model to oblique and end mill cutting

˜ Program of the trimming make model by performing experiments to validate the algorithm

˜ Prediction of trimming push coefficients from the slicing force data

˜ Deriving an algorithm to forecast cutting force coefficients from experiments

˜ Understanding the variations in cutting force coefficients over tool life

Chapter 2: Books Review

2. 1 Technicians of Orthogonal Cutting

Mathematically, if two vectors are known as orthogonal, this means they can be perpendicular to one another (i. e form right angles with each other). This theory supports for orthogonal lowering as well. In orthogonal reducing, the materials is removed by the cutting edge that is perpendicular to the way of the work-piece motion.

Though this concept is only considered in two dimensional terms, this lays the building blocks for metal clipping. 5 below shows the orthogonal lowering in progress. Chip formation is the forming of the cut material from a work-piece.

Since orthogonal trimming is two-dimensional, the cutting forces are just exerted in the directions of the chopping velocity and the uncut chip width known as tangential make and feed force respectively. [1] The tangential and feed causes are shown in 6 displayed by Fp and Fn respectively.

There are three deformation zones in the lowering process. The principal zone is the region where the advantage of the tool penetrates in to the work-piece to create the chip. The extra zone is where in fact the chip moves across the rake face of the tool. The tertiary zone is the friction area where the flank area of the tool rubs on the newly machined surface. [1] 7 below shows the three zones with the tertiary zone indicated by the 3rd deformation area.

2. 2 Mechanistic Modelling of Trimming Forces

Mechanistic modelling is a way used to estimate the average clipping forces. With the data of the reducing forces, the tool's design life and the evaluation of specific trimming processes can be carried out. The advantage of the mechanistic power model is its capability to estimate the cutting forces over a variety of chopping conditions with a reasonable accuracy while by using a minimal variety of orthogonal cutting exams. [5Yong HuangAssistant Professor, Department of Mechanical Engineering, Clemson College or university, Clemson, SC 29634-0921Modeling of Chopping Forces UnderHard Turning Conditions Considering Tool Wear Effect]

In the two dimensional approach found in orthogonal slicing, there are two main pushes that contribute to the resultant make (i. e tangential and give food to force). As such, these two causes can be indicated in the conditions of these tool geometry, chopping conditions and materials dependant terms:

Therefore the clipping coefficients are symbolized by, However, the prediction of shear perspectives is still under much research. Therefore, because of the inaccuracy that could be present in the prediction of the shear viewpoint, the cutting pushes are defined mechanistically as, The slicing constants and border coefficients will be calibrated from, specific tool and work-piece mix, metal cutting experiments.

2. 3 Oblique Cutting

Oblique reducing differs from orthogonal clipping in that cutting velocity is perpendicular to the cutting edge in orthogonal cutting whereas in oblique trimming, it is inclined at an serious angle i to the plane normal to the cutting edge. [1]

7 depicts the oblique cutting process with chip flow viewpoint () being shown above. Chip movement angle symbolizes the angle of which the sheared chip moves above the rake face planes measured from a vector on the rake face but normal to the leading edge. Since there are now three planes to consider, the forces exist in all three directions in oblique reducing.

The oblique reducing parameters can be determined predicated on three main key points; A theoretical shear angle prediction approach proposed by Altintas and Shamoto, the minimum amount energy principle found in two-dimensional orthogonal lowering technicians and the empirical methodology predicated on empirical chip circulation route and other empirical assumptions. [1]

Once the oblique slicing parameters have been settled, the cutting pushes can be forecasted using equations based on Armarego's traditional oblique model.

Hence the corresponding reducing constants are, The next equations may be used to anticipate the oblique trimming forces from the orthogonal trimming database. [1]

2. 4 Helical End Mill

With the inception of helical end mills in the tests, the changing chip load needs to be accounted for along the helical flutes of the end mill. Consequently, the lag viewpoint is used to judge the forces.

Lag viewpoint is the position at which a specific point on the axis of the cutting edge is lagging behind by with respect to the helix position.

2. 5 Clipping Force Model

In machining certain parameters like the depth of trim is continually changing. Though there are machining handbooks that provide averaged worth, the reducing geometry for each and every tool and work-piece match is different. To judge values for each is time consuming and financial absurd. To conquer this problem, research workers come up with cutting drive models to forecast the makes for particular tool work-piece set.

The ball end mill cutter found in the following tests gets the particular geometry as shown in 9 below.

Most of the reducing push models use a semi-mechanistic strategy. The leading edge is split into discrete leading edge elements. The reducing forces acting on engaged leading edge elements are then calculated. Once the cutting causes on each component is obtained, the resultant lowering force is calculated by numerical integration of trimming forces functioning on the engaged leading edge elements. [6Estimation andexperimentalvalidationofcuttingforcesinball-endmilling of sculpturedsurfaces YuwenSun _, FeiRen, DongmingGuo, ZhenyuanJia]

Chapter 3: Experimental Setup and Procedures

3. 1 Experimental Setup

The experimental setup for the assessments to be carried out included the milling machine, tool and work-piece couple, dynamometer, data acquisition unit and three charge amplifiers.

The three axis vertical milling machine (Roeders Tec 760) was used alongside the tool which really is a 6mm diameter ball nasal end mill cutter (Mitsubishi Materials Organization) while the work part was Stavax Metallic. The pushes applied during the experiments were assessed by the dynamometer (Kistler - Type 9254) and this data was then amplified so the data can be collated. Three demand amplifiers are required to represent the forces from the three guidelines. The info is then collated and stored in the info acquisition product (2980 Dewetron). For the initial experiment, the conditions are tabulated in Table 1 below.

Table 1: Chopping Conditions

Cutting Tool

6mm Ball Nose End Mill Cutter

Rake Angle

14є

Clearance Angle

13є

Feed Rate

0. 05mm/flute

Helix Angle

30

Spindle Speed

800rpm

Depth of Cut

1. 5mm

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