机械加工工艺夹具类外文文献翻译、中英文翻译、外文翻译

TOOL WEAR MECHANISMS ON THE FLANK SURFACE OF CUTTING

INSERTS

FOR HIGH SPEED WET MACHINING

5.1 Introduction

Almost every type of machining such as turning, milling, drilling, grinding..., uses a cutting fluid to assist in the cost effective production of pa rts as set up standard required by the producer [1]. Using coolant with some cutting tools material causes severe failure due to the lack of their resistance to thermal shock (like AL2O3 ceramics), used to turn steel. Other cutting tools materials like cubic boron nitride (CBN) can be used without coolant, due to the type of their function. The aim of using CBN is to raise the temperature of the workpice to high so it locally softens and can be easily machined.The reasons behind using cutting fluids can be summarized as follows.

® Extending the cutting tool life achieved by reducing heat generated and as a result less wear rate is achieved. It will also eliminate the heat from the

shear zone and the formed chips.

® Cooling the work piece of high quality materia l under operation plays an important role since thermal distortion of the surface and subsurface

damage is a result of excessive heat that must be eliminated or largely

reduced to produce a high quality product.

Reducing cutting forces by its lubricating e ffect at the contact interface region and washing and cleaning the cutting region during machining from small chips. The two main reasons for using cutting fluids are cooling and lubrication.

Cutting Fluid as a Coolant:

The fluid characteristics and condition of use determine the coolant action of the cutting fluid, which improves the heat transfer at the shear zone between the cutting edge, work piece, and cutting fluid. The properties of the coolant in this case must include a high heat capacity to carry away heat and good thermal conductivity to absorb the heat from the cutting region. The water-based coolant emulsion with its excellent high heat capacity is able to reduce tool wear [44]. Cutting Fluid as a Lubricant:

The purpose is to reduce friction bet ween the cutting edge, rake face and the work piece material or reducing the cutting forces (tangential component). As the friction drops the heat generated is

dropped. As a result, the cutting tool wear rate is reduced and the surface finish is improved.

Cutting Fluid Properties

Free of perceivable odor

Preserve clarity throughout life

Kind and unirritated to skin and eyes.

Corrosion protection to the machine parts and work piece.

Cost effective in terms off tool life, safety, dilution ratio, and fluid lif e.

[1]

5.1.1 Cutting Fluid Types

There are two major categories of cutting fluids

Neat Cutting Oils

Neat cutting oils are poor in their coolant characteristics but have an excellent lubricity. They are applied by flooding the work area by a pump and re-circulated through a filter, tank and nozzles. This type is not diluted by water, and may contain lubricity and extreme-pressure additives to enhance their cutting performance properties. The usage of this type has been declining for their poor cooling ability, causing fire risk, proven to cause health and safety risk to the operator [1].

® Water Based or Water Soluble Cutting Fluids

This group is subdivided into three categories:

1.Emulsion ` mineral soluble' white-milky color as a result of emulsion of oil in

water. Contain from 40%-80% mineral oil and an emulsifying agent beside corrosion inhibitors, beside biocide to inhibit the bacteria growth.

2.Micro emulsion `semi-synthetic' invented in 1980's, has less oil concentration

and/or higher emulsifier ratio 10%-40% oil. Due to the high levels of

emulsifier the oil droplet size in the fluid are smaller which make the fluid more translucent and easy to see the work piece during operation. Other

important benefit is in its ability to emulsify any leakage of oil from the

machine parts in the cutting fluid, a corrosion inhibitors, and bacteria control.

3.Mineral oil free `synthetic' is a mix of chemicals, water, bacteria control,

corrosion inhibitors, and dyes. Does not contain any mineral oils, and

provides good visibility