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1、11CHAPTER VTOOL WEAR MECHANISMS ON THE FLANK SURFACE OF CUTTING INSERTSFOR HIGH SPEED WET MACHINING5.1 IntroductionAlmost every type of machining such as turning, milling, drilling, grinding., uses a cutting fluid to assist in the cost effective production of parts as set up standard required by the
2、 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 functio
3、n. 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 ac
4、hieved. It will also eliminate the heat from the shear zone and the formed chips. Cooling the work piece of high quality material 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 red
5、uced to produce a high quality product.Reducing cutting forces by its lubricating effect 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
6、: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 he
7、at and good thermal conductivity 22to 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 between the cutting edge, rake face and the work piece m
8、aterial or reducing the cutting forces (tangential component). As the friction drops the heat generated isdropped. As a result, the cutting tool wear rate is reduced and the surface finish is improved.Cutting Fluid PropertiesFree of perceivable odorPreserve clarity throughout lifeKind and unirritate
9、d 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 life. 15.1.1 Cutting Fluid TypesThere are two major categories of cutting fluidsNeat Cutting OilsNeat cutting oils are poor in their coolant characteri
10、stics 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
11、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 FluidsThis group is subdivided into three categories:331. Emulsion mineral soluble white-milky color as a result of emulsion
12、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 1980s, has less oil concentration and/or higher emulsifier ratio 10%-40% oil. Due to the high levels of e
13、mulsifier 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 co
14、ntrol.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.23 to the work piece. bare in mind that the lack of mineral oil in this type of cuttingfluid needs to take more attentio
15、n to machine parts lubrication since it should not leave an oily film on the machine parts, and might cause seals degradation due the lack of protection.5.1.2 Cutting Fluid SelectionMany factors influence the selection of cutting fluid; mainly work piece material, type of machining operation, machin
16、e tool parts, paints, and seals. Table 5-1 prepared at the machine tool industry research association 2 provides suggestions on the type of fluid to be used.5.1.3 Coolant ManagementTo achieve a high level of cutting fluids performance and cost effectiveness, a coolant recycling system should be installed in the factory. This system will reduce the amount of new purchased coolant concentrate and coolant disposable, which will reduce manufacturing cost. It either d
