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球型研磨机设计,研磨机,设计
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高速研磨技术的应用与展望摘要基本原理和应用技术在高速研磨上占有相当的地位。除了发展高速切削的相关技术外，磨床、冷却系统、磨轮也需要适应高速加工。文章最后提出了当前和今后的研究发展方面的高速磨削，发展用立方淡化硼砂轮的高速磨床。1、 引子经过多年的高速机的发展，其应用领域不断扩大，从古典磨削加工工艺，一直到完成高性能机械加工过程中。高速磨削发挥了重要作用，而且生产出的产品优质高产。其中一个因素是在创新的过程中，必须提高生产力的常规整理过程。在发展过程中显然高速磨削加工工艺过程与初步理论基础的配合接近完成，使配置过程顺序与新的高性能能力提高。同时采用适当的工具机、研磨机，还有可能扩大到高性能软材料切削机的发展。首先，在讨论原理的基础研究过程中，磨软材料的有关配置工具也需要达到要求，实施有效的环保制冷系统，调查工作也同时是适合高速磨削技术影响的一个变数。2、 高速磨削的理论基础由于随机分配切割边缘和尖锐部分的随机分布，得以使统计分析的方法应用于切割机原理。使得平均厚度改变，hcu ，平均长度的控制，都被认为是造型的变数用来描述的。改变的厚度取决于Cstat和几何构造等变量，相当于：这些的工作是速度vs即砂轮的速度、砂轮直径deq、另还有大于零、等参数，根据这种关系，假设所有其他条件不变，可以认为增加切割速度，将减少切削厚度的转变。机械与材料片工作大量磨料接触。同时，由于一些材料磨损老化，这导致了高速磨削的优势特点得以减少，工作表面粗糙度增加。因此，提高的砂轮速度可以增加工作的质量，或者增加了生产力，这一进程取决于技术特点和对质量要求。随着切削速度的增加，产生的热量随之增加。增加切削速度一般不是伴随着磨削力的比例减少而减少，从而导致磨削过程增加力的大小。 缩短研磨时间同样是可以减少热量的一种方式。切削率增加了必要的过程，同样是为了实现这一目标，在磨料厚度增加的过程中用降低切割速度来降低超载的砂轮负荷。试验结果表明，切割速度提高了两个要素，同时保持相同的金属清除率可降低导致的寿命短缩，但同时会导致增加过多的工作量。由于经常在速度提高时都伴随有增加能量的过程，每一次工作完成，随后产生的总热能都增加。当然金属清除率提高了，同时也提高了磨削机的工作能力。热能数量引进工作是一件和最初时的情况一样的工作，适用于机器工作片数量虽然减少速度但保持较高的速度增长的金属。这些因素表明，产量可提高机械使用高速磨削热而不接受不良影响部分。目前的高速机有如下三个方面的技术，这些是：1. 高速研磨机，CBN砂轮机。2. 高速磨削与研磨氧化铝车轮。3. 氧化铝研磨机床。金属清除率超比例增加，导致的生产力部分机械已达到每个领域的工业应用技术标准，如第五章附图1。芯片相当于0.5至10微米厚度的一个特点是高速磨床。高速磨削大部份就是采用了这样的应用。这项技术的一个重要特点是使用时的表现是切削速度高。3.高速磨削工具机CBN高速切削阻力方面有特别的要求，需要良好阻尼特性、高硬度，也需要良好的导热性能。这些工具通常包括一组具有很高的结构强度和薄涂层的磨料用高粘合剂附在刚体上。含有立方氮化硼作为磨料适合于高速磨削黑色物质，因为它的硬度高和具有极好的耐磨性和耐热性。首先实现高切割速度与金属焊接系统(附图2)。方法之一，这种系统是利用电镀的方式，使机轮与生产单一层次的涂层材料镀在其表面。这就构成了一个高性能的、切削速度可达到280米每秒的磨具，一直到磨料层磨损完后使用寿命才结束。零件表面粗糙度对切割机磨轮也有不利的影响。粗糙度对产品的质量有非常重要的影响，造成产品不同的形位误差。虽然CBN切削磨轮并不算是传统意义上的磨削工具，结果工件表面粗糙度也可能在影响范围内，通过微小切削过程，这将使周边材料的磨料涂层通过很小的步骤使切削深度减2至4微米，从而有效地减少粗糙度。CBN切削磨轮包括砂轮金属连接、树脂连接、玻璃化连接，多层金属高硬度连接等特有连接和穿阻力。分析这些工具，更是一个复杂的过程，但由于其结构强度高，合成树脂的连接在允许的范围内具有广泛的适应性相结合的特点，使得这些工具也需要一个标准的处理化过程，玻璃化实际应用的潜力还没有得到充分的发挥。配合适当的设计机构，保证新发展的速度超过砂轮允许的速度范围。相对于其他类型的连接方式，连接的玻璃化形式很容易在同时拥有高抗性。与树脂和金属不透水连接相比，砂轮玻璃化连接的调整可以应用于广泛的不同制造过程和设计过程中。图 3显示了一个典型的微观结构砂轮白玻璃化。选择适当的玻璃化砂轮高速磨削比铝基轮氧化更为严重，在这里，所含磨料金属颗粒大小取决于其具体的金属清除率、表面粗糙度要求。直径相当的砂轮，玻璃化实际上为突破口，图4显示的是含有磨料颗粒大小不同的关系，相当于直径和金属迁移率的具体行动外直径的关系。然而，选择也取决于磨料表面粗糙度的要求，粗糙度是有限制的，具体的金属清除率也有要求。除了要按照适当的原理选择适当机制的规定的适用问题外，组织结构，以及优化的要求需要满足砂轮切割速度高的特点。对于高切割速度、砂轮的常规设计和组织结构，都往往导致过度延伸的引起不规则裂痕及的磨料涂层的磨损。为了消除高速机床可能出现的问题，工件与磨具形状必须能配合以达到高切割速度。4、高速机床的发展前景高速机床所具有的优势是能实现有效调整，机床切割速度高。为了达到很高的速度，砂轮轴承运转速度必须达到一定大小，砂轮转动系统必须极度平稳，以减少震动。因此，必须很好的固定整个机床。保持高速磨轮高的切削速度，必须对磨轮进行平衡，这些技术措施，使更多的工件和产品质量得到保持。另一项重要因素是驱动力需要增加时，转速变得很大。因而必须削减由PC、功耗等引起的功率：其中由切割速度引起的功率：功率损失，由：测量图6所示，确认了影响切割速度的因素。然而，更多的能耗在空转中。切割机的电力、PC、相对少量的速度增长，并使所有其他切割机参数保持不变。不过，这意味着需要大量的电力，适用于最大切割速度产生强劲的电力需要是因为转动的砂轮、冷却液供应以及修整砂轮。制冷量和供应的压力，砂轮清洗过程中，重点是机床设计。如图所示，除了电力损失与换轮的损失外，砂轮与冷却剂清洗磨轮以及供应都引起能量损失。加工的工艺参数取决于能耗，需最佳发挥高速磨床的切削能力。除了有效降低机器所需的电力，更要符合理想的生态环保效益，同时供应冷却的系统也需要使其数量减少。各种方法都可使供应的冷却液等自由从喷头流通，用传统的喷头确保润滑液流量减少，混合喷头可保证最低数量润滑油浪费，共同的任务是确保有足够制冷系统的砂轮装置，如图7所示。喷头或通过砂轮供应，也可将其用于与制冷装置接触不多的磨轮区。体积流量大幅减少，这样才能实现。通过供应砂轮的喷头设计和生产工艺比较复杂，需要的设备及砂轮。利用这一系统提供的，是一个独立的过程中特别严重的现象。 两种方式有减少供应砂轮的加速冷却效果，更要有效地减少制冷剂的数量及制冷效果。供应量很小，达每小时几毫升冷却液。由于冷却效果降低，以现代化的接触方式将喷嘴配到专用区，。目前国内冷却系统用于高速磨轮的方式已经审查通过。5. 品质因素 以高速切削取代传统加工等业务，高速磨削加工过程可在最短的时间完成大量零件的加工。这样可能导致质量受损，成为等同机晶片厚度增加。机床必须要能够承受这样大的力量，可以减小砂轮的工作速度。但是，迄今为止的实践经验表明，并不是所有的材料在高速磨削时其机械特性都好。在极其恶劣的条件下，用耐高温的材料，如镍合金的基础上，增加了工作的进程，以至于因此无法避免微观结构破坏，但是这些材料可以更有效地利用在表面的加工进程。 High-speed grinding -applications and future technologyM.J. Jackson,*, C.J. Davis, M.P. Hitchhiker, B. MillsAbstractThe basic mechanisms and the applications for the technology of high-speed grinding with CBN grinding wheels are presented. In addition to developments in process technology associated with high-speed machining, the grinding machine, coolant system, and the grinding tool also need to adapt to high-speed machining. Work piece-related factors inurning the results of machining are also discussed. The paper concludes with a presentation of current research and future developments in the area of high-speed grinding, and the development of high-speed CBN camshaft grinding. All rights reserved.1. IntroductionMore than 25 years of high-speed grinding have expanded the field of application for grinding from classical finish machining to high-performance machining. High-speed grinding offers excellent potential for good component quality combined with high productivity. One factor behind the innovative process has been the need to increase productivity for conventional finishing processes. In the course of process development it has become evident that high-speed grinding in combination with preliminary machining processes close to the finished contour enables the configuration of new process sequences with high-performance capabilities. Using the appropriate grinding machines and grinding tools, it is possible to expand the scope of grinding to high-performance machining of soft materials. Initially, a basic examination of process mechanisms is discussed that relates the configuration of grinding tools and the requirements of grinding soft materials. The effect of an effective and environmentally friendly coolant system is also investigated in addition to the effect of work piece-related variables on the suitability of using high-speed grinding techniques.2. Theoretical basis of high-speed grindingIn view of the random distribution of cutting edges and cutting-edge shapes, statistical methods are applied to analyses the cutting mechanism in grinding. The mean unreformed chip thickness, hcu, and the mean chip length, lcu, are employed as variables to describe the shape of the chip. The unreformed chip thickness is dependent on the static density of cutting edges, Cstat, and on the geometric and kinematics variables 1,2: (1)where Vw is the work piece speed, VS the grinding wheel speed, ae the depth of cut, deq the equivalent grinding wheel diameter, and ， are greater than zero. On the basis of this relationship, it can be established that an increase in the cutting speed, assuming all other conditions are constant, will result in a reduction in the unreformed chip thickness. The work piece material is machined with a larger number of abrasive grain contacts. At the same time, the number of cutting edges involved in the process decreases. This leads to the advantages promised by high-speed grinding which is characterized by a reduction in grinding forces, grinding wheel wear, and in work piece surface roughness. Consequently, increasing the speed of the grinding wheel can lead to an increase in the quality of the work piece material, or alternatively, an increase in productivity. The process technology depends on the characteristics and quality requirementsof the work piece to be machined.As the cutting speed increases, the quantity of thermal energy that is introduced into the work piece also increases. An increase in cutting speed is not normally accompanied by a proportional reduction in the tangential grinding force, and thus results in an increase in process power. Reducing the length of time the abrasive grain is in contact with the work piece can reduce the quantity of heat into the work piece. An increase in the machining rate of the process is necessary for this to happen, where the chip thickness is increased to the level that applies to lower cutting speeds without overloading the grinding wheel.Experimental results 3 illustrate that increasing the cutting speed by a factor of two while maintaining the same metal removal rate leads to a reduction in the tangential force but, unfortunately, leads to an increase in the amount of work done. Owing to constant grinding time, there is an increase in the process energy per work piece and, subsequently, in the total thermal energy generated. When the material removal rate is also increased the rising tangential force results in a further increase in grinding power. The quantity of thermal energy introduced into the work piece is lower than the initial situation when the same-machined work piece volume applies despite the higher cutting speed and increased metal removal rate. These considerations show that machining productivity can be increased using high-speed grinding without having to accept undesirable thermal effects on ground components.There are three fields of technology that have become established for high-speed grinding. These are1. High-speed grinding with CBN grinding wheels.2. High-speed grinding with aluminum oxide grinding wheels.3. Grinding with aluminum oxide grinding wheels in conjunction with continuous dressing techniques (CD grinding).Material removal rates resulting in a super proportional increase in productivity for component machining have been achieved for each of these fields of technology in industrial applications 4,5 (Fig. 1). High equivalent chip thickness of between 0.5 and 10 mm are a characteristic feature of high-speed grinding. CBN high-speed grinding is employed for a large proportion of these applications. An essential characteristic of this technology is that the performance of CBN is utilized when high cutting speeds are employed.3. Grinding tools for high-speed grindingCBN grinding tools for high-speed machining are subject to special requirements regarding resistance to fracture and wear. Good damping characteristics, high rigidity, and good thermal conductivity are also desirable. Such tools normally consist of a body of high mechanical strength and a comparably thin coating of abrasive attached to the body using a high-strength adhesive. The suitability of cubic boron nitride as an abrasive material for high-speed machining of ferrous materials is attributed to its extreme hardness and its thermal and chemical durability.High cutting speeds are attainable above all with metal bonding systems (Fig. 2). One method that uses such bonding systems is electroplating, where grinding wheels are produced with a single-layer coating of abrasive CBN grain material. The electro-deposited nickel bond displays outstanding grain retention properties. This provides a high-level grain projection and large chip spaces. Cutting speeds of 280 m s-1 are possible 6. The service life ends when the abrasive layer wears out.The high roughness of the cutting surfaces of electroplated CBN grinding wheels has disadvantageous effects. The high roughness is accountable to exposed grain tips that result from different grain shapes and grain diameters. Although electroplated CBN grinding wheels are not considered to be dressable in the conventional sense, the resultant workpiece surface roughness can nevertheless be influenced within narrow limits by means of a so-called touch-dressing process. This involves removing the peripheral grain tips from the abrasive coating by means of very small dressing infeed steps in the range of dressing depths of cut between 2 and 4 mm, thereby reducing the effective roughness of the grinding wheel 7.Multi-layer bonding systems for CBN grinding wheels include sintered metal bonds, resin bonds, and vitrified bonds. Multi-layer metal bonds possess high bond hardness and wear resistance. Profiling and sharpening these tools is a complex process, however, on account of their high mechanical strength. Synthetic resin bonds permit a broad scope of adaptation for bonding characteristics. However, these tools also require a sharpening process after dressing. The potential for practical application of vitrified bonds has yet to be fully exploited. In conjunction with suitably designed bodies, new bond developments permit grinding wheel speeds of up to 200 m s-1. In comparison with other types of bonds, vitrified bonds permit easy dressing while at the same time possess high levels of resistance to wear. In contrast to impermeable resin and metal bonds, the porosity of the vitrified grinding wheel can be adjusted over a broad range by varying the formulation and the manufacturing process. As the structure of vitrified bonded CBN grinding wheels results in a subsequently increased chip space after dressing, the sharpening process is simplified, or can be eliminated in numerous applications. Fig. 3 shows a typical microstructure of a vitrified CBN grinding wheel.The selection of the appropriate grade of vitrified CBN grinding wheel for high-speed grinding is more complicated than for aluminium oxide grinding wheels. Here, the CBN abrasive grain size is dependent on specific metal removal rate, surface roughness requirement, and the equivalent grinding wheel diameter. As a starting point when specifying vitrified CBN wheels, Fig. 4 shows the relationship between CBN abrasive grain size, equivalent diameter, and specific metal removal rate for outside diameter grinding operations. However, the choice of abrasive grain is also dependent on the surface roughness requirement and is restricted by the specific metal removal rate. Table 1 shows the relationship between CBN grain size and their maximum surface roughness and specific metal removal rates. The workpiece material has a significant influence on the type and volume ofvitrified bond used in the grinding wheel. Table 2 shows the wheel grade required for a variety of workpiece materials that are based on crankshaft and camshaft grinding operations. The stiffness of the component being ground has a significant effect on the workpiece/wheel speed ratio. Fig. 5 demonstrates the relationship between this ratio and the stiffness of the component. Steels such as AISI 1050 can be ground in the hardened and the soft state. Hardened 1050 steels are in the range 6268 HRc. They are burn sensitive and as such wheels speeds are limited to 60 m s1. The standard structure contains the standard bonding system up to 23 vol.%. Whereas the abrasive grain volume is contained at 37.5 vol.%. Lower power machine tools usually have grinding wheels where a part of the standard bonding system contains hollow glass spheres (up to 12 vol.%) exhibiting comparable grinding ratios to the standard structure system. These specifications also cover most powdered metal components based on AISI 1050 and AISI 52100 ball bearing steels. Softer steels are typically not burn sensitive, but do tend to burr when ground. Maximum wheel and work speeds are required in order to reduce equivalent chip thickness. High pressure wheel scrubbers are required in order to prevent the grinding wheel from loading. Grinding wheel specification is based on an abrasive content in the region of 50 vol.% and a bonding content of 20 vol.% using the standard bonding system operating at 120 m s-1. Tool steels are very hard and grinding wheels should contain 23 vol.% standard bonding system and 37.5 vol.% CBN abrasive working at speeds of 60 m s-1. Inconel materials are extremely burn sensitive, and limited to wheel speeds of 50 m s-1 and have large surface roughness requirements, typically 1 m (Ra). These grinding wheels contain porous glass sphere bonding systems with 29 vol.% bond, or 11 vol.% bond content using the standard bonding system.In addition to the need to select the appropriate bonding system for grinding wheels in accordance with the requirements of the application concerned, the strength of the body of the grinding wheel requires optimization with high cutting speeds. In the case of very high cutting speeds, conventional grinding wheel designs involving a rectangular body and a bore often leads to excessive and irregular extensions of the body and cracking of the abrasive coating. In order to eliminate the possibility of high-speed grinding wheels failing, the material and the geometry of the body must be able to cope with very high cutting speeds. A further aim of the body of the grinding wheel must be to reduce the magnitude of centrifugal forces by optimizing the shape of the body of the grinding wheel without impairing operational safety. Excessive stress in the body of the grinding wheel is to be avoided, and the smallest possible extension of the body is tolerated. A reduction in mass is also necessary to move critical natural frequencies of the system in the direction of higher rotational speeds. Developments in high-speed grinding wheel design have focused on redesigning and optimizing the shape of body for both vitrifiedCBN 8,9 and electroplated CBN grinding wheels 10.4. High-speed machine tool developmentThe advantages of high-speed CBN grinding can only be realised in an effective manner if the machine tool is adapted to operate at high cutting speeds. In order to attain very high cutting speeds, grinding wheel spindles and bearings are required to operate at speeds in the order of 20 000 rpm. The grinding wheel/spindle/motor system must run with extreme accuracy and minimum vibration in order to minimise the level of dynamic process forces. Therefore, a high level of rigidity is required for the entire machine tool. Balancing of high-speed grinding wheels is also necessary at high operating speeds using dynamic balancing techniques. These techniques are required so that workpiece quality and increased tool life is preserved.Another important consideration is the level of drive power required when increases in rotational speed become considerable. The required total output is composed of the cutting power, Pc, and the power loss, Pl:The cutting power is the product of the tangential grinding force and the cutting speed:The power loss of the drive is comprised of the idle power of the spindle, PL, and power losses caused by the coolant, PKSS, and by spray cleaning of the grinding wheel, PSSP, thusThe power measurements shown in Fig. 6 confirm the influence of the effect of cutting speed on the reduction of cutting power. However, idling power has increased quite significantly. The grinding power, Pc, increases by a relatively small amount when the cutting speed increases and all other grinding parameters remain constant. However, this means that the substantial power requirement that applies at maximum cutting speeds results from a strong increase in power is due to rotation of the grinding wheel, the supply of coolant, and the cleaning of the wheel.The quantities and pressures of coolant supplied to the grinding wheel and the wheel cleaning process are the focus of attention by machine tool designers. This is shown in Fig. 7 11. The power losses associated with the rotation of the grinding wheel are supplemented by losses associated with coolant supply and wheel cleaning. The losses are dependent on machining parameters implying that machine settings and coolant supply need to be optimised for high-speed grinding.In addition to the advantage of effectively reducing the power required for grinding, optimisation of the coolant supply also offers ecological benefits as a result of reducing the quantities of coolant required. Various methods of coolant supply are available such as the free-flow nozzle that is conventionally used, the shoe nozzle that ensures reduced quantity lubrication, and the mixture nozzle that ensures minimum quantity lubrication. The common task is to ensure that an adequate supply of coolant is presented at the grinding wheelworkpiece interface 12. The systems differ substantially regarding their operation and the amount of energy required supp
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