SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING Among the various parameters of machining accuracy, the shape accuracy of part surfaces relies on the cutting tools, and the relative motions between cutting tools and workpieces The dimensional accuracy, including accuracy of dimensions of part surfaces themselves and dimensions between part surfaces, can be achieved through different method Methods for Obtaining required Dimensional Accuracy In machining, different measures can be adopted to attain the required dimensional accuracy. There are basically two different methods: trial cutting (or grinding) and automatic dimension maintenance Trial Cutting 试切法 Trial cutting achieves the required dimensional accuracy in several trial cutting(or grinding) passes. A certain length of the surface to be machined is first cut and measured. (c)
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING Among the various parameters of machining accuracy, the shape accuracy of part surfaces relies on the cutting tools, and the relative motions between cutting tools and workpieces. The dimensional accuracy, including accuracy of dimensions of part surfaces themselves and dimensions between part surfaces, can be achieved through different method. Methods for Obtaining Required Dimensional Accuracy In machining, different measures can be adopted to attain the required dimensional accuracy. There are basically two different methods: trial cutting (or grinding) and automatic dimension maintenance. Trial Cutting Trial cutting achieves the required dimensional accuracy in several trial cutting (or grinding) passes. A certain length of the surface to be machined is first cut and measured.(c) 试切法
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING (c) The cutting tool position with respect to the workpiece is then adjusted in the next cutting pass. The process repeats until the machined dimension falls into the specified tolerance limits After that, the entire length of the surface is machined in a single pass and the dimensional accuracy can be ensured. For example, when turning a shaft on a lathe, in order to obtain the diameter d and length I with their required accuracy, several trial cutting passes are first performed on a certain length of the cylindrical surface. After each cut, the diameter is measured and the turning tool is then adjusted. When the measured diameter enters its tolerance limits. the entire length of the cylindrical surface is turned with the automatic feed. Before the tool reaches the stepped face, the continuous feed should be stopped and the trial cutting and measuring are performed until the dimension of length l enters its tolerance limits
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING (c) The cutting tool position with respect to the workpiece is then adjusted in the next cutting pass. The process repeats until the machined dimension falls into the specified tolerance limits. After that, the entire length of the surface is machined in a single pass and the dimensional accuracy can be ensured. For example, when turning a shaft on a lathe, in order to obtain the diameter d and length l with their required accuracy, several trial cutting passes are first performed on a certain length of the cylindrical surface. After each cut, the diameter is measured and the turning tool is then adjusted. When the measured diameter enters its tolerance limits, the entire length of the cylindrical surface is turned with the automatic feed. Before the tool reaches the stepped face, the continuous feed should be stopped, and the trial cutting and measuring are performed until the dimension of length l enters its tolerance limits
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING Trial cutting is characterized by its low production efficiency and is not suitable for large volume production However. using this method. the machine tool does not need to be preset in advance. Moreover, the effect of dimensional variation of the blanks(shape, sizes and hardness of the material, etc. can be reduced in machining operations. For these reasons, it has been widely used in traditional small batch production The machining accuracy of the trial cutting method depends mainly upon the minimum possible thickness of the chip removal in the last trial cutting pass and the skill level of the operator. That is the reason why it is easier to attain higher machining accuracy by using a grinding operation than a turning operation
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING Trial cutting is characterized by its low production efficiency and is not suitable for large volume production. However, using this method, the machine tool does not need to be preset in advance. Moreover, the effect of dimensional variation of the blanks (shape, sizes and hardness of the material, etc.) can be reduced in machining operations. For these reasons, it has been widely used in traditional smallbatch production. The machining accuracy of the trial cutting method depends mainly upon the minimum possible thickness of the chip removal in the last trial cutting pass and the skill level of the operator. That is the reason why it is easier to attain higher machining accuracy by using a grinding operation than a turning operation
SCIENCE AND TECHNOLOGY ENGLIAH FOR MECHANICAL ENGINEERING Automatic Dimension maintenance This method automatically ensures thereamer绞刀 attainment of the required machining accuracy without the need of trial cutting, broaches fiLTJ and measuring and correction of the cutting tool position tap丝锥,螺丝攻 There are different ways to automaticall obtain the required machining accuracy 1. Use of fixed dimension cutting tools. The required machining accuracy is obtained by using cutting tools with fixed shape and dimensions. such as reamers. broaches and taps
SCIENCE AND TECHNOLOGY ENGLISH FOR MECHANICAL ENGINEERING Automatic Dimension Maintenance This method automatically ensures the attainment of the required machining accuracy without the need of trial cutting, and measuring and correction of the cutting tool position. There are different ways to automatically obtain the required machining accuracy. l. Use of fixed dimension cutting tools. The required machining accuracy is obtained by using cutting tools with fixed shape and dimensions, such as reamers, broaches and taps. reamer 绞刀 tap 丝锥，螺丝攻 broaches 拉刀