机械制造作业考研题目答案分享——金属切削规律2

金属减削规律的四道题目以及答案解释(english version)。

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文章目录

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• (1) Explain the essential of cutting deformation.
• (2) What are the indices to measure the deformation degree? How do they relate with each other? Can they really reflect the physical essentials of the chip forming? Why?
• (3) Explain the different index to measure the machinability of workpiece material.
• (4) Write down the steps to establish the formula of cutting forces

(1) Explain the essential of cutting deformation.

Cutting deformation refers to the change in size or shape of materials by shear force and pressure with the help of cutting tools.
When the plastic metal is under pressure, the metal produces elastic deformation and plastic deformation successively with the increase of external force. And it will cause the metal lattice to slip and then break. For example, if the effects of friction, temperature and strain rate are neglected, the metal cutting process is like the compression process. That is, the cutting layer by the tool extrusion also produces plastic deformation.

(2) What are the indices to measure the deformation degree? How do they relate with each other? Can they really reflect the physical essentials of the chip forming? Why?

衡量切削变形的程度的指标:变形系数、相对滑移和剪切角三个指标。
衡量切削变形的程度的指标的相互关系:剪切角、相对滑移和变形系数是通常用以表示切屑变形程度的三种方法。它们是根据纯剪切的观点提出的。但切削过程是复杂的,它既有剪切,又有前刀面对切屑的挤压和摩擦作用(第二变形区), 用这些简单的方式不能反映变形的实质。
它们不能真实的反映了切屑形成过程的物理本质。原因为切削过程是复杂的,它既有剪切,又有前刀面对切屑的挤压和摩擦作用(第二变形区),用这些简单的方式不能反映变形的实质。切屑的变形和形成过程实际上经历了弹性变形、塑性变形、挤裂、切离四个阶段。

(3) Explain the different index to measure the machinability of workpiece material.

There are two main indexes to measure the machinability of workpiece material.
Tool life indicator
The cutting speed $v_{60}$ is an allowable speed after 60 min machining process. If the workpiece is difficult to be machined, then we use $v_{20}$. The higher $v_{60}$ or $v_{20}$, the better machinability on the same working situation.
Surface roughness indicator
The higher surface roughness, the better machinability of the workpiece.
Sometimes chip shape or cutting force can also be used to measure the machinability.

(4) Write down the steps to establish the formula of cutting forces

答案是用车削力的实验公式建立过程来回答。
Establishment of turning force’ experimental formula
Single factor method was used. That is to say, fix other experimental conditions, change the back draft af and feed f respectively, read out the corresponding cutting force value from the force measuring instrument, and then get the functional relationship between them after data processing.
The general form of turning force experimental formula established by cutting force experiment is as follows:

$$F_c=C_{(}{F}_c)a_p^{(}{x}_{(}{F}_c))f^{(}{y}_{(}{F}_c))K_{(}{F}_c)$$

$$F_p=C_{(}{F}_p)a_p^{(}{x}_{(}{F}_p))f^{(}{y}_{(}{F}_p))K_{(}{F}_p)$$

$$F_f=C_{(}{F}_f)a_p^{(}{x}_{(}{F}_f))f^{(}{y}_{(}{F}_f))K_{(}{F}_f)$$

CFc、CFp 、CFf ------Influence coefficient, its size is related to the experimental conditions
xFf、xFp、xFc----------Influence index of back draft on cutting force
yFf、yFp、yFc ---------Influence index of feed rate on cutting force
KFf、KFp、KFc--------- Correction coefficient of cutting force when calculation and experiment conditions are different。

According to many corresponding values of ap-Fc and f-Fc obtained from experiments, two straight lines can be connected in double logarithmic coordinates
The logarithmic equation of the line graph is：

$$lg{F}_c=lg{C}_{(}{a}_F)+lg{a}_p$$

$$lg{F}_c=lg{C}_{(}{a}_p)+x_{(}{F}_c)lg{a}_p$$

$$lg{F}_f=lg{C}_f+y_{(}{F}_c)lgf$$

The above formula can be rewritten as：

$$F_p=C_{(}{a}_p)a_p^{(}{x}_{(}{F}_p))$$

$$F_c=C_f{f}^{(}{y}_{(}{F}_p))$$

Combining the above two formulas, the experimental formula is obtained:

$$F_c=C_{(}{F}_c)a_p^{(}{x}_{(}{F}_p))f^{(}{y}_{(}{F}_p))$$