Grinding Force and Heat of Titanium Alloy Abrasive Belt and Its Effect on Surface Integrity

: Key rotating parts such as integral blisks and blades of aero-engines are widely made of titanium alloys. Abrasive belt grinding is one of the effective methods to improve the surface integrity. However, the grinding process produces greater grinding force and higher Grinding temperature ， which have an impact on surface quality. At present, the force-heat coupling relationship in the grinding process and its influence on surface quality have not been explored. In this paper, a titanium alloy belt experiment is carried out to detect the force and temperature in the grinding process, this paper explores the influence of the grinding process parameters on the grinding force and temperature, and analyzes the influence on surface integrity of the force and temperature in the grinding process. The results show that the decrease of the belt linear speed, the increase of the feed speed and the grinding depth leads to the increase of the grinding force, the decrease of the feed speed, the increase of the belt linear speed and the grinding depth cause the temperature to rise. The effect of grinding depth on grinding force and grinding temperature is the most significant. And High grinding force and grinding temperature will cause the surface quality to deteriorate and even more serious defects. However, when the maximum temperature of the grinding temperature field reaches above 120℃, the surface roughness of the workpiece decreases from 1.596μm to 1.093μm, and the height of the surface undulation is reduced from 32μm to 19μm. This paper provides a reference for improving the surface integrity of the grinding process.


Introduction
Titanium alloy is widely used in aircraft, ships and other fields because of its excellent characteristics such as low density, high strength, heat resistance and corrosion resistance. However, due to the large margin in the milling process, in order to improve the machining efficiency and ensure the surface quality of titanium alloy, the traditional cutting and milling metho  [1,2], so it is necessary to grind titanium alloy.
In the grinding process, due to the large grinding depth, higher grinding force and grinding temperature will be produced in the grinding process, and the grinding force and grinding temperature have an important impact on the surface quality of the workpiece ground by abrasive belt. Therefore, it is of great significance to explore the variation law of grinding force and temperature in the process of belt grinding to improve grinding efficiency and surface quality.
For titanium alloy grinding, Fu [3] used slotted electroplated CBN grinding wheel for creep feed grinding of titanium alloy, which provided a research direction for efficient grinding of titanium alloy.
Nosenko [4] used SiC grin-ding wheel to grind titanium alloy to explore the influence factors of titanium alloy surface roughness. Nosenko [5] deeply grinded titanium alloy under grinding wheel grinding and nongrinding conditions to explore the surface quality of titanium alloy. Wang et al. [6]  It can be seen from the research of many scholars above that there are still few studies on the grinding force and heat of workpiece in titanium alloy abrasive belt grinding and its influence of surface integrity.
Therefore, based on the process method of titanium alloy abrasive belt grinding, this paper explores the influence law of different grinding parameters on grinding force and heat in the grinding process and the influence of force and heat on surface integrity. It provides a reference for grinding titanium alloy and ensuring surface quality.

Experimental materials
The material used in this experiment is TC17 titanium alloy, the size specification is 400mm×200mm×5mm, and the experiment adopts the method of surface grinding. The chemical composition and physical properties of the titanium alloy at room temperature (25°C ) are shown in Table 1 and Table 2, respectively.

Experimental equipment and methods
In this experiment, a seven-axis six-linkage adaptive CNC belt grinder is used as a processing grinder. The specific structure of the grinder is shown in Fig. 1 Fig. 7 The influence of feed speed and linear speed on tangential grinding force

The law of influence of process parameters on grinding temperature field
The article explores the influence of the grinding process parameters on the grinding temperature field.
Where, s U is the specific grinding energy, which is related to the properties of the material, and B is the thickness of the contact wheel.
Grinding heat consists of heat flowing into the air, heat taken away by grinding debris, heat flowing into the workpiece and heat entering the contact wheel. The grinding heat is mainly the maximum temperature in the grinding area, which has the greatest impact on the surface. Based on the moving heat source theory, Rowe [22] proposed the formula of the maximum temperature max T of the workpiece surface in the grinding area as follows: Where,  is the thermal conductivity, w  is the thermal contact coefficient, B is the belt width, and c l is the length of the grinding path.
According to the above grinding force and grinding temperature model, the relationship between the force and temperature model is constructed, and the coupling It can be seen from the formula that the coupling coefficient K is a function of linear speed and feed speed, which is directly proportional to the linear speed of abrasive belt and inversely proportional to the feed speed of workpiece.

Influence of grinding force and heat on surface roughness
Surface roughness is one of the important indexes of surface quality evaluation. In this paper, the surface roughness of workpiece under different grinding temperature and grinding force is obtained through titanium alloy abrasive belt grinding experiment, as shown in Table 3. It can be seen that the influence of grinding force and temperature on surface roughness presents a non-linear relationship. Fig. 11 shows the influence of different grinding forces and grinding temperatures on the surface roughness. It can be observed that as the grinding force increases, the surface roughness of the workpiece increases from 0.699 μm to 1.596 μm, and as the grinding force increases the change in surface roughness is more significant. This is because the greater the grinding contact force, the more conducive the abrasive belt abrasive grains to produce deeper pear grooves and greater plastic deformation, which in turn increases the highest point of the grinding surface and the distance between the lowest points is to increase the roughness value. As the grinding temperature changes, the surface roughness does not change significantly, and the surface roughness is mainly affected by the grinding force. When the grinding force is 3.429N, the maximum temperature of the grinding temperature field is 130.6℃, and the surface roughness decreases from 1.596μm to 1.093μm.
This is related to the plastic deformation during the grinding process, because the grinding temperature during the grinding process will also cause the material to flow to both sides of the groove and curling occurs.

Influence of grinding force and heat on threedimensional surface morphology
The three-dimensional surface morphology is one of the important indicators for evaluating the surface integrity. Fig. 12 shows the three-dimensional surface morphology at the highest temperature of different tangential grinding forces and temperature fields. From the analysis in Section 3, it is concluded that reducing the linear speed of the abrasive belt, increasing the workpiece feed speed and increasing the grinding depth will increase the tangential grinding force. When reducing the linear speed of the abrasive belt, the grinding thickness of a single abrasive particle will increase, the number of abrasive particles participating in grinding per unit time will decrease, the ripple density of the grinding surface along the axial direction of the abrasive belt will decrease, and the gully length along the grinding direction will increase. When the tangential force caused by the feed rate increases, the chip thickness of a single abrasive particle increases, and when the tangential grinding force caused by the grinding depth increases, the chip thickness of a single abrasive particle also increases, which will increase the fluctuation height. In Fig. 12 (a) ~ (c), although the material has a certain plastic deformation in the process of temperature increase, its grinding depth is small.
Abrasive belt grinding is cold grinding, and the temperature generated in the grinding process is low.
Therefore, the generated temperature cannot increase the plasticity of the material, and the plasticity of the material is relatively poor. Therefore, the grinding force plays a leading role in the fluctuation height. In Fig. 12 (d), due to the large grinding depth and high grinding force and grinding temperature, the grinding temperature is appropriate, which can change the plasticity of the material. Therefore, the plasticity of the material is good, and the fluctuation height of the material can be reduced during the grinding process.
Moreover, it can be seen from the three figures in Fig.   12 (a) ~ (c) that with the continuous increase of tangential grinding force, the surface texture of grinding is not clear, and the phenomenon of surface folding and wrinkling is easy to occur. The workpiece in Fig. 12 (c) has a certain bulge, which may be that the abrasive particles in the abrasive belt fall off and adhere to the work-piece.

Influence of grinding force and heat on twodimensional surface morphology
Based on the observation of the two-dimensional morphology of the workpiece surface, it can be seen that the two-dimensional morphology of the workpiece surface changes significantly with the increase of grinding force and temperature. As shown in Fig. 13, the grinding force generated in the grinding process is small and the grinding temperature is relatively low, so there are no grinding cracks, but the changes of grinding force and grinding temperature lead to the generation of grinding defects. It can be seen from the figure that with the increase of grinding force and grinding temperature, more abrasive particles adhere to the workpiece surface gradually. When the grinding force is 2.15N and the grinding temperature is 90℃, the surface flatness is good. As shown in Fig. 13 (a), the surface quality is good and no defects are observed. However, when the grinding force is 3.85 N and the grinding temperature is 105.4 ℃, As shown in Fig. 13 (b), there are still few surface defects, and abrasive particles adhere to the workpiece surface in very few places, and when the grinding force increases to 5.5N, the grinding temperature increases to 135.8 ℃, serious defects appear on the workpiece surface. As shown in Fig. 13 (c), most of the workpiece surface is adhered to by abrasive particles, and there are burns to a certain extent.

Conclusion
In this paper, the grinding experiment of titanium alloy abrasive belt is carried out, and the effects of process parameters on grinding force and heat and force and heat on workpiece surface integrity are explored.
The following conclusions can be drawn.
(1) With the decrease of belt linear speed, the increase of workpiece feed speed and grinding depth, the belt grinding force increases gradually. The grinding depth has the most significant effect on the change of grinding force.
(2) With the decrease of belt linear speed, the increase of workpiece feed speed and the increase of grinding depth, the belt grinding temperature increases gradually, but the overall grinding temperature field is low, all within 150 ℃.
(3) With the increase of grinding force and grinding temperature, the surface roughness gradually increases and the surface fluctuation height increases. However, when the temperature rises to more than 120 ℃, the surface roughness decreases and the surface fluctuation height decreases. The reason may be that the temperature changes the plasticity of the workpiece. (4) With the increase of grinding force and temperature, the surface morphology of the workpiece gradually becomes worse. When the grinding force reaches 5.5N and the grinding temperature reaches 135.8 ℃, there are a certain degree of burns and more surface defects.

Declaration
Ethical Approval: Ethical approval was not required for this study.
Consent to Participate: Written informed consent was obtained from individual or guardian participants.