QianJiu machining

Surface milling quality analysis

Release time:May 08, 2019 Visits:

Key words: plane milling; quality analysis
  Planar milling is one of the most basic and important tasks in milling machine processing, and it is the basis for further understanding of other complex surfaces. The so-called milling plane refers to the plane in which the workpiece is machined by milling. The quality of the plane in the process is mainly measured from the flatness and surface roughness of the plane, and is evaluated by the flatness and surface roughness values of the shape tolerance items. As shown in the figure below, the rectangular dimension of the surface is 0.05mm (that is, the upper surface must be located in two parallel planes with a distance of 0.05mm), and the surface roughness Ra of the surface should be no more than 6.3μm.
  There are two methods for milling the plane on the milling machine: circumferential milling and end milling. The circumferential milling is performed by cutting the blade distributed on the cylindrical surface of the milling cutter and forming a plane. It is mainly suitable for machining with a cylindrical milling cutter on a horizontal machine tool. . End milling is performed by cutting and forming a flat surface on the end face of the milling cutter. It is mainly suitable for machining with end mills on vertical milling machines. The plane error of the plane machined by the cylindrical milling cutter mainly depends on the cylindricity error of the milling cutter. Therefore, the grinding requirement of the cylindrical milling cutter is strict, and the sharpening of the cylindrical milling cutter is time-consuming and laborious. Grinding tools with a slight cone or diameter will directly affect the parts we process and will also affect economic benefits. Therefore, our school mainly uses X5032 and vertical rocker drilling and milling machine (commonly known as turret milling) to process the plane in the practice teaching. The material of the workpiece is mainly used HT200. The other used is also a self-made flat knife row. 45° small flying knife to achieve cutting.
  The quality of the machined surface is not only related to the quality of the machine tools, fixtures and cutters used in milling, but also to the factors such as the amount of milling and the rational selection of the cutting fluid. In the processing we have to fully consider and choose a reasonable amount of cutting to ensure processing requirements. The so-called reasonable cutting amount refers to obtaining high productivity and low cost cutting processing under the premise of making full use of the cutting performance of the tool and the performance of the machine tool and ensuring the processing quality of the workpiece. Different processing properties, the requirements for cutting processing are not the same. Therefore, the focus of consideration is also different when choosing the amount of cutting. When roughing, try to ensure a high metal removal rate and the necessary tool durability. Therefore, when selecting the cutting amount, first select the largest amount of backing knife; secondly, according to the constraints of machine power and rigidity, select the largest possible feed amount; finally, determine the appropriate cutting speed according to the tool durability requirements. When finishing, firstly determine the amount of backing knife according to the margin of roughing; secondly, according to the surface roughness requirement of the machined surface, select the appropriate feed amount; finally, under the premise of ensuring the durability of the tool, select as high as possible Cutting speed.
  By detecting the processed rectangular body parts, it is found that there are mainly some quality problems in the plane milling:
  (1) The surface of the milled rectangular body has a one-way curved blade and the surface is concave.

(2) There are joint marks on the surface of the milled rectangular parallelepiped parts.

(3) The plane has layers of different heights.

(4) The surface roughness of the milled rectangular body is large.

  Exploring the reasons for its occurrence, there are mainly the following influencing factors: 
  (1) When the milling axis is not perpendicular to the longitudinal feed direction of the table (the “zero position” of the vertical milling head is not allowed), the milling cutter tip mills a unidirectional curved blade on the working surface, and the surface is concave. In particular, the turret milling machine can not only deflect the vertical milling head within ±45° of the horizontal plane, but also tilt it by ±45°. Therefore, we need to correct the horizontal direction and correct the tilting position in the machining. "on.
  (2) The hexahedral surface has the influence factor of the knife mark. It is mainly due to the condition limitation during milling. The plane cutter row used is smaller than the width of the workpiece surface after the 45° small flying knife is installed. In the machining, we generally use a cutter row with a diameter of 1.4 to 1.6 times the width of the workpiece for machining to ensure the processing needs.
  (3) The plane has different layers of high and low, and the influencing factors are mainly the large vibration during processing. The workpieces used in the machining are mainly gray cast iron, while the gray cast iron of the milling cutter is hard, the turret milling machine itself is rigid and the strength is poor, and the turret milling cutter has a smaller diameter and rigidity. The strength is poor, so the vibration is large, causing deformation of the plane. On the other hand, due to the weak clamping of the workpiece, the stability in milling is poor. In the third machining, the spindle locking handle is not locked due to negligence. Under the action of the milling force, the spindle is tilted up and down to make the plane have different heights. Floor.
  (4) Factors that lead to a large surface roughness value: the number of spindle revolutions during milling is low, and the feed rate is too large, especially when machining on turret milling, the feed speed is completely controlled by hand, plus in feed Intermittent pauses occur, which directly affects the surface roughness. On the other hand, we mainly use 45° small flying knives during machining. The geometric parameters of the milling cutter are not correct when sharpening, which leads to increased friction, which affects the surface roughness. Third, when the milling cutter rotates, the workpiece is removed from the workpiece without landing the workpiece, and the surface of the workpiece is scratched. Fourth, although the milling cutter stops rotating, the workpiece is withdrawn from the workpiece without landing the workpiece, and the surface of the workpiece is scratched. Fifth, the milling cutter becomes dull due to its own wear during long-term machining. In summary, we can see that most of the factors causing the surface roughness value during processing can be avoided or reduced by the operator's correct and meticulous operation.
  In short, the plane milling is the basis of our subsequent processing, we must do every step of the process, in order to obtain good economic benefits.

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