Selection Of Milling Methods

The surface of milling parts is no more than plane, plane contour, curved surface, hole and thread, etc. The selected machining method should be compatible with the surface characteristics of the parts, the required accuracy and surface roughness.

Analysis Of Surface Processing Scheme

The only machining method of plane, plane contour and surface in boring and milling machining centers is milling. After rough milling, the dimensional accuracy of the plane can reach it12 ~ IT14 (referring to the size between two planes), and the surface roughness Ra value can reach 12.5 ~ 50 μ m。 After rough and finish milling, the dimensional accuracy of the plane can reach it7 ~ it9, and the surface roughness Ra value can reach 1.6 ~ 3.2 μ m.

1) Plane contour machining plane contour is mostly composed of straight lines, arcs or various curves. Three coordinate NC milling machine is usually used for two axis and half coordinate machining.

2) Fixed bevel plane processing fixed bevel plane is an inclined plane with a fixed included angle with the horizontal plane. The following processing methods are commonly used.

(1) When the size of the part is not large, it can be processed after being leveled with inclined base plate; If the spindle of the machine tool can swing at an angle, it can be placed at an appropriate fixed angle and processed with different tools. When the size of the part is large and the slope is small, the line cutting method is often used.

(2) For the surface of positive circular table and inclined rib, it can generally be processed with special angle forming milling cutter. Its effect is better than that of swing angle machining with five coordinate NC milling machine.

3) There are two commonly used machining schemes for variable bevel machining:

(1) For the variable angle surface with small curvature change, the CNC milling machine with four coordinate linkage of X, y, Z and a is selected, and the end milling cutter is used to swing the angle in the way of interpolation.

(2) For the variable angle surface with large curvature change, it is difficult to meet the processing requirements by four coordinate linkage processing. It is best to use the five coordinate linkage NC milling machine of X, y, Z, a and B (or C rotating axis) to swing angle processing by circular arc interpolation.

machining center

Hole Processing Method Analysis

There are drilling, expanding, reaming and boring. Large diameter holes can also be milled by circular interpolation.

1) For diameters greater than φ For the processing of 30mm holes with cast or forged blank holes, generally, the scheme of rough boring, half fine boring, orifice chamfering and fine boring is adopted. For larger holes, the scheme of rough milling and fine milling with end milling cutter can be adopted. When there is an empty slot, the saw blade milling cutter can be used to finish milling after semi precision boring and before precision boring, or the boring cutter can be used for single tool boring, but the efficiency of single tool boring is low.

2) For diameters less than φ The hole processing of 30nnn blank free hole usually adopts the processing scheme of spot facing the end face, drilling a central hole, drilling an expansion, chamfering an orifice and reaming. For small holes with coaxiality requirements, the processing scheme of spot facing the end face, drilling a central hole, drilling half, fine boring, chamfering an orifice and fine boring (or reaming) must be adopted. In order to improve the position accuracy of the hole, the countersunk end face and the central hole must be arranged before the drilling step. The chamfering of orifice shall be arranged after semi finishing and before finishing to prevent burr in the hole.

3) The processing of thread is based on the hole diameter. Generally, the thread with diameter between M6 ~ m20mm is usually processed by tapping. For the thread with diameter less than M6mm, the bottom hole shall be processed on the machining center, and the thread shall be tapped by other means. Because the energy-saving machine controls the processing state by tapping on the machining center, the small-diameter tap is easy to break. Threads with a diameter of more than m20mm can be bored with a boring blade.

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