Points to note when milling curved surfaces, how much do you know?

Problems that must be paid attention to when milling curved surfaces: rough milling, semi-finishing milling, finishing, ball-end milling cutters are milling curved surfaces, avoiding vertical cutting, etc.

1. Tool selection

Most of the tools used by CNC machine tools in processing molds are the same as general-purpose tools. Milling cutters with indexable carbide inserts are often used without re-grinding. Since there are many cavities formed by curved surfaces in the mold, it is often necessary to use ball-end cutters and ring cutters (that is, the end milling cutter has a circular arc chamfered tip).

2. Matters needing attention in assembling milling machine fixtures

According to the feed mode during milling, the milling machine fixtures are usually divided into linear feed type, circumferential feed type, and profiling milling fixture. So what problems should be paid attention to when assembling these fixtures to the milling machine?

First, in order to improve the stability of the milling machine fixture installed on the machine tool and the dynamic vibration resistance performance, the structure of various devices should be compact, the center of gravity of the fixture should be as low as possible, and the contact area of u200bu200bthe fixture with the machine table To be big.

Second, the use of milling machines has high milling productivity (short cutting time). When designing fixtures, it is necessary to consider how to quickly install the workpiece to shorten the auxiliary time, generally in fixture BU. There are also elements for determining the position and direction, so that the relative position of the fixture and the machine tool can be adjusted quickly.

Third, when assembling the milling machine fixture, it is also necessary to consider the outflow of chips and the convenience of cleaning. A large number of chips are generated during milling, and there should be enough space for chip removal. For large fixtures, chip removal ports and chip flutes should be considered; protective covers should be added to parts and spaces that are not easy to remove chips. When cutting fluid is used during machining, the specific design of the clamp should consider the flow direction and recovery of the cutting fluid. For heavy-duty milling machine jigs, in order to facilitate handling, lifting rings should also be set on the jigs.

3. Problems that should be paid attention to when milling curved surfaces

(1) Rough milling. Rough milling should be based on the margin given by the machined surface, milling layer by layer with an end mill according to the contour surface, this kind of rough milling efficiency is high. The rough-milled surface resembles a terrace on a hillside. The height of the steps depends on the rough milling accuracy.

(2) Semi-finish milling. The purpose of semi-finishing milling is to mill away the steps of the terraces and make the processed surface closer to the theoretical curved surface. The use of a ball-end milling cutter generally leaves a machining allowance of about 0.5 mm for the finishing process. The row spacing and step distance of semi-finishing can be larger than that of finishing.

(3) Finishing. Finally, the theoretical surface is processed. When finishing the curved surface with a ball-end milling cutter, the line cutting method is generally used. For parts with better openness, the turning point of the row cutting should be selected outside the curve table, that is, the curved surface should be extended outwards during programming. For parts with poor openness, due to the change in cutting speed when turning back, it is easy to leave tool marks on the machined surface and the blocking surface due to pauses and vibrations. Therefore, during processing and programming, one is to reduce the feed speed when turning back, and the other is when programming, the turning point of the processed surface should be slightly away from the blocking surface. The intersecting line of the curved surface and the blocking surface should be processed separately by a root removal program, so that the processed curved surface and the blocking surface will be smoothly connected without large knife marks.

(4) When the ball end milling cutter is milling the curved surface, the cutting speed at the tip of the ball cutter is very low. If the ball cutter is used to mill a relatively smooth curved surface perpendicular to the machined surface, the surface quality cut by the tip of the ball cutter It is relatively poor, so the spindle speed should be increased appropriately, and cutting with the tool tip should be avoided.

(5) Avoid vertical cutting. There are two types of flat-bottomed cylindrical milling cutters, one is that the end face has a center hole, and the end edge is not in the center. The other is that there is no center hole on the end face, and the end edges are connected and pass the center. When milling a curved surface, an end mill with a center hole must not feed vertically downwards like a drill, unless the process hole is drilled in advance. Otherwise, the milling cutter will be broken. If you use an end knife without a center hole, you can feed it vertically downwards, but because the blade angle is too small and the axial force is large, it should be avoided as much as possible. The best way is to feed the tool diagonally downward, and then use the side edge to cut laterally after reaching a certain depth. When milling the groove surface, the process hole can be pre-drilled for cutting. Although the vertical feed effect of the ball-end milling cutter is better than that of the flat-bottomed end milling cutter, it is best not to use this cutting method because of the excessive axial force that affects the cutting effect.

(6) In the milling of curved parts, if the parts are found to have poor heat treatment, cracks, uneven structure, etc., the processing should be stopped in time to avoid wasting man-hours.

(7) When milling the complex surface of the mold cavity, a longer cycle is generally required. Therefore, the machine tool, fixtures, and tools should be properly inspected before each start of milling to avoid failures in the middle of the process. Machining accuracy can even cause waste.

(8) When the mold cavity is milled, the filing allowance should be properly grasped according to the roughness of the machined surface. For parts that are more difficult to mill, if the machined surface roughness is poor, you should leave more trimming allowance; for flat, right-angle grooves and other easy-to-machine parts, the machined surface roughness value should be reduced as much as possible to reduce the filing work To avoid affecting the accuracy of the cavity surface due to large-area repairing.