How to choose the cutting tools in mould processing?

In the forming and manufacturing of modern moulds, due to the complex mould structure and high precision requirements, the surface characteristics and materials of different parts are greatly different, so the mould milling cutters used are also different.

The mould processing process can be divided into rough machining, semi-finishing and finishing, and sometimes even super-finishing. Indexable tools are generally used for roughing and semi-finishing processes, and integral tools are used for finishing processes.

When the mould cavity is a complex three-dimensional curved surface, copy milling processing is more efficient and is especially suitable for rough machining of the cavity. Commonly used tools in copying milling include round blade milling cutters, ball nose milling cutters, replaceable milling head ball nose milling cutters and solid carbide ball nose end mills. The following table compares these four commonly used copy milling cutters in terms of cutting stability, cost productivity and other aspects.


Issues that should be paid attention to when processing mould surface


(1) Rough milling


To pursue the maximum material removal rate per unit of time, the end mill should be milled layer by layer according to the contour surface according to the margin given by the processed surface, which is highly efficient. Small moulds are mostly processed with integral end mills. Large molds are mostly processed with machine-type end mills with indexable blades considering their economy and processing efficiency. They mainly include R-type round blades and square shoulder milling blades. Face milling inserts, etc.


(2) Semi-finish milling


To make the processed surface closer to the theoretical curved surface, a ball-end milling cutter can be used, generally leaving a machining allowance of about 0.5mm for the finishing process.


(3) Finishing


Finally, the theoretical surface is processed. Generally, solid end mills or ball end mills are used. When finishing a curved surface with a ball end mill, the line-cutting method is generally used to appropriately increase the spindle speed, select a suitable reversal point, and reduce tool marks caused by pauses and vibrations.


(4) Avoid cutting vertically


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, process holes can be pre-drilled to facilitate cutting.

(5) When milling curved surface parts, if it is found that the part material is not heat treated well, has cracks, uneven structure and other abnormal phenomena, the processing should be stopped in time to avoid wasting working hours.

(6) Before each start of milling, machine tools, fixtures, and cutting tools should be properly inspected to avoid malfunctions occurring midway, affecting processing accuracy, and even causing waste products.

(7) When milling the mold cavity, the filing allowance should be appropriately controlled according to the roughness of the machined surface. For parts that are difficult to mill, more filing allowance should be left. For parts that are easy to process, such as flat surfaces and right-angle grooves, the roughness value of the machined surface should be reduced as much as possible to reduce filing.

In mold processing and manufacturing, the selection of cutting tools needs to be comprehensively considered from several aspects such as workpiece material, working conditions, cutting stability, cost productivity and processing accuracy. Only by rationally selecting cutting tools can we improve processing quality and efficiency, meet product aesthetics and functional requirements, and improve mold processing technology.

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