In the forming and manufacturing of modern molds, with the improvement of the aesthetics and functional requirements of new products in machinery and electronics, automobiles, home appliances and other industries, more and more complex parts make the mold surface increasingly complex, and the proportion of free-form surfaces is increasing. This puts forward higher requirements for mold processing technology. Due to the complex structure of the mold, high precision requirements, different parts of the surface characteristics and materials have a larger difference, the use of mold milling cutter is also different, Figure 4-82 for the mold processing commonly used in several milling cutter.

Mould Milling Cutter Selection (I) Different Processing Methods

1. Select the tool for mold numerical control milling. In the mold numerical control processing, flat-bottomed end mills are commonly used for milling the inner and outer contours of parts and milling planes. For the processing of some three-dimensional profiles and variable-angle contours, spherical milling cutters, annular milling cutters, drum milling cutters, conical milling cutters and disk milling cutters are commonly used.

Mold milling cutter is used to process the forming surface of the mold cavity, and the processing of the cavity part mainly depends on various end mills. Mold milling cutter is evolved from the end mill, according to the shape of the working part can be divided into conical flat head, cylindrical ball head, conical ball head three. According to the material is divided into hard alloy mold milling cutter, high speed steel mold milling cutter, etc. Cemented carbide mold milling cutter is widely used. In addition to milling various mold cavities, it can also replace hand files and grinding wheels to clean the flash of casting, forging and welding workpieces, as well as finishing some forming surfaces. Table 4-17 shows the selection of die milling cutters for different processing methods.

2. Mold milling cutter to choose a reasonable tool life is generally divided into the highest productivity tool life and the lowest cost tool life two, the former according to the single-piece working hours of the minimum target, the latter according to the lowest process cost of the target.

Compared with ordinary machine tool processing methods, CNC machining has put forward higher requirements for the tool, which not only requires good rigidity and high precision, but also requires dimensional stability, high tool life, and convenient installation and adjustment to meet the requirements of high efficiency of CNC machine tools. The tools used on CNC machine tools are often used to adapt to high-speed cutting tool materials, and the use of indexable inserts. For multi-tool machine tools and combination machine tools with complex tool loading, tool change and tool adjustment, the tool life setting standard should be selected higher, and the tool reliability should be guaranteed. When the productivity of a process in the workshop limits the productivity of the entire workshop, or when the plant-wide expenditure shared by a process unit of time is large, the tool life should also be selected lower.

Factors such as tool manufacturing, cost and complexity of sharpening can be considered when formulating tool life. For the machine clamp indexable tool with short tool change time, in order to improve production efficiency and give full play to its cutting performance, the tool life can be selected to be lower. The life of a complex and high-precision tool should be selected to be higher than that of a single-edged tool. When finishing large parts, in order to ensure that at least one feed is completed and to avoid changing the tool in the middle of cutting, the tool life should be determined according to the precision and surface roughness of the parts.

Selection of Mould Milling Cutter Structure for Machining (II) Different Mold Surface

Mold processing in different processing stages of the tool structure is also different, mold roughing and finishing can choose the structure of the tool as shown in Figure 4-83.

The processing of small and medium-sized blanks can be processed with advanced tools, thereby improving the processing quality and production efficiency. Large mold should be based on the size of the mold is different, rough finishing requirements are different, processing parts are different, choose to use the corresponding end mill. For small molds such as mobile phone molds (see Figure 4-84a), integral end mills are mostly used for processing, and for large molds such as bumper injection cavities (see Figure 4-84b), machine-clamped end mills with indexable inserts are mostly used for considering economy and improving processing efficiency, while integral end mills are generally used for finishing.

Table 4-18 summarizes the different configurations of die milling cutters for different die surfaces. According to the characteristics of different mold surfaces, the correct and reasonable choice can greatly improve the efficiency of mold milling and reduce the waste of tools, reduce production costs.

The main goal of die roughing is to pursue the metal removal rate per unit time and prepare the geometric profile of the workpiece for semi-finishing. The main goal of mold semi-finishing is to make the contour shape of the workpiece flat and the surface finishing allowance uniform. In the mold roughing, semi-finishing mainly for large feed efficient economic processing, can use indexable insert milling cutter and large feed high-speed milling cutter. Among them, the large feed high-speed milling cutter can cut under very high cutting parameters, and its table feed is very high, but the cutting thickness is small, which belongs to the large feed but small back cutting amount. The cutting force is mainly generated in the axial direction, which can reduce the vibration trend and obtain a high metal removal rate.

(1) Rough machining, semi-finishing different surface milling cutter selection points

1) for rough machining of large profile (plane, inclined plane, etc.), indexable insert end mills, face milling cutters and large feed high-speed milling cutters should be selected.

2) rough machining, semi-finishing smaller surface, should be selected with a round blade end mill, circular blade arc radius, blade strength.

3) roughing, semi-finishing smaller surface, should choose indexable blade ball end milling cutter, blade shape can choose the willow shape, cutting force is small, high processing efficiency.

The ball end milling cutter is used for surface finishing. The ball radius of the ball end milling cutter should be selected as large as possible to increase the rigidity of the tool, increase the heat dissipation, and reduce the surface roughness value. In general, the radius of curvature of the finishing surface should be greater than 1.5 times the radius of the tool to avoid sudden changes in the feed direction. However, the radius of the ball head of the milling cutter must be less than the minimum radius of curvature of the curved surface to be processed when processing concave arcs. The ball end milling cutter performs semi-fine milling and fine milling of curved surfaces. Small diameter ball end milling cutter can finish milling small chamfers of steep surfaces/straight walls.

However, when the ball end milling cutter is used to improve the processing efficiency by increasing the amount of back cutting, the workpiece will leave obvious cutting residues after processing, which will increase the processing load of the subsequent finishing tool. Although the rough machining efficiency is very high, it will reduce the machining efficiency of the subsequent process.

(2) milling cutter selection points when finishing different types of surface

1) Finishing larger surface can choose indexable ball head finishing end mills to achieve high-precision machining; finishing smaller surface can choose the whole ball head end mills to achieve high-precision machining.

2) For the finishing of the R part of the tiny arc, a high-precision ball end milling cutter (see Figure 4-85) can be used to achieve high-precision machining.

3) For deep grooves and corners with small width, small diameter carbide tools can be selected for root cleaning and corner cleaning of each workpiece (see Figure 4-86).

Selection of Copying Tools in (III) Die Processing

When the mold cavity is a complex three-dimensional surface, and it is difficult to decompose into a number of simple surfaces to process, it is appropriate to use copying milling processing, copying milling processing efficiency is higher, especially suitable for the roughing of the cavity. Copying milling covers multi-axis milling of two-and three-dimensional convex and concave shapes. The larger the part and the more complex the shape to be machined, the more important the process planning becomes. A typical profile milling is shown in Figure 4-88.

Copying milling mainly refers to the milling of convex cavities and curved surfaces, and is often used in the processing of mold manufacturing contours. The profile milling cutter mostly adopts circular arc cutting edge, which can obtain smaller machining residual area under the same feed condition compared with ordinary milling, so as to improve the surface processing quality.

1. The characteristics of the profile milling cutter The profile milling cutter is a tool equipped with an indexable insert with a round cutting edge. The milling cutter has all round cutting edges (indexable inserts for circular face milling cutters or ball end milling cutters) or some round cutting edges. The classification of copying milling cutters includes sleeve milling cutters, milling cutters with spiral tool handles, modular (spiral) milling cutters, etc.

The use of circular blades for profiling cutters makes profiling cutters have a variety of advantages, which can be realized.

Now small back to eat the amount of knives, large feed, which is a supplement to the development trend of high-speed processing, profiling milling tool has the following advantages:

1) into the knife ability. Some profile milling cutters can feed directly into the workpiece like a drill.

2) Spiral interpolation. The large diameter hole can be easily and quickly machined by using the copying milling cutter and the spiral interpolation.

3) cutting edge strength. Since there is no sharp corner, the circular blade can withstand greater tool deflection and vibration, allowing processing to increase the speed, increase the feed, while reducing the risk of chipping.

4) Number of cutting edges. Round inserts have more available cutting edges. According to the size of the blade and the amount of back knife, the round blade can have 4 to 8 effective indexation, and the amount of material removal is at least twice that of the ordinary diamond and square blades. This advantage can reduce the number of times the operator changes the blade, with high efficiency and good economy.

5) efficient cutting. The use of circular inserts does not require high machine power to have a high metal cutting rate. Because of the high strength of the circular blade, it can be processed with a larger feed than the right-angle milling cutter, and even roughing with a larger load on the light machine tool.

6) The surface accuracy of the workpiece is higher after rough machining. The surface after milling with a circular insert is not like the right-angle tool after roughing the surface, and the surface residual height is lower. The surface precision of the workpiece after roughing with circular blades is high, and it can be directly semi-finished or even directly finished.

2. Selection of copying milling cutter

1) the classification and selection of profiling milling cutter blade. Copying milling cutters are mainly round blade milling cutters and ball end milling cutters. The milling cutter with circular inserts is shown in Figure 4-88. Ball end milling cutter and insert as shown in Figure 4-89.

2) the choice of knife body and blade. The selection of the shape milling cutter body can be determined according to the application conditions (see Table 4-19).

3) the choice of processing stage. Roughing generally uses round blade tools, finishing uses integral carbide ball end mills, and end mills with interchangeable integral carbide cutting heads (see Figure 4-90).

4) In copying milling, the commonly used tools include round blade milling cutter, ball end milling cutter, replaceable milling head ball end milling cutter and integral carbide ball end milling cutter. Table 4-20 compares these four commonly used profiling cutters in terms of machining stability, machining costs, and productivity.