CNC Knowledge: Seven steps to teach you how to use Mastercam programming and tool selection!

01

Preface

Mastercam milling includes 2D processing, 3D processing and multi-axis processing (more than four axes). Among them, 2D processing is also called point processing, that is, 2.5-3 axis processing based on straight lines and curves. is also called surface treatment (solid machining) or three-axis three-dimensional machining; Multi-axis machining is four or five axis machining, that is, positioning and processing of 4 or 5 surfaces.

This article conducts technical discussions on geometry, tool path strategy and tool selection respectively.

02

Point machining strategy and tool selection

Point machining is programming based on the defined origin of the part, including positioning, drilling, chamfering, reaming and tapping, all of which are tool path definitions after capturing the coordinates of the point. Programming is carried out according to the process sequence, including setting coordinate points (geometry), setting tool, and setting program parameters. Select tip processing, drilling processing, tapping tools, boring tools and reaming processing tools according to the specific use of tips.[1]Specific selection rules and tool descriptions are shown in Table 1 ~ Table 5.

Hole processing is the main process of product processing. The processing types mainly include ordinary drilling processing, general precision hole processing, threaded hole and thread processing and super precision hole processing. The precision and roughness of the hole surface is the main basis of hole processing technology and tool selection. In order to ensure accuracy, the hole should have a lower surface roughness value as much as possible. When the lower value of surface roughness cannot be achieved, ultra-precision machining strategies should be adopted to process holes by extrusion, sharpening, polishing, etc.[2]. The specific hole processing technology and tool selection are shown in Table 6.

Table 1 Point machining tools

Table 2 Drilling tools

Note: D is the effective diameter of the tool.

Table 3 Types of tapping tools

Table 4 Processing of boring tools

Table 5 Reaming tools

Table 6 Hole processing technology and tool selection

03

2D milling toolpath strategy and tool selection

Types of advanced CNC machining tools are evolving and developing rapidly. The emergence of high-speed feed tools, diamond milling tools, interchangeable head cutters and other types of tools not only improve the processing efficiency, but also reduce the overall tool cost. and the descriptions of the cutters are shown in Table 7. The work steps strategy and tool selection are shown in Table 8.

Table 7 Categories and descriptions of strawberries

Table 8 Processing step strategy and tool selection

The 2D toolpath adopts a 2D geometric line framework, including straight lines, R arcs, curves, etc. for milling processing. Path types include profile milling, 2D grooving, plane milling, keyway milling, and model edges. geometry to perform a variety of features of milling operations. The elements required for processing are: geometry, geometry origin, tool, processing parameters and cutting parameters, etc. The 2D tool selection path is shown in Table 9.

Table 9 2D toolpath tool selection strategy

Profile milling includes side edge milling, which is divided into rough milling and fine milling. The trajectory types of grooving tools can be roughly divided into two categories: bidirectional and equidistant ring cutting, parallel ring cutting, parallel ring cutting and corner clearance, high-speed cutting, spiral cutting, unidirectional and gradient ring cut. A dialectical selection can be made depending on the room conditions. For rough machining, indexable shoulder cutters, rapid feed cutters, corn cutters, etc. are used. can be used for finish machining, square shoulder cutters, solid carbide cutters; , and spiral milling of welding edges can be used. Straight groove welding edge cutters and cutters, etc.[3]. Characterize the selection based on accuracy and differentiate between down milling and up milling.

There are many toolpaths for grooving and you can choose from many types. You can choose according to the actual room conditions. Generally, you can choose square shoulder milling, rapid feed milling or corn milling. profile milling and milling. You can use indexable tools: square shoulder milling, round nose square shoulder milling, solid carbide milling, helical welded edge milling and straight groove welded edge milling, etc. Grooving is a multi-process integration during integral grooving and milling. integral surface treatment can be carried out, various methods can be used, the most commonly used tool is round nose knife. The step length in the XY direction of roughing is implemented as 55% Dc ~ 85% Dc, and the step length in the XY direction of finishing is implemented as 40% Dc ~ 45% Dc, where Dc is the effective diameter of the milling. cutter.[4]。

2D processing is a common processing method for processing product parts. You can first draw a 2D wireframe for programming, then import the workpiece surface or solid body to extract or select the surface, set 2D geometric programming, and flexibly set contour milling and 2D . grooving, plane milling, etc. The specific trajectory selection strategy is presented in Table 10.

Table 10 2D grooving tool path selection strategy

Tool selection for surface milling is relatively simple. When the surface treatment requires flatness and low surface roughness, the rough machining and finish machining are separated, and the XY step distance is strictly controlled to match the cutting parameters. it is easier to obtain surface precision and roughness; When the part is a thin-walled part, it is easy to vibrate. It is necessary to consider the overall process, take vibration reduction measures and use indexable tools. It is recommended to use uneven and positive rake angle inserts with low cutting force. , and use larger front and back angles. To reduce cutting force, use an indexable square shoulder cutter if necessary.[5]the tool path adopts down milling, so that the cutting speed vc is as low as possible, and the tool feed speed gradually increases.

Keyway milling is mainly used when processing keyways. The tools chosen here are mainly keyway cutters, solid carbide tools or high speed steel keyway cutters. Plunge cutters can also process larger keyways.

1) A 2-edged cutter can be cut vertically and then cut in the XY direction. 3-edged, 4-edged and multi-edged cutters are not recommended.

2) 3-blade, 4-blade and multi-blade machines can be used for precision keyway milling to improve processing efficiency.

3) After pre-drilling, 3, 4 and multi-edge cutters can be used for roughing and finishing.

4) Dynamic oblique insertion cutting tools with smaller Z direction can also adopt 2~6 edge milling cutters.

5) When the workpiece material hardness is <32HRC, oblique insert cutting can be used, and the processing path is also oblique insert, which can greatly improve the overall efficiency.

6) The appropriate side tolerance determines the diameter of the keyway cutter. Set one side to 0.05~0.2mm, depending on the keyway size. Since sometimes the blank is overcut due to vibration and tool deflection, this is caused by the tool diameter being too large. This should be taken into account when selecting treatment. If the keyway has higher precision and surface roughness requirements, coarse and fine processing should be carried out. carried out separately. In addition, it is also necessary to consider the impact of a certain cutting fluid pressure and chip removal on processing.

Process according to product requirements. Model chamfering is a necessary process for product processing. According to chamfering and rounding (including reverse chamfering, inner R rounding, outer R rounding and reverse chamfering of automobile parts). The selection of tools depends on different processing methods.

04

Surface machining measurement and tool selection

Surface machining strategy generally refers to a comprehensive set of mold processing strategies, including roughing, secondary roughing, and finishing toolpath machining strategies. The roughing is generally carried out here with a round nose milling cutter or a rapid feed milling cutter. Finishing is mainly carried out with various ball end mills. When cleaning corners, a ball end cutter, flat bottom cutter or round nose cutter is generally used. The selection of knives Generally, the selection is dialectical according to the angle R in the Z direction and the angle R in the XY direction of the mold. Additionally, the distinction between steep slopes and non-steep slopes is the main factor in distinguishing curved surfaces. It is also a more scientific way to select tools based on this. It is more scientific to choose a flat-bottomed knife when processing steep slopes. , and a round nose knife and a ball knife when processing non-steep slopes.[6]。

When surface roughing and secondary roughing, convex and concave molds are mainly used to distinguish the punch and mold cavity. When processing grooves and punches overall, it is necessary to analyze the overall mold size, the R angle size in the Z direction and the R angle size in the XY direction, and select the round nose size. R tool based on these factors. In addition, it is also necessary to consider the size of the Z-layer cutting tool, the step size in the XY direction, the efficiency level and the size of the spindle processing load. When considering the principle of maximum entity, maximum rigidity, maximum efficiency and minimum should be followed. The cost principle, the best quality principle and the most stable processing principle are adopted, and several factors such as interference, overhang, power, chip removal, cost, quality, l efficiency, cost. performance and stability are also considered.

Curved surface roughing and dynamic roughing should consider efficiency, tool cost and processing stability. Consider selecting tools from these aspects. See Table 11 and Table 12 for specific breeding strategies. Surface finishing should take into account the best quality and precision of the tool. The best quality should take into account the dimensions of surface roughness, texture and machining precision.

The factors include toolholder runout, dimensional tolerance, coating and R angle accuracy. In the mold finishing process, texture equalization and contouring of tool paths are an important subject.[7]is also the focus of tool path selection and tool selection, see Table 13.

Table 11 Tool selection for surface roughing

Table 12 Tool selection for dynamic surface machining

Table 13 Selection of surface finishing tools

05

Five-axis machining strategy and tool selection

The tool path strategy for five-axis machining is relatively complex and requires consideration of many factors, including tool interference, tool stiffness, tool holder interference , machining adaptability, machining effect and machining tool cost. Custom tools are also required if necessary. Five-axis machining requires physical programming, physical simulation, machine tool virtual reality simulation and interference inspection steps. See Table 14 for specific tool selection.

Table 14 Five-axis machining strategy and tool selection

06

Database and tool selection settings

The cutting parameters are considered from two aspects, one is the material of the mold and processing parts, and the other is the material of the processing tool. A database is established from these two aspects. When compiling the program, global consideration is given. whether to give priority to the workpiece material or the tool material, to let the software automatically select the database. It is recommended that the workpiece material database uses the six major international material groups to distinguish materials and select cutting parameters. The specific characteristics of mold materials and the selection plan of processing tools are shown in Table 15.

Table 15 Characteristics of mold materials and selection of processing tools

07

Cutting methods and tool selection techniques

When processing molds and products, tool cutting is the main factor to consider. It is generally divided into several methods such as external cutting, oblique cutting, spiral cutting and pre-drilled cutting. Pre-drilling involves drilling a hole in the die in advance for the Z cutter to use for down cutting, which can improve cutting efficiency and tool life. See Table 16 for cutting method strategy and tool selection. External cutting is to cut the empty space outside the blank to achieve the goal of rapid cutting, thereby improving efficiency. Generally, the punch is cut from outside the body and the concave mold is not applicable for pressing the mold; cutting vector to move at a certain angle. The degree is made up of two variables: the inclination of the lower knife and the vertical distance of the lower knife. Generally used in processing concave molds or in the groove part of the punch; Spiral cutter is a spiral cutting tool, with three variables: spiral radius, pitch in Z direction and slope, as shown in Figure 1.

a) Spiral radius b) Pitch in Z direction c) Slope

Figure 1 Spiral cutting parameters

Table 16 Cutting strategy and tool selection

08

Mold material and product material corresponding tool material selection technology

To process molds and product parts, first sorting the mold and product materials, analyzing the material processing performance, and selecting the most suitable cutting tool material and blade geometry are important factors to achieve a trouble-free and high productivity machining process. , as shown in Figure 2. Take the part model as an example, the material is 40Cr. The MnMo7 hot work steel is pre-quenched and tempered with a hardness of 28~40HRC. No post-thermal treatment is carried out, wet treatment is carried out and finally surface treatment by mirror polishing is carried out. toolpaths, etc.) are also crucial to achieve satisfactory results. Important, see Table 17 for cases.

Figure 2 Parts model

Table 17 Overall processing technology strategy and tooling plan for plastic molds

09

Conclusion

The distribution of work steps based on machining technology and the adaptation of tools to individual process steps constitute an extremely complex application of tool technology.

In the process of matching tool and software technologies, the tool and its cutting parameters are very important.

Subdivide the process, work steps and technical requirements, refine tool types and technical details, and achieve high quality, high efficiency, low cost and ecology.