CNC Prototypes Manufacturing 2 : 2D and 3D milling

2D milling

cnc machine

Mastercam 2D CNC machining automatic programming ability is the most advanced of all automatic programming software. Complete functions, fast post-processing speed and high efficiency.

Two-dimensional CNC machining is also called 2.5-axis machining, which mainly includes machining paths such as contour milling, slotting, face milling, and drilling. Here are a few main tool paths to make a brief introduction.

1. Shape milling

The object of contour milling is the contour of the part. Generally, contour processing is mostly used for two-dimensional milling. The cutting depth of the two-dimensional contour milling tool path is fixed.

In fact, the shape processing of MASTERCAM implies a 3D option. As long as the line to be processed is a spatial line and the composition surface is 3D, it will be processed in a spatial manner. The following mainly introduces the first three processing types of two-dimensional processing.

1.1 2D shape milling

When performing two-dimensional profile milling, the milling depth of the entire tool path is the same, and its Z coordinate value is the absolute or relative milling depth value set.

1.2 Forming knife processing

The processing generally needs to be arranged after the contour milling is completed. The reference line of the processing is the original line before the figure chamfering. The tool used for processing must be a forming milling cutter. When used for chamfering, the angle is determined by the tool.

1.3 Spiral shape processing

Generally, it is used to process contours with a large milling depth, and the tool is gradually cut according to the set angle to perform contour processing, but this processing method cannot replace layering at present.

2. 2D grooving and milling

The 2D grooving module is mainly used to cut the material surrounded by the shape. The series used to define the shape can be a closed series or an unclosed series. But each series must be coplanar series and parallel to the composition plane.

In the slotting module parameter setting, the general processing parameters are consistent with the shape processing settings. The following only introduces the settings and characteristics of its unique slotting parameters and rough and finishing parameters.

2.1 Grooving processing method

There are 5 processing methods for the grooving module. The first 4 processing methods are closed series processing methods. When there are unclosed series in the selected series, the Open processing method can be adopted.


Standard (general grooving) is a standard grooving method, that is, only the material in the defined groove is milled, and the outside of the boundary or islands are not milled;
Facing (boundary reprocessing) is equivalent to the function of the face milling module. During the processing, only the selected surface is guaranteed to be processed, regardless of whether the material outside the boundary or islands will be milled;


Island facing (using island depth grooving) can mill the island to the set depth. This method is equivalent to multiple grooving processing. Not only the programming steps are reduced, but the processing path and program are streamlined and optimized.

2.1 Rough machining parameters for grooving

In grooving processing, the machining allowance is generally relatively large, and the processing efficiency can be improved by setting the rough and finishing parameters. Mastercam 9.0 provides 8 kinds of rough cutting methods: Zigzag (two-way cutting) Constant Overlap Spiral (equal distance circular cutting), Parallel Spirall (surround cutting), Parallel Clean Cornres (circular cutting and clear angle) Morph Spiral (according to the shape) The 8 cutting methods of Circumferential Cutting, High Speed, One Way, and True Spiral can be further divided into two categories: line cutting and circumferential cutting.

Line cutting includes two-way cutting and one-way cutting. Two-way cutting generates a set of spaced reciprocating linear tool paths to cut grooves; the tool path generated by one-way cutting is similar to that of two-way cutting, except that one-way cutting completes a straight line. After that, the tool lifts back quickly and then starts a new round, you can always maintain the down milling or up-cut milling mode.

The ring cutting method is to process from the inside to the outside or from the outside to the inside according to the shape. There are many types. The ring cutting can keep the milling method unchanged. The spiral method also avoids the shifting and commutation between the rings. The main problem of the ring cutting is that it needs enough Convolute space, sometimes the graphics are complicated, and the convolute coverage may not be complete. Row cutting and circular cutting are the two most important cutting methods in CNC machining, and we will discuss them in detail later.

3. Surface milling

Surface milling is mainly used for the plane processing of the prototype model to ensure the installation plane reference. When the diameter of the tool is greater than the width of the surface of the milled workpiece, one-time milling can be adopted, and the position of the tool path is the center position of the geometric model.

The key to Surface milling is the amount of tool path overlap and additional distance, as well as the way the tool moves between milling. Since the plastic material processed by the prototype model is relatively soft, in order to improve the processing efficiency, the overlap of the tool path can be reduced, the additional distance of the starting point and the additional distance of the end point can be shortened, and the tool will quickly move to the starting point of the next milling in a straight line.

3D Milling

The most difficult surface machining in traditional prototype model making is very convenient in CNC machining. Mastercam provides 8 rough machining paths and 11 finishing paths, which can basically meet the requirements of surface machining, but various types of machining paths The efficiency and the effect of the system are different, and you must be careful when choosing.
In rough machining, grooving is most used. Due to the good cutting performance of plastic machining, semi-finish machining such as rough machining of residual material is actually rarely performed. In the finishing machining, the rounding equidistant finishing machining has a good cutting effect, and the intersecting line clear corner finishing is very useful in model machining. The machining efficiency is high, and commands such as slotting rough machining are rarely used. Let’s analyze several main processing methods and characteristics:

1 Parallel processing

Parallel machining tool path is one of the most widely used machining methods. The projection of the tool path on the XY plane is parallel, while in the Z direction, there are different distributions as the surface changes. Parallel machining is divided into rough machining and fine machining.

There are two types of machining. Rough machining is processed in layers according to the blank allowance. Finish machining directly processes the specified surface. Parallel rough machining and finishing can be used in pairs or combined with other operations. Parallel machining toolpaths are most suitable for areas that are milled down on a shallow plane, but they will not be well milled in steep places.
The main parameters are:

1.1 Tool path error

The tool path error is the fitting error of the tool path and the geometric curve. The smaller the error value is set, the closer the processed surface is to the geometric model, but the programming and processing speed is lower. In order to improve the calculation speed and processing speed, the roughing does not involve forming accuracy at all, so its value can be slightly larger.

1.2 Line spacing

The line spacing is the maximum distance between two adjacent cutting paths. The setting value must be smaller than the diameter of the tool. The larger the value is set, the fewer the number of tool paths generated, and the rougher the processing result; the smaller the setting, the more the number of tool paths generated and the smoother the processing result, but the processing time for generating the tool path is longer.

1.3 milling angle

The machining angle refers to the angle between the tool path and the X axis, which can weaken the influence of steep curved surfaces.

1.4 Starting point of tool path

The starting point of the tool path is preferably a free space outside the blank to facilitate cutting, otherwise the system will select the nearest corner of the workpiece as the starting point of the tool path.

1.5 milling depth

The layered processing depth of three-dimensional roughing is set according to the milling ability of the tool, and the total machining allowance is generally set by incremental coordinates. This puts forward high requirements for the unification and setting of coordinates. Model processing also involves reversal secondary processing, and the unification of various benchmarks must be guaranteed.

Parallel finishing parameters have basically the same meaning as those in rough machining. Since finishing processing does not perform layered processing, there is no setting of layer feed amount and cutting/lifting method. The cutting allowance is very small during finishing, which allows the tool to cut along the ascending and descending direction of the curved surface.

2 Contour processing

There are two types of contour machining, rough machining and finishing, but only one layer is processed. The parameter setting of contour machining is basically the same as parallel machining, but the generated tool path is along the part with a given height in the Z direction.

The contour is processed. Contour machining is the best method for finishing steep walls, similar to parallel machining toolpaths, but the machining effect is not good at shallow planes, even if the shallow plane toolpath encryption option is selected. Therefore, contour processing can generally be combined with parallel processing.

3 Rough machining of curved surface grooving

Rough machining of curved surface grooving is one of the most widely used rough machining methods. Mastercam’s rough machining of grooves must specify the boundary, which requires that an auxiliary boundary be added in advance, and the boundary should be one tool diameter larger than the original boundary. When grooving on a curved surface, in order to avoid direct cutting, the circular arc spiral cutting is generally used. In fact, the cutting tool can be gradually lowered according to the appearance to avoid insufficient maneuvering room and empty knives.

The cutting force is very large during rough machining. The cutting depth, cutting width and cutting feed rate should be set according to the allowable values ​​of the tool and machine tool. Many research institutions are studying how to adjust the feed speed according to the actual cutting force of the machine tool. Israel’s OMAT company has developed GMAT technology to control cutting force.

OMAT technology is an index-controlled machine tool whose speed is automatically adjusted according to the cutting volume during the cutting process to ensure that the machine tool is always in full load operation. Give full play to the efficiency of machine tools to improve processing efficiency. Using GMAT technology combined with the characteristics of high-efficiency and high-precision high-speed cutting, the required cutting processing can be completed in a short processing time.

4 Projection processing

Projection machining has two types of rough machining and finishing. The existing tool path or geometry can be projected onto the selected surface to generate the tool path. It is often used for surface carving. The model material is soft and the finishing can be performed directly when the depth is not large.

5 Intersecting line clear angle finishing

“Pencil”‘ Intersecting Line Clear Angle Finishing is used to remove the residual material at the intersections between the curved surfaces. It is very useful in the processing of prototype models. It is often used after surface finishing. It can be processed with a small diameter ball knife or a flat knife. Intersection. The setting of the intersection line clear angle parameter is basically the same as that of other tool paths.

6 Surround equidistant finishing

Orbital equidistant machining is that the tool path moves tangentially along the surface of the part by one row at a time. The biggest difference from other processing methods is that parallel machining is controlled by the distance of the XY plane, and the contour machining is controlled by height, and the distance of the circular equidistant infeed According to the distance control in the three-dimensional space, it can be used as the final finishing method to process the entire part, and complete the area that the first two methods cannot process due to size limitations.

Summary

We discussed the main points and optimization measures of automatic programming on the Mastercam platform.
1) Conversion of CAD standard files
The conversion error of the CAD model is objective. Before automatic programming, the datum plane and datum line should be re-established. Lines and planes with matching requirements should be processed by copying the objects produced after the conversion. The converted objects cannot be regarded as completely the same.
The CAD model cannot be directly programmed for processing. The necessary lines and surfaces must be added according to the processing needs. When adding, the needs of high-efficiency and high-precision model processing should be considered. Prototype model processing should also consider the influence of boundary and worktable interference on surface processing.


2) The machining efficiency of CNC programs varies greatly, and the planning of the tool path is the key.
This chapter discusses the optimization measures of the programming process from the level of programming settings. Many default settings in Mastercam are designed based on the safe and stable operation of the machine tool. The material of the prototype model is soft and can be modified and improved. The cutting parameters should be based on the basic cutting of the tool and material. Speed ​​and basic feedrate are scientifically calculated and set.


This chapter makes a preliminary comparison and analysis of various tool paths. The efficiency and accuracy of 2D machining far exceed 3D machining. When programming, efforts should be made to make the actual movement path of the tool the shortest. On the basis of completing the machining task, it is not necessary to use all the blank materials. resection.

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