The demand for manufactured or machined parts, both standard, and custom is increasing in various industries, and CNC milling is the most preferred method for performing various techniques to achieve the desired shape and size. It has a high level of productivity and can perform difficult tasks with the highest precision. It can even perform repetitive and mundane tasks with the same accuracy and detail, regardless of the scale of complexity. The toolpath is essentially its planning mode, which helps finish the workpiece as needed.
Using CAD/CAM software technology, CNC machining shops can create the programs discussed in the article, which then transform complex designs into desired physical parts. If you’re new to CNC machining, the term „toolpath” can be confusing. The software provides a series of coordinates that the machine follows to meet the exact requirements of the material being machined. This is the trajectory that the cutting machine follows to obtain the correct geometry of the workpiece being developed. Today, almost all CNC machining techniques use this one, and CNC milling is no exception. Would you like to learn more about this topic? What is a toolpath mode? What factors affect patterns in CNC milling? If so, this article will answer all these questions in detail. After reading it, you will be up to date.
A brief overview of toolpath mode
There are many factors that affect feeds and speeds. As mentioned earlier, toolpaths operate as separate programs during machining. CAD and CAM technologies stimulate them, creating coordinated positions. The cutting tools follow these coordinates during operation, and this, in turn, allows you to detect toolholder mesh and workpiece alignment, calculate the speed of the operation and learn the details of other important parameters. CNC milling paths can be divided into 2D, 3D, 4-axis, or 5-axis, depending on the number of machine axes and how they are moved. Axis terminology can be confused with 2D, as there is a Z-axis value for the former. However, it is worth mentioning that it only represents the position of the tool at a certain depth and is constant during operation. That’s why 2D toolpath make sense since the cutting operation takes place only on the x and y axes.
Factors affecting toolpath mode in CNC machines
Below is a list of some common factors that affect tool path patterns in CNC milling. So let’s take a look at them. The first and most important of these to consider before starting work is the workpiece material, as it determines the mode of the machine. The workpiece material does not directly affect the feed rate but will have an extremely significant impact on the choice of tool size, material, machining method, etc. The geometry of the workpiece, such as shape and size, is reflected in the uniformity of the distribution of the machining allowance for the required part. Similarly, workpieces with optional blanks affect the distribution of development strategies and clamping methods. This will result in a different tool feed method, and consequently also has an indirect effect on the tool’s mode of operation. This may include adding additional forces to the cutting method, vibration variation, etc.
Another important point is the selection of the tool or tools themselves. This can include very different parameters, such as the material used, the length of the tool, the number of teeth on it, etc. These technical specifications determine the contact area and frequency between the workpiece and the machine. This, in turn, helps determine the volume per unit of finished material, wear rate, machine tool load, etc.
Routing determines the optimal sequence of operations to achieve the cutting targets. In addition, it determines the roughing lines, the sequence of machining areas and the partitions or dividing lines between semi-finishing and finishing. The desired intent can be achieved through various process paths, which determine the selection of the CNC machine tool’s program mode.
Proper work procedures are extremely important to obtain clean and precise parts when performing various CNC milling operations. Depending on the application requirements, different tool path strategies can be selected. This will increase machine life, overall cost efficiency and cycle time. Today, almost every CNC shop/workshop offers high-precision machining, as well as diverse, state-of-the-art tooling solutions. One of these is BDE manufacturing technology (BDE). With years of market experience and skilled personnel, the company meets customers’ needs in various industries through efficient CAD/CAM programming of complex parts.
Practice and methods of feed selection
When selecting a feed method, there are two points to consider: the length of machining time and whether the machining allowance is set uniformly. The circular cutting mode based on the shape and allowance of the workpiece is generally considered a relatively uniform cutting method. A characteristic of the inline cutting method is that the machining allowance is relatively uneven. To provide more clearance, increase the length of the tool path to make a circle of cuts around the border. The sizes of straight cutting tool paths are often short, and this is the case if the requirements for material inhomogeneity are not met. When uneven margins are taken into account to increase the length of the circular cutting path when the machining area boundary is large, the circular tool path around the boundary has a greater impact on the total machining time.
Horizontal cutting paths are generally more efficient than circular ones. It is easier to calculate the tool position through tool placement, which is also a big plus, by the way, it takes less memory. However, it is worth adding that in this case the tool must be used repeatedly. If you use a circular tool path, you will have to move the ring boundary and remove it from the self-intersection line frequently.
Selection by appearance features
The way a workpiece is machined depends on its shape. Using various machining designs, workpieces can be divided into flat surfaces with grooves or any shape. Row cuts are used to create grooves with a flat coating. These types of workpieces have large allowances because they are usually formed by roughing and turning, such as bases. In-line machining is an excellent way to improve the progress of a machine tool. Inline cutting is faster, more efficient, and provides a better work surface than circular cutting. Circular cuts are suitable for any surface shape. This is because the area is usually cast from solid material and the edges are not evenly distributed. In such cases, there are also higher precision requirements. The surface can be closer to its true form than when it has good machining properties.
Choosing a strategy for better feeds and speeds
Machining a part is usually divided into three stages: roughing, semi-finishing and finishing. Sometimes there is also a finishing stage. To ensure machining accuracy, it is important to separate the steps into reasonable segments. Traditional techniques are limited to only one function of the machine. Therefore, the boundaries of each step are displayed along the route. However, with CNC milling processes, these are blurred and can be mixed. The primary purpose of roughing is to reduce the amount of material removed in a given unit of time and to prepare the geometry of the workpiece for semi-finishing. Overlaying is often done by cutting rows and blending. The primary purpose of semi-finishing is to smooth the contour of the material and unify the surface finish allowance. The so-called „edging” method is commonly used. The geometric characteristics of the texture to be developed dictate the use of the internal cutting method, while the circumferential cutting method is used for edges and joints.
Choose a programming strategy for pocket toolpath
You should be able to achieve the desired machining in terms of precision and surface roughness, as well as reduce downtime and minimize the complexity of numerical calculations by choosing the right strategy. It is worth considering minimizing the amount of work we need to put into its preparation and programming. Here are some valuable considerations we need to keep in mind when planning:
- The in-line cutting method reduces tool to lift,
- For cavities with a flat shape, a given area can be divided by the in-line cutting method,
- The free-form circular milling method approximates the shape,
- Programming options depend on the size of the blank,
- The blank can be enlarged to make it easier to clamp. Alternatively, the free-form surface created by circular cutting can be converted to linear cutting,
- Semifinished parts can be extensively cut to improve machining efficiency.
Tool life can be improved by tool engagement in the cutter, CNC machining in various ways. Among others, with the help of the right program, proper material removal, polishing.