CNC numerical control plunge milling processing method
CNC plunge milling greatly improves cutting efficiency and tool life
Much of the significant advances in improving metal cutting efficiency are the result of a joint effort of tool manufacturers, machine tool builders and software developers. Plunge milling (Z-axis milling) machining is a good example.
During the plunge milling process, the rotating tool cuts directly into the workpiece along the Z-axis direction, and retracts in the Z-axis direction, then traverses a distance in the X-axis or Y-axis direction, and then overlaps with the previous cutting portion. Cut vertically to remove more workpiece material.
Plunge milling has many benefits. Especially in long overhang machining (such as milling deep cavity), the traditional face milling method (ie milling from one side of the workpiece to the other side) has to reduce the cutting in order to minimize the lateral forces that cause chattering. speed. In the case of plunge milling, the cutting force is directly transmitted to the machine spindle and table, so that a much higher metal removal rate than conventional milling is obtained. According to AMT Software, the company's Prospector CAM software package incorporates the plunge-cutting function, which reduces the metal removal rate by at least 50% compared to traditional planar roughing with button-type face milling cutters.
Since plunge milling minimizes lateral loads on machine components, it can be used on old or light machine tools with insufficient rigidity to increase productivity. Doosan Machine Tool's marketing manager, John Ross, agrees that plunge milling can reduce the cutting forces acting on low-performance machines, but adds that the new machine tools that are structurally designed to facilitate plunge milling can maximize The advantages of this process. He pointed out that since the cutting force is directly transmitted to the machine tool spindle and table, it can minimize the problems caused by the workpiece clamping is not strong.
Bill Fiorenza, product manager for mold production at Ingersoll Tooling, says plunge milling helps reduce the heat of cutting in the incoming tool and workpiece. He said, “In the case of plunge milling, there is not much heat transferred into the workpiece, because the speed of cutting in and out of the workpiece is very fast when the tool rotates. Only a small part of the moving step is in contact with the tool.”
This feature is particularly advantageous when cutting difficult materials such as stainless steel, superalloys and titanium alloys. Fiorenza explained in the plug-in demonstration, “Usually, the temperature of the metal chips is very high, you can even heat a sandwich in the chip pile. However, when the plunge machining is finished, you can put your hand right away. On the workpiece, it feels cooler when touched.” Reducing the heat of cutting not only extends tool life, but also minimizes workpiece distortion.
[Design features of the plunge cutter]
Tool manufacturers have developed a variety of plunge cutters that take full advantage of the technology of plunge milling. Meyers of Seco Tools said that the cutting forces of such tools are basically directly transmitted back to the Z axis. The geometry of the plunge cutter is very similar to that of a 90° square shoulder cutter. The difference is that the front and rear faces of the plunge insert are offset by a few degrees, possibly 87° instead of 90°. “If you use a 90° milling cutter to insert the side wall down, the entire cutting edge of the insert will rub against the side wall. If the tool front angle is 87°, there is a clearance between the cutting edge and the workpiece sidewall.” The plunge cutter should be cut with the cutting edge at the bottom of the insert to avoid cutting on the side of the insert, because the transition from the bottom to the side is the weakest part of the insert, and machining with the side of the insert can cause radial cutting forces that can cause vibration.
[Factors to be considered for CAM plunge milling]
Fiorenza pointed out that although the application of the plunge-cutting technology has been at least 15 years old, in recent years, the processing shop is becoming more and more aware that plunge milling can achieve higher material removal rates and programming due to the path of the pass. And verification has become easier, and the application of plunge milling has become easier than in the past. More and more CAM systems have been developed specifically for the algorithm of plunge milling. In addition, with the cutting simulation software, the shop floor can verify its reliability before running the plunge milling program. Fiorenza said, “You really need to verify the movement of the tool along the path of the tool, because the dedicated plunge cutter is usually not the center tool.” When using a non-center tool, if the selected step is not suitable, or it is not clear The machining allowance of the workpiece may cause a knife.
[Plug Milling and Large Feed Milling]
Plunge milling is a metal cutting strategy with high productivity. The choice of whether to use this technology or other milling strategies depends on a number of factors.
In order to maximize the advantages of plunge milling, a dedicated plunge cutter and careful CAM programming are required. In many cases, high feed milling can be an easier alternative to plunge milling. Large feed milling cutters are basically straight edge milling cutters with large front angles. The large front angle makes the chips thinner, and in order to maintain sufficient chip thickness, the feed rate must be increased. The high-feed milling cutter quickly cuts metal material at high feed rates and small depths of cut, while minimizing lateral loads on machine tools and tools.
[Select the right plunge milling machine]
While general-purpose machines have the advantage of “one machine multi-purpose”, in order to maximize productivity (and reduce distortion), the use of dedicated machine tools is often a better choice. Doosan Machine Tool Co., Ltd., which manufactures vertical machining centers (VMC) and horizontal boring and milling machines, offers a wide range of machine tools ranging from light tapping centers to high-speed five-axis machining centers for heavy-duty cutting of molds. Metal processing WeChat, the content is good, it is worthy of attention. Marketing manager John Ross said the company can tailor machine tools for different processes (and even different geographies). For example, some machines use linear guides, while others use stronger hard rails. “When we enter the market for cutting light materials in some parts of California, the linear guide machine is just right. When we enter the market for machining aerospace materials and superalloys in the Midwest, users need to be able to withstand large cutting forces. A more rugged hard-rail machine."
The high-speed die-machining machine with linear guides excels in the rapid removal of a small amount of workpiece material, and the use of plunge milling technology can further improve its roughing capability. However, this machine is less capable of withstanding chip loads than hard-rail machines.