numerical control machiningIn the process, the selection of knives andCutting volumeCAD/CAM technology has been developed, which makes it possible to make use of CAD design data directly during CNC machining, especially microcomputers connected to CNC machines, which allows the entire process of design, process planning and programming to be completed on the computer. This allows the entire process of design, process planning and programming to be completed on a computer, generally without the need to output files specifically designed to represent the process.
At this moment, many CAD/CAM software packages are equipped with automatic programming functions, this kind of software is usually in the programming interface to the process of planning the relevant issues to be prompted. Such as, tool selection, machining path planning, cutting amount of setting. Once the programmer has set the relevant parameters, the NC programme can be generated automatically and transmitted to the CNC machine to achieve the processing. Therefore, the selection of tools and the determination of cutting dosage in CNC machining are done under the state of human-computer interaction, which constitutes a significant contrast with ordinary machine tool machining, and also requires that programmers must masterTool SelectionAs well as the basic guidelines for the determination of the cutting amount, in the programming time to fully consider the characteristics of CNC machining. This paper discusses the problems of tool selection and cutting volume determination that must be faced in CNC programming, gives some principles and suggestions, and discusses the problems that should be noted.
I. Types and characteristics of commonly used tools for CNC machining
Generally speaking, CNC machining tools must be adapted to CNC machine tools with high speed, high efficiency and high degree of automation of these characteristics, which usually covers the general-purpose tools, general-purpose connection shanks, as well as a small number of specialised shanks. The role of the toolholder is to connect the tool and assembled in the machine tool power head, so gradually towards standardisation and serialisation. There are many ways to classify CNC tools. According to the structure of the tool can be divided into: ① integral; ② inlaid, it uses welding or machine clamped connection, machine clamped and can be divided into two cases of non-rotation and can be rotated; ③ special type, such as composite tools, vibration-damping tools, and so on. According to the manufacture of cutting tools to divide the material, can be divided into such categories: one for high-speed steel cutting tools; the second is carbide cutting tools; the third is diamond cutting tools; the fourth is made of other materials, such as cubic boron nitride cutting tools, ceramic cutting tools and so on. According toCutting processTo distinguish, and can be divided into: one for turning tools, including cylindrical, bore, threading, cutting tools and other types; the second is a drilling tool, covering drills, reamers, taps, etc.; the third is a boring tool; the fourth is a milling tool, and so on. This news shows that in order to adapt to the CNC machine tool for tool durability, good stability, easy to debug, with interchangeability and other aspects of the requirements, in recent years, machine clamped indexable tools have been widely used, in terms of the number of CNC cutting tools, it reaches the whole of the 30% to 40%, and in the amount of metal removal, which accounted for the total number of 80% to 90%.
Used for machining CNC tools, with the normal swing in the ordinary kind of machine tools used on top of the comparison, there will be a lot of different requirements, mainly with the following characteristics:
(1) Good rigidity (especially for roughing tools), high precision, low vibration resistance and thermal deformation;
(2) Good interchangeability for quick tool changes;
(3) High life, stable and reliable cutting performance;
(4) The size of the tool is easily adjustable to reduce tool change adjustment time;
(5) The tool shall be capable of reliably breaking or coiling chips to facilitate chip removal;
(6) Serialisation and standardisation for programming and tool management.
Second, the choice of CNC machining tools
Knife selection in the CNC programming at that time in the human-computer interaction situation to carry out, in accordance with the machine's processing capacity, the performance of the workpiece material, processing procedures, cutting dosage, as well as other relevant factors to the correct choice of tools and shanks, the tool selection of the general principle is to facilitate the installation and adjustment, good rigidity, durability and high precision, in order to meet the processing needs of the premise, try to select a shorter tool shank to improve the processing of the tool Rigidity.
Selection of tools, you have to let the tool size and the surface size of the workpiece to be processed, production, for the processing of the peripheral contour of the plane parts, often use end milling cutter, milling plane, should select the carbide inserts milling cutter, the processing of convex, groove, to choose high-speed steel end milling cutter, processing of rough surface or roughing holes, you can choose to set the carbide inserts of the maize milling cutter, for some of the three-dimensional type of face and the processing of variable bevel contour shape often use ball end milling cutter, ring milling cutter, cone milling cutter and disc milling cutter. For some three-dimensional surface and the processing of variable bevel profile, often use ball milling cutter, ring milling cutter, cone milling cutter and disc milling cutter.
There is a situation that when carrying out the operation of free-form surface machining, because the cutting speed of the end of the ball-end tool is zero, so in order to ensure that the machining accuracy meets the requirements, the cutting rows will usually be more dense, so the ball-end is often used for surface finishing. In addition, the flathead tool in the surface processing quality and cutting efficiency, better than the ball tool, so as long as the premise of ensuring that there will be no overcutting of this condition, no matter the surface of the roughing or finishing, should give priority to choose the flathead tool. In addition, the degree of durability and precision of the tool, and the price of the tool has a great correlation, it must be noted that in most cases, the selection of good quality tools, although the cost of the tool will increase, but the resulting quality of machining and machining efficiency can make the overall processing costs significantly reduced.
On a machining centre, a wide variety of tools are mounted in a tool magazine and are programmed to select and change tools at any time. Therefore, it is necessary to use a standard toolholder, so that drilling, boring, expanding, milling and other processes used in the standard tool, quickly and accurately loaded into the machine tool spindle or tool magazine up. Programmers should know the structure of the machine tool shank size, adjustment methods and adjustment range, in order to determine the radial and axial dimensions of the tool in the programming. Currently our machining centres use the TSG tooling system, which has a kind of straight shank, i.e. three specifications, and a kind of taper shank, i.e. four specifications, covering a total of 16 kinds of shanks for different purposes.
In the economic CNC machining, tool sharpening, measurement and replacement of most of the manual manual to carry out, which takes up auxiliary time is relatively long, so ah, must be reasonable to arrange the order of the tool. Generally speaking, we must follow these principles: First, try to reduce the number of tools; Second, a tool clamped after the completion of all the parts of the processing it can be carried out; Third, roughing and finishing tools to be used separately, even if it is the same size and specifications of the tool; Fourth, first milling and then drilling; Fifth, first to do the surface finishing, and then after two-dimensional contouring finishing; Sixth, under the conditions of the possibility, to make use of the CNC machine as much as possible. To make use of the automatic tool change function of CNC machine tools as far as possible, so as to improve productivity and so on.
Third, CNC machining cutting volume determination
In roughing, the principle of reasonable choice of cutting is generally to improve productivity as the main goal, but also to take into account the economy and the cost of machining; while in semi-finishing and finishing, it should be in the premise of ensuring the quality of machining, while taking into account the efficiency of cutting, economy and cost of machining. Specific values need to be based on machine instructions, cutting manuals, and combined with experience to determine.
(1) depth of cut t, in the machine tool, workpiece and tool rigidity allows the case, t is equivalent to the machining allowance, which is an effective measure to enhance productivity, in order to ensure that the machining accuracy and surface roughness of the parts, usually should be reserved a certain amount of allowance for finishing, CNC machine tools can be slightly smaller than the general machine tool finishing allowance.
(2) cutting width L, usually, L and tool diameter d shows a proportional relationship, and L and the depth of cut shows an inversely proportional relationship, in the economic CNC machining, the general range of values of L is such: L is equal to (0.6 to 0.9) multiplied by d.
The Joe Xing fairy is a good example of a tool. Increasing v is an initiative to increase productivity, however, v is closely related to tool durability. As v increases, tool durability decreases dramatically, so the selection of v is mainly dependent on tool durability. In addition, the cutting speed and processing materials also have a great correlation, for example, with end milling cutter milling alloy just, v can be used about 8m/min; and with the same end milling cutter milling aluminium alloy, v can be selected more than 200m/min.
(4) The speed of the spindle, measured in revolutions per minute (r/min). It is usually selected according to the cutting speed v. And the formula is this:
Where, d is the diameter of the tool or workpiece (mm).
CNC machine tool control panel, usually equipped with a spindle speed adjustment switch, that is, the multiplier switch, in the machining process, the spindle speed to carry out the adjustment of the whole times.
Feed rate vF, vF should be selected according to the requirements of the machining accuracy of the parts, but also according to the requirements of the surface roughness to choose, and in accordance with the tool and workpiece materials to choose, vF increase can improve productivity, machining surface roughness requirements of the low, vF can be selected to be a little larger in the process of machining, vF can be manually adjusted with the help of the machine tool control panel on the repair switch, but the maximum feed rate will be limited by equipment rigidity, but also the feed system performance and other limitations. However, the maximum feed rate will be limited by the rigidity of the equipment, but also by the performance of the feed system and other limitations.
CNC programming is one of the key issues in CNC machining due to the wide use of CNC machines in production. CNC programming, the need for human-computer interaction in the state, instant selection of tools, to determine the amount of cutting. Therefore, the programmer must be familiar with the tool selection method, as well as cutting amount to determine the principle, so as to ensure the quality of parts processing and machining efficiency, give full play to the advantages of CNC machine tools, to enhance the economic efficiency of enterprises and production level.
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