1. The influencing factors of nc tool selection
When choosing a tool types and specifications, mainly consider the following factors:
(1) the nature of the production
Here production nature refers to the batch size of the parts, mainly from the consideration on the tooling cost for the influence of the cutting tool selection.
In mass production when the use of special tools, for example, can be economical, but in single piece or small batch production, the choice is more suitable for some standard tools.
(2) types of machine tools
Used to complete the process of nc machine tools to the choice of cutting tool type (drilling, turning or milling cutter). In the guarantee system of workpiece and cutting tool system under the condition of good rigidity, allowed the use of high productivity tools, such as high-speed cutting tool and feed cutting tool.
(3) the nc machining program
Different CNC processing program can use different types of cutting tools. Such as processing can be used to drill hole and reaming drilling, drilling and boring cutter can be used to carry on the processing.
(4) the size and shape of the workpiece
Size and shape of the workpiece also affect the choice of the cutting tool types and specifications, such as special surface should use special tool to processing.
(5) the processing surface roughness
Machining surface roughness influence the structure shape of cutting tool and cutting parameter, such as casting rough milling processing, can use coarse milling cutter, finish-milling, had better use fine-tooth milling cutter.
(6) the machining accuracy
Machining accuracy affect the finishing tool types and structural shapes, such as the precision of the hole at the end of the treatment according to the hole can be used drilling, reaming drill, reamer, or boring cutter to process.
(7) the workpiece material
Workpiece materials will determine the selection of geometric parameters of cutting tool materials and cutting part, cutting tool material and workpiece machining accuracy, material hardness, etc.
2. The performance requirements of the numerical control cutting tools
Because of nc machine tool has high machining accuracy, high processing efficiency, processing process focus and fewer parts clamping characteristics, the use of CNC cutting tools is put forward higher request. Tell from the cutting tool performance, nc cutting tools shall be higher than that of ordinary machine tool used by the tool.
Choosing nc knives, should first should first choose standard tool, when it is necessary to choose a variety of high efficiency composite cutting tools and special cutting tools. In selection criteria, numerical control cutting tools should be combined with the actual situation, as far as possible choose all kinds of advanced cutting tools, such as indexable tool, solid carbide cutting tools, ceramic knives, etc.
When choosing a numerical control machine tool, but should also consider the following issues:
(1) the type, specifications, and precision of the nc cutter level should be able to meet the processing requirements, cutting tool material should be in line with the workpiece materials.
(2) cutting performance is good. In order to adapt to tools in rough machining or workpiece machining of difficult-to-machine materials can use large amount of turning and high feeding, cutting tool should be able to withstand high speed cutting and strong performance. At the same time, the same cutting tool in cutting performance and cutting tool life must be stable, so as to achieve according to the cutting tool service life of the tool change or by the CNC system to supervise and control the tool life.
(3) high precision. In order to adapt to the requirements such as high precision and automatic tool change CNC processing, the cutting tool must have high accuracy, such as some integral vertical milling cutter radial dimension precision up to 0.005 mm.
(4) high reliability. To ensure not happen in the nc machining tool accident damage and potential defects and affect the process is smooth, request tool, and with the combination of attachment must be have good reliability and strong adaptability.
(5) high durability. Nc machining tool, no matter in rough machining or finish machining, shall have higher durability than ordinary machine tool processing cutting tool used and to minimize the number of replacement or knife and the knife, so as to improve the processing efficiency of CNC machine tools and ensure the quality of machining.
(6) chip breaking and chip removal performance is good. Nc machining, the chip breaking and chip removal is not like ordinary machine tool processing in a timely manner by the artificial processing, chip easy winding on the tool and the workpiece, will damage the cutter and cut work-piece machined surface, even hurt and equipment accident, affects the processing quality and the safe operation of machine tool, cutting tool is required has good chip breaking and chip removal performance.
3. The selection method of cutting tool
Cutting tool selection is one of the important content of nc machining process, not only affects the processing efficiency of machine tool, but also directly affect the machining quality of parts. Because of nc machine tool spindle speed and the range is far higher than that of ordinary machine tool, and the main shaft output power is larger, so compared with traditional processing methods, puts forward higher requirements on nc machining tool, including high precision, high strength, good rigidity, durability, and the required size is stable, easy to install. Which requires the tool rational structure standardization, seriation, geometric parameters. CNC cutting tools is one of the prerequisite to enhance the efficiency of the machining, selection of it depends on the geometry of the parts processed material selection state, fixture and machine tool, cutting tool rigidity. Should consider the following aspects:
(1) according to the parts material selection tool cutting performance. Such as turning or milling high-strength steel, titanium alloy, stainless steel parts, suggest that choose better wearability indexable carbide cutting tools.
(2) according to the parts of the processing phase selection tool. Rough machining stage to remove allowance is given priority to, should choose good rigidity, low precision cutting tools, semi-finishing and finish machining stage to ensure the machining accuracy of parts and the quality of the products is given priority to, should choose high durability, high precision cutting tools, the early stage of the cutting tool used minimum accuracy, and finishing tool used in the highest accuracy. If rough, finishing the same cutting tool choice, suggest finishing out the tool down, at the beginning of rough machining because of finishing out of the tool wear condition for blade is mostly minor wear and tear, coating wear light, continue to use will affect the finishing machining quality, but have less effect on the rough machining.
(3) according to the characteristics of the machining area selection tool and geometry parameters. In the case of parts structure allows large diameter should be chosen, small length to diameter ratio of the cutting tool; Cutting thin walled, super thin wall parts center should have enough centripetal end milling cutter blade Angle, in order to reduce the cutting tool and the cutting force of cutting parts. Processing of soft materials such as aluminum, copper parts should choose when the rake Angle slightly bigger endmill, number of teeth is not more than 4 teeth.
Selection of cutting tools, to make the size of the cutter and the surface of the processed workpiece size. Production, peripheral contour plane parts processing, often adopt vertical milling cutter; When milling flat, choose the carbide blade milling cutter; When machining convex sets, groove, select HSS end mill; Rough surface or rough machining the hole, can select carbide tipped blade corn milling cutter; For some set of body surface and change the bevel contour shape processing, often adopts the ball end milling cutter, circular milling cutter, taper milling cutters and disc cutter.
In free-form surface machining, as a result of the ball end cutter end cutting speed is zero, therefore, in order to ensure the machining accuracy, cutting spacing generally small, so the ball head milling cutter is suitable for the surface finishing. And end milling cutter in surface machining quality and is much better than the ball head milling cutter in machining efficiency, therefore, on the premise of ensure parts processing but cut, roughing and semi-finishing surface, try to choose end milling cutter. Precision and cutting tool and cutting tool durability and price relationship is great, must pay attention that in most cases, choose good although increased the cost of tools, but as a result of the processing quality and processing efficiency, can make whole processing cost is reduced greatly.
On machining center, all cutting tools in advance in a knife library, all through the nc program choose knife and tool change instruction tool change accordingly. Must choose suitable for machine tool system specifications of the corresponding standard the handle, so that nc machining tool to quickly and accurately with knife library installed on the spindle or returned. Programmers should be able to know the structure of machine tool used to handle size, adjustment method and the content of the adjusting range, etc, to ensure that the set at the programming tools of radial and axial size, reasonable arrangement of the order of the knives.