1. The impact of processing technology on the quality of parts processing
Machining process specifications generally include the following contents: the process route of workpiece processing, the specific content of each process, and the equipment and processes used. Inspection items and inspection methods of equipment and workpieces, cutting quantities, time quotas, etc. We mainly analyze from the following points.
1. Equipment used in each process
The equipment used in CNC turning is mainly cutting tools. Cutting tools of different materials and different angles have a greater impact on the processing quality. During the cutting process, on the one hand, the cutting tool is subject to high temperature, high pressure and severe friction, which requires high hardness, good wear resistance and heat resistance; on the other hand, it is subject to impact and vibration, requiring good plasticity and toughness. Therefore, it is necessary to analyze the workpiece material and specific processing stages, and select the appropriate tool material to improve the processing quality.
Commonly used tool materials on the market include high-speed steel, carbide, ceramic materials and super-hard materials. The main advantages of high-speed steel are that it is easy to sharpen and has good strength and toughness. High-speed steel is often used in drill bits, taps, saw blades, hobs, gear shaper cutters, broaches and other precision tools. It is especially suitable for manufacturing complex thin edges and impact resistance. of metal cutting tools. Cemented carbide is made of carbide (WC, TiC) micron powder of high hardness refractory metal as the main component, with cobalt (Co), nickel (Ni), and molybdenum (Mo) as binders. Powder metallurgy products sintered in reduction furnaces. There are two types of commonly used cemented carbide: YG (tungsten-cobalt) and YT (tungsten-titanium-cobalt). Their heat-resistant temperature ranges from 800 to 1,000°C. They are much harder, more wear-resistant, and more heat-resistant than high-speed steel. The allowable cutting speed is 3 to 10 times higher than that of high-speed steel, while coated carbide is 2 to 10 times higher than uncoated carbide. The disadvantage of this material is that it is brittle, afraid of impact and vibration, and is more difficult to grind than high-speed steel. , cutting fluid cannot be used during sharpening, and it is also suitable for processing non-ferrous metals and fiber layer materials.
For tool preparation, in addition to the correct selection of tool materials, the reasonable selection of tool geometric angles and the reasonable use of tool tip transition shapes are very important to improve processing quality. The geometric angles of turning tools include main declination angle, Tool tip angle, secondary deflection angle, edge inclination angle, rake angle, relief angle and secondary relief angle. The entering angle affects the strength of the tool tip and the cross-sectional shape of the cutting layer. When turning slender shafts and thin-walled parts, in order to prevent the radial cutting force from causing bending deformation of the workpiece, the entering angle should be larger (such as 90°); the end face , the main deflection angle of the step surface turning tool is about 93°; for rough turning of general workpieces, when the main deflection angle is 75°, the strength and heat dissipation performance of the tool are the best. The tool tip angle is a major angle in thread turning tools. As a forming tool, the tip angle directly determines the tooth shape. For ordinary thread turning tools, when the edge inclination angle is 10°, the tool tip angle is 59°16′, and the tool tip angle is 59°16′. The larger the radius of the tip arc, the finer the surface roughness produced by the turning tool, the larger the front and back angles of the tool, the sharper the tool, and the finer the surface, but the strength becomes worse.
2. Reasonable selection of cutting amount
Rational selection of cutting amount is crucial to improving the processing quality of CNC lathes. Cutting amount is the general term for all motion parameters during cutting, including cutting speed. , feed amount and back cutting amount. Determination of the back cutting amount ap: When the stiffness of the process system and the power of the machine tool allow, select a larger back cutting amount as much as possible to reduce the number of feeds. When the precision requirements of the parts are high, you should consider leaving a finishing allowance. The finishing allowance is generally smaller than that left in ordinary turning, and is often 0.1 to 0.5 mm. Feed f: The selection of feed f should be compatible with the amount of back cutting and the spindle speed. On the premise of ensuring the processing quality of the workpiece, a higher feed speed can be selected. Determination of the spindle speed n: The spindle speed when bare turning the outer circle. The spindle speed when bare turning the outer circle should be determined according to the diameter of the part to be processed and the cutting speed allowed by the conditions such as the part and tool material and the processing properties.
3. Selection of workpiece clamping method
In addition to the general shaft parts that are directly clamped with a three-jaw self-centering chuck, for some special parts, the clamping must be reasonably selected. Method, otherwise it will have a negative impact on the quality of parts processing, and the advantages of high-precision machining of CNC lathes cannot be exerted. When turning slender shaft parts, due to poor heat dissipation conditions of the workpiece, the temperature rises and the axial thermal deformation causes a large elongation. If the "one clamp, one top" method is used for clamping, the tailstock top cannot be used. Fix the top, otherwise the slender shaft is prone to bending and deformation. The scientific and reasonable clamping method is to use steel wire transition clamping. In addition, a center frame or a tool rest can be installed in the middle, and it is pressed tightly during the support adjustment of the tool rest. The force should be moderate. If there is a gap, the purpose of improving the rigidity of the workpiece will not be achieved. If the pressing force is too large, the surface of the slender shaft will appear "bamboo" shaped after processing, affecting the cylindricity. In order to prevent the workpiece from deforming due to radial clamping force when turning thin-walled workpieces, axial clamping, split ring transition clamping or soft claw clamping can be used. In addition, a thicker process can be left at one end. flange. When turning the crankshaft, a center frame can be placed in the middle to increase the rigidity of the workpiece to prevent deformation due to the influence of cutting forces.
2. Tips for improving the processing quality of CNC lathes
In addition to requiring the operator to have strong theoretical knowledge and necessary operating skills, processing parts with CNC lathes also requires the operator to have strong theoretical knowledge and necessary operating skills. Quality also requires operators to use machine tools flexibly and skillfully.
1. Eliminate the influence of the tool tip on different processing surfaces
When the turning tool processes surfaces at different positions, the offset value of the tool tip is different. For example, the No. 1 turning tool number is T01, one tool tip turns the outer circle, and the other tool tip turns the end face. The tool setting value of the outer circle tool tip is input into the offset number "T0001", then when programming the outer circle turning tool: In "T0101", the end-face tool tip setting value is input into the offset number "T0002", then the command when programming the end-face turning tool is "T0102". It can be seen that one turning tool acts as two turning tools and can be used indirectly. The tool magazine capacity of the rotary tool holder is expanded, and the tool angle is better selected.
2. Effective use of kinetic energy of "Tool tip arc radius compensation"
There is a "Tool tip arc radius compensation" function in the CNC system, which is suitable for the arc of shaft parts. The guarantee of surface machining accuracy is very effective and greatly reduces the process system error. The tool tip with arc radius is an imaginary point in a space. CNC programming is based on this imaginary point. When actually cutting an arc surface, the actual cutting points of the tool are the actual distribution points on the tool tip arc, which will inevitably cause overcutting on one side and undercutting on the other side. When encountering the tool tip arc radius compensation function (i.e. G41 , G42 and G40), can perform calculations and always ensure that the current tool tip point is the tangent point between the tool arc and the theoretical outer circle contour. This function is simple, effective and very important when used on CNC lathes.
3. Reasonable use of tool "wear"
Whether it is mass production or small batch production per unit, when CNC lathes process workpieces, there must be a process of processing test pieces. How to To ensure the processing dimensional accuracy quickly and accurately, the tool compensation function is now added to the CNC lathe system, which can effectively realize the rapid adjustment of the workpiece size.