Internal cooling system for precision turning and control method thereof

A control method of an internal cooling system for precision turning, wherein the internal cooling system for precision comprises a hydraulic circuit, an internal cooling turning tool and an electromagnetic control circuit;

• the hydraulic circuit comprises a hydraulic main circuit and several hydraulic branch circuits, and the main circuit comprises a hydraulic source with overflow valve (1), a filter (2), a pressure gauge (3), an adjustable throttle valve (4) and an air-cooled water cooler (5), wherein the hydraulic source with overflow valve (1), the filter (2), the adjustable throttle valve (4) and the air-cooled water cooler (5) are connected in sequence through hydraulic hoses, and the pressure gauge (3) is arranged between the filter (2) and the adjustable throttle valve (4);
• pipelines derived from the air-cooled water cooler (5) are divided into a first hydraulic branch circuit, a second hydraulic branch circuit and a third hydraulic branch circuit, wherein the first hydraulic branch circuit, the second hydraulic branch circuit and the third hydraulic branch circuit are respectively controlled by a first electromagnetic directional valve (6), a second electromagnetic directional valve (7) and a third electromagnetic directional valve (8), and are connected with the hydraulic main circuit through ferrule joints;
• a first internal cooling channel (91), a second internal cooling channel (93) and a third internal cooling channel (95) are formed in the internal cooling turning tool (9), and first pipe threads (92), second pipe threads (94) and third pipe threads (96) are respectively formed at the tail parts of the three channels;
• the pipe threads are matched with external threads at the tail parts of internal cooling sleeves (10), so as to realize the communication between each hydraulic branch circuit and the internal cooling channels of the turning tool;
• platen screws are penetrated through screw mounting holes (112) to fix a platen (11) on the internal cooling turning tool (9), and pressing force between the platen (11) and a turning insert (12) is adjusted to ensure that the turning insert (12) is tightly pressed against the internal cooling turning tool (9);
• a first internal cooling hole (97), a second internal cooling hole (98) and a third internal cooling hole (99) are formed in the tool nose of the internal cooling turning tool (9), and a cooling medium is sprayed out through the internal cooling holes to cool and lubricate the flank face of the turning insert (12);
• a first nozzle (111), a second nozzle (113) and a third nozzle (114) which are communicated with the internal cooling channels are arranged in the platen (11), and the cooling medium is sprayed out through the nozzles to cool and lubricate the rake face of the turning insert (12);
• wherein the method comprises the following steps:
• step 1, conducting parameterization representation for cutting edges of the turning tool;
• obtaining the coordinates of partial data points located on a major cutting edge, a minor cutting edge and a tool nose arc profile of the turning insert (12), and using a cubic non-uniform rational B spline to construct a turning tool cutting edge profile curve passing through each data point;
• step 2, analyzing a time-varying contact state related to a tool pose;
• firstly, adjusting the initial pose of the tool in a workpiece coordinate system according to the actual cutting process of a curved surface;
• establishing a tool coordinate system, wherein the XOY plane of the coordinate system is located in a cutting plane, the origin of the coordinate system is located at the center of symmetry of a rhombic insert, and the Y axis is collinear with the symmetric axes of the major cutting edge and the minor cutting edge;
• discretizing the turning tool cutting edge profile curve into a point set Po in the tool coordinate system;
• establishing a workpiece coordinate system, wherein the X′OY′ plane of the workpiece coordinate system is also located in the cutting plane, the origin of the coordinate system is located at the intersection point of a workpiece rotation axis and a workpiece clamping surface, and the Y′ axis is collinear with the workpiece rotation axis;
• conducting a matrix translation operation to make the turning tool position point, namely the center of the tool nose arc, coincide with the origin of the workpiece coordinate system, and conducting a matrix rotation operation to make the initial included angle between the major cutting edge of the tool and the Y′ axis become φ1, wherein the value range of φ1 is 60°-120°;
• after the rotation and translation operations, determining a discrete point set Pt for the cutting edge profile curve in the workpiece coordinate system by the following formula:
• P
• t
• =
• [
• cos
• ⁢
• (
• φ
• 1
• +
• k
• θ
• 2
• )
• -
• sin
• ⁢
• (
• φ
• 1
• +
• k
• θ
• 2
• )
• 0
• sin
• ⁢
• (
• φ
• 1
• +
• k
• θ
• 2
• )
• cos
• ⁢
• (
• φ
• 1
• +
• k
• θ
• 2
• )
• 0
• 0
• 0
• 1
• ]
• [
• 1
• 0
• -
• T
• x
• 0
• 1
• -
• T
• y
• 0
• 0
• 1
• ]
• ⁢
• P
• o
• (
• 1
• )
• where kθ is the included angle between the major cutting edge and the minor cutting edge of the turning tool, Tx is the x-coordinate of the center of the tool nose arc in the tool coordinate system, and Ty is the y-coordinate of the center of the tool nose arc in the tool coordinate system;
• secondly, calculating the intersection points of the cutting edges with a machined surface and a work surface, wherein the profile distance between two points is the contact length of the cutting edges in the current tool pose, which changes along with the change of the tool pose in the turning process of a curved surface component;
• two intersection points are formed between a cutting edge profile and a curved surface profile, wherein the intersection point of the major cutting edge or the adjacent tool nose arc with the curved surface profile is PN, and the intersection point of the minor cutting edge or the adjacent tool nose arc with the curved surface profile is PG, and point PN is the intersection point of the tool and the work surface;
• defining an auxiliary straight line according to the geometry of the curved surface component and cutting parameters, wherein the intersection point of the auxiliary straight line and each cutting edge of the turning tool is the intersection point PM of the tool and the machined surface;
• determining the slope of the auxiliary straight line by the following formula:
• k
• =
• tan
• [
• θ
• i
• -
• arctan
• ⁢
• (
• f
• 2
• ⁢
• R
• -
• 2
• ⁢
• ap
• )
• ]
• (
• 2
• )
• where θ1 is the included angle between the normal vector of the curved surface and the X′ axis in the current tool pose, ap is the cutting depth of the tool, f is the feed rate of the tool in per rotation, and R is the curvature radius of the work surface in the current cutting position;
• finally, discretizing a motion track of the tool, and traversing and calculating the contact state of the tool at each discrete tool position point to master the moving rule and moving range of the contact area of the tool in the turning process of the curved surface component;
• step 3, decomposing the contact state based on the analysis of the coverage area of the cooling medium;
• selecting the type of the cooling medium according to the material property of the curved surface component, and adjusting the temperature and flow rate of the cooling medium by the air-cooled water cooler (5) and the adjustable throttle valve (4);
• dividing the moving range of the whole contact area into three parts in sequence according to the spraying position and spraying range of the cooling medium from the pipeline of each channel, and defining the three parts as contact state 1, contact state 2 and contact state 3 respectively;
• calculating the cutting durations of the three contact states according to the tool feed speed and the geometrical characteristics of the curved surface component, and recording the cutting durations as t1, t2 and t3 respectively;
• therefore, the corresponding times after the end of the three contact states are respectively T1=t1, T3=t1+t3 and T5=t1+t2+t3;
• step 4, designing an electromagnetic control system oriented to an optimal tool cooling efficiency;
• completing the action control of the hydraulic circuit based on a designed electromagnetic control system, and pressing down a normally open key switch S, thus an electromagnetic coil Y1 is connected, and an indicator light L1 is lightened;
• at this moment, the first electromagnetic directional valve (6) is switched from a normally closed state to a working state, and the hydraulic main circuit is communicated with the first hydraulic branch circuit;
• the cooling medium passes through the first internal cooling channel (91), one part of the cooling medium passes through the cooling channel in the platen (11) and is sprayed out through the first nozzle (111) to realize the functions of cooling and chip breaking of the major rake face, and the other part of the cooling medium is sprayed out through the first internal cooling hole (97) to solve the problem of cooling and lubrication of the major flank face;
• after a duration T1, a time-delay closing coil C1 is switched on, an associated normally open contact C11 is closed, an electromagnetic coil Y2 is switched on, an indicator light L2 is lightened, and a time-delay closing coil C2 starts timing;
• at this moment, the second electromagnetic directional valve (7) is switched from a normally closed state to a working state, and the hydraulic main circuit is communicated with the second hydraulic branch circuit;
• the cooling medium passes through the second internal cooling channel (93), one part of the cooling medium passes through the cooling channel in the platen (11) and is sprayed out through the second nozzle (113) to realize the functions of cooling and chip breaking of the rake face near to the tool nose arc, and the other part of the cooling medium is sprayed out through the second internal cooling hole (98) to solve the problem of cooling and lubrication of the flank face near to the tool nose arc;
• in a transition process of the two contact states, the first hydraulic branch circuit and the second hydraulic branch circuit are communicated simultaneously, and the duration is T2;
• then the time-delay closing coil C2 is switched on, an associated normally closed contact C22 is switched off, the indicator light L1 is extinguished, the electromagnetic coil Y1 is powered off, the first electromagnetic directional valve (6) is reset under the action of a spring and restored to the normally closed state, and at this moment, only the second hydraulic branch circuit is communicated;
• after the hydraulic circuit is in continuous communication for a time of T3, a time-delay closing coil C3 is switched on, an associated normally open contact C33 is closed, an electromagnetic coil Y3 is switched on, an indicator light L3 is lightened, and a time-delay closing coil C4 starts timing;
• at this moment, the third electromagnetic directional valve (8) is switched from a normally closed state to a working state, and the hydraulic main circuit is communicated with the third hydraulic branch circuit;
• the cooling medium passes through the third internal cooling channel (95), one part of the cooling medium passes through the cooling channel in the platen (11) and is sprayed out through the third nozzle (114) to realize the functions of cooling and chip breaking of the minor rake face, and the other part of the cooling medium is sprayed out through the third internal cooling hole (99) to solve the problem of cooling and lubrication of the minor flank face;
• in a transition process of the two contact states, the second hydraulic branch circuit and the third hydraulic branch circuit are communicated simultaneously, and the duration is T4;
• then the time-delay closing coil C4 is switched on, an associated normally closed contact C44 is switched off, the indicator light L2 is extinguished, the electromagnetic coil Y2 is powered off, the second electromagnetic directional valve (7) is reset under the action of a spring and restored to the normally closed state, and at this moment, only the third hydraulic branch circuit is communicated;
• after the hydraulic circuit is in continuous communication for a time of T5, a time-delay closing coil C5 is switched on, an associated normally closed contact C55 is switched off, the indicator light L3 is extinguished, the electromagnetic coil Y3 is powered off, and the third electromagnetic directional valve (8) is reset under the action of a spring and restored to the normally closed state;
• at this moment, the whole-domain turning process of the curved surface component in the condition of the current cutting parameters is completed, the electromagnetic control circuit is reset, and none of the hydraulic branch circuits is communicated;
• the turning tool is retreated to the initial position, the action process of the hydraulic circuit can be repeated by pressing down the normally open key switch S again before the next turning is started, and the operation is continued until the turning of the curved surface component is completed.