Magnetic shear thickening nanofluid micro-lubrication method and device

Abstract

This invention discloses a method and apparatus for micro-lubrication of magnetic shear-thickening nanofluid, belonging to the field of micro-lubrication and cooling in machining. The method is based on a micro-lubrication system, which includes an air pump, a pressure valve, a Rank-Hillsch vortex tube, a reservoir, a reciprocating pump, a flow controller, and a micro-lubrication nozzle. The reciprocating pump pressurizes and delivers the magnetic shear-thickening fluid from the reservoir to the micro-lubrication nozzle. Compressed air, after being pressurized by the pressure valve, enters the vortex tube for diversion. The hot airflow at the hot end of the vortex tube preheats the fluid in the reservoir, shear-thinning it to improve its flowability. The low-temperature cold air at the cold end mixes with the fluid within the nozzle. Under the influence of the built-in magnetic field in the nozzle, a low-temperature nano-atomized particle cluster spray is formed and directed towards the machining area. Upon contact with the workpiece, the spray transforms into the magnetic shear-thickening fluid, forming a lubricating film at the tool-workpiece interface, achieving efficient cooling and lubrication and improving machining quality.

Description

Technical Field

[0001] This invention provides a method and apparatus for micro-lubrication of magnetic shear-thickened nanofluids, belonging to the field of micro-lubrication and cooling in machining. Background Technology

[0002] With the rapid development of high-end manufacturing fields such as aerospace, defense, precision instruments, and biomedicine, the application ratio of parts made from difficult-to-machine materials such as titanium alloys, high-temperature alloys, engineering ceramics, and cemented carbide has significantly increased. Achieving high-efficiency and high-quality milling, turning, and grinding of these materials has significant engineering value. Machining, as a crucial link in the precision forming and surface quality control of parts, determines the dimensional accuracy and surface integrity of the workpiece. However, difficult-to-machine materials have poor thermal conductivity and high processing temperatures during cutting, which can easily lead to problems such as thermal damage to the workpiece surface, phase transformation, and residual tensile stress. Currently, micro-lubrication technology is widely used in the machining of difficult-to-machine materials due to its advantages such as low cutting fluid consumption, environmental friendliness, and the ability to balance cooling and lubrication.

[0003] Patent application CN202210053005.5, entitled "An Intelligent Cooling and Lubrication Device and Method for CNC Machine Tools," proposes an intelligent cooling and lubrication device integrating eddy current cooling and micro-lubrication. By connecting the cold end of the eddy current cooling component to a gas-liquid mixing component, it achieves the mixing and atomization of low-temperature compressed air and cutting fluid, resulting in good cooling and lubrication effects. However, in this method, the hot airflow discharged from the hot end of the eddy current tube is directly discharged after passing through a temperature regulator, without recovering and utilizing residual heat, resulting in low overall energy utilization efficiency. Patent application CN201710005238.7, entitled "Supersonic Nozzle Eddy Current Tube Cooling and Nanofluid Micro-Lubrication Coupled Supply System," proposes a supersonic nozzle eddy current tube cooling and nanofluid micro-lubrication coupled supply system. It increases the nozzle exit velocity of the eddy current tube through a supersonic nozzle and employs enhanced heat exchange measures on the eddy current tube heat pipe to improve cooling efficiency, achieving good cooling performance and tribological characteristics. However, this method does not involve the technical means of using residual heat to preheat and reduce the viscosity of non-Newtonian fluids to improve their fluidity. Application number CN202010148381.3, patent "A Nanofluid Magnetic Grinding Fluid and Magnetic Field Assisted Micro-Lubrication System" proposes a nanofluid magnetic grinding fluid and a magnetic field assisted micro-lubrication system. It utilizes iron oxide nanoparticles adsorbed on the graphene surface to form magnetic lubricating mixed particles. Under the action of a magnetic field assisted device, the magnetic lubricating mixed particles in the spray are evenly spread on the workpiece processing area, achieving a good lubrication and cooling effect. However, this method requires the configuration of an additional magnetic field assisted device, the system structure is complex, and it does not use eddy current tubes for hot and cold flow separation, so it cannot simultaneously achieve low-temperature cooling of the processing area and preheating and viscosity reduction of the lubricating medium.

[0004] Existing micro-lubrication grinding systems generally suffer from difficulties in fluid delivery and unstable atomization when dealing with high-viscosity non-Newtonian fluids. Furthermore, the lubricating film in the machining zone is prone to rupture under high temperature and pressure during processing, leading to lubrication failure. In addition, existing systems lack effective means of utilizing the waste heat from the hot end of the vortex tube, resulting in low overall energy utilization efficiency. To address these issues, this invention proposes a magnetic shear-thickening nanofluid micro-lubrication method and apparatus, which has significant theoretical and practical value for lubrication and cooling during the machining of difficult-to-machine materials. Summary of the Invention

[0005] This invention provides a method and apparatus for micro-lubrication of magnetic shear-thickening nanofluids. Compressed air is supplied by an air pump, and after pressure regulation by a pressure valve, it is split between a Rank-Hillsch vortex tube and a micro-lubrication nozzle. A reciprocating pump pressurizes the magnetic shear-thickening fluid in the reservoir and delivers it to the micro-lubrication nozzle, overcoming the high viscosity resistance of non-Newtonian fluids. The hot airflow from the hot end outlet of the Rank-Hillsch vortex tube is preheated in the reservoir, causing a shear-thinning effect to improve fluidity. Simultaneously, the low-temperature cold air from the cold end outlet mixes with the fluid within the nozzle, forming a low-temperature nano-atomized particle cluster spray under the influence of the nozzle's built-in magnetic field and being sprayed onto the processing area. Upon contact with the workpiece, the spray transforms into magnetic shear-thickening fluid, forming a robust lubricating film at the tool-workpiece interface, achieving efficient cooling and lubrication, and improving the surface quality of the processed material.

[0006] This invention provides a method and apparatus for micro-lubrication of magnetic shear-thickened nanofluids, and the technical solution provided is as follows:

[0007] The aforementioned method for micro-lubrication of magnetic shear-thickened nanofluids can be achieved through the following steps:

[0008] (1) A processing system is constructed, the system including an air pump, a pressure valve, a Rank-Hills vortex tube, a liquid storage tank, a reciprocating pump, a flow controller, a micro-lubrication nozzle, a cutting tool, a fixture and a force gauge; the liquid storage tank is equipped with a stirring device, and the Rank-Hills vortex tube has a cold end outlet and a hot end outlet.

[0009] (2) Clamp the workpiece to be processed on the fixture, prepare a suitable magnetic shear thickening fluid according to the material properties and surface processing requirements of the workpiece, and select the tool type and processing parameters;

[0010] (3) Based on the geometric characteristics of the workpiece and the processing requirements, plan the processing path, spindle speed, feed rate, cutting depth and micro-lubrication supply parameters, input the parameters into the control system, and set the control range of fluid pressure, flow rate and vortex tube hot end temperature during processing.

[0011] (4) According to the set processing parameters, the control system controls the air pump, reciprocating pump, flow controller and pressure valve to work together and start processing according to the planned processing path;

[0012] (5) During the processing, compressed air enters the Rank-Hills vortex tube after being regulated by the pressure valve and is divided into two paths: the first path exits the hot end outlet of the Rank-Hills vortex tube to preheat the magnetic shear thickening fluid in the storage tank, and uses the heat energy to cause the fluid to undergo shear thinning effect, improve the fluid flow and promote the suction efficiency of the reciprocating pump; the second path exits the cold end outlet of the Rank-Hills vortex tube to exit the cold air, enters the air inlet of the micro-lubrication nozzle, and mixes with the magnetic shear thickening fluid after being pressurized by the reciprocating pump and regulated by the flow controller in the nozzle. Under the action of the magnetic field generated by the built-in magnetic pole of the nozzle, a low-temperature nano-atomized particle cluster spray is formed.

[0013] (6) During the processing, the micro-lubrication nozzle sprays low-temperature nano-atomized particle clusters onto the contact interface between the tool and the workpiece fixed by the fixture. After the spray comes into contact with the workpiece surface, it is transformed into a magnetic shear thickening fluid under the action of high shear rate and temperature field in the processing zone. The viscosity increases sharply, forming a solid lubricating film to achieve lubrication. At the same time, the micro-nano particles in the fluid enhance the ability to carry and remove chips. The cutting force in the processing zone is monitored in real time by a force measuring instrument, and the cutting temperature is controlled by adjusting the cold end temperature of the vortex tube and the fluid flow rate.

[0014] The hot end outlet of the Rank-Hillsch vortex tube is connected to the heat exchange structure on the outer wall of the storage tank through a pipeline. The temperature and flow rate of the return hot air are controlled by adjusting the opening of the hot end valve, so as to precisely control the temperature of the magnetic shear thickening fluid in the storage tank and keep it in the optimal shear thinning temperature range.

[0015] The reciprocating pump is a plunger pump, and its working pressure is monitored in real time by a pressure gauge. Feedback control is used to maintain a constant fluid delivery pressure to ensure a continuous and stable supply of non-Newtonian fluid in long-distance pipelines.

[0016] The magnetic shear-thickening fluid is a non-Newtonian fluid containing nanodiamond particles, nanomagnetic particles, nanosilica particles, and additives. Under the action of high shear rate in the processing zone, its viscosity increases sharply, forming a strong lubricating film.

[0017] The cold end outlet temperature range of the Rank-Hills vortex tube is -5°C to 15°C. The low-temperature nano-atomized particle cluster spray formed by the mixing of low-temperature cold air and fluid quickly removes heat from the processing area by enhancing convective heat transfer, thus inhibiting thermal damage to the workpiece surface.

[0018] The storage tank is equipped with a stirring device to prevent magnetic particles from settling and to maintain fluid homogeneity.

[0019] A magnetic shear-thickening nanofluid micro-lubrication device is used to implement the method described in any of the above-mentioned embodiments, comprising: an air pump, a pressure valve, a Rank-Hillsch vortex tube, a storage tank, a reciprocating pump, a flow controller, and a micro-lubrication nozzle; the outer wall of the storage tank is provided with a heat exchange structure, which is connected to the hot end outlet of the vortex tube through a pipeline; the micro-lubrication nozzle has a liquid inlet and an air inlet, and the cold end outlet of the vortex tube is connected to the air inlet of the nozzle, for mixing the magnetic shear-thickening fluid with low-temperature compressed air to form a low-temperature nano-atomized particle cluster spray and spraying it into the processing area.

[0020] The present invention has the following significant advantages: 1. The magnetic shear-thickening nanofluid micro-lubrication method and apparatus of the present invention uses a reciprocating pump to pressurize and transport high-viscosity magnetic shear-thickening fluid, solving the problem of the difficulty in stably supplying non-Newtonian fluids in traditional micro-lubrication systems. 2. The magnetic shear-thickening nanofluid micro-lubrication method and apparatus of the present invention utilizes the residual heat from the hot end outlet of the Rank-Hillsch vortex tube to preheat the magnetic shear-thickening fluid in the storage tank, causing the fluid to undergo a shear-thinning effect. This improves fluid flowability while achieving energy reuse and improving system energy efficiency. 3. The magnetic shear-thickening nanofluid micro-lubrication method and apparatus of the present invention uses low-temperature cold air provided from the cold end outlet of the vortex tube to mix with the fluid to form a low-temperature nano-atomized particle cluster spray. After the spray contacts the workpiece, it transforms into magnetic shear-thickening fluid to form a strong lubricating film, significantly enhancing the cooling and lubrication capabilities of the machining area, effectively suppressing thermal damage to the workpiece surface, and improving the surface quality and tool life. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the milling structure of a magnetic shear-thickening nanofluid micro-lubrication method and device according to the present invention.

[0022] Figure 2 This is a schematic diagram of the internal structure of the micro-lubrication nozzle of a magnetic shear-thickening nanofluid micro-lubrication method and device according to the present invention.

[0023] Figure 3 This is a schematic diagram of the grinding structure of a magnetic shear-thickening nanofluid micro-lubrication method and device according to the present invention.

[0024] Figure 4 This is a schematic diagram of the turning structure of a magnetic shear-thickening nanofluid micro-lubrication method and apparatus according to the present invention. Detailed Implementation

[0025] Example 1: Milling process, combined with Figure 1 and Figure 2 illustrate:

[0026] (1) The workpiece is milled. The micro-lubrication system is selected from the milling configuration. The cutting tool (1-5) is a carbide milling cutter. The fixture (1-7) is a precision flat-jaw vise. The magnetic shearing thickening fluid (1-2) is a non-Newtonian fluid containing nano-diamond particles, nano-magnetic particles, nano-silica particles and additives.

[0027] (2) Clamp the workpiece (1-6) to be processed on the fixture (1-7). Based on the material properties of the workpiece (1-6) and the milling requirements, plan the milling path, spindle speed, feed rate, depth of cut and micro-lubrication supply parameters. Input the processing parameters into the control system and set the control range of fluid pressure, flow rate and hot end temperature of the Rank-Hills vortex tube (1-10) during processing.

[0028] (3) According to the set processing parameters, the control system controls the air pump (1-4), reciprocating pump (1-1), flow controller (1-9) and pressure valve (1-14) to work together and start processing according to the planned milling path;

[0029] (4) During the processing, compressed air is regulated by pressure valve (1-14) and enters Rank-Hillsch vortex tube (1-10) and is divided into two paths: the first path is the hot air flow discharged through the hot end outlet (1-12) of Rank-Hillsch vortex tube (1-10) to preheat the magnetic shear thickening fluid (1-2) in the storage tank (1-3) so that the fluid undergoes shear thinning effect to improve fluidity; the second path is the cold air flow discharged through the cold end outlet of Rank-Hillsch vortex tube (1-10) and mixes with the magnetic shear thickening fluid (1-2) after being pressurized by reciprocating pump (1-1) and regulated by flow controller (1-9) in the micro-lubrication nozzle (1-13). Under the action of the magnetic field generated by the built-in magnetic pole (2-1) of the nozzle, a low-temperature nano-atomized particle cluster spray (2-2) is formed.

[0030] (5) During the machining process, the micro-lubrication nozzle (1-13) sprays low-temperature nano-atomized particle clusters onto the contact interface between the milling cutter and the workpiece (1-6) fixed by the fixture (1-7). After the spray comes into contact with the surface of the workpiece (1-6), it transforms into a magnetic shear thickening fluid under the action of high shear rate and temperature field in the milling zone. The viscosity increases sharply, forming a solid lubricating film to achieve machining lubrication. At the same time, the micro-nano particles in the fluid enhance the ability to carry and remove chips. The cutting force in the milling zone is monitored in real time by the force gauge (1-8), and the cutting temperature is controlled by adjusting the cold end temperature of the vortex tube and the fluid flow rate, thereby achieving precise and efficient milling of the workpiece.

[0031] Example 2: Grinding process, combined with Figure 2 and Figure 3 illustrate:

[0032] (1) Grinding is performed on the workpiece. The micro-lubrication system is selected for grinding. The workpiece (3-6) to be processed is clamped on the fixture (3-7). According to the material properties of the workpiece (3-6) and the grinding requirements, the grinding path, grinding wheel speed, feed rate, cutting depth and micro-lubrication supply parameters are planned. The processing parameters are input into the control system, and the control range of fluid pressure, flow rate and hot end temperature of the Rank-Hills vortex tube (3-10) during processing is set.

[0033] (2) According to the set processing parameters, the control system controls the air pump (3-4), reciprocating pump (3-1), flow controller (3-9) and pressure valve (3-14) to work together and start processing according to the planned grinding path;

[0034] (3) During the processing, compressed air is regulated by pressure valve (3-14) and enters Rank-Hills vortex tube (3-10) and is divided into two paths: the first path is the hot air flow discharged through the hot end outlet (3-12) of Rank-Hills vortex tube (3-10) to preheat the magnetic shear thickening fluid (3-2) in the storage tank (3-3) so that the fluid undergoes shear thinning effect to improve fluidity; the second path is the cold air flow discharged through the cold end outlet of Rank-Hills vortex tube (3-10) and mixes with the magnetic shear thickening fluid (3-2) after being pressurized by reciprocating pump (3-1) and regulated by flow controller (2-9) in the micro-lubrication nozzle (3-13). Under the action of the magnetic field generated by the built-in magnetic pole (2-1) of the nozzle, a low-temperature nano-atomized particle cluster spray (2-2) is formed.

[0035] (4) During the processing, the micro-lubrication nozzle (3-13) sprays low-temperature nano-atomized particle clusters onto the contact arc area between the grinding wheel (3-5) and the workpiece (3-6) fixed by the fixture (3-7). After the spray contacts the surface of the workpiece (3-6), it transforms into a magnetic shear thickening fluid under the action of high shear rate and temperature field in the grinding zone. The viscosity increases sharply, forming a solid lubricating film. At the same time, the micro-nano particles in the fluid increase the number of effective abrasive particles in the grinding zone and improve the material removal rate. The grinding force in the grinding zone is monitored in real time by the force gauge (3-8). The grinding temperature is controlled by adjusting the cold end temperature of the vortex tube and the fluid flow rate, thereby achieving efficient and low-damage grinding of the workpiece.

[0036] Example 3: Turning machining, combined with Figure 2 and Figure 4 illustrate:

[0037] (1) The workpiece is turned. The micro-lubrication system is selected for turning. The fixture (4-6) is a three-jaw chuck. The workpiece (4-5) to be processed is clamped on the fixture (4-6). According to the material properties of the workpiece (4-5) and the turning requirements, the turning path, spindle speed, feed rate, depth of cut and micro-lubrication supply parameters are planned. The processing parameters are input into the control system, and the control range of fluid pressure, flow rate and hot end temperature of the Rank-Hillsch vortex tube (4-9) during processing is set.

[0038] (2) According to the set machining parameters, the control system controls the air pump (4-4), reciprocating pump (4-1), flow controller (4-8) and pressure valve (4-13) to work together and start machining according to the planned turning path;

[0039] (3) During the processing, compressed air is regulated by pressure valve (4-13) and enters Rank-Hillsch vortex tube (4-9) and is divided into two paths: the first path is the hot air flow discharged through the hot end outlet (4-11) of Rank-Hillsch vortex tube (4-9) to preheat the magnetic shear thickening fluid (4-2) in the storage tank (4-3) so that the fluid undergoes shear thinning effect to improve fluidity; the second path is the cold air flow discharged through the cold end outlet of Rank-Hillsch vortex tube (4-9) and mixes with the magnetic shear thickening fluid (4-2) after being pressurized by reciprocating pump (4-1) and regulated by flow controller (4-8) in the micro-lubrication nozzle (4-12). Under the action of the magnetic field generated by the built-in magnetic pole (2-1) of the nozzle, a low-temperature nano-atomized particle cluster spray (2-2) is formed.

[0040] (4) During the machining process, the micro-lubrication nozzle (4-12) sprays low-temperature nano-atomized particle clusters onto the contact area between the rake face of the lathe tool and the chip. After the spray comes into contact with the workpiece (4-5) and the tool surface, it transforms into a magnetic shear thickening fluid under the action of high shear rate and temperature field in the turning zone. The viscosity increases sharply, forming a strong lubricating film to achieve machining lubrication. At the same time, the micro-nano particles in the fluid form a protective layer on the rake face of the lathe tool to reduce tool wear. The cutting temperature is controlled by adjusting the cold end temperature of the vortex tube and the fluid flow rate, thereby achieving high-precision turning of the workpiece.

[0041] The specific embodiments described above are merely illustrative or explanatory of the principles of the present invention and do not constitute a limitation on the scope of protection of the present invention. Therefore, any modifications, alterations, equivalent substitutions, equivalent structures, and equivalent process changes made to the present invention without departing from the principles and scope of protection described herein should be covered within the scope of protection of the present invention.

Claims

1. A method for micro-lubrication of magnetic shear-thickened nanofluids, characterized in that, The method is implemented through the following steps: Step 1: Fluid supply and pressurization. The magnetic shear thickening fluid (1-2) is placed in the storage tank (1-3), and the magnetic shear thickening fluid (1-2) is pressurized and transported using a reciprocating pump (1-1) to overcome the high viscosity resistance of the non-Newtonian fluid. After the flow rate is regulated by the flow controller (1-9), the fluid is delivered to the liquid inlet of the micro-lubrication nozzle (1-13); Step 2: Compressed air diversion and temperature control. The compressed air supplied by the air pump (1-4) is regulated by the pressure valve (1-14) and enters the Rank-Hillsch vortex tube (1-10), where it is divided into two paths: the first path enters the air inlet of the micro-lubrication nozzle (1-13) through the cold end outlet of the Rank-Hillsch vortex tube (1-10); the second path heats the liquid storage tank (1-3) through the hot end outlet (1-12) of the Rank-Hillsch vortex tube (1-10). Step 3: Heat recovery assists in viscosity reduction. The hot gas flow discharged from the hot end outlet (1-12) of the Rank-Hills vortex tube (1-10) is led to the heat exchange structure on the outer wall of the storage tank (1-3) through the pipeline to preheat the magnetic shear thickening fluid (1-2). The heat energy is used to cause the fluid to undergo shear thinning effect to improve fluidity and promote the suction efficiency of the reciprocating pump (1-1). Step 4: Low-temperature nano-atomized particle cluster spraying. The low-temperature cold air discharged from the cold end outlet of the Rank-Hills vortex tube (1-10) mixes with the magnetic shear thickening fluid (1-2) in the micro-lubrication nozzle (1-13). Under the action of the magnetic field generated by the built-in magnetic pole (2-1) of the nozzle, a low-temperature nano-atomized particle cluster spray (2-2) is formed and sprayed into the processing area. Step 5: Machining lubrication. After the low-temperature nano-atomized particle cluster spray (2-2) contacts the surface of the workpiece (1-6) fixed by the fixture (1-7), it transforms into a magnetic shear thickening fluid under the action of high shear rate and temperature field in the machining zone. A lubricating film is formed at the contact interface between the tool (1-5) and the workpiece (1-6) to achieve machining lubrication. At the same time, the micro-nano particles in the magnetic shear thickening fluid (1-2) enhance the ability to carry and remove chips, thereby improving the surface quality of the machined surface and reducing the machining temperature. The cutting force during the machining process is monitored in real time by a force measuring instrument (1-8).

2. The method for micro-lubrication of magnetic shear-thickened nanofluids according to claim 1, characterized in that: In step three, by adjusting the valve opening at the hot end of the Rank-Hills vortex tube (1-10), the temperature and flow rate of the hot air returning to the heat exchange structure of the storage tank (1-3) are controlled, so as to precisely control the temperature of the magnetic shear thickening fluid (1-2) in the storage tank (1-3) and keep it in the optimal shear thinning temperature range.

3. The method for micro-lubrication of magnetic shear-thickened nanofluids according to claim 1, characterized in that: The magnetic shear thickening fluid (1-2) is a non-Newtonian fluid containing nanodiamond particles, nanomagnetic particles, nanosilica particles and additives. Under the action of high shear rate in the processing zone, its viscosity increases sharply, forming a strong lubricating film.

4. The method for micro-lubrication of magnetic shear-thickened nanofluids according to claim 1, characterized in that: The cold end outlet temperature range generated by the Rank-Hills vortex tube (1-10) is -5℃ to 15℃. The low-temperature cold air mixed with the magnetic shear thickening fluid forms a low-temperature nano-atomized particle cluster spray that quickly removes heat from the processing area by enhancing convective heat transfer, thus inhibiting thermal damage to the workpiece surface.

5. A magnetic shear-thickening nanofluid micro-lubrication device, used to implement the method according to any one of claims 1 to 4, characterized in that, include: Air pumps (1-4) are used to supply compressed air; A pressure valve (1-14), connected to the air pump (1-4), is used to regulate the compressed air pressure; a Rank-Hillsch vortex tube (1-10), whose inlet is connected to the outlet of the pressure valve (1-14), has a cold end outlet and a hot end outlet (1-12), the cold end outlet being connected to the air inlet of a micro-lubrication nozzle (1-13); a liquid storage tank (1-3), used to store magnetic shear thickening fluid (1-2), its outer wall being provided with a heat exchange structure, the heat exchange structure being connected to the Rank-Hillsch vortex tube (1-10) A hot-end outlet (1-12) is connected via a pipeline; a reciprocating pump (1-1) is connected to the outlet of the storage tank (1-3) for pressurizing and delivering the magnetic shear thickening fluid (1-2); a flow controller (1-9) is located between the reciprocating pump (1-1) and the micro-lubrication nozzle (1-13); the micro-lubrication nozzle (1-13) has a liquid inlet and an air inlet for mixing and atomizing the magnetic shear thickening fluid with low-temperature compressed air and spraying it into the processing area, and the nozzle outlet has a built-in magnetic pole (2-1). A pressure gauge (1-11) is used to monitor the working pressure of the reciprocating pump (1-1) in real time; a force gauge (1-8) is used to monitor the cutting force during the processing in real time; a fixture (1-7) is used to fix the workpiece (1-6).

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