A machining method for a hollow camshaft with a large length-to-diameter ratio

Abstract

A method for machining a hollow camshaft with a large length-to-diameter ratio includes the following steps: blanking, turning the end face and outer diameter, and drilling the center hole; ensuring the overall length of the camshaft; performing a first straightening and tempering; machining grooves at each journal in sections; performing a second straightening and tempering; rough grinding each journal; machining the locating pin hole at one end of the camshaft; rough grinding each cam on the camshaft to form the basic outline of the camshaft; heat treating the camshaft; semi-finish grinding each journal; machining through holes and threaded holes at one end of the camshaft; installing process plugs on the camshaft; performing a third straightening and tempering; semi-finish grinding each journal; semi-finish grinding each cam on the camshaft; finish grinding the end face of the journal and the locating pin hole; finish grinding each cam on the camshaft; removing the process plugs. This invention eliminates the problem of interference between the pin and the center used during machining and inspection, reduces deformation during machining, and ensures the dimensional accuracy and geometric tolerances of the finished camshaft.

Description

Technical Field

[0001] This invention pertains to a processing method, specifically a processing method for a hollow camshaft with a large length-to-diameter ratio. Background Technology

[0002] As is well known, the camshaft is a key component of the valve train in a diesel engine, and its machining quality directly affects the engine's intake and exhaust volume, combustion efficiency, and overall performance. To meet the weight reduction requirements of diesel engines, camshaft design has largely focused on hollow structures. These camshafts have a large length-to-diameter ratio, thin bore walls, are prone to deformation during machining, have difficult-to-guarantee dimensional and positional tolerances, poor surface finish, and are difficult to manufacture. Currently, camshaft machining generally uses the center holes at both ends as references, machining the journals and cams sequentially to ensure the coaxiality and runout of the outer surfaces of each journal. For hollow camshafts, a pre-machined center hole is used for positioning before machining the hollow through hole. After machining the through hole, chamfers machined at both ends or tapered holes machined at both ends are used for positioning, and the camshaft is connected to a pin using a chuck for subsequent machining.

[0003] Since the blank of a hollow camshaft is solid, from the perspective of selecting a positioning datum, a center hole is generally used for positioning, and the through-hole machining process is placed later. However, the through-hole machining process requires the removal of a large amount of metal, which can cause shaft deformation and affect the machining quality.

[0004] To prevent deformation of the hollow camshaft during heat treatment, drilling and tapping are typically performed after heat treatment. Therefore, the through hole should be machined after rough machining of the journal and cam. However, after machining the through hole, if the center hole at one end of the camshaft is too close to the pin hole used to connect the chuck, the pin used for machining and inspection will interfere with the center used for machining and inspection, making it impossible to continue subsequent machining and inspection after rough machining. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a machining method for a hollow camshaft with a large length-to-diameter ratio that can reduce deformation during the machining process and ensure the dimensional accuracy and form and position tolerance of the finished camshaft.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for machining a hollow camshaft with a large length-to-diameter ratio includes the following steps: 1) Material preparation and conditioning of raw blanks; 2) Rough turn the end face and outer diameter of the blank on a CNC lathe, and drill the center hole; ensure the overall length of the camshaft; 3) The first straightening is performed using a dedicated camshaft straightening machine, followed by tempering in a tempering furnace; 4) The grooves are machined in sections on a CNC lathe to machine the grooves at each journal and the outer circle of the auxiliary support to prepare for the subsequent installation of the auxiliary support; 5) Perform a second straightening using a dedicated camshaft straightening machine, followed by tempering in a tempering furnace; 6) Rough grind each journal on an external cylindrical grinding machine; 7) Machining a locating pin hole at one end of the camshaft on a horizontal machining center; 8) Roughly grind each cam on the camshaft on a CNC camshaft profile grinding machine to form the basic outline of the camshaft; during rough grinding, an auxiliary support frame is set on the grinding machine to support the outer circle of the auxiliary support. 9) The camshaft is heat-treated by medium-frequency induction hardening; 10) Perform semi-finish grinding on an external cylindrical grinding machine on each journal; 11) Machining through holes and threaded holes at one end of the camshaft on a horizontal machining center; 12) Install a process plug in the center hole at one end of the locating pin hole on the camshaft; this is used to increase the distance between the locating pin hole and the reference center hole. 13) Perform a third straightening using a dedicated camshaft straightening machine, and then temper it in a tempering furnace; 14) Grind the center hole on the other end of the process plug on the camshaft on a conventional lathe; 15) On an external cylindrical grinding machine, the journals are semi-finished by positioning them through the center hole of the process plug and the center hole of the camshaft located at the other end of the process plug; 16) On a CNC camshaft profile grinding machine, each cam on the camshaft is positioned for semi-finish grinding through the center hole of the process plug and the center hole of the camshaft located at the other end of the process plug; during semi-finish grinding, an auxiliary support frame is set on the grinding machine to support the outer circle of the auxiliary support; 17) Grind the journal on a CNC camshaft journal grinding machine, and grind the end face of one end of the camshaft's locating pin hole on an external cylindrical grinding machine; 18) Each cam on the camshaft is precision ground on a CNC camshaft profile grinding machine; during precision grinding, an auxiliary support frame is set on the outer circle of the auxiliary support on the grinding machine; 19) Remove process blockages.

[0007] A further improvement of the technical solution of the present invention is that: when machining the groove in sections in step 4), multiple grooves are first machined at one end close to the starting zero point, and then multiple grooves are machined at the other end after turning around; finally, the middle section is machined and used as an auxiliary support for the outer circle.

[0008] A further improvement of the technical solution of the present invention is that: in step 3), the straightening runout is set to be within 0.2 mm during the first straightening, the tempering temperature is 160℃, and the holding time is 2.5 hours.

[0009] A further improvement of the technical solution of the present invention is that: in step 5), during the second straightening, the straightening runout is set to be within 0.15mm, the tempering temperature is 160℃, and the holding time is 2.5 hours.

[0010] A further improvement of the technical solution of the present invention is that: in step 13), the straightening runout is set to be within 0.10 mm during the third straightening, the tempering temperature is 160℃, and the holding time is 2.5 hours.

[0011] A further improvement of the technical solution of the present invention is that: when installing the process plug in step 12), the pre-processed process plug is immersed below the liquid nitrogen surface for cooling for 20-30 minutes, and then pressed in.

[0012] A further improvement of the technical solution of the present invention is that: before setting the auxiliary support frame in step 16), the outer circle of the auxiliary support is ground in a small amount to reduce the deformation during the camshaft machining process.

[0013] A further improvement of the technical solution of the present invention is that: before setting the auxiliary support frame in step 18), the outer circle of the auxiliary support is ground in a small amount to reduce the deformation during the camshaft machining process.

[0014] The technological advancements achieved by this invention are: 1. This invention reduces the runout of the camshaft during subsequent processing through multiple straightening and tempering processes. It also reduces the deformation of the camshaft during processing by removing a large amount of metal through segmented machining and setting auxiliary supports. By designing and installing process plugs, the distance between the locating pin hole and the reference center hole can be increased, thereby eliminating the problem of interference between the pin and the center used during processing and inspection. This allows the camshaft to be machined with a larger hole diameter, achieving a better weight reduction effect.

[0015] 2. The method of this invention for processing hollow camshafts with a large length-to-diameter ratio is simple to operate, can reduce camshaft deformation during processing, ensure the dimensional accuracy and form and position tolerance of the finished camshaft, improve the yield, and avoid material waste. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the camshaft structure processed according to the present invention.

[0017] Figure 2 yes Figure 1 The left view.

[0018] Figure 3 This is a schematic diagram of the cam grinding chuck in this invention.

[0019] Figure 4 This is a schematic diagram of the process plug in this invention.

[0020] In the figure: camshaft 1, journal 101, intermediate section groove 102, locating pin hole 103; cam 104, through hole 105, threaded hole 106, cam grinding chuck 2, pin 3, process plug 4. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings: like Figures 1-4 As shown, the present invention relates to a method for machining a hollow camshaft with a large length-to-diameter ratio, comprising the following steps: 1) Material preparation and conditioning of raw blanks; 2) Rough turn the end face and outer diameter of the blank on a CNC lathe, and drill the center holes at both ends; ensure that the total length of camshaft 1 is the design dimension; set one end of camshaft 1 as the starting zero point; 3) Use a dedicated camshaft straightening machine for the first straightening, and then temper it in a tempering furnace; during the first straightening, set the straightening runout to within 0.2mm, the tempering temperature to 160℃, and the holding time to 2.5 hours; 4) The grooves are machined in sections on a CNC lathe to machine the grooves at each journal 101 and the outer circle of the auxiliary support is machined to prepare for the subsequent installation of the auxiliary support; When machining grooves in sections, first machine multiple grooves near the starting zero point, then turn around and machine multiple grooves near the other end; finally, machine the middle section groove 102, which serves as an auxiliary support for the outer circle; during machining, the outer diameter of each groove is slightly larger than the forming outer diameter by 1-2 mm. 5) Use a dedicated camshaft straightening machine for a second straightening, and then temper it in a tempering furnace; during the second straightening, set the straightening runout to within 0.15mm, the tempering temperature to 160℃, and the holding time to 2.5 hours; 6) Roughly grind each journal 101 on an external cylindrical grinding machine using the center holes at both ends for positioning; 7) Machining a locating pin hole 103 at the starting end of camshaft 1 on a horizontal machining center; used to locate the phase angle of each cam on camshaft 1; 8) Roughly grind each cam 104 on the camshaft 1 on a CNC camshaft profile grinding machine to form the basic outline of the camshaft 1; during rough grinding, a cam grinding chuck 2 is set on the grinding machine and bolted to the starting end of the camshaft 1, and the pin 3 set on the cam grinding chuck 2 is inserted into the positioning pin hole 103. Then, an auxiliary support frame is set on the grinding machine to support the outer circle of the auxiliary support. 9) The camshaft 1 is heat-treated by medium-frequency induction hardening; 10) On an external cylindrical grinding machine, semi-finish grind each journal 101 through the center holes at both ends; 11) Machining a through hole 105 located at the center of camshaft 1 and a threaded hole 106 located in the center hole at the starting end of camshaft 1 on a horizontal machining center; 12) Install a stepped process plug 4 with a center hole in the center hole at the starting end of the locating pin hole on the camshaft 1; when installing the process plug, immerse the pre-processed process plug 4 below the liquid nitrogen surface for cooling for 20-30 minutes, and then press it in; this is used to increase the distance between the locating pin hole and the reference center hole. 13) Use a camshaft straightening machine for the third straightening, and then temper it in a tempering furnace; during the third straightening, set the straightening runout to within 0.10mm, the tempering temperature to 160℃, and the holding time to 2.5 hours.

[0022] 14) Grind the center hole on the camshaft 1 at the other end of the process plug 4 to the forming size on a conventional lathe; 15) On an external cylindrical grinding machine, the journals are semi-finished by positioning them through the center hole of the process plug 4 and the center hole of the camshaft 1 located at the other end of the process plug; 16) On a CNC camshaft profile grinding machine, each cam 104 on the camshaft 1 is semi-finish ground by positioning it through the center hole of the process plug and the center hole of the camshaft 1 located at the other end of the process plug; during semi-finish grinding, the outer circle of the auxiliary support is first ground in a small amount, and then an auxiliary support frame is set on the grinding machine to support the outer circle of the auxiliary support; in order to reduce the deformation of the camshaft 1 during the machining process; 17) Grind journal 101 on a CNC camshaft journal grinding machine, and grind the end face of one end of the locating pin hole of camshaft 1 on an external cylindrical grinding machine. 18) Grind each cam 104 on the camshaft 1 on a CNC camshaft profile grinding machine; during the fine grinding, first grind a small amount of the outer circle of the auxiliary support, and then set an auxiliary support frame on the grinding machine to support the outer circle of the auxiliary support; so as to reduce the deformation during the camshaft machining process.

[0023] 19) Remove process blockage 4, then perform final inspection on the camshaft, and put the qualified camshaft 1 oil seal into the warehouse.

[0024] This invention reduces camshaft runout during subsequent processing by adding multiple straightening and tempering processes. It also reduces camshaft deformation during processing by removing a large amount of metal through segmented machining and setting auxiliary supports. By designing and installing process plugs, the distance between the locating pin hole and the reference center hole can be increased, thereby eliminating the problem of interference between the pin and the center used during processing and inspection. This allows the camshaft to be machined with a larger hole diameter, achieving a better weight reduction effect.

[0025] The method of this invention can be used to process hollow camshafts with a large length-to-diameter ratio. The length of the processed camshaft can reach 550-600mm, the journal diameter can reach φ22mm, and the hollow through hole can reach φ16mm. The operation is simple, which can reduce the deformation of the camshaft during the processing, ensure the dimensional accuracy and form and position tolerance of the finished camshaft, improve the yield, and avoid material waste.

[0026] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for machining a hollow camshaft with a large length-to-diameter ratio, characterized in that, The steps include the following: 1) Material preparation and conditioning of raw blanks; 2) Rough turn the end face and outer diameter of the blank on a CNC lathe, and drill the center hole; ensure the overall length of the camshaft; 3) The first straightening is performed using a dedicated camshaft straightening machine, followed by tempering in a tempering furnace; 4) The grooves are machined in sections on a CNC lathe to machine the grooves at each journal and the outer circle of the auxiliary support to prepare for the subsequent installation of the auxiliary support; When machining the grooves in sections, first machine multiple grooves near the starting zero point, then turn around and machine multiple grooves near the other end; finally, machine the middle section, which serves as an auxiliary support for the outer circle. 5) Perform a second straightening using a dedicated camshaft straightening machine, followed by tempering in a tempering furnace; 6) Rough grind each journal on an external cylindrical grinding machine; 7) Machining a locating pin hole at one end of the camshaft on a horizontal machining center; 8) Roughly grind each cam on the camshaft on a CNC camshaft profile grinding machine to form the basic outline of the camshaft; during rough grinding, an auxiliary support frame is set on the grinding machine to support the outer circle of the auxiliary support. 9) The camshaft is heat-treated by medium-frequency induction hardening; 10) Perform semi-finish grinding on an external cylindrical grinding machine on each journal; 11) Machining through holes and threaded holes at one end of the camshaft on a horizontal machining center; 12) Install a process plug in the center hole at one end of the locating pin hole on the camshaft; this is used to increase the distance between the locating pin hole and the reference center hole. 13) Perform a third straightening using a dedicated camshaft straightening machine, and then temper it in a tempering furnace; 14) Grind the center hole on the other end of the process plug on the camshaft on a conventional lathe; 15) On an external cylindrical grinding machine, the journals are semi-finished by positioning them through the center hole of the process plug and the center hole of the camshaft located at the other end of the process plug; 16) On a CNC camshaft profile grinding machine, each cam on the camshaft is positioned for semi-finish grinding through the center hole of the process plug and the center hole of the camshaft located at the other end of the process plug; during semi-finish grinding, an auxiliary support frame is set on the grinding machine to support the outer circle of the auxiliary support; before setting the auxiliary support frame, the outer circle of the auxiliary support is ground to reduce the deformation during the camshaft machining process; 17) Grind the journal on a CNC camshaft journal grinding machine, and grind the end face of one end of the camshaft's locating pin hole on an external cylindrical grinding machine; 18) Grind each cam on the camshaft on a CNC camshaft profile grinding machine; during the grinding process, an auxiliary support frame is set on the grinding machine to support the outer circle of the auxiliary support; before setting the auxiliary support frame, the outer circle of the auxiliary support is ground to reduce the deformation during the camshaft machining process; 19) Remove process blockages.

2. The machining method for a hollow camshaft with a large length-to-diameter ratio according to claim 1, characterized in that: In step 3), the straightening runout is set to be within 0.2 mm during the first straightening, the tempering temperature is 160℃, and the holding time is 2.5 hours.

3. The machining method for a hollow camshaft with a large length-to-diameter ratio according to claim 1, characterized in that: In step 5), during the second straightening, the straightening runout is set to be within 0.15 mm, the tempering temperature is 160℃, and the holding time is 2.5 hours.

4. The machining method for a hollow camshaft with a large length-to-diameter ratio according to claim 1, characterized in that: In step 13), during the third straightening, the straightening runout is set to be within 0.10 mm, the tempering temperature is 160℃, and the holding time is 2.5 hours.

5. The machining method for a hollow camshaft with a large length-to-diameter ratio according to claim 1, characterized in that: In step 12), when installing the process plug, the pre-processed process plug is immersed below the liquid nitrogen surface for cooling for 20-30 minutes, and then pressed in.

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