Crankshaft and camshaft journal finishing method and journal

Abstract

The present disclosure provides a "journal finishing method and journal of a crankshaft and a camshaft". A method for grinding a crankshaft surface is provided. The method includes grinding the surface of the crankshaft by a grinding wheel, and polishing the surface of the crankshaft ground by the grinding wheel by swinging the polishing wheel in a transverse direction perpendicular to the longitudinal direction of the crankshaft.

Description

Technical Field

[0001] The present disclosure relates to metalworking processes and, more particularly, to methods for grinding and finishing various surfaces of a crankshaft or camshaft. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] Internal combustion engines typically require the use of a crankshaft to convert linear motion into rotational motion. Multiple surfaces of the crankshaft with various functions require machining to ensure proper operation of the crankshaft. Typically, some machining processes require rotating the crankshaft about a longitudinal axis (which defines the main bearing journal axis of the crankshaft) while machining multiple different surfaces using a rotating grinding wheel. This process is called machine grinding.

[0004] During machine grinding, extreme heat and aggressive cutting may change the microstructure and base metal hardness, resulting in slight dimensional and surface defects such as blurred peaks, ripples and chatter. A superfinishing process may then be performed to improve the surface finish and workpiece geometry by removing the amorphous layer formed during the grinding process.

[0005] The typical superfinishing process can be performed by using either an abrasive belt or a grinding stone. Belt finishing is more commonly used. Both abrasive belt finishing and grinding stone finishing systems utilize a series of mechanical clamping arms that must be positioned axially in line with the journal to be finished. Regardless of which system is used, the grinding stone or abrasive belt is clamped to the journal and held stationary while the crankshaft rotates.

[0006] Performing the superfinishing process requires switching from the grinder to the superfinishing system, positioning the various clamping arms of the superfinishing system, and positioning the tool (grinding stone or abrasive belt) relative to the crankshaft journal. As a result, the typical method for grinding and finishing crankshafts is complex, time-consuming, and expensive.

[0007] The present disclosure is directed to improving processes associated with grinding and finishing journals and crankshafts. Summary of the invention

[0008] In one form, a method of grinding a crankshaft surface is provided, which includes grinding the crankshaft surface by a grinding wheel, and polishing the crankshaft surface ground by the grinding wheel by oscillating the polishing wheel in a transverse direction perpendicular to the longitudinal direction of the crankshaft.

[0009] In other features, the polishing wheel oscillates at a frequency of 8 Hz (mm / s) with a stroke of 0.5 mm and can be a vitrified or resin-bonded cubic boron nitride (CBN) wheel with a particle size of no more than 46 microns (equivalent to 400 mesh). However, it should be understood that the oscillation stroke and frequency can be changed according to the application while remaining within the scope of the present disclosure. In one form, the particle size of the grinding wheel is 151 microns (equivalent to 120 mesh). The method also includes applying a coolant during the polishing process. The coolant may include 6% oil-free water (water-soluble), but other coolants such as oil-based coolants may be used while remaining within the scope of the present disclosure. The polishing wheel can remove raw material from the crankshaft at a depth between 10 and 50 microns and at a depth of 20 microns in one form. The grinding performed by the grinding wheel is plunge-cut grinding using a CBN wheel. The surface of the crankshaft may be the surface of the main bearing journal that may require precision machining, the surface of the pin journal of the crankshaft, or the crank seal surface, etc.

[0010] In another form, a method of grinding and polishing a crankshaft surface is provided, comprising grinding the crankshaft surface with a grinding wheel and polishing the crankshaft surface with a vitrified or resin bonded CBN wheel having a grit size no greater than 75 microns and in one form no greater than 46 microns.

[0011] In another form, a method of grinding and polishing the main bearing journals and pin journals of a crankshaft is provided, which includes grinding the crankshaft surface by a grinding wheel, and oscillating the polishing wheel in a transverse direction perpendicular to the longitudinal axis of the crankshaft with a stroke between 0.05 and 1.0 mm and in one form 0.5 mm to polish the surface ground by the grinding wheel. Generally speaking, for a given mesh number, the oscillation further reduces the surface finish because the motion engages a set of different abrasive particles on the wheel. Due to excessive oscillation, the edge of the polishing wheel may break and then lose shape. In addition, on journals / parts with shoulders on either side, the amount of oscillation limits the width of the polishing wheel, which again affects the damage of the polishing wheel. In other features, the polishing wheel oscillates at a frequency between 2 and 25 Hz and in one form at a frequency of 8 Hz, and the particle size of the polishing wheel is not greater than 46 microns.

[0012] Further areas of applicability will become apparent from the description provided herein.It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0014] Figure 1 is a schematic diagram of a crankshaft and a grinding machine that performs a method of grinding a crankshaft surface according to the teachings of the present disclosure;

[0015] Figure 2 is an enlarged view of portion A showing the movement of the polishing wheel relative to the main bearing journal of the crankshaft;

[0016] Figure 3 depicts a bar graph comparing the average roughness (Ra) of a polished surface of a crankshaft obtained by a non-belt polishing process of the present disclosure, a typical belt polishing process, and a partial belt polishing process;

[0017] Figure 4 depicts a bar graph comparing the load ratio (Rmr) (0.4 um slice) of the polished surface of a crankshaft obtained by a beltless polishing process of the present disclosure, a typical belt polishing process, and a partial belt polishing process;

[0018] Figure 5 depicts a bar graph comparing the fraction (Mr2) of a polished surface that will be subjected to a load obtained by a beltless polishing process of the present disclosure, a typical belt polishing process, and a partial belt polishing process;

[0019] Figure 6 depicts a bar graph comparing the unfiltered raw profile (Pt) of the polished surface of a crankshaft obtained by a beltless polishing process of the present disclosure, a typical belt polishing process, and a partial belt polishing process;

[0020] Figure 7 depicts a bar graph comparing the average maximum height (Rz) of the polished surface of a crankshaft obtained by a non-belt polishing process of the present disclosure, a typical belt polishing process, and a partial belt polishing process;

[0021] Figure 8 depicts a bar graph comparing the single largest valley below the plateau (Rvk) of the polished surface of a crankshaft obtained by a beltless polishing process of the present disclosure, a typical belt polishing process, and a partial belt polishing process; and

[0022] Fig. 9 Depicted is a bar graph comparing the single largest valley on a platform (Rpk) of a polished surface of a crankshaft obtained by a non-belt polishing process of the present disclosure, a typical belt polishing process, and a partial belt polishing process.

[0023] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0024] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[0025] Reference Figure 1, a grinder 10 is shown for grinding and polishing various surfaces of a crankshaft 12. The crankshaft 12 includes opposite ends 14 and 16 defining a longitudinal axis X of the crankshaft 12. The crankshaft 12 is rotatably supported at the opposite ends 14 and 16 by a fixture 18 that fixes and rotates the crankshaft 12 about the longitudinal axis X.

[0026] The crankshaft 12 generally includes a plurality of main bearing journals 20 (aligned along a longitudinal axis X), a plurality of pin journals 22, and a flywheel 24. The pin journals 22 are disposed offset from the longitudinal axis X in a transverse direction Y perpendicular to the longitudinal direction X.

[0027] The grinding machine 10 includes a first spindle 30 supporting a grinding wheel 32 and a second spindle 34 supporting a polishing wheel 36. The grinding wheel 32 includes an outer peripheral surface for cutting and removing stock from the main bearing journal 20 and the pin journal 22 of the crankshaft 12 to achieve the desired geometry. The polishing wheel 36 includes an outer peripheral surface for polishing and finishing the surface ground by the grinding wheel 32. The grinding wheel 32 can be made of a hard material such as cubic boron nitride (CBN), aluminum oxide, or a hybrid composition, the particle size of which is between about 91 and 252 microns and in one form is about 151 microns (equivalent to 120 mesh). The grinding wheel 36 can be made of a hard material such as vitrified or resin-bonded CBN, aluminum oxide, or a hybrid composition, the particle size of which is between about 15 and 76 microns and in one form is about 46 microns (equivalent to 400 mesh).

[0028] The grinding machine 10 further includes a motor 40 for rotating the first and second spindles 30, 34 about a central axis 42 and for driving the first and second spindles 30, 34 in a transverse direction Y radial to the main bearing journals 20 of the crankshaft 12 and in an axial direction B parallel to the longitudinal axis X of the crankshaft 12. Figure 2 The controller 46 is configured to control the motor 40 and the driver 44 to rotate the first spindle 30 and the second spindle 34 around the center direction 42, and to move the first spindle 30 and the second spindle 34 in the axial direction B and the lateral direction Y.

[0029] In order to grind the surfaces of the crankshaft 12, such as the surfaces of the main bearing journals 20 and the pin journals 22, the crankshaft 12 is rotated about the longitudinal axis X, and the first spindle 30 is rotated about the central axis 42 and moved toward the crankshaft 12 in the Y direction. When the outer peripheral surface of the grinding wheel 32 contacts the main bearing journals 20 and / or the pin journals 22, the stock is removed from the main bearing journals 20 and / or the pin journals 22 to achieve the desired geometry. The grinding process of the grinding wheel 32 can be plunge grinding. Using a grinding process to achieve a desired geometry is known in the art, so for the sake of clarity, a detailed description thereof is omitted herein.

[0030] After the grinding of the main bearing journals 20 and / or the pin journals 22 of the crankshaft 12 is completed to achieve the desired geometry, the first spindle 30 is moved away from the crankshaft 12. The second spindle 34 is rotated about the central axis 42, moved to align with the main bearing journals 20 and / or the pin journals 22, and moved toward the main bearing journals 20 and / or the pin journals 22 for a subsequent polishing process.

[0031] Reference Figure 2 During polishing, the polishing wheel 36 oscillates with a stroke of about 0.5 mm and a frequency of about 8 Hz (mm / s) in the lateral direction Y. The polishing process has a small degree of oscillation sufficient to engage a set of abrasive particles, which reduces the surface finish and enables the use of a relatively large grit and enhanced wheel bonding.

[0032] A coolant comprising 6% oil-free water may be used. The polishing wheel 36 may be a vitrified or resin bonded CBN wheel having a particle size of 46 microns (equivalent to 400 mesh). The polishing wheel 36 may remove stock from the crankshaft to a depth of 20 microns.

[0033] The polishing method of the present disclosure without the use of an abrasive belt provides a polished surface that is superior to that obtained by a typical belt finishing process. In addition, the standard deviation of the surface finish characteristics is much narrower, resulting in a more controlled and stable process. In Table 1 below, various surface roughness measurements achieved by the process of the present disclosure using a polishing wheel 36 and by a typical superfinishing process using an abrasive belt are compared.

[0034] Table 1

[0035]

[0036] *: Better than with finishing, >15%

[0037] ∆: Same as belt finishing, within 15%

[0038] X: Better than fine processing, >15%

[0039] As shown in Table 1, the beltless process of the present disclosure generally has a better standard deviation than that achieved by a typical belt finishing process. The minimum value of the polished surface obtained by the beltless process of the present disclosure is slightly higher than that of a typical belt finishing. This is because the polishing wheel 36 of the present disclosure has a larger grit size of 46 microns compared to the 20 micron grit size of the abrasive belt used in a typical superfinishing process. Therefore, the surface roughness can be further reduced by reducing the grit of the polishing wheel.

[0040] Reference Figure 3, depicts a bar graph comparing the average roughness (Ra) of the polished surfaces of main bearing journals and pin journals obtained by the disclosed no-belt process (T), a typical belt polishing process (P), and a partial belt polishing process (B). Ra is the average of a set of individual measurements of the peaks and valleys of the surface.

[0041] Reference Figure 4 , depicts a bar graph comparing the load ratio (Rmr) (0.4µm slice) of the polished surfaces of the main bearing journals and pin journals obtained by the disclosed beltless process (T), a typical belt polishing process (P), and a partial belt polishing process (B). The typical belt polishing process uses a belt with a grit size of 20 microns, while the disclosed beltless polishing process uses a polishing wheel with a grit size of about 46 microns.

[0042] Reference Figure 5 , depicts a bar graph comparing the fraction of load-bearing peaks (Mr2) of polished surfaces obtained by the disclosed beltless process (T), a typical belt polishing process (P), and a partial belt polishing process (B). As shown, the fraction of load-bearing peaks obtained by the disclosed beltless process (T) using a polishing wheel is similar to that of a typical belt polishing process.

[0043] Reference Figure 6 , depicts a bar graph comparing the unfiltered raw profile (Pt) of a polished surface obtained by the disclosed beltless process (T), a typical belt polishing process (P), and a partial belt polishing process (B). As shown, the disclosed beltless process achieves a more uniform unfiltered raw profile than the typical belt polishing process or the partial belt polishing process.

[0044] Reference Figure 7 , depicts a bar graph comparing the average maximum height (Rz) of a polished surface obtained by a beltless process (T) of the present disclosure, a typical belt polishing process (P), and a partial belt polishing process (B).

[0045] Reference Figure 8 , depicts a bar graph comparing the single largest valley under the platform (Rvk) of the polished surface obtained by the beltless process (T) of the present disclosure, the typical belt polishing process (P) and the partial belt polishing process (B). The beltless polishing process of the present disclosure achieves a more uniform Rvk.

[0046] Reference Fig. 9 , depicts a bar graph comparing the single largest valley on the plateau (Rpk) of the polished surface obtained by the disclosed beltless process (T), a typical belt polishing process (P), and a partial belt polishing process (B). The disclosed beltless process achieves a slightly higher Rpk than the typical belt polishing.

[0047] The disclosed beltless polishing process uses vitrified or resin bonded CBN polishing wheels to achieve precision machined surfaces on crankshaft main bearing journals and pin journals. No separate superfinishing system and abrasive belts are required, thereby simplifying tooling and saving equipment costs and changeover time.

[0048] Moreover, in contrast to consumable abrasive belts, polishing wheels can be self-dressing, thereby reducing the cost of consumable tools. Dressing a grinding wheel refers to removing the current abrasive layer to expose a new and sharp surface to the working surface. The process of the present disclosure reduces mechanical complexity, geometry variation, and overall cost while increasing flexibility and quality.

[0049] In addition, the disclosed stripless polishing process provides improved geometric and dimensional control and achieves a more consistent surface finish. The disclosed stripless method can process parts that have been case hardened after preliminary journal finishing, thereby providing advantages because the case depth level can be reduced to increase productivity by 100% or more.

[0050] The description of the present disclosure is merely exemplary in nature, and therefore, variations that do not depart from the essence of the present disclosure are intended to fall within the scope of the present disclosure. Such variations should not be regarded as departing from the spirit and scope of the present disclosure.

[0051] According to the present invention, a method for grinding a workpiece surface comprises grinding the surface of the workpiece by a grinding wheel; and polishing the workpiece surface ground by the grinding wheel by swinging the polishing wheel in a lateral direction perpendicular to the longitudinal direction of a crankshaft.

[0052] According to one embodiment, the above invention is further characterized by causing the polishing wheel to oscillate with a stroke between 0.05 and 1.0 mm.

[0053] According to one embodiment, the above invention is further characterized by oscillating the polishing wheel at a frequency between 2 and 25 Hz.

[0054] According to one embodiment, the above invention is further characterized by applying a coolant during the polishing process.

[0055] According to one embodiment, the coolant comprises 6% water.

[0056] According to one embodiment, the polishing wheel is a cubic boron nitride (CBN) wheel.

[0057] According to one embodiment, the grit size of the polishing wheel is between 15 and 76 microns.

[0058] According to one embodiment, the polishing wheel has a 400 grit.

[0059] According to one embodiment, the polishing wheel is a vitrified CBN wheel.

[0060] According to one embodiment, the polishing wheel is a resin bonded CBN wheel.

[0061] According to one embodiment, the polishing wheel removes stock from the crankshaft at a depth of 20 microns.

[0062] According to one embodiment, the above invention is further characterized in that the grinding is performed by plunge grinding.

[0063] According to one embodiment, plunge grinding is performed by using a CBN wheel.

[0064] According to one embodiment, the CBN wheel used for plunge grinding has a grit size of 151 microns.

[0065] According to one embodiment, the CBN wheel has 120 mesh.

[0066] According to one embodiment, the surface is the surface of a main bearing journal or a pin journal of the crankshaft.

[0067] According to the present invention, a method for grinding and polishing a crankshaft surface comprises grinding the crankshaft surface by a grinding wheel; and polishing the crankshaft surface ground by a vitrified or resin-bonded cubic boron nitride (CBN) wheel having a particle size of not more than 46 microns.

[0068] According to the present invention, a method for grinding and polishing the main bearing journal and pin journal of a crankshaft comprises grinding the surface of the crankshaft by a grinding wheel; and oscillating the polishing wheel with a stroke between 0.05 and 1.0 mm in a transverse direction perpendicular to the longitudinal axis of the crankshaft to polish the surface ground by the grinding wheel.

[0069] According to one embodiment, the above invention is further characterized by oscillating the polishing wheel at a frequency between 2 and 25 Hz.

[0070] According to one embodiment, the grit size of the polishing wheel is no greater than 46 microns.

Claims

1. A method for grinding a workpiece surface, the method comprising: Grinding the surface of the workpiece by a grinding wheel; as well as The workpiece surface ground by the grinding wheel is polished by oscillating the polishing wheel in a transverse direction perpendicular to the longitudinal direction of the crankshaft.

2. The method of claim 1 further comprising oscillating the polishing wheel with a stroke between 0.05 and 1.0 mm.

3. The method of claim 1 or 2, further comprising oscillating the polishing wheel at a frequency between 2 and 25 Hz.

4. The method of claim 1, further comprising applying a coolant during polishing.

5. The method of claim 4, wherein the coolant comprises 6% water. The method of claim 1 , wherein the polishing wheel is a cubic boron nitride (CBN) wheel.

7. The method of claim 6, wherein the polishing wheel has a grit size between 15 and 76 microns.

8. The method of claim 6, wherein the polishing wheel has a 400 grit.

9. The method of claim 6, wherein the polishing wheel is a vitrified CBN wheel.

10. The method of claim 6, wherein the polishing wheel is a resin bonded CBN wheel.

11. The method of claim 1 , wherein the polishing wheel removes stock from the crankshaft to a depth of 20 microns.

12. The method of claim 1, further comprising performing the grinding by plunge grinding.

13. The method according to claim 12, wherein the plunge grinding is performed by using a CBN wheel.

14. The method of claim 13, wherein the grit size of the CBN wheel used for the plunge grinding is 151 microns.

15. The method of claim 13, wherein the CBN wheel has 120 mesh.

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