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Automotive Camshaft Processing Technology

Writer: Kangding metal Pubdate:2018-04-05 Source:CNC Machining Factory
Description:Automotive Camshaft Processing Technology Product Description The camshaft is a key component in the valve train of an automobile engine, and its performance directly affects the overall performance of the engine. Therefore, the machining p...


Automotive Camshaft Processing Technology

Product Description
The camshaft is a key component in the valve train of an automobile engine, and its performance directly affects the overall performance of the engine. Therefore, the machining process of the camshaft has special requirements. Reasonable machining processes have great practical significance for reducing the processing cost, reducing the production process and rationally arranging the camshaft production line.
This paper focuses on the processing characteristics of the camshaft, combined with the actual conditions of the factory, and starts with the preliminary planning.
The camshaft processing technology is analyzed and studied in depth.The establishment of a numerical control without a model method.Convex contours were calculated and inferred. The processing of cam profiles was discussed and a machining method suitable for engine camshafts was proposed.

Key words: engine; camshaft; process analysis; shaft machining; CNC machining; turning; lathe machining
Material: (FCA-3) copper chromium molybdenum alloy cast iron

Engine performance requirements:
(1) High power performance.
(2) High fuel economy.
(3) High working reliability and sufficient service life.
(4) Compact structure, small size and light weight.
(5) High environmental performance, low emissions, low consumption, and low pollution.


Camshaft performance requirements
In various parts and mechanisms of automotive engines. The camshaft is the most important and critical component of the valve train. It determines the lift curve of the valve and the valve switching time, which directly affects the intake and exhaust of the engine, and affects the dynamic performance, economy, and emissions of the engine.

Since the development trend of the engine is a multi-cylinder and multi-valve design, the intake and exhaust of each valve must be controlled by the cam profile on the camshaft. So the development trend of the camshaft is that more and more cams are arranged on a camshaft. If it is a three-cylinder engine, whether it is a two-valve or a four-valve, The exhaust cam and the intake cam can also be arranged on a camshaft. If it is more than four cylinders, it must be equipped with two camshafts, one of which controls the intake valve and the other controls the exhaust valve.

The camshaft is one of the key components in the internal combustion engine distribution system. The entire valve distribution mechanism is driven by the camshaft. The design of the cam plays a decisive role in the performance of the entire distribution system. The camshaft has poor rigidity and is easily deformed; the precision is high and the processing is difficult; therefore, many requirements have been put forward for the design, processing, material selection, and processing technology of the camshaft.

main project General requirements
 
Support bearings
size(mm) IT5~IT6
Surface roughness(μm)
 
Rz0.4
Cylindricity(mm) 5 Level precision
Camshaft surface roughness(mm)
Rz0.4
The runout of the middle journal relative to the journal at both ends (mm) 0.06
Radially adjacent two journals beating (mm) 0.02
The angular deviation of the center plane of the camshaft symmetrical to the center plane of the keyway of the positive gear or the axis of the positioning pin(′) ±30′

Camshaft production planning
In terms of preliminary preparation, process design, theoretical calculation, production practice, and product inspection, a set of design ideas and methods for camshaft machining are described, which has an important reference role for component processing in engine manufacturing.
2.1.1 Structural Features of Parts
The camshaft production line supports the machining of each engine camshaft, using one camshaft per engine.
Material: (FCA-3) copper chromium molybdenum alloy cast iron, hardness of each main journal and end surface HB180~240, cam HRC48.
2.1.2 Camshaft schematic

凸轮轴简图

2.1.3 Main Processing Content and Accuracy Requirements of Engine Camshaft
(1) Support shaft diameter

Front shaft diameter front endφ32  -0.015~ -0.045,rear endφ32 -0.02~-0.04,Surface roughness Rz3.2
Intermediate shaft diameter φ47.5 -0.09~ -0.115 Surface roughness Rz3.2
Rear axle diameter φ 48.5 -0.06~ -0.085 Surface roughness Rz3.2

(2) Cam
6 cam base circle size is φ16.7 
-0.015~ -0.045, Surface roughness Rz3.2
The tolerance of radial runout of each cam base circle relative to the reference axis of the front and rear journals is 0.03mm
Relative degree of parallelism of the base axis of each cam relative to the reference axis of the front and rear journals is 0.01mm
The relative positional deviation (phase angle) of each cam centerline relative to the keyway ±20'

The cam profile error segment ±0.05mm
Cam profile error section ±0.02mm
One cylinder camshaft to keyway position 112°32′±20′


(3) Helical gear
Number of teeth: 13, helix angle: 53 ° (right) ± 1'46" public normal length: 38.611 ~ 38.806
Tooth error ≤ 0.025; Tooth error ≤ 0.017; Tooth groove angle to keyway 20° ± 2°

(4) Keyway
Width
4-0.05, depth 3+0.2, degree of symmetry 0.025

Camshaft Technology Analysis
(1) Ensure that the process has reasonable advancement, and on the basis of reassuring beats, absorb advanced technology to improve the competitiveness of the product.
(2) For key equipment and technologies, priority should be given to the advanced equipment of reliable manufacturers at home and abroad.
(3) Combining advanced and economical guarantees and reducing product costs under the premise of reassuring product quality
(4) Fully consider the safety of each production mitigation and the convenience of operation.
(5) Considering flexible production as far as investment is concerned.
Due to the slender and complex shape of the camshaft, the technical requirements are high, especially the machining of the cam, and therefore the machining process is poor.In the machining process of the camshaft, there are two main factors that affect its machining accuracy. One is the ease of deformation and the second is the difficulty of processing.

3.1.1 Selection of Positioning Baseline
For a typical shaft part, its axis is its design reference. The camshaft of the engine follows this design reference. Since the machining of the camshaft surfaces is difficult to complete in a single clamping operation, reducing the positioning error of the workpiece in multiple clampings becomes the key to ensuring the machining accuracy of the camshaft. In this paper, two top holes are used as the positioning reference for the shaft parts. This not only avoids the positioning error caused by the transformation of the positioning reference during the multiple clamping of the workpiece, but also serves as the positioning reference for the subsequent process. That is consistent with the "benchmark unification" principle.

This method not only makes the mounting of the workpiece easy and reliable. Simplification of the work of the process of formulation, so that each process used the same or similar fixture structure, thereby reducing the design and manufacture of fixture time and cost, and it is possible to process more surface in a fixture. For mass production, it is not only convenient to use high-efficiency special machine tools and equipment to increase the production efficiency, but also to have high mutual position accuracy between the processed surfaces.
3.1.2 The three stages of the machining of the engine camshaft:
(1) The roughing stage includes each bearing journal, gear outer journal and coarse grinding cam. This stage requires that the machine is rigid and that the amount of cutting is chosen to be as large as possible in order to remove most of the machining allowances at increased productivity.
(2) Semi-finishing is the support journal of the finishing carriage and the outer journal of the precision grinding gear. This stage is mainly to prepare for the processing of supporting the journal gear.
(3) Finishing includes grinding of each bearing journal, thrust surface and cam, and helical gear machining. At this stage, the machining allowance and cutting amount are small, and the machining accuracy is high.
Process layout: First, take the blank planes of φ32 and φ48.5 as the reference, and then use the large end of the outer circle as the axial positioning, specifically the positioning reference and clamping position of each sequence. See Table 3-1 for an overview of the engine camshaft production process.

3.1.3  Arrangement of process sequence
The arrangement of the processing sequence is related to the quality requirements of the parts, and whether the process arrangement is reasonable has a great influence on the machining quality, productivity, and economy of the camshaft. For each supporting journal is according to the rough car - fine car - fine grinding processing, for the cam rough grinding - fine grinding process, for the helical gear is according to the rough car - fine car - fine grinding - Hobbing machined. The processing sequence of each surface is from coarse to fine, and the main surface and the secondary surface of the processing process cross each other. Overall speaking, it conforms to the processing principle of “first coarse and then fine”.
 

Table 3.1 Introduction of Engine Camshaft Production Process

NO. Process content Positioning benchmark Clamping position Note
 
 
 
10
Milling face, hit the center hole Φ52.5 outer circle V2 (Survival size φ48.5)
φ36 outer circle V2(Survival sizeφ32)φ52.5 End face V1
 
 
φ52.5 outer circle
φ36 outer circle
special plane
 
 
20
Rough turning spindle neck φ37.5 Cylindrical V1(Survived sizeφ37.2)
Center hole at both ends V4
 
 
φ37.5Cylindrical
 
Semi-automatic hydraulic profiling lathe
 
30
 
Turning the main spindle neck and grooving
φ37.5 Cylindrical V1
Center hole at both ends V4
 
φ37.5Cylindrical
Semi-automatic hydraulic profiling lathe
 
 
 
40
 
 
Drilling holes at both ends, Expansion, tapping, repair center hole
φ48.9 Cylindrical V2(Survived sizeφ48.5)
φ32.4 Cylindrical V2(Survived sizeφ32)
φ52.5End faceV1
 
 
φ48.9 Cylindrical
φ32.4 Cylindrical
special plane
 
50
 
Big end cylindrical grinding
Center hole at both ends V1
φ37.5 Cylindrical V1
 
φ37.5 Cylindrical
Semi-automatic End faceCylindrical grinder
 
60
 
Front axle grinding
Center hole at both ends V4
φ37.5 Cylindrical V1
 
φ37.5 Cylindrical
 
CNC grinder
 
70
Intermediate journal, rear journal and thrust end face grinding Center hole at both ends V4
φ32CylindricalV2
 
φ32 Cylindrical
 
CNC grinder
 
 
 
80
Milling keyway φ48.5 Cylindrical V2
φ32 Cylindrical V2
φ30End faceV1
Angular orientation 90°V1
 
 
 
φ48.5 Cylindricalφ32 Cylindrical
special plane
 
 
90
Rough grinding cam (by grinding) Center hole at both ends V4
key V1
Chuck V1
 
φ22 Cylindrical
 
 
Cam grinder
 
 
100
Grinding cam (without grinding) φ30End faceV1
Center hole at both ends V2
key V1
 
 
φ22 Cylindrical
 
 
Cam grinder
 
 
120
 
Hobbing
φ30End faceV3
Center hole at both ends V2
key V1
 
 
φ22 Cylindrical
 
 
130
Cleaning φ30 & 1IN Non-machined surface V2
φ3 & 3EX Non-machined surface V2
 
No clamping
 
 
3.1.4  Engine Camshaft Process Features:
    (1) blank High hardness ( Cchilled area HRC45, Non-chilled area HB229~302)
    (2) Production beat 1.75 minutes
    (3) Axle CNC lathes for rough machining of journals
    (4) The cam portion is cold-induced during casting and does not require post-processing quenching
    (5) The coarse and fine grinding of the cam is used to grind the car and the cam profile is ground directly
    (6) CNC finishing grinding with full CNC grinding
    (7) The main positioning reference center hole in machining is used after hole drilling to ensure the processing quality.

Technical Difficulties
1, Spindle neck roughness guarantee
Difficulties in the production of camshafts are that the roughness of the main journals does not meet the requirements of the drawings, the drawing requirements are Rz3.2, and the actual processing conditions are Rz ≤ 5.2, which brings a lot of trouble to verification.

According to the actual situation, first of all, by changing the cutting amount of the machine tool, the prescribed cutting amount of the machine tool is completely changed, and a set of data is tested, and the final result is still not good. Finally, under the condition that the grinding wheel is not changed, the grinding speed F of the diamond dresser and the dressing amount μ are changed to increase the roughness of the workpiece. Through repeated trials, several sets of better data were obtained.

μ=0.08       F30         Rz=2.66Z~3.79Z

μ=0.04       F15         Rz=2.50Z~3.50Z

μ=0.06       F30         Rz=2.60Z~3.66Z

μ=0.04       F35         Rz=2.00Z~3.20Z

Through comparison, it was decided to use the data of μ = 0.04, F30, grinding 5 parts once, roughness <3.2Z.
1) axis neck Clip marks:
The cam shaft 120 is positioned with the keyway when the cam is ground, and the outer circumference of the φ22 is clamped.The long-term use of the three-jaw causes φ22 to be surrounded by three bright bands on the outer circle, and the roughness is qualified.
The cam grinder has a bright band at the time of equipment acceptance. It is understood that most of the cams in the cam grinding process use the tongue and groove angle to position the three-jaw clamping workpiece at the small end of the outer circle. The center frame supports the radial surface of the shaft to complete the grinding process. This scheme is bound to produce a pinch mark.
The process is used by Toyota Motor and FAW-Volkswagen. The new 1SZ camshaft is also machined from the outside using this machining process. This process plan can continue to be used.
2) The next step in the thorough elimination of the gripping process is to use a reverse-sequencing process, first grinding the peaches and grinding the small-ends.
a) Use this method, which involves changing parts: cam grinding to three-jaw, center frame. The keyway milling machine relocates the positioning block and the measuring tool process size chain to change all the process files.


 

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