Constant friction at lobes surface, calling for good fatigue and surface wear properties.
Current Manufacturing Methods
-Chilled Casting (Rough Grinding, Finish Grinding)
-S G Iron Casting (Copy Turning, Heat Treatment, Rough Grinding,Finish Grinding)
Short Comings
- Fairly oversize casting
- Chances of non uniform surface hardness
- Occurrence of burn marks in grinding
- Hardness < 48 HRc
- Distortion in heat treatment in case of S G iron Shaft.
Short Comings
- Oversize forging
- Distortion in heat treatment
- Difficulties in induction hardening
High Performance Engines
Lighter Weight.
Accurate profile of cam lobes.
Higher wear resistance on cam lobe surface.
Suitability for integration with other engine system.
Facilitating lubrication.
Balanced component.
Alternate Route for Camshaft Manufacture
Manufacture cam lobes by Powder Metal Route.
Manufacture shafts from bars or tubes ( hollow shaft ) by machining.
Assemble cam lobes on solid or hollow shaft.
Grind the assembly.
Manufacture of Cam Lobe by Powder Metal Route
Selected powder should offer :
- Good compressibility.
- Consistent dimensional accuracy.
- Response to Heat treatment.
- Good wear resistance.
- Minimal distortion.
Astaloy Mo
- Water atomized.
- Pre alloyed with 1.5% molybdenum.
- Offers high compressibility.
- Homogeneous microstructure on sintering.
- Excellent for parts requiring surface hardening.
Using P/M Technology, Manufacturing of cam lobes individually is a fairly straight forward proposition.
To have improved density thereby to achieve higher strength, method of 2P 2S adopted. 2P 2S Method
- 1st pressing (compacting).
- 1st sintering.
- 2nd pressing.
- 2nd sintering.
- Design and fabrication of tools – A major factor in success of project.
- Detailed study of powder characteristics w.r.t. sintering parameters is essential.
- 1st and 2nd compacting stage tooling designed based on this study to produce net to size lobes.
Methods available are :
- Shot peening.
- Rolling.
- Burnishing.
The process should give high dense zone on lobe periphery, of about 95% theoretical density of metal.
Hardening of Cam Lobe :
- Casehardening.
- Hardness achieved 50—55 HRc on surface, core is soft.
- Case Depth 1.5 mm.
- Distortion Minimal.
Casehardening Process to be selected to suit method of joining with shaft
Manufacture of Shafts
Shafts are of two types - Solid - Hollow
Solid shafts are produced from bars by machining.
Hollow shafts are produced from appropriate tubes.
Joining Methods
Method for cam lobes fitting over shafts - Press fitting - Shrink fitting - Copper brazing - Diffusion bonding - Hydro forming (in case of hollow shafts)
Fixturing required for proper location of lobes on shafts.
Post Operations
Finish grinding of lobes.
Finish grinding of bearing surface.
Normally done at customer end.
As lobes are almost net to size, grinding allowances are minimal avoiding heat marks.
Advantages of Proposed Method
Cam lobe width can be reduced.
Hollow shaft components facilitate lubrication.
Total process reduces work in process inventory.
Process offers flexibility to integrate with other engine system e.g. oil pump drivers, gears, with single drive.
Variable speed camshaft design is feasible.
Prototype development is faster. Fine tuning of relative positions easier.
Total cost of camshaft compared to conventional method is lower.
