High-Performance Industrial Grinding: Recent Advances and Case Studies from Automotive Industry

Transcription

1 1 High-Performance Industrial Grinding: Recent Advances and Case Studies from Automotive Industry Peter Krajnik, Ph.D. 2. Wiener Produktionstechnik Kongress Vienna,

2 2 The world of Scania Production units Regional Product Centres Sales and services units Production units 1891 Sweden 1957 Brazil 1964 Netherlands 1976 Argentina 1992 France 1993 Poland Sales and services units 1,000 sales points 1,600 workshops More than 95% parts availability Round-the-clock assistance Number of employees 37,500 persons

3 3 Resource productivity Vehicles per production employee Vehicles produced per employee Vehicles Employees ,0 78,400 80,400 84,000 8,0 6,6 67,700 6,8 7,2 6,6 55,600 6,0 46,400 31,800 4,8 3,8 35,800 3,5 4,0 3, ,100 11,600 11,800 11,800 2,0 9,500 10,300 11, ,0

4 4 In-house production of engine parts Camshaft Size: Length: 1052 mm Weight: 35 kg Balanceshaft Size: Lenght: 600 mm Weight: 8 kg Cylinder Liner Size: Inner diameter: 130 mm Height : 272 mm Weight: 6,5 kg Crankshaft Size: Length: 1006 mm Weight: 110 kg V8 Cylinderblock Straight Cylinder Block Size: Length : 1025 mm Height : 537 mm Width: 364 mm Weight: 266 kg Size: Length: 866 mm Height: 551 mm Weight: 370 kg Connecting Rod Size: 255 mm (C-C) Weight: 4,8 kg Cylinder Head Size: Length : 256 mm Height : 125 mm Weight: 17 kg

5 5 Industrial challenges in grinding Industrial challenges in grinding are driven by higher production capacity demands as well as changes in part design and materials (high variation in incoming quality). Opportunity for widening implementation of CBN in industrial grinding. A better guidance on the advantages of CBN-use needs to be cleared-up for the industry. Preparing skilled engineering staff that can comprehend the fundamentals of grinding technologies and apply them in practice. There is a major need for providing training to practitioners (machine operators and process planners). Large investments in high-performance machine tools. Adapted from: Oliveira et al. (2009) Industrial challenges in grinding, CIRP Annals - Manufacturing Technology

6 6 Evolution of the drivers - "Need for Speed" The idea of increasing wheel speed to improve the profitability in grinding (Krug) Research on high-speed grinding concept (Opitz, Gühring) - wheel speed of 100 m/s Reaching the extreme (König, Ferlemann) - wheel speed of 500 m/s High-performance industrial grinding (Nissan Motor Co.) - wheel speed of 240 m/s Low wheel speeds (40-80 m/s) are being used for the majority (~40%) of industrial CBN grinding operations

7 7 Chip thickness vs. grinding aggressiveness v c v w Chip thickness: h m é 4 æ öæ ö vw = ae ç ç Cr èv øè ø ê s de ë 1/2 1/2 ù úû Larger aggressiveness deeper grit penetration larger forces on grits more wheel wear lower relative heat generation higher productivity lower quality v c v w C - cutting-point density r - chip width to chip thickness ratio Grinding aggressiveness: aggr æ öæ ö 6 vw = ae 10 ç ç èv øè d ø s e 1/2 Source: The Grinding Doc Consulting (2010)

8 8 Productivity vs. quality Specific energy into the workpiece e w [J/mm 3 ] q m Grinding sweet spot e w (aggr) q m (aggr) - rough grinding q m (aggr) - finish grinding = Q e ( ) w w aggr krc l v p c w Workpiece surface temperature q m [ C] Aggressiveness number aggr

9 9 Surface integrity in grinding Corrosion HV Tempering (softening) Tensile residual stresses Cracks Surface finish Rehardening Thermal damage Oxidation burn The most important aspects of surface integrity are associated with thermal damage caused by high grinding temperatures. Thermal damage affects part quality and limits the production rate. Source: Brinksmeier et al. (2004) Chemical aspects of machining processes, CIRP Annals - Manufacturing Technology

10 10 Barkhausen Noise measurements

11 11 Barkhausen Noise vs. grinding temperature Barkhausen Noise Range of measured Barkhausen signal Hypothetical Barkhausen response curve T sft Z rh < mm Z rh = 0.0 mm Grinding temperature (ºC) T s 2 T RH 3 Z rh = mm Z rh = mm

12 12 Visual inspection for cracks

13 13 Applications in the automotive industry Engine Transmission

14 Grinding of crankshafts 14

15 Grinding of crankshafts 15 Consist of sequences that range from simple (crankpin and journal diameters) to complex (pin sidewalls). HEDG of crankshafts can attain Q w =2000 mm 3 /(mm s). The avoidance of thermal damage in this scenario is possible by utilizing high work speeds (only viable for small crankshafts used in car engines). Crankshafts used in commercial vehicles are much heavier (~120 kg), limiting the achievable work speeds and hence productivity. Critical crack

16 16 Grinding of camshafts

17 17 Grinding of camshafts Cam-lobe grinding in a single setup can replace the multi-set-up operations of soft machining, hardening and conventional grinding. The total stock removal can be as high as 0.7 to 1 mm. The achievable productivity (e.g. Q w = mm 3 /(mm s) is not as high as in crankshaft grinding. This is due to machine limitations - speed, acceleration, and jerk of both workdrive and wheelhead. Grinding of cam lobes is a complex non-round cylindrical grinding process.

18 18 Constant-temperature grinding process New concepts in non-round cylindrical grinding to: (1) choose process parameters based on a thermal model for achieving a constant temperature; (2) optimize the grinding process for shorter cycle times while applying the concept of constant temperature. P - index 1,4 constant Q'w 1,2 constant P constant θm 1,0 0,8 0,6 0,4 0,2 0,0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 t - index q w v d aggr = e ( aggr ) C k c n * s * w aggr r p i = vs cosy 0, i 2 rs ( R0, i + rs ) aggr * n C d R aggr ws, i 0, i d * Source: Krajnik et al. (2014) Cycle optimization in cam-lobe grinding for high productivity, CIRP Annals - Manufacturing Technology

19 19 Optimal number of feed increments 1,1 1,2 t g - index 1,0 0,9 0,8 0,7 0,6 0, n θ*= 400 C θ*= 450 C θ*= 500 C θ*= 550 C θ*= 600 C t g - index 1,1 1,0 0,9 0,8 0,7 0,6 0,5 cam lobe1, machine1 cam lobe1, machine2 cam lobe2, machine1 no limitations 0, n cam lobe1 cam lobe2 Source: Krajnik et al. (2014) Cycle optimization in cam-lobe grinding for high productivity, CIRP Annals - Manufacturing Technology

20 20 Effect of wheel speed on cycle-time 1,3 1,2 t - ratio 1,1 1,0 0,9 0,8 vs = 80m/s vs = 120m/s vs = 160m/s n

21 21 Effect of wheel speed on aggressiveness aggr vs = 80m/s (n = 18) vs = 120m/s (n = 19) vs = 160m/s (n = 22) j ws [ ]

22 22 Effect of wheel speed on temperature q m [ C] vs = 80m/s (n = 18) vs = 120m/s (n = 19) vs = 160m/s (n = 22) j ws [ ]

23 23 Conclusions OEMs should develop their own high-performance grinding processes and set requirements for design of machine tools. The recently developed innovative solutions for cam-lobe grinding, namely the implementation of a constanttemperature process, can lead to increased productivity along with a better ability to avoid thermal damage. High wheel speeds in roughing are beneficial for achieving the set constant-temperature, even though the productivity is slightly reduced. In an industrial environment an minor reduction of productivity is tolerated if higher quality gains are attained.