DIE CASTING PROCESS FULLY EXLAINED IN DETAIL.pptx

DIE CASTING PROCESS FULLY EXLAINED IN DETAIL

1. DIE CASTING 1

2. 2 CASTING TYPES SAND MOULDING GRAVITY DIE CASTING LOW PRESSURE DIE CASTING HIGH PRESSURE DIE CASTING INVESTMENT CASTINGS In general the term “DIE CASTING” refers to high pressure die casting.

3. 3 HIGH PRESSURE DIE CASTING

4. 4 A PROCESS IN WHICH MOLTEN METAL IS INJECTED INTO A PRECISELY DIMENSIONED STEEL MOULD(DIE), WITHIN WHICH PRESSURE IS MAINTAINED UNTILL SOLIDIFICATION. THE PRODUCT IS A METAL CASTING WITH FINEST IMPRESSION OF DIE & HIGH DEGREE OF DIMENSIONAL INVARIANCE. PROCESS DEFINITION

5. 5 ALLOY REQUIREMENTS Good mechanical properties in cast condition like Tensile strength, Ductility, Hardness Dimensional stability Good machinability Suitable for pressure tightness Low melting point

6. 6 ALLOY REQUIREMENTS Good castability (Fluidity) Less & even shrinkage Less oxidation in molten condition Corrosive resistance Ability to excellent finishing such as polishing, plating, painting

7. 7 CASTABLE ALLOYS ALUMINIUM ZINC MAGNESIUM COPPER

8. 8 ALUMINIUM ALLOY MOST PREFERABLE ALLOY FOR ITS LOW DENSITY AND COMPARITIVELY HIGH TENSILE STRENGTH.

9. 9 MECHANICAL & PHYSICAL PROPERTIES BRINELL HARDNESS  65 Kg/Sq.cm. TENSILE STRENGTH  22 Kg/Sq.cm. MELTING POINT  595 o C SOLIDIFICATION Pt.  570 o C SHRINKAGE  0.6% CASTING TEMP  640 ~ 720 o C SPECIFIC GRAVITY  2.7gms/cc

10. 10 ALLOYING ELEMENTS COPPER Increases proportionately the fluidity, tensile strength and hardness. Reduces ductility and corrosion. Should not exceed 4% for a fair amount of silicon

11. 11 ALLOYING ELEMENTS SILICON Most important alloying element. Upto 13% increases fluidity. Reduces machinability & not suitable for anodising. Al. alloys with silicon less than 13% are called as Hyper-eutectic alloys and more than 13% are called as Hypo-eutectic alloy.

12. 12 ALLOYING ELEMENTS MAGNESIUM Improves physical properties of aluminium alloy. Alloy with 8% Mg are good corrosion reisitive and suitable for anodising. Are easier to machine. Addition of more Mg will have poor casting finish and tend to solder heavily on die walls.

13. 13 ALLOYING ELEMENTS IRON Iron free aluminium alloy tend to solder. This can be eliminated by addition of Iron between 1 to 1.3%. Iron decreased ductility & machinability, more so with high % of silicon.

14. 14 ALLOYING ELEMENTS NICKLE Balances the negative effect of Iron to some extent & increases the tensile strength. Reduces the corrosion resistance.

15. 15 MELTING AND SOLIDIFICATION MELTING The change of state of matter from solid to fluid & vice versa does not takes place suddenly, but within a stretch of melting process. The casting temperature is always well above the melting range.The difference of temperature is called over heating and it can be as high as 100 C or more.

16. 16 MELTING AND SOLIDIFICATION SOLIDIFICATION Structure and Quality of casting is influenced by the speed and nature of solidification The very fast solidification in Pressure die casting is due to High speed injection and the die temperature being 300 deg less than the solidification temperature of metal. Type of casting Speed of solidification Time, Unit Sand casting Slowest Secs, min Gravity casting Faster Pressure die casting Extremely faster Milli secs

17. 17

18. 18 DIE CASTING PRINCIPLES I PHASE: The metal is slowly brought up to the gate in accordance with shot volume and procedure. Time taken has to be 1 ~ 3 secs.

19. 19 DIE CASTING PRINCIPLES II PHASE The metal is rapidly injected into the die and the entire cavity is filled with metal in accordance with volume and procedure. Cavity fill time to be around 20 to 100 milli sec

20. 20 DIE CASTING PRINCIPLES III PHASE Consolidation of liquid metal in the die under high pressure of 400 to 1000 bar in very short time of 0.01 to 0.2 seconds of completion of shot.

21. 21 METAL PRESSURE I PHASE  5 BAR II PHASE  30 TO 120 BAR III PHASE  400 TO 1000 BAR

22. 22 METAL SPEED (VELOCITY) I PHASE  0.1 TO 0.5 m/sec II PHASE  20 TO 60 m/sec III PHASE  0

23. 23 SHOT CURVE

24. 24 Calculations FOLLOWING DATAS TO BE COLLECTED FOR ANY DIE Sleeve dia in mm Active sleeve length in mm Projected area of casting in sq.mm Gate area in sq.mm Shot weight in grams Weight after gate in grams (casting + overflow wt.) Casting type. (Standard, Technical or Pressure tight part)

25. 25 FILLING RATIO FILLING RATIO = SHOT VOLUME SLEEVE VOLUME SHOT VOLUME= Shot weight/Density. Sleeve volume = Cross section area of plunger X Active sleeve length Filling ratio to be between 40 to 70%

26. 26 Specific casting pressure STANDARD PART  400 TO 600BAR (Frisco cover, chasis) TECHNICAL PART  600 – 800BAR (Bosch Stop housing) PRESSURE TIGHT PART 800 – 1000BAR (Clutch housing, Transmission case)

27. 27 DIE LOCKING FORCE Die lock force = Die open force X 1.1 Die open force= Sp. Casting pressureX Projected area/100 = --------- KN Die open force in Tons = (-----KN) / 9.8 For eg: Die open force is 620 Ton Lock force reqd. is 620X1.1= 682Ton For this nearest higher capacity machine 730T has to be selected.

28. 28 I PHASE STROKE LENGTH I Phase stroke length (S1) = Active plunger stroke – (Height of metal in sleeve + biscuit thickness) Height of metal (Casting fill stroke) = Volume of metal / C.S.Area of plunger.

29. 29 I PHASE STROKE LENGTH Volume of molten metal : (Weight of metal after gate) / (Density of Al.X 0.95) Weight in grams C.S.Area of plunger: (3.14 X d 2 ) / 4 Diameter in mm.

30. 30 II PHASE VELOCITY II Phase velocity (V2 or Hi speed) = Casting filling stroke / (Cavity fill timeX1000) II phase velocity described in m/sec. Cavity fill time to be selected from chart of average wall thickness & cavity fill time.

31. 31 CAVITY FILL TIME Average wall thickness Fill time in sec 1.5mm 0.01 ~ 0.03 1.8mm 0.02 ~ 0.04 2.0mm 0.02 ~ 0.06 2.5mm 0.04 ~ 0.09 3.0mm 0.05 ~ 0.10 3.8mm 0.05 ~ 0.12 4.0mm 0.06 ~ 0.20 4.5mm 0.08 ~ 0.36 0.01 sec = 10milli second

32. 32 METAL VELOCITY AT GATE METAL VELOCITY = (Plunger velocity X C.S.Area of plunger) / Gate area Gate area = Length of gate X Thickness When there are multiple gates individual area should be calculated and summed up

33. 33 VARIABLES In Die casting process, many a variables affect the product quality. The most critical of them can be classified as follows. PRESSURE VARIABLES TEMPERATURE VARIABLES PROCESS VARIABLES

34. 34 PRESSURE VARIABLES PUMP PRESSURE: Pump pressure should be as per manufacturer specification. Different machines has got different pressure. It ranges from 110 bar to 160 bar. When pump pressure drops accumulator pressure & die lock force drops resulting in fast shot jerking and die flashing. NITROGEN GAS PRESSURE: Pressure should be as per manufacturer specification. Most of the cases it is a % of pump pressure. When N2 pressure drops Accumulator charging pressure, second phase speed and in some cases intensification pressure drops.

35. 35 PRESSURE VARIABLES INJECTION PRESSURE (I.P.) Injection pressure has to be set as per the casting’s requirement. If I.P. drops it will result in blow hole, shrinkage & Non filling. ACCUMULATOR CHARGING PRESSURE This pressure should be as per manufacturer’s recommendation. If drops will affect II Phase speed resulting in non filling problem.

36. 36 TEMPERATURE VARIABLES DIE TEMPERATURE Die temp should be maintained between 180 to 250 C Low die temp will result in cold defects like non fill, cold shut, shrinkage, flowline, wrinkles. High die temp will lead to die flashing, metal soldering, crack, casting breaking, warpage.

37. 37 TEMPERATURE VARIABLES METAL TEMPERATURE The casting temp suitable for die casting is in the range of 640 to 680 o C. It is important to operate the process with a tolerance band of +/- 5 o C for best results. For thick walled parts temp range of 640 to 650 o C & for thin walled parts temp range of 660 to 680 o C will be desirable.

38. 38 TEMPERATURE VARIABLES HYDRAULIC OIL TEMPERATURE Machine performance will be good when oil temperature is maintained between 26 to 40 o C. When oil temperature shoots up above 50 deg Pump press and related pressure drops and oil leakage occurs.

39. 39 PROCESS VARIABLES PLUNGER SPEED Casting quality gets affected by variation in plunger speed from shot to shot. Reason for variation: Friction between sleeve & plunger tip. Variation in metal temperature Variation of accumulator charging pressure Misalignment of shot sleeve & sprue bush Misalignment of shot piston and shot sleeve.

40. 40 PROCESS VARIABLES DIE FLASHING This results in poor casting quality in terms of filling & blow holes. Reason for flashing: High metal temperature High plunger speed High injection pressure Low die lock force Cores misaligned Poor die matching Tie rod strain variation.

41. 41 PROCESS VARIABLES METAL VARIATION Metal variation results in variation in casting quality. Metal variation is determined by the varying biscuit thickness. Biscuit thick should be maintained bet 20 to 40mm. Reasons Metal spillage on the path or during pouring. Leakage from laddle cup. Big size ladle cup or excess ladle wait time near pour hole resulting in metal solidifying in ladle cup. Die flashing. Faulty auto ladle. Less metal volume results in non filling & shrinkage. Excess metal volume results in II Phase speed not achieved, runner breaking, fix die clamps breaking, increase in melting loss.

42. 42 PROCESS VARIABLES CYCLE TIME Production process needs consistent cycle time. Variation in cycle time affects casting quality & productivity. Full automation helps to achieve consistent quality & quantity. In semiautomatic machines operator skill plays a major role in achieving out put and better quality. The die casting machine operator should know to make best use of time so that the cycle time is maintained at minimum and no time wastage is there. Other factor affecting the cycle time is the small frequent breaks (ie. Cycle break)

43. 43 PROCESS VARIABLES REASON FOR CYCLE BREAK M/C tripping Die flashing Hydraulic core jamming Casting breaking Runner breaking due to metal variation or poor condition of sprue bush or poor /no cooling Over flows sticking in die Faulty limit switch or sensor. Plunger tip jamming in sleeve / sprue bush Low metal level / temperature Unskilled operator.

44. 44 DEFECTS

45. 45 DEFECTS

46. 46 DEFECTS

47. 47 DEFECTS

48. 48 DEFECTS

49. 49 DEFECTS

50. 50 DEFECTS

51. 51 DEFECTS

52. 52 PRINCIPLE OF DIE LUBRICATION DIE LUBRICANT HAS 3 MAIN TASKS PARTING EFFECT LUBRICATION COOLING

53. 53 DIE SPRAYING PARTING EFFECT Before taking a shot die surface needs to be burned with a suitable agent. By this a thin oxide layer forms on die surface to prevent metal to metal contact and good release of casting and free of soldering on die. Oil in emulsifiers & polymer base die lub are used.

54. 54 DIE SPRAYING LUBRICATION The spraying agent should poses good lubrication property for ejector pins and moving slides COOLING EFFECT Short coming of die cooling system should be compensated. So the spraying agent need to act as cooling agent. The water content in the die spraying agents serves the purpose.

55. 55 DIE SPRAYING (Dancing bubble)

56. DIE PARTS