Hiixocastiiig
Chapter 3 Test and Experiment Methods
3.5 Casting the two planar model parts Method
The insert die was assembled to create to the first planar model. Six shots were fired into this die.
The injection of the shots were interrupted at the six critical areas (short shots) - gate, bottom ellipse, bottom of hour glass, middle of hour glass, top of hour glass and the top ellipse. These short shots are shown in diagram 4-22.
Two full shots were cast. The process parameters for the casting are in table 3-7. The short shots were done stopping the injection plunger at the positions given in table 3-8.
Table 3-7: Process Parameters Metal
Temperature 580
Die Temperature
250
Plunger injection velocity
0.5ms"1
Hydraulic Presssure
16MPa
Table 3-8: Injection Plunger halt positions
Volume # X[mm]
T[ms]
Gate
1 241.61 482.2
Bottom Ellipse 2 257.4 514.8
Bottom hour glass 3 258.6 517.2
Middle of hour glass 4
263 526
Top of hour glass 5
270 540
Top of ellipse
6 279 558
The injection positions (table 3-8) are calculated from first taking in to account the distance required to move for the metal to come into contact with start of the gate and then second adding the volume of the section as well as the preceding sections to come to the section of interest.
The sleeve length is 341mm including the die plate but excluding the cavity depth (25mm). To move the billet (120mm in length and 55mm in diameter) to the start of the cavity, a displacement of 221 of the plunger is needed.
X , = 2 2 1 + -
(CrossSectionalAreaOfSlug)
(28X70X25)
• = 221 + = 241.61mm
;r(55)2/4
X, =221 + (V,+V2)
(CrossSectionA reaOfSIug) • = 258.6mm
Where Xn = plunger position ; Vn = volume of the section (for dimensions drawings of the inserts are in Appendix 3).
T = X.
UAx)
Where Tn= time to reach position Xn and U„ = velocity function of displacement (x) Un is a const for this experiment kept at 0.5ms"1.
With this information the injection profile maybe set up to produce the short fills,
\felnciry [nis" J 0.6
0.5 0.4 0.3 0.2 0.1 0
Diagram 3-6: Injection Profile of short shots
Injection PlttGles of the Short Shots Iron? the First Plane of the Modular Die
100 200 300
Tmic |nis)
400 500 BOO
-Gate
• Bottom 1-Hipse - Bottom hour glass - Mddle of hour glass
• Top of hour glass - Top of ellipse
The injection profiles are entered into the computer which controls the modified 50ton Edgewick die casting machine. The die temperature was set and then forty five minutes is needed for the die to reach the set temperature. A thermocouple, mounted in both back plates of the platen onto which each die half is bolted, is used to measure and control the die temperature.
The metal is prepared by preheating a 50mm diameter by 120mm billet, machined from continuous cast A356 semi solid feed stock from Pechiney as described in section 3.2.3.4 Metal Preparation and Machine Parameters. The first injection profile is selected, "Gate". The billet is placed into the shot sleeve and the injection ram is initiated. The injection ram moves according to the selected profile in diagram 3-6. The casting is allowed to cool in the die for 20 seconds and then the die is opened and the casting is removed from the mould. The next billet preheated to 580°C and the next injection profile selected. The casting procedure is repeated. This procedure is done until all six castings have been cast using the six different injection profiles. Thus the six short fill castings are cast.
After the short fill castings have been cast two complete castings were made. Again a billet was machined from the feedstock to the same size and preheated to the same temperature. This time the injection profile in diagram 3-7 was used. An explanation is necessary to understand the profile.
The velocity is set to the injection speed of 0.5ms"1 and then it is held at that speed for five seconds.
The injection piston would have reached the end of its stroke by [0.300mm / 0.5ms"1] 0.6s but the speed is held at 0.5ms'1 for longer than this, this is clearly not possible. The piston will come to a dead stop even before this, due to cavity being full and the excess metal in the shot sleeve creating
the biscuit and holding the piston stationary. Now since the injection plunger is controlled via an electrically actuated infinitely variable proportional hydraulic valve by closed loop PID (proportional integral and differential) control using the injection profile entered in the computer as reference, what the impossible reference of 0.5ms'1 does in reality, is cause the PID control to keep the proportional valve fully open, to try to achieve the 0.5ms'1 even though the piston has come to a dead stop due to mechanical constraints and allow full hydraulic pressure to act on the piston and so intensify the molten metal as it cools. The intensifying of the metal assists in forcing metal from the hot reservoir of metal in the biscuit into the casting and aid in feeding new molten metal to areas of the casting still connected to the biscuit via a molten metal pathway as these areas solidify and shrink and so aid directional solidification"31.
Diagram 3-7: Profile of Full Shot
Full injection Profile
\fekicity [nis' ] 0.6 |
0 . 5 i • •
0.4 0.3 0.2 0.1
0 I 1
0 1000 2000 3000 4000 5000 6000 Time [m»l
Two castings were done using the injection profile in diagram 3-7. Giving a total of eight castings of the first planar model from the insert die.
The modular die was then dismantled and then reassembled using different inserts to create the geometry to cast the second planar model. A casting produced from the Modular die arrangement for the second planar model (diagram 3-5(b)) diagram 3-8. Four castings were done of the second planar die. Using the injection profile in diagram 3-9.
Again the speed is held constant to intensify the solidifying metal. The slower speed at the start of the profile is to aid in releasing the air from the mould and sleeve. The injection profile is entered into the computer in die same manner as the first planar model. The metal is prepared as for the first planar model at 580°C. The die temperature is set to 250°C. The hydraulic pressure is set to 16MPa.
Diagram 3-8: Casting produced using Modular for second planar model
\fck>city Ims" ] 0 . 6
Diagram 3-9: Second Planar Model Injection Profile
liikvii<>• Profile. JM«k.l.ii Die,secondFlarar M « k I
as
a4 a 3
0.2 0.1 <>
5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 0 T i n s [m>]
4500 5000
When the metal reaches 580°C it is placed into the shot sleeve of machine and the metal is injected into the die. This was done four times to create four full castings for the second planar model.
3.6 Evaluation and analysis of parts made from two planar model dies - identification of