Generic Pq2 Diagram 47r3w

GENERIC PQ2 DIAGRAM 1 A completed PQ2 diagram is shown bellow. Noticed that the gole is to predict where a given die will operate when mounted on a machine with known performance. Also shown is an operating window that developed to match the needs of the casting quality requirements. The object is to make a design that will have the die and the machine operate within the range of the developed operating window.

1.Plotting machine power

The first step in constructing the PQ2 diagram is to plot the machine power line. The machine power line is a straight line with one end represented by the “static” metal pressure and the other end represented by the maximum machine flow rate performance (dry shot speed) as it is calculated with a know shot sleeve diameter. The “static” metal pressure is calculated from hydraulic pressure on the cylinder that is transferred to the metal cylinder that transferred to the metal through the plunger tip. The hydraulic pressure used is the shot bottle pressure or the hydraulic pressure used during the cavity-filling portion of the cycle, not the final intensified pressure. The formula used is: Pm = ph *(dh2/dp2)…………………………Eq. 1

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Where:

Pm –metal pressure in kg/cm2 ph –hydraulic pressure in kg/cm2 dh2- effective hydraulic cylinder diameter dp2 – plunger diameter in cm

in cm

Pm Tailrod

ph Plunger Hydraulic cylinder piston

Picture 1. Hydraulic cylinder with Tailrod. Substitute for dh in Eq.1 2

dh2 = dc2 – dr 2

Where:

dh2- Effective hydraulic cylinder diameter in cm dc2 – Main hydraulic cylinder diameter in cm dr2 – Tailrod diameter in cm

Pm kg/cm2

3

Q (cm /sec) Casting Excellence MAGMASOFT® Committed to Casting Excellence

The other end of the machine line is defined as the maximum machine performance. It is calculated by multiplying the maximum dry shot speed(at the hydraulic ‘shot’ pressure used above) time the area of the plunger.

Qmax = vp * (п dp2/4)

……………………………….

Eq. 2

Where.

Qmax = maximum fill rate in cm3/sec vp = max. Dry shot speed in cm/sec п = 3.142-constant Dry shot speed-if there is no molten metal available in shot sleeve, there is no resistance to the motion of the shot cylinder piston other than the resistance of machine elements, in that apt the plunger velocity will be maximum and this velocity is called as dry shot speed.

Pm kg/cm2

Q (cm3/sec) MAGMASOFT® Committed to Casting Excellence Casting Excellence

Higher hydraulic pressure

Pm kg/cm2

Q (cm3/sec) Lower hydraulic pressure

Smaller plunger

Larger plunger Pm kg/cm2 Smaller plunger

Q (cm3/sec)

Effect of Plunger size MAGMASOFT® Committed to Casting Excellence Casting Excellence

Larger plunger

2.Plotting Theoretical Filling Time. Once filling time is identified for the volume of the casting being produced, a fill rate is calculated. This fill rate is considered the theoretical minimum fill rate that can be used to produce the highest quality casting. Filling time is identified as ‘t’ sec, and is calculated.

t = k *T { (Ti - Tf + SZ) / (Tf - Td )} ………………..Eq. 3 Where:

t

= The ideal filling time in sec.

K

= Empricalcally derived constant, sec/ cm. = casting thinness in mm.

T Ti Tf Td S Z

= Temperature of the molten metal as it enter the die in 0C. = Minimum flow temperature of the metal as enter in 0C. = Temperature of the die cavity surface just metal enter in 0C. = Percentage solid fraction allowable in the metal at the end of the filling in %. = Unit conversion factor in 0C / % .

Filing time can also be chosen by experience or general practice as shown in bellow table.

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Cavity volume is the amount of metal that flows through the gate during the cavity fill. Volume are calculated by .

Vcav = W /density (kg/cm )……………………Eq. 4 3

Where :

Vcav = W =

volume of the metal ing through the gates in cm3. weight of the metal ing through the gates in kg.

Once the volume, and filling time is known the filling rate Q can be calculated by

Qth = Vcav/ t…………………………..Eq.5 Where : Qth = Theoretical filling rate calculated in cm3/sec. Vcav= casting and overflow volume in cm3 t = theoretically fill time in sec Theoretical fill rate is plotted as a vertical line on the PQ2 diagram as shown bellow

Pm

kg/cm2

Q

(cm3/sec)

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3.Metal Pressure To further identify a proper die cast process gate area and the velocities through gate play a major role. The next step is identify the metal pressure required to move metal through the gate at different values of gate velocity.

Bernoulli’s Equations Gate velocity is the speed at which molten metal moves through an orifice or gate. The load on the die casting machine’s injection system comes from the force required to push the molten metal through the die orifice or gate and can be represented as the discharge pressure that is developed when the metal is forced through the gate at the desire gate velocity. pm

= ( rho * 2g) * ( vg/cd )2 …………………Eq. 6

Where : p = metal pressure in kg/cm2 g = 981 cm/sec2 vg = gate velocity cm/sec cd = coefficient of discharge cd for Al - 0.5 to o.6 Zinc – 0.6 to 0.7 Mg – 0.6 to 0.7 Velocity of the gate is calculated by using Vg = Q/ Ag ……………………………..

Eq. 7

Gate velocity can be chosen from the reformation

m/sec

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Pm

kg/cm2

Q

(cm3/sec)

4.Die line (Gate Area) Any point within the process window is an acceptable process that can be run on the diecast machine for the specific casting to be produced. The best starting point is to pick a process that is in the center of the process window. This allows the process very within the process window due to normal variations within the die casting process.

Pm

kg/cm2

Q

3

(cm /sec) Casting Excellence MAGMASOFT® Committed to Casting Excellence

Prepared by Maheshwar N Morab