generic pq2 diagram

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MAGMASOFT ® Committed to Casting Excellence Casting Excellence GENERIC PQ 2 DIAGRAM 1 A completed PQ 2 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 PQ 2 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: P m = p h *(d h 2 /d p 2 )…………………………Eq. 1

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Page 1: Generic Pq2 Diagram

MAGMASOFT® Committed to Casting Excellence Casting Excellence

GENERIC PQ2 DIAGRAM

1

A completed PQ

2 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 PQ

2 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/dp

2)…………………………Eq. 1

Page 2: Generic Pq2 Diagram

MAGMASOFT® Committed to Casting Excellence Casting Excellence

Where:

Pm –metal pressure in kg/cm2

ph –hydraulic pressure in kg/cm2

dh2- effective hydraulic cylinder diameter in cm

dp2 – plunger diameter in cm

Pm

ph

Picture 1. Hydraulic cylinder with Tailrod.

Substitute for dh2 in Eq.1

dh2 = dc

2 – dr

2

Where:

dh2- Effective hydraulic cylinder diameter in cm

dc2 – Main hydraulic cylinder diameter in cm

dr2 – Tailrod diameter in cm

Plunger

Hydraulic cylinder piston

Tailrod

Pm

kg/cm2

Q (cm3/sec)

Page 3: Generic Pq2 Diagram

MAGMASOFT® Committed to Casting Excellence 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)

Page 4: Generic Pq2 Diagram

MAGMASOFT® Committed to Casting Excellence Casting Excellence

Pm

kg/cm2

Q (cm3/sec)

Higher hydraulic pressure

Lower hydraulic pressure

Q (cm3/sec)

Pm

kg/cm2

Smaller plunger

Larger plunger

Smaller plunger Larger plunger

Effect of Plunger size

Page 5: Generic Pq2 Diagram

MAGMASOFT® Committed to Casting Excellence Casting Excellence

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.

T = casting thinness in mm.

Ti = Temperature of the molten metal as it enter the die in 0C.

Tf = Minimum flow temperature of the metal as enter in 0C.

Td = Temperature of the die cavity surface just metal enter in 0C.

S = Percentage solid fraction allowable in the metal at the end of the filling in %.

Z = Unit conversion factor in 0C / % .

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

table.

Page 6: Generic Pq2 Diagram

MAGMASOFT® Committed to Casting Excellence Casting Excellence

Cavity volume is the amount of metal that flows through the gate during the cavity fill.

Volume are calculated by .

Vcav = W /density (kg/cm3)……………………Eq. 4

Where :

Vcav = volume of the metal passing through the gates in cm3.

W = weight of the metal passing 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

Q (cm3/sec)

Pm kg/cm2

Page 7: Generic Pq2 Diagram

MAGMASOFT® Committed to Casting Excellence Casting Excellence

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

Page 8: Generic Pq2 Diagram

MAGMASOFT® Committed to Casting Excellence Casting Excellence

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.

Q (cm3/sec)

Pm kg/cm2

Q (cm3/sec)

Pm kg/cm2

Prepared by

Maheshwar N Morab