Bumper Body Mold

Here we are going to introduce some basic points for a bumper body mold design.

Normally a plastic bumper wall thickness is between 2.5mm and 3.5mm, while gas assisted one could be thinner, and if the front bumper body with a grille integrated then the grille needs a wall thickness of more than 2mm and make the draft angle more than 2 degree. For other design details we share as below:

Water cooling system

See left below the main view for cooling circuit. As PP requires greater cooling that temperature needs to be controlled ±5°, when we make the water cooling circut design as 1.5D≤A≤2.5D; 2.5D≤B≤3.5D

Cuboid guide pillar is used which should be Cr12 with quenching treatment and wear plates should be copper+graphite;5° slope lock for four mold sides and plus Cr12 quenched wear plates with hardness of 54－56HRC on slopes.

Due to its complicated undercuts we need to make an ejection mechanism with lifter A,B,C,D,E,F and push part G,H for product release from bumper mold. Set product ejection stroke S 300mm, see below table for lifters eject angle and stroke figures.

As lifter A moves horizontally and lifter B 14° from horizontal which needs to rid the undercut at side, we can set A 5 ° and B 10° for eject angle to avoid contacting by slope difference a. Calculation formulas as followed:

SA（stroke A）＝TAN 5° x S (part stroke), SB＝TAN 10° x S, LA＝TAN32° x SA, LC＝SIN 14° x SB, LB＝TAN32° x COS14° x SB, LA＜LB-LC

For slope difference b: SA＝TAN 5° x S , SC＝TAN 9° x S, LA＝TAN25° x SA, LC＝SIN 8° x SB, LB＝TAN25° x COS8° x SB, LA＜LB-LC

As E moves vertically, slope c needs to get away for room to avoid contacting, so calculation formulas: SB＝TAN 10° x S , LA＝TAN 14° x SB, LB＝TAN 15° x (LA / SIN 14°), SE＝TAN 5° x S, proving that SE＜LA+LB

Next to lifter F there is one rib which needs to be reduced thickness at bottom, necessarily to make F move downwards delayed by 30°.

To make a pogo-pin mechanism for two small holes on product by reason that when mold open the product will move by some distance along with the fixed half and don’t depart until getting off the undercut.So when moving 80mm, pogo-pin springs 7mm to get undercut part at holes departed.

Hidden parting line mold demoulding solution as picture viewed. Given product eject stroke 300mm, lifter area undercut maximum 10mm, lifter A max. stroke 26mm, we can do the calculation LA=10mm+830mm(distance between mold center and undercut)x1.2%(part shrinkage)=20mm(actual distance to rid undercut).

As product deforms by lifter A stroke whose eject angle is 5° and undercut distance 2.2mm, make the lifter eject 80mm, deform 7mm, the undercut will get off. Then the lifter go on to stroke limit that mold open finish and take out product.

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