Undercut Process

This trial version can use only a part of item.

Undercut Process

In this chapter you will learn about the process for an undercut part.

Undercut refers to the convex or concave area of part. When removing the part from the mold, you need some device so that the part of the mold which contacts to the undercut can be moved to remove the part from the mold since the part will not be removable directly without the device.
This process is called Undercut process.
Undercut process uses different methods depending upon whether the undercut is outside or inside the part.

Here are some examples of parts with undercut.


Push-pin	Grip of a driver	Grip of a cup

Now, let's learn about external slide core method, internal slide method, and hydraulic cylinder method of undercut process.

External Slide Core Method

The external slide core method is usually used for the process of outer undercut.
Working along with the open / close movement of a mold, this method slides the slide core to process the undercut.
The hydraulic cylinder method is also available, which will be explained in detail later

Slide Core Body Unit

The portion where the undercut process is performed linked along with the movement of mold opening. The amount of movement of the slide core and the angle and the length of the angular pin are key factors to this unit.
The locking block installed to the cavity plate receives the pressure from the injection when closing the mold. Upon opening of the mold, the slide core moves backward by the force from the angular pin and the spring, thus releasing the part.
As the hole will be misaligned and the angular pin will not be inserted if the slide core moves too far backward, a core stop block needs to be installed.
This correlation is illustrated below.

(Click each name in the figure to display the description.)

The relief distance and the tilt angle of the angular pin are as follows:

S: Undercut amount
S1: Slide stroke amount

: Tilt angle of slide core

: Tilt angle of angular pin
S1 = S + 5mm up

+(2- 5)

In order to prevent the slide core and the loking block from intervening with each other in mold opening and closing, make the tilt angle of the angular pin smaller than that of the locking block.
Also, a gap of 0.5mm is added to the hole for angular pin for errors occurring at processing.

Push Back Spring

The mass when the slide core is sliding varies depending on the direction of sliding.

<Example>: Suppose you install a 5kg slide core on the side parallel to the ground. How long should the spring be? The stroke is 20mm.

D: Spring diameter
L: Spring free length (see a catalog by each manufacturer)
E: Spring close length (see a catalog by each manufacturer)
F: Stroke
G: Length of shrinkage by slide weight
K: Spring constant (see a catalog by each manufacturer)
W: Slide weight

If using light load [K = 0.6kgf / mm] for spring:

Spring constant (K)	Free length (L)	Max. deflection (F + G)	Outer diameter (D)	Usage count
0.6kg/mm	65mm	32.5mm	16mm	350,000 times

To figure out the slide mass, it is 1.5 times the weight of the slide core:
W =5*1.5=7.5kg

As the length of shrinkage due to the weight of the slide mass is: G = W/K :
G = 7.5/0.6 = 12.5mm

As the free length of the spring is: L = E + F + G :
L = 32.5 + 20 + 12.5 = 65. Referring to the catalog,
Use the spring with L = 65.

Answer D = 16 L = 65mm