DE4331488C2 - Process for punching plastic sheets - Google Patents

Description

The invention relates to a method for punching Plastic films or sheets.

Punching plastics using top and bottom terstempel has been a process that has been known for years geometrically defined from flat plastics Punching out shaped bodies or in flat plastics to introduce geometrically defined recesses.

The quality of the cut edges in this process plays a particularly important role in high-quality plastic parts significant role. Ideally, the cutting edge of the Workpiece with plane-parallel plates perpendicular to Surface and be absolutely burr-free.

This requirement is only approximated by 2 Plastics with a high modulus of elasticity and low mecha stretch.

Most known plastics based on e.g. B. Polyarylates, polyvinyl chloride, ABS, polyurethanes, po lyolefins, cellulose esters, thermoplastic polyacrylics laten, show the mechanical stress a so-called cold flow during the stamping process behave, which has the consequence that plastic material in the cavity of the lower die flows. Because of this cold The plastic will flow with the previously usual punching process over wide areas  the thickness sheared and not cut. The result is messy, fibrous Cut edges.

Efforts to date to solve this problem by cutting air between Avoiding the upper and lower stamps did not work, especially for large series desired success.

From the German patent DE 29 04 620 C2 a device for removing or Removing flat articles (e.g. plastic films) known with a Wall notch are provided as a predetermined tear, the outside of the edge notch located part of the film is mechanically clamped and the part to be removed the film by means of compressed air, if necessary through the intermediation of an intermediate membrane is torn from the outer part. With this method you can only notched foils are cut out. The problem with a mechanical Punching by means of upper punches with cutting edges on plastic foils occurs DE 29 04 620 C2 nothing known.

From the "Techniker Handbuch", publisher Alfred Böge, 5th edition, publisher Friedrich Vieweg & Sohn, Braunschweig / Wiesbaden, page 806 is fine punching of sheet metal is known in which a cutting punch in a punching device 90 ° cutting edges on the opposite side of the workpiece pressure stamp is juxtaposed. The surface quality is achieved by fine stamping of the cut surfaces increased. On the special problems of cutting Plastic films occur due to the cold flow behavior of the plastic in the nothing mentioned.

Efforts to address this problem by introducing a mechanical counter Solving the pressure plate in the lower stamp brought an improvement, however likewise not the desired success.  

The invention relates to a method for punching films or sheets Plastic with cutting punch and cutting plate, in which the flat plastic is first pressed against the cutting plate from the cutting punch side, then from the opposite side within the cut edge back pressure is defined and then simultaneously at the same time is cut from the cutting punch, characterized in that the Back pressure is generated by compressed air from 2 to 300 bar.

In the method according to the invention, the flat plastic is during the Cutting pneumatically pressed against the upper punch and thus the shear counteracted, whereby clean, burr-free cut edges are achieved. On The advantage is that the upper stamp no longer has to be immersed in the lower stamp, which significantly increases the lifespan of a punch.

The preferred method according to the invention is characterized in that the flat plastic resilient on the outer periphery of the upper punch, z. B. with With the help of a hold-down device, the lower stamp is pressed.

In a further preferred variant of the method according to the invention, the Top punch in the course of the cutting edge a relief of 3 to 60 °.

The depth of the relief grinding particularly preferably corresponds to the thickness of the stamping plastic.

The invention is explained in more detail by way of example with reference to FIG. 1.

Fig. 1 shows an apparatus suitable for carrying out the method punch assembly. The arrangement has the upper punch 1 , the lower punch 2 , a hold-down 3 , the plastic plate or film 4 and an air supply 5 for the compressed air.

example 1

In a film made of polycarbonate 750 µm thick, a rectangular Aus Saving of 6 × 30 mm by the method according to the invention when used a back pressure of 10 bar and with a cutting air of the punch from Punched 10 µm.

The cut edge of the punched-out part is rectangular and burr-free.

Without using the pneumatic back pressure according to the invention, this shows stamped part a fibrous cut edge and the cut edge a chamfer 5 °.

In the method according to the invention, the flat plastic is made by means of pressure is pressed against the upper stamp at the time when the upper stamp Plastic touches. The hold-down used in the preferred embodiment, preferably consisting of rubber-elastic plastic, largely prevents a drop in pressure in the lower stamp. During the intrusion of the The upper stamp in the plastic prevents the back pressure from bending and thus shearing off the plastic in the cutting gap. As soon as the upper stamp has reached the parting plane to the lower stamp is a completely burr-free exit separation of the geometrically defined part achieved.

When the upper punch is raised, the excess pressure that is still present ensures Discharge of the punched-out part.

With the help of the method according to the invention, it was possible to increase the service life of the Punching tool from typically 10,000 punchings to over 50,000 Stan increase tongues.

Claims (6)

1. Method for punching plastic sheets or plates with cutting stamp and cutting plate, in which the flat plastic is first pressed from the cutting punch side against the cutting plate, then from the opposite side within the opening defined by the cutting edge with back pressure and then simultaneously cut out from the cutting punch, characterized in that the back pressure is generated by compressed air from 2 to 300 bar. 2. The method according to claim 1, characterized in that compressed air from 3 to 30 bar is used. 3. The method according to claims 1 to 2, characterized in that the flat plastic (4) is pressed on the outer periphery of the punch (1) resiliently against the bottom ram (2). 4. The method according to claims 1 to 3, characterized in that the upper punch ( 1 ) has an undercut of 3 to 60 ° in the course of the cutting edge. 5. The method according to claims 1 to 4, characterized in that the depth of the relief corresponds to the thickness of the plastic to be punched ( 4 ). 6. The method according to claims 1 to 5, characterized in that the plastic ( 4 ) is a thermoplastic.