De-gating of sprues made easy
In the plastics industry, one of the first steps after the plastic part is extracted from the injection moulding machine is the separation of sprues. Most plastic products from the injection moulding machine have sprues, (electroplating) tabs, overflows or ridges.
In further production process the sprues are usually removed. For de-gate various options are available. For example, sharp knives, heated wires or blades, laser technology or mechanical solutions such as a separating drum. Much of these cutting tasts is done by sprue-nippers:
ASS Maschinenbau offers to a wide range of nipper bodies and nipper blades in order to solve the different tasks. In particular in the automotive plastic injection moulding have high quality standards. To meet these standards, the parties always develop new de-gating solutions.
Nippers and nipper blades for various cutting tasks
The original ASS Robot Hand Kit (EOAT) offers more than 30 sprue nippers and approximately 70 different cutting inserts, so called nipper blades for almost unlimited applications.
The nippers are in different versions available: automatically or manually operating, single or double acting, force amplified, round, square or regular. The strongest nipper has a maximum of power: cutting force of 7,700 N at 0.6 MPa. For light cutting tasks there is a model with 150N available. The achievable actual cutting force is always dependent on the used nipper blades and the air pressure.
The nipper blades are available in a variety of geometries: straight versions SEG (nipper blade straight), SEK inserts for pinching, as well as various SES standard inserts with angular positions of 15° to 40°, 90° angled inserts SEW and Z-shaped nipper blades SEZ.
To cover the different tasks of application in plastic injection moulding optimally the nipper blades have steel alloy or carbide insert and various cutting lengths of ten to 50 millimeters. If necessary, also customized special nipper blades may be manufactured and used.
By default the cutting inserts come with a spring return. For over two years ASS offers selected nipper blades with magnetic resetting, they can replace one-on-one the ones with spring return.
The cutting inserts with magnetic resetting are nearly maintenance-free of springs superfluous and significantly increases the safety of the robot gripper. For best cutting-success the nipper blades are made of forged steel.
Various components, such as on sprue nippers optimized strokes, sprue holders, fixings or adjustable mountings for grippers extend the capabilities of the nippers.
Life optimization - Sensor option - Protection
A frequently asked request to the nipper blades is the query option of gripper position: the sprue was separated cleanly and did the nipper blades open or do they stick together.
If the blades are stucked together it is a serious risk that the tool and the robot hand can be damaged. An easy sensoring of the piston position is not enough to check this.
ASS has developed a solution: As a novelty ASS presented a query option for nippers (ASN SH). This new gripper components allows to proof the closed and/or open position of selected nipper blades directly. This new development increases the process safety in the injection moulding machine, because now is immediately recognizable when the blades have not reopened. In particular, the use of single-acting nippers can be significantly increased level of security.
Also new in the scope of delivery of the ASS Robot Hand Kit (EOAT) are nipper blade protectors SK. These caps are made of polyamide and offer a cost-effective protection for nipper blades and staff, for example, when changing the robot hands or maintenance. The caps come in red colour.
Individual consultation - Optimal cooperation
In practice, the selection of suitable nipper blades and the use is dependent on the geometry of the component and must be selected individually. A universal solution is rarely implemented by the many influencing factors.
Various parameters have an impact on the right choice of the cutting insert:
The shear strength, the plastic material and its temperature, is reinforced glass fiber in the material and how is is direction, is the material tempered or has it to be cut after cooling down, it is fragile and brittle or soft? And it is particularly important for the proper selection, whether the sprue is to be cutted in the viewing area and needs to be cut particularly clean. These and other issues must be clarified for the best solution of the de-gating.
In the laboratory ASS does cutting tests on sample parts for practicing the best solution (picture below shows an experimental setup for de-gating). With this information a customized, individual robot hand is designed and built.