With five internal threads and multiple undercuts, demolding a Festo pneumatic maintenance unit takes skill, patience, and the right tools. In November last year, the Krallmann Group developed a quick yet high precision solution to this task using Servomold’s servoelectric unscrewing devices.
Developed by Servomold and distributed by sister company, i-mold, these unscrewing devices were designed to provide clean, precision-controlled and gentle demolding of threads in injection-molded parts. At least five such systems were combined by the Krallmann Group in a mould used by Festo Polymer GmbH, St. Ingbert, to make the complex housing of the DB Mini pneumatic maintenance unit for Festo.
The demolding process
Festo Polymer produces the cube-shaped housing with an edge length of approx. 40 mm from a high-modulus, high-strength glass fibre reinforced polyamide (PA66-GF50). The moulding comprises five female threads having diameters of ⅛”, ¼” and 36 mm each, measuring between 12 and 22 mm in length.
In line with the positions of these threads, four of the associated unscrewing spindles are arranged at 90-deg. angles to each other, in parallel to the parting surface, on the ejector side of the single-cavity mould. A fifth spindle moves parallel to the ejector set in the central machine axis.
Servomold selected and sized the five unscrewing devices to match the appropriate torques (T), which were found to range from 6 to 33 Nm in a series of in-house trials. Accordingly, the mould is now equipped with four units of the smallest available standard type SAEW040-050-12-0055 device (T up to 23 Nm) for the ⅛” and ¼” threads plus one SWZ070-16-0207 type (T up to 75 Nm) angular (“cogwheel” type) servo drive for the large metric thread. Control is provided by a mobile SRS-8.6 rack-type servo controller capable of managing up to 6 servo motors. This controller adapts the speed of each spindle individually, so that, as the five liquid-cooled thread cores are screwed in, all will reach their respective limit positions simultaneously. The SRS also performs continuous torque monitoring of each servo unit and outputs appropriate signals when preset threshold values are reached.
The servo motors are equipped with resolver-type position encoders whose zero positions are individually referenced on the clamped and preheated mold in each case. Stefan Bernhard, managing director of Servomold, explains: “We like to use resolvers to protect the mold from damage during closing, for in everyday operation the molding machine controller will issue a start clearance only when the SRS unit reports that these reference points are reached.”
Why a servoelectric solution?
There are several reasons why servoelectric unscrewing devices are a better choice for this application than conventional, hydraulically operated counterparts:
- The servoelectric motor unit requires less mounting space and yields shorter cycle times than a hydraulic solution.
- The device allows the operator to control the individual motions of each core with high precision.
- The respective unscrewing torques can be individually monitored and controlled.
- The threads (that vary in depth) can be demolded at the optimum speed.
- The risk of soiling due to oil leaks is eliminated.
- Servoelectric systems support continuous force monitoring, which allows incipient mold damage to be detected at an early stage when low-cost troubleshooting options are still available.
Individually controlled demolding of five internal threads quickly and gently with high precision.
At Motion Tronic, we believe in technology that’s forward-thinking and time-efficient while never compromising on quality and output. That’s why we work with suppliers like i-mold and are proud to be the official agents for i-mold’s Servomold in south africa.