Groth Kunststofftechnik relies on KNARR for demoulding complex parts

When it comes to demoulding complex undercuts, mould makers often use multi-level tools. The mould makers at Groth in Vlotho rely on the high-quality latch locks from the extensive range of their standard parts partner KNARR for tool solutions like these.

The Claus Groth company, based in Vlotho, East Westphalia, has been manufacturing complex and technically sophisticated injection moulding tools since 1948. In addition, the plastics specialists produce injection-moulded products in their in-house moulding facility. As a family-run business, Groth is a reliable partner for clients in the automotive industry, mechanical engineering, furniture construction as well as transport technology.

The company’s production experts can respond flexibly to customer requirements – from just a few hundred parts per year to production volumes of up to two million. “We manufacture injection moulds up to a size of 800 x 600 mm,” explains Jens Strate, Managing Director of the company located in the Lipper Bergland region. “Our injection moulding machines operate with clamping forces of up to 300 tonnes. And for over 30 years, we have also been supplying our customers with assemblies and plastic-metal composites.”

The majority of products
are technical components

Jens Strate, Managing Director at Claus Groth: “With KNARR, we have a very cooperative business relationship. We can rely on the high quality and longevity. We are confident that wear will not become an issue with the latch locks anytime soon.” – Image: Pergler Media

Groth currently employs 32 staff members. In production, six specialists per shift oversee the 20 machines, which operate in two shifts. Four specialists work in toolmaking, while five are responsible for assembly. The material receiving, storage, and shipping departments each have two employees. The remaining staff members work in sales, management, and administration. For design work, the company relies on experienced external specialists, and electrode manufacturing is also handled by trusted external partners.

The toolmaking department primarily processes standard tool steels, as well as case-hardened materials and occasionally stainless steel. Typically, the mould specialists manufacture tools with four or eight cavities, designed for continuous operation and almost exclusively used in their own injection moulding facility. The tools are engineered for high process reliability and stability, meeting stringent quality standards. Tolerances of 10 µm or less are the benchmark.

The majority of injection moulded products are technical parts, many of which are made from POM. These thermoplastics are used for the production of precision parts, not least because of their high rigidity, low coefficients of friction and good dimensional stability – Image: Pergler Media

Creative Solutions for Complex Manufacturing Tasks

The majority of injection-moulded products are technical components, many of which are made of polyoxymethylenes (POM). These high-molecular, partially crystalline thermoplastics are generally used for the production of precision parts, not least because of their high rigidity, low friction values and good dimensional stability. However, other technical plastics are also processed on a large scale in Vlotho.

The team around Strate often finds creative solutions for their clients. Especially when the workpieces have geometries that place high demands on the injection mould and especially on the demoulding process. For example, when complex geometries with undercuts in the demoulding direction are to be produced. Then the task of demoulding such parts quickly and gently is often a real challenge. Generally, tool and mould makers use sliders or jaws when undercuts, notches or openings on injection moulded parts cannot be reliably demoulded using conventional mould separation.

Project with Three Different Diameters

In a recent project, the plastics specialists manufactured three very similar components for chassis applications, differing only in their dimensions. The diameters measure 62, 67, and 68 mm.

For this task, the toolmakers built three four-cavity moulds with multiple parting lines, enabling the simultaneous injection moulding of four identical black POM components per cycle.
The exact order quantities are yet to be determined by the client, but Groth’s moulding facility is fully prepared for series production and exceptionally well-equipped.

Demoulding as a Challenge

The chassis component made from black POM is characterised by deep ribs and some undercuts. In a project, the plastic experts at Groth are set to produce these parts in three different diameter sizes. – Image: Pergler Media

‘We then complete these parts in the assembly with an O-ring seal made of softer, more elastic TPE material, which is firmly affixed to the POM part using adhesive dots,’ says Strate, describing the assembly to be manufactured. ’The O-ring seal is in contact with the metal of the vehicle and absorbs any small relative movements of the components to each other, which may arise, for example, due to vibrations when driving. This also helps to prevent unwanted noise, among other things.’
One challenge in the injection moulding and subsequent demoulding is the deep ribbing of the products – but also the undercuts, which could not be demoulded with a classic open-close mould design. ‘These areas are partly located in the depth of the cavity of the injection mould,’ says Strate, outlining the challenge for the toolmakers. ’We therefore decided to free the undercuts of these plastic products with the help of underfloor slides. In addition, an inner core must also be pulled out for demoulding.’

The parts just before ejection. Before this step, undercuts must be cleared, and cores pulled. For this, the plate is moved on the nozzle side – the gap in the mould on the right illustrates the travel path before the opening at the parting line. – Image: Pergler Media

The chassis components can be removed as free-falling parts or defined by robot extraction – for both options, Groth is well-equipped. Here, an employee is currently mounting the appropriate gripper. – Image: Pergler Media

Safe Ejection for Complex Components

Underfloor slides are slides, but also core pulls, that the mould maker has installed below the parting line. They ensure that the undercuts are released just before the mould is actually opened. Underfloor slides are often moved with hydraulic cylinders, especially in larger tools. However, this type of drive is too complex and also too prone to error for smaller moulds. Other variants are generally used here.

‘A proven method of pulling the slide gates in particular before demoulding is to drive them via an additional plate in the mould,’ explains Strate. ’This is activated before the parting line is opened and the resulting movement ensures that the slide gates release the plastic parts. This means that they can be easily removed from the nozzle-side mould half when the mould is actually opened at the parting line.’

Two Latch Locks Control the Movement

Four identical parts are produced in the injection mould with each shot. The cycle times are around 55 seconds. In the project for the three moulds for the chassis component, the moving plate is precisely controlled by two latch mechanisms, which are installed in the centre at the top and bottom of the injection moulding tool.

‘The two latch units ensure that the mould’s parting line initially remains closed until the platen that drives the underfloor slide gates has reached its end position,’ explains Strate. ‘Only then do the two latch slides release the opening of the tool at the actual mould parting line, the injection-moulded part is demoulded on the nozzle side and finally ejected on the ejector side and removed by a robot.’

The components of the latch locks are well made and, where possible, pre-assembled. This makes it easier for the toolmakers to correctly and quickly install the latch locks on the tool, especially in critical assembly situations. – Image: Pergler Media

The control plate of a KNARR latch lock. The latches are clearly visible. They ensure that the latch bar only releases the opening of the mould parting plane for demoulding once the plate, which controls the core pulls and sliders, has reached its final position. – Image: Pergler Media

KNARR has an excellent reputation in the East Westphalia region

The latch locks for all three tools come from the standard parts specialist KNARR, based in the Franconian town of Helmbrechts. KNARR originally specialised in ejection technology. While still a leader in this area, it has since expanded its portfolio to offer a complete range and has been able to convince many users, particularly in the East Westphalia region.

“We’ve had a very collaborative business relationship with our standard parts partner KNARR for many years,” emphasises Strate. “The close contact with the field service plays an important role here, but above all, it’s the high quality and durability of all components. We can rely on that. We can be sure that wear and tear on the latch locks will not be a problem in the foreseeable future.”

Quick and Simple Installation

For the precise control of the movements in this tool, the high-quality latch locks from KNARR are the key factor. The compact, pre-assembled unit enables the toolmakers to install it quickly and easily into the injection mould. Depending on the application, the control elements are available in both an on-mounted and pinned version as well as a recessed and inserted version. The team at Groth opted for the on-mounted solution for these three tools.

In product development at KNARR, the developers placed great importance on sensible installation dimensions and practical standard size definitions. KNARR configures the control bracket and latch bar to customer specifications in terms of length and with the necessary mounting holes. For the standard sizes, the standard parts manufacturer delivers the latch locks completely ready for installation.

Individual Configuration of Components

All components were packed together and delivered ready for assembly to the toolmakers. The external designer commissioned by Groth obtained the 3D data for the standard latch locks from KNARR’s portal and adapted them precisely to the application. The machinists at Groth then shortened the latch bar made of nitrided 1.2312 to the correct length and also carried out the precise alignment.

“In processing, it becomes clear that KNARR supplies high-quality components here – you get a good feeling working with their products, you can feel the quality. This applies to both the material and the precise workmanship. And the accompanying data fits exactly. Then there’s the ease of handling during mounting – as the latch lock is already pre-assembled, KNARR eliminates the otherwise laborious task of assembling a ‘latch lock kit.’”

Claus Groth GmbH Innovative Plastics Technology
Claus Groth GmbH has been manufacturing technically sophisticated injection molding tools and injection-molded products since 1948. With over 75 years of experience in injection molding and toolmaking, the family-run company is a reliable partner for companies in the automotive, mechanical engineering, furniture and transportation industries. The company promises its clients maximum flexibility, not only in the areas of development and toolmaking, but also in production and order volume. Whether you need a few hundred parts a year or 2 million components, the company promises an economical solution for every volume. For more than 30 years, it has also been active in the areas of assemblies or plastic-metal compounds.

High-Quality Components Ensure Optimal Function

With carefully coordinated materials and coated components, KNARR guarantees minimal wear of the latch locks, optimised service life, and thus significantly reduced maintenance. The fast opening and closing of the injection mould in a purely mechanically driven tool solution also allows for the minimisation of cycle time. A latching system on the latch lock, which locks the backing plate in position and thus prevents possible collisions, ensures a stable production process.

“We can rely on the high quality of the standard parts, the ability to deliver, and the professional advice from our standard parts partner KNARR,” summarises Strate. “Although we also source material from other suppliers, KNARR is our go-to full-service supplier, especially for our smaller tools. We know that everything is taken care of and everything will fit, and we feel in good hands with our standard parts partner.”

Latch Lock
The latch lock is a purely mechanical control element. It controls the movement sequence of the individual moulding plates when opening an injection mould to eject the plastic products. With a robust latching system for the latch locks, KNARR supports high process stability for the user—the latch lock securely locks the intermediate plate in absolute position accuracy. Collisions are inherently excluded. A significant advantage, especially for assembly and disassembly, is that KNARR has firmly integrated the internal components of the latch housing—it cannot accidentally fall out and does not need to be “assembled” first. This is particularly beneficial in complex assembly situations.

Safe Solution for Underfloor Slides
There are many different solutions for moving slides and core pulls in injection molding tools. Starting with direct drive via hydraulic cylinders or servo drives to purely mechanical variants. Particularly useful for smaller tools are solutions in which the opening stroke of the injection molding machine is used to pull these elements. In this case, the drive can be provided by an additional movable plate in the injection mold. Controlling the movement of such a plate is a task that a latch pull can solve perfectly. This function, which creates an additional mold level, uses a part of the opening movement of the injection molding machine that can be defined via the configuration of the latch pull to first move the plate and thus the slides and core pulls. This clears the plastic part in the direction of demolding. Only after this first part of the process movement does the latch release enable the mold to open fully in the actual parting line, and the part can be demolded.

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