Quality Assurance in Mold Making A deburring press from China ensures tool quality

When finalizing complex molds, trimming remains essential. HPF chose a trimming press from the Chinese manufacturer SXKH, equipped with European control components. The advantage: European quality at a Chinese price.

In the manufacture of high-precision injection molds for the medical, hygiene, and automotive industries, even modern FEM simulations reach their thermal and mechanical limits. In particular, for molds used in high-temperature applications involving PEEK or thermosetting plastics, as well as for multi-cavity molds with hot-runner direct injection, complex slide mechanisms and thermal expansion affect the closing behavior.

Calculating all correction parameters often proves to be time-consuming in day-to-day operations. Iterative touch-up under actual process conditions therefore remains the most reliable method for ensuring the required dimensional accuracy and surface finish before the first inspection.

HPF, a toolmaker and injection molding company based in Großdubrau in eastern Saxony, manufactures tools and products for a wide range of industries—from automotive to medical and hygiene technology. The company has earned a strong reputation as a full-service provider of complex parts and assemblies. When it comes to machinery, those in charge typically procure German or at least European products. This makes it all the more remarkable that, for quality assurance and the final finishing of the molds, they rely on the HMG 70XS1510 trimming press from the Chinese manufacturer SXKH.

Comprehensive Range of Manufacturing Services

HPF, founded in 1990 as a tool grinding shop, is synonymous with high quality. Since its inception, this family-owned business has evolved into a sought-after specialist in small- to medium-sized tools and components. A current example of this is a 32-cavity hot-runner mold with direct hot-runner injection for cylindrical medical and hygiene products. 

“We manufacture a wide variety of components,” explains Clemens Menzel, Head of Project Management at HPF. “For our clients, we cover the entire process chain, from development to the finished product. We operate across a range of industries. Our customers come from a wide variety of sectors, including medical technology, the hygiene industry, the automotive industry, and the packaging sector.”

The company’s range of services includes the manufacture of everything from single-cavity molds to multi-cavity injection molds, the construction of stamping and forming dies, and component manufacturing. One of the company’s areas of expertise is the manufacture of multi-cavity injection molds with direct hot-runner injection for thin-walled components used in the medical and hygiene industries.

“In addition, we develop and manufacture injection molding and compression molding tools for processing sophisticated high-performance plastics such as PEEK and thermosetting materials,” adds Menzel. “For some time now, we have also been working on mold solutions for processing bio-based and biodegradable plastics.” 

Today, as a full-service provider, the family-owned company offers a wide range of services —ranging from the development, design, and manufacture of injection molds and progressive dies to the serial production of plastic parts on what has now grown to 15 injection molding machines with clamping forces ranging from 25 to 180 metric tons.

State-of-the-art machinery

HPF has a high-performance, state-of-the-art machine park at its disposal for manufacturing. From turning to milling and EDM to 3D contour laser cutting, all relevant technologies are available in-house, and many machines are automated. For example, the milling of graphite electrodes and the EDM process are largely unmanned. “The only time we have to send parts off-site is for heat treatment,” explains Menzel. “In toolmaking, at least three to four employees are assigned to each technology—this ensures that we remain operational.”

Those in charge are continuously upgrading their machinery and constantly adapting it to the latest technical developments. When purchasing new or replacement machinery, the Upper Lusatian company generally relies on manufacturers from Germany—or at the very least, from Europe. “This ensures that, in the event of service needs, distances are short and replacement parts are available locally,” Menzel emphasizes. “This approach has always served us very well in the past.”

First Machine for HPF from China

Against this backdrop, the choice of the new laminating press is all the more surprising: “We opted for an HMG 70XS1510 laminating press from the Chinese manufacturer SXKH,” explains Menzel. “We have good reasons for relying on a Chinese press for this key position.”

After all, even at HPF, they have to respond to economic challenges. “Some clients are now even requiring us to have part of the order manufactured in China,” reports Menzel. “We can make that happen—we’ve known our partners in China very well for many years and know exactly what they’re capable of and what level of quality we can reliably expect from them. They are all partners we’ve known personally for years and who have the technical expertise and knowledge to deliver the required quality.”

A simulation is only as good as its data

From a business perspective, the decision to invest in a trimming press is often very difficult to justify. It is needed to prepare tools for production and to ensure quality, but it does not produce any parts itself.  In many companies, trimming presses are far from operating at full capacity and sit virtually unused most of the time. Furthermore, much of the correction work can now be replaced by intelligent simulations. 

“A lot—but not everything,” Menzel emphasizes. “Among other things, we also build tools for high-temperature applications. Anyone who wants to simulate how the tools behave under large thermal differences would first have to identify, collect, or calculate all relevant production parameters in order to perform a valid simulation. This is especially true when, for example, sliders increase the complexity of the tools.” 

Laborious Data Collection

Sure, with enough effort, you could record all the relevant parameters. Even though the machining of a tool’s individual components—as is the case at HPF—takes place under controlled, climate-controlled conditions, and the geometries are therefore precisely known, new insights often emerge when these components interact. Collecting the relevant data for this is often a challenge.

In many cases, this is far too time-consuming and tedious in day-to-day work—especially when there are high demands on dimensional accuracy and surface quality, but also for molds with sliders and other moving components, hand-finishing with iterative correction cycles is often the significantly faster and more efficient path to precision. This is because, in many cases, there is simply no substitute for the mold maker’s experience in assessing and making manual corrections during the final phase before the mold is sent to the injection molding machine.

Touch-up work is quick and precise

The finalization of a mold is a cost factor that is reflected in the prices charged to the client. The effort involved must therefore be in the right proportion to the benefits. Particularly for molds that exhibit complex behavior during the injection molding process, test runs under near-real operating conditions—such as heating the molds to the actual processing temperature for high-temperature plastics—can quickly and easily provide valuable insights for later use in mass production.

“We already had a small core-setting press on site, but we were looking for a larger machine that, in addition to simple open-close operations, is also capable of performing tasks such as core pulling without an auxiliary unit,” explains Menzel. “It also needed to be up to date in terms of safety features. It goes without saying that it must maintain parallelism with a high degree of precision.”

Ergonomic design and compact construction

The toolmakers decided against using a rotary table, such as one used for coating multi-component tools. If necessary, they plan to reposition the tools by hand. “In addition to the functional and safety features, what was particularly important to us was ergonomic work at the press,” explains Menzel. “This means that the lower table must be able to extend out of the press and tilt, and the upper table should also be adjustable so that the toolmaker can perform his tasks comfortably and in a natural working posture.”

Added to this—as is the case in many organically grown tool and mold-making companies—was the low ceiling height at HPF. “This ruled out most manufacturers, since they had mounted the press’s drive cylinders at the top, which significantly exceeded our available headroom,” Menzel emphasizes. “We need a press with a very compact design that allows the overhead crane to still pass over it and load the dies onto the press, and that combines all the functions we require.”

Components from international manufacturers

To procure a new ink-coating press, Menzel’s team conducted research with numerous partners and other companies. “Not just in Germany—but also abroad, such as with our partners in China,” explains the project manager. “They rely on laminating presses from SXKH—a manufacturer that has continuously developed itself and its technologies—and we found a model in their portfolio that perfectly meets our requirements.”

The system’s capabilities, which the toolmakers examined closely, were impressive, and the mechanical construction appeared very solid. And a detailed look “under the hood” also dispelled concerns regarding service availability: “We were able to confirm that all relevant key components of the SXKH trimming presses come from established international manufacturers,” reports Menzel. “For example, the supplier for the drives and control system is Siemens. The photoelectric sensors are from Sick, the encoders from Kübler (all in Germany), the servo drive from Phase (Italy), and the contactors from Schneider (France). And the valves are from Vickers (U.S.); here, too, rapid availability and expert service are guaranteed.  With this configuration, we can be confident that, if necessary, we can obtain competent on-site support without any complications.”

The machine of choice is an HMG 70XS1510 die-setting press—the model designation indicates a maximum clamping force of 70 metric tons with a usable table area of 1,500 x 1,000 mm². The upper table can support a load of 2.5 metric tons, while the lower table can accommodate tool halves weighing up to 8 metric tons. Both tables can be tilted and moved into positions that allow for ergonomic and comfortable tool machining. 

In addition, the machine is equipped with a complete closed-loop servo system. Its very compact design also makes the press ideal for use in low-ceilinged facilities.

Two connections for core pullers on each side—four in total—complete the system. With this setup and external peripherals, toolmakers at HPF can put molds weighing up to 6 metric tons through their paces under realistic operating conditions. This enables rational, efficient, and cost-effective finalization of the molds.

European quality  at a Chinese price 

“The Chinese manufacturer was very open to our requests—from a German-language user interface to a color scheme in our corporate colors,” recalls Menzel. “Ultimately, however, one of the most important factors was the attractive price-performance ratio. For a comparable scope of delivery, the purchase price was about half that of the competitors we had inquired with. The press can do everything we need. It uses components from established international manufacturers and is easy to maintain thanks to its straightforward design. And since all of that was covered, the cost was the deciding factor. Because in the end, it all comes down to what the client is willing to pay. Thanks to this press’s attractive price-performance ratio, we can offer our clients the high quality they demand at competitive terms. And that, after all, is what counts.”