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Precision teflon parts manufactured with injection molding technology

Сase studies
01

Examples for micro parts produced at Rohde & Schwarz.
(Photos: Rohde & Schwarz)

In the production of Teflon micro parts, Rohde & Schwarz plays a pioneer role. These high-frequency technology components – until recently still produced as turned parts – are now manufactured on WITTMANN BATTENFELD machines, specially designed for the injection molding of small and micro parts.

The family-owned company Rohde & Schwarz, established in 1933 and based in Munich, has been known for their high-quality standards, precision and innovation in all areas of wireless communication technology for more than 80 years. The electronics group, with a workforce of just under 10,000 employees, is a leading global player in its primary business areas of measurement technology, radio and media technology, safe communication and cyber safety, and radio monitoring and radio orientation technology. In the fields of mobile radio, EMC measurement technology and broadcasting, and measurement technology for digital terrestrial television, Rohde & Schwarz is the global market leader.

The company’s facility in Teisnach was opened in 1969. The Teisnach plant, where more than 1,400 workers are employed, is a system supplier and competence center for mechanical and electronic manufacturing in Rohde & Schwarz’s network. The product portfolio supplied by the Teisnach plant includes high-precision and surface engineering, housing technology, manufacturing of circuit boards and the assembly of electro-mechanical components, and even testing and automation solutions. For high-precision mechanical engineering, Rohde & Schwarz in Teisnach offers both non-cutting machining processes and cutting production technologies such as turning, milling and drilling combined with the appropriate high-precision surface engineering.

Micro-machines from WITTMANN BATTENFELD

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High-precision Teflon parts to be built into high-frequency components.

To produce high-precision plastic parts with tolerances down to ±7 µm, Rohde & Schwarz has been using WITTMANN BATTENFELD micro injection molding machines since the end of 2012. In November 2012, the Microsystem 50 machine model designed for injection molding of micro parts was commissioned. In November 2014, this was followed by a MicroPower 15/7.5, a latest generation micro machine from WITTMANN BATTENFELD. As a fully integrated production cell, the MicroPower is equipped with a W8VS2 SCARA robot from WITTMANN and an integrated TEMPRO plus D Micro temperature controller that is also specially developed for micro applications.

Apart from their high cost-efficiency and productivity, the machines from the MicroPower series stand out primarily due to their extremely high precision, which is partly achieved using a two-step screw-and-plunger injection aggregate with shot volumes ranging from 0.05 to 4 cm³. This high standard of precision is exactly what Rohde & Schwarz needs to produce its micro parts, which are primarily built into the high-frequency components that are also assembled at Rohde & Schwarz. The company produces 100% of the hardened steel molds in-house. Its mold-making shop is equipped with high-precision eroding machines, which allow mold components to be manufactured primarily by wire-cut EDM within tolerances down to ±3 µm. The equip ment is also designed in-house at Rohde & Schwarz. This feature not only enables the company to manufacture molds with the accuracy required for the production of its highprecision parts, but also offers the advantage of short lead times in mold production for a highly flexible response to market demands and the needs of its customers.

Changing over to micro molding

Typical micro parts made by Rohde & Schwarz in Teisnach are, for example, power plugs with a tolerance margin around ±12 µm between the internal and external conductors. The company’s latest product, newly developed in the area of high-precision micro injection molding, is a Teflon spacer that is used in high-frequency components. This part, originally manufactured as a turned part, can now be produced by micro injection molding at significantly lower cost than before. The complex and challenging preparatory work necessary to achieve the changeover of this originally turned part made of Teflon to production by micro injection molding was due primarily to the specific characteristics of Teflon. Since certain gases and/or fluorine compounds, which are detrimental to health, can be released at high temperatures in hot processing of Teflon, several analyses had to be carried out to ascertain which decomposition products may be formed, in which quantities these would be released, and whether they could create any health hazards for the workers. The quantities of the decomposition products depend on the plastic material processed as such and on the additives contained in it, the hot processing method used and the temperatures involved. The micro-machines from WITTMANN BATTENFELD operating at a temperature of about 350 °C are completely encased and equipped with an extraction unit.

Process analysis and tests

To identify the gases released, a thermo microbalance combined with an infrared spectrometer was used. An analysis of the changes in mass and outgassing substances was carried out. The changes in mass were measured with the thermo balance. Integrated flow controllers ensured precisely regulated flow quantities for two flushing gases and one shielding gas. The gases released from the samples by the thermal analysis were passed directly into the Fourier-Transform infrared spectrometer, which covers a spectral range from 500 cm-1 up to 6,000 cm-1. The data were then transferred online during the measurements. With this method, Rohde & Schwarz was able to prove beyond doubt that processing Teflon with their method does not involve any health or safety hazard for the workers.

Next, a trial mold was produced to examine how Teflon could be processed on a micro injection molding machine. Following a positive outcome and a calculation of the shrinkage behavior, Rohde & Schwarz undertook the construction of a mold for series production, which was manufactured on a high-precision eroding machine in the company’s own mold making shop. After sampling and adjustment of the mold and an analysis of process capability, the approval for series production could be granted.

Successful with the right equipment

In producing micro parts made of Teflon using highprecision micro injection molding, Rohde & Schwarz is truly a pioneer in the market. These elements, originally manufactured as turned parts, are now produced on two micro machines from WITTMANN BATTENFELD which, due to their specific design, offer a high level of process reliability and precision.

Consequently, they are also ideally suited for the continuous production of parts whose tolerances are in the magnitude of one thousandth. To achieve these extremely low tolerance margins, the micro machines stand in an air-conditioned room where both temperature and humidity are kept constant. The molds and the material are also stored in this room for the same reasons.

Since the parts produced with the micro machines do not have to be deburred, the downstream finishing that was previously required for turned parts is eliminated, which makes for a significantly more cost-efficient production of the elements. Apart from the positive results that Rohde & Schwarz has achieved with the micro machines from WITTMANN BATTENFELD in the production of Teflon parts, the company particularly appreciates the machines’ modest space requirements. This is due to the design of the machines as well as the complete integration of the robots and peripheral appliances specially developed for them, as well as the integrated image processing device. Moreover, the micro machines from WITTMANN BATTENFELD come equipped with rotary disks that perfectly fit the mold concept of Rohde & Schwarz, and are therefore quickly upgradable. Rohde & Schwarz also appreciates the possibility of purchasing both machines and peripherals from a single source within the WITTMANN Group. Johann Haimerl, responsible for high-precision technology in the company, puts it in a nutshell: “At WITTMANN BATTENFELD we have just one contact partner for the entire package. That facilitates negotiations enormously.”

The micro injection molding segment at Rohde & Schwarz has seen rapid growth since its introduction in 2012 and is expected to grow further. For reasons of precision and cost-effectiveness it plans to gradually introduce the production of other parts by micro injection molding instead of turning and milling.

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