Small thread in record time

As a technology partner, Kern Microtechnik supports precision manufacturing companies in every respect - including the highly productive manufacturing of small internal threads.

Precision machine builder integrates Punch Tap technology for M1 to M3

As a technology partner, Kern Microtechnik supports precision manufacturing companies in every respect - including the highly productive manufacturing of small internal threads.
From now on, the complete "Micro" series can use the "Punch Tap" process from EMUGE. Tests conducted by the tool manufacturer have shown time savings of up to 66 %.
 
Producing extremely precise, small components reliably and joining them together as assembly parts is a special challenge for companies in the watch/jewellery industry and in high-frequency and vacuum technology, among others. It requires innovative machining centres such as a Kern Micro, which guarantee permanent precision of less than 1 μm as well as reproducible surface qualities Ra in the low nanometre range, if required.

Kern Microtechnik from Eschenlohe employs approximately 200 people and operates successfully in more than 30 countries worldwide. The company focuses on two business areas: the development and manufacture of high-precision machining centres and the contract manufacturing of milled parts in the micro and nano range. Kern milling centres are used, among other things, in the company's own series contract manufacturing. The machine manufacturer is therefore perfectly equipped not only to manufacture high-precision machines, but also to support their users with the necessary process know-how.

The product portfolio of contract manufacturing includes prototype, single-part and series production as well as component assembly and support in the design process. The parts are machined by milling, drilling, spark erosion and grinding. In addition to high quality, the precision machines from Kern, must also meet the same productivity requirements.

This is another aspect where the engineers in charge regularly optimise their technology. Chip removal performance and axis acceleration are constantly being increased; and now micro internal threads in sizes M1 to M3 can be produced in aluminium, for example, up to three times faster than was previously possible.
 

The fast punch threads can achieve productivity advantages in many markets: for example, in the watch/jewellery industry (the picture shows a watch plate) as well as in high-frequency and vacuum technology. Picture: Kern Microtechnik

Punch tools introduced as micro series

The key to this performance is a new method of thread production, the EMUGE Punch Tap. It was launched into the market around five years ago and was originally designed for the automotive industry in the industry-standard size M6.

EMUGE-FRANKEN gained a lot of experience with it and expanded the tool range in the next step to include diameters M3 to M10. Jürgen Lange, developer at EMUGE, explains: "Upwards, the thread size is limited by the high torques that a Punch Tap requires. However, downwards we still saw scope for usage and extended our range accordingly."

In 2019, EMUGE-FRANKEN introduced the "micro" series" tools, which include diameters M1 to M3. They are popular with smartphone manufacturers and are also attracting interest from Kern Microtechnik. Alexander Stauder, Head of Application Technology at Kern, makes it clear: "We have recognised the high productivity potential of this process and want to make it possible for our customers to tap into it." The basis for the Punch Tap is an innovative machining principle. With two rows of teeth arranged opposite each other, the special threading tool,is pushed into a pre-drilled hole in a fraction of a second. This process creates two grooves.

Then the spindle rotates 180 ° counterclockwise while the axial feed axis simultaneously retracts by half a thread pitch. This movement creates the thread by cold-forming. Since the rows of teeth are now again in the previously created grooves, the tool can then simply be retracted - done.
 

Punching threads in lead-free brass

Another prerequisite for the success of the Punch Tap is the type of material to be machined: "The materials must be easy to form, such as cast and wrought aluminium alloys. Steel is currently not machinable, and “regular” brass alloys are not suitable either, as their elongation breaking point is too low to be machined with a forming process." However, in some core customer markets - such as watchmaking - "EcoBrass" (lead-free brass) is often used.

Due to the absence of lead, this material can be formed well and is therefore also a candidate for the Punch Tap. This was reason enough for Kern and EMUGE-FRANKEN to carry out specific thread-punching trials on various machining centres in March and October 2020 to determine a suitable cycle variant for EcoBrass.

In the meantime, the Punch Tap process also works reliably in EcoBrass and has been implemented for the micro thread series on the entire Kern Micro platform. The usable thread size ultimately depends on the spindle of the respective machining centre. For example, HSK-25 spindles (1.1 Nm torque) can produce threads up to 2 x D. If the machine has an HSK-40 spindle (5.9 Nm torque), all thread sizes up to M3 can be produced.
 

Punch Tap cycle in Kern machines

The Punch Tap cycle is now available as standard in all new machines of the Kern Micro series. Kern engineer Stauder adds: "At the request of our customers, we also equip their existing machines with it, parameterise them and enable the cycle in the control system". This can be easily integrated into the relevant programmes by the responsible programmer.

The thread-punch cycle contains basically three different movement sequence variants. Which one to use depends on the material, thread size and spindle. The fastest variant is often suitable in aluminium. It is somewhat different with EcoBrass, as the test engineers discovered during the trials.

EMUGE developer Lange explains: "The lead-free brass does not flow as well as aluminium. Therefore, we recommend a soft cycle variant for this, which reforms the thread again." According to Kern, the productivity advantage with lead-free brass compared to tapping/cutting is still almost 60 %. The threads are always true to gauge and meet the highest quality standards.
 

Cold-forming versus Punch Tap

Various tests with small thread tools show significant productivity advantages for the Punch Tap in the M2 comparison test. An example from the test workshop: M2-6H threads with a thread depth of 4 mm were produced in aluminium. During thread forming at 3000 min-1 , a production time of approximately 0.9 s was achieved.

The Punch Tap produced the thread at 400 min-1 in 0.3 s to 0.4 s - depending on the cycle variant used. The time saving is therefore up to 66 %.
 

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