Quality Is Profitable: Faster Machining Time With Tool Holders

  • Wednesday, 02 August 2017 06:50

In order to increase the productivity of the milling process in a die and mould company, one cannot concentrate only on the high performance machining centres. Contributed by Haimer

Die and mould company Langer GmbH & Co found out that proper usage of tool holders could reduce the total machining times on several applications almost in half.

The company, located in Illmensee, 17 km north of Lake Constance in Germany, is a die and mould producer with approximately 140 employees. The services that they offer include the development and production of prototypes of serial tools for injection die moulding, up to the sampling of pre-series and small series production.

Injection Die Moulding

The die and mould department’s 60 employees focus on finishing the tools for injection die moulding in the quickest possible time, while reaching the high quality requirements of the automotive industry.

The data to be transcribed out of the design department into high quality tools out of aluminium-wrought alloy or profile steel of type 2312 and 2767 is the job of the company’s NC Machining team. Their team leader, Jörg Lehmann explains that along with the machines, tool holders and tools are the main factors that affect machining times. In his department there are six modern, three to five axis machining centres from DMG, Mikron and Hermle.

Langer was not satisfied with the current shrink fit chucks they were using, however. After a few shrink cycles, those shrink fit chucks were no longer giving the required clamping forces.

Theory And Application

The proper shrink fit machine is also required
for the shrink fit chucks. An inductive shrink
fit machine can be adjusted to the length and
diameter of the chuck. Due to this only the
clamping range of the chuck is heated,which
considerably reduces the cooling time,among
other things.

An important feature of shrink fit chucks is a tight fitting bore that holds the tool in the longest range possible. The entry chamfer of the shrink fit chuck plays a very important role, as this is where the protruding length and the rigidity of the tool are decided. Shrink fit chucks from various producers allow the entry chamfer to be five to 10 mm long.

As a result, there is often no clamping in this position, and the protruding length of the tool is unnecessarily increased. This can also similarly happen on the back end of the fit, where the chuck often has too much material turned out. There are also no clamping forces that hold the tool here. Due to these factors, the range of the fit is relatively short.

Mr Lehmann tried the chucks from Haimer, and shared his observations. “The chucks offer a lot of mass in the upper range, which reduces vibrations and the slim form in the lower range enables machining in tight contours,” Mr Lehmann said.

Made For Mould & Die

From left to right: Joerg Lehmann, team leader NC
machining, Langer,and Oliver Lechner, Haimer.

The company developed the Power Mini Shrink Chuck especially for the requirements of five-axis milling in the mould and die industry, where they are suitable due to their special combination of a slim tip and strong base.

A prominent feature of the chuck is the slim outside three-degree angle contour, which is the draft angle that is used in injection die moulding. The chuck has a strengthened contour at the bottom end of the chuck. Due to this, the shrink fit chuck can cut in deep mould cavities but is rigid enough to absorb heavy side forces occurring at five axis machining.

“We can go for much higher cutting values and save time with pre-work, for example groove milling in steel. Here we use a two mm diameter ball cutter to pre-finish first to 1/10 of a millimetre. We can reach the desired result in one finishing pass. The machining time is then reduced by up to 50 percent,” said Mr Lehmann.

Optimal Surface Finishing

The finishing was made in one pass and met all quality

Mould and die makers often use high rpm in order to achieve optimal surface finishes. When milling in deep cavities or pockets however, it is important that the chips are properly washed away. That works only when the coolant stream hits the right point with high pressure.

Haimer recognised this problem in their production. The company’s previous solution was the Cool Jet System, which integrated coolant bores into shrink fit chucks and other tool holders. Through the use of two or three nozzles, the coolant is transported directly onto the tool cutter.

The company used this approach to develop the Cool Flash system, which can be integrated into shrink fit chucks. At the top of the shrink chuck, a disc is inserted onto the Cool Jet bores, which has a small ring gap left open with slots opposite to the tool shaft. The coolant is not fed through points but is transferred in a ring form to the cutter and can lie around the tool like a coating. The coolant then clings and slides on the miller shaft, also at high rpm, as a coating over the chip flute to the cutting edge. The shrinking process is not an issue and the system does not involve any assembly.

High-Speed Cutting

The Cool Flash System enabled cooling and
chip-removing effect up to 20,000 rpm.

In order to have high-quality finishing results, the milling cutter must be cooled externally to flush chips out of the way, but many milling cutters may not have an internal bore for the coolant due to stability reasons.

In Langer’s testing of the new system alongside the typical flush cooling from the coolant hose, Mr Lehmann said that the system has allowed for speeds of 20,000 rpm, compared to previous tests which started to have wide dispersion at 6,000 rpm.

“Where we used to have to decrease feed rates by critical operations such as pocket milling, we can now work in normal speeds. There aren’t any chips that get stuck and the millers do not break. In addition to the increased process stability, we also save on coolant usage compared to the flush cooling from outside,” said Mr Lehmann.

APMEN Machine Tools, August 2017

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  • Last modified on Wednesday, 02 August 2017 07:21
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