Broach (metalworking)

The space is a machining method for the production of the inner and outer profiles.

The most common application is the areas of the inner profiles, in which the tool, the broach is drawn by a hydraulic cylinder through the hole of the workpiece. The required tensile forces, depending on the diameter of the profile at 100-200 kN (formerly 10-20 t) or even higher.

The broach can be pressed through the workpiece, such as a press. Only short broaches can be used because of the risk of buckling.

Examples of cleared inner profiles

  • Internal square, hexagon sockets
  • Splines to DIN 5461-5465, DIN 5471, DIN 5472, DIN ISO 14
  • Gear hub profiles ( internal gears according to DIN 5480, DIN 5482, etc.)
  • Keyways
  • Polygonal profiles
  • Special profiles

Normally evacuated profiles run parallel to the axis of the workpiece bore. On modern machines, a room with swirl is possible, so that may be vacated on such machines internal helical gears ( used, for example in the automotive industry ).

Broaching machines are built in horizontal or vertical arrangement, which today dominates the vertical arrangement.

Broaching

Indoors

When indoors the broach is first performed in the pre-drilled hole of the workpiece and gripped by the other side before the actual work begins movement. The broach is with its many cutting through the workpiece is pulled through or pressed through and generates breakthrough in the workpiece, the contour of the broach.

Outdoor spaces

If the tool is guided along the outside of the workpiece during the power stroke, one speaks of the so-called outdoor spaces. Here, a pre-processed outer contour on the workpiece, for example the mouth opening of a forged wrench is finished by the broach. Due to the large cut - and Abdrängkräfte the material to be processed must be rigidly clamped and supported. When outdoor spaces you can let go of passing at a fixed or continuously workpieces. This process is called chain spaces

Exterior layout spaces

The exterior layout spaces is the simplest broaching. It is often used for grading the interface between the engine block and cylinder head.

Helical broaching

The teeth of the broach are helically arranged in the helical broaching ( helical broaching ). The workpiece is inserted into the receptacle is rotatably mounted and is rotated in the spaces formed by the flanks of the teeth as required by the geometry to be produced.

Exterior and interior spaces you can either print or Zugräumen:

  • Pressure chambers: The Räumdorn is the stem of the broaching machine by the workpiece or by pressing a pre- opening of the workpiece. For small and medium series. Cons: buckling stress of the relatively thin Räumdorns; Only workpieces that are smaller than the maximum lifting height of the broaching machine can be edited.
  • Zugräumen: Increased cutting speeds than with the pressure chambers. Despite smaller numbers, it is worth in mass production in tool and machine. The tool for Zugräumen of inner contours is the broach.

Broaching Tools

Broaching tools are usually made of HS. However, it may be ( cobalt alloy) or HSS-PM ( powdered metal ) or tools with titanium nitride coating, depending on the application, HSS-E.

  • Outdoor spaces: Räumdorn
  • Indoors: broach

Broaching tools consist of shaft, introduction, teeth, guide piece and tail. In Spanungsteil the teeth caused by staggering the incisors is, the chip thickness The Schruppzähne take over most of the chip removal. The Schlichtzahnung consists of at least three teeth. Here, the last finishing tooth and the first tooth of the reserve produce the finished size. Each tool has at least three spare teeth that have the same profile and identical dimensions and the material surface smooth ( calibrate). They also serve as back- sharpening and thus ensure that the expensive tool can be used longer. The cutting angle and chip chambers depend on the length of the to -clearing area and the machinability of the material. The clearance angle is very small, so that when sharpening the tooth face profile is maintained. Prevent chip breaker grooves in the open spaces, the chips between the lateral free surfaces and the already cleared areas penetrate and tear them. The tooth must be chosen so that whenever possible cut two to six teeth at the same time. The more teeth are in fact engaged, the smoother running of the broaching operation. However, increases with the number of teeth on the broaching force required. The average speed is 1-60m/min. The chip thickness is 0.05 mm for roughing and finishing at 0.005 mm.

Cooling

The cooling system is very important in areas as you can so dramatically improve the durability. Nowadays oils with a few additives or water -based coolant used. There is also the minimum quantity lubrication; this technology is environmentally friendly and is mainly applied in tools made ​​of HSS -PM or with TiAlN coating.

Others

Rooms offers all advantages where contours by rotating tools (Milling) or rotating workpieces ( turning) can not be generated. The process is secure compliance with the dimensional tolerances and high surface quality, such as wrenches, gear wheels or grooves.

It is particularly suitable for processing of larger numbers, as well as complicated profiles can be made ​​in no time.

The manufacture of broaches is quite expensive, so the tools are correspondingly expensive and have long lead times.

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