Internal Broaching Machines by Karl Klink

Double-column table-up machines with 2 drives (D-Drive) from KARL KLINK boast special design features:

• An extremely rigid machine body design
• All guide and drive elements (2 each) lie in a line of action with the broaching stations
• The drives are arranged above the working area
• “Open” machine design (accessible from the front and rear)

The extremely high rigidity of the machine body and the central force application between the guide columns minimise the tilting and bending moments and also the transverse forces that arise as a result of the machining process.

The arrangement of the drives outside the working area and the “open” design prevents heating on one side and allows rapid temperature equalisation.

The resulting extreme stability brings about greater geometrical accuracy of the workpieces, longer tool life and less guide wear. With the result that optimum process reliability is achieved over a long operational period.

The machine concept is also very automation-friendly: The automatic loading and unloading can be performed from the rear of the machine, and at different levels. At the same time, the front of the machine is kept clear to allow convenient access for setting up, tool changes, manual loading and unloading, and maintenance work.

For adapting the double-column table-up machines concept to the respective application, there are 3 basic series with:

• hydraulic or electro-mechanical drives
• Broaching strokes from 600 – 3000 mm
• Broaching forces from 25 – 1200 kN

The range of applications for the double-column table-up machine extends from conventional applications to hard and dry broaching through to complex helical broaching processes.

Remarkable special versions of the KARL KLINK double-column table-up machine D-Drive were developed for the specific applications of these processes:

• Hard broaching machine
• Dry broaching machine
• Helical broaching machine

The excellent configuration features of this special design are:

• servo-hydraulic or electro-mechanical fast broaching drive
• alignment unit for profile orientation of the workpieces
• fully-automatic coolant filtering system (cycle time parallel)

Broaching speeds in excess of 60 m/min are required for hard broaching. These very high speed for the broaching process can be generally achieved using hydraulic or electro-mechanical drives.

Hydraulic drives have the great advantage of superior dynamics combined with much lower investment costs compared with an electromechanical drive. The modern hydraulic drive, with pressure accumulator charging, also offers the possibility of significantly reducing the connected load compared with alternative drives, while at the same time providing greater dynamics.

The servo-hydraulic drive works as a hydraulic NC axis with a programmable broaching speed profile throughout the broaching stroke, and nowadays allows speeds of up to 120 m/min in industrial production.

For hard broaching, the workpiece must be brought into the broaching position aligned in a defined way in order to allow the broaching tool to be inserted in a way that suits the profile. The workpieces are aligned main time parallel. Here, the workpiece is aligned in the loading gripper by profile mandrels.

Cutting oils are used to cool and lubricate the workpiece. The very fine, hard chips that are produced by hard broaching must be filtered out reliably.

If they reach the broaching station via the coolant circuit, high tool wear is the result. Automatic edge gap filters guarantee optimum filtering results combined with minimum maintenance work. The cleaning process is optimally integrated into the machine cycle by the control system, with the result that no interruption to production is necessary.

Typical design characteristics of the dry broaching machine are:

• hydraulic or electromechanical drive for broaching speeds of up to 30 m/min
• funnel-shaped machine cavity lining
• efficient chip suction removal by a side duct compressor
• tool cooling
• brush fixtures for the broaching tool and broaching supports
• noise reduction lining

In industrial production, the storage, handling, disposal and recycling of cooling lubricants are becoming increasingly difficult and, above all, more cost-intensive due to strict environmental and occupational safety regulations.

In wet broaching room processes (surge cooling), the coolants performs 3 tasks directly at the cutting point and, secondarily, in the close proximity of the machine cavity:

• Lubrication
• Cooling
• Chip transport

These direct functions of the coolant can be substituted by modern hard material coatings with good sliding properties, high resistance to wear and good thermal insulation on a suitable base substrate.

The longest tool life and best surface properties are achieved at broaching speeds of 25 m/min. The necessary broaching forces are only slitly above the level of comparable wet machining, thanks to the favourable sliding properties of the dry broaching area.

On the drive side, hydraulic drives with pressure accumulator charging are preferred because of their higher dynamics and lower investment costs.

Modern helical broaching machines are characterised by:

• CNC-controlled kinematics
• electro-mechanical drives with very high rigidity by means of Transroll spindles
• programmable broaching speed profile throughout the broaching stroke
• programmable helical unit for tool or workpiece by means of backlash-free gears
• hydraulic workpiece clamping with programmable clamping pressure throughout the broaching stroke

In the past, the rotary motion of the tool or workpiece required in the helical broaching machines was created mechanically via leadspindles.

To achieve the most flexible machine technology possible, in modern helical broaching machines the screw-type relative movement of the tool cutting edges is realised through the workpiece via CNC-controlled linear interpolation. The kinematics are adapted to a new tooth profile by CNC programming.

CNC helical broaching machines require an extremely rigid drive. This means maintaining the programmed broaching speed as precisely as possible (linearity) throughout the broaching stroke. Only electro-mechanical drives meet these requirements, with roller spindles mainly being used today.

Rotating the workpiece or the tool requires a torsionally rigid and low-backlash gear unit that transfers the torque required according to the helix angle.

In contrast to simple internal broaching applications, in helical broaching this means that the workpiece must be clamped to secure it against turning. This is mostly done using a hydraulic clamping fixture. In the case of thin-walled sun gears, it must be possible to change the clamping pressure throughout the broaching stroke.

In this traditional type of vertical internal broaching machine, the broaching tool is drawn from top to bottom through the workpiece. A pit or pedestal is required.

The broaching tool is pressed from the top down through the workpiece.

Hydraulic pre-clamping of the tools between the lower broach guiding slide and the upper driven broaching slide allows high accuracy to be achieved with regard to eccentricity and axial run-out.

The use of push-type broaching is limited by the possible risk of the broaching tool breaking.