Broaching machine
A broaching machine is a machine tool , with the workpieces through the manufacturing process space can be edited. A broaching tool , which has several cutting edges one behind the other, is guided past the workpiece (external spaces) or through an existing hole (internal spaces). The working movement thus consists of a single linear movement; In addition, there is only the assembly with the raw parts and the removal of the finished parts, which can be done manually or automatically. In broaching machines, a distinction is made between external and internal broaching machines and between horizontal and vertical machines with corresponding tool movement. The internal broaching machines are usually designed vertically and the external broaching machines horizontally. Broaching machines are usually of a simple structure compared to other machine tools such as lathes or milling machines and consist of a frame, a hydraulic or electric drive, a clamping device for the workpieces and one for the tool. Sometimes several tools and workpieces are used at the same time.
General
Types, classification, standardization
The sizes and connection dimensions are standardized in DIN 55141 to DIN 55145. Although the standards have been withdrawn, the manufacturers are still orienting themselves towards them so that existing tools can also be used on new machines. There is a letter scheme for the designation of the types, which is supplemented by a sequence of numbers.
- 1st letter: R - broaching machine
- 2nd letter:
- A - outside
- I - inside
- K - continuously working (chain drive / chain broaching machine)
- 3rd letter:
- S - perpendicular
- W - horizontal
- 4th letter:
- A - table that can be approached and withdrawn
- AT - Partial table that can be approached and retracted
- F - Fixed table
- H - lifting table or lifting table
- K - tilt table
- M - mechanical drive
- T - part table
- X - special version
- Z - two-cylinder design
This is followed by a number that indicates the broaching force ( cutting force during broaching) in megapascals (10 × kN). another for the stroke length in millimeters and the size in millimeters. This is the width of the clamping plate for internal broaching machines or the width of the tool slide for external broaching machines. In the case of chain broaching machines, the number of workpiece carriers also follows.
- Example RISH 16 × 2000 × 400
This describes a vertical internal broaching machine with a lifting table. It has a broaching force of 160 kN, a stroke length of 2000 mm and a clamping plate width of 400 mm.
Personnel qualification
The room machine personnel usually do not require any special qualifications. Since the cycle times are short, the machines are often equipped with automatic loading and unloading devices.
conditions
All machine tools should be as productive as possible while maintaining the required levels of accuracy. In the case of broaching machines, this results in demands for the highest possible cutting speed, which is limited, however, since the tools must be accelerated at the beginning of machining and then braked again at the end. The achievable cutting speeds are usually around 30 m / min, with special measures up to 120 m / min are also possible. The clearing forces are very high and must be absorbed by the frame and frame during processing. In addition, the broaching force changes every time another tooth of the tool penetrates or leaves the workpiece, which leads to vibrations that have a negative effect on the accuracy that can be achieved. Broaching machines and their drives should therefore have a high static and dynamic rigidity as possible. This also applies to the workpiece holder and the guides of the slide, which should also be wear-resistant. In addition, good chip removal is required.
Drives
For a long time, primarily hydraulic drives were used on broaching machines, which are characterized by low acquisition costs and high accelerations. Electric motors with mechanical gears, which are characterized by high rigidity, energy efficiency and low operating costs, are increasingly being used in newer machines.
Hydraulic drives
Hydraulic drives are often used with vertical broaching machines up to a broaching length of around 2.5 meters and with horizontal broaching machines with short stroke lengths. They are cheap to buy, have a high performance ( power-to- weight ratio ) based on their weight and can achieve high accelerations at a limited top speed. However, since the liquids are principally compressible, the drives are not rigid. The energy efficiency is also rather low, the operating costs are high and the use of modern CNC controls is somewhat more complex, since the electrical controls first have to control the hydraulic valves. Servo or proportional valves are used for this.
Axial piston pumps, vane pumps and gear pumps are possible designs. The vane pumps are characterized by their low sound pressure level at low speeds.
Most hydraulic drives work in the low pressure range of 80 to 100 bar. For higher cutting speeds, pressures of up to 150 bar are used, making speeds of 60 m / min possible. Higher speeds of up to 120 m / min are feasible, but the required volume flows increase. Large cylinder diameters are required, as well as special and complex hydraulic circuits. Electromechanical drives are therefore mostly used at high speeds.
Electromechanical drives
Electromechanical drives consist of an electric motor and a mechanical gear to convert the rotary motor movement into a linear working movement. For horizontal broaching machines with a long stroke to be rack - pinion used systems, otherwise also come ball screws or roller screw spindles in question. Electric drives are characterized by a lower power requirement. The energy costs are lower in idle operation and can also be reduced with vertical machines through the energy recovery. The greatest advantage of the electromechanical drives is their high rigidity, which leads to lower vibrations and thus more precise workpieces. They are used for tasks with particularly high requirements, such as the processing of thin-walled pipes or materials that are difficult to machine . The connection with CNC controls is easier with them. In addition, the pressure medium of the hydraulic drives is eliminated. Therefore, electromechanical drives are more environmentally friendly and suitable for dry machining consider when hard machining is standard. Between 2000 and 2015, the use of electromechanical drives increased steadily, which was also favored by stricter environmental protection legislation.
The standard structure of the drives consists of the motor, a coupling, a belt drive and a transmission gear. Torque motors can generate very high torques and are suitable as direct drives , i.e. without a clutch and gearbox, which leads to greater rigidity and dynamics of the drive and thus ultimately to higher productivity.
Horizontal and vertical machines
With vertical broaching machines, the tool hangs in the holder and is therefore not subjected to bending; the achievable accuracies are thus higher. In addition, the chips can more easily fall out of the tool and be transported away. They make optimal use of the available space and can also be easily integrated into fully automated production lines. The disadvantage is that machines with a two-cylinder design must have a special foundation. This is more often rejected because of the high costs, which has led to the use of vertical broaching machines with lifting tables. These do not require a special foundation.
In the case of horizontal machines, the workpieces do not have to be lifted or hardly need to be lifted. This is particularly advantageous for large and heavy workpieces.
Internal broaching machines
Internal broaching machines are used for internal broaching. They are mostly designed as vertical machines. A distinction is made between machines with a stationary table on which the workpiece rests and moving tools and machines with lifting tables (moving workpieces and stationary tools.)
Internal broaching machines with moving tools
Internal broaching machines with moving tools have long been the standard design. They are often equipped with two hydraulic cylinders for tool movement. The workpiece lies on the table which is about halfway up the machine. At the start of machining, the tool is located directly above the hole to be broached and is held by an end piece holder. It hangs there and is moved down and inserted into the hole. The shaft holder then grips the front part of the tool from below and locks it. Then the hydraulic pistons move and press the shank holder down via the pulling cross member, which pulls the broach through the bore. The workpiece is then removed and the shank holder moves up again so that the end piece holder can pick up the tool. Then a new workpiece can be placed on the table.
Internal broaching machines with moving workpieces and lifting tables
These are characterized by a lower overall height. In addition, shorter cycle times are possible because the individual components can move at the same time.
The workpiece is placed on the lifting table, which is located at the lower end of the machine. The broach hangs above this in the end piece holder. If the lifting table were to move in the direction of the tool, the tool would be subjected to pressure, with the risk of buckling. Therefore, the end piece holder first moves down a little and guides the shank of the tool through the hole in the workpiece. Then the shank holder grips the tool from below and only then does the lifting table move upwards and thus perform the working movement. During this time, only the lifting table is moved in order to reduce vibrations, which has a positive effect on the accuracy achieved.
After machining, the tool is released from the end piece holder and pulled completely through the workpiece by the shaft holder so that the workpiece can still be removed from the lifting table in the upper position. The lifting table then moves back to its lower starting position and the tool is transferred back to the end piece holder.
Special machines for swirl and tube broaching
In swirl broaching , a rotating movement is superimposed on the straight main movement. This means that helical gears for planetary gears can also be produced. These machines therefore require two controlled axes.
The Tubusräumen (also called pot rooms) is used for the production of closed outer profiles as external gears. The machines for this, however, are derived from internal broaching machines. The broach consists of a hollow cylinder with inwardly directed cutting edges. The machines are mostly designed as a two-cylinder design and mostly have fixed tools, lifting tables but no end piece holders. The workpieces are placed on the lifting table and pressed from below through the broaching tool and removed from above. However, there are also versions with moving tools.
Norms
- DIN 8665 Acceptance Conditions for Machine Tools; Vertical broaching machines
- DIN 8666 acceptance conditions for machine tools; Horizontal broaching machines
- DIN 8667 acceptance conditions for machine tools; Vertical broaching machines
- DIN 8668 acceptance conditions for machine tools; Horizontal broaching machines
- DIN 55141 vertical external broaching machines ; Sizes (withdrawn in 2003)
- DIN 55142 Horizontal external broaching machines ; Sizes (withdrawn in 2003)
- DIN 55143 vertical internal broaching machines ; Broaching by tool movement, sizes (withdrawn in 2003)
- DIN 55144 Horizontal internal broaching machines ; Sizes (withdrawn in 2003)
- DIN 55145 machine tools. Horizontal external broaching machines working continuously (chain broaching machines); Sizes (withdrawn in 2003)
Individual evidence
- ↑ Christoph Klink, Karlheinz Hasslach, Walther Maier: clearing , p. 481 f. in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur (Eds.): Handbuch Spanen. 2nd edition, Hanser, Munich 2014.
- ↑ Christoph Klink, Karlheinz Hasslach, Walther Maier: clearing , p. 483 in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur (eds.): Handbuch Spanen. 2nd edition, Hanser, Munich 2014.
- ↑ Christoph Klink, Karlheinz Hasslach, Walther Maier: clearing , p. 482 in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur (eds.): Handbuch Spanen. 2nd edition, Hanser, Munich 2014.
- ↑ Reimund Neugebauer (Ed.): Machine tools: Structure, function and application of cutting and removing machine tools . Springer, Berlin Heidelberg 2012, p. 150.
- ↑ Christoph Klink, Karlheinz Hasslach, Walther Maier: clearing , p. 482 f. in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur (Eds.): Handbuch Spanen. 2nd edition, Hanser, Munich 2014.
- ↑ Christoph Klink, Karlheinz Hasslach, Walther Maier: clearing , p. 483 in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur (eds.): Handbuch Spanen. 2nd edition, Hanser, Munich 2014.
- ↑ Christoph Klink, Karlheinz Hasslach, Walther Maier: clearing , p. 484 f. in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur (Eds.): Handbuch Spanen. 2nd edition, Hanser, Munich 2014.
- ↑ Reimund Neugebauer (Ed.): Machine tools: Structure, function and application of cutting and removing machine tools . Springer, Berlin Heidelberg 2012, p. 150.
- ↑ Christoph Klink, Karlheinz Hasslach, Walther Maier: clearing , p. 482 in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur (eds.): Handbuch Spanen. 2nd edition, Hanser, Munich 2014.
- ↑ Christoph Klink, Karlheinz Hasslach, Walther Maier: clearing , p. 486 in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur (eds.): Handbuch Spanen. 2nd edition, Hanser, Munich 2014.
- ↑ Manfred Weck, Christian Brecher : Machine tools. Volume 1: Types of machines and areas of application . 6th edition, Springer Berlin 2005, p. 216.
- ↑ Reimund Neugebauer (Ed.): Machine tools: Structure, function and application of cutting and removing machine tools. Springer, Berlin Heidelberg 2012, p. 150.
- ↑ Christoph Klink, Karlheinz Hasslach, Walther Maier: clearing , p. 486 in: Uwe Heisel, Fritz Klocke, Eckart Uhlmann, Günter Spur (eds.): Handbuch Spanen. 2nd edition, Hanser, Munich 2014.