Skiving in, Rolling out.
The Cogsdill skive burnishing tool combines two machining processes into one seamless operation. On the initial stroke, the skiving tool, which operates as a ‘floating reamer’, utilises supported carbide inserts to slice away chips and produce a geometrically round bore – an ideal pre-finish for roller burnishing. On the return stroke, connected air pressure forces the inserts on the skiving head to retract, allowing the multi-roll burnishing tool to engage and compress any residual peaks.
This process is the fastest method for producing mirror-like finishes to inside diameters of cylinders, benefitting from; a tough work-hardened surface, improved fatigue life and introducing a residual stress layer to the internal wall. This makes the burnished surface the preferred choice for manufacturers of pneumatic and hydraulic cylinders with seamless or Drawn over Mandrel (DOM) tubing – offering typical savings of 80-90% compared to honing.
The tool produces a superior surface finish as fine as Ra= 0.05-0.20 μm (2-8 μinch) with a bore tolerance of IT8, and localised work hardness of up to 50%, thereby reducing the sealing wear making it ideal for pistons.
Standard Cogsdill skive burnishing tools are designed as ‘dual-pass’ so that the tool parameters can be optimised for both the skiving and roller burnishing – allowing power and feed force to be kept to a minimum and ensuring that the part is not damaged when retracting the tool. The tools can be used in a rotating, non-rotating or both rotating configuration as required.
Note: Single-pass skive burnishing tools are available for when a feed rate is not available on the return stroke for the burnishing operation.
Cogsdill Skive Burnishing Tools were previously supplied by Sandvik Coromant. Our UK Facility now supplies all tools, spares and consumables for the global Skive Burnishing market. For pricing and availability, please contact us »
Skive Burnishing Tool Operation
Two thin chips are cut at a high feed rate of 1-4 mm/rev (0.04-0.16 inches/rev) while the tool passes through the workpiece. This cutting operation determines the finished diameter and tolerance of the cylinder. Surface finish Ra= 4-10 μm (skiving).
|2||Roller burnishing operation:
Roller burnishing is performed on the return stroke. The plastic deformation taking place provides a surface finish of Ra= 0.05-0.20 μm – better than broaching, grinding or even honing. Localized surface hardness is increased by approximately 50% (steel).
Benefits of skive burnishing over honing
- 80-90% reduction in machining time
- Reduced tool costs per metre (foot) of tube length
- Produces an even, mirror-like finish ideal for pistons – reducing sealing wear
- Superior surface finish – down to 0.05-0.20 μm (2-8 μinch)
- Improved size control – bore tolerance of IT8 (0.004 inch) or better may be achieved
- Improved cylinder fatigue life – up to 300%
- Localised work hardness – up to 50%
- Introduction of a residual stress layer to the cylinder wall
- Enhanced corrosion resistance
- Cleaner than honing or other abrasive operations
Rounder. Smoother. Faster.
Work harden to a superior finish in one seamless operation. Burnishes cylinders effortlessly.
A standard range of tools are available,
from 32mm (1.259 inch) to 380 mm (14.960 inch) diameter.
Please contact us for delivery.
Machine set-up and requirements
Cogsdill skive burnishing tools can be interfaced to any dedicated skive burnishing machine, or more typically, adapted to suit deep-hole drilling machines (as shown in the photograph). These machines tend to have long beds that are designed to hold and support long cylindrical components that lend themselves to the skive burnishing process. With the correct set-up, successful results can also be achieved utilising honing machines or converted lathes equipped with an Oil Pressure Head (OPH) and a coolant tank unit.
The key features for deep-hole drilling machines are:
- Pressure head to provide high volume coolant to the working area
- The pressure head also serves as a start pilot for the tool and a face seal against the component being machined
- Coolant and chip evacuation through the machine head stock which is directed into the coolant tank and filter system
- Component steady rest system
- Driven tail stock to provide rotation for the working tools usually by flange mounted tube clamp holders to suit drill tube diameter
- Tube style commonly used Single Tube System (STS) or Ejector
- Travelling steadies secured by moving clamp dampers
- Air or hydraulic feed through the tube for connection to the skiving head activates cutter retract after skive stroke
- These machines usually have a long bed length to accommodate component length primarily then, the working head and tail stocks, pressure head, travelling tube steadies and component steadies.
Coolant supply and Oil Pressure Heads
The easiest supply method for coolant is through an Oil Pressure Head (OPH) so that that coolant passes over the tool and through the workpiece. The recommended coolant volume for safe chip evacuation out of the workpiece is 4 x DC (l/min), which usually gives very low coolant pressure.
Alternatively coolant can be applied through the drill tube (rotating or fixed connector for respective tools). An adapter is required to direct the coolant forwards over the tool, and a cover behind the tool to prevent coolant leaking backwards.
Note that deep hole drilling machines for Ejector drilling must be equipped with an OPH or with an extra adaptor for internal coolant supply plus a stuffing/sealing box (similar to OPH).
Honing machines can also be adapted providing the feed rate can be kept constant and at sufficient speed. Likewise lathes can be used providing they are equipped for these operations with an OPH and a coolant system.
Typical Coolant Configurations » | Recommended Coolant Volume »
Air connection for insert retraction
On the initial skiving stroke, spring pressure retains the cutting inserts at their preset diameter. Upon completion of the skiving operation, the connected air or hydraulic feed through the drill tube is activated, which compresses the inner air piston and automatically retracts the inserts. This ensures there is no damage to the bore after it has been roller burnished.
Standard workshop air pressure supply of at least 5 bar (73 psi) is sufficient. It should be connected to the rear end of the tool through the machine spindle. The use of a rotary connector is required if the tool is rotating.
Note: When the air is “off”, ensure that the remaining air can be evacuated and does not stay trapped inside the air cylinder – the air piston must be free to spring back.
Drill tubes for extended reach applications
The Cogsdill skive burnishing system is designed to interface onto standard STS, BTA or Ejector drill tube sizes. Both 4-Start and 1-Start thread configurations are available across a range of tool sizes from 32mm (1.259 inch) to 380 mm (14.960 inch) diameter. This modular set-up offers rigid vibration-free interchangeability and a simple, easy installation with no special operator skills required.
Workpiece preparation, fixturing by clamping and bushings
Before the operation can start, the workpiece ends must be machined at 90 degrees. The burnishing tool must be able to pass through the end of the component prior to expanding and it will drop from center line if no support is provided. End caps can overcome this issue.
Tool Setting and Maintenance
Setting of the skiving head
- Turn the air supply off to the tool or disconnect it – this will set the skiving tool to the set cut diameter.
- Ensure the wedges are set equally on both sides or set the tool to minimum diameter.
- Check the diameter.
- Undo the locking screw (item 9).
- Turn the adjustment screw. One turn gives 0.2 mm radial movement (item 10).
- Repeat adjustment equally for both sides.
- It is essential that the inserts are the same radius +/- 0.1 mm. Remember one turn gives 0.2 mm radial movement.
- Tighten the locking screw (item 9).
- Check the diameter again. Repeat the adjusting procedure if necessary. Remember to keep the wedges adjusted equally.
- Check final diameter with both locking screws tight.
- Remember that the skiving tool should be set 0.076 – 0.127 mm below the roller burnishing tool diameter.
Changing skiving tool spare parts
- Unscrew the screw and spring (items 1 and 2).
- Loosen the screw (item 3).
- Remove the two parallel pins and cartridges (item 4).
- Loosen the screw (item 5) and remove the cap (item 6). Consider the spring tension.
- Pull the push rod to extract the control gear (item 7) while pushing the peg (item 8).
Setting of the roller burnishing tool
Size is set by the adjustment nut (item 1). When the master ring (item 2) can just about be pulled over the rolls (item 3), the tool is at the master ring size (e.g. 80.005 mm).
From this master ring size we can set the tool to any size by using the scale graduation on the adjustment nut – e.g. to 80.18 mm as in the example below.
- Loosen adjustment nut (item 1).
- With master ring (item 2) on the rolls (item 3) draw ring and cage (item 5) up close to the mandrel tip (item 4), turn the ring part of a revolution clockwise until tip, rolls and ring are in close contact.
- Screw adjustment nut until it is in contact with the cage.
With this method the tool is already at “0” set a little bit bigger size than with method 1.
- Set skiving head diameter to 80.05 mm (depends on wall thickness).
- Hole after skiving 80.02 mm.
- Set roller burnishing head to 80.18 mm.
- Hole diameter after burnishing will be 80.06 mm
Rule of thumb: Skiving tool diameter will be approximately the finished diameter after roller burnishing.
Changing roller burnishing tool spare parts
- Loosen the adjustment nut (item 1) by the hexagon key.
- Remove the cage adapter (item 8).
- Remove the lock nut (item 7).
- Remove the cage (item 5), the rolls (item 3) and the mandrel tip (item 4) as one single unit.
- Insert the new rolls (item 3) and mandrel tip (item 4) in the cage (item 5) with the aid of grease.
- Insert the assembly gently onto the drive shank (item 6).
- Tighten the lock nut (item 7) until it reaches the stop position.
- Set the roller burnishing tool to the desired diameter.
Speeds and feeds (AP = 0.3 mm)
|Skiving||Tool Diameter||Roller Burnishing|
|Ø mm||Speed||Machine feed (s)
|1-4||160||38 – 43.9||max 200||1.2||0.9 – 1.0|
|180||44 – 51.9||1.3||1.0 – 1.1|
|220||52 – 56.9||max 250||1.3||1.1 – 1.5|
|1-4||250||57 – 67.9||1.8||1.1 – 1.5|
|320||68 – 90.9||1.8 – 2.1||1.5 – 1.9|
|1-5||400||91 – 110.9||max 300||2.2 – 2.6||1.9 – 2.4|
|500||111 – 148.9||2.7 – 3.8||2.4 – 3.4|
|650||149 – 185.9||3.7 – 4.8||3.4 – 4.4|
|800||186 – 221.9||4.7 – 5.6||4.4 – 5.2|
|1000||222 – 257.9||5.5 – 6.3||5.2 – 5.9|
|1200||258 – 305.9||6.2 – 7.1||5.9 – 6.7|
* If machine feed is used, it must exceed the tool self-feed (SF) by 10%.
** Cutting data is material dependent and data shown is for Cold Drawn Seamless and Hot Rolled Tubes only.
Normal cutting depth for DOM-tubes is 0.3 mm. Reduce feed for greater depths.
|Range*||Theor. max. AP||Insert|
|3 = 38 – 56.9||3 = 1.496 – 2.240||0.61||0.024||R 420.37-060200-01 GC1025|
|4 = 57 – 90.9||4 = 2.244 – 3.579||1.0||0.039||R 420.37-070800-01 GC1025|
|5 = 91 – 305.6||5 = 3.583 – 12.031||1.6||0.063||R 420.37-111200-01 GC1025|
* For greater depths, counterboring is required.
Summary of Performance
- Surface finish Ra= 4-10 μm, Rt= 20-60 μm, at normal feeds (1-4 mm/rev) and a speed of vc: 200 m/min.
- Lower feeds improve the surface finish.
- The skiving tool determines the finished diameter and produces a very accurate finish from entrance to exit. On thin-walled tubes, elastic deformation from clamping and machining will influence the finished diameter.
- The skiving tool follows the inner diameter (ID) of the component which secures the straightness.
- Surface finish Ra= 0.05-0.20 μm.
- If the tube is very thin-walled, the burnishing will not be as effective as for normal tubes with t/ID = 0.1 – where t is wall thickness.
- The tolerance grade is IT8 or better.
- Strong clamping, cross holes or irregular tube shape can deform the tube in different ways. Uneven wall thickness can cause ovality.
- The localized surface hardness can be typically increased by up to 50%.
- Finish can be better than grinding or honing.